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The electrical and biological interfacial properties of invasive electrodes have a significant impact on the performance and longevity of neural recordings in the brain. In this study, we demonstrated rapid electrophoretic deposition and electrochemical reduction of graphene oxide (GO) on metal-based neural electrodes. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and other characterizations confirmed the existence of a uniform and effectively reduced graphene oxide coating. Electrochemically reduced graphene oxide (ErGO) coated Pt/Ir neural electrodes exhibited 15.2-fold increase in charge storage capacity (CSC) and 90% decrease in impedance with only 3.8% increase in electrode diameter. Patch clamp electrophysiology and calcium imaging of primary rat hippocampus neurons cultured on ErGO demonstrated that there was no adverse impact on the functional development of neurons. Immunostaining showed a balanced growth of excitatory and inhibitory neurons, and astrocytes. Acute recordings from the auditory cortex and chronic recordings (19 days) from the somatosensory cortex found ErGO coating improved the performance of neural electrodes in signal-to-noise ratio (SNR) and amplitude of signals. The proposed approach not only provides an in-depth evaluation of the effect of ErGO coating on neural electrodes but also widens the coating methods of commercial neural electrodes.

Parkinson's disease (PD) is a progressive neurological disorder, in which dopaminergic midbrain neurons degenerate, leading to dopamine depletion that is associated with neuronal death. In this Review, we initially describe the pathogenesis of PD and established therapies that unfortunately only delay progression of the disease. With a rapidly escalating incidence in PD, there is an urgent need to develop new therapies that not only halt progression but even reverse degeneration. Biomaterials are playing critical roles in these new therapies which include controlled and site-specific delivery of neurotrophins, increased engraftment of implanted neural stem cells, and redirection of endogenous stem cell populations away from their niche to encourage reparative mechanisms. This Review will therefore cover important design features of biomaterials used in regenerative medicine and tissue engineering strategies targeted at PD.

Paclitaxel (PTX)-coated drug eluting balloon catheters (DEBc) used in the management of neointimal hyperplasia (NIH) have been associated with safety concerns. Alternative coating agents and targeted delivery systems may improve safety and DEBc efficacy. Utilizing a multi-platform approach we designed, developed and evaluated Lumi-Solve, a novel DEBc, coated with ultraviolet (UV) 365 nm-activated caged metacept-3 (c-MCT-3), an epigenetic agent from the histone deacetylase inhibitor (HDACi) class. In vitro catheter and contrast media transmission of UV365nm was evaluated spectroscopically. UV365nm conversion of c-MCT-3 to MCT-3 was evaluated chromatographically. Cellular toxicity and HDACi activity of c-MCT-3 ∓UV365nm was evaluated in vitro. In vivo UV365nm conversion of c-MCT-3 to MCT-3 was evaluated in an ovine carotid artery model. Catheter material and dilute contrast media did not attenuate UV365nm transmission or c-MCT-3 activation. c-MCT-3 demonstrated less cellular toxicity than MCT-3 and PTX. UV365nm-activated c-MCT-3 demonstrated HDACi activity. In vivo activation of c-MCT-3 produced MCT-3. Lumi-Solve, a novel DEBc device developed utilizing a combination of chemical, fibre-optic and catheter based technology platforms, demonstrated potential for targeted delivery of bioactive HDACi to the blood vessel wall supporting direct application to the management of NIH and warranting additional in vivo studies.

Recent developments in photochemistry have introduced new methods to prepare hydrogels initiated by nonharmful light which is essential for encapsulation of cells and bioactive components. However, bioorthogonal photoclick reactions generally requires two components for cross-linking and, in many cases, the formation of a reactive intermediate that may cross-react with nucleophiles in biological media. Here we report the utilization of a visible light triggered dimerization of electron-rich anthracene for polymer cross-linking to form bulk hydrogels and microgels. Incorporation of gelatin within the hydrogel enhanced cell attachment and viability after 7 days of culture and spatiotemporal conjugation of a bioactive component using photochemical dimerization of anthracene was demonstrated. This work therefore introduces a simple yet powerful tool for light modulated bioorthogonal polymer cross-linking, which can be utilized in various bioengineering applications.

Reversible photocycloaddition reactions have previously been employed in chemical cross-linking for the preparation of biomaterial scaffolds. However, the processes require activation by high-energy UV light, rendering them unsuitable for modification in biological environments. Here we demonstrate that the [2 + 2] photocycloaddition of styrylpyrene can be activated by visible light at λ = 400–500 nm, enabling rapid and effective conjugation and cross-linking of poly(ethylene glycol) (PEG) in water and under mild irradiation conditions (I = 20 mW cm–2). Notably, the reversion of the cycloaddition can be triggered by low-energy UV light at λ = 340 nm, which allows for efficient cleavage of the dimer adduct. Using this wavelength-gated reversible photochemical reaction we are able to prepare PEG hydrogels and modulate their mechanical properties in a bidirectional manner. We also demonstrate healing of the fractured hydrogel by external light triggers. Furthermore, we show that human mesenchymal stem cells ...

Microgels are emerging as an outstanding platform for tissue regeneration because they overcome issues associated with conventional bulk/macroscopic hydrogels such as limited cell-cell contact and cell communication and low diffusion rates. Owing to the enhanced mass transfer and injectability via a minimally invasive procedure, these microgels are becoming a promising approach for bone regeneration applications. Nevertheless, there still remains a huge gap between the understanding of how the hydrogel matrix composition can influence cell response and overall tissue formation when switching from bulk formats to microgel format, which is often neglected or rarely studied. Here, we fabricated polyethylene glycol-based microgels and bulk hydrogels incorporating gelatin and hyaluronic acid (HA), either individually or together, and assessed the impact of both hydrogel composition and format upon the osteogenic differentiation of encapsulated human bone marrow-derived mesenchymal stem cells (hBMSCs). Osteogenesis was significantly greater in microgels than bulk hydrogels for both gelatin alone (Gel) and gelatin HA composite (Gel:HA) hydrogels, as determined by the expression of Runt-related transcription factor (Runx2) and alkaline phosphatase (ALP) genes and mineral deposition. Interestingly, Gel and Gel:HA hydrogels behaved differently between bulk and microgel format. In bulk format, overall osteogenic outcomes were better in Gel:HA hydrogels, but in microgel format, while the level of osteogenic gene expression was equivalent between both compositions, the degree of mineralization was reduced in Gel:HA microgels. Investigation into the affinity of hydroxyapatite for the different matrix compositions indicated that the decreased mineralization of Gel:HA microgels was likely due to a low affinity of hydroxyapatite to bind to HA and support mineral deposition, which has a greater impact on microgels than bulk hydrogels. Together, these findings suggest that both hydrogel composition and format can determine the success of tissue formation and that there is a complex interplay of these two factors on both cell behavior and matrix deposition. This has important implications for tissue engineering, showing that hydrogel composition and geometry must be evaluated together when optimizing conditions for cell differentiation and tissue formation.

Ultrasound-guided needle interventions are common procedures in medicine, and tissue-mimicking phantoms are widely used for simulation training to bridge the gap between theory and clinical practice in a controlled environment. This review assesses tissue-mimicking materials from 24 studies as candidates for a high-fidelity ultrasound phantom, including methods for evaluating relevant acoustic and mechanical properties and to what extent the reported materials mimic the superficial layers of biological tissue. Speed of sound, acoustic attenuation, Young's modulus, hardness, needle interaction forces, training efficiency and material limitations were systematically evaluated. Although gelatin and agar have the closest acoustic values to tissue, mechanical properties are limited, and strict storage protocols must be employed to counteract dehydration and microbial growth. Polyvinyl chloride (PVC) has superior mechanical properties and is a suitable alternative if durability is desired and some ultrasound realism to human tissue may be sacrificed. Polyvinyl alcohol (PVA), while also requiring hydration, performs well across all categories. Furthermore, we propose a framework for the evaluation of future ultrasound-guided needle intervention tissue phantoms to increase the fidelity of training programs and thereby improve clinical performance.

Ischaemic stroke remains one of the leading causes of death and disability worldwide, without any long-term effective treatments targeted at regeneration. Limitations of existing and proposed cell- and drug-based therapies have led to the investigation of hydrogel-based strategies for new and improved therapies. They aim to enhance the intrinsic repair mechanisms, improve engraftment of therapeutic stem cells, and deliver drugs/biologics in a controlled manner in the post-stroke brain. The following article will explore the pathophysiology of stroke, and the need for injectable hydrogels in neural tissue engineering, focusing on a class of injectable hydrogels based on self-assembling peptides (SAPs). The various types of these materials will be addressed based on their mechanisms of self-assembly, including their novelties and benefits over conventional hydrogels, as well as recent experimental research that demonstrates the potential of these biomaterials in the treatment of stroke.

Injectable hydrogels have been employed extensively as versatile materials for cartilage regeneration due to their excellent biocompatibility, tunable structure, and ability to accommodate bioactive factors , as well as their ability to be locally delivered via minimally invasive injection to fill irregular defects. More recently, in vitro and in vivo studies have revealed that processing these materials to produce cell-laden microgels can enhance cell-cell and cell-matrix interactions and boost nutrient and metabolite exchange. Moreover, these studies have demonstrated gene expression profiles and matrix regeneration that are superior compared to conventional injectable bulk hydrogels. As cell-laden microgels and their application in cartilage repair are moving closer to clinical translation, this review aims to present an overview of the recent developments in this field. Here we focus on the currently used biomaterials and crosslinking strategies, the innovative fabrication techniques being used for the production of microgels, the cell sources used, the signals used for induction of chondrogenic differentiation and the resultant biological responses, and the ability to create three-dimensional, functional cartilage tissues. In addition, this review also covers the current clinical approaches for repairing cartilage as well as specific challenges faced when attempting the regeneration of damaged cartilage tissue. New findings related to the macroporous nature of the structures formed by the assembled microgel building blocks and the novel use of microgels in 3D printing for cartilage tissue engineering are also highlighted. Finally, we outline the challenges and future opportunities for employing cell-laden microgels in clinical applications.

Injury to the peripheral nervous system (PNS) and central nervous system (CNS) may result in severe functional loss. Spontaneous regeneration is limited to small lesions within the injured PNS and is actively suppressed within the CNS. In this chapter we discuss the pathology and changes in the physiological environment following PNS/CNS injury. Several key factors such as the glial scar and inhibitory biomolecules are addressed. Neural tissue engineering approaches attempt to provide an alternative to nerve autografts, and have shown some promising regenerative outcomes. The scaffolds are designed to provide mechanical support for endogenous/transplanted cells at the lesion site, provide guidance cues to neurites and for the attachment or delivery of biomolecules that promote regeneration. Unfortunately many of the current scaffolds used for neural tissue engineering provide only limited regulation of cellular response due to insufficient control of physical support, topological stimulation, degradability and inflammatory/foreign body responses.

T cells are predominantly produced by the thymus and play a significant role in maintaining our adaptive immune system. Physiological involution of the thymus occurs gradually with age, compromising naive T cell output, which can have severe clinical complications. Also, T cells are utilized as therapeutic agents in cancer immunotherapies. Therefore, there is an increasing need for strategies aimed at generating naive T cells. The majority of in vitro T cell generation studies are performed in two-dimensional (2D) cultures, which ignore the physiological thymic microenvironment and are not scalable; therefore, we applied a new three-dimensional (3D) approach. Here, we use a gelatin-based 3D microgel system for T lineage induction by co-culturing OP9-DL4 cells and mouse fetal-liver-derived hematopoietic stem cells (HSCs). Flow cytometric analysis revealed that microgel co-cultures supported T lineage induction similar to 2D cultures while providing a 3D environment. We also encapsulated mouse embryonic thymic epithelial cells (TECs) within the microgels to provide a defined 3D culture platform. The microgel system supported TEC maintenance and retained their phenotype. Together, these data show that our microgel system has the capacity for TEC maintenance and induction of in vitro T lineage differentiation with potential for scalability.

Myocardial tissue engineering is a promising therapy for myocardial infarction recovery. The success of myocardial tissue engineering is likely to rely on the combination of cardiomyocytes, prosurvival regulatory signals, and a flexible biomaterial structure that can deliver them. In this study, poly(glycerol sebacate) (PGS), which exhibits stable elasticity under repeated tensile loading, was engineered to provide physical features that aligned cardiomyocytes in a similar manner to that seen in native cardiac tissue. In addition, a small molecule mimetic of brain derived neurotrophic factor (BDNF) was polymerized into the PGS to achieve a continuous and steady release. Micropatterning of PGS elastomers increased cell alignment, calcium transient homogeneity, and cell connectivity. The intensity of the calcium transients in cardiomyocytes was enhanced when cultured on PGS which released a small molecule BDNF mimetic. This study demonstrates that robust micropatterned elastomer films are a potential candidate for the delivery of functional cardiomyocytes and factors to the injured or dysfunctional myocardium, as well as providing novel in vitro platforms to study cardiomyocyte physiology.

β

Light triggered release of an antibiotic from a click crosslinked hydrogel was developed by conjugating ciprofloxacin through a photo-cleavable linker to the hydrogel network structure. Upon irradiation of the hydrogel material with UV light (365 nm) at low intensity, native ciprofloxacin was released into the surrounding environment and could be detected by HPLC. The antimicrobial activity of the released compound on Staphylococcus aureus was demonstrated.

β3-peptides uniquely form shear thinning hydrogels which are proteolytically stable and biocompatible. Herein we describe the synthesis, material and optical characterization of a new class of fluorescently labeled hydrogelators based on a helical N-acetylated β3-peptide backbone. The resulting hydrogels were analyzed using fluorescence microscopy to confirm successful incorporation of the fluorophore within the fiber matrix without compromising the β3-peptide self-assembly. Serial, noninvasive conscious animal imaging was used to monitor the injected hydrogel, delivered via subcutaneous injection, while tracking their degradation patterns in real-time. The hydrogels demonstrated persistent, high-intensity fluorescence when monitored over a 14-day period.

On-demand photo-uncaging of reactive thiols have been employed in engineering biomaterial scaffolds for regulation of cellular activities. A drawback of the current photo-uncaging chemistry is the utilization of high energy UV light or 2-photon laser light, which may be harmful to cells and cause undesired side reactions within the biological environment. We introduce an effective approach for the caging of thiol using monobromobimane, which can be removed under irradiation of light at λ = 420 nm and in the presence of electrophiles, such as acrylate, propiolate and maleimide, for trapping of the newly release thiol. This chemical approach can be used in visible light-induced polymer coupling and cross-linking for the preparation of cell-laden hydrogels.

Current clinical approaches to treat articular cartilage degeneration provide only a limited ability to regenerate tissue with long-term durability and functionality. In this application, injectable bulk hydrogels and microgels containing stem cells can provide a suitable environment for tissue regeneration. However insufficient cell–cell interactions, low differentiation efficiency and poor tissue adhesion hinder the formation of high-quality hyaline type cartilage. Here, we have designed a higher order tissue-like structure using injectable cell-laden microgels as the building blocks to achieve human bone marrow-derived mesenchymal stem cell (hBMSC) long-term maintenance and chondrogenesis. We have demonstrated that a 4-arm poly(ethylene glycol)-N-hydroxysuccinimide (NHS) crosslinker induces covalent bonding between the microgel building blocks as well as the surrounding tissue mimic. The crosslinking process assembles the microgels into a 3D construct and preserves the viability and cellular functions of the encapsulated hBMSCs. This assembled microgel construct encourages upregulation of chondrogenic markers in both gene and glycosaminoglycan (GAG) expression levels. In addition, the regenerated tissue in the assembled microgels stained positively with Alcian blue and Safranin O exhibiting unique hyaline-like cartilage features. Furthermore, the immunostaining showed a favourable distribution and significantly higher content of type II collagen in the assembled microgels when compared to both the bulk hydrogel and pellet cultures. Collectively, this tissue adhesive hBMSC-laden microgel construct provides potential clinical opportunities for articular cartilage repair and other applications in regenerative medicine. Statement of Significance A reliable approach to reconstruct durable and fully functional articular cartilage tissue is required for effective clinical therapies. Here, injectable hydrogels together with cell-based therapies offer new treatment strategies in cartilage repair. For effective cartilage regeneration, the injectable hydrogel system needs to be bonded to the surrounding tissue and at the same time needs to be sufficiently stable for prolonged chondrogenesis. In this work, we utilised injectable hBMSC-laden microgels as the building blocks to create an assembled construct via N-hydroxysuccinimide-amine coupling. This crosslinking process also allows for rapid bonding between the assembled microgels and a surrounding tissue mimic. The resultant assembled microgel-construct provides both a physically stable and biologically dynamic environment for hBMSC chondrogenesis, leading to the production of a mature hyaline type cartilage structure.

Tetrazine-norbornene ligation has previously been applied in bioorthognal polymer crosslinking to form hydrogels suitable for 3D cell culture. However, the tetrazine group is prone to reduction by the free thiol in a biological environment, reducing the crosslinking efficiency and shortening the storage of tetrazine containing linkers. Here, we introduce a method to form a tetrazine group in situ by catalytic oxidation of the dihydrogen tetrazine using horse radish peroxidase (HRP). Enzymatic oxidation is highly efficient at a low HRP concentration and does not require hydrogen peroxide, allowing for rapid gelation when HRP was added to an aqueous solution of 4-arm PEG dihydrogentetrazine and gelatin norbornene. The storage modulus of the resultant gels can be varied by changing the concentration of the crosslinker, which is in the range of 1.2-3.8 kPa. Human mesenchymal stem cells encapsulated within these gels, with varying stiffness, display varied interactions and morphologies and can be maintained with prolonged culture periods of at least 32 days of 3D culture. The enzymatic activation of tetrazine-norbornene is therefore an attractive addition to the tetrazine ligation that is highly suitable for cell related studies in tissue engineering.

In this work, we demonstrate the potential of surface-initiated single electron transfer living radical polymerization for surface modification applications that confer low-fouling properties. The versatility of the technique, which can be applied to a wide variety of substrates, has been displayed by the successful grafting of a range of monomers after immobilizing a bromine initiator on the surface via plasma polymerization. The thickness of the grafted surfaces can be controlled through variation of reaction parameters such as monomer concentration, reaction time, and the ratio between catalyst and ligand. Furthermore, the low-fouling properties of the resulting surfaces were demonstrated against fully concentrated serum proteins and adhesive fibroblast cells, via grafting of N-hydroxyethyl acrylamide (N-HEA) or [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA). This rapid and versatile coating technique, which has the ability to be applied to a wide range of substrates, can be performed in aqueous conditions without the exclusion of atmospheric oxygen, and shows excellent potential for the surface modification of biomaterial surfaces that require low-fouling properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Stem cell injections for the treatment of articular cartilage damage are a promising approach to achieve tissue regeneration. However, this method is encumbered by high cell apoptosis rates, low retention in the cartilage lesion, and inefficient chondrogenesis. Here, we have used a facile, very low cost-based microfluidic technique to create visible light-cured microgels composed of gelatin norbornene (GelNB) and a poly(ethylene glycol) (PEG) cross-linker. In addition, we have demonstrated that the process enables the rapid in situ microencapsulation of human bone marrow-derived mesenchymal stem cells (hBMSCs) under biocompatible microfluidic-processing conditions for long-term maintenance. The hBMSCs exhibited an unusually high degree of chondrogenesis in the GelNB microgels with chondro-inductive media, specifically toward the hyaline cartilage structure, with significant upregulation in type II collagen expression compared to the bulk hydrogel and "gold standard" pellet culture. Overall, we have demonstrated that these protein-based microgels can be engineered as promising therapeutic candidates for articular cartilage regeneration, with additional potential to be used in a variety of other applications in regenerative medicine.

Staphylococcus capitis is an opportunistic pathogen often implicated in bloodstream infections in the neonatal intensive care unit (NICU). This is assisted by its ability to form biofilms on indwelling central venous catheters (CVC), which are highly resistant to antibiotics and the immune system. We sought to understand the fundamentals of biofilm formation by S. capitis in the NICU, using seventeen clinical isolates including the endemic NRCS-A clone and assessing nine commercial and two modified polystyrene surfaces. S. capitis clinical isolates from the NICU initiated biofilm formation only in response to hyperosmotic conditions, followed by a developmental progression driven by icaADBC expression to establish mature biofilms, with polysaccharide being their major extracellular polymer substance (EPS) matrix component. Physicochemical features of the biomaterial surface, and in particular the level of the element oxygen present on the surface, significantly influenced biofilm development of S. capitis. A lack of highly oxidized carbon species on the surface prevented the immobilization of S. capitis EPS and the formation of mature biofilms. This information provides guidance in regard to the preparation of hyperosmolar total parenteral nutrition and the engineering of CVC surfaces that can minimize the risk of catheter-related bloodstream infections caused by S. capitis in the NICU.

Functional deficits due to neuronal loss are a common theme across multiple neuropathologies, including traumatic brain injury (TBI). Apart from mitigating cell death, another approach to treating brain injuries involves re-establishing the neural circuitry at the lesion site by utilizing exogeneous and/or endogenous stem cells to achieve functional recovery. While there has been limited success, the emergence of new bioactive matrices that promote neural repair introduces new perspectives on the development of regenerative therapies for TBI. This review briefly discusses current development on cell-based therapies and the use of bioactive matrices, hydrogels in particular, when incorporated in regenerative therapies. Desirable characteristics of bioactive matrices that have been shown to augment neural repair in TBI models were identified and further discussed. Understanding the relative outcomes of newly developed biomaterials implanted in vivo can better guide the development of biomaterials as a therapeutic strategy, for biomaterial-based cellular therapies are still in their nascent stages. Nonetheless, the value of bioactive matrices as a treatment for acute brain injuries should be appreciated and further developed. STATEMENT OF SIGNIFICANCE: Cell-based therapies have received attention as an alternative therapeutic strategy to improve clinical outcome post-traumatic brain injury but have achieved limited success. Whilst the incorporation of newly developed biomaterials in regenerative therapies has shown promise in augmenting neural repair, studies have revealed new hurdles which must be overcome to improve their therapeutic efficacy. This review discusses the recent development of cell-based therapies with a specific focus on the use of bioactive matrices in the form of hydrogels, to complement cell transplantation within the injured brain. Moreover, this review consolidates in vivo animal studies that demonstrate relative functional outcome upon the implantation of different biomaterials to highlight their desirable traits to guide their development for regenerative therapies in traumatic brain injury.

Hydrogels are attractive candidates for use in tissue-engineering and the encapsulation and subsequent differentiation of mesenchymal stem/stromal cells (MSCs) is a strategy that holds great promise for the repair and regeneration of bone and cartilage. However, MSCs are well-known for their sensitivity to mechanical cues, particularly substrate stiffness, and so the inherent softness of hydrogels is poorly matched to the mechanical cues that drive efficient osteogenesis. One approach to overcome this limitation is to harness mechanotransductive signalling pathways and override the signals cells receive from their environment. Previous reports demonstrate that mechanosensitive miRNAs, miR-100-5p and miR-143-3p can enhance MSC osteogenesis, using a complex multi-step procedure to transfect, encapsulate and differentiate the cells. In this study, we develop and characterise a facile system for in situ transfection of MSCs encapsulated within a light-crosslinkable gelatin-PEG hydrogel. Comparing the influence of different transfection agents and hydrogel compositions, we show that particle size, charge, and hydrogel mechanical properties all influence the diffusion of embedded transfection agent complexes. By incorporating both MSCs and transfection agents into the hydrogels we demonstrate successful in situ transfection of encapsulated MSCs. Comparing the efficacy of pre- and in situ transfection of miR-100-5p/miR-143-3p on the osteogenic capacity of hydrogel-encapsulated MSCs, our data demonstrates superior mineralisation and osteogenic gene expression following in situ transfections. Overall, we demonstrate a simple, one-pot system for in situ transfection of miRNAs to enhance MSC osteogenic potential and thus demonstrates significant promise to improve the efficiency of MSC differentiation in hydrogels for bone tissue-engineering applications. STATEMENT OF SIGNIFICANCE: Mesenchymal stromal cells (MSCs) are sensitive to cues from their surrounding microenvironment. Osteogenesis is enhanced in MSCs grown on stiffer substrates, but this is limited when using hydrogels for bone tissue-engineering. Modulating pro-osteogenic genes with mechanosensitive microRNAs (miRNAs) represents a potential tool to overcome this challenge. Here we report a hydrogel platform to deliver miRNAs to encapsulated MSCs. We characterise effects of hydrogel composition and transfection agent type on their mobility and transfection efficiency, demonstrating successful in situ transfection of MSCs and showing that miRNAs can significantly enhance osteogenic mineral deposition and marker gene expression. This system was simpler and more effective than conventional 2D transfection prior to encapsulation and therefore holds promise to improve MSC differentiation in bone tissue-engineering.

Hydrogels prepared from naturally derived gelatin can provide a suitable environment for cell attachment and growth, making them favourable materials in tissue engineering. However, physically crosslinked gelatin hydrogels are not stable under physiological conditions while chemical crosslinking of gelatin by radical polymerization may be harmful to cells. In this study, we attached the norbornene functional group to gelatin, which was subsequently crosslinked with a polyethylene glycol (PEG) linker via the nitrile oxide-norbornene click reaction. The rapid crosslinking process allows the hydrogel to be formed within minutes of mixing the polymer solutions under physiological conditions, allowing the gels to be used as injectable materials. The hydrogels properties including mechanical strength, swelling and degradation, can be tuned by changing either the ratio of the reacting groups or the total concentration of the polymer precursors. Murine embryonic fibroblastic cells cultured in soft gels (2 wt% of gelatin and 1 wt% of PEG linker) demonstrated high cell viability as well as similar phenotypic profiles (PDGFRα and MTS15) to Matrigel cultures over 5 days. Thymic epithelial cell and fibroblast co-cultures produced epithelial colonies in these gels following 7 days incubation. These studies demonstrate that gelatin based hydrogels, prepared using "click" crosslinking, provide a robust cell culture platform with retained benefits of the gelatin material, and are therefore suitable for use in various tissue engineering applications.

We have described a new class of hydrogelator based on helical β(3)-peptides carrying a bioactive payload. The β(3)-peptides self-assemble in aqueous solution to form a nanofibrous mesh resulting in a stable hydrogel. The simple design provides the versatility for attaching different functional payloads to the β(3)-peptide scaffold to develop new materials.

We report a new class of β-peptide based hydrogel for neural tissue engineering. Our β-peptide forms a network of nanofibres in aqueous solution, resulting in a stable hydrogel at physiological conditions. The hydrogel shows excellent compatibility with neural cells and provides a suitable environment for cells to adhere and proliferate.

While polycaprolactone (PCL) and similar polyesters are commonly used as degradable scaffold materials in tissue engineering and related applications, non-specific adsorption of environmental proteins typically precludes any control over the signalling pathways that are activated during cell adhesion to these materials. Here we describe the preparation of PCL-based fibres that facilitate cell adhesion through well-defined pathways while preventing adhesion via adsorbed proteins. Surface-initiated atom transfer radical polymerisation (SI-ATRP) was used to graft a protein-resistant polymer brush coating from the surface of fibres, which had been electrospun from a brominated PCL macroinitiator. This coating also provided alkyne functional groups for the attachment of specific signalling molecules via the copper-mediated azide-alkyne click reaction; in this case, a cyclic RGD peptide with high affinity for αvβ3 integrins. Mesenchymal stem cells were shown to attach to the fibres via the peptide, but did not attach in its absence, nor when blocked with soluble peptide, demonstrating the effective control of cell adhesion pathways.

Bilayer plasma polymer (PP) films were examined using a combination of X-ray and neutron reflectometery and X-ray photoelectron spectroscopy to gain an understanding of the interfacial structures that form between the films. Three different PP films were produced from the monomers hexamethyldisiloxane (HMDSO), di(ethylene glycol) dimethyl ether (DG), and allylamine (AA) at different load powers. These films were used as "substrates" for the subsequent deposition of a deuterated DG (dDG) PP top film. The width of the interfacial region was found to be strongly dependent on the chemical and physical properties of the substrate film. These findings have relevance to the general use and application of plasma polymer films. We examine the effect of load power and monomer chemistry on the interface that forms between a plasma polymer substrate and a deuterated plasma polymer top film.

Antibacterial hydrogels containing quaternary ammonium (QA) groups were prepared via a facile thiol-ene “click” reaction using multifunctional poly(ethylene glycol) (PEG). The multifunctional PEG polymers were prepared by an epoxy-amine ring opening reaction. The chemical and physical properties of the hydrogels could be tuned with different crosslinking structures and crosslinking densities. The antibacterial hydrogel structures prepared from PEG Pendant QA were less well-defined than those from PEG Chain-End QA. Furthermore, functionalization of the PEG-type hydrogels with QA groups produced strong antibacterial abilities against Staphylococcus aureus, and therefore has the potential to be used as an anti-infective material for biomedical devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 656–667

This communication describes the first application of cycloaddition between an in situ generated nitrile oxide with norbornene leading to a polymer crosslinking reaction for the preparation of poly(ethylene glycol) hydrogels under physiological conditions. Hydrogels with high water content and robust physical strength are readily formed within 2-5 min by a simple two-solution mixing method which allows 3D encapsulation of neuronal cells. This bioorthogonal crosslinking reaction provides a simple yet highly effective method for preparation of hydrogels to be used in bioengineering.

It is often difficult to achieve a satisfactory balance of compliance and biocompatibility simultaneously in a pure elastomeric material. In this work, we successfully fabricated an elastomeric fibrous mat from poly(glycerol sebacate) (PGS) with a 2:3 mol ratio of glycerol to sebacic acid, using the core/shell electrospinning technology of poly(vinyl alcohol) (PVA) as a temporary shell and PGS prepolymer as the core. After the core/shell electrospinning, the PGS core was crosslinked by thermal treatment and the PVA shell was partially removed by dissolution in water. The resulting PGS fibre mat was as soft as many soft tissues (e.g., muscle), and demonstrated nonlinear, J-shaped stress–strain curves (the slope continuously increased with increasing strain) when saturated with water. In vitro evaluations showed that the spun PGS 2:3 mat had good cytocompatibility, better than the culture medium and the control material, PLLA fibrous mat. Hence, the newly developed electrospun PGS 2:3 fibre mats may offer a much better choice of scaffolds than existing products for engineering of soft tissues working in dynamic conditions.

A.E.R. was supported in this work by an Australian Postgraduate Award and by the Cooperative Research Centre for Polymers. D.R.N. was supported by an NHMRC CDA Fellowship.

Ordered hetero-junctions using one dimensional inorganic nanostructures have been widely studied to develop devices such as high efficiency photovoltaic devices, light emitting diodes, catalysts, supercapacitors, lithium ion batteries and nanogenerators. High quality Schottky contacts can be obtained by the spin coating of conducting polymer dispersions/solutions onto inorganic nanostructures; however, the interaction of polar surfaces of the nanostructures with chemically active materials in the spin coating solution makes the junctions less reliable. In the present work, we show that high quality junctions can be fabricated by either directly growing the nanostructures onto the vapour phase polymerised (VPP) poly(3,4-ethylenedioxythiophene) (PEDOT) substrates or sandwiching VPP polymerised substrates, thereby avoiding any unwanted interactions with the acidic additives from the polymer solution at the organic–inorganic interfaces. The I–V measurements proved that the direct growth of ZnO NWs on PEDOT coated substrates creates an ohmic contact, whereas the PEDOT layer on top surface produces a Schottky contact due to the dipole moment with the polar ends.

This paper reports a detailed discussion on the aqueous chemical growth of ZnO nanowires (NWs) on 2-D and 3-D polyethersulfone. Substrate surface chemistry and substrate placement in the growth solution is found to affect the morphology of the grown nanostructures and indeed the growth direction of the NWs. We report for the first time a-axis ZnO NWs using a low temperature synthesis method. The electrochemical behaviour regarding water oxidation showed significant differences depending on the growth directions but this difference was eliminated after annealing, both in dark and under illumination.

We introduce a click and visible-light triggered unclick approach via thio-bromo reaction and hydroquinone photoreduction/trimethyl lock cleavage for polymer modifications. Both reactions can be carried out in water and at ambient temperature, enabling preparation of bioorthogonal hydrogels for encapsulation and controlled release of various cells.

We introduce an efficient method for the preparation of photolabile polymer linkers to be used in the fabrication of bioorthogonal and photodegradable hydrogels. The versatility of this synthesis strategy allows for incorporation of a series of chromophores responsive to addressable wavelengths of UV and broad spectrum visible light. Consequently, selective release of different cell types from composite hydrogels by user-defined timing can be achieved by irradiating the materials with different wavelengths of light.

Swelling of hydrogels leads to a decrease in mechanical performance coupled with complications in solute diffusion. In addition, hydrogel swelling affects patient safety in biomedical applications such as compression of tissue and fluid blockage. A conventional strategy for suppressing swelling is to introduce a thermoresponsive polymer with a lower critical solution temperature (LCST) within the network structure to counter the water uptake at elevated temperature. However, altering the gel's mechanical strength via modification of the network structure often affects the water uptake behavior and thus a nonswelling platform with tunable mechanical properties suitable for various biomedical applications is desirable. In this study we applied the commercially available triblock PEG-PPG-PEG (Pluronic) as a cross-linker for the preparation of nucleophilic thiol-yne click cross-linked hydrogels with suppressed swelling at physiologically relevant temperature. The mechanical properties and degradation rate of these nonswelling hydrogels can be tuned by judicious combinations of the available linkers. The Pluronic linkers can be applied to prepare biologically relevant gelatin based hydrogels with suppressed swelling under physiological conditions that support attachment of fibroblast cells in 2D culture and controlled release of albumin, paving the way for the development of reliable and better performing soft biomaterials.

Regeneration of the brain following injury is often slow or ineffective due to a dearth of cellular cues that support and guide neural regeneration. Scaffolds have been actively investigated for new therapies targeting neurodegenerative diseases and traumatic brain injury. Electrospinning offers many advantages for the fabrication of a diverse and tunable range of neural scaffolds. The architecture of electrospun scaffolds can be tailored to meet specific requirements such as the culture of different types of neural cells and the incorporation and delivery of bioactive molecules. Electrospun fibers have been highly successful in providing both biological and physical cues to repair the injured brain. This chapter provides an overview of the design principles of electrospun scaffolds for neural tissue engineering, with a focus on brain repair.

Cells respond to their environment in complex and sometimes poorly understood ways. Protein, peptide and synthetic peptidomimetic ligands may all be used to stimulate cells via receptor signaling, using interactions that are often highly specific. Polymer substrates that present these ligands provide a promising way to control cell development, both for applications in biotechnology and for fundamental studies of cell biology. Here we review a large range of techniques that have been employed to create and characterize ligand-functionalized substrates, with a particular focus on techniques that allow specific and consistent stimulation.

Background: Adequate cell–scaffold interactions and neurotrophin support are essential factors for neural regeneration. Aim: To provide insight into the biofunctionalization of complex 3D scaffolds with nanoscale precision, as well as the effect of spatial distribution of brain-derived neurotrophic factor (BDNF) and its prolonged stimulation in combination with enhanced cell affinity of nanofibrous scaffolds on the survival/proliferation and neurite outgrowth. Methods & materials: We developed a versatile approach using layer-by-layer self-assembly to incorporate cell adhesion and spatial representation of neurotrophic factors into complex nanofibrous scaffolds. Results: Heparin/poly-L-lysine (PLL) polyelectrolyte multilayers (PEMs) were deposited on electrospun poly-ε-caprolatone nanofibers. Well-controlled amounts of BDNF were immobilized on the PEM-modified nanofibers. In addition, longer neurite outgrowth was observed in neural progenitor cells cultured on PLL-terminating PEM scaffolds. The immobilized BDNF on PLL-terminated PEM scaffolds resulted in significantly longer neurites and higher cell numbers (p < 0.01) compared with BDNF-free and BDNF-adsorbed PLL-terminating scaffolds. Interestingly, there was no upregulation of TrkB-FL, TrkB-T1 or GAP-43 mRNAs with immobilized BDNF in day 5 cultures. Discussion & conclusion: This work reinforces the importance of the combinatorial effects of biomaterial scaffold nanostructure and spatial presentation of neurotrophins in directing neural progenitor cell fates. Original submitted 18 January 2013; Revised submitted 3 May 2013

Brain repair following disease and injury is very limited due to difficulties in recruiting and mobilizing stem cells towards the lesion. More importantly, there is a lack of structural and trophic support to maintain viability of the limited stem/progenitor cells present. This study investigates the effectiveness of an injectable gelatin-based hydrogel in attracting neural progenitor cells (NPCs) from the subventricular zone (SVZ) towards the implant. Glial cell-line-derived neurotrophic factor (GDNF) encapsulated within the hydrogel and porosity within the hydrogel prevents glial scar formation. By directly targeting the hydrogel implant towards the SVZ, neuroblasts can actively migrate towards and along the implant tract. Significantly more doublecortin (DCX)-positive neuroblasts surround implants at 7 d post-implantation (dpi) compared with lesion alone controls, an effect that is enhanced when GDNF is incorporated into the hydrogels. Neuroblasts are not observed at the implant boundary at 21 dpi, indicating that neuroblast migration has halted, and neuroblasts have either matured or have not survived. The development of an injectable gelatin-based hydrogel has significant implications for the treatment of some neurodegenerative diseases and brain injuries. The ability of GDNF and porosity to effectively prevent glial scar formation will allow better integration and interaction between the implant and surrounding neural tissue.

The chemistry of substrate–film interface (underside) of di(ethylene glycol) dimethyl ether plasma polymer (DGpp) films has been studied directly and compared to the top layer of the film (topside). By depositing the plasma polymer films onto indium tin oxide (ITO) glass, the films were easily delaminated from the substrate. The top- and underside of the films were examined by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that a rapid increase in pressure during plasma polymerization results in steep chemical gradients in the films, while small pressure changes do not lead to chemical gradient formation. These observations validate the findings of previous neutron reflectometry modeling studies of this class of plasma polymer thin film. In addition, subtle variations in plasma polymer film chemistry were observed between different substrates they were deposited onto. This approach will allow additional studies on the mechanisms of early plasma polymer thin film formation with various monomers.

The controlled ring-opening polymerisation (ROP) of an e-caprolactone derivative that contains an ATRP initiator pendant to the ring, γ-(2-bromo-2-methyl propionyl)-e-caprolactone (γ-BMPCL), and its copolymerisation with e-caprolactone (CL) is reported. Functional PCL copolymers that contained pendant ATRP initiators were obtained with higher than previously reported molecular weights using diphenyl phosphate (DPP) as the catalyst at room temperature. Surface-initiated ATRP grafting of oligo(ethylene glycol) methacrylate was successfully carried out on the surface of two dimensional (2D) substrates comprising thin films of a functional PCL copolymer.

Multi-responsive poly(acrylic acid)–poly(ethylene glycol) (PAA–PEG) hydrogels with well-defined crosslinking structures were synthesized using atom transfer radical polymerization (ATRP) and copper-catalyzed 1,3-dipolar azide-alkyne cycloaddition (CuAAC) techniques. The well-defined PAA–PEG hydrogels with different degrees of crosslinking were produced from controlling the molecular weight of the PAA and PEG chains. The prepared multi-responsive hydrogels exhibit regular physical and mechanical properties by adjusting the pH and Ca2+ ion secondary crosslinking. With increasing pH, the swelling ratio of the well-defined multi-responsive PAA–PEG hydrogels increased remarkably. Furthermore, the well-defined PAA–PEG hydrogels with Ca2+ secondary crosslinking possessed a significantly higher crosslinking density as reflected by the lower swelling ratio, higher storage modulus, higher electrical conductivity and thermal stability. An in vitro cell viability assay also indicated that well-defined multi-responsive PAA–PEG hydrogels are biocompatible and have potential for implantable biomaterials.

OBJECTIVE: To systematically compare the in vitro electrochemical and mechanical properties of several electrode coatings that have been reported to increase the efficacy of medical bionics devices by increasing the amount of charge that can be delivered safely to the target neural tissue. APPROACH: Smooth platinum (Pt) ring and disc electrodes were coated with reduced graphene oxide, conductive hydrogel, or electrodeposited Pt-Ir. Electrodes with coatings were compared with uncoated smooth Pt electrodes before and after an in vitro accelerated aging protocol. The various coatings were compared mechanically using the adhesion-by-tape test. Electrodes were stimulated in saline for 24 hours/day 7 days/week for 21 d at 85 °C (1.6-year equivalence) at a constant charge density of 200 µC/cm2/phase. Electrodes were graded on surface corrosion and trace analysis of Pt in the electrolyte after aging. Electrochemical measurements performed before, during, and after aging included electrochemical impedance spectroscopy, cyclic voltammetry, and charge injection limit and impedance from voltage transient recordings. MAIN RESULTS: All three coatings adhered well to smooth Pt and exhibited electrochemical advantage over smooth Pt electrodes prior to aging. After aging, graphene coated electrodes displayed a stimulation-induced increase in impedance and reduction in the charge injection limit (p

Mitochondrial DNA haplotypes are associated with various phenotypes, such as altered susceptibility to disease, environmental adaptations, and aging. Accumulating evidence suggests that mitochondrial DNA is essential for cell differentiation and the cell phenotype. However, the effects of different mitochondrial DNA haplotypes on differentiation and development remain to be determined. Using embryonic stem cell lines possessing the same Mus musculus chromosomes but harboring one of Mus musculus, Mus spretus, or Mus terricolor mitochondrial DNA haplotypes, we have determined the effects of different mitochondrial DNA haplotypes on chromosomal gene expression, differentiation, and mitochondrial metabolism. In undifferentiated and differentiating embryonic stem cells, we observed mitochondrial DNA haplotype-specific expression of genes involved in pluripotency, differentiation, mitochondrial energy metabolism, and DNA methylation. These mitochondrial DNA haplotypes also influenced the potential of embryonic stem cells to produce spontaneously beating cardiomyocytes. The differences in gene expression patterns and cardiomyocyte production were independent of ATP content, oxygen consumption, and respiratory capacity, which until now have been considered to be the primary roles of mitochondrial DNA. Differentiation of embryonic stem cells harboring the different mitochondrial DNA haplotypes in a 3D environment significantly increased chromosomal gene expression for all haplotypes during differentiation. However, haplotype-specific differences in gene expression patterns were maintained in this environment. Taken together, these results provide significant insight into the phenotypic consequences of mitochondrial DNA haplotypes and demonstrate their influence on differentiation and development. We propose that mitochondrial DNA haplotypes play a pivotal role in the process of differentiation and mediate the fate of the cell.