Biomaterial and tissue-engineering strategies for the treatment of brain neurodegeneration

The incidence of neurodegenerative diseases is increasing due to changing age demographics and the incidence of sports-related traumatic brain injury is tending to increase over time.Currently approved medicines for neurodegenerative diseases only temporarily reduce the symptoms but cannot cure or delay disease progression.Cell transplantation strategies offer an alternative approach to facilitating central nervous system repair,but efficacy is limited by low in vivo survival rates of cells that are injected in suspension.Transplanting cells that are attached to or encapsulated within a suitable biomaterial construct has the advantage of enhancing cell survival in vivo.A variety of biomaterials have been used to make constructs in different types that included nanoparticles,nanotubes,microspheres,microscale fibrous scaffolds,as well as scaffolds made of gels and in the form of micro-columns.Among these,Tween 80-methoxy poly(ethylene glycol)-poly(lactic-co-glycolic acid)nanoparticles loaded with rhynchophylline had higher transport across a blood-brain barrier model and decreased cell death in an in vitro model of Alzheimer’s disease than rhynchophylline or untreated nanoparticles with rhynchophylline.In an in vitro model of Parkinson’s disease,trans-activating transcriptor bioconjugated with zwitterionic polymer poly(2-methacryoyloxyethyl phosphorylcholine)and protein-based nanoparticles loaded with non-Fe hemin had a similar protective ability as free non-Fe hemin.A positive effect on neuron survival in several in vivo models of Parkinson’s disease was associated with the use of biomaterial constructs such as trans-activating transcriptor bioconjugated with zwitterionic polymer poly(2-methacryoyloxyethyl phosphorylcholine)and protein-based nanoparticles loaded with non-Fe hemin,carbon nanotubes with olfactory bulb stem cells,poly(lactic-co-glycolic acid)microspheres with attached DI-MIAMI cells,ventral midbrain neurons mixed with short fibers of poly-(L-lactic acid)scaffolds and reacted with xyloglucan with/without glial-derived neurotrophic factor,ventral midbrain neurons mixed with Fmoc-DIKVAV hydrogel with/without glial-derived neurotrophic factor.Further studies with in vivo models of Alzheimer’s disease and Parkinson’s disease are warranted especially using transplantation of cells in agarose micro-columns with an inner lumen filled with an appropriate extracellular matrix material.

Repair of Sheep Metatarsus Defects by Using Tissue-engineering Technique

Tissue-engineering bone with porous β-tricalcium phosphate (β-TCP) ceramic and autologous bone marrow mesenchymal stem cells (MSC) was constructed and the effect of this composite on healing of segmental bone defects was investigated. 10-15 ml bone marrow aspirates were harvested from the iliac crest of sheep, and enriched for MSC by density gradient centrifugation over a Percoll cushion (1.073 g/ml). After cultured and proliferated, tissue-engineering bones were constructed with these cells seeded onto porous β-TCP, and then the constructs were implanted in 8 sheep left metatarsus defect (25 mm in length) as experimental group. Porous β-TCP only were implanted to bridge same size and position defects in 8 sheep as control group, and 25 mm segmental bone defects of left metatarsus were left empty in 4 sheep as blank group. Sheep were sacrificed on the 6th, 12th, and 24th week postoperatively and the implants samples were examined by radiograph, histology, and biomechanical test. The 4 sheep in blank group were sacrificed on the 24th week postoperatively. The results showed that new bone tissues were observed either radiographic or histologically at the defects of experimental group as early as 6th week postoperatively, but not in control group, and osteoid tissue, woven bone and lamellar bone occurred earlier than in control group in which the bone defects were repaired in “creep substitution” way, because of the new bone formed in direct manner without progression through a cartilaginous intermediate. At the 24th week, radiographs and biomechanical test revealed an almost complete repair of the defect of experimental group, only partly in control group. The bone defects in blank group were non-healing at the 24th week. It was concluded that engineering bones constructed with porous β-TCP and autologous MSC were capable of repairing segmental bone defects in sheep metatarsus beyond “creep substitution” way and making it healed earlier. Porous β-TCP being constituted with autologous MSC may be a good option in healing critical segmental bone defects in clinical practice and provide insight for future clinical repair of segmental defect.

Development of a Powder Extruder System for Dual-pore Tissue-engineering Scaffold Fabrication

In this study,we developed a powder extruder system that can extrude and deposit powder mixtures to overcome the reported limitations of conventional dualpore scaffold manufacturing methods.To evaluate the extrusion and deposition capability of the powder extruder system,3D tissue-engineering scaffolds with dual-pore characteristics were fabricated with a PCL/PEO/NaCl(polycaprolactone/polyethylene oxide/sodium chloride)powder mixture.In addition,to evaluate the fabricated scaffolds,their compressive modulus,morphology,and in-vitro cell activity were assessed.Consequently,it was confirmed that the proposed powder extruder system can fabricate dual-pore scaffolds with well-interconnected pores as well as arbitrary 3D shapes shown by the fabrication of a 3D femur-shape scaffold similar to the femur model.The results of the cell proliferation and Cell Counting Kit-8(CCK-8)assays,DNA content analysis and viability assays confirm that the dual-pore scaffold fabricated by the powder extruder system improves cell attachment,proliferation,and viability.

Transplantation of tissue-engineered human corneal epithelium in limbal stem cell deficiency rabbit models

AIM: To evaluate the biological functions of tissue-engineered human corneal epithelium (TE-HCEP) by corneal transplantation in limbal stem cell deficiency (LSCD) rabbit models. METHODS: TE-HCEPs were reconstructed with DiI-labeled untransfected HCEP cells and denuded amniotic membrane (dAM) in air-liquid interface culture, and their morphology and structure were characterized by hematoxylin-eosin (HE) staining of paraffin-sections, immunohistochemistry and electron microscopy. LSCD models were established by mechanical and alcohol treatment of the left eyes of New Zealand white rabbits, and their eyes were transplanted with TE-HCEPs with dAM surface outside by lamellar keratoplasty (LKP). Corneal transparency, neovascularization, thickness, and epithelial integrality of both traumatic and post transplantation eyes were checked once a week by slit-lamp corneal microscopy, a corneal pachymeter, and periodic acid-Schiff (PAS) staining. At day 120 post surgery, the rabbits in each group were sacrificed and their corneas were examined by DiI label observation, HE staining, immunohistochemistry and electron microscopy. RESULTS: After cultured for 5 days on dAM, HCEP cells, maintaining keratin 3 expression, reconstructed a 6-7 layer TE-HCEP with normal morphology and structure. The traumatic rabbit corneas, entirely opaque, conjunctivalized and with invaded blood vessels, were used as LSCD models for TE-HCEP transplantation. After transplantation, obvious edema was not found in TE-HCEP-transplanted corneas which became more and more transparent, the invaded blood vessels reduced gradually throughout the monitoring period. The corneas decreased to normal thickness on day 25, while those of dAM eyes were over 575 mu m in thickness during the monitoring period. A 45 layer of epithelium consisting of TE-HCEP originated cells attached tightly to the anterior surface of stroma was reconstructed 120 days after TE-HCEP transplantation, which was similar to the normal control eye in morphology and structure. In contrast, intense corneal edema, turbid, invaded blood vessels were found in dAM eyes, and no multilayer epithelium was found but only a few scattered conjunctiva-like cells appeared. CONCLUSION: The TE-HCEP, with similar morphology and structure to those of innate HCEP, could reconstruct a multilayer corneal epithelium with normal functions in restoring corneal transparency and thickness of LSCD rabbits after transplantation. It may be a promising HCEP equivalent for clinical therapy of corneal epithelial disorders.

In vitro reconstruction and characterization of tissue-engineered human corneal epithelium with seeder cells from an untransfected human corneal epithelial cell line

AIM: To demonstrate the morphology and structure of in vitro reconstructed tissue-engineered human corneal epithelium (TE-HCEP) with seeder cells from an untransfected HCEP cell line. METHODS: The TE-HCEPs were reconstructed in vitro with seeder cells from an untransfected HCEP cell line, and scaffold carriers of denuded amniotic membrane (dAM) in air-liquid interface culture for 3, 5, 7 and 9 days, respectively. The specimens were examined with hematoxylin-eosin (HE) staining of paraffin-section, immunocytochemical staining, scanning and transmission electron microscopy. RESULTS: During in vitro reconstruction of TE-HCEP, HCEP cells formed a 3-4, 6-7 and 8-10 layers of an HCEP-like structure on dAMs in air-liquid interface culture for 3, 5 and 7 days, respectively. But the cells deceased to 5-6 layers and the structure of straified epithelium became loose at day 9. And the cells maintained positive expression of marker proteins (keratin 3 and keratin 12), cell-junction proteins (zonula occludens-1, E-cadherin, connexin 43 and integrin beta 1) and membrane transport protein of Na+-K+ ATPase. The HCEP cells in TE-HCEP were rich in microvilli on apical surface and established numerous cell-cell and cell-dAM junctions at day 5. CONCLUSION: The morphology and structure of the reconstructed TE-HCEP were similar to those of HCEP in vivo. The HCEP cells in the reconstructed TE-HCEP maintained the properties of HCEP cells, including abilities of forming intercellular and cell-extracellular matrix junctions and abilities of performing membrane transportation. The untransfected HCEP cells and dAMs could promisingly be used in reconstruction HCEP equivalent for clinical corneal epithelium transplantation.

Angiogenesis in tissue-engineered nerves evaluated objectively using MICROFIL perfusion and micro-CT scanning

Angiogenesis is a key process in regenerative medicine generally, as well as in the specific field of nerve regeneration. However, no convenient and objective method for evaluating the angiogenesis of tissue-engineered nerves has been reported. In this study, tissue-engineered nerves were constructed in vitro using Schwann cells differentiated from rat skin-derived precursors as supporting cells and chitosan nerve conduits combined with silk fibroin fibers as scaffolds to bridge 10-mm sciatic nerve defects in rats. Four weeks after surgery, three-dimensional blood vessel reconstructions were made through MICROFIL perfusion and micro-CT scanning, and parameter analysis of the tissue-engineered nerves was performed. New blood vessels grew into the tissue-engineered nerves from three main directions： the proximal end, the distal end, and the middle. The parameter analysis of the three-dimensional blood vessel images yielded several parameters, including the number, diameter, connection, and spatial distribution of blood vessels. The new blood vessels were mainly capillaries and microvessels, with diameters ranging from 9 to 301 μm. The blood vessels with diameters from 27 to 155 μm accounted for 82.84% of the new vessels. The microvessels in the tissue-engineered nerves implanted in vivo were relatively well-identified using the MICROFIL perfusion and micro-CT scanning method, which allows the evaluation and comparison of differences and changes of angiogenesis in tissue-engineered nerves implanted in vivo.

Bridging sciatic nerve gap using tissue-engineered nerves constructed with neural tissue-committed stem cells derived from bone marrow

BACKGROUND： Schwann cells are the most commonly used cells for tissue-engineered nerves. However, autologous Schwann cells are of limited use in a clinical context, and allogeneic Schwann cells induce immunological rejections. Cells that do not induce immunological rejections and that are relatively easy to acquire are urgently needed for transplantation. OBJECTIVE： To bridge sciatic nerve defects using tissue engineered nerves constructed with neural tissue-committed stem cells （NTCSCs） derived from bone marrow; to observe morphology and function of rat nerves following bridging; to determine the effect of autologous nerve transplantation, which serves as the gold standard for evaluating efficacy of tissue-engineered nerves. DESIGN, TIME AND SETTING： This randomized, controlled, animal experiment was performed in the Anatomical Laboratory and Biomedical Institute of the Second Military Medical University of Chinese PLA between September 2004 and April 2006. MATERIALS： Five Sprague Dawley rats, aged 1 month and weighing 100-150 g, were used for cell culture. Sixty Sprague Dawley rats aged 3 months and weighing 220-250 g, were used to establish neurological defect models. Nestin, neuron-specific enolase （NSE）, glial fibrillary acidic protein （GFAP）, and S-100 antibodies were provided by Santa Cruz Biotechnology, Inc., USA. Acellular nerve grafts were derived from dogs. METHODS： All rats, each with 1-cm gap created in the right sciatic nerve, were randomly assigned to three groups. Each group comprised 20 rats. Autograft nerve transplantation group： the severed 1-cm length nerve segment was reverted, but with the two ends exchanged; the proximal segment was sutured to the distal sciatic nerve stump and the distal segment to the proximal stump. Blank nerve scaffold transplantation group： a 1-cm length acellular nerve graft was used to bridge the sciatic nerve gap. NTCSC engineered nerve transplantation group： a 1-cm length acellular nerve graft, in which NTCSCs were inoculated, was used to bridge the sciatic nerve gap. MAIN OUTCOME MEASURES： Following surgery, sciatic nerve functional index and electrophysiology functions were evaluated for nerve conduction function, including conduction latency, conduction velocity, and action potential peak. Horseradish peroxidase （HRP, 20%） was injected into the gastrocnemius muscle to retrogradely label the 1-4 and L5 nerve ganglions, as well as neurons in the anterior horn of the spinal cord, in the three groups. Positive expression of nestin, NSE, GFAP, and S-100 were determined using an immunofluorescence double-labeling method. RESULTS： NTCSCs differentiated into neuronal-like cells and glial-like cells within 12 weeks after NTCSC engineered nerve transplantation. HRP retrograde tracing displayed a large amount of HRP-labeled neurons in I-45 nerve ganglions, as well as the anterior horn of the spinal cord, in both the autograft nerve transplantation and the NTCSC engineered nerve transplantation groups. However, few HRP-labeled neurons were detected in the blank nerve scaffold transplantation group. Nerve bridges in the autograft nerve transplantation and NTCSC engineered nerve transplantation groups exhibited similar morphology to normal nerves. Neither fractures or broken nerve bridges nor neuromas were found after bridging the sciatic nerve gap with NTCSCs-inoculated acellular nerve graft, indicating repair. Conduction latency, action potential, and conduction velocity in the NTCSC engineered nerve transplantation group were identical to the autograft nerve transplantation group （P 〉 0.05）, but significantly different from the blank nerve scaffold transplantation group （P 〈 0.05）. CONCLUSION＂ NTCSC tissue-engineered nerves were able to repair injured nerves and facilitated restoration of nerve conduction function, similar to autograft nerve transplantation. ＂

Preliminary studies of constructing a tissue-engineered lamellar corneal graft by culturing mesenchymal stem cells onto decellularized corneal matrix

AIM:To construct a competent corneal lamellar substitute in order to alleviate the shortage of human corneal donor.METHODS:Rabbit mesenchymal stem cells(MSCs)were isolated from bone marrow and identified by flow cytometric,osteogenic and adipogenic induction.Xenogenic decellularized corneal matrix(XDCM)was generated from dog corneas.MSCs were seeded and cultured on XDCM to construct the tissueengineered cornea.Post-transplantation biocompatibility of engineered corneal graft were tested by animal experiment.Rabbits were divided into two groups then underwent lamellar keratoplasty(LK)with different corneal grafts:1)XDCM group(n=5):XDCM;2)XDCM-MSCs groups(n=4):tissue-engineered cornea made up with XDCM and MSCs.The ocular surface recovery procedure was observed while corneal transparency,neovascularization and epithelium defection were measured and compared.In vivo on focal exam was performed 3 mo postoperatively.RESULTS:Rabbit MSCs were isolated and identified.Flow cytometry demonstrated isolated cells were CD90 positive and CD34,CD45 negative.Osteogenic and adipogenic induction verified their multipotent abilities.MSC-XDCM grafts were constructed and observed.In vivo transplantation showed the neovascularization in XDCMMSC group was much less than that in XDCM group postoperatively.Post-transplant 3-month confocal test showed less nerve regeneration and bigger cell-absent area in XDCM-MSC group.CONCLUSION:This study present a novel corneal tissue-engineered graft that could reduce post-operatively neovascularization and remain transparency,meanwhile shows that co-transplantation of MSCs may help increase corneal transplantation successful rate and enlarge the source range of corneal substitute to overcome cornea donor shortage.

Tissue-engineered nerve for repair of sciatic nerve injury

Three articles regarding the use of nerve fragments bridging regeneration chambers, three-dimensional bionic nerve conduits and multiwalled carbon nanotubes for repair of sciatic nerve injury were reported in Neural Regeneration Research. We hope that our readers find these papers useful to their research.

Editor's Choice—Application of tissue-engineered materials in the repair of spinal cord injury

The development of tissue-engineered technology brings hope to the treatment of spinal cord injury. Preparation of a tissue-engineered spinal cord stent with three-dimensional bionic structure has important value in the construction of tissue-engineered spinal cord and the repair of spinal cord injury. Acellular scaffolds can be produced with chemical extraction,

Sequential treatment for diabetic foot ulcers in dialysis patients:A case report

BACKGROUND Diabetic foot ulcers(DFUs)are common in patients with diabetes,especially those undergoing hemodialysis.In severe cases,these ulcers can cause damage to the lower extremities and lead to amputation.Traditional treatments such as flap transposition and transfemoral amputation are not always applicable in all cases.Therefore,there is a need for alternative treatment methods.CASE SUMMARY This report describes a 62-year-old female patient who was admitted to the hospital with plantar and heel ulcers on her left foot.The patient had a history of renal failure and was undergoing regular hemodialysis.Digital subtraction angiography showed extensive stenosis and occlusion in the left superficial femoral artery,left peroneal artery and left posterior tibial artery.Following evaluation by a multidisciplinary team,the patient was diagnosed with type 2 DFUs(TEXAS 4D).Traditional treatments were deemed unsuitable,and the patient was treated with endovascular surgery in the affected area,in addition to supportive medical treatment,local debridement,and sequential repair using split-thickness skin and tissue-engineered skin grafts combined with negative pressure treatment.After four months,the wound had completely healed,and the patient was able to walk with a walking aid.CONCLUSION This study demonstrates a new treatment method for DFUs was successful,using angioplasty,skin grafts,and negative pressure.

AB020.Inhibition of cyclic-AMP-response element binding protein and its impact on corneal wound healing in vitro and in vivo

Background:The cornea composes the outer surface of the eye and its transparency is required to allow light transmission to the retina.However,because of its position,the cornea is subjected to chemical and mechanical injuries that may lead to blindness.Our studies conducted using the human tissue-engineered cornea(hTEC)as a model provided evidence that the cyclic-AMP-response element binding protein(CREB)pathway is repressed during closure of corneal wounds.Based on these results,we hypothesized that closure of corneal wounds can be enhanced by preventing activation of CREB with the pharmacological inhibitor C646.Our goals were to proceed to the pharmacological inhibition of CREB(I)in vitro using the hTECs as a model,and then(II)in vivo using the rabbit as a model.Methods:The self-assembly approach was used to create hTECs,that were then wounded with an 8-mm diameter biopsy punch to create an epithelial defect.The tissues were then incubated with 10μM of C646(n=8).DMSO was used alone as a negative control(n=4).Closure of the wounds was monitored over a period of 5 days.Besides,the cornea of New Zealand white rabbits was debrided with an ethanol 70%solution to create an epithelial defect of 8-mm diameter.Several concentrations of C646(1,10,100μM et 1 mM)were applied as eye drops 3 times a day for up to 7 days.The wounded corneas(n=4 per concentration)were stained with fluorescein and photographed every day.Results:In vitro pharmacological inhibition of CREB with C646 considerably accelerated wound closure of all treated hTECs(4 days)compared to the control group(7 days).Moreover,the in vivo C646 treatment also accelerated wound healing of the corneas compared to the control group.The most effective concentration of C646 tested was the lowest(1μM),as it considerably enhanced the wound healing process.Conclusions:This study demonstrates that wound healing both in vitro and in vivo can be enhanced by preventing activation of CREB using a pharmacological inhibition approach.Most of all,this experiment suggests mediators from the CREB pathway as potential therapeutic targets on which we may influence to alter the wound healing dynamic of the cornea.We believe this study will lead to significant advancements in the clinical field of corneal defects.

Functionalization of in vivo tissue-engineered living biotubes enhance patency and endothelization without the requirement of systemic anticoagulant administration

Vascular regeneration and patency maintenance,without anticoagulant administration,represent key developmental trends to enhance small-diameter vascular grafts(SDVG)performance.In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties.However,mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs.Previously fabricated poly(ε-caprolactone)skeleton-reinforced biotubes(PBs)circumvented mechanical issues and achieved vascular regeneration,but orally administered anticoagulants were required.Here,highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens.The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy(DMPE)-PEG-conjugated anti-coagulant bivalirudin(DPB)and DMPE-PEG-conjugated endothelial progenitor cell(EPC)-binding TPS-peptide(DPT)modifications possessed functionality conducive to promoting vascular graft patency.Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability.DPB repellent of non-specific proteins,DPB inhibition of thrombus formation,and DPB protection against functional masking of DPT’s EPC-capture by blood components,which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration.This strategy offers a safe,facile,and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

Evaluation of corneal cell growth on tissue engineering materials as artificial cornea scaffolds

The keratoprosthesis(KPro;artificial cornea)is a special refractive device to replace human cornea by using heterogeneous forming materials for the implantation into the damaged eyes in order to obtain a certain vision.The main problems of artificial cornea are the biocompatibility and stability of the tissue particularly in penetrating keratoplasty.The current studies of tissue-engineered scaffold materials through comprising composites of natural and synthetic biopolymers together have developed a new way to artificial cornea.Although a wide agreement that the long-term stability of these devices would be greatly improved by the presence of cornea cells,modification of keratoprosthesis to support cornea cells remains elusive.Most of the studies on corneal substrate materials and surface modification of composites have tried to improve the growth and biocompatibility of cornea cells which can not only reduce the stimulus of heterogeneous materials,but also more importantly continuous and stable cornea cells can prevent the destruction of collagenase.The necrosis of stroma and spontaneous extrusion of the device,allow for maintenance of a precorneal tear layer,and play the role of ensuring a good optical surface and resisting bacterial infection.As a result,improvement in corneal cells has been the main aim of several recent investigations;some effort has focused on biomaterial for its well biological properties such as promoting the growth of cornea cells.The purpose of this review is to summary the growth status of the corneal cells after the implantation of several artificial corneas.

Skeletal muscle-derived cells repair peripheral nerve defects in mice

Skeletal muscle-derived cells have strong secretory function,while skeletal muscle-derived stem cells,which are included in muscle-derived cells,can differentiate into Schwann cell-like cells and other cell types.However,the effect of muscle-derived cells on peripheral nerve defects has not been reported.In this study,5-mm-long nerve defects were created in the right sciatic nerves of mice to construct a peripheral nerve defect model.Adult female C57BL/6 mice were randomly divided into four groups.For the muscle-derived cell group,muscle-derived cells were injected into the catheter after the cut nerve ends were bridged with a polyurethane catheter.For external oblique muscle-fabricated nerve conduit and polyurethane groups,an external oblique muscle-fabricated nerve conduit or polyurethane catheter was used to bridge the cut nerve ends,respectively.For the sham group,the sciatic nerves on the right side were separated but not excised.At 8 and 12 weeks post-surgery,distributions of axons and myelin sheaths were observed,and the nerve diameter was calculated using immunofluorescence staining.The number,diameter,and thickness of myelinated nerve fibers were detected by toluidine blue staining and transmission electron microscopy.Muscle fiber area ratios were calculated by Masson’s trichrome staining of gastrocnemius muscle sections.Sciatic functional index was recorded using walking footprint analysis at 4,8,and 12 weeks after operation.The results showed that,at 8 and 12 weeks after surgery,myelin sheaths and axons of regenerating nerves were evenly distributed in the muscle-derived cell group.The number,diameter,and myelin sheath thickness of myelinated nerve fibers,as well as gastrocnemius muscle wet weight and muscle area ratio,were significantly higher in the muscle-derived cell group compared with the polyurethane group.At 4,8,and 12 weeks post-surgery,sciatic functional index was notably increased in the muscle-derived cell group compared with the polyurethane group.These criteria of the muscle-derived cell group were not significantly different from the external oblique muscle-fabricated nerve conduit group.Collectively,these data suggest that muscle-derived cells effectively accelerated peripheral nerve regeneration.This study was approved by the Animal Ethics Committee of Plastic Surgery Hospital,Chinese Academy of Medical Sciences(approval No.040)on September 28,2016.

Overcoming scarring in the urethra: Challenges for tissue engineering

Urethral stricture disease is increasingly common occurring in about 1%of males over the age of 55.The stricture tissue is rich in myofibroblasts and multi-nucleated giant cells which are thought to be related to stricture formation and collagen synthesis.An increase in collagen is associated with the loss of the normal vasculature of the normal urethra.The actual incidence differs based on worldwide populations,geography,and income.The stricture aetiology,location,length and patient’s age and comorbidity are important in deciding the course of treatment.In this review we aim to summarise the existing knowledge of the aetiology of urethral strictures,review current treatment regimens,and present the challenges of using tissue-engineered buccal mucosa(TEBM)to repair scarring of the urethra.In asking this question we are also mindful that recurrent fibrosis occurs in other tissuesdhow can we learn from these other pathologies?

Corneal stromal mesenchymal stem cells: reconstructing a bioactive cornea and repairing the corneal limbus and stromal microenvironment

Corneal stroma-derived mesenchymal stem cells(CS-MSCs) are mainly distributed in the anterior part of the corneal stroma near the corneal limbal stem cells(LSCs). CS-MSCs are stem cells with self-renewal and multidirectional differentiation potential. A large amount of data confirmed that CS-MSCs can be induced to differentiate into functional keratocytes in vitro, which is the motive force for maintaining corneal transparency and producing a normal corneal stroma. CS-MSCs are also an important component of the limbal microenvironment. Furthermore, they are of great significance in the reconstruction of ocular surface tissue and tissue engineering for active biocornea construction. In this paper, the localization and biological characteristics of CS-MSCs, the use of CS-MSCs to reconstruct a tissue-engineered active biocornea, and the repair of the limbal and matrix microenvironment by CS-MSCs are reviewed, and their application prospects are discussed.

Integrated gradient tissue-engineered osteochondral scaffolds:Challenges,current efforts and future perspectives

The osteochondral defect repair has been most extensively studied due to the rising demand for new therapies to diseases such as osteoarthritis.Tissue engineering has been proposed as a promising strategy to meet the demand of simultaneous regeneration of both cartilage and subchondral bone by constructing integrated gradient tissue-engineered osteochondral scaffold(IGTEOS).This review brought forward the main challenges of establishing a satisfactory IGTEOS from the perspectives of the complexity of physiology and microenvironment of osteochondral tissue,and the limitations of obtaining the desired and required scaffold.Then,we comprehensively discussed and summarized the current tissue-engineered efforts to resolve the above challenges,including architecture strategies,fabrication techniques and in vitro/in vivo evaluation methods of the IGTEOS.Especially,we highlighted the advantages and limitations of various fabrication techniques of IGTEOS,and common cases of IGTEOS application.Finally,based on the above challenges and current research progress,we analyzed in details the future perspectives of tissue-engineered osteochondral construct,so as to achieve the perfect reconstruction of the cartilaginous and osseous layers of osteochondral tissue simultaneously.This comprehensive and instructive review could provide deep insights into our current understanding of IGTEOS.