Preliminary study on the preparation of lyophilized acellular nerve scaffold complexes from rabbit sciatic nerves with human umbilical cord mesenchymal stem cells

BACKGROUND The gold standard of care for patients with severe peripheral nerve injury is autologous nerve grafting;however,autologous nerve grafts are usually limited for patients because of the limited number of autologous nerve sources and the loss of neurosensory sensation in the donor area,whereas allogeneic or xenografts are even more limited by immune rejection.Tissue-engineered peripheral nerve scaffolds,with the morphology and structure of natural nerves and complex biological signals,hold the most promise as ideal peripheral nerve“replacements”.AIM To prepare allogenic peripheral nerve scaffolds using a low-toxicity decellularization method,and use human umbilical cord mesenchymal stem cells(hUCMSCs)as seed cells to cultivate scaffold-cell complexes for the repair of injured peripheral nerves.METHODS After obtaining sciatic nerves from New Zealand rabbits,an optimal acellular scaffold preparation scheme was established by mechanical separation,varying lyophilization cycles,and trypsin and DNase digestion at different times.The scaffolds were evaluated by hematoxylin and eosin(HE)and luxol fast blue(LFB)staining.The maximum load,durability,and elastic modulus of the acellular scaffolds were assessed using a universal material testing machine.The acellular scaffolds were implanted into the dorsal erector spinae muscle of SD rats and the scaffold degradation and systemic inflammatory reactions were observed at 3 days,1 week,3 weeks,and 6 weeks following surgery to determine the histocompatibility between xenografts.The effect of acellular scaffold extracts on fibroblast proliferation was assessed using an MTT assay to measure the cytotoxicity of the scaffold residual reagents.In addition,the umbilical cord from cesarean section fetuses was collected,and the Wharton’s jelly(WJ)was separated into culture cells and confirm the osteogenic and adipogenic differentiation of mesenchymal stem cells(MSCs)and hUC-MSCs.The cultured cells were induced to differentiate into Schwann cells by the antioxidant-growth factor induction method,and the differentiated cells and the myelinogenic properties were identified.RESULTS The experiments effectively decellularized the sciatic nerve of the New Zealand rabbits.After comparing the completed acellular scaffolds among the groups,the optimal decellularization preparation steps were established as follows:Mechanical separation of the epineurium,two cycles of lyophilization-rewarming,trypsin digestion for 5 hours,and DNase digestion for 10 hours.After HE staining,no residual nuclear components were evident on the scaffold,whereas the extracellular matrix remained intact.LFB staining showed a significant decrease in myelin sheath composition of the scaffold compared with that before preparation.Biomechanical testing revealed that the maximum tensile strength,elastic modulus,and durability of the acellular scaffold were reduced compared with normal peripheral nerves.Based on the histocompatibility test,the immune response of the recipient SD rats to the scaffold New Zealand rabbits began to decline3 weeks following surgery,and there was no significant rejection after 6 weeks.The MTT assay revealed that the acellular reagent extract had no obvious effects on cell proliferation.The cells were successfully isolated,cultured,and passaged from human umbilical cord WJ by MSC medium,and their ability to differentiate into Schwann-like cells was demonstrated by morphological and immunohistochemical identification.The differentiated cells could also myelinate in vitro.CONCLUSION The acellular peripheral nerve scaffold with complete cell removal and intact matrix may be prepared by combining lyophilization and enzyme digestion.The resulting scaffold exhibited good histocompatibility and low cytotoxicity.In addition,hUC-MSCs have the potential to differentiate into Schwann-like cells with myelinogenic ability following in vitro induction.

Optimization of nanofiber scaffold properties towards nerve guidance channel design

Nerve guidance channels are limited by lack of topographical guidance：Treatment of sizeable nerve gaps remains problematic following peripheral nerve injury.Functional outcomes are good when neurorrhaphy,or direct end-to-end suture repair,is possible.The problem arises when there is significant segmental loss,which can occur following trauma as well as oncological procedures.

A decellularized nerve matrix scaffold inhibits neuroma formation in the stumps of transected peripheral nerve after peripheral nerve injury

Traumatic painful neuroma is an intractable clinical disease characterized by improper extracellular matrix(ECM)deposition around the injury site.Studies have shown that the microstructure of natural nerves provides a suitable microenvironment for the nerve end to avoid abnormal hyperplasia and neuroma formation.In this study,we used a decellularized nerve matrix scaffold(DNM-S)to prevent against the formation of painful neuroma after sciatic nerve transection in rats.Our results showed that the DNM-S effectively reduced abnormal deposition of ECM,guided the regeneration and orderly arrangement of axon,and decreased the density of regenerated axons.The epineurium-perilemma barrier prevented the invasion of vascular muscular scar tissue,greatly reduced the invasion ofα-smooth muscle actin-positive myofibroblasts into nerve stumps,effectively inhibited scar formation,which guided nerve stumps to gradually transform into a benign tissue and reduced pain and autotomy behaviors in animals.These findings suggest that DNM-S-optimized neuroma microenvironment by ECM remodeling may be a promising strategy to prevent painful traumatic neuromas.

A substrate scaffold for assessment of nerve regeneration and neurodegenerative diseases

Neuroregenerafion is a complex topic in neurosci- ence and includes 3 concepts： neurogenesis, neuro- plasticity, and neurorestoration. After injury of the nervous system, axons have the capacity for self-re- pair, regrowth or proliferation. The peripheral ner- vous system is more effective at restoring damaged axons than the central nervous system （CNS）. This is because formation of scar tissue in the CNS in- fluences neural regrowth or synthesis of growth-in- hibiting proteins, thereby preventing reconstruction of a neural circuit （Silver and Miller, 2004; Enciu et al., 2011）. Parkinson＇s disease （PD） and Alzheimer＇s disease （AD） are two most common degenerative diseases of the CNS among the elderly.

Repair of sciatic nerve defects using tissue engineered nerves

In this study, we constructed tissue-engineered nerves with acellular nerve allografts in Sprague-Dawley rats, which were prepared using chemical detergents-enzymatic digestion and mechanical methods, in combination with bone marrow mesenchymal stem cells of Wistar rats cultured in vitro, to repair 15 mm sciatic bone defects in Wistar rats. At postoperative 12 weeks, electrophysiological detection results showed that the conduction velocity of regenerated nerve after repair with tissue-engineered nerves was similar to that after autologous nerve grafting, and was higher than that after repair with acellular nerve allografts. Immunohistochemical staining revealed that motor endplates with acetylcholinesterase-positive nerve fibers were orderly arranged in the middle and superior parts of the gastrocnemius muscle; regenerated nerve tracts and sprouted branches were connected with motor endplates, as shown by acetylcholinesterase histochemistry combined with silver staining. The wet weight ratio of the tibialis anterior muscle at the affected contralateral hind limb was similar to the sciatic nerve after repair with autologous nerve grafts, and higher than that after repair with acellular nerve allografts. The hind limb motor function at the affected side was significantly improved, indicating that acellular nerve allografts combined with bone marrow mesenchymal stem cell bridging could promote functional recovery of rats with sciatic nerve defects.

Dynamic culture of a thermosensitive collagen hydrogel as an extracellular matrix improves the construction of tissue-engineered peripheral nerve

Tissue engineering technologies offer new treatment strategies for the repair of peripheral nerve injury, hut cell loss between seeding and adhesion to the scaffold remains inevitable. A thermosensitive collagen hydrogel was used as an extracellular matrix in this study and combined with bone marrow mesenchymal stem cells to construct tissue-engineered peripheral nerve composites in vitro. Dynamic culture was performed at an oscillating frequency of 0.5 Hz and 35° swing angle above and below the horizontal plane. The results demonstrated that bone marrow mesenchymal stem cells formed membrane-like structures around the poly-L-lactic acid scaffolds and exhibited regular alignment on the composite surface. Collagen was used to fill in the pores, and seeded cells adhered onto the poly-L-lactic acid fibers. The DNA content of the bone marrow mesenchymal stem cells was higher in the composites constructed with a thermosensitive collagen hydrogel compared with that in collagen I scaffold controls. The cellular DNA content was also higher in the thermosensitive collagen hydrogel composites constructed with the thermosensitive collagen hydrogel in dynamic culture than that in static culture. These results indicate that tissue-engineered composites formed with thermosensitive collagen hydrogel in dynamic culture can maintain larger numbers of seeded cells by avoiding cell loss during the initial adhe-sion stage. Moreover, seeded cells were distributed throughout the material.

A partition-type tubular scaffold loaded with PDGF-releasing microspheres for spinal cord repair facilitates the directional migration and growth of cells

The best tissue-engineered spinal cord grafts not only match the structural characteristics of the spinal cord but also allow the seed cells to grow and function in situ.Platelet-derived growth factor（PDGF） has been shown to promote the migration of bone marrow stromal cells;however,cytokines need to be released at a steady rate to maintain a stable concentration in vivo.Therefore,new methods are needed to maintain an optimal concentration of cytokines over an extended period of time to effectively promote seed cell localization,proliferation and differentiation.In the present study,a partition-type tubular scaffold matching the anatomical features of the thoracic 8–10 spinal cord of the rat was fabricated using chitosan and then subsequently loaded with chitosan-encapsulated PDGF-BB microspheres（PDGF-MSs）.The PDGF-MS-containing scaffold was then examined in vitro for sustained-release capacity,biocompatibility,and its effect on neural progenitor cells differentiated in vitro from multilineage-differentiating stress-enduring cells（MUSE-NPCs）.We found that pre-freezing for 2 hours at-20°C significantly increased the yield of partition-type tubular scaffolds,and 30 μL of 25% glutaraldehyde ensured optimal crosslinking of PDGF-MSs.The resulting PDGF-MSs cumulatively released 52% of the PDGF-BB at 4 weeks in vitro without burst release.The PDGF-MS-containing tubular scaffold showed suitable biocompatibility towards MUSE-NPCs and could promote the directional migration and growth of these cells.These findings indicate that the combination of a partition-type tubular scaffold,PDGF-MSs and MUSENPCs may be a promising model for the fabrication of tissue-engineered spinal cord grafts.

Development of ovalbumin implants with different spatial configurations for treatment of peripheral nerve injury

Peripheral nerve injury(PNI)seriously affects the health and life of patients,and is an urgent clinical problem that needs to be resolved.Nerve implants prepared from various biomaterials have played a positive role in PNI,but the effect should be further improved and thus new biomaterials is urgently needed.Ovalbumin(OVA)contains a variety of bioactive components,low immunogenicity,tolerance,antimicrobial activity,non-toxicity and biodegradability,and has the ability to promote wound healing,cell growth and antimicrobial properties.However,there are few studies on the application of OVA in neural tissue engineering.In this study,OVA implants with different spatial structures(membrane,fiber,and lyophilized scaffolds)were constructed by casting,electrospinning,and freeze-drying methods,respectively.The results showed that the OVA implants had excellent physicochemical properties and were biocompatible without significant toxicity,and can promote vascularization,show good histocompatibility,without excessive inflammatory response and immunogenicity.The in vitro results showed that OVA implants could promote the proliferation and migration of Schwann cells,while the in vivo results confirmed that OVA implants(the E5/70%and 20 kV 20μL/min groups)could effectively regulate the growth of blood vessels,reduce the inflammatory response and promote the repair of subcutaneous nerve injury.Further on,the high-throughput sequencing results showed that the OVA implants up-regulated differential expression of genes related to biological processes such as tumor necrosis factor-α(TNF-α),phosphatidylinositide 3-kinases/protein kinase B(PI3K-Akt)signaling pathway,axon guidance,cellular adhesion junctions,and nerve regeneration in Schwann cells.The present study is expected to provide new design concepts and theoretical accumulation for the development of a new generation of nerve regeneration implantable biomaterials.