Xili Ding

Electrospinning of nanofibers for tissue engineering applications

Electrospinning is a method in which materials in solution are formed into nano- and micro-sized continuous fibers. Recent interest in this technique stems fromboth the topical nature of nanoscale material fabrication and the considerable potential for use of these nanoscale fibres in a range of applications including, amongst others, a range of biomedical applications processes such as drug delivery and the use of scaffolds to provide a framework for tissue regeneration in both soft and hard tissue applications systems. The objectives of this review are to describe the theory behind the technique, examine the effect of changing the process parameters on fiber morphology, and discuss the application and impact of electrospinning on the fields of vascular, neural, bone, cartilage, and tendon/ligament tissue engineering.

Graphene-Based Materials in Regenerative Medicine.

Graphene possesses many unique properties such as two-dimensional planar structure, super conductivity, chemical and mechanical stability, large surface area, and good biocompatibility. In the past few years, graphene-based materials have risen as a shining star on the path of researchers seeking new materials for future regenerative medicine. Herein, the recent research advances made in graphene-based materials mostly utilizing the mechanical and electrical properties of graphene are described. The most exciting findings addressing the impact of graphene-based materials on regenerative medicine are highlighted, with particular emphasis on their applications including nerve, bone, cartilage, skeletal muscle, cardiac, skin, adipose tissue regeneration, and their effects on the induced pluripotent stem cells. Future perspectives and emerging challenges are also addressed in this Review article.

In Vitro Evaluation of Combined Sulfated Silk Fibroin Scaffolds for Vascular Cell Growth

A combined sulfated silk fibroin scaffold is fabricated by modifying a knitted silk scaffold with sulfated silk fibroin sponges. In vitro hemocompatibility evaluation reveals that the combined sulfated silk fibroin scaffolds reduce platelet adhesion and activation, and prolong the activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT). The response of porcine endothelial cells (ECs) and smooth muscle cells (SMCs) on the scaffolds is studied to evaluate the cytocompatibility of the scaffolds. Vascular cells are seeded on the scaffolds and cultured for 2 weeks. The scaffolds demonstrate enhanced EC adhesion, proliferation, and maintenance of cellular functions. Moreover, the scaffolds inhibit SMC proliferation and induce expression of contractile SMC marker genes.

Delivery of demineralized bone matrix powder using a salt-leached silk fibroin carrier for bone regeneration

Demineralized bone matrix (DBM) has been widely used for bone regeneration due to its osteoinductivity and osteoconductivity. However, the use of DBM powder is limited due to the difficulties in handling, the tendency to migrate from graft sites and the lack of stability after surgery. In this study, a mechanically stable, salt-leached porous silk fibroin carrier was used to improve the handling properties of DBM powder and to support the attachment, proliferation and osteogenic differentiation of rat bone marrow derived mesenchymal stem cells (rBMSCs). The DBM-silk fibroin (DBM/SF) scaffolds were fabricated with different contents of DBM powder (0%, 10%, 20%, 40% and 80% DBM/SF scaffolds). It was found that the DBM/SF scaffolds could form a stable composite preventing the migration of DBM powder. Moreover, the microarchitecture and mechanical properties of the scaffolds were influenced by the DBM powder. rBMSCs were seeded on the DBM/SF scaffolds and cultured for 14 days. Cell proliferation assays and cell morphology observations indicated that 20% DBM/SF scaffolds exhibited good cell attachment and proliferation. In addition, compared with the other groups, the cellular function was more actively exhibited on 20% DBM/SF scaffolds, as evident by the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for osteoblast-related gene markers (e.g. COL1A1, ALP and cbfa1), the immunocytochemical evaluations of osteoblast-related extracellular matrix components (e.g. COL1A1, OCN and ONN) and the ALP activities. All the data suggested that DBM powder could be delivered using a silk fibroin carrier with improved handling characteristics and that 20% DBM/SF scaffolds had great potential as osteogenesis promoting scaffolds for successful applications in bone regeneration.

Hydroxyapatite-containing silk fibroin nanofibrous scaffolds for tissue-engineered periosteum

The periosteum plays an indispensable role in both bone formation and bone defect healing. The purpose of this study was to construct a functional periosteum in vitro. We developed a simple technology to generate a hydroxyapatite (HA)-containing silk fibroin nanofibrous scaffold as a potential substitute for periosteum. The chemical structural characteristics of the scaffold were evaluated and the results confirmed the presence of HA in the scaffolds. In addition, the Youngs modulus of silk fibroin–hydroxyapatite (SF/HA) scaffolds increased with the increasing content of HA. Rat bone marrow derived mesenchymal stem cells (rBMSCs) were cultured on the scaffolds for 7, 14, and 21 days without adding any osteogenic factors. Cell proliferation assay and cell morphology observation indicated that 30% SF/HA scaffolds exhibited good cell attachment and proliferation. In addition, differentiation of rBMSCs into osteogenic lineage was more actively exhibited on 30% SF/HA scaffolds, as evident by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for osteoblast-related gene markers (e.g., COL1A1, ALP, and Runx2), ALP activities, mineral deposits and immunocytochemical evaluations of osteoblast-related extracellular matrix components (e.g., OPN, ONN, and OCN). All the data in this study suggested that 30% SF/HA scaffolds had great potential as osteogenesis promoting scaffolds for constructing tissue-engineered periosteum.

Comparison of cellular responses of mesenchymal stem cells derived from bone marrow and synovium on combined silk scaffolds

As a brand new member in mesenchymal stem cells (MSCs) families, synovium-derived mesenchymal stem cells (SMSCs) have been increasingly regarded as a promising therapeutic cell species for musculoskeletal regeneration. However, there are few reports mentioning ligamentogenesis of SMSCs and especially null for their engineering use towards ligament regeneration. The aim of this study was to investigate and compare the cellular responses of MSCs derived from bone marrow and synovium on combined silk scaffolds that can be used to determine the cell source most appropriate for tissue-engineered ligament. Rabbit SMSCs and bone marrow-derived mesenchymal stem cells (BMSCs) were isolated and cultured in vitro for two weeks after seeding on the combined silk scaffolds. Samples were studied and compared for their cellular morphology, proliferation, collagen production, gene, and protein expression of ligament-related extracellular matrix (ECM) markers. In addition, the two cell types were transfected with green fluorescent protein to evaluate their fate after implantation in an intraarticular environment of the knee joint. After 14 days of culturing, SMSCs showed a significant increase in proliferation as compared with BMSCs. The transcript and protein expression levels of ligament-related ECM markers in SMSCs were significantly higher than those in BMSCs. Moreover, 6 weeks postoperatively, more viable cells were presented in SMSC-loaded constructs than in BMSC-loaded constructs. Therefore, based on the cellular response in vitro and in vivo, SMSCs may represent a more suitable cell source than BMSCs for further study and development of tissue-engineered ligament.

Preparation and characterization of silk fibroin/poly(l-lactide-co-ε-caprolactone) nanofibrous membranes for tissue engineering applications

In recent years, silk fibroin has become one of the most promising tissue engineering materials because of its excellent cytocompatibility. Poly(l-lactide-co-ε-caprolactone), the copolymer of poly(l-lactide) and poly(ε-caprolactone), possesses good mechanical properties, and its degradation rates can be manipulated by varying the ratio of the constituent polymers. In this study, in order to combine their respective characteristics, silk fibroin/poly(l-lactide-co-ε-caprolactone) nanofibrous membranes were fabricated through electrospinning with different mass ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. The surface properties, thermodynamic properties, mechanical properties, and cytocompatibility of silk fibroin/poly(l-lactide-co-ε-caprolactone) blended membranes were evaluated, and an optimal blending ratio was identified. The results showed that the silk fibroin/poly(l-lactide-co-ε-caprolactone) blended membranes containing 75% of silk fibroin and 25% of poly(l-lactide-co-ε-caprolactone) achieved the most improved performances compared with the single-component membranes or the blended membranes with other mixing ratios. The results from this study indicated that 75/25 silk fibroin/poly(l-lactide-co-ε-caprolactone) blended membranes which combined the advantages of poly(l-lactide-co-ε-caprolactone) and silk fibroin might be a suitable candidate material for use in tissue engineering.

The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters

Abstract Aliphatic biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices. The performances during biodegradation process play crucial roles for final realization of their functions. Because physiological and biochemical environment in vivo significantly affects biodegradation process, large numbers of studies on effects of mechanical loads on the degradation of aliphatic biodegradable polyesters have been launched during last decades. In this review article, we discussed the mechanism of biodegradation and several different mechanical loads that have been reported to affect the biodegradation process. Other physiological and biochemical factors related to mechanical loads were also discussed. The mechanical load could change the conformational strain energy and morphology to weaken the stability of the polymer. Besides, the load and pattern could accelerate the loss of intrinsic mechanical properties of polymers. This indicated that investigations into effects of mechanical loads on the degradation should be indispensable. More combination condition of mechanical loads and multiple factors should be considered in order to keep the degradation rate controllable and evaluate the degradation process in vivo accurately. Only then can the degradable devise achieve the desired effects and further expand the special applications of aliphatic biodegradable polyesters.

Preparation and characterization of electrospun graphene/silk fibroin conductive fibrous scaffolds

Electroactive scaffolds which can carry electrical stimulation to the cells growing on them have attracted more and more attention in recent years. In this study, a conductive fibrous scaffold made of silk fibroin (SF) and graphene was developed using electrospinning techniques. The chemical structural characterization of the obtained scaffolds confirmed the presence of graphene in the fibrous scaffolds. The surface morphologies, mechanical and electrochemical properties and cytocompatibility of the scaffolds were evaluated. The average diameters of the G/SF fibrous scaffolds increased with the addition of graphene until the content of graphene reached 4%. The G/SF scaffolds exhibited improved thermal stability with the addition of graphene, which confirmed that they were more crystalline than pure SF scaffolds. The 3% G/SF fibrous scaffolds showed improved electroactivity and mechanical properties. In addition, they could support the growth and expansion of rat bone mesenchymal stem cells (rBMSCs) based on cell morphology, viability and proliferation studies in vitro. Thus, all the data in this study suggested that the 3% G/SF scaffolds might represent an adequate substrate to successfully scaffold electroactive tissue during regeneration or engineering.

Trilayered sulfated silk fibroin vascular grafts enhanced with braided silk tube

The scaffold component is a major barrier to the development of a clinically useful small-diameter tissue-engineered vascular graft. Scaffold requirements include matching the mechanical and structural properties with those of native vessels and optimizing the microenvironment for cell integration, adhesion, and growth. Trilayered sulfated silk fibroin graft was developed to mimic native tissue structure and function. Physical properties and cell studies were assessed to evaluate the viability of their usage in small-diameter tissue-engineered vascular grafts. Compared with previously fabricated silk fibroin vascular grafts, these trilayered grafts provided comparable water permeability, tensile strength, burst pressure, as well as suture retention strength, to saphenous veins for vascular grafts. In addition, the in vitro results showed good cytocompatibility of the trilayered grafts. These physical and cellular outcomes indicate potential utility of these trilayered sulfated silk fibroin grafts for small-diameter vascular grafts.