Hydroxyapatite-coated tendon chitosan tubes with adsorbed laminin peptides facilitate nerve regeneration in vivo

Chitosan/alginate scaffold enhanced with Berberis vulgaris extract for osteocyte differentiation of ovine fetal stem cells

Designing biocompatible polymers using plant derivatives can be extremely useful in tissue engineering, nanomedicine, and many other fields of medicine. In this study, it was first looked into how chitosan/alginate scaffolds were made and characterized in the presence of berberine and barberry fruit extract. Second, the process of proliferation and differentiation of ovine fetal BM-MSCs (bone marrow-mesenchymal stem cells) was assessed on these scaffolds after BM-MSCs were extracted and confirmed by developing into osteocyte and adipose cells. To investigate the differentiation, treatment groups include (1) ovine fetal BM-MSCs were plated in Dulbecco's modified eagle medium culture medium with high glucose containing 10% fetal bovine serum and antibiotics (negative control), (2) ovine fetal BM-MSCs were plated in osteogenic differentiation medium (positive control group), (3) positive control group + barberry fruit extract, (4) positive control group + berberine, (5) ovine fetal BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate scaffold (hydrogel group), (6) ovine fetal BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/barberry fruit extract scaffold (hydrogel group containing barberry fruit extract), and (7) ovine fetal BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/berberine scaffold (hydrogel group containing berberine). Alkaline phosphatase (ALP) enzyme concentrations, mineralization rate using a calcium kit, and mineralization measurement by alizarin staining quantification were all found after 21 days of culture. In addition, real-time quantitative reverse transcription polymerase chain reaction was used to assess the expression of the ALP, COL1A2, and Runx2 genes. Days 5 and 7 had the lowest water absorption by the hydrogel scaffold containing barberry extract, which was significant in comparison to other groups (p < .05). Among the hydrogel scaffolds under study, the one containing barberry extract exhibited the lowest tensile strength, and this difference was statistically significant (p < .05). The chitosan/alginate hydrogel has the highest tensile strength of all of them. In comparison to the control and other treatment groups, the inclusion of berberine in the chitosan/alginate hydrogel significantly increased the expression of the ALP, Runx2, and COL1A2 genes (p < .05). The osteocyte differentiation of mesenchymal stem cells in in vitro settings appears to have been enhanced by the inclusion of berberine in the chitosan/alginate scaffold.

Natural polysaccharides and their derivatives as potential medical materials and drug delivery systems for the treatment of peripheral nerve injuries

Peripheral nerve repair following injury is one of the most serious problems in neurosurgery. Clinical outcomes are often unsatisfactory and associated with a huge socioeconomic burden. Several studies have revealed the great potential of biodegradable polysaccharides for improving nerve regeneration. We review here the promising therapeutic strategies involving different types of polysaccharides and their bio-active composites for promoting nerve regeneration. Within this context, polysaccharide materials widely used for nerve repair in different forms are highlighted, including nerve guidance conduits, hydrogels, nanofibers and films. While nerve guidance conduits and hydrogels were used as main structural scaffolds, the other forms including nanofibers and films were generally used as additional supporting materials. We also discuss the issues of ease of therapeutic implementation, drug release properties and therapeutic outcomes, together with potential future directions of research.

Bioceramics/Electrospun Polymeric Nanofibrous and Carbon Nanofibrous Scaffolds for Bone Tissue Engineering Applications

Bone tissue engineering integrates biomaterials, cells, and bioactive agents to propose sophisticated treatment options over conventional choices. Scaffolds have central roles in this scenario, and precisely designed and fabricated structures with the highest similarity to bone tissue have shown promising outcomes. On the other hand, using nanotechnology and nanomaterials as the enabling options confers fascinating properties to the scaffolds, such as precisely tailoring the physicochemical features and better interactions with cells and surrounding tissues. Among different nanomaterials, polymeric nanofibers and carbon nanofibers have attracted significant attention due to their similarity to bone extracellular matrix (ECM) and high surface-to-volume ratio. Moreover, bone ECM is a biocomposite of collagen fibers and hydroxyapatite crystals; accordingly, researchers have tried to mimic this biocomposite using the mineralization of various polymeric and carbon nanofibers and have shown that the mineralized nanofibers are promising structures to augment the bone healing process in the tissue engineering scenario. In this paper, we reviewed the bone structure, bone defects/fracture healing process, and various structures/cells/growth factors applicable to bone tissue engineering applications. Then, we highlighted the mineralized polymeric and carbon nanofibers and their fabrication methods.

Applications of chitosan-based biomaterials: From preparation to spinal cord injury neuroprosthetic treatment

Spinal cord injury (SCI)-related disabilities are a serious problem in the modern society. Further, the treatment of SCI is highly challenging and is urgently required in clinical practice. Research on nerve tissue engineering is an emerging approach for improving the treatment outcomes of SCI. Chitosan (CS) is a cationic polysaccharide derived from natural biomaterials. Chitosan has been found to exhibit excellent biological properties, such as nontoxicity, biocompatibility, biodegradation, and antibacterial activity. Recently, chitosan-based biomaterials have attracted significant attention for SCI repair in nerve tissue engineering applications. These studies revealed that chitosan-based biomaterials have various functions and mechanisms to promote SCI repair, such as promoting neural cell growth, guiding nerve tissue regeneration, delivering nerve growth factors, and as a vector for gene therapy. Chitosan-based biomaterials have proven to have excellent potential for the treatment of SCI. This review aims to introduce the recent advances in chitosan-based biomaterials for SCI treatment and to highlight the prospects for further application.

Exploring the Impact of Chitosan Composites as Artificial Organs

Chitosan and its allies have in multiple ways expanded into the medical, food, chemical, and biological industries and is still expanding. With its humble beginnings from marine shell wastes, the deacetylated form of chitin has come a long way in clinical practices. The biomedical applications of chitosan are truly a feather on its cap, with rarer aspects being chitosan’s role in tissue regeneration and artificial organs. Tissue regeneration is a highly advanced and sensitive biomedical application, and the very fact that chitosan is premiering here is an authentication of its ability to deliver. In this review, the various biomedical applications of chitosan are touched on briefly. The synthesis methodologies that are specific for tissue engineering and biomedical applications have been listed. What has been achieved using chitosan and chitosan composites in artificial organ research as well as tissue regeneration has been surveyed and presented. The lack of enthusiasm, as demonstrated by the very few reports online with respect to chitosan composites and artificial organs, is highlighted, and the reasons for this lapse speculated. What more needs be done to expand chitosan and its allies for a better utilization and exploitation to best benefit the construction of artificial organs and building of tissue analogs has been discussed.

Cell-encapsulated chitosan-collagen hydrogel hybrid nerve guidance conduit for peripheral nerve regeneration

Nerve guidance conduits (NGCs) composed of biocompatible polymers have been attracting attention as an alternative for autograft surgery in peripheral nerve regeneration. However, the nerve tissues repaired by NGCs often tend to be inadequate and lead to functional failure because of the lack of cellular supports. This paper presents a chitosan-collagen hydrogel conduit containing cells to induce peripheral nerve regeneration with cellular support. The conduit composed of two coaxial hydrogel layers of chitosan and collagen is simply made by molding and mechanical anchoring attachment with holes made on the hydrogel tube. A chitosan layer strengthens the conduit mechanically, and a collagen layer provides a scaffold for cells supporting the axonal extension. The conduits of different diameters (outer diameter approximately 2-4 mm) are fabricated. The conduit is bioabsorbable with lysozyme, and biocompatible even under bio absorption. In the neuron culture demonstration, the conduit containing Schwann cells induced the extension of the axon of neurons directed to the conduit. Our easily fabricated conduit could help the high-quality regeneration of peripheral nerves and contribute to the nerve repair surgery.

Bioactive Glasses and Glass/Polymer Composites for Neuroregeneration: Should We Be Hopeful?

Bioactive glasses (BGs) have been identified as highly versatile materials in tissue engineering applications; apart from being used for bone repair for many years, they have recently shown promise for the regeneration of peripheral nerves as well. They can be formulated in different shapes and forms (micro-/nanoparticles, micro-/nanofibers, and tubes), thus potentially meeting the diverse requirements for neuroregeneration. Mechanical and biological improvements in three-dimensional (3D) polymeric scaffolds could be easily provided by adding BGs to their composition. Various types of silicate, borate, and phosphate BGs have been examined for use in neuroregeneration. In general, BGs show good compatibility with the nervous system compartments both in vitro and in vivo. Functionalization and surface modification plus doping with therapeutic ions make BGs even more effective in peripheral nerve regeneration. Moreover, the combination of BGs with conductive polymers is suggested to improve neural cell functions at injured sites. Taking advantage of BGs combined with novel technologies in tissue engineering, like 3D printing, can open new horizons in reconstructive approaches for the nervous system. Although there are great potential opportunities in BG-based therapies for peripheral nerve regeneration, more research should still be performed to carefully assess the pros and cons of BGs in neuroregeneration strategies.

Evaluation methods as quality control in the generation of decellularized peripheral nerve allografts

Nowadays, the high incidence of peripheral nerve injuries and the low success ratio of surgical treatments are driving research to the generation of novel alternatives to repair critical nerve defects. In this sense, tissue engineering has emerged as a possible alternative with special attention to decellularization techniques. Tissue decellularization offers the possibility to obtain a cell-free, natural extracellular matrix (ECM), characterized by an adequate 3D organization and proper molecular composition to repair different tissues or organs, including peripheral nerves. One major problem, however, is that there are no standard quality control methods to evaluate decellularized tissues. Therefore, in this review, a brief description of current strategies for peripheral nerve repair is given, followed by an overview of different decellularization methods used for peripheral nerves. Furthermore, we extensively discuss the available and currently used methods to demonstrate the success of tissue decellularization in terms of the cell removal, preservation of essential ECM molecules and maintenance or modification of biomechanical properties. Finally, orientative guidelines for the evaluation of decellularized peripheral nerve allografts are proposed.

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.

Chitin/Chitosan: Versatile Ecological, Industrial, and Biomedical Applications

Chitin is a linear polysaccharide of N-acetylglucosamine, which is highly abundant in nature and mainly produced by marine crustaceans. Chitosan is obtained by hydrolytic deacetylation. Both polysaccharides are renewable resources, simply and cost-effectively extracted from waste material of fish industry, mainly crab and shrimp shells. Research over the past five decades has revealed that chitosan, in particular, possesses unique and useful characteristics such as chemical versatility, polyelectrolyte properties, gel- and film-forming ability, high adsorption capacity, antimicrobial and antioxidative properties, low toxicity, and biocompatibility and biodegradability features. A plethora of chemical chitosan derivatives have been synthesized yielding improved materials with suggested or effective applications in water treatment, biosensor engineering, agriculture, food processing and storage, textile additives, cosmetics fabrication, and in veterinary and human medicine. The number of studies in this research field has exploded particularly during the last two decades. Here, we review recent advances in utilizing chitosan and chitosan derivatives in different technical, agricultural, and biomedical fields.

Efficacy of chitosan and sodium alginate scaffolds for repair of spinal cord injury in rats

Spinal cord injury results in the loss of motor and sensory pathways and spontaneous regeneration of adult mammalian spinal cord neurons is limited. Chitosan and sodium alginate have good biocompatibility, biodegradability, and are suitable to assist the recovery of damaged tissues, such as skin, bone and nerve. Chitosan scaffolds, sodium alginate scaffolds and chitosan-sodium alginate scaffolds were separately transplanted into rats with spinal cord hemisection. Basso-Beattie-Bresnahan locomotor rating scale scores and electrophysiological results showed that chitosan scaffolds promoted recovery of locomotor capacity and nerve transduction of the experimental rats. Sixty days after surgery, chitosan scaffolds retained the original shape of the spinal cord. Compared with sodium alginate scaffolds- and chitosan-sodium alginate scaffolds-transplanted rats, more neurofilament-H-immunoreactive cells (regenerating nerve fibers) and less glial fibrillary acidic protein-immunoreactive cells (astrocytic scar tissue) were observed at the injury site of experimental rats in chitosan scaffold-transplanted rats. Due to the fast degradation rate of sodium alginate, sodium alginate scaffolds and composite material scaffolds did not have a supporting and bridging effect on the damaged tissue. Above all, compared with sodium alginate and composite material scaffolds, chitosan had better biocompatibility, could promote the regeneration of nerve fibers and prevent the formation of scar tissue, and as such, is more suitable to help the repair of spinal cord injury.

Nanoparticles/thermosensitive hydrogel reinforced with chitin whiskers as a wound dressing for treating chronic wounds

Nanoparticles/thermosensitive hydrogel reinforced with chitin whiskers as a wound dressing for treating chronic wounds.

The Micro/Nanohybrid Structures Enhancing B35 Cell Guidance on Chitosan

A novel chitosan scaffold with micro- and nano-hybrid structures was proposed in this study. The hemispheric array of the barrier layer of an anodic aluminum oxide (AAO) film was used as the substrate. Microelectromechanical systems and nickel electroforming techniques were integrated for fabricating chitosan scaffolds with different micro/nanohybrid structures. Nerve cells were then cultured on the conduits. It was demonstrated that the scaffold with pure microstructures can guide the nerve cells to grow along the ridges of the microstructure and some cells to grow across the groove in between two ridges of the microstructure. It was also shown that the scaffold with microscale ridges and nanopatterns on the groove between two ridges can more effectively guide the cells to grow along the ridges, thus enhancing the proliferation of nerve cells.

Synthesis and characterization of nanocrystalline forsterite coated poly(L-lactide-co-β-malic acid) scaffolds for bone tissue engineering applications

In this research, after synthesizing poly(L-lactide-co-β-malic acid) (PLMA) copolymer, hybrid particles of ice and nanocrystalline forsterite (NF) as coating carriers were used to prepare NF-coated PLMA scaffolds. The porous NF-coated scaffolds were directly fabricated by a combined technique using porogen leaching and freeze-drying methods. The obtained results indicate that the scaffolds were structurally porous with NF particles on their surfaces. When compared to the uncoated scaffolds, the NF coating improved both mechanical properties as well as enhanced bioactivity of the scaffolds. In addition, in vitro biological response of the rat bone marrow stromal cells indicated that NF significantly increased the biocompatibility of NF-coated scaffolds compared with PLMA.

Tubulization with chitosan guides for the repair of long gap peripheral nerve injury in the rat

Biosynthetic guides can be an alternative to nerve grafts for reconstructing severely injured peripheral nerves. The aim of this study was to evaluate the regenerative capability of chitosan tubes to bridge critical nerve gaps (15 mm long) in the rat sciatic nerve compared with silicone (SIL) tubes and nerve autografts (AGs). A total of 28 Wistar Hannover rats were randomly distributed into four groups (n = 7 each), in which the nerve was repaired by SIL tube, chitosan guides of low (∼2%, DAI) and medium (∼5%, DAII) degree of acetylation, and AG. Electrophysiological and algesimetry tests were performed serially along 4 months follow-up, and histomorphometric analysis was performed at the end of the study. Both groups with chitosan tubes showed similar degree of functional recovery, and similar number of myelinated nerve fibers at mid tube after 4 months of implantation. The results with chitosan tubes were significantly better compared to SIL tubes (P < 0.01), but lower than with AG (P < 0.01). In contrast to AG, in which all the rats had effective regeneration and target reinnervation, chitosan tubes from DAI and DAII achieved 43 and 57% success, respectively, whereas regeneration failed in all the animals repaired with SIL tubes. This study suggests that chitosan guides are promising conduits to construct artificial nerve grafts.

3D porous chitosan scaffolds suit survival and neural differentiation of dental pulp stem cells

A key aspect of cell replacement therapy in brain injury treatment is construction of a suitable biomaterial scaffold that can effectively carry and transport the therapeutic cells to the target area. In the present study, we created small 3D porous chitosan scaffolds through freeze-drying, and showed that these can support and enhance the differentiation of dental pulp stem cells (DPSCs) to nerve cells in vitro. The DPSCs were collected from the dental pulp of adult human third molars. At a swelling rate of ~84.33 ± 10.92 %, the scaffold displayed high porosity and interconnectivity of pores, as revealed by SEM. Cell counting kit-8 assay established the biocompatibility of the chitosan scaffold, supporting the growth and survival of DPSCs. The successful neural differentiation of DPSCs was assayed by RT-PCR, western blotting, and immunofluorescence. We found that the scaffold-attached DPSCs showed high expression of Nestin that decreased sharply following induction of differentiation. Exposure to the differentiation media also increased the expression of neural molecular markers Microtubule-associated protein 2, glial fibrillary acidic protein, and 2',3'-cyclic nucleotide phosphodiesterase. This study demonstrates that the granular 3D chitosan scaffolds are non-cytotoxic, biocompatible, and provide a conducive and favorable micro-environment for attachment, survival, and neural differentiation of DPSCs. These scaffolds have enormous potential to facilitate future advances in treatment of brain injury.

Challenges for nerve repair using chitosan-siloxane hybrid porous scaffolds

The treatment of peripheral nerve injuries remains one of the greatest challenges of neurosurgery, as functional recover is rarely satisfactory in these patients. Recently, biodegradable nerve guides have shown great potential for enhancing nerve regeneration. A major advantage of these nerve guides is that no foreign material remains after the device has fulfilled its task, which spares a second surgical intervention. Recently, we studied peripheral nerve regeneration using chitosan-γ-glycidoxypropyltrimethoxysilane (chitosan-GPTMS) porous hybrid membranes. In our studies, these porous membranes significantly improved nerve fiber regeneration and functional recovery in rat models of axonotmetic and neurotmetic sciatic nerve injuries. In particular, the number of regenerated myelinated nerve fibers and myelin thickness were significantly higher in rat treated with chitosan porous hybrid membranes, whether or not they were used in combination with mesenchymal stem cells isolated from the Wharton's jelly of the umbilical cord. In this review, we describe our findings on the use of chitosan-GPTMS hybrids for nerve regeneration.

Comparison of morphology and biocompatibility of acellular nerve scaffolds processed by different chemical methods

To investigate the morphological differences among acellular rat nerve scaffolds processed by different chemical methods and compare the biocompatibility between rat nerve grafts processed by different chemical methods and rat adipose-derived stem cells in vitro. Acellular rat sciatic nerve scaffolds processed by two different chemical methods (the Sondell method and the optimized method) and normal rat sciatic nerves were used as control. The structure and components of nerve scaffold were observed under microscopy, the degrees of decellularization and demyelination of nerve scaffold and integrity of nerve fiber tubes were assessed. The rat adipose-derived stem cells growth and adherence on scaffold were studied by scanning electron microscopy, the activity and adhesive ratio of rat adipose-derived stem cells in the nerve scaffold were compared. The basal lamina tubes and the extracellular matrix in the epineurium and perineurium in the nerve graft of optimized method were better preserved than the nerve graft of the Sondell method. After co-cultured with scaffolds, the difference of cell activity between three groups (two cell-scaffold combinations and control group) at the same observation time were not statistically significant (P > 0.05),the adhesive ratio of rat adipose-derived stem cells in the scaffold of the optimized method was better than that of the Sondell method. The scaffold of the optimized method is more effective than the scaffold of the Sondell method for peripheral nerve tissue engineering.

3D nano/microfabrication techniques and nanobiomaterials for neural tissue regeneration

Injuries of the nervous system occur commonly among people of many different ages and backgrounds. Currently, there are no effective strategies to improve neural regeneration; however, tissue engineering provides a promising avenue for regeneration of many tissue types, including the neural context. Functional nerve conduits derived from tissue engineering techniques present bioengineered 3D artificial substitutes for implantation and rehabilitation of injured nerves. In particular, nanotechnology as a versatile vehicle to create biomimetic nanostructured tissue-engineered neural scaffolds provides great potential for the development of innovative and successful nerve grafts. Nanostructured conduits derived from traditional and novel tissue engineering techniques have been shown to be superior for successful neural function construction due to a high degree of biomimetic character. In this paper, we will focus on current progress in developing 3D nano/microstructured neural scaffolds via electrospinning, emerging 3D printing and self-assembly techniques, nanobiomaterials and bioactive cues for enhanced neural tissue regeneration.

Recent advances in nerve tissue engineering

Nerve injury secondary to trauma, neurological disease or tumor excision presents a challenge for surgical reconstruction. Current practice for nerve repair involves autologous nerve transplantation, which is associated with significant donor-site morbidity and other complications. Previously artificial nerve conduits made from polycaprolactone, polyglycolic acid and collagen were approved by the FDA (USA) for nerve repair. More recently, there have been significant advances in nerve conduit design that better address the requirements of nerve regrowth. Innovations in materials science, nanotechnology, and biology open the way for the synthesis of new generation nerve repair conduits that address issues currently faced in nerve repair and regeneration. This review discusses recent innovations in this area, including the use of nanotechnology to improve the design of nerve conduits and to enhance nerve regeneration.

Synthesis and character investigation of new collagen Hydrolysate/polyvinyl alcohol/hydroxyapatite Polymer-Nano-Porous Membranes: I. Experimental design optimization in thermal and structural properties

ABSTRACT

Development of bioorganic-inorganic composites has drawn eyes to extensive attention in biomedical fields and tissue engineering. So many attempts to prepare hydroxyapatite (HA), in conjunction with various binders including polyvinyl alcohol (PVA), and collagen has performed for late 20 years. We applied a method based on the phase separation for making of polymer porous membranes. This procedure is induced through the addition of a small quantity of water (polymer-rich phase) to a solution with HA precursors (polymer-poor phase). Thermal and structural composite properties of collagen Hydrolysate (CH)-PVA/HA Polymer-Nano-Porous Membranes were analyzed by Design of experiment that was undertaken using D-optimal approach, to select the optimal combination of nano composites precursor. The resulted composite characters were investigated by Fourier transform infrared, scanning electron microscopy (SEM) and thermal gravimetric analysis. Based on the SEM images, this new method could be clearly concluded to porous CH-PVA/HA hybrid materials. Finally the hemocompatibility of nanocomposite membranes were evaluated by the hemolysis study.

Polymer chains incorporating caprolactone and arginine–glycine–aspartic acid functionalities: Synthesis, characterization and biological response in vitro of the Schwann cell

This study describes a strategy for the covalent immobilization of active adhesion peptide moieties onto polymers through the intermediacy of itaconic acid. The arginine–glycine–aspartic acid peptide was grafted to a novel poly(caprolactone 2-(methacryloyloxy) ethyl ester)- co-itaconic acid bulk biomaterial, in order to improve the cell adhesion of the polymer. First, the arginine–glycine–aspartic acid sequence was grafted onto itaconic acid via an amidation reaction using N-(3-dimethylaminopropyl)- N′-ethylcarbodiimide hydrochloride/ N-hydroxysuccinimide as activation complex. The itaconic acid–arginine–glycine–aspartic acid macromer was characterized by Fourier transform infrared spectroscopy and 1H-NMR, yielding a functionalization degree of 85%. In a second step, poly(caprolactone 2-(methacryloyloxy) ethyl ester- co-itaconic acid–arginine–glycine–aspartic acid) (with a feed mixture of 90 wt% of caprolactone 2-(methacryloyloxy) ethyl ester and 10 wt% of itaconic acid–arginine–glycine–aspartic acid macromer) and a series of copolymers of caprolactone 2-(methacryloyloxy) ethyl ester and itaconic acid with different compositions (weight fractions of itaconic acid up to 20 wt%) were synthesized by radical copolymerization. The microstructure and network architecture of the new polymer systems were investigated. Mechanical moduli of poly(caprolactone 2-(methacryloyloxy) ethyl ester- co-itaconic acid), evaluated by dynamic–mechanical analysis, increase with the itaconic acid content. In poly(caprolactone 2-(methacryloyloxy) ethyl ester- co-itaconic acid–arginine–glycine–aspartic acid), the glass transition temperature and the mechanical moduli of the system are smaller than in the nonfunctionalized poly(caprolactone 2-(methacryloyloxy) ethyl ester- co-itaconic acid) copolymers, and the polymer is less hydrophilic. The results indicate that arginine–glycine–aspartic acid grafting of poly(caprolactone 2-(methacryloyloxy) ethyl ester- co-itaconic acid) copolymer networks can be useful for tissue engineering applications, because regenerative processes in the nervous system can be promoted and accelerated, thus, opening a possibility to generate materials with a high potential for clinical applicability.

The use of chitosan-based scaffolds to enhance regeneration in the nervous system

Various biomaterials have been proposed to build up scaffolds for promoting neural repair. Among them, chitosan, a derivative of chitin, has been raising more and more interest among basic and clinical scientists. A number of studies with neuronal and glial cell cultures have shown that this biomaterial has biomimetic properties, which make it a good candidate for developing innovative devices for neural repair. Yet, in vivo experimental studies have shown that chitosan can be successfully used to create scaffolds that promote regeneration both in the central and in the peripheral nervous system. In this review, the relevant literature on the use of chitosan in the nervous tissue, either alone or in combination with other components, is overviewed. Altogether, the promising in vitro and in vivo experimental results make it possible to foresee that time for clinical trials with chitosan-based nerve regeneration-promoting devices is approaching quickly.

Repairing rat sciatic nerve injury by a nerve-growth-factor-loaded, chitosan-based nerve conduit

We have developed a nerve conduit made up of chitosan, on which nerve growth factor (NGF) was immobilized via genipin cross-linking. The nerve conduit was used to bridge a 10-mm-long sciatic nerve gap in rats. At 24 weeks after surgery, electrophysiological assessment, behavioral analysis, and histological examination were conducted to evaluate the outcomes of peripheral nerve repair. The nerve conduit allowed nerve reconstruction between two stumps and reinnervation of the target gastrocnemius muscle. For two groups of rats repaired respectively by the nerve conduit and autologous nerve graft, the density of regenerated axons was 3.55 ± 0.51 and 3.91 ± 0.14 (P = 0.712), and the cross-sectional area of target muscles was 1,159.68 ± 305.85 and 1,307.06 ± 301.25 (P = 0.922), respectively, without significant differences between the two groups. Our data suggest the feasibility of using chitosan-based, NGF-loaded nerve conduits for peripheral nerve repair.

Enhancement of nerve regeneration along a chitosan conduit combined with bone marrow mesenchymal stem cells

Many studies have been dedicated to the development of scaffolds for improving post-traumatic nerve regeneration with different biomaterials. Nerve autografting is the most common surgical procedure currently used to repair nerve defects as a gold standard. To address the disadvantages of limited availability of donor nerves and donor site morbidity, we have fabricated chitosan conduits and seeded them combined with bone marrow mesenchymal stem cells (BMSCs) as an alternative. The conduits were tested for efficacy in bridging the critical gap (8 mm) in sciatic nerves of adult rats, which including sciatic nerve function index (SFI), ethology observation, histologic detection, immunohistochemistry detection. The BMSCs were tested for survival rate and differentiation by fluorescence labeling. Six weeks after operation, the SFI, average regenerated fiber density, and fiber diameter in nerves bridged with BMSCs were similar to those treated with autograft, but significantly higher than those bridged with chitosan conduits only (P < 0.05) because of the differentiation of BMSCs. Evidence is thus provided to support the effect of using multi-channel chitosan conduits seeded with BMSCs to treat critical defects in peripheral nerves. This provides the basis to pursue chitosan and BMSCs combination is an effective method to improve the nerve healing, which may be used as an alternative to the conventional nerve autografts.

BDNF blended chitosan scaffolds for human umbilical cord MSC transplants in traumatic brain injury therapy

This study tested the cytotoxicity of a BDNF blended chitosan scaffold with human umbilical cord mesenchymal stem cells (hUC-MSCs), and the in vitro effect of BDNF blended chitosan scaffolds on neural stem cell differentiation with the aim of contributing alternative methods in tissue engineering for the treatment of traumatic brain injury (TBI). The chitosan scaffold based on immobilization of BDNF by genipin (GP) as a crosslinking agent referred to hereafter as a CGB scaffold was prepared by freezing-drying technique. hUC-MSCs were co-cultured with the CGB scaffold. Fluorescent nuclear staining (Hoechst 33342) was employed to determine the attachment of the hUC-MSCs to CGB scaffolds on the 1st, 3rd, 7th and 10th day of co-culture. The viability of hUC-MSCs adhered to the CGB scaffold was determined by digesting with 0.25% trypsin and evaluating with the cell counting kit-8 (CCK-8). Prior to this, the diameter and porosity of CGB scaffolds were measured. The amount of BDNF released from CGB over a 30 day period was determined by ELISA. Finally, we investigated whether the released BDNF can induce NSC to differentiate into neurons. There were no significant differences in diameter and porosity of individual CGB scaffolds (P > 0.05). There were on average more cells on the CGB scaffold on the first day than on any other day sampled (P < 0.05). The CGB scaffolds released BDNF in a uniform profile, whereas the CB scaffolds only released BDNF during the first 3 days. BDNF released from CGB scaffold promoted neuronal differentiation of NSCs and led to significant differences in differentiation rate and average neuron perimeter compared with the control group. The results of this study demonstrate that CGB scaffolds are biocompatible with hUC-MSCs and that granular CGB scaffolds covered with hUC-MSCs are expected to generate new advances for future treatment of traumatic brain injury.

A biomaterials approach to peripheral nerve regeneration: bridging the peripheral nerve gap and enhancing functional recovery

Microsurgical techniques for the treatment of large peripheral nerve injuries (such as the gold standard autograft) and its main clinically approved alternative--hollow nerve guidance conduits (NGCs)--have a number of limitations that need to be addressed. NGCs, in particular, are limited to treating a relatively short nerve gap (4 cm in length) and are often associated with poor functional recovery. Recent advances in biomaterials and tissue engineering approaches are seeking to overcome the limitations associated with these treatment methods. This review critically discusses the advances in biomaterial-based NGCs, their limitations and where future improvements may be required. Recent developments include the incorporation of topographical guidance features and/or intraluminal structures, which attempt to guide Schwann cell (SC) migration and axonal regrowth towards their distal targets. The use of such strategies requires consideration of the size and distribution of these topographical features, as well as a suitable surface for cell-material interactions. Likewise, cellular and molecular-based therapies are being considered for the creation of a more conductive nerve microenvironment. For example, hurdles associated with the short half-lives and low stability of molecular therapies are being surmounted through the use of controlled delivery systems. Similarly, cells (SCs, stem cells and genetically modified cells) are being delivered with biomaterial matrices in attempts to control their dispersion and to facilitate their incorporation within the host regeneration process. Despite recent advances in peripheral nerve repair, there are a number of key factors that need to be considered in order for these new technologies to reach the clinic.

Microfluidic generation of haptotactic gradients through 3D collagen gels for enhanced neurite growth

We adapted a microfluidic system used previously to generate durotactic gradients of stiffness in a 3D collagen gel, to produce haptotactic gradients of adhesive ligands through the collagen gel. Oligopeptide sequences that included bioactive peptide sequences from laminin, YIGSR, or IKVAV, were grafted separately onto type I collagen using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Solutions of peptide-grafted collagen and untreated collagen were then used as source and sink input solutions, respectively, in an H-shaped microfluidic network fabricated using traditional soft lithography. One-dimensional gradients of the peptide-grafted collagen solution were generated in the channel that connected the source and sink channels, and these gradients became immobilized upon self-assembly of the collagen into a 3D fibrillar gel. The slope and average concentration of the gradients were adjusted by changing the concentration of the source solutions and by changing the length of the cross-channel. A separate, underlying channel in the microfluidic construct allowed the introduction of a chick embryo dorsal root ganglion into the network. Neurites from these explants grew significantly longer up steep gradients of YIGSR, but shallow gradients of IKVAV in comparison to untreated collagen controls. When these two gradients were presented in combination, the bias in growth acceleration was the largest and most consistent. No differences were observed in the number of neurites choosing to grow up or down the gradients in any condition. These results suggest that the incorporation of distinct gradients of multiple bioactive ligands can improve directional acceleration of regenerating axons.

Spider silk constructs enhance axonal regeneration and remyelination in long nerve defects in sheep

BACKGROUND

Surgical reapposition of peripheral nerve results in some axonal regeneration and functional recovery, but the clinical outcome in long distance nerve defects is disappointing and research continues to utilize further interventional approaches to optimize functional recovery. We describe the use of nerve constructs consisting of decellularized vein grafts filled with spider silk fibers as a guiding material to bridge a 6.0 cm tibial nerve defect in adult sheep.

METHODOLOGY/PRINCIPAL FINDINGS

The nerve constructs were compared to autologous nerve grafts. Regeneration was evaluated for clinical, electrophysiological and histological outcome. Electrophysiological recordings were obtained at 6 months and 10 months post surgery in each group. Ten months later, the nerves were removed and prepared for immunostaining, electrophysiological and electron microscopy. Immunostaining for sodium channel (NaV 1.6) was used to define nodes of Ranvier on regenerated axons in combination with anti-S100 and neurofilament. Anti-S100 was used to identify Schwann cells. Axons regenerated through the constructs and were myelinated indicating migration of Schwann cells into the constructs. Nodes of Ranvier between myelin segments were observed and identified by intense sodium channel (NaV 1.6) staining on the regenerated axons. There was no significant difference in electrophysiological results between control autologous experimental and construct implantation indicating that our construct are an effective alternative to autologous nerve transplantation.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates that spider silk enhances Schwann cell migration, axonal regrowth and remyelination including electrophysiological recovery in a long-distance peripheral nerve gap model resulting in functional recovery. This improvement in nerve regeneration could have significant clinical implications for reconstructive nerve surgery.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

The effect of topology of chitosan biomaterials on the differentiation and proliferation of neural stem cells

Neural stem cells (NSCs) are capable of self-renewal and differentiation into three principle central nervous system cell types under specific local microenvironments. Chitosan films (Chi-F), chitosan porous scaffolds (Chi-PS) and chitosan multimicrotubule conduits (Chi-MC) were used to investigate their effects on the differentiation and proliferation of NSCs isolated from the cortices of fetal rats. In the presence of 10% fetal bovine serum most NSCs cultured on Chi-F differentiated into astrocytes, NSCs cultured on Chi-MC showed a significant increase in neuronal differentiation, while Chi-PS somewhat promoted NSCs to differentiate into neurons. However, in serum-free medium with 20 ng ml(-1) basic fibroblast growth factor NSCs cultured on Chi-F showed the greatest proliferation, NSCs cultured on Chi-MC showed moderate cell proliferation, but NSCs cultured on Chi-PS exhibited the least cell proliferation. These observations indicate that chitosan topology can play an important role in regulating differentiation and proliferation of NSCs and raise the possibility of the utilization of chitosan in various structural biomaterials in neural tissue engineering.

Effect of implant surface microtopography on proliferation, neurotrophin secretion, and gene expression of Schwann cells

The purpose of this study was to evaluate the effect of different implant surface properties on the morphology, proliferation, neurotrophin secretion, and gene expression of Schwann cells. Four types of implant surfaces, including ground (smooth surface), sandblasted and acid-etched (SLA), hydroxyapatite-coated (HA), and titanium plasma spray (TPS) surfaces were fabricated and photographed by a scanning electron microscopy (SEM). Schwann cells derived from neonatal rats were cultured on the implant surfaces and assessed via SEM observation and methylthiazol tetrazolium (MTT) colorimetric assay. The secretions and mRNA levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were measured by enzyme-linked immunosorbent assay (ELISA) and quantitative real time RT-PCR, respectively, on days 3 and 7. Tissue culture plastic was used as a control. The results demonstrated that Schwann cells exhibited typical bipolar spindle morphology on various surfaces, and proliferated faster than the control. Neurotrophin secretion and gene expression of both BDNF and NGF were also increased by implant surfaces. This study suggests that the function of Schwann cells can be enhanced by implant implants.

A nerve graft constructed with xenogeneic acellular nerve matrix and autologous adipose-derived mesenchymal stem cells

Since synthetic nerve conduits do not exhibit the characteristics of regeneration, they are generally inadequate substitutes for autologous nerve graft in the repair of long peripheral nerve defects. To resolve this problem, in this study, we constructed a nerve regeneration characteristics-containing nerve graft through integrating xenogeneic acellular nerve matrix (ANM) with autologous neural differentiated adipose-derived mesenchymal stem cells (ADSCs). Xenogeneic ANM was processed by a protocol removing cells and myelin sheath completely, meanwhile preserving growth factors and extracellular matrix (ECM) microstructure of natural nerve, such as porous and basal lamina tube. Cytocompatibility and immunocompatibility evaluation revealed that ANM could support cell attachment and proliferation, and did not stimulate vigorous host reject response. After inoculation of neural differentiated ADSCs onto ANM, differentiated cells were observed to align along longitudinal axis of ANM, resembling band of büngner, and persistently express NGF, GDNF, and BDNF. In vivo, neural differentiated ADSCs also presented glial cell characteristics and promote nerve regeneration 7 days post transplantation. We repaired 1cm Sprague Dawley rat sciatic nerve defects using this nerve graft construction and nerve gap regeneration was indicated by electrophysiology, retrograde labeling and histology analysis. Therefore, we conclude that constructed nerve graft, offering nerve regeneration characteristics, hold great promise to replace autologous in repair peripheral nerve defect.