Anlin Yin

Fabrication of chitosan/silk fibroin composite nanofibers for wound-dressing applications.

Chitosan, a naturally occurring polysaccharide with abundant resources, has been extensively exploited for various biomedical applications, typically as wound dressings owing to its unique biocompatibility, good biodegradability and excellent antibacterial properties. In this work, composite nanofibrous membranes of chitosan (CS) and silk fibroin (SF) were successfully fabricated by electrospinning. The morphology of electrospun blend nanofibers was observed by scanning electron microscopy (SEM) and the fiber diameters decreased with the increasing percentage of chitosan. Further, the mechanical test illustrated that the addition of silk fibroin enhanced the mechanical properties of CS/SF nanofibers. The antibacterial activities against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) were evaluated by the turbidity measurement method; and results suggest that the antibacterial effect of composite nanofibers varied on the type of bacteria. Furthermore, the biocompatibility of murine fibroblast on as-prepared nanofibrous membranes was investigated by hematoxylin and eosin (H&E) staining and MTT assays in vitro, and the membranes were found to promote the cell attachment and proliferation. These results suggest that as-prepared chitosan/silk fibroin (CS/SF) composite nanofibrous membranes could be a promising candidate for wound healing applications.

Genipin-crosslinked silk fibroin/hydroxybutyl chitosan nanofibrous scaffolds for tissue-engineering application

To improve water-resistant ability and mechanical properties of silk fibroin (SF)/hydroxybutyl chitosan (HBC) nanofibrous scaffolds for tissue-engineering applications, genipin, glutaraldehyde (GTA), and ethanol were used to crosslink electrospun nanofibers, respectively. The mechanical properties of nanofibrous scaffolds were obviously improved after 24 h of crosslinking with genipin and were superior to those crosslinked with GTA and ethanol for 24 h. SEM indicated that crosslinked nanofibers with genipin and GTA vapor had good water-resistant ability. Characterization of the microstructure (porosity and pore structure) demonstrated crosslinked nanofibrous scaffolds with genipin and GTA vapor had lager porosities and mean diameters than those with ethanol. Characterization of FTIR-ATR and (13)C NMR clarified both genipin and GTA acted as crosslinking agents for SF and HBC. Furthermore, genipin could induce SF conformation from random coil or α-helix to β-sheet. Although GTA could also successfully crosslink SF/HBC nanofibrous scaffolds, in long run, genipin maybe a better method due to lower cytotoxicity than GTA. Cell viability studies and wound-healing test in rats clarified that the genipin-crosslinked SF/HBC nanofibrous scaffolds had a good biocompatibility both in vitro and in vivo. These results suggested that genipin-crosslinked SF/HBC nanofibrous scaffolds might be potential candidates for wound dressing and tissue-engineering scaffolds.

Hierarchically designed injectable hydrogel from oxidized dextran, amino gelatin and 4-arm poly(ethylene glycol)-acrylate for tissue engineering application

Hydrogels are high in water content and have physical properties similar to native extracellular matrix (ECM), and thus they have been widely studied as three-dimensional (3D) tissue engineering scaffolds for cell culture. In this work, a two-step process was introduced to fabricate injectable hydrogel from oxidized dextran (ODex), amino gelatin (MGel) and 4-arm poly(ethylene glycol)-acrylate (4A-PEG-Acr) for cell encapsulation. A primary network was formed based on a Schiff based reaction between ODex and MGel, then a UV light-induced radical reaction of 4A-PEG-Acr was used to produce the independent secondary network. Both of the reactions were carried out under physiological conditions in the presence of living cells with no toxicity. The primary network depending on natural polymers could degrade rapidly to provide space and nutrition for encapsulated cells’ growth, and the secondary network could provide long-term mechanical stability. The attachment and spreading of pre-osteoblasts (MC3T3-E1) on IPN hydrogels were observed by DEAD/LIVE kit staining. Furthermore, cell spreading and cell proliferation within IPN hydrogels were observed using confocal microscopy after phalloidin/DAPI staining. The results showed that the as-prepared interpenetrating polymer network (IPN) hydrogels possessed good mechanical properties, a controllable degradation rate and favorable biocompatibility. Therefore, the hierarchically designed hydrogel in this study could be a promising candidate for bone or cartilage tissue engineering applications.

A multi-layered vascular scaffold with symmetrical structure by bi-directional gradient electrospinning.

Multi-layered scaffolds are advantageous in vascular tissue engineering, in consideration of better combination of biomechanics, biocompatibility and biodegradability than the scaffolds with single structure. In this study, a bi-directional gradient electrospinning method was developed to fabricate poly(l-lactide-co-caprolactone) (P(LLA-CL)), collagen and chitosan based tubular scaffold with multi-layered symmetrical structure. The multi-layered composite scaffold showed improved mechanical property and biocompatibility, in comparison to the blended scaffold using the same proportion of raw materials. Endothelialization on the multi-layered scaffold was accelerated owing to the bioactive surface made of pure natural materials. hSMCs growth showed the similar results because of its better biocompatibility. Additionally, fibers morphology change, pH value balance and long term mechanical support results showed that the gradient structure effectively improved biodegradability.

Fabrication of cell penetration enhanced poly (l-lactic acid-co-ɛ-caprolactone)/silk vascular scaffolds utilizing air-impedance electrospinning.

In the vascular prosthetic field, the prevailing thought is that for clinical, long-term success, especially bioresorbable grafts, cellular migration and penetration into the prosthetic structure is required to promote neointima formation and vascular wall development. In this study, we fabricated poly (l-lactic acid-co-ɛ-caprolactone) P(LLA-CL)/silk fibroin (SF) vascular scaffolds through electrospinning using both perforated mandrel subjected to various intraluminal air pressures (0-300kPa), and solid mandrel. The scaffolds were evaluated the cellular infiltration in vitro and mechanical properties. Vascular scaffolds were seeded with smooth muscle cells (SMCs) to evaluate cellular infiltration at 1, 7, and 14 days. The results revealed that air-impedance scaffolds allowed significantly more cell infiltration as compared to the scaffolds fabricated with solid mandrel. Meanwhile, results showed that both mandrel model and applied air pressure determined the interfiber distance and the alignment of fibers in the enhanced porosity regions of the structure which influenced cell infiltration. Uniaxial tensile testing indicated that the air-impedance scaffolds have sufficient ultimate strength, suture retention strength, and burst pressure as well as compliance approximating a native artery. In conclusion, the air-impedance scaffolds improved cellular infiltration without compromising overall biomechanical properties. These results support the scaffolds potential for vascular grafting and in situ regeneration.

Electrospun poly(L-lactide-co-caprolactone)–collagen–chitosan vascular graft in a canine femoral artery model

Poly(l-lactide-co-caprolactone)-collagen-chitosan (P(LLA-CL)-COL-CS) composite grafts were electrospun in this study. Based on the test results for mechanical properties, biodegradability and in vitro cellular compatibility, the optimal weight ratio of P(LLA-CL) to COL/CS was set as 3 : 1. In vivo study was further performed in a canine femoral artery model. The results showed that the 3 : 1 grafts possessed excellent structural integrity, higher patency rate, better endothelial cell (EC) and smooth muscle cells (SMC) growth, as well as higher levels of gene and protein expression of angiogenesis-related cues than those of grafts based on P(LLA-CL). The findings confirmed that the addition of natural materials, such as collagen and chitosan, could effectively improve endothelialization, SMC incursion into the tunica media, and vascular remodeling for tissue engineering.

Electrospun macroporous fibrous scaffolds

combinations of PTDs such as Tat and 9R, and protein to find an optimum combination for efficient transduction effect. Various combinations of PTDs were fused with green fluorescent protein (GFP) in a recombinant way, which allows intracellular protein trafficking and measurement of transduction efficiency. We focused on not only transduction efficiency but also retention ability of PTDconjugated GFP. The tat-conjugated GFP showed high transduction efficiency, while 9R-conjugated GFPs had good retention abilities. GFPs conjugated with both Tat and 9R demonstrated synergistic effects showing high transfection efficiency and long retention ability.