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This study aimed to improve the performance and mode of administration of a glass-reinforced hydroxyapatite synthetic bone substitute, Bonelike by Biosckin® (BL®), by association with a dextrin-based hydrogel, DEXGEL, to achieve an injectable and moldable device named DEXGEL Bone., Open access funding provided by FCT|FCCN (b-on). The authors were funded by FEDER and NORTE 2020 through project no. 003262 titled “iBONE therapies: advanced solutions for bone regen eration.” This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of the UID/BIO/04469 unit and COMPETE 2020 (POCI-01–0145- FEDER-006684) and BioTecNorte operation (NORTE-01–0145- FEDER-000004) funded by the European Regional Development Fund under the scope of Norte 2020—Programa Operacional Regional do Norte. The authors were granted a scholarship (SFRH/BD/132000/2017) by Portuguese FCT. This work was also funded by project UIDB/CVT/00772/2020 supported by FCT., info:eu-repo/semantics/publishedVersion

Inflammatory responses of nucleus pulposus (NP) can induce imbalanced anabolism and catabolism of extracellular matrix, and the cytosolic dsDNA accumulation and STING–NF–κB pathway activation found in NP inflammation are considered as fairly important cause of intervertebral disc (IVD) degeneration. Herein, we constructed a siSTING delivery hydrogel of aldehyde hyaluronic acid (HA-CHO) and poly(amidoamine) PAMAM/siRNA complex to intervene the abnormal STING signal for IVD degeneration treatment, where the formation of dynamic Schiff base bonds in the system (siSTING@HPgel) was able to overcome the shortcomings such as low cellular uptake, short half-life, and rapid degradation of siRNA-based strategy. PAMAM not only formed complexes with siRNA to promote siRNA transfection, but also served as dynamic crosslinker to construct hydrogel, and the injectable and self-healing hydrogel efficiently and steadily silenced STING expression in NP cells. Finally, the siSTING@HPgel significantly eased IVD inflammation and slowed IVD degeneration by prolonging STING knockdown in puncture-induced IVD degeneration rat model, revealing that STING pathway was a therapeutic target for IVD degeneration and such novel hydrogel had great potential for being applied to many other diseases for gene delivery., Graphical abstract Image 1, Highlights • STING-NF-κB pathway activation was identified an important cause of intervertebral disc degeneration. • PAMAM was employed as both linker and gene vector for siRNA delivery. • The injectable self-healing hydrogel could significantly ease the IVD inflammation and degeneration by prolonging STING knockdown. • This novel hydrogel system opened new ways of thinking and had great potential for gene delivery.

Cardiovascular diseases such as myocardial infarction (MI) are among the major causes of death worldwide. Although intramyocardial injection of hydrogels can effectively enhance the ventricular wall, this approach is limited because of its restriction to the poor vascularization in the infarcted myocardium. Here, we reported a new type of hydrogel composed of alginate (ALG) and hyaluronic acid (HA) with lyophilized platelet-rich fibrin (Ly-PRF) for releasing abundant growth factors to realize their respective functions. The results of in vitro studies demonstrated favorable mechanical property and release ability of ALG-HA with Ly-PRF. When injected into the infarcted myocardium, this composite hydrogel preserved heart function and the Ly-PRF within the hydrogel promoted angiogenesis and increased vascular density in both infarcted and border zone, which rescued the ischemic myocardium. These beneficial effects were also accompanied by macrophage polarization and regulation of myocardial fibrosis. Moreover, the autologous origin of Ly-PRF with ALG-HA hydrogel offers myriad advantages including safety profile, easiness to obtain and cost-effectiveness. Overall, this study demonstrated the versatile therapeutic effects of a novel composite hydrogel ALG-HA with Ly-PRF, which optimizes a promising vascularized substitution strategy for improving cardiac function after MI., Graphical abstract Image 1, Highlights • Alginate (ALG) alone has a limited vascularized ability in vivo. • ALG with 20% hyaluronic acid (HA) could attenuate LV remodeling and promote angiogenesis. • ALG-HA with lyophilized platelet-rich fibrin (Ly-PRF) could make further improvement in angiogenesis. • The Ly-PRF is promising for further clinical application because of autologous source and definite therapeutic effects.

Traditional hydrogels have drawbacks such as surgical implantation, large wound surfaces, and uncontrollable drug release during tumor treatment. In this paper, targeted nanomedicine has been combined with injectable hydrogel for photothermal–chemotherapy combination therapy. First, targeted nanomedicine (ICG—MTX) was fabricated by combining near-infrared (NIR) photothermal reagents (ICG) and chemotherapy drugs (MTX). The ICG—MTX was then mixed with the hydrogel precursor and radical initiator to obtain an injectable hydrogel precursor solution. Under the irradiation of NIR light, the precursor solution could release alkyl radicals, which promote the transition of the precursor solution from a liquid to a colloidal state. As a result, the nanomedicine could effectively remain at the site of the tumor and continue to be released from the hydrogel. Due to the targeted nature of MTX, the released ICG—MTX could target tumor cells and improve the accuracy of photothermal–chemo combination therapy. The results indicated that the injectable nanomedicine–hydrogel system has a favorable therapeutic effect on tumors.

For the delivery of anticancer drugs, an injectable in situ hydrogel with thermal responsiveness and prolonged drug release capabilities shows considerable potential. Here, we present a series of thermosensitive in situ hydrogels that serve as drug delivery systems for the treatment of liver cancer. These hydrogels were created by utilizing the polydimethylsiloxane (PDMS) oligomer, polyethylene glycol (PEG) and polypropylene glycol (PPG)’s chemical cross-linking capabilities. Doxorubicin (DOX) was encapsulated in a hydrogel with a hydrophobic core and hydrophilic shell to enhance DOX solubility. Studies into the behavior of in situ produced hydrogels at the microscopic and macroscopic levels revealed that the copolymer solution exhibits a progressive shift from sol to gel as the temperature rises. The hydrogels’ chemical composition, thermal properties, rheological characteristics, gelation period, and DOX release behavior were all reported. Subcutaneous injection in mice was used to confirm the injectability. Through the in vitro release of DOX in a PBS solution that mimics the tumor microenvironment, the hydrogel’s sustained drug release behavior was confirmed. Additionally, using human hepatocellular hepatoma, the anticancer efficacy of thermogel (DEP-2@DOX) was assessed (HepG2). The carrier polymer material DEP-2 was tested for cytotoxicity using HepG2 cells and its excellent cytocompatibility was confirmed. In conclusion, these thermally responsive injectable hydrogels are prominent potential candidates as drug delivery vehicles for the treatment of hepatocellular carcinoma.

Injectable therapies for intervertebral disc (IVD) repair are gaining much interest. Recently, a chitosan (CH)-based injectable scaffold has been developed that has similar mechanical properties to human nucleus pulposus (NP) and provides a suitable environment for encapsulated NP cell survival and proteoglycan production. The hypothesis of the study was that the biological response of the encapsulated cells can be further increased by adding gelatine and Link N (LN, a naturally occurring peptide present in cartilage and IVD extracellular matrix), known to increase cell adhesion and proteoglycan production, respectively. The effect of gelatine on the mechanical properties of a CH hydrogel was evaluated through rheological and compressive mechanical tests. Production of proteoglycan [assessed as glycosaminoglycan (GAG)] by encapsulated NP cells was determined in the presence or absence of gelatine in normal or degenerative medium supplemented with LN. Normal and degenerative media replicate the healthy and degenerative disc environment, respectively. Gelatine slightly reduced the gelation rate of CH hydrogel but improved its final mechanical properties in compression. LN had a minimal effect in normal medium but induced significantly more GAG production in degenerative medium (p < 0.001, 4.7-fold superior to the control), reaching similar results to transforming growth factor (TGF)-β (used as a positive control). GAG production was further increased in CH-gelatine hydrogels, confirming an additive effect of LN and gelatine in a degenerative environment. The results supported the concept that CH-gelatine hydrogels supplemented with LN can help restore the function of the NP during the early stages of IVD degeneration.

Lumbar disc degeneration is a common cause of chronic low back pain and an important contributor to various degenerative lumbar spinal disorders. However, currently there is currently no effective therapeutic strategy for treating disc degeneration. The pro-inflammatory cytokine interleukin-1β (IL-1β) mediates disc degeneration by inducing apoptotic death of nucleus pulposus (NP) cells and degradation of the NP extracellular matrix. Here, we confirmed that extracellular secretion of IL-1β via secretory autophagy contributes to disc degeneration, and demonstrate that a thermosensitive reactive oxygen species (ROS)-responsive hydrogel loaded with a synthetic growth hormone-releasing hormone analog (MR409) can protect against needle puncture-induced disc degeneration in rats. Methods: The expression levels of proteins related to secretory autophagy such as tripartite motif-containing 16 (TRIM16) and microtubule-associated protein light chain 3B (LC3B) were examined in human and rat disc tissues by histology and immunofluorescence. The effects of TRIM16 expression level on IL-1β secretion were examined in THP-1 cells transfected with TRIM16 plasmid or siRNA using ELISA, immunofluorescence, and immunoblotting. The in vitro effects of MR409 on IL-1β were examined in THP-1 cells and primary rat NP cells using ELISA, immunofluorescence, immunoblotting, and qRT-PCR. Further, MR409 was subcutaneously administered to aged mice to test its efficacy against disc degeneration using immunofluorescence, X-ray, micro-CT, and histology. To achieve controllable MR409 release for intradiscal use, MR409 was encapsulated in an injectable ROS-responsive thermosensitive hydrogel. Viscosity, rheological properties, release profile, and biocompatibility were evaluated. Thereafter, therapeutic efficacy was assessed in a needle puncture-induced rat model of disc degeneration at 8 and 12 weeks post-operation using X-ray, magnetic resonance (MR) imaging, histological analysis, and immunofluorescence. Results: Secretory autophagy-related proteins TRIM16 and LC3B were robustly upregulated in degenerated discs of both human and rat. Moreover, while upregulation of TRIM16 facilitated, and knockdown of TRIM16 suppressed, secretory autophagy-mediated IL-1β secretion from THP-1 cells under oxidative stress, MR409 inhibited ROS-induced secretory autophagy and IL-1β secretion by THP-1 cells as well as IL-1β-induced pro-inflammatory and pro-catabolic effects in rat NP cells. Daily subcutaneous injection of MR409 inhibited secretory autophagy and ameliorated age-related disc degeneration in mice. The newly developed ROS-responsive MR409-encapsulated hydrogel provided a reliable delivery system for controlled MR409 release, and intradiscal application effectively suppressed secretory autophagy and needle puncture-induced disc degeneration in rats. Conclusion: Secretory autophagy and associated IL-1β secretion contribute to the pathogenesis of disc degeneration, and MR409 can effectively inhibit this pathway. The ROS-responsive thermosensitive hydrogel encapsulated with MR409 is a potentially efficacious treatment for disc degeneration.

The temporomandibular joint (TMJ) is commonly affected during fundamental oral activities, reducing the quality of life. Herein, we synthesized a heparin-conjugated poloxamer hydrogel (HEP) as a thermo-responsive injectable hydrogel for the treatment of TMJ disorders. While the gelation temperature of synthesized HEP (25% [w/v]) was 29.8-30.0 degrees C, there was a slight difference between loss and storage modulus. HEP decreased the friction of the TMJ, thus requires less energy during load-bearing jaw movement in comparison to POL. Moreover, the oscillation test dependent on strain ranges from 0.01% to 1000% validated that POL and HEP3 hydrogels showed a similar critical strain of about 5.6%. The total elastic recovery percentage of HEP3 (53.50%) was higher than POL (45.55%), indicating a better recovery of the deformed hydrogel structure. Along with the suitable viscoelastic properties for temporomandibular cavity, both hydrogels increased the proliferation of fibroblasts (L929) and chondrocytes (ATDC5) (cell viabilities were above 100%). However, newly synthesized HEP induced differentiated cell proliferation of chondrogenic cells at increasing concentrations up to 0.0156 mg/mL (p < 0.0001) compared to POL and the control group. The promising rheological properties and effects on chondrogenic cell proliferation of injectable heparin-conjugated hydrogel make them candidates for intra-articular injections used for the treatment of TMJ., Turkiye Bilimsel ve Teknolojik Arascedil; tirma Kurumu [117M843], Turkiye Bilimsel ve Teknolojik Arascedil; tirma Kurumu, Grant/Award Number: 117M843

The highest disease caused by low back pain is herniated nucleus pulposus (HNP) where nucleus pulposus (NP) protrudes out through the annulus fibrosis. Injectable hydrogel is a method to restore NP function with minimal invasive surgery. Variation concentration of NFC were studied in detail toward affects on PEGDMA (poly(ethylene glycol)dimethacrylate):NFC hydrogel mechanically and injectability. The characteristics of PEGDMA and nanofibrillated cellulose (NFC) based injectable hydrogels through the photoinitiator Irgacure 2959 in the formation of hydrogels with variations composition 1:0; 1:0.25; 1:0.5; 1:0.75. In the morphological test on NFC a fibre with a diameter of 100 nm was formed from the results of electrospinning on ethyl cellulose (EC). The FTIR showed of photopolymerization of the conjugation bond between Irgacure 2959 and PEGDMA producing C-C at a frequency of 1349.20 cm−1. Swelling test used phosphate buffer saline (PBS) fulfilled the standard at a variation of 1:0.25; 1:0.5; and 1:0.75, 87.07%, 84.84% and 80.42% respectively. Viscosity test in the injectability of hydrogels showed a result of 73.67 dPa.s. The compressive strength test obtained good results in samples 1:0.75 showed a result of 3.42 kPa. In vitro injection model showed increasing of NFC concentration indicates the gel state when released from agarose will be less rupture. PEGDMA/NFC hydrogel biocomposite has the potential to be applied as an injectable hydrogel for the treatment of HNP patients based on the results.

The impairment of regenerative processes induced by high blood-glucose level (hyperglycemia) and excessive reactive oxygen species (ROS) contributes to the diabetic complication progression and development. In this study, an injectable, in situ crosslinkable chitosan hydrogel with ROS-scavenging capability was developed by conjugating gallic acid onto the chitosan backbone (CGA). We hypothesized that gallic acid serves as both antioxidant and crosslinking moieties to form hydrogel in situ by means of enzymatic crosslinking with horseradish peroxidase (HRP). The rapid gelation (from 30 s) was observed by vial tilting. The mechanical properties and microstructures of CGA hydrogels can be well controlled by varying the concentrations of H2O2. The ROS-scavenging ability of these CGA hydrogels was demonstrated against DPPH radical, hydroxyl radical, and total reducing power. Notably, in an in vitro hyperglycemia environment, CGA hydrogels significantly improved the proliferation and migration of human dermal fibroblast cells, which are closely related to diabetic wound healing. These results suggest that CGA hydrogels have potential as advanced materials for the treatment of diabetes-related diseases via attenuating the excessive ROS production and improving cellular behaviors.

This work describes the development of electroconductive hydrogels as injectable matrices for neural tissue regeneration by exploiting a biocompatible conductive polymer - poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT:PSS) - combined with a biomimetic polymer network made of gelatin. Our approach involved also genipin - a natural cross-linking agent - to promote gelation of gelatin networks embedding PEDOT:PSS. The achieved results suggest that physical-chemical properties of the resulting hydrogels, like impedance, gelation time, mechanical properties, swelling and degradation in physiological conditions, can be finely tuned by the amount of PEDOT:PSS and genipin used in the formulation. Furthermore, the presence of PEDOT:PSS (i) enhances the electrical conductivity, (ii) improves the shear modulus of the resulting hydrogels though (iii) partially impairing their resistance to shear deformation, (iv) reduces gelation time and (v) reduces their swelling ability in physiological medium. Additionally, the resulting electroconductive hydrogels demonstrate enhanced adhesion and growth of primary rat cortical astrocytes. Given the permissive interaction of hydrogels with primary astrocytes, the presented biomimetic, electroconductive and injectable hydrogels display potential applications as minimally invasive systems for neurological therapies and damaged brain tissue repair.

In pain relief, lidocaine has gained more attention as a local anesthetic. However, there are several side effects that limit the use of local anesthetics. Therefore, it is hypothesized that a hydrogel system with facile design can be used for prolonged release of lidocaine. In this study, we developed a formulation comprises of sodium alginate (SA) and graphene oxide (GO) to prolong the release of lidocaine. The gelation was induced by physically crosslinking the alginate with Ca2+ ions. The formation of blank SA and GO-reinforced SA hydrogels was investigated with different concentration of Ca2+ ions. The controlled release of lidocaine hydrochloride (LH) on both hydrogel systems was studied in PBS solution. The GO-reinforced SA hydrogels exhibited more sustained release than SA hydrogels without GO. In vitro biocompatibility test in L929 fibroblast cells confirmed the non-toxic property of hydrogels. Furthermore, to prove the in-situ gelation and biodegradability of hydrogels the hydrogels were injected on mice model and confirmed the stable gel formation. The hydrogels implanted onto the subcutaneous tissue of hydrogels retained over one week. These results indicate that LH-loaded GO-reinforced SA hydrogel can be a potential biomaterial for controlled release of local anesthetics.

Background Cartilage defects pose a significant burden on medical treatment, leading to an urgent need to develop regenerative medicine approaches for cartilage repair, such as stem cell therapy. However, the direct injection of stem cells can result in insufficient delivery or inaccurate differentiation. Hence, it is necessary to choose appropriate stem cell delivery scaffolds with high biocompatibility, injectability and chondral differentiation induction ability for cartilage regeneration. Methods In this study, the photocrosslinked gelatin methacrylate (GelMA) hydrogel with high cell affinity and plasticity was selected and strengthened by incorporating methacrylic anhydride-modified poly(amidoamine) (PAMAM-MA) to fabricate an adipose-derived stromal/stem cells (ASCs) delivery scaffold for cartilage repair. The physiochemical properties of the GelMA/PAMAM-MA hydrogel, including the internal structure, stability and mechanical properties, were tested. Then, ASCs were encapsulated into the hydrogels to determine the in vitro and in vivo chondrogenic differentiation induction abilities of the GelMA/PAMAM-MA hydrogel. Results Compared with the GelMA hydrogel, the GelMA/PAMAM-MA hydrogel exhibited more uniform structure, stability and mechanical properties. Moreover, on the basis of good biocompatibility, the hybrid hydrogel was proven to exert a sufficient ability to promote cartilage regeneration by in vitro three-dimensional (3D) culture of rASCs and in vivo articular cartilage defect repair. Conclusions The injectable photocrosslinked GelMA/PAMAM-MA hydrogel was proven to be a capable stem cell carrier for cartilage repair and provides new insight into the design strategy of stem cell delivery scaffolds.

Conductive hydrogels are promising materials in bioelectronics that ensure a tissue-like soft modulus and re-enact the electrophysiological function of damaged tissues. However, recent approaches to fabricating conductive hydrogels have proved difficult: fixing of the conductive hydrogels on the target tissues hydrogels requires the aids from other medical glues because of their weak tissue-adhesiveness. In this study, an intrinsically conductive and tissue-adhesive granular hydrogel consisting of a PEDOT:PSS conducting polymer and an adhesive catechol-conjugated alginate polymer was fabricated via an electrohydrodynamic spraying method. Because alginate-based polymers can be crosslinked by calcium ions, alginate-catechol polymers mixed with PEDOT:PSS granular hydrogels (ACP) were easily fabricated. The fabricated ACP exhibited not only adhesive and shear-thinning properties but also conductivity similar to that of muscle tissue. Additionally, the granular structure makes the hydrogel injectable through a syringe, enabling on-tissue printing. This multifunctional granular hydrogel can be applied to soft and flexible electronics to connect humans and machines.

Granular polymer hydrogels based on dynamic covalent bonds are attracting a great deal of interest for the design of injectable biomaterials. Such materials generally exhibit shear-thinning behavior and properties of self-healing/recovery after the extrusion that can be modulated through the interactions between gel microparticles. Herein, bulk macro-hydrogels based on thiolated-hyaluronic acid were produced by disulphide bond formation using oxygen as oxidant at physiological conditions and gelation kinetics were monitored. Three different thiol substitution degrees (SD%: 65%, 30% and 10%) were selected for hydrogel formation and fully characterized as to their stability in physiological medium and morphology. Then, extrusion fragmentation technique was applied to obtain hyaluronic acid microgels with dynamic disulphide bonds that were subsequently sterilized by autoclaving. The resulting granular hyaluronic hydrogels were able to form stable filaments when extruded through a syringe. Rheological characterization and cytotoxicity tests allowed to assess the potential of these materials as injectable biomaterials. The application of extrusion fragmentation for the formation of granular hyaluronic hydrogels and the understanding of the relation between the autoclaving processes and the resulting particle size and rheological properties should expand the development of injectable materials for biomedical applications.

Injectable hydrogel has the advantage to fill the defective area and thereby shows promise as therapeutic implant or cell/drug delivery vehicle for tissue repair. In this study, an injectable hyaluronic acid hydrogel in situ dual-enzymatically cross-linked by galactose oxidase (GalOx) and horseradish peroxidase (HRP) was synthesized and optimized, and the therapeutic effect of this hydrogel encapsulated with bone mesenchymal stem cells (BMSC) and nerve growth factors (NGF) for traumatic brain injury (TBI) mice was investigated. Results from in vitro experiments showed that either tyramine-modified hyaluronic acid hydrogels (HT) or NGF loaded HT hydrogels (HT/NGF) possessed good biocompatibility. More importantly, the HT hydrogels loaded with BMSC and NGF could facilitate the survival and proliferation of endogenous neural cells probably by neurotrophic factors release and neuroinflammation regulation, and consequently improved the neurological function recovery and accelerated the repair process in a C57BL/6 TBI mice model. All these findings highlight that this injectable, BMSC and NGF-laden HT hydrogel has enormous potential for TBI and other tissue repair therapy., Graphical abstract An injectable hyaluronic acid hydrogel loaded with BMSC and NGF accelerates the neurological function recovery of traumatic brain injury.Image 1

Background: Diabetic wound (DW) is the most devastating complication resulting in significant mortality and morbidity in diabetic patients. The objective of the current study was to formulate Epidermal Growth Factor loaded Chitosan nanoparticle impregnated with thermos-responsive injectable hydrogel with protease inhibitor. EGF, shown in all stages of wound healing from inflammation to proliferation and remodelling, combined with Doxycycline, a well-known anti-inflammatory and anti-bacterial drug, could be a better strategy in diabetic wound healing. However, EGF’s low stability makes it difficult to use. Methodology: The nanoparticles were prepared using the ionic gelation method. The prepared nanoparticles were evaluated for particle size, zeta potential, entrapment efficiency, and SEM studies. Further, the optimized nanoparticle batch was loaded into hydrogel with a protease inhibitor. The hydrogel was evaluated for morphology, protease degradation, in vitro drug release, anti-bacterial activity, cell migration, in vitro cell biocompatibility, and in vivo wound healing studies. Results and Conclusion: The particle size analysis of nanoparticles revealed the size (203 ± 1.236 nm), Zeta potential (+28.5 ± 1.0 mV), and entrapment efficiency of 83.430 ± 1.8%, respectively. The hydrogel showed good porous morphology, injectability, thermo-responsive, biocompatibility, and controlled drug release. In vitro anti-bacterial studies revealed the potential anti-bacterial activity of doxycycline against various microbes. In vivo data indicated that combining EGF and DOX considerably reduced inflammation time-dependent than single-agent treatment. Furthermore, histological studies corroborated these findings. After topical application of hydrogel, histopathology studies revealed significant collagen synthesis and a fully regenerated epithelial layer and advancement in all three stages (proliferation, remodelling, and maturation), which are required to improve the diabetic wound healing process by any dressing. These findings demonstrated that hydrogel promoted cutaneous wound healing in STZ-induced rats by suppressing inflammation at the wound site. Furthermore, histological studies corroborated these findings. After topical application of hydrogel, histopathology studies revealed significant collagen synthesis, a fully regenerated epithelial layer, and advancement in all three stages (proliferation, remodelling, and maturation), which are required to improve the diabetic wound healing process by any dressing. These findings demonstrated that hydrogel promoted cutaneous wound healing in STZ-induced rats by suppressing inflammation at the wound site.

A drawback in the development of treatments that can reach the retina is the presence of barriers in the eye that restrain compounds from reaching the target. Intravitreal injections hold promise for retinal delivery, but the natural defenses in the vitreous can rapidly degrade or eliminate therapeutic molecules. Injectable hydrogel implants, which act as a reservoir, can allow for long-term drug delivery with a single injection into the eye, but still suffer due to the fast clearance of the released drugs when traversing the vitreous and random diffusion that leads to lower pharmaceutic efficacy. A combination with HA-covered nanoparticles, which can be released from the gel and more readily pass through the vitreous to increase the delivery of therapeutic agents to the retina, represents an advanced and elegant way to overcome some of the limitations in eye drug delivery. In this article, we developed hybrid PLGA-Dotap NPs that, due to their hyaluronic acid coating, can improve in vivo distribution throughout the vitreous and delivery to retinal cells. Moreover, a hydrogel implant was developed to act as a depot for the hybrid NPs to better control and slow their release. These results are a first step to improve the treatment of retinal diseases by protecting and transporting the therapeutic treatment across the vitreous and to improve treatment options by creating a depot system for long-term treatments.

Extracellular matrix (ECM) hydrogels provide advantages such as injectability, the ability to fill an irregularly shaped space, and the adequate bioactivity of native matrix. In this study, we developed decellularized cartilage ECM (dcECM) hydrogels from porcine ears innovatively via the main method of enzymatic digestion and verified good biocompatible properties of dcECM hydrogels to deliver chondrocytes and form subcutaneous cartilage in vivo. The scanning electron microscopy and turbidimetric gelation kinetics were used to characterize the material properties and gelation kinetics of the dcECM hydrogels. Then we evaluated the biocompatibility of hydrogels via the culture of chondrocytes in vitro. To further explore the dcECM hydrogels in vivo, grafts made from the mixture of dcECM hydrogels and chondrocytes were injected subcutaneously in nude mice for the gross and histological analysis. The structural and gelation kinetics of the dcECM hydrogels altered according to the variation in the ECM concentrations. The 10 mg/ml dcECM hydrogels could support the adhesion and proliferation of chondrocytes in vitro. In vivo, at 4 weeks after transplantation, cartilage-like tissues were detected in all groups with positive staining of toluidine blue, Safranin O, and collagen II, indicating the good gelation of dcECM hydrogels. While with the increasing concentration, the tissue engineering cartilages formed by 10 mg/ml dcECM hydrogel grafts were superior in weights, volumes, collagen, and glycosaminoglycan (GAG) content compared to the dcECM hydrogels of 1 mg/ml and 5 mg/ml. At 8 weeks after grafting, dcECM hydrogel grafts at 10 mg/ml showed very similar qualities to the control, collagen I grafts. After 12 weeks of in vivo culture, the histological analysis indicated that 10 mg/ml dcECM hydrogel grafts were similar to the normal cartilage from pig ears, which was the source tissue. In conclusion, dcECM hydrogel showed the promising potential as a tissue engineering biomaterial to improve the regeneration and heal injuries of ear cartilage.

Articular cartilage is an important load-bearing tissue distributed on the surface of diarthrodial joints. Due to its avascular, aneural and non-lymphatic features, cartilage has limited self-regenerative properties. To date, the utilization of biomaterials to aid in cartilage regeneration, especially through the use of injectable scaffolds, has attracted considerable attention. Various materials, therapeutics and fabrication approaches have emerged with a focus on manipulating the cartilage microenvironment to induce the formation of cartilaginous structures that have similar properties to the native tissues. In particular, the design and fabrication of injectable hydrogel-based scaffolds have advanced in recent years with the aim of enhancing its therapeutic efficacy and improving its ease of administration. This review summarizes recent progress in these efforts, including the structural improvement of scaffolds, network cross-linking techniques and strategies for controlled release, which present new opportunities for the development of injectable scaffolds for cartilage regeneration.

A high risk of local relapse is the main challenge of HER2+ breast cancer after breast-conserving surgery. We aimed to develop a long-acting delivery system for Herceptin, a HER2-targeting antibody, using injectable and thermosensitive hydrogels as the carrier to prevent the local relapse of HER2+ breast tumors while minimizing systemic side effects, especially cardiotoxicity. Methods: Two poly(lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers with different PEG/PLGA proportions were synthesized. Their mixtures with rational mix proportions displayed sol-gel transitions in water with rising of temperature and the Herceptin-loaded hydrogel systems were then prepared. Both the in vivo antitumor and anti-relapse efficacies were evaluated after hypodermic injection of the Herceptin-loaded hydrogel, and the cardiotoxicity was also detected. Results: The gel performance, degradation rate and drug release kinetics of hydrogels were easily adjustable by simply varying the mix proportion. The hydrogel matrix with a specific mix proportion not only avoided initial burst release but also achieved sustained release of Herceptin in vitro for up to 80 days, which is the longest period of Herceptin delivery that has ever been reported. In vivo biodistribution studies performed in SK-BR-3 tumor-bearing mice revealed that a single hypodermic administration of the Herceptin-loaded hydrogel adjacent to the tumor tissue promoted the intratumoral antibody accumulation. This resulted in a better antitumor efficacy compared to weekly hypodermic injections of Herceptin solution for 28 days. A tumor relapse model was also established by imitative breast-conserving surgery on tumor-bearing mice, and both the single injection of the Herceptin-loaded hydrogel and the weekly injection of the Herceptin solution achieved superior anti-relapse efficacy. Furthermore, both antitumor and anti-relapse experiments demonstrated that the weekly pulsed administration of the Herceptin solution caused cardiotoxicity; however, the sustained release of Herceptin from the hydrogel effectively prevented this side effect. Conclusion: The Herceptin-loaded hydrogel has great potential for preventing the relapse of HER2+ breast tumors after breast-conserving surgery with enhanced therapeutic efficacy, improved patient compliance and significantly reduced side effects.

Strategies combining nanomaterials’ chemotherapy and photothermal therapy hold an enormous potential for improving cancer treatment. Still, the translation of this modality has been hindered by the immunogenicity triggered by some of the polymers used for coating nanomaterials as well as by the nanostructures’ poor tumor uptake after systemic administration. To address this bottleneck, the formulation of injectable polymeric matrices capable of delivering/confining chemotherapeutics and nanomaterials into the tumor site has been gathering a great interest. In this work, ionotropically crosslinked chitosan-based injectable in situ forming hydrogels co-incorporating Dopamine-reduced graphene oxide (DOPA-rGO; photothermal nano-agent) and Resveratrol (RES; chemotherapeutic drug), were prepared for the first time, to be applied in cancer chemo- photothermal therapy. The formulated hydrogels displayed injectability and in situ gelation as well as suitable physicochemical properties and good cytocompatibility. In vitro, the hydrogels’ photothermal therapy (DOPA- rGO@Gel +NIR light) only diminished the breast cancer cells’ viability to 72%. Moreover, cancer cells exposed to the hydrogels’ chemotherapy (RES+DOPA-rGO@Gel) still displayed a viability of 75%. In stark contrast, the hydrogels’ chemo-photothermal therapy (RES+DOPA-rGO@Gel +NIR light) was capable of decreasing cancer cells’ viability to just 31%. Overall, RES+DOPA-rGO@Gel presents an enormous potential for the chemo- photothermal therapy of breast cancer cells.

Disulfiram (DSF) is an important drug for the treatment and management of alcohol dependency. This drug has been approved by US-FDA, and its activity against the tumor is dependent on copper ion (Cu2+). However, the copper toxicity (caused via external copper) and its intrinsic anfractuous distribution in the human body have adversely suppressed the mechanism of DSF in in vivo. In this study, we aimed to design an injectable hydrogel, as CRC (Cu2+ release controller) for the effective treatment of tumors. The hydrogels of agarose have been used for wrapping of CuCl2, and hierarchical microparticles (HMP) for the generation of CRC system. When the laser irradiations (808 nm) have been provided to the system, light energy is transferred into heat energy, which results in the hydrogel hydrolysis (reversible) due to the overheating effect. This is followed by a reaction with DSF (pre-injected) to suppress tumor progression. Hence, the CRC system brings innovative ideas for designing of a Cu2+ delivery system.

Although osteoarthritis (OA) is a chronic inflammatory degenerative disease affecting millions of people worldwide, the current therapies are limited to palliative care and do not eliminate the necessity of surgical intervention in the most severe cases. Several dietary and nutraceutical factors, such as hydroxytyrosol (Hyt), have demonstrated beneficial effects in the prevention or treatment of OA both in vitro and in animal models. However, the therapeutic application of Hyt is limited due to its poor bioavailability following oral administration. In the present study, a localized drug delivery platform containing a combination of Hyt-loading chitosan nanoparticles (Hyt-NPs) and in situ forming hydrogel have been developed to obtain the benefits of both hydrogels and nanoparticles. This thermosensitive formulation, based on Pluronic F-127 (F-127), hyaluronic acid (HA) and Hyt-NPs (called Hyt@tgel) presents the unique ability to be injected in a minimally invasive way into a target region as a freely flowing solution at room temperature forming a gel at body temperature. The Hyt@tgel system showed reduced oxidative and inflammatory effects in the chondrocyte cellular model as well as a reduction in senescent cells after induction with H2O2. In addition, Hyt@tgel influenced chondrocytes gene expression under pathological state maintaining their metabolic activity and limiting the expression of critical OA-related genes in human chondrocytes treated with stressors promoting OA-like features. Hence, it can be concluded that the formulated hydrogel injection could be proposed for the efficient and sustained Hyt delivery for OA treatment. The next step would be the extraction of “added-value” bioactive polyphenols from by-products of the olive industry, in order to develop a green delivery system able not only to enhance the human wellbeing but also to promote a sustainable environment.

A gellan gum (GG) hydrogel must demonstrate a number of critical qualities&mdash, low viscosity, degradability, desirable mechanical properties, anti-swelling properties, and biocompatibility&mdash, in order to be regarded as suitable for retinal pigment epithelium (RPE) regeneration. In this study, we investigated whether the application of an eggshell membrane (ESM) to a GG hydrogel improved these critical attributes. The crosslinking of the ESM/GG hydrogels was most effectively reduced, when a 4 w/v% ESM was used, leading to a 40% less viscosity and a 30% higher degradation efficiency than a pure GG hydrogel. The compressive moduli of the ESM/GG hydrogels were maintained, as the smaller pores formed by the addition of the ESM compensated for the slightly weakened mechanical properties of the ESM/GG hydrogels. Meanwhile, due to the relatively low hydrophilicity of ESM, a 4 w/v% ESM enabled an ESM/GG hydrogel to swell 30% less than a pure GG hydrogel. Finally, the similarity in components between the ESM and RPE cells facilitated the proliferation of the latter without any significant cytotoxicity.

Hydrogels are one of the most commonly explored classes of biomaterials. Their chemical and structural versatility has enabled their use across a wide range of applications, including tissue engineering, drug delivery, and cell culture. Hydrogels form upon a sol–gel transition, which can be elicited by different triggers designed to enable precise control over hydrogelation kinetics and hydrogel structure. The chosen hydrogelation trigger and chemistry can have a profound effect on the success of the targeted application. In this Progress Report, a critical overview of recent advances in hydrogel design is presented, with a focus on the available strategies used to trigger the formation of hydrogel networks (e.g., temperature, light, ultrasound). These triggers are presented within a new classification system, and their suitability for six key hydrogel‐based applications is assessed. This Progress Report is intended to guide trigger selection for new hydrogel applications and inspire the rational design of new hydrogelation trigger mechanisms.

Osteoarthritis (OA) is the most common form of the joint disease associated with age, obesity, and traumatic injury. It is a disabling degenerative disease that affects synovial joints and leads to cartilage deterioration. Despite the prevalence of this disease, the understanding of OA pathophysiology is still incomplete. However, the onset and progression of OA are heavily associated with the inflammation of the joint. Therefore, studies on OA treatment have sought to intra-articularly deliver anti-inflammatory drugs, proteins, genes, or cells to locally control inflammation in OA joints. These therapeutics have been delivered alone or increasingly, in delivery vehicles for sustained release. The use of hydrogels in OA treatment can extend beyond the delivery of anti-inflammatory components to have inherent immunomodulatory function via regulating immune cell polarization and activity. Currently, such immunomodulatory biomaterials are being developed for other applications, which can be translated into OA therapy. Moreover, anabolic and proliferative levels of OA chondrocytes are low, except initially, when chondrocytes temporarily increase anabolism and proliferation in response to structural changes in their extracellular environment. Therefore, treatments need to restore matrix protein synthesis and proliferation to healthy levels to reverse OA-induced damage. In conjugation with injectable and/or adhesive hydrogels that promote cartilage tissue regeneration, immunomodulatory tissue engineering solutions will have robust potential in OA treatment. This review describes the disease, its current and future immunomodulatory therapies as well as cartilage-regenerative injectable and adhesive hydrogels.

This work was supported by the Ministry of Science, Innovation and Universities (Spain) (MAT2017-2017-84277-R) and CIBER-BBN (Instituto de Salud Carlos III, Spain). The authors thank Rosana Ramirez (ICTP-CSIC) for the excellent technical assistance with cell culture experiments and the Department of Human Anatomy and Histology of Faculty of Medicine, University of Salamanca, for assistance in histological preparations.

Hydrogels are encouraging for different clinical purposes because of their high water absorption and mechanical relation to native tissues. Injectable hydrogels can modify the invasiveness of utilization, which decreases recovery and surgical costs. Principal designs applied to create injectable hydrogels incorporate in situ formation owing to chemical or/and physical crosslinking. Here, we report nontoxic, thermosensitive, injectable hydrogels composed of gelatin (GEL) and oxidized alginate (OA) reinforced by silicon carbide nanoparticles (SiC NPs) and crosslinked with N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The mechanical characteristics of the hydrogels were examined via rheological analysis. The outcomes reveal that extending the SiC NPs contents enhances the mechanical properties around five times. The cross-sectional microstructure of the scaffolds comprising 0.25, 1.0, and 1.5% SiC NPs was scrutinized by FESEM, verifying porous structure with interconnected pores. Because of the smaller pore sizes in the hydrogels, the swelling rate has reduced at the higher content of SiC, which diminishes the water uptake. Additionally, the biodegradation study unveils that the hydrogels with SiC are more long-lasting than the hydrogel without SiC. By adding SiC NPs, a decrease is observed in the biodegradation and swelling ratio. The scaffold with a higher SiC NPs content (1.5%) manifested better cell attachment and was less cytotoxic than hydrogel without SiC. OA/GEL composites embedded SiC NPs have manifested excellent physical properties for tissue engineering in comparison with hydrogel without nanoparticles.

Injectable hydrogels, which are formed in situ by changing the external stimuli, have the unique characteristics of easy handling and minimal invasiveness, thus providing the advantage of bypass surgical operation and improving patient compliance. Using external temperature stimuli to realize the sol-to-gel transition when preparing injectable hydrogel is essential since the temperature is stable in vivo and controllable during ex vivo, although the hydrogels obtained possibly have low mechanical strength and stability. In this work, we designed an in situ fast-forming injectable cellulose/albumin-based hydrogel (HPC-g-AA/BSA hydrogels) that responded to body temperature and which was a well-stabilized hydrogen-bonding network, effectively solving the problem of poor mechanical properties. The application of localized delivery of chemotherapeutic drugs of HPC-g-AA/BSA hydrogels was evaluated. In vitro and in vivo results show that HPC-g-AA/BSA hydrogels exhibited higher antitumor efficacy of reducing tumor size and seem ideal for localized antitumor therapy.

Hydrogel-based local delivery systems provide a good delivery platform for cancer immunotherapy. Injectable hydrogels can directly deliver antitumor drugs to the tumor site to reduce systemic toxicity and achieve low-dose amplification immunotherapy. Therefore, it may overcome the problems of low drug utilization rate and the systemic side effects in cancer immunotherapy through systemic immune drugs, and it provides simple operation and little invasion at the same time. This study aimed to review the research progress of injectable hydrogels in tumor immunotherapy in recent years. Moreover, the local delivery of multiple drugs using injectable hydrogels in tumors is introduced to achieve single immunotherapy, combined chemo-immunotherapy, combined radio-immunotherapy, and photo-immunotherapy. Finally, the application of hydrogels in tumor immunotherapy is summarized, and the challenges and prospects for injectable hydrogels in tumor immunotherapy are proposed.

Cartilage tissue has a relatively low regenerative capacity which leads to a need for disease‐modifying active pharmaceutical ingredients (APIs) which can stimulate its regeneration and more urgently, effective ways of introducing APIs into the cartilage defects. Herein, an integrated system is proposed in which a hyaluronic acid (HA)‐based injectable hydrogel scaffold is embedded with API‐loaded poly(d,l‐lactide‐co‐glycolide) microspheres (PLGA MPs). This new injectable drug delivery system can successfully deliver APIs locally, increase drug retention time, and promote endogenous cartilage regeneration. In this study, resveratrol (RSV), a small hydrophobic compound is introduced as the selected API. PLGAs with differing copolymer ratios and endgroups are evaluated to study their effects on particle formation, RSV encapsulation, and drug release kinetics. This system is optimized as a 1 month sustained release formulation. In addition, the long‐acting chondrogenic induction of the RSV‐loaded system is evaluated by coculturing with cartilage‐derived progenitor cells in vitro. PLGA–RSV MPs stimulated the expression of cartilage‐related genes and the production of the cartilage‐specific extracellular matrix. This integrated system shows great potential as an injectable formulation for long‐acting chondrogenesis and endogenous cartilage tissue regeneration.

Uveal melanoma (UM) is the most prevalent primary intraocular malignant tumor with a high lethal rate. Patients who undergo conventional enucleation treatments consistently suffer permanent blindness, facial defects, and mental disorders, therefore, novel therapeutic modalities are urgently required. Herein, an injectable and stimuli‐responsive drug delivery antibacterial hydrogel (CP@Au@DC_AC50) is constructed via a facile grinding method that is inspired by the preparation process of traditional Chinese medicine. The incorporation of gold nanorods can enhance the mechanical strength of the hydrogel and realize photothermal therapy (PTT) and thermosensitive gel‐sol transformation to release the gene‐targeted drug DC_AC50 on demand in response to low‐density near‐infrared (NIR) light. The orthotopic model of UM is built successfully and indicates the excellent efficiency of CP@Au@DC_AC50 in killing tumors without damage to normal tissue because of its synergistic mild temperature PTT and gene‐targeted therapy. Moreover, the eyeball infection model reveals the remarkable antibacterial properties of the hydrogel which can prevent endophthalmitis in the eyeball. There is negligible difference between the CP@Au@DC_AC50+NIR group and normal group. This NIR light‐triggered gene‐targeted therapy/PTT/antibacterial treatment pattern provides a promising strategy for building multifunctional therapeutic platform against intraocular tumors and exhibits great potential for the clinical treatment of UM., Inspired by the grinding method in traditional Chinese medicine preparation, the injectable antibacterial self‐assembling nanofiber CP@Au@DC_AC50 hydrogels are first constructed. NIR light‐triggered drug release/photothermal/gene‐targeted therapy of CP@Au@DC_AC50 exhibits brilliant synergistic antitumor and antibacterial efficiency without damage to intraocular tissue in vitro and in vivo. The gene‐targeted therapy/PTT/antibacterial platform has potential for future application in ocular tumor therapy.

Grafting bone substitute is paramount to prevent the alveolar ridge resorption after tooth extraction and facilitate the subsequent implant treatment. An ideal bone substitute should acquire the excellent osteogenic property, more importantly, possess the suitable remodeling rate in balance with bone formation and desirable clinical manageability. However, none of bone substitute is simultaneously characterized by these features, and currently, the limited remodeling property leads to the excessive waiting time before implantation. Enlightened by woven bone, the transitional tissue that is able to induce osteogenesis during bone healing could be easily remodeled within a short period and depend on the favorable injectability of hydrogel, an injectable woven bone-like hydrogel (IWBLH) was constructed in this study to address the above problems. To mimic the component and hierarchical structure of woven bone, amorphous calcium phosphate (ACP) and mineralized collagen fibril were synthesized and compounded with alginate to form IWBLHs with various ratio. Screened by physiochemical characterization and in vitro biological assays, an optimal IWBLH was selected and further explored in rat model of tooth extraction. Compared with the most widely used bone substitute, we showed that IWBLH could be easily handled to fully fill the tooth socket, perform a comparable function to prevent the alveolar bone resorption, and completely remodeled within 4 weeks. This IWBLH stands as a promising candidate for alveolar ridge preservation (ARP) in future.

The worldwide incidence of bone disorders is raising, mainly due to ageing population. The lack of effective treatments is pushing the development of synthetic bone substitutes (SBSs). Most ceramic-based SBSs commercially available display limited handling properties. Attempting to solve these issues and achieve wider acceptance by the clinicians, granular ceramics have been associated with hydrogels to produce injectable/moldable SBSs. Dextrin, a low-molecular-weight carbohydrate, was used to develop a fully resorbable and injectable hydrogel. It was firstly oxidized with sodium periodate and then cross-linked with adipic acid dihydrazide. The in vivo biocompatibility and safety of the dextrin-based hydrogel (HG) was assessed by subacute systemic toxicity and skin sensitization tests, using rodent models. The results showed that the HG did not induce any systemic toxic effect, skin reaction or genotoxicity, neither impaired the bone repair/regeneration process. Then, the HG was successfully combined with granular bone substitute, registered as Bonelike® (250-500 ?m) to obtain a mouldable/injectable SBS, which was implanted in tibial fractures in goats for 3 and 6 weeks. The obtained results showed that HG allowed the stabilization of the granules into the defect, ensuring effective handling and moulding properties of the formulation, as well as an efficient cohesion of the granules. This article is protected by copyright. All rights reserved., Isabel Pereira was supported by the grant SFRH/BD/ 90066/ 2012 from FCT, Portugal. This work was funded by the project “DEXGELERATION – Advanced solutions for bone regeneration based on dextrin hydrogels” (Norte-07-0202-FEDER-038853) and the project “iBone Therapies – innovative therapies for bone regeneration” (NORTE-01-0247-FEDER-003262). The authors acknowledge the funding from FCT under the scope of the strategic funding of UID/BIO/04469/2013 and UID/BIM/04293/2013 units and COMPETE 2020 (POCI-010145-FEDER-006684), BioTecNorte operation (NORTE-010145-FEDER-000004) and NORTE-01-0145-FEDER-000012 funded by FEDER under the scope of Norte2020—Programa Operacional Regional do Norte., info:eu-repo/semantics/publishedVersion

Intravitreal injections are clinically established procedures in the treatment of posterior eye diseases, such as wet age-related macular degeneration (wet AMD) which requires monthly intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) protein drugs that can lead to complications due to frequent dosing. In this study, we designed a composite drug delivery system (DDS) consisting of drug-loaded poly (lactide–co–glycolide) (PLGA) nanoparticles and a chemically crosslinked hyaluronan hydrogel to reduce the dosing frequency. The morphology, size, composition, and drug loading efficiency of the prepared nanoparticles were characterized. The properties of the modified hyaluronan polymers used were also examined. The degree of swelling/degradation and controlled release ability of the hyaluronan hydrogel and the composite DDS were identified using bovine serum albumin (BSA) as a model drug. The results show that this system can retain 75% of its wet weight without losing its integrity and release the model drug at the rate of 0.4 μg/day for more than two months under physiological conditions. In addition, the nanoparticulate formulation of the system can further improve bioavailability of the drugs by penetrating deep into the retinal layers. In conclusion, the proposed composite DDS is easily prepared with biocompatible materials and is promising for providing the sustained release of the protein drugs as a better treatment for ocular neovascular diseases like wet AMD.

Bone loss associated with degenerative disease and trauma is a clinical problem increasing with the aging population. Thus, effective bone augmentation strategies are required; however, many have the disadvantages that they require invasive surgery and often the addition of expensive growth factors to induce osteoblast differentiation. Here, we investigated a LaponiteÒ crosslinked, pNIPAM-DMAc copolymer (L-pNIPAM-co-DMAc) hydrogel with hydroxyapatite nanoparticles (HAPna), which can be maintained as a liquid ex vivo, injected via narrow-gauge needle into affected bone, followed by in situ gelation to deliver and induce osteogenic differentiation of human mesenchymal stem cells (hMSC). L-pNIPAM-co-DMAc hydrogels were synthesised and HAPna added post polymerisation. Commercial hMSCs from one donor (Lonza) were incorporated in liquid hydrogel, the mixture solidified and cultured for up to 6 weeks. Viability of hMSCs was maintained within hydrogel constructs containing 0.5 mg/mL HAPna. SEM analysis demonstrated matrix deposition in cellular hydrogels which were absent in acellular controls. A significant increase in storage modulus (G') was observed in cellular hydrogels with 0.5 mg/mL HAPna. Semi-quantitative immunohistochemistry and histological analysis demonstrated that bone differentiation markers and collagen deposition was induced within 48 h, with increased calcium deposition with time. The thermally triggered hydrogel system, described here, was sufficient without the need of additional growth factors or osteogenic media to induce osteogenic differentiation of commercial hMSCs. Preliminary data presented here will be expanded on multiple patient samples to ensure differentiation is seen in these samples. This system could potentially reduce treatment costs and simplify the treatment strategy for orthopaedic repair and regeneration.

Generation of reactive oxygen species, delayed blood clotting, prolonged inflammation, bacterial infection, and slow cell proliferation are the main challenges of effective wound repair. Herein, a multifunctional extracellular matrix‐mimicking hydrogel is fabricated through abundant hydrogen bonding among the functional groups of gelatin and tannic acid (TA) as a green chemistry approach. The hydrogel shows adjustable physicochemical properties by altering the concentration of TA and it represents high safety features both in vitro and in vivo on fibroblasts, red blood cells, and mice organs. In addition to the merit of facile encapsulation of cell proliferation‐inducing hydrophilic drugs, accelerated healing of skin injury is obtained through pH‐dependent release of TA and its multifaceted mechanisms as an antibacterial, antioxidant, hemostatic, and anti‐inflammatory moiety. The developed gelatin‐TA (GelTA) hydrogel also shows an outstanding effect on the formation of extracellular matrix and wound closure in vivo via offered cell adhesion sites in the backbone of gelatin that provide increased re‐epithelialization and better collagen deposition. These results suggest that the multifunctional GelTA hydrogel is a promising candidate for the clinical treatment of full‐thickness wounds and further development of wound dressing materials that releases active agents in the neutral or slightly basic environment of infected nonhealing wounds.

Cardiovascular disease (CVD) remains the leading cause of death in Western countries. Post-myocardial infarction heart failure can be considered a degenerative disease where myocyte loss outweighs any regenerative potential. In this scenario, regenerative biology and tissue engineering can provide effective solutions to repair the infarcted failing heart. The main strategies involve the use of stem and progenitor cells to regenerate/repair lost and dysfunctional tissue, administrated as a suspension or encapsulated in specific delivery systems. Several studies demonstrated that effectiveness of direct injection of cardiac stem cells (CSCs) is limited in humans by the hostile cardiac microenvironment and poor cell engraftment; therefore, the use of injectable hydrogel or pre-formed patches have been strongly advocated to obtain a better integration between delivered stem cells and host myocardial tissue. Several approaches were used to refine these types of constructs, trying to obtain an optimized functional scaffold. Despite the promising features of these stem cells’ delivery systems, few have reached the clinical practice. In this review, we summarize the advantages, and the novelty but also the current limitations of engineered patches and injectable hydrogels for tissue regenerative purposes, offering a perspective of how we believe tissue engineering should evolve to obtain the optimal delivery system applicable to the everyday clinical scenario.

Injectable hydrogels have been widely applied in the field of regenerative medicine. However, current techniques for injectable hydrogels are facing a challenge when trying to generate a biomimetic, porous architecture that is well-acknowledged to facilitate cell behaviors. In this study, an injectable, interconnected, porous hyaluronic acid (HA) hydrogel based on an in-situ bubble self-generation and entrapment process was developed. Through an amide reaction between HA and cystamine dihydrochloride activated by EDC/NHS, CO2 bubbles were generated and were subsequently entrapped inside the substrate due to a rapid gelation-induced retention effect. HA hydrogels with different molecular weights and concentrations were prepared and the effects of the hydrogel precursor solution&rsquo, s concentration and viscosity on the properties of hydrogels were investigated. The results showed that HA10-10 (10 wt.%, MW 100,000 Da) and HA20-2.5 (2.5 wt.%, MW 200,000 Da) exhibited desirable gelation and obvious porous structure. Moreover, HA10-10 represented a high elastic modulus (32 kPa). According to the further in vitro and in vivo studies, all the hydrogels prepared in this study show favorable biocompatibility for desirable cell behaviors and mild host response. Overall, such an in-situ hydrogel with a self-forming bubble and entrapment strategy is believed to provide a robust and versatile platform to engineer injectable hydrogels for a variety of applications in tissue engineering, regenerative medicine, and personalized therapeutics.

Orthopedic Implant associated infections (OlAls) are the most serious complications in the orthopedic surgery. Such complications are of major concern unless encountered during initial stages of contamination due to the bacterial biofilm formation. Thus, our aim is to eradicate bacteria at the early stages of infection. Herein, we develop a vancomycin-loaded chitosan nanoparticles (CNPs) and povidone-iodine (PI) containing in situ alginate (CNPs-PI-Alg) gel for antibacterial and antibiofilm activity, respectively. The CNPs were synthesized by ionic gelation method and the processing parameters were optimized to attain nanoparticles of 200-250 nm size and 37.13 +/- 3.18 mV charge. A PI-loaded in situ alginate (PI-Alg) gel served as a carrier wherein, the CNPs were incorporated to attain sustained release of an antibacterial agent. The CNPs-PI-Alg gel showed more stability and mechanical properties compared to the Blank-Alg gel. The CNPs-PI-Alg gel exhibited sustained release of vancomycin and PI over a period of 10-15 days. The hemolysis and cytocompatibility studies demonstrated the safety and biocompatibility of CNPs-PI-Alg gel. Furthermore, significant antibacterial and antibiofilm effect against Staphylococcus aureus showed that the CNPs-PI-Alg in situ gel has a potential for the prevention of OIAIs. (C) 2018 Elsevier B.V. All rights reserved.

Chronic rhinosinusitis is a condition with severe clinical symptoms and limited therapeutic solutions. It has been reported that vascular endothelial growth factor (VEGF) can promote nasal epithelial cell growth and result in hyperplasia of the sinuses. Therefore, the downregulation of VEGF may inhibit the process of hyperplasia. In the present study, small interfering RNA (siRNA) targeting VEGF was used to silence the expression of VEGF, and injectable chitosan based hydrogel, which is suitable for sinus injection and exhibits long-term retention, was prepared as the siRNA carrier. Human bronchial epithelial cells were cultured directly on the hydrogel to observe the biological performance in vitro. Further in vivo effects were investigated by the injection of the hydrogel into the sinus cavity. Following the introduction of siRNA introducing, the expression of VEGF in the bronchial epithelial cells was significantly suppressed at mRNA and protein levels. The number of living cells on the gel was significantly decreased, thus resulting in the inhibition of proliferation. However, the cytoskeletal arrangement of the remaining cells were not affected substantially. The hydrogel was able to retain the siRNA for an extended duration, which enabled a sustained supply of siRNA. The in vivo sinus mucosa analysis revealed that the siRNA was able to collocate with cells and the mucosa thickness was substantially decreased. In conclusion, the results of the present study suggested that injectable chitosan based hydrogel, treated with siRNA targeting VEGF, may be used as a convenient therapeutic option for chronic rhinosinusitis.

Injectable delivery systems that respond to biologically relevant stimuli present an attractive strategy for tailorable drug release. Here, the design and synthesis of unique polymers are reported for the creation of hydrogels that are formed in situ and degrade in response to clinically relevant endogenous and exogenous stimuli, specifically reducing microenvironments and externally applied light. Hydrogels are formed with polyethylene glycol and heparin-based polymers using a Michael-type addition reaction. The resulting hydrogels are investigated for the local controlled release of low molecular weight proteins (e.g., growth factors and cytokines), which are of interest for regulating various cellular functions and fates in vivo yet remain difficult to deliver. Incorporation of reduction-sensitive linkages and light-degradable linkages affords significant changes in the release profiles of fibroblast growth factor-2 (FGF-2) in the presence of the reducing agent glutathione or light, respectively. The bioactivity of the released FGF-2 is comparable to pristine FGF-2, indicating the ability of these hydrogels to retain the bioactivity of cargo molecules during encapsulation and release. Further, in vivo studies demonstrate degradation-mediated release of FGF-2. Overall, our studies demonstrate the potential of these unique stimuli-responsive chemistries for controlling the local release of low molecular weight proteins in response to clinically relevant stimuli.

Post-operative epidural fibrosis is a biological response after laminectomy that may lead to clinical symptoms, such as radicular pain. An ideal material for prevention of epidural fibrosis should be able to inhibit fibroblast adhesions and reduce formation of scar tissue. An injectable hydrogel would be the material of choice for this purpose, since it could fill an irregular surgical defect completely, gelate in situ and be delivered in a minimally-invasive manner. The objective of this study was to evaluate, in vitro and in vivo, the cytocompatibility and anti-adhesive effect of an oxidised hyaluronic acid/adipic acid dihydrazide (oxi-HA/ADH) hydrogel. Different cell types present in the spine were used to test the cytocompatibility of the hydrogel. The hydrogel extraction medium had no deleterious effects on neural cells (PC-12), but reduced fibroblasts viability (NIH/3T3). Although the hydrogel did not change the release of lactate dehydrogenase from myoblasts (C2C12) and Schwann cells (RSC96), the extraction medium concentration slightly affected the mitochondrial activity of these two cell types. qPCR showed that the hydrogel down-regulated S100a and P4hb expression in NIH/3T3 cells, supporting the hypothesis that the hydrogel might inhibit fibroblast activity. The animal study showed a reduction of scar tissue formation as well as severity of adhesion between scar tissue and the dura mater in a rat laminectomy model. Superficially, the peel-off test showed significantly decreased tenacity. In conclusion, the oxi-HA/ADH hydrogel is a promising injectable and thermosensitive material for prevention of post-operative epidural fibrosis.

Thixotropy is one of the oldest documented rheological phenomenon in colloid science and may be defined as an increase of viscosity in a state of rest and a decrease of viscosity when submitted to a constant shearing stress. This behavior has been exploited in recent years to prepare injectable hydrogels for application in drug delivery systems. Thixotropic hydrogels may be profitably used in the field of regenerative medicine, which promotes tissue healing after injuries and diseases, as the molten hydrogel may be injected by syringe and then self-adapts in the space inside the injection site and recovers the solid form. We will focus our attention on the preparation, properties, and some applications of biocompatible thixotropic hydrogels.

Tissue engineering has emerged as a new treatment approach for bone repair and regeneration seeking to address limitations associated with current therapies, such as autologous bone grafting. While many bone tissue engineering approaches have traditionally focused on synthetic materials (such as polymers or hydrogels), there has been a lot of excitement surrounding the use of natural materials due to their biologically inspired properties. Fibrin is a natural scaffold formed following tissue injury that initiates hemostasis and provides the initial matrix useful for cell adhesion, migration, proliferation, and differentiation. Fibrin has captured the interest of bone tissue engineers due to its excellent biocompatibility, controllable biodegradability, and ability to deliver cells and biomolecules. Fibrin is particularly appealing because its precursors, fibrinogen, and thrombin, which can be derived from the patient's own blood, enable the fabrication of completely autologous scaffolds. In this article, we highlight the unique properties of fibrin as a scaffolding material to treat bone defects. Moreover, we emphasize its role in bone tissue engineering nanocomposites where approaches further emulate the natural nanostructured features of bone when using fibrin and other nanomaterials. We also review the preparation methods of fibrin glue and then discuss a wide range of fibrin applications in bone tissue engineering. These include the delivery of cells and/or biomolecules to a defect site, distributing cells, and/or growth factors throughout other pre-formed scaffolds and enhancing the physical as well as biological properties of other biomaterials. Thoughts on the future direction of fibrin research for bone tissue engineering are also presented. In the future, the development of fibrin precursors as recombinant proteins will solve problems associated with using multiple or single-donor fibrin glue, and the combination of nanomaterials that allow for the incorporation of biomolecules with fibrin will significantly improve the efficacy of fibrin for numerous bone tissue engineering applications.

The objective of this study was to develop an injectable and biocompatible hydrogel which can efficiently deliver a nanocomplex of graphene oxide (GO) and vascular endothelial growth factor-165 (VEGF) pro-angiogenic gene for myocardial therapy. For the study, an efficient nonviral gene delivery system using polyethylenimine (PEI) functionalized GO nanosheets (fGO) complexed with DNAVEGF was formulated and incorporated in the low-modulus methacrylated gelatin (GelMA) hydrogel to promote controlled and localized gene therapy. It was hypothesized that the fGOVEGF/GelMA nanocomposite hydrogels can efficiently transfect myocardial tissues and induce favorable therapeutic effects without invoking cytotoxic effects. To evaluate this hypothesis, a rat model with acute myocardial infarction was used, and the therapeutic hydrogels were injected intramyocardially in the peri-infarct regions. The secreted VEGF from in vitro transfected cardiomyocytes demonstrated profound mitotic activities on endothelial cells. A significant increase in myocardial capillary density at the injected peri-infarct region and reduction in scar area were noted in the infarcted hearts with fGOVEGF/GelMA treatment compared to infarcted hearts treated with untreated sham, GelMA and DNAVEGF/GelMA groups. Furthermore, the fGOVEGF/GelMA group showed significantly higher (p < 0.05, n = 7) cardiac performance in echocardiography compared to other groups, 14 days postinjection. In addition, no significant differences were noticed between GO/GelMA and non-GO groups in the serum cytokine levels and quantitative PCR based inflammatory microRNA (miRNA) marker expressions at the injected sites. Collectively, the current findings suggest the feasibility of a combined hydrogel-based gene therapy system for ischemic heart diseases using nonviral hybrid complex of fGO and DNA.

One of the major problems in the treatment of cardiovascular diseases is the inability of myocardium to self-regenerate. Current therapies are unable to restore the heart's function after myocardial infarction. Myocardial tissue engineering is potentially a key approach to regenerate damaged heart muscle. Myocardial patches are applied surgically, whereas injectable hydrogels provide effective minimally invasive approaches to recover functional myocardium. These hydrogels are easily administered and can be either cell free or loaded with bioactive agents and/or cardiac stem cells, which may apply paracrine effects. The aim of this review is to investigate the advantages and disadvantages of injectable stem cell-laden hydrogels and highlight their potential applications for myocardium repair.

Success of tissue engineering applications in regenerative medicine requires the preservation of tissue-engineered products at a low temperature. This can be successfully achieved by the use of cryoprotective agent (CPA). In this study, we formulated a unique injectable hydrogel for the purpose of cell delivery after cryopreservation by using polyampholyte CPA. The polyampholyte showed excellent post-thaw cell survival, and after thawing, the polymeric CPA did not have to be removed because of its low cytotoxicity. The polyampholyte could be transformed into a hydrogel by mixing with nanosilicates. Previously, nanosilicates were used to improve mechanical properties, but this is the first report of the use of a nanosilicate together with CPA to formulate hydrogels. Inclusion of the nanosilicate led to the formation of thixotropic hydrogels, which can be injected using fine needles. These gels with tunable mechanical properties can be injected into defect sites to form scaffolds for cell growth and tissue repair, and they do not require any separate seeding of cells before injection, thus eliminating the need for cell harvesting and cell maintenance. This is a distinct system in which cells can be cryopreserved until before usage; when required, the cells in the polyampholyte can be revived to their original state and the thixotropic hydrogel can be formed. The combination of thixotropy and cytocompatibility of the gels could enable a wide range of biomedical applications such as cell delivery and orthopedic repair.

Photopolymerization is a common method to harden materials initially in a liquid state. A surgeon can directly trigger the solidification of a dental implant or a bone or tissue filler by using ultra-violet light. Traditionally, photopolymerization has been used mainly in dentistry. Over the last decade advances in material development including a wide range of biocompatible gel-and cement-systems open up a new avenue for in-situ photopolymerization. We designed a miniaturized light probe where a photoactive material can be 1) mixed, pressurized and injected 2) photopolymerized or photoactivated and 3) monitored during the chemical reaction. The device enables surgeries to be conducted through a hole smaller than 500 mu m in diameter. Using a combination of Raman and fluorescence spectroscopy, the current state of the photopolymerization was inferred and monitored in real time within an in-vitro tissue model. It was also possible to determine roughly the position of the probe within the tissue cavity by analysing the fluorescence signal. Using the technique hydrogels were successfully implanted into a bovine intervertebral disc model. Mechanical tests could not obstruct the functionality of the implant. Finally, the device was also used for other application such as the implantation of a hydrogel into an aneurysm tissue cavity which will be presented at the conference.