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The field of medicine has traditionally relied solely on small molecular drugs and conventional surgical procedures. However, recent advancements have shifted the focus toward innovative approaches, such as tissue engineering and regenerative medicine, which aim to overcome the limitations of traditional treatments through personalized and precision medicine. This thesis investigates tissue repair strategies using minimally invasive methods, specifically through the application of injectable biomaterials with or without cell-derived therapeutic factors. To this end, a series of novel injectable hydrogels were developed, alongside protocols for the reliable isolation of extracellular vesicles. These components were then integrated to create injectable therapeutic hydrogels. In Paper I, an injectable collagen-based hydrogel was developed. The injectable hydrogel maintained its shape in aqueous buffers, was biodegradable by the body's own enzymes, and supported the encapsulation and attachment of model cells. In Paper II, the collagen hydrogel from Paper I was further developed for use as a corneal sealant in corneal perforations. The hydrogel retained its beneficial properties of being shape-holding, biodegradable, and supporting cell attachment. Additionally, it exhibited increased transparency and tunable mechanical properties through minor adjustments in stoichiometry. It also successfully withstood burst pressures exceeding normal intraocular pressure levels and demonstrated adhesive properties comparable to fibrin glue, while supporting corneal epithelialization. Altogether, showing promise as an injectable corneal sealant. In Paper III, extracellular vesicles from corneal epithelial cells were isolated, purified and characterized based on their size, morphology, surface protein pattern and protein content. Corneal epithelial extracellular vesicles are thought to promote wound healing which could be confirmed with a functional in vitro scratch assay. These therap

The field of medicine has traditionally relied solely on small molecular drugs and conventional surgical procedures. However, recent advancements have shifted the focus toward innovative approaches, such as tissue engineering and regenerative medicine, which aim to overcome the limitations of traditional treatments through personalized and precision medicine. This thesis investigates tissue repair strategies using minimally invasive methods, specifically through the application of injectable biomaterials with or without cell-derived therapeutic factors. To this end, a series of novel injectable hydrogels were developed, alongside protocols for the reliable isolation of extracellular vesicles. These components were then integrated to create injectable therapeutic hydrogels. In Paper I, an injectable collagen-based hydrogel was developed. The injectable hydrogel maintained its shape in aqueous buffers, was biodegradable by the body's own enzymes, and supported the encapsulation and attachment of model cells. In Paper II, the collagen hydrogel from Paper I was further developed for use as a corneal sealant in corneal perforations. The hydrogel retained its beneficial properties of being shape-holding, biodegradable, and supporting cell attachment. Additionally, it exhibited increased transparency and tunable mechanical properties through minor adjustments in stoichiometry. It also successfully withstood burst pressures exceeding normal intraocular pressure levels and demonstrated adhesive properties comparable to fibrin glue, while supporting corneal epithelialization. Altogether, showing promise as an injectable corneal sealant. In Paper III, extracellular vesicles from corneal epithelial cells were isolated, purified and characterized based on their size, morphology, surface protein pattern and protein content. Corneal epithelial extracellular vesicles are thought to promote wound healing which could be confirmed with a functional in vitro scratch assay. These therap

The field of medicine has traditionally relied solely on small molecular drugs and conventional surgical procedures. However, recent advancements have shifted the focus toward innovative approaches, such as tissue engineering and regenerative medicine, which aim to overcome the limitations of traditional treatments through personalized and precision medicine. This thesis investigates tissue repair strategies using minimally invasive methods, specifically through the application of injectable biomaterials with or without cell-derived therapeutic factors. To this end, a series of novel injectable hydrogels were developed, alongside protocols for the reliable isolation of extracellular vesicles. These components were then integrated to create injectable therapeutic hydrogels. In Paper I, an injectable collagen-based hydrogel was developed. The injectable hydrogel maintained its shape in aqueous buffers, was biodegradable by the body's own enzymes, and supported the encapsulation and attachment of model cells. In Paper II, the collagen hydrogel from Paper I was further developed for use as a corneal sealant in corneal perforations. The hydrogel retained its beneficial properties of being shape-holding, biodegradable, and supporting cell attachment. Additionally, it exhibited increased transparency and tunable mechanical properties through minor adjustments in stoichiometry. It also successfully withstood burst pressures exceeding normal intraocular pressure levels and demonstrated adhesive properties comparable to fibrin glue, while supporting corneal epithelialization. Altogether, showing promise as an injectable corneal sealant. In Paper III, extracellular vesicles from corneal epithelial cells were isolated, purified and characterized based on their size, morphology, surface protein pattern and protein content. Corneal epithelial extracellular vesicles are thought to promote wound healing which could be confirmed with a functional in vitro scratch assay. These therap

The tissue engineering field is currently advancing towards minimally invasive procedures to reconstruct soft tissue defects. In this regard, injectable hydrogels are viewed as excellent scaffold candidates to support and promote the growth of encapsulated cells. Cross-linked gelatin methacryloyl (GelMA) gels have received substantial attention due to their extracellular matrix-mimicking properties. In particular, GelMA microgels were recently identified as interesting scaffold materials since the pores in between the microgel particles allow good cell movement and nutrient diffusion. The current work reports on a novel microgel preparation procedure in which a bulk GelMA hydrogel is ground into powder particles. These particles can be easily transformed into a microgel by swelling them in a suitable solvent. The rheological properties of the microgel are independent of the particle size and remain stable at body temperature, with only a minor reversible reduction in elastic modulus correlated to the unfolding of physical cross-links at elevated temperatures. Salts reduce the elastic modulus of the microgel network due to a deswelling of the particles, in addition to triple helix denaturation. The microgels are suited for clinical use, as proven by their excellent cytocompatibility. The latter is confirmed by the superior proliferation of encapsulated adipose tissue-derived stem cells in the microgel compared to the bulk hydrogel. Moreover, microgels made from the smallest particles are easily injected through a 20G needle, allowing a minimally invasive delivery. Hence, the current work reveals that powdered cross-linked GelMA is an excellent candidate to serve as an injectable hydrogel for adipose tissue engineering.

Injectable hydrogels show great promise in developingnovel regenerativemedicine solutions and present advantages for minimally invasive applications.Hydrogels based on extracellular matrix components, such as collagen,have the benefits of cell adhesiveness, biocompatibility, and degradabilityby enzymes. However, to date, reported collagen hydrogels possesssevere shortcomings, such as nonbiocompatible cross-linking chemistry,significant swelling, limited range of mechanical properties, or gelationkinetics unsuitable for in vivo injection. To solvethese issues, we report the design and characterization of an injectablecollagen hydrogel based on covalently modified acetyl thiol collagencross-linked using thiol-maleimide click chemistry. The hydrogel isinjectable for up to 72 h after preparation, shows no noticeable swelling,is transparent, can be molded in situ, and retainsits shape in solution for at least one year. Notably, the hydrogelmechanical properties can be fine-tuned by simply adjusting the reactantstoichiometries, which to date was only reported for synthetic polymerhydrogels. The biocompatibility of the hydrogel is demonstrated in vitro using human corneal epithelial cells, which maintainviability and proliferation on the hydrogels for at least seven days.Furthermore, the developed hydrogel showed an adhesion strength onsoft tissues similar to fibrin glue. Additionally, the developed hydrogelcan be used as a sealant for repairing corneal perforations and canpotentially alleviate the off-label use of cyanoacrylate tissue adhesivefor repairing corneal perforations. Taken together, these characteristicsshow the potential of the thiol collagen hydrogel for future use asa prefabricated implant, injectable filler, or as sealant for cornealrepair and regeneration.

Injectable hydrogels show great promise in developingnovel regenerativemedicine solutions and present advantages for minimally invasive applications.Hydrogels based on extracellular matrix components, such as collagen,have the benefits of cell adhesiveness, biocompatibility, and degradabilityby enzymes. However, to date, reported collagen hydrogels possesssevere shortcomings, such as nonbiocompatible cross-linking chemistry,significant swelling, limited range of mechanical properties, or gelationkinetics unsuitable for in vivo injection. To solvethese issues, we report the design and characterization of an injectablecollagen hydrogel based on covalently modified acetyl thiol collagencross-linked using thiol-maleimide click chemistry. The hydrogel isinjectable for up to 72 h after preparation, shows no noticeable swelling,is transparent, can be molded in situ, and retainsits shape in solution for at least one year. Notably, the hydrogelmechanical properties can be fine-tuned by simply adjusting the reactantstoichiometries, which to date was only reported for synthetic polymerhydrogels. The biocompatibility of the hydrogel is demonstrated in vitro using human corneal epithelial cells, which maintainviability and proliferation on the hydrogels for at least seven days.Furthermore, the developed hydrogel showed an adhesion strength onsoft tissues similar to fibrin glue. Additionally, the developed hydrogelcan be used as a sealant for repairing corneal perforations and canpotentially alleviate the off-label use of cyanoacrylate tissue adhesivefor repairing corneal perforations. Taken together, these characteristicsshow the potential of the thiol collagen hydrogel for future use asa prefabricated implant, injectable filler, or as sealant for cornealrepair and regeneration.

Injectable hydrogels show great promise in developingnovel regenerativemedicine solutions and present advantages for minimally invasive applications.Hydrogels based on extracellular matrix components, such as collagen,have the benefits of cell adhesiveness, biocompatibility, and degradabilityby enzymes. However, to date, reported collagen hydrogels possesssevere shortcomings, such as nonbiocompatible cross-linking chemistry,significant swelling, limited range of mechanical properties, or gelationkinetics unsuitable for in vivo injection. To solvethese issues, we report the design and characterization of an injectablecollagen hydrogel based on covalently modified acetyl thiol collagencross-linked using thiol-maleimide click chemistry. The hydrogel isinjectable for up to 72 h after preparation, shows no noticeable swelling,is transparent, can be molded in situ, and retainsits shape in solution for at least one year. Notably, the hydrogelmechanical properties can be fine-tuned by simply adjusting the reactantstoichiometries, which to date was only reported for synthetic polymerhydrogels. The biocompatibility of the hydrogel is demonstrated in vitro using human corneal epithelial cells, which maintainviability and proliferation on the hydrogels for at least seven days.Furthermore, the developed hydrogel showed an adhesion strength onsoft tissues similar to fibrin glue. Additionally, the developed hydrogelcan be used as a sealant for repairing corneal perforations and canpotentially alleviate the off-label use of cyanoacrylate tissue adhesivefor repairing corneal perforations. Taken together, these characteristicsshow the potential of the thiol collagen hydrogel for future use asa prefabricated implant, injectable filler, or as sealant for cornealrepair and regeneration.

Injectable hydrogels show great promise in developingnovel regenerativemedicine solutions and present advantages for minimally invasive applications.Hydrogels based on extracellular matrix components, such as collagen,have the benefits of cell adhesiveness, biocompatibility, and degradabilityby enzymes. However, to date, reported collagen hydrogels possesssevere shortcomings, such as nonbiocompatible cross-linking chemistry,significant swelling, limited range of mechanical properties, or gelationkinetics unsuitable for in vivo injection. To solvethese issues, we report the design and characterization of an injectablecollagen hydrogel based on covalently modified acetyl thiol collagencross-linked using thiol-maleimide click chemistry. The hydrogel isinjectable for up to 72 h after preparation, shows no noticeable swelling,is transparent, can be molded in situ, and retainsits shape in solution for at least one year. Notably, the hydrogelmechanical properties can be fine-tuned by simply adjusting the reactantstoichiometries, which to date was only reported for synthetic polymerhydrogels. The biocompatibility of the hydrogel is demonstrated in vitro using human corneal epithelial cells, which maintainviability and proliferation on the hydrogels for at least seven days.Furthermore, the developed hydrogel showed an adhesion strength onsoft tissues similar to fibrin glue. Additionally, the developed hydrogelcan be used as a sealant for repairing corneal perforations and canpotentially alleviate the off-label use of cyanoacrylate tissue adhesivefor repairing corneal perforations. Taken together, these characteristicsshow the potential of the thiol collagen hydrogel for future use asa prefabricated implant, injectable filler, or as sealant for cornealrepair and regeneration.

Injectable hydrogels show great promise in developingnovel regenerativemedicine solutions and present advantages for minimally invasive applications.Hydrogels based on extracellular matrix components, such as collagen,have the benefits of cell adhesiveness, biocompatibility, and degradabilityby enzymes. However, to date, reported collagen hydrogels possesssevere shortcomings, such as nonbiocompatible cross-linking chemistry,significant swelling, limited range of mechanical properties, or gelationkinetics unsuitable for in vivo injection. To solvethese issues, we report the design and characterization of an injectablecollagen hydrogel based on covalently modified acetyl thiol collagencross-linked using thiol-maleimide click chemistry. The hydrogel isinjectable for up to 72 h after preparation, shows no noticeable swelling,is transparent, can be molded in situ, and retainsits shape in solution for at least one year. Notably, the hydrogelmechanical properties can be fine-tuned by simply adjusting the reactantstoichiometries, which to date was only reported for synthetic polymerhydrogels. The biocompatibility of the hydrogel is demonstrated in vitro using human corneal epithelial cells, which maintainviability and proliferation on the hydrogels for at least seven days.Furthermore, the developed hydrogel showed an adhesion strength onsoft tissues similar to fibrin glue. Additionally, the developed hydrogelcan be used as a sealant for repairing corneal perforations and canpotentially alleviate the off-label use of cyanoacrylate tissue adhesivefor repairing corneal perforations. Taken together, these characteristicsshow the potential of the thiol collagen hydrogel for future use asa prefabricated implant, injectable filler, or as sealant for cornealrepair and regeneration.

Stem cell bioengineering and therapy require different model systems and materials in different stages of development. If a chemically defined biomatrix system can fulfill most tasks, it can minimize the discrepancy among various setups. By screening biomaterials synthesized through a coacervation-mediated self-assembling mechanism, a biomatrix system optimal for human mesenchymal stromal cell (hMSC) two dimensional (2D) culture and osteogenesis is identified. Its utility for hMSC bioengineering has been further demonstrated in coating porous bioactive glass scaffolds and nano-particle synthesis for esiRNA delivery to knock down the SOX-9 gene with high delivery efficiency. The self-assembled injectable system was further utilized for three dimensional (3D) cell culture, segregated co-culture of hMSC with Human umbilical vein endothelial cells (HUVEC) as angiogenesis model, and 3D bioprinting. Most interestingly, the coating of bioactive glass with the self-assembled biomatrix not only supports the proliferation and osteogenesis of hMSC in the 3D scaffold but also induces the amorphous bioglass scaffold surface to form new apatite crystals resembling the bone-like plate structures. Thus, the self-assembled biomatrix system can be utilized in various dimensions, scales, and geometries for many different bioengineering applications.

INTRODUCTION: The development of wound dressing materials that combine healing properties, ability to self-repair the material damages, skin-friendly adhesive nature, and competent mechanical properties have surpassing functional importance in healthcare. Due to their specificity, hydrogels have been recognized as a new gateway in biological materials to treat dysfunctional tissues. The design and creation of injectable hydrogel-based scaffolds have extensively progressed in recent years to improve their therapeutic efficacy and to pave the way for their easy minimally invasive administration. Hence, injectable hydrogel biomaterials have been prepared to eventually translate into minimally invasive therapy and pose a lasting effect on regenerative medicine.AREAS COVERED: This review highlights the recent development of adhesive and injectable hydrogels that have applications in wound healing and wound dressing. Such hydrogel materials are not only expected to improve therapeutic outcomes but also to facilitate the easy surgical process in both wound healing and dressing.EXPERT OPINION: Wound healing seems to be an appealing approach for treating countless life-threatening disorders. With the average increase of life expectancy in human societies, an increase in demand for injectable skin replacements and drug delivery carriers for chronic wound healing is expected.

The development of wound dressing materials that combine healing properties, ability to self-repair the material damages, skin-friendly adhesive nature, and competent mechanical properties have surpassing functional importance in healthcare. Due to their specificity, hydrogels have been recognized as a new gateway in biological materials to treat dysfunctional tissues. The design and creation of injectable hydrogel-based scaffolds have extensively progressed in recent years to improve their therapeutic efficacy and to pave the way for their easy minimally invasive administration. Hence, injectable hydrogel biomaterials have been prepared to eventually translate into minimally invasive therapy and pose a lasting effect on regenerative medicine. This review highlights the recent development of adhesive and injectable hydrogels that have applications in wound healing and wound dressing. Such hydrogel materials are not only expected to improve therapeutic outcomes but also to facilitate the easy surgical process in both wound healing and dressing. Wound healing seems to be an appealing approach for treating countless life-threatening disorders. With the average increase of life expectancy in human societies, an increase in demand for injectable skin replacements and drug delivery carriers for chronic wound healing is expected.

Glioblastoma multiforme (GBM) is an aggressive primary brain cancer and although patients undergo surgery and chemoradiotherapy, residual cancer cells still migrate to healthy brain tissue and lead to tumor relapse after treatment. New therapeutic strategies are therefore urgently needed to better mitigate this tumor recurrence. To address this need, we envision after surgical removal of the tumor, implantable biomaterials in the resection cavity can treat or collect residual GBM cells for their subsequent eradication. To this end, we systematically characterized a poly(ethylene glycol)-based injectable hydrogel crosslinked via a thiol-Michael addition reaction by tuning its hydration level and aqueous NaHCO3 concentration. The physical and chemical properties of the different formulations were investigated by assessing the strength and stability of the polymer networks and their swelling behavior. The hydrogel biocompatibility was assessed by performing in vitro cytotoxicity assays, immunoassays, and immunocytochemistry to monitor the reactivity of astrocytes cultured on the hydrogel surface over time. These characterization studies revealed key structure-property relationships. Furthermore, the results indicated hydrogels synthesized with 0.175 M NaHCO3 and 50 wt% water content swelled the least, possessed a storage modulus that can withstand high intracranial pressures while avoiding a mechanical mismatch, had a sufficiently crosslinked polymer network, and did not degrade rapidly. This formulation was not cytotoxic to astrocytes and produced minimal immunogenic responses in vitro. These properties suggest this hydrogel formulation is the most optimal for implantation in the resection cavity and compatible toward GBM therapy. Statement of significance: Survival times for glioblastoma patients have not improved significantly over the last several decades, as cancer cells remain after conventional therapies and form secondary tumors. We characterized a biodegradabl

Glioblastoma multiforme (GBM) is an aggressive primary brain cancer and although patients undergo surgery and chemoradiotherapy, residual cancer cells still migrate to healthy brain tissue and lead to tumor relapse after treatment. New therapeutic strategies are therefore urgently needed to better mitigate this tumor recurrence. To address this need, we envision after surgical removal of the tumor, implantable biomaterials in the resection cavity can treat or collect residual GBM cells for their subsequent eradication. To this end, we systematically characterized a poly(ethylene glycol)-based injectable hydrogel crosslinked via a thiol-Michael addition reaction by tuning its hydration level and aqueous NaHCO3 concentration. The physical and chemical properties of the different formulations were investigated by assessing the strength and stability of the polymer networks and their swelling behavior. The hydrogel biocompatibility was assessed by performing in vitro cytotoxicity assays, immunoassays, and immunocytochemistry to monitor the reactivity of astrocytes cultured on the hydrogel surface over time. These characterization studies revealed key structure-property relationships. Furthermore, the results indicated hydrogels synthesized with 0.175 M NaHCO3 and 50 wt% water content swelled the least, possessed a storage modulus that can withstand high intracranial pressures while avoiding a mechanical mismatch, had a sufficiently crosslinked polymer network, and did not degrade rapidly. This formulation was not cytotoxic to astrocytes and produced minimal immunogenic responses in vitro. These properties suggest this hydrogel formulation is the most optimal for implantation in the resection cavity and compatible toward GBM therapy. Statement of significance: Survival times for glioblastoma patients have not improved significantly over the last several decades, as cancer cells remain after conventional therapies and form secondary tumors. We characterized a biodegradabl

An artificial ovary is a promising approach for preserving fertility in prepubertal girls and women who cannot undergo current cryopreservation strategies. However, this approach is in its infancy, due to the possible challenges of creating a suitable 3D matrix for encapsulating ovarian follicles and stromal cells. To maintain the ovarian stromal cell viability and proliferation, as a first step towards developing an artificial ovary, in this study, a double network hydrogel with a high water swelling capacity (swelling index 15–19) was developed, based on phenol conjugated chi-tosan (Cs-Ph) and silk fibroin (SF) through an enzymatic crosslinking method using horseradish peroxidase. The addition of SF (1%) to Cs (1%) decreased the storage modulus (G’) from 3500 Pa (Cs1) to 1600 Pa (Cs-SF1), and the hydrogels with a rapid gelation kinetic produced a spatially ho-mogeneous distribution of ovarian cells that demonstrated 167% proliferation after 7 days. This new Cs-SF hydrogel benefits from the toughness and flexibility of SF, and phenolic chemistry could pro-vide the potential microstructure for encapsulating human ovarian stromal cells., SCOPUS: ar.j, info:eu-repo/semantics/published

Fistulas are abnormal connections between two body parts that can impair the quality of life. The use of biological glues represents the least invasive procedure to fill the fistula; however, it is limited by the need of multiple injections, the persistence of infection and the failure in the treatment of high-output fistulas. We describe herein the use of an injectable nanocomposite hydrogel that is able to form in situ a tissue-mimicking matrix as an innovative material for the treatment of esophageal fistulas. Injectable hydrogels that have the dual advantage of being implantable with a minimally invasive approach and of adapting their shape to the target cavity, while the introduction of mesoporous silica nanoparticles opens the possibility of drug/biomolecules delivery. The hydrogel is based on hyaluronic acid (HA), the crosslinking process occurs at physiological conditions leading to a hydrogel made of >96% by water and with a large-pore micro-architecture. The kinetic profile of the hydrogel formation is studied as a function of HA molecular weight and concentration with the aim of designing a material that is easily injectable with an endoscopic needle, is formed in a time compatible with the surgical procedure and has final mechanical properties suitable for cell proliferation. The in vivo experiments (porcine model) on esophageal-cutaneous fistulas, showed improved healing in the animals treated with the hydrogel compared with the control group.

Novel injectable thermosensitive PNIPAM/hyaluronic acid hydrogels containing various amounts of chitosan-g-acrylic acid coated PLGA (ACH-PLGA) micro/nanoparticles were synthesized and designed to facilitate the regeneration of cartilage tissue. The ACH-PLGA particles were used in the hydrogels to play a triple role: first, the allyl groups on the chitosan-g-acrylic acid shell act as crosslinkers for PNIPAM and improved the mechanical properties of the hydrogel to mimic the natural cartilage tissue. Second, PLGA core acts as a carrier for the controlled release of chondrogenic small molecule melatonin. Third, they could reduce the syneresis of the thermosensitive hydrogel during gelation. The optimum hydrogel with the minimum syneresis and the maximum compression modulus was chosen for further evaluations. This hydrogel showed a great integration with the natural cartilage during the adhesion test, and also, presented an interconnected porous structure in scanning electron microscopy images. Eventually, to evaluate the cytotoxicity, mesenchymal stem cells were encapsulated inside the hydrogel. MTT and Live/Dead assay showed that the hydrogel improved the cells growth and proliferation as compared to the tissue culture polystyrene. Histological study of glycosaminoglycan (GAG) showed that melatonin treatment has the ability to increase the GAG synthesis. Overall, due to the improved mechanical properties, low syneresis, the ability of sustained drug release and also high bioactivity, this injectable hydrogel is a promising material system for cartilage tissue engineering.

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.

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.

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., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/15418

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.

Poly(L-lactic acid) (PLLA) microfibers were surface functionalized by graft photopolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the fiber surface. Grafted fibers were easily dispersed in enzymatically gelling tyramine-substituted gelatin, forming a homogeneous dispersion without hindering subsequent gelatin crosslinking. The obtained injectable hydrogels showed improved mechanical properties compared to analogues based on non-modified fibers. The composite with 1% (w/v) of surface modified fibers had a three-fold higher shear storage modulus (535.2 +/- 90 Pa) than pure gelatin (184.9 +/- 32 Pa) while no significant increase was observed in the case of non-grafted fiber composites. Moreover, PHEMA grafting on PLLA fibers did not compromise cell viability and proliferation within the hydrogel. The new injectable hydrogels offer improved potential as substrates for the regeneration of soft tissues., QC 20151022

The growth of tissues and organs is regulated by orchestrated biological signals such as enzymes and growth factors (GFs). The ability to deliver biologics and small molecule drugs in response to these signals holds great promise for tissue repair and regeneration. This dissertation focuses on two aspects, enhancing angiogenesis and preventing infection, as therapeutic and prophylactic means to promoting wound healing. Pro-angiogenic factors regulate the formation of new blood vessels and the renewal of vasculature after wounding, which is crucial for ischemic tissue repair. The mode of GF delivery has become increasingly important, as the narrow therapeutic window and threshold of GF dosage for normal angiogenesis is more and more clear. However the majority of delivery vehicles nowadays rely on hydrolysable scaffolds and thin films of protein-containing polymers for constitutive GF release, which cannot be programmed to respond to biological signals. Here, a delivery platform based on enantiomeric protein nanocapsules is demonstrated, which enables controlled delivery of multiple proteins in response to wound proteases. Exemplified by stroke and diabetic wound healing in mice, sequential delivery of vascular endothelial GF (VEGF) and platelet-derived GF greatly enhances tissue revascularization and vessel maturation. Furthermore, the molecular mechanism for sustained released VEGF in enhancing angiogenesis was studied and revealed differential receptor activation and downstream signaling dynamics.Meanwhile, delivery of hydrophobic drugs to diseased tissue (e.g. antibiotics to an infected wound) is a common therapeutic approach, although little has been done to combine hydrophobic drug release with a scaffold that could provide structural support and additional signals to promote tissue healing. Motivated as such, an injectable amphiphilic synthetic hydrogel is introduced that can effectively solubilize hydrophobic drugs while serving as a scaffold for tissue heali

[EN] Poly(L-lactic acid) (PLLA) microfibers were surface functionalized by graft photopolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the fiber surface. Grafted fibers were easily dispersed in enzymatically gelling tyramine-substituted gelatin, forming a homogeneous dispersion without hindering subsequent gelatin crosslinking. The obtained injectable hydrogels showed improved mechanical properties compared to analogues based on non-modified fibers. The composite with 1% (w/v) of surface modified fibers had a three-fold higher shear storage modulus (535.2 +/- 90 Pa) than pure gelatin (184.9 +/- 32 Pa) while no significant increase was observed in the case of non-grafted fiber composites. Moreover, PHEMA grafting on PLLA fibers did not compromise cell viability and proliferation within the hydrogel. The new injectable hydrogels offer improved potential as substrates for the regeneration of soft tissues.

The growth of tissues and organs is regulated by orchestrated biological signals such as enzymes and growth factors (GFs). The ability to deliver biologics and small molecule drugs in response to these signals holds great promise for tissue repair and regeneration. This dissertation focuses on two aspects, enhancing angiogenesis and preventing infection, as therapeutic and prophylactic means to promoting wound healing. Pro-angiogenic factors regulate the formation of new blood vessels and the renewal of vasculature after wounding, which is crucial for ischemic tissue repair. The mode of GF delivery has become increasingly important, as the narrow therapeutic window and threshold of GF dosage for normal angiogenesis is more and more clear. However the majority of delivery vehicles nowadays rely on hydrolysable scaffolds and thin films of protein-containing polymers for constitutive GF release, which cannot be programmed to respond to biological signals. Here, a delivery platform based on enantiomeric protein nanocapsules is demonstrated, which enables controlled delivery of multiple proteins in response to wound proteases. Exemplified by stroke and diabetic wound healing in mice, sequential delivery of vascular endothelial GF (VEGF) and platelet-derived GF greatly enhances tissue revascularization and vessel maturation. Furthermore, the molecular mechanism for sustained released VEGF in enhancing angiogenesis was studied and revealed differential receptor activation and downstream signaling dynamics.Meanwhile, delivery of hydrophobic drugs to diseased tissue (e.g. antibiotics to an infected wound) is a common therapeutic approach, although little has been done to combine hydrophobic drug release with a scaffold that could provide structural support and additional signals to promote tissue healing. Motivated as such, an injectable amphiphilic synthetic hydrogel is introduced that can effectively solubilize hydrophobic drugs while serving as a scaffold for tissue heali

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.

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.

Hydrogels are promising substrates for tissue engineering applications because of their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics. Cryopreservation of cell-containing constructs using such hydrogel scaffolds is in high demand in tissue-engineering applications for the production of “off-the-shelf” tissue-engineered products. However, cryopreservation of regenerated tissues including cell sheets and cell constructs is not easy compared to preservation of cell suspensions, even when cryoprotectants are used. Here, we report a dextran-based polyampholyte hydrogel that itself shows cryoprotective properties, which could be useful for cell encapsulation and tissue engineering applications involving hydrogel formation. Amination was performed by introducing poly-L-lysine onto azide groups conjugated with dextran, and a portion of the amino groups was converted into carboxyl groups. These dextran-based polyampholytes showed good cryoprotective properties for mammalian cells, and addition of dextran substituted with dibenzylcyclooctyne acid induced in situ hydrogel formation via Cu-free click chemistry with high biocompatibility. Cells encapsulated with such in situ hydrogels can be cryopreserved well without the addition of any cryoprotectants. Thus, these hydrogels can serve as scaffolds with cryoprotective properties that also provide structural integrity to tissue constructs., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/12281

Hydrogels are promising substrates for tissue engineering applications because of their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics. Cryopreservation of cell-containing constructs using such hydrogel scaffolds is in high demand in tissue-engineering applications for the production of “off-the-shelf” tissue-engineered products. However, cryopreservation of regenerated tissues including cell sheets and cell constructs is not easy compared to preservation of cell suspensions, even when cryoprotectants are used. Here, we report a dextran-based polyampholyte hydrogel that itself shows cryoprotective properties, which could be useful for cell encapsulation and tissue engineering applications involving hydrogel formation. Amination was performed by introducing poly-L-lysine onto azide groups conjugated with dextran, and a portion of the amino groups was converted into carboxyl groups. These dextran-based polyampholytes showed good cryoprotective properties for mammalian cells, and addition of dextran substituted with dibenzylcyclooctyne acid induced in situ hydrogel formation via Cu-free click chemistry with high biocompatibility. Cells encapsulated with such in situ hydrogels can be cryopreserved well without the addition of any cryoprotectants. Thus, these hydrogels can serve as scaffolds with cryoprotective properties that also provide structural integrity to tissue constructs.

Hyaluronic acid-based hydrogels are proven biocompatible materials and excellent carriers of bone morphogenetic protein-2 (BMP-2) that have been successfully tested for bone generation in vivo. Different formulations, with or without nanohydroxyapatite, have shown promise for craniofacial applications. In this study, 28 rats were used to investigate whether it is possible to achieve mandibular bone augmentation upon injection of novel hyaluronic acid-based hydrogels containing nanohydroxyapatite and different concentrations of BMP-2 (0, 5 and 150ÎŒg/ml). The biomaterials were injected subperiosteally through fine needles into the innate mandibular diastema, imitating a clinical procedure for resorbed mandibles. No incisions, flaps or sutures were necessary. After 8weeks the mandibles were evaluated by peripheral quantitative computed tomography (pQCT), micro-computed tomography (ÎŒCT), histology, immunohistochemistry and fluorochrome labelling. As a result, engineered bone was observed in all treated mandibles, with a statistically significant increase in mandibular bone volume correlated with the amount of BMP-2 loaded in the hydrogel formula. We therefore demonstrated that minimally invasive mandibular bone augmentation is possible upon injection in rats, when using the appropriate injectable scaffolds. This represents an attractive clinical alternative for oral implantology patients., Correspondence Address: Hilborn, J.; Polymer Chemistry, Department of Chemistry - Å…ngström Laboratory, Science for Life Laboratory email: hilborn@mkem.uu.se