Comparison and characterization of multiple biomaterial conduits for peripheral nerve repair

BDNF-loaded chitosan-based mimetic mussel polymer conduits for repair of peripheral nerve injury

Care for patients with peripheral nerve injury is multifaceted, as traditional methods are not devoid of limitations. Although the utilization of neural conduits shows promise as a therapeutic modality for peripheral nerve injury, its efficacy as a standalone intervention is limited. Hence, there is a pressing need to investigate a composite multifunctional neural conduit as an alternative treatment for peripheral nerve injury. In this study, a BDNF-loaded chitosan-based mimetic mussel polymer conduit was prepared. Its unique adhesion characteristics allow it to be suture-free, improve the microenvironment of the injury site, and have good antibacterial properties. Researchers utilized a rat sciatic nerve injury model to evaluate the progression of nerve regeneration at the 12-week postoperative stage. The findings of this study indicate that the chitosan-based mimetic mussel polymer conduit loaded with BDNF had a substantial positive effect on myelination and axon outgrowth. The observed impact demonstrated a favorable outcome in terms of sciatic nerve regeneration and subsequent functional restoration in rats with a 15-mm gap. Hence, this approach is promising for nerve tissue regeneration during peripheral nerve injury.

Extrusion 3D-printing and characterization of poly(caprolactone fumarate) for bone regeneration applications

Polycaprolactone fumarate (PCLF) is a cross-linkable PCL derivative extensively considered for tissue engineering applications. Although injection molding has been widely used to develop PCLF scaffolds, platforms developed using such technique lack precise control on architecture, design, and porosity required to ensure adequate cellular and tissue responses. In particular, the scaffolds should provide a suitable surface for cell attachment and proliferation, and facilitate cell-cell communication and nutrient flow. 3D printing technologies have led to new architype for biomaterial development with micro-architecture mimicking native tissue. Here, we developed a method for 3D printing of PCLF structures using the extrusion printing technique. The crosslinking property of PCLF enabled the unique post-processing of 3D printed scaffolds resulting in highly porous and flexible PCLF scaffolds with compressive properties imitating natural features of cancellous bone. Generated scaffolds supported excellent attachment and proliferation of mesenchymal stem cells (MSC). The high porosity of PCLF scaffolds facilitated vascularized membrane formation demonstrable with the stringency of the ex ovo chicken chorioallantoic membrane (CAM) implantation. Furthermore, upon implantation to rat calvarium defects, PCLF scaffolds enabled an exceptional new bone formation with a bone mineral density of newly formed bone mirroring native bone tissue. These studies suggest that the 3D-printed highly porous PCLF scaffolds may serve as a suitable biomaterial platform to significantly expand the utility of the PCLF biomaterial for bone tissue engineering applications.

Neural stem cell-derived exosomes-loaded adhesive hydrogel controlled-release promotes cerebral angiogenesis and neurological function in ischemic stroke

OBJECTIVE

Ischemic stroke has become one of the leading diseases for international death, which brings burden to the economy and society. Exosomes (Exos) derived following neural stem cells (NSCs) stimulation promote neurogenesis and migration of NSCs. However, Exos themselves are easily to be removed in vivo. Our study is to investigate whether adhesive hyaluronic acid (HAD) hydrogel loading NSCs-derived-Exo (HAD-Exo) would promote the recovery of ischemic stroke.

METHODS

A mouse model of middle cerebral artery occlusion (MCAO) was established. PBS, Exo, HAD, and HAD-Exo groups were independently stereotactically injected in mice, respectively. The modified neurological severity score scale and behaviour tests were used to evaluate neurological improvement. Neuroimagings were used to observe the improvement of cerebral infarct volume and vessels. Immunofluorescence staining was used to verify the expression of vascular and cell proliferation-related proteins.

RESULTS

The structural and mechanical property of HAD and HAD-Exo were detected. Behavioral results showed that HAD-Exo significantly improved neurological functions, especially motor function. Neuroimagings showed that HAD-Exo significantly promoted infarct volume and angiogenesis. Immunofluorescence staining showed that HAD-Exo significantly promoted the cerebral angiogenesis and anti-inflammation.

CONCLUSION

NSCs derived exosomes-loaded adhesive HAD hydrogel controlled-release could promote cerebral angiogenesis and neurological function for ischemic stroke.

Electrical stimulation via repeated biphasic conducting materials for peripheral nerve regeneration

Improved materials for peripheral nerve repair are needed for the advancement of new surgical techniques in fields spanning from oncology to trauma. In this study, we developed bioresorbable materials capable of producing repeated electric field gradients spaced 600 μm apart to assess the impact on neuronal cell growth, and migration. Electrically conductive, biphasic composites comprised of poly (glycerol) sebacate acrylate (PGSA) alone, and doped with poly (pyrrole) (PPy), were prepared to create alternating segments with high and low electrically conductivity. Conductivity measurements demonstrated that 0.05% PPy added to PSA achieved an optimal value of 1.25 × 10-4 S/cm, for subsequent electrical stimulation. Tensile testing and degradation of PPy doped and undoped PGSA determined that 35-40% acrylation of PGSA matched nerve mechanical properties. Both fibroblast and neuronal cells thrived when cultured upon the composite. Biphasic PGSA/PPy sheets seeded with neuronal cells stimulated for with 3 V, 20 Hz demonstrated a 5x cell increase with 1 day of stimulation and up to a 10x cell increase with 3 days stimulation compared to non-stimulated composites. Tubular conduits composed of repeated high and low conductivity materials suitable for implantation in the rat sciatic nerve model for nerve repair were evaluated in vivo and were superior to silicone conduits. These results suggest that biphasic conducting conduits capable of maintaining mechanical properties without inducing compression injuries while generating repeated electric fields are a promising tool for acceleration of peripheral nerve repair to previously untreatable patients.

Nerve regeneration using decellularized tissues: challenges and opportunities

In tissue engineering, the decellularization of organs and tissues as a biological scaffold plays a critical role in the repair of neurodegenerative diseases. Various protocols for cell removal can distinguish the effects of treatment ability, tissue structure, and extracellular matrix (ECM) ability. Despite considerable progress in nerve regeneration and functional recovery, the slow regeneration and recovery potential of the central nervous system (CNS) remains a challenge. The success of neural tissue engineering is primarily influenced by composition, microstructure, and mechanical properties. The primary objective of restorative techniques is to guide existing axons properly toward the distal end of the damaged nerve and the target organs. However, due to the limitations of nerve autografts, researchers are seeking alternative methods with high therapeutic efficiency and without the limitations of autograft transplantation. Decellularization scaffolds, due to their lack of immunogenicity and the preservation of essential factors in the ECM and high angiogenic ability, provide a suitable three-dimensional (3D) substrate for the adhesion and growth of axons being repaired toward the target organs. This study focuses on mentioning the types of scaffolds used in nerve regeneration, and the methods of tissue decellularization, and specifically explores the use of decellularized nerve tissues (DNT) for nerve transplantation.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

Artificial PGA/Collagen-based Bilayer Conduit in Short Gap Interposition Setting Provides Comparable Regenerative Potential to Direct Suture

The aim of this study was to evaluate whether the Nerbridge, an artificial polyglycolic acid conduit with collagen matrix, is comparable to direct nerve suture in a rat sciatic nerve injury model in a short-gap interposition (SGI) setting.

Methods

Sixty-six female Lewis rats were randomly divided into the sham group (n = 13); no reconstruction (no-recon) group (n = 13; rat model with 10 mm sciatic nerve defect); direct group (n = 20; rat sciatic nerve injury directly connected by 10-0 Nylon); and SGI group (n = 20; sciatic nerve injury repaired using 5-mm Nerbridge). Motor function and histological recovery were evaluated. The sciatic nerve and gastrocnemius muscle were harvested for quantification of the degree of nerve regeneration and muscle atrophy.

Results

The SGI and direct groups achieved equal recovery in both functional and histological outcomes. At weeks 3 and 8 postsurgery, there was a significant improvement in the sciatic functional index of the SGI group when compared with that of the no-recon group (P < 0.05). Furthermore, the direct and SGI groups had less muscle atrophy at 4 and 8 weeks postsurgery compared with the no-recon group (P < 0.05). The axon density and diameter at the distal site in the SGI group were significantly higher than that in the no-recon group and comparable to that in the direct and sham groups.

Conclusion

An artificial nerve conduit has equal potential as direct suture in motor nerve reconstruction when used in the SGI setting.

Promotion of Adrenal Pheochromocytoma (PC-12) Cell Proliferation and Outgrowth Using Schwann Cell-Laden Gelatin Methacrylate Substrate

Peripheral nerve injuries cause different degrees of nerve palsy and function loss. Due to the limitations of autografts, nerve tissue engineering (TE) scaffolds incorporated with various neurotrophic factors and cells have been investigated to promote nerve regeneration. However, the molecular mechanism is still poorly understood. In this study, we co-cultured Schwann cells (SCs) and rat adrenal pheochromocytoma (PC-12) cells on 50% degrees of methacryloyl substitution gelatin methacrylate (GelMA) scaffold. The SCs were encapsulated within the GelMA, and PC-12 cells were on the surface. A 5% GelMA was used as the co-culture scaffold since it better supports SCs proliferation, viability, and myelination and promotes higher neurotrophic factors secretion than 10% GelMA. In the co-culture, PC-12 cells demonstrated a higher cell proliferation rate and axonal extension than culturing without SCs, indicating that the secretion of neurotrophic factors from SCs can stimulate PC-12 growth and axonal outgrowth. The mRNA level for neurotrophic factors of SCs in 5% GelMA was further evaluated. We found significant upregulation when compared with a 2D culture, which suggested that this co-culture system could be a potential scaffold to investigate the mechanism of how SCs affect neuronal behaviors.

Photodynamic Activity of Protoporphyrin IX-Immobilized Cellulose Monolith for Nerve Tissue Regeneration

The development of nerve conduits with a three-dimensional porous structure has attracted great attention as they closely mimic the major features of the natural extracellular matrix of the nerve tissue. As low levels of reactive oxygen species (ROS) function as signaling molecules to promote cell proliferation and growth, this study aimed to fabricate protoporphyrin IX (PpIX)-immobilized cellulose (CEPP) monoliths as a means to both guide and stimulate nerve regeneration. CEPP monoliths can be fabricated via a simple thermally induced phase separation method and surface modification. The improved nerve tissue regeneration of CEPP monoliths was achieved by the activation of mitogen-activated protein kinases, such as extracellular signal-regulated kinases (ERKs). The resulting CEPP monoliths exhibited interconnected microporous structures and uniform morphology. The results of in vitro bioactivity assays demonstrated that the CEPP monoliths with under 0.54 ± 0.07 μmol/g PpIX exhibited enhanced photodynamic activity on Schwann cells via the generation of low levels of ROS. This photodynamic activation of the CEPP monoliths is a cell-safe process to stimulate cell proliferation without cytotoxic side effects. In addition, the protein expression of phospho-ERK increased considerably after the laser irradiation on the CEPP monoliths with low content of PpIX. Therefore, the CEPP monoliths have a potential application in nerve tissue regeneration as new nerve conduits.

Guided neural regeneration with autologous fat grafting and oxygen hyperbaric therapy

The loss of continuity of the nerve structure interrupts the transmission of nerve impulses and leads to the disorganization of functional activities. Many methods, as the use of neurogenic factors, aid in the process of neural regeneration by accelerating or improving peripheral nerves neoformation. The adipose tissue is abundant in the human body, and it has presented promising results in the regeneration of peripheral nerves. We carried out a randomized controlled study in 9 months, using 45 male Wistar rats, 80 days old, and the sciatic nerve was chosen for analysis. The control animals were divided into three groups - Initial group (IG), Final group (FG), and denervated group (DG) - with seven animals each. The experimental groups, with twelve animals each, were polyethylene tube filled with fat (EGF) and polyethylene tube without filling (EGwf). All groups, except IG, were submitted to 10 sessions of hyperbaric oxygen treatment of 1h 45 min in alternating days. Functional evaluation by walking-track was assessed using the Catwalk XT® software and tissues were harvested and stained with 1% toluidine blue for histological analysis. Quantitative data were first analyzed with the Kolmogorov Smirnov normality test. Comparison between the four groups was analyzed by ANOVA followed by Tukey Test. We concluded that hyperbaric oxygen therapy had positive results on morphometric and functional parameters. However, no significant differences were found regarding the use of autologous fat graft.

Effect of Electrical and Electromechanical Stimulation on PC12 Cell Proliferation and Axon Outgrowth

Peripheral nerve injuries have become a common clinical disease with poor prognosis and complicated treatments. The development of tissue engineering pointed a promising direction to produce nerve conduits for nerve regeneration. Electrical and mechanical stimulations have been incorporated with tissue engineering, since such external stimulations could promote nerve cell proliferation, migration and differentiation. However, the combination of electrical and mechanical stimulations (electromechanical stimulation) and its effects on neuron proliferation and axon outgrowth have been rarely investigated. Herein, silver nanowires (AgNWs) embedded polydimethylsiloxane (PDMS) electrodes were developed to study the effects of electromechanical stimulation on rat pheochromocytoma cells (PC12 cells) behaviors. AgNWs/PDMS electrodes demonstrated good biocompatibility and established a stable electric field during mechanical stretching. PC12 cells showed enhanced proliferation rate and axon outgrowth under electrical stimulation alone, and the cell number significantly increased with higher electrical stimulation intensity. The involvement of mechanical stretching in electrical stimulation reduced the cell proliferation rate and axon outgrowth, compared with the case of electrical stimulation alone. Interestingly, the cellular axons outgrowth was found to depend on the stretching direction, where the axons prefer to align perpendicularly to the stretch direction. These results suggested that AgNWs/PDMS electrodes provide an in vitro platform to investigate the effects of electromechanical stimulation on nerve cell behaviors and can be potentially used for nerve regeneration in the future.

Newly regenerated axons via scaffolds promote sub-lesional reorganization and motor recovery with epidural electrical stimulation

Here, we report the effect of newly regenerated axons via scaffolds on reorganization of spinal circuitry and restoration of motor functions with epidural electrical stimulation (EES). Motor recovery was evaluated for 7 weeks after spinal transection and following implantation with scaffolds seeded with neurotrophin producing Schwann cell and with rapamycin microspheres. Combined treatment with scaffolds and EES-enabled stepping led to functional improvement compared to groups with scaffold or EES, although, the number of axons across scaffolds was not different between groups. Re-transection through the scaffold at week 6 reduced EES-enabled stepping, still demonstrating better performance compared to the other groups. Greater synaptic reorganization in the presence of regenerated axons was found in group with combined therapy. These findings suggest that newly regenerated axons through cell-containing scaffolds with EES-enabled motor training reorganize the sub-lesional circuitry improving motor recovery, demonstrating that neuroregenerative and neuromodulatory therapies cumulatively enhancing motor function after complete SCI.

Biomaterials for Neural Tissue Engineering

The therapy of neural nerve injuries that involve the disruption of axonal pathways or axonal tracts has taken a new dimension with the development of tissue engineering techniques. When peripheral nerve injury (PNI), spinal cord injury (SCI), traumatic brain injury (TBI), or neurodegenerative disease occur, the intricate architecture undergoes alterations leading to growth inhibition and loss of guidance through large distance. To improve the limitations of purely cell-based therapies, the neural tissue engineering philosophy has emerged. Efforts are being made to produce an ideal scaffold based on synthetic and natural polymers that match the exact biological and mechanical properties of the tissue. Furthermore, through combining several components (biomaterials, cells, molecules), axonal regrowth is facilitated to obtain a functional recovery of the neural nerve diseases. The main objective of this review is to investigate the recent approaches and applications of neural tissue engineering approaches.

Xenogeneic Decellularized Extracellular Matrix-based Biomaterials For Peripheral Nerve Repair and Regeneration

Peripheral nerve injury could lead to either impairment or a complete loss of function for affected patients, and a variety of nerve repair materials have been developed for surgical approaches to repair it. Although autologous or autologous tissue-derived biomaterials remain preferred treatment for peripheral nerve injury, the lack of donor sources has led biomedical researchers to explore more other biomaterials. As a reliable alternative, xenogeneic decellularized extracellular matrix (dECM)-based biomaterials have been widely employed for surgical nerve repair. The dECM derived from animal donors is an attractive and unlimited source for xenotransplantation. Meanwhile, as an increasingly popular technique, decellularization could retain a variety of bioactive components in native ECM, such as polysaccharides, proteins, and growth factors. The resulting dECM-based biomaterials preserve a tissue's native microenvironment, promote Schwann cells proliferation and differentiation, and provide cues for nerve regeneration. Although the potential of dECM-based biomaterials as a therapeutic agent is rising, there are many limitations of this material restricting its use. Herein, this review discusses the decellularization techniques that have been applied to create dECM-based biomaterials, the main components of nerve ECM, and the recent progress in the utilization of xenogeneic dECM-based biomaterials through applications as a hydrogel, wrap, and guidance conduit in nerve tissue engineering. In the end, the existing bottlenecks of xenogeneic dECM-based biomaterials and developing technologies that could be eliminated to be helpful for utilization in the future have been elaborated.

Enhanced nerve cell proliferation and differentiation on electrically conductive scaffolds embedded with graphene and carbon nanotubes

Conduits that promote nerve regeneration are currently of great medical concern, particularly when gaps exist between nerve endings. To address this issue, our laboratory previously developed a nerve conduit from biodegradable poly(caprolactone fumarate) (PCLF) that supports peripheral nerve regeneration. The present study improves upon this work by further developing an electrically conductive, positively charged PCLF scaffold through the incorporation of graphene, carbon nanotubes (CNTs), and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC) (PCLF-Graphene-CNT-MTAC) using ultraviolet (UV) induced photocrosslinking. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were used to assess the incorporation of CNTs and graphene into PCLF-Graphene-CNT-MTAC scaffolds, which displayed enhanced surface roughness and reduced electrochemical impedance when compared to neat PCLF. Scaffolds with these surface modifications also showed improved growth and differentiation of rat pheochromocytoma 12 cells in vitro, with enhanced cell growth, neurite extension, and cellular migration. Furthermore, an increased number of neurite protrusions were observed when the conduit was electrically stimulated. These results show that the electrically conductive PCLF-Graphene-CNT-MTAC nerve scaffolds presented here support the cellular behaviors that are critical for nerve regeneration, ultimately making this material an attractive candidate for regenerative medicine applications.

Protocol for a phase I trial of a novel synthetic polymer nerve conduit 'Polynerve' in participants with sensory digital nerve injury (UMANC)

Background: Peripheral nerve injuries are common, with approximately 9,000 cases in the UK annually. Young working individuals are predominantly affected, leading to significant health and social implications. Functional recovery is often poor with impaired hand sensation, reduced motor function and pain and cold intolerance. Where a nerve gap exists, nerve grafting remains the gold-standard treatment but creates a second surgical site, sensory deficit at the donor site, possible neuroma formation and has limited availability. Current commercially available synthetic and resorbable nerve conduit alternatives are reported to be rigid and inflexible. This study will set out to examine the first-in-man use of a new nerve conduit device ‘Polynerve’ to repair small nerve gaps in digital sensory nerves of the hand. Polynerve is a degradable co-polymer of poly-ε-caprolactone and poly-l-lactic acid, which is shaped as a cylinder that has greater tensile strength, flexibility and less acidic degradation compared with current commercially available synthetic nerve conduits. In addition, it has a novel micro-grooved internal lumen that aids Schwann cell ingress and alignment to improve nerve regeneration.

Methods: In total, 17 eligible participants will be recruited to undergo repair of a transected sensory nerve of the hand using the Polynerve device. All participants that receive the nerve conduit device will be followed for a period of 12 months post-surgery. The primary endpoint is safety of the device and the secondary endpoint is degree of sensory nerve regeneration through the conduit assessed using standard sensory testing (2-PD, WEST monofilament testing and locognosia).

Discussion: The ‘UMANC’ trial is a single-centre UK-based, prospective, unblinded, phase I clinical trial of a novel nerve conduit device. We aim to demonstrate the safety of Polynerve as a synthetic, biodegradable nerve conduit and improve the treatment options available to patients with significant nerve injuries.

Registration: Clinicaltrials.gov: NCT02970864; EudraCT: 2016-001667-37.

Methylcobalamin-Loaded PLCL Conduits Facilitate the Peripheral Nerve Regeneration

The feasible fabrication of nerve guidance conduits (NGCs) with good biological performance is important for translation in clinics. In this study, poly(d,l-lactide-co-caprolactone) (PLCL) films loaded with various amounts (wt; 5%, 15%, 25%) of methylcobalamin (MeCbl) are prepared, and are further rolled and sutured to obtain MeCbl-loaded NGCs. The MeCbl can be released in a sustainable manner up to 21 days. The proliferation and elongation of Schwann cells, and the proliferation of Neuro2a cells are enhanced on these MeCbl-loaded films. The MeCbl-loaded NGCs are implanted into rats to induce the regeneration of 10 mm amputated sciatic nerve defects, showing the ability to facilitate the recovery of motor and sensory function, and to promote myelination in peripheral nerve regeneration. In particular, the 15% MeCbl-loaded PLCL conduit exhibits the most satisfactory recovery of sciatic nerves in rats with the largest diameter and thickest myelinated fibers.

Fabrication and Evaluation of a Xenogeneic Decellularized Nerve-Derived Material: Preclinical Studies of a New Strategy for Nerve Repair

The repair and regeneration of transected peripheral nerves is an important area of clinical research, and the adhesion of anastomosis sites to surrounding tissues is a vital factor affecting the quality of nerve recovery after nerve anastomosis. This study involves the generation of a novel nerve repair membrane derived from decellularized porcine nerves using a unique, innovative technique. The decellularized nerve matrix was verified to be effective in eliminating cellular components, and it still retained some neural extracellular matrix components and bioactive molecules (collagens, glycosaminoglycans, laminin, fibronectin, TGF-β, etc.), which were mainly determined by proteomic analysis, histochemistry, immunohistochemistry, and enzyme-linked immunosorbent assay. Cytotoxicity, intracutaneous reactivity, hemolysis, and cell affinity analyses were conducted to confirm the biosecurity of the nerve repair membrane. The in vivo functionality was assessed in a rat sciatic nerve transection model, and indices of functional nerve recovery, including the measurement of the claw-spread reflex, nerve anastomosis site adhesion, electrophysiological properties, and the number of regenerated nerve fibers, were evaluated. The results indicated that the nerve repair membrane could effectively prevent adhesion between the nerve anastomosis sites and the surrounding tissues and enhance nerve regeneration, which could be attributed to its various bioactive components. In conclusion, the novel nerve repair membrane derived from xenogeneic decellularized nerves described in this study shows great potential auxiliary clinical treatment for peripheral nerve injuries.

A micropatterned conductive electrospun nanofiber mesh combined with electrical stimulation for synergistically enhancing differentiation of rat neural stem cells

The micropatterned conductive nanofiber mesh combined with ES effectively facilitates the differentiation of NSCs into neuron and suppresses the formation of astrocytes.

Multi-dimensional bioinspired tactics using an engineered mussel protein glue-based nanofiber conduit for accelerated functional nerve regeneration

Limited regenerative capacity of the nervous system makes treating traumatic nerve injuries with conventional polymer-based nerve grafting a challenging task. Consequently, utilizing natural polymers and biomimetic topologies became obvious strategies for nerve conduit designs. As a bioinspired natural polymer from a marine organism, mussel adhesive proteins (MAPs) fused with biofunctional peptides from extracellular matrix (ECM) were engineered for accelerated nerve regeneration by enhancing cell adhesion, proliferation, neural differentiation, and neurite formation. To physically promote contact guidance of neural and Schwann cells and to achieve guided nerve regeneration, MAP was fabricated into an electrospun aligned nanofiber conduit by introducing synthetic polymer poly(lactic-co-glycolic acid) (PLGA) to control solubility and mechanical property. In vitro and in vivo experiments demonstrated that the multi-dimensional tactics of combining adhesiveness from MAP, integrin-mediated interaction from ECM peptides (in particular, IKVAV derived from laminin α1 chain), and contact guidance from aligned nanofibers synergistically accelerated functional nerve regeneration. Thus, MAP-based multi-dimensional approach provides new opportunities for neural regenerative applications including nerve grafting. STATEMENT OF SIGNIFICANCE: Findings in neural regeneration indicate that a bioinspired polymer-based nerve conduit design should harmoniously constitute various factors, such as biocompatibility, neurotrophic molecule, biodegradability, and contact guidance. Here, we engineered three fusion proteins of mussel-derived adhesive protein with ECM-derived biofunctional peptides to simultaneously provide biocompatibility and integrin-based interactions. In addition, a fabrication of robust aligned nanofiber conduits containing the fusion proteins realized suitable biodegradability and contact guidance. Thus, our multi-dimensional strategy on conduit design provided outstanding biocompatibility, biodegradability, integrin-interaction, and contact guidance to achieve an accelerated functional nerve regeneration. We believe that our bioengineered mussel adhesive protein-based multi-dimensional strategy would offer new insights into the design of nerve tissue engineering biomaterials.

Rat sciatic nerve regeneration across a 10-mm defect bridged by a chitin/CM-chitosan artificial nerve graft

Chitosan as a natural bioactive biopolymer has been commonly employed in guidance conduit for repairing peripheral nerve injury, due to its excellent properties of low toxicity, antibacterial properties, high biocompatibility and biodegradability. In this study, chitin and CM-chitosan were prepared from pharmaceutical grade chitosan. Moreover, a novel composite chitosan-based nerve graft comprising microporous chitin-based conduit and internal CM-chitosan fiber was constructed and applied to bridge sciatic nerve across a 10-mm defect in SD rats. The chitin/CM-chitosan artificial nerve graft could promote the proliferation of rat Schwann cells (RSC96) with good cell biocompatibility. After implantation, the artificial nerve graft showed slow degradation. No apparent toxicity was observed, and tissue inflammation was very slight after implantation, indicating favorable bio-safety of the nerve graft. Furthermore, the chitin/CM-chitosan artificial nerve graft could effectively promote restoration of damaged neurons with similar effect compared to the autograft. In conclusion, the composite biodegradable chitin/CM-chitosan nerve grafts possessed favorable biocompatibility and good potential in repairing peripheral nervous injury.

Poly (lactide-co-glycolide) (PLGA) Scaffold Induces Short-term Nerve Regeneration and Functional Recovery Following Sciatic Nerve Transection in Rats

Peripheral nerve injury is an important cause of incapability and has limited available treatment. Autologous donor nerve implant is the golden standard treatment, however, may cause secondary deficits. Stem cells show positive results in preclinical settings, preserving tissue and function. We tested the efficacy of stem cells derived from human exfoliated deciduous teeth seeded in poly (lactide-co-glycolide) scaffolds in sciatic nerve transection model. Seventy-two adult male Wistar rats had 7-mm nerve gap bridge using scaffolds with (or without) stem cells. Animals were randomly divided into: sham-operated; sham-operated without scaffold; sham-operated + scaffold + stem cells; sciatic transection + no treatment; sciatic transection + acellular scaffolds; sciatic transection + scaffold + stem cells. Sciatic Functional Index and Ladder Rung Walking tests were performed before (-1), 14 and 28 days after surgery. Morphometric nerve measurement and muscle weights were assessed. Scaffolds with stem cells improved function in Sciatic Functional Index. Acellular scaffold was effective, promoting functional recovery and nerve regeneration following nerve injury. Scaffolds provide better nerve regeneration and functional recovery after sciatic transection. Despite cell therapy promoting faster recovery after sciatic transection in the Sciatic Index Score, stem cells did not improve functional and morphological recovery after nerve injury. This is the first study testing the potential use of scaffolds combined with stem cells in the early stages after injury. Scaffolds with stem cells could accelerate nerve recovery and favor adjuvant therapies, evidencing the need for further studies to increase the knowledge about stem cells' mechanisms.

Biodegradable Spheres Protect Traumatically Injured Spinal Cord by Alleviating the Glutamate-Induced Excitotoxicity

New treatment strategies for spinal cord injury with good therapeutic efficacy are actively pursued. Here, acetalated dextran (AcDX), a biodegradable polymer obtained by modifying vicinal diols of dextran, is demonstrated to protect the traumatically injured spinal cord. To facilitate its administration, AcDX is formulated into microspheres (≈7.2 µm in diameter) by the droplet microfluidic technique. Intrathecally injected AcDX microspheres effectively reduce the traumatic lesion volume and inflammatory response in the injured spinal cord, protect the spinal cord neurons from apoptosis, and ultimately, recover the locomotor function of injured rats. The neuroprotective feature of AcDX microspheres is achieved by sequestering glutamate and calcium ions in cerebrospinal fluid. The scavenging of glutamate and calcium ion reduces the influx of calcium ions into neurons and inhibits the formation of reactive oxygen species. Consequently, AcDX microspheres attenuate the expression of proapoptotic proteins, Calpain, and Bax, and enhance the expression of antiapoptotic protein Bcl-2. Overall, AcDX microspheres protect traumatically injured spinal cord by alleviating the glutamate-induced excitotoxicity. This study opens an exciting perspective toward the application of neuroprotective AcDX for the treatment of severe neurological diseases.

Biomimetic Architectures for Peripheral Nerve Repair: A Review of Biofabrication Strategies

Biofabrication techniques have endeavored to improve the regeneration of the peripheral nervous system (PNS), but nothing has surpassed the performance of current clinical practices. However, these current approaches have intrinsic limitations that compromise patient care. The "gold standard" autograft provides the best outcomes but requires suitable donor material, while implantable hollow nerve guide conduits (NGCs) can only repair small nerve defects. This review places emphasis on approaches that create structural cues within a hollow NGC lumen in order to match or exceed the regenerative performance of the autograft. An overview of the PNS and nerve regeneration is provided. This is followed by an assessment of reported devices, divided into three major categories: isotropic hydrogel fillers, acting as unstructured interluminal support for regenerating nerves; fibrous interluminal fillers, presenting neurites with topographical guidance within the lumen; and patterned interluminal scaffolds, providing 3D support for nerve growth via structures that mimic native PNS tissue. Also presented is a critical framework to evaluate the impact of reported outcomes. While a universal and versatile nerve repair strategy remains elusive, outlined here is a roadmap of past, present, and emerging fabrication techniques to inform and motivate new developments in the field of peripheral nerve regeneration.

3D scaffolds for brain tissue regeneration: architectural challenges

Critical analysis of experimental studies on 3D scaffolds for brain tissue engineering.

Electrically conductive nanocomposite hydrogels embedded with functionalized carbon nanotubes for spinal cord injury

Electrically conductive hydrogels incorporated with CNTs support PC12 cell growth and differentiation and hold promise for nerve regeneration.

Effective nerve cell modulation by electrical stimulation of carbon nanotube embedded conductive polymeric scaffolds

Biomimetic biomaterials require good biocompatibility and bioactivity to serve as appropriate scaffolds for tissue engineering applications.

Optimization of micropatterned poly(lactic-co-glycolic acid) films for enhancing dorsal root ganglion cell orientation and extension

Nerve conduits have been a viable alternative to the 'gold standard' autograft for treating small peripheral nerve gap injuries. However, they often produce inadequate functional recovery outcomes and are ineffective in large gap injuries. Ridge/groove surface micropatterning has been shown to promote neural cell orientation and guide growth. However, optimization of the ratio of ridge/groove parameters to promote orientation and extension for dorsal root ganglion (DRG) cells on poly(lactic-co-glycolic acid) (PLGA) films has not been previously conducted. Photolithography and micro-molding were used to define various combinations of ridge/groove dimensions on PLGA films. The DRG cells obtained from chicken embryos were cultured on micropatterned PLGA films for cell orientation and migration evaluation. Biodegradation of the films occurred during the test period, however, this did not cause deformation or distortion of the micropatterns. Results from the DRG cell orientation test suggest that when the ridge/groove ratio equals 1 (ridge/groove width parameters are equal, i.e., 10 μm/10 μm (even)), the degree of alignment depends on the size of the ridges and grooves, when the ratio is smaller than 1 (groove controlled) the alignment increases as the ridge size decreases, and when the ratio is larger than 1 (ridge controlled), the alignment is reduced as the width of the grooves decreases. The migration rate and neurite extension of DRG neurons were greatest on 10 μm/10 μm and 30 μm/30 μm micropatterned PLGA films. Based on the data, the 10 μm/10 μm and 30 μm/30 μm micropatterned PLGA films are the optimized ridge/groove surface patterns for the construction of nerve repair devices.

Functionalized Carbon Nanotube and Graphene Oxide Embedded Electrically Conductive Hydrogel Synergistically Stimulates Nerve Cell Differentiation

Nerve regeneration after injury is a critical medical issue. In previous work, we have developed an oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel incorporated with positive charges as a promising nerve conduit. In this study, we introduced cross-linkable bonds to graphene oxide and carbon nanotube to obtain the functionalized graphene oxide acrylate (GOa) and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive hydrogel was then fabricated by covalently embedding GOa and CNTpega within OPF hydrogel through chemical cross-linking followed by in situ reduction of GOa in l-ascorbic acid solution. Positive charges were incorporated by 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTAC) to obtain rGOaCNTpega-OPF-MTAC composite hydrogel with both surface charge and electrical conductivity. The distribution of CNTpega and GOa in the hydrogels was substantiated by transmission electron microscopy (TEM), and strengthened electrical conductivities were determined. Excellent biocompatibility was demonstrated for the carbon embedded composite hydrogels. Biological evaluation showed enhanced proliferation and spreading of PC12 cells on the conductive hydrogels. After induced differentiation using nerve growth factor (NGF), cells on the conductive hydrogels were effectively stimulated to have robust neurite development as observed by confocal microscope. A synergistic effect of electrical conductivity and positive charges on nerve cells was also observed in this study. Using a glass mold method, the composite hydrogel was successfully fabricated into conductive nerve conduits with surficial positive charges. These results suggest that rGOa-CNTpega-OPF-MTAC composite hydrogel holds great potential as conduits for neural tissue engineering.

Fibrin glue as a stabilization strategy in peripheral nerve repair when using porous nerve guidance conduits

Porous conduits provide a protected pathway for nerve regeneration, while still allowing exchange of nutrients and wastes. However, pore sizes >30 µm may permit fibrous tissue infiltration into the conduit, which may impede axonal regeneration. Coating the conduit with Fibrin Glue (FG) is one option for controlling the conduit's porosity. FG is extensively used in clinical peripheral nerve repair, as a tissue sealant, filler and drug-delivery matrix. Here, we compared the performance of FG to an alternative, hyaluronic acid (HA) as a coating for porous conduits, using uncoated porous conduits and reverse autografts as control groups. The uncoated conduit walls had pores with a diameter of 60 to 70 µm that were uniformly covered by either FG or HA coatings. In vitro, FG coatings degraded twice as fast as HA coatings. In vivo studies in a 1 cm rat sciatic nerve model showed FG coating resulted in poor axonal density (993 ± 854 #/mm²), negligible fascicular area (0.03 ± 0.04 mm²), minimal percent wet muscle mass recovery (16 ± 1 in gastrocnemius and 15 ± 5 in tibialis anterior) and G-ratio (0.73 ± 0.01). Histology of FG-coated conduits showed excessive fibrous tissue infiltration inside the lumen, and fibrin capsule formation around the conduit. Although FG has been shown to promote nerve regeneration in non-porous conduits, we found that as a coating for porous conduits in vivo, FG encourages scar tissue infiltration that impedes nerve regeneration. This is a significant finding considering the widespread use of FG in peripheral nerve repair.

PEOT/PBT Guides Enhance Nerve Regeneration in Long Gap Defects

Development of new nerve guides is required for replacing autologous nerve grafts for the repair of long gap defects after nerve injury. A nerve guide comprised only of electrospun fibers able to bridge a critical (15 mm) nerve gap in a rat animal model is reported for the first time. The nerve conduits are made of poly(ethylene oxide terephthalate) and poly(butylene terephthalate) (PEOT/PBT), a biocompatible copolymer composed of alternating amorphous, hydrophilic poly(ethylene oxide terephthalate), and crystalline, hydrophobic poly(butylene terephthalate) segments. These guides show suitable mechanical properties, high porosity, and fibers aligned in the longitudinal axis of the guide. In vitro studies show that both neurites and Schwann cells exhibit growth alignment with PA fibers. In vivo studies reveal that, after rat sciatic nerve transection and repair with PEOT/PBT guides, axons grow occupying a larger area compared to silicone tubes. Moreover, after repair of limiting (10 mm) and critical (15 mm) nerve gaps, PEOT/PBT guides significantly increase the percentage of regenerated nerves, the number of regenerated myelinated axons, and improve motor, sensory, and autonomic reinnervation in both gaps. This nerve conduit design combines the properties of PEOT/PBT with electrospun structure, demonstrating that nerve regeneration through long gaps can be achieved through the design of instructive biomaterial constructs.

Self-assembling peptide nanostructures on aligned poly(lactide-co-glycolide) nanofibers for the functional regeneration of sciatic nerve

Aim: Regeneration of functional peripheral nerve tissue at critical-sized defect requires extracellular matrix analogs impregnated with appropriate biosignals to regulate the cell fate process and subsequent tissue progression. The aim of the study was to develop electrospun aligned nanofibers as architectural analogs integrated with RADA16-I-BMHP1 as biofunctional peptides. Materials & methods: Aligned poly(lactide-co-glycolide) (PLGA)-RADA16-I-BMHP1 nanofibers were fabricated and characterized for their in vitro potential using rat Schwann cell line and in vivo potential using a 10 mm sciatic nerve transection rat model. Results: PLGA-peptide scaffolds significantly promoted higher expression of genotypic markers and bipolar extension of Schwann cells. Further, PLGA-peptide treated animals promoted the native collagen organization, remyelination and showed significantly higher recovery of sensorimotor and motor function than PLGA-treated groups (p < 0.05). Conclusion: Our results demonstrate that self-assembling peptide nanostructures on aligned PLGA nanofibers provided better cell–matrix communication with significant functional restoration of the sciatic nerve.

Covalent crosslinking of graphene oxide and carbon nanotube into hydrogels enhances nerve cell responses

Healing of nerve injuries is a critical medical issue. Biodegradable polymeric conduits are a promising therapeutic solution to provide guidance for axon growth in a given space, thus helping nerve heal. Extensive studies in the past decade reported that conductive materials could effectively increase neurite and axon extension in vitro and nerve regeneration in vivo. In this study, graphene oxide and carbon nanotubes were covalently functionalized with double bonds to obtain crosslinkable graphene oxide acrylate (GOa) sheets and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive reduced GOa-CNTpega-oligo(polyethylene glycol fumarate) (OPF) hydrogel (rGOa-CNTpega-OPF) was successfully fabricated by chemically crosslinking GOa sheets and CNTpega with OPF chains followed by in situ chemical reduction in l-ascorbic acid solution. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging showed homogenous distribution of GOa/CNTpega carbon content in the rGOa-CNTpega-OPF composite hydrogel, resulting in a significant increase of electrical conductivity compared with neutral OPF without carbon content. Cell studies showed excellent biocompatibility and distinguished PC12 cell proliferation and spreading on the rGOa-CNTpega-OPF composite hydrogel. Fluorescent microscopy imaging demonstrated robustly stimulated neurite development in these cells on a conductive rGOa-CNTpega-OPF composite hydrogel compared with that on neutral OPF hydrogels. These results illustrated a promising potential for the rGOa-CNTpega-OPF composite hydrogel to serve as conduits for neural tissue engineering.

Myelinating glia differentiation is regulated by extracellular matrix elasticity

The mechanical properties of living tissues have a significant impact on cell differentiation, but remain unexplored in the context of myelin formation and repair. In the PNS, the extracellular matrix (ECM) incorporates a basal lamina significantly denser than the loosely organized CNS matrix. Inhibition of non-muscle myosin II (NMII) enhances central but impairs peripheral myelination and NMII has been implicated in cellular responses to changes in the elasticity of the ECM. To directly evaluate whether mechanotransduction plays a role in glial cell differentiation, we cultured Schwann cells (SC) and oligodendrocytes (OL) on matrices of variable elastic modulus, mimicking either their native environment or conditions found in injured tissue. We found that a rigid, lesion-like matrix inhibited branching and differentiation of OL in NMII-dependent manner. By contrast, SC developed normally in both soft and stiffer matrices. Although SC differentiation was not significantly affected by changes in matrix stiffness alone, we found that expression of Krox-20 was potentiated on rigid matrices at high laminin concentration. These findings are relevant to the design of biomaterials to promote healing and regeneration in both CNS and PNS, via transplantation of glial progenitors or the implantation of tissue scaffolds.

Ligament Tissue Engineering Using a Novel Porous Polycaprolactone Fumarate Scaffold and Adipose Tissue-Derived Mesenchymal Stem Cells Grown in Platelet Lysate

PURPOSE

Surgical reconstruction of intra-articular ligament injuries is hampered by the poor regenerative potential of the tissue. We hypothesized that a novel composite polymer "neoligament" seeded with progenitor cells and growth factors would be effective in regenerating native ligamentous tissue.

METHODS

We synthesized a fumarate-derivative of polycaprolactone fumarate (PCLF) to create macro-porous scaffolds to allow cell-cell communication and nutrient flow. Clinical grade human adipose tissue-derived human mesenchymal stem cells (AMSCs) were cultured in 5% human platelet lysate (PL) and seeded on scaffolds using a dynamic bioreactor. Cell growth, viability, and differentiation were examined using metabolic assays and immunostaining for ligament-related markers (e.g., glycosaminoglycans [GAGs], alkaline phosphatase [ALP], collagens, and tenascin-C).

RESULTS

AMSCs seeded on three-dimensional (3D) PCLF scaffolds remain viable for at least 2 weeks with proliferating cells filling the pores. AMSC proliferation rates increased in PL compared to fetal bovine serum (FBS) (p < 0.05). Cells had a low baseline expression of ALP and GAG, but increased expression of total collagen when induced by the ligament and tenogenic growth factor fibroblast growth factor 2 (FGF-2), especially when cultured in the presence of PL (p < 0.01) instead of FBS (p < 0.05). FGF-2 and PL also significantly increased immunostaining of tenascin-C and collagen at 2 and 4 weeks compared with human fibroblasts.

SUMMARY

Our results demonstrate that AMSCs proliferate and eventually produce a collagen-rich extracellular matrix on porous PCLF scaffolds. This novel scaffold has potential in stem cell engineering and ligament regeneration.

Electrospinning of PELA/PPY Fibrous Conduits: Promoting Peripheral Nerve Regeneration in Rats by Self-Originated Electrical Stimulation

Peripheral nerve injuries represent a great challenge for surgeons. The conductive neural scaffold has experienced increasing interest because of its good biocompatibility and similar electrical properties as compared to those of a normal nerve. Herein, nerve conduits made from poly(d,l-lactide)-co-poly(ethylene glycol) and polypyrrole (20%, 30%, and 50%) (PELA-PPY) were prepared by electrospinning, and used in regeneration of peripheral nerve defects. The results of an in vitro experiment indicated a high biocompatibility for the as-prepared materials, supporting the attachment and proliferation of a rat pheochromocytoma PC-12 cell. Furthermore, the PELA-PPY nerve conduit implanted in the sciatic nerve defects (10 mm) of the Spraguee-Dawley rats for 12 weeks showed similar results with the autograft, while it demonstrated a better outcome than the PELA nerve conduit in electrophysiological examination, sciatic function index, total amount of regenerated myelinated nerve fibers, axon diameter, myelin thickness, and several immunohistochemistry indices (S-100, laminin, neurofilament, bromodeoxyuridine, and glial fibrillary acidic portein). We supposed that the bioactivity is mainly generated by the PPY in composite nanofibers which could transmit self-originated electrical stimulation between cells. Due to the facile preparation and excellent in vivo performance, the PPY-PELA nerve conduit is promising for use as a bioengineered biomaterial for peripheral nerve regeneration.

Positively Charged Oligo[Poly(Ethylene Glycol) Fumarate] Scaffold Implantation Results in a Permissive Lesion Environment after Spinal Cord Injury in Rat

Positively charged oligo[poly(ethylene glycol) fumarate] (OPF+) scaffolds loaded with Schwann cells bridge spinal cord injury (SCI) lesions and support axonal regeneration in rat. The regeneration achieved is not sufficient for inducing functional recovery. Attempts to increase regeneration would benefit from understanding the effects of the scaffold and transplanted cells on lesion environment. We conducted morphometric and stereological analysis of lesions in rats implanted with OPF+ scaffolds with or without loaded Schwann cells 1, 2, 3, 4, and 8 weeks after thoracic spinal cord transection. No differences were found in collagen scarring, cyst formation, astrocyte reactivity, myelin debris, or chondroitin sulfate proteoglycan (CSPG) accumulation. However, when scaffold-implanted animals were compared with animals with transection injuries only, these barriers to regeneration were significantly reduced, accompanied by increased activated macrophages/microglia. This distinctive and regeneration permissive tissue reaction to scaffold implantation was independent of Schwann cell transplantation. Although the tissue reaction was beneficial in the short term, we observed a chronic fibrotic host response, resulting in scaffolds surrounded by collagen at 8 weeks. This study demonstrates that an appropriate biomaterial scaffold improves the environment for regeneration. Future targeting of the host fibrotic response may allow increased axonal regeneration and functional recovery.

The Incidence of Positive Modifications to Nerve Conduits in Rodent Nerve Repair Models

BACKGROUND

The nerve conduit is a generally accepted tool to facilitate the repair of short nerve gaps. Limitations in effectiveness have been recognized, and a steady stream of possible conduit improvements has been published in the scientific literature. Analysis of this information, particularly when small animal models have been utilized, seems to indicate that nearly any modification of a nerve conduit improves outcomes in repairs of short gaps over standard nerve conduits. This seems statistically and biologically improbable and suggests a bias in the literature.

METHODS

A standardized systemic review of the scientific literature on rodent model studies assessing conduit modifications was undertaken to determine the incidence of positive or supportive outcomes.

RESULTS

Modifications were deemed superior in 97.3% of studies when compared with unmodified conduits and deemed equivalent or superior in 52.1% of studies when compared with autograft.

CONCLUSIONS

A seemingly disproportionate number of positive results suggest that the literature on nerve conduit modifications may be skewed. We believe that there is a publication bias in the literature, and this warrants further investigation.

Advances in the neurological and neurosurgical management of peripheral nerve trauma

Peripheral nerve trauma frequently affects younger people and may result in significant and long-lasting functional disability. Currently, diagnosis and monitoring of peripheral nerve injury relies on clinical and electrodiagnostic information, supplemented by intraoperative electrophysiological studies. However, in a significant proportion of nerve injuries, the likelihood of spontaneous regeneration resulting in good functional outcome remains uncertain and unnecessary delays to treatment may be faced while monitoring for recovery. Advances in non-invasive imaging techniques to diagnose and monitor nerve injury and regeneration are being developed, and have the potential to streamline the decision-making process. In addition, advances in operative and non-operative treatment strategies may provide more effective ways to maximise functional outcomes following severe peripheral nerve trauma. This review discusses these advances in light of the current state of the art of management of peripheral nerve trauma.

Controlled Delivery of Vancomycin via Charged Hydrogels

Surgical site infection (SSI) remains a significant risk for any clean orthopedic surgical procedure. Complications resulting from an SSI often require a second surgery and lengthen patient recovery time. The efficacy of antimicrobial agents delivered to combat SSI is diminished by systemic toxicity, bacterial resistance, and patient compliance to dosing schedules. We submit that development of localized, controlled release formulations for antimicrobial compounds would improve the effectiveness of prophylactic surgical wound antibiotic treatment while decreasing systemic side effects. Our research group developed and characterized oligo(poly(ethylene glycol)fumarate) / sodium methacrylate (OPF/SMA) charged copolymers as biocompatible hydrogel matrices. Here, we report the engineering of this copolymer for use as an antibiotic delivery vehicle in surgical applications. We demonstrate that these hydrogels can be efficiently loaded with vancomycin (over 500 μg drug per mg hydrogel) and this loading mechanism is both time- and charge-dependent. Vancomycin release kinetics are shown to be dependent on copolymer negative charge. In the first 6 hours, we achieved as low as 33.7% release. In the first 24 hours, under 80% of total loaded drug was released. Further, vancomycin release from this system can be extended past four days. Finally, we show that the antimicrobial activity of released vancomycin is equivalent to stock vancomycin in inhibiting the growth of colonies of a clinically derived strain of methicillin-resistant Staphylococcus aureus. In summary, our work demonstrates that OPF/SMA hydrogels are appropriate candidates to deliver local antibiotic therapy for prophylaxis of surgical site infection.

Dual-factor loaded functional silk fibroin scaffolds for peripheral nerve regeneration with the aid of neovascularization

Dual-factor loaded functional silk fibroin scaffolds enhanced peripheral nerve regeneration with the aid of neovascularization.