Guoping Guan

Influence of Layer-by-Layer Polyelectrolyte Deposition and EDC/NHS Activated Heparin Immobilization onto Silk Fibroin Fabric

To enhance the hemocompatibility of silk fibroin fabric as biomedical material, polyelectrolytes architectures have been assembled through the layer-by-layer (LbL) technique on silk fibroin fabric (SFF). In particular, 1.5 and 2.5 bilayer of oppositely charged polyelectrolytes were assembled onto SFF using poly(allylamine hydrochloride) (PAH) as polycationic polymer and poly(acrylic acid) (PAA) as polyanionic polymer with PAH topmost. Low molecular weight heparin (LMWH) activated with 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was then immobilized on its surface. Alcian Blue staining, toluidine blue assay and X-ray photoelectron spectroscopy (XPS) confirmed the presence of heparin on modified SFF surfaces. The surface morphology of the modified silk fibroin fabric surfaces was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and obtained increased roughness. Negligible hemolytic effect and a higher concentration of free hemoglobin by a kinetic clotting time test ensured the improved biological performance of the modified fibroin fabric. Overall, the deposition of 2.5 bilayer was found effective in terms of biological and surface properties of the modified fibroin fabric compared to 1.5 bilayer self-assembly technique. Therefore, this novel approach to surface modification may demonstrate long term patency in future in vivo animal trials of small diameter silk fibroin vascular grafts.

Preparation and evaluation of bicomponent and homogeneous polyester silk small diameter arterial prostheses

The development of a small diameter (≤5 mm) arterial prosthesis requires the appropriate selection of materials, structure and fabrication method so as to provide adequate mechanical properties, superior biocompatibility and precise control over the diameter. In this study, 100% polyester, 100% silk fibroin and a combination of both yarns were woven into seamless tubular prototype prostheses with different basic weaves. After degumming/scouring they met a target inner diameter of 3.9±0.3 mm which demonstrates that weaving is a precise way to manufacture small caliber arterial prostheses. In conclusion, the bicomponent polyester/silk woven samples had superior mechanical properties and improved cytocompatibility compared to commercial ePTFE devices.

Surface modification of silk fibroin fabric using layer-by-layer polyelectrolyte deposition and heparin immobilization for small-diameter vascular prostheses.

There is an urgent need to develop a biologically active implantable small-diameter vascular prosthesis with long-term patency. Silk-fibroin-based small-diameter vascular prosthesis is a promising candidate having higher patency rate; however, the surface modification is indeed required to improve its further hemocompatibility. In this study, silk fibroin fabric was modified by a two-stage process. First, the surface of silk fibroin fabric was coated using a layer-by-layer polyelectrolyte deposition technique by stepwise dipping the silk fibroin fabric into a solution of cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA) solution. The dipping procedure was repeated to obtain the PAH/PAA multilayers deposited on the silk fibroin fabrics. Second, the polyelectrolyte-deposited silk fibroin fabrics were treated in EDC/NHS-activated low-molecular-weight heparin (LMWH) solution at 4 °C for 24 h, resulting in immobilization of LMWH on the silk fibroin fabrics surface. Scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray data revealed the accomplishment of LMWH immobilization on the polyelectrolyte-deposited silk fibroin fabric surface. The higher the number of PAH/PAA coating layers on the silk fibroin fabric, the more surface hydrophilicity could be obtained, resulting in a higher fetal bovine serum protein and platelets adhesion resistance properties when tested in vitro. In addition, compared with untreated sample, the surface-modified silk fibroin fabrics showed negligible loss of bursting strength and thus reveal the acceptability of polyelectrolytes deposition and heparin immobilization approach for silk-fibroin-based small-diameter vascular prostheses modification.

Surface Modification and Characterisation of Silk Fibroin Fabric Produced by the Layer-by-Layer Self-Assembly of Multilayer Alginate/Regenerated Silk Fibroin

Silk-based medical products have a long history of use as a material for surgical sutures because of their desirable mechanical properties. However, silk fibroin fabric has been reported to be haemolytic when in direct contact with blood. The layer-by-layer self-assembly technique provides a method for surface modification to improve the biocompatibility of silk fibroin fabrics. Regenerated silk fibroin and alginate, which have excellent biocompatibility and low immunogenicity, are outstanding candidates for polyelectrolyte deposition. In this study, silk fabric was degummed and positively charged to create a silk fibroin fabric that could undergo self-assembly. The multilayer self-assembly of the silk fibroin fabric was achieved by alternating the polyelectrolyte deposition of a negatively charged alginate solution (pH = 8) and a positively charged regenerated silk fibroin solution (pH = 2). Finally, the negatively charged regenerated silk fibroin solution (pH = 8) was used to assemble the outermost layer of the fabric so that the surface would be negatively charged. A stable structural transition was induced using 75% ethanol. The thickness and morphology were characterised using atomic force microscopy. The properties of the self-assembled silk fibroin fabric, such as the bursting strength, thermal stability and flushing stability, indicated that the fabric was stable. In addition, the cytocompatibility and haemocompatibility of the self-assembled silk fibroin fabrics were evaluated. The results indicated that the biocompatibility of the self-assembled multilayers was acceptable and that it improved markedly. In particular, after the self-assembly, the fabric was able to prevent platelet adhesion. Furthermore, other non-haemolytic biomaterials can be created through self-assembly of more than 1.5 bilayers, and we propose that self-assembled silk fibroin fabric may be an attractive candidate for anticoagulation applications and for promoting endothelial cell adhesion for vascular prostheses.

Influence of structures on the mechanical and absorption properties of a textile pile debridement material and its biological evaluation

Debridement describes the removal of necrotic tissue, cell debris and bacteria from a wound site. It aids the wound healing process and is considered as the cornerstone in proper wound management. The present work introduces a feasible approach to fabricate textile pile debridement materials with controllable structures. Six pile materials with variable pile densities and numbers of ground yarns were prepared based on the sliver knitting technology followed by back-coating, heat setting and shearing. Their surface morphology and chemistry were inspected by using SEM and FTIR. The mass per unit area and stitch density were measured to describe the basic geometric structures of the pile materials. The mechanical, liquid absorption and biological properties for the textile pile materials were assessed and compared with a commercial cotton gauze which is commonly used in clinical practice. The influence of structures on the mechanical, liquid absorption properties of the textile pile materials was also analyzed. Results show that pile density is the primary structure factor that affects the properties of the textile pile materials. Furthermore, all the six pile materials prepared in this study exhibited superior performance in both mechanical behaviors and liquid absorption capacity compared to the commercial gauze control. In addition, the results of biological evaluation indicate a satisfactory biocompatibility of the pile debridement material. Therefore the textile pile material offers a potential for wound debridement application.

The significance of cadherin for cell–cell interactions and cell adhesions on biomaterials

Cadherins are surface glycoproteins on plasma membranes and exist in many forms: T-cadherin, neuronal cadherin (N-cadherin), epithelial cadherin (E-cadherin), and vascular endothelial (VE-cadherin). Cadherins play critical roles in cell–cell interactions and are involved in multiple functions related to cell growth and proliferation. Findings from numerous reports have indicated that VE-cadherin regulates the remodeling, gating, and maturation of vascular vessels. The surface morphology of materials also impacts endothelial cell adhesion. This report is an overview of recent research on the effects of cadherins on cell–cell interactions, along with cell adhesions as examined on different materials. This summary will provide novel insights and approaches for research on cell–cell and cell–material interactions and illuminate some of the mechanisms of cell growth on different materials.

Deformation Mechanisms of Prototype Composite Braided Stent-grafts in Bending Fatigue for Peripheral Artery Application

Stent-grafts in peripheral arteries suffer from complex cyclic loadings in vivo, including pulsatile, axial bending and torsion. Normal fatigue durability evaluation technologies, however, are majorly based on pulsation and thus are short of accuracy under the complicated stress conditions experienced physiologically. While there is a little research focused on the cyclic fatigue of stent-grafts in bending, it remains an almost total lack of deformation or fatigue mechanisms. In this work, composite braided stent-grafts incorporating Nitinol (NiTi) yarns and polyethylene terephthalate (PET) multifilament yarns were cycled in bending by the self-developed testing system to investigate their deformation behaviors. Deformation mechanisms at the yarn level were discussed, and NiTi yarn crossover structure was considered the primary factor affecting the deformation modes. Four yarn-crossover-based deformation modes (accordion buckling, diamond-shaped buckling, neck propagation and microbuckling) revealed the mechanisms of energy absorption of braided stent-grafts on the mesoscopic scale. Further, mechanical modes were applied to help regulate stent designs.

Mechanical and biocompatibility performance of bicomponent polyester/silk fibroin small-diameter arterial prostheses

Background In this study, we fabricated prototype bicomponent polyester/silk fibroin small-diameter arterial prostheses using a specially designed narrow ribbon shuttle loom. Methods The 2-layered flat fabrics were then heatset on a mandrel to form tubes with a round cross section. Results The woven samples had a wall thickness between 0.23 mm and 0.29 mm and an inner diameter between 3.53 mm and 3.95 mm, depending on the yarn type and the weave structure. Conclusions The bicomponent polyester/silk fibroin samples had superior bursting strength, circumferential strength and suture retention strength compared with a commercial small-diameter arterial prosthesis made from ePTFE. In addition, these prototype samples had greater suture retention strengths than a dog femoral artery, which indicates that they have adequate biostability for clinical use. While their amount of radial compliance was superior to that of the ePTFE commercial graft control, it did not match that of a natural artery. So there is still a need for future improvement in compliance. All of the woven prototypes had water permeability values between 26 and 180 ml/(cm2*min), which confirms that none of these arterial prostheses needs to be preclotted at the time of implantation. The biocompatibility of the woven prototypes was evaluated using porcine endothelial cells and an MTT assay. Their cytocompatibility was found to be superior to the ePTFE commercial control, and the level of cell attachment was observed to increase on these prototypes woven with a higher silk fibroin content.

A novel Silk/Polyester woven small diameter arterial prosthesis: Degumming and the influence on cytocompatibility

Sericin gum is like a two edged sword! It acts as the natural binder to maintain the structural integrity of silk filaments as well as to make the yarn more abrasion resistant. However, when used as an implantable device, for example, an arterial prosthesis, the presence of sericin increases the toxicity of the material. It is therefore necessary to remove all sericin before implantation. Although there are many methods to remove the sericin in the silk yarns or flat fabrics fabricated from silk yarns, there is little report about the method to degum silk in the tubular fabrics especially about small diameter (d≤6 mm) ones. In this study, small diameter arterial prostheses were woven using silk yarns still coated in sericin until the weaving process was completed. Then the samples were scoured to remove the sericin gum in sodium carbonate (0.05 wt. %) at 87 °C for 90 min with mechanical action. In order to make sure 90 min is enough to remove the sericin, the degumming time was extended to 210 min for some samples. Moreover, the degumming effect was examined on both inner and outer surfaces of the tubular samples to test the efficiency of the degumming method. The samples were first dyed with a picric acid-camine compound dye liquor which produces a red color with sericin and a yellow color with silk fibroin. After 90 min scouring, the samples showed a yellow color which indicates that the sericin had been removed completely by the degumming process. The effect of degumming was confirmed gravimetrically by measuring the weight loss, which was between 13.79 % and 23.99 % and remained steady after 90 min. Above all, the cytotoxicity was applied as one of the method to inspect the efficiency of degumming, which showed the result that, after degumming the samples were cytocompatible which is fit for implantation.

Experimental and analytical evaluation on the mass transfer performance of braided stent-grafts.

Endoleak and luminal loss related to blood permeation and microthrombus migration remain the main challenges in the aneurysm treatment, although stent-grafts have been widely applied. Stent-grafts provide a boundary to shield blood and microemboli transport, which are correlated with their mass transfer performance. Water permeability of vascular prostheses with woven and knitted structures has been analyzed and documented by many researchers, as well as oxygen and protein transfer. However, it is almost a total lack of blood and microemboli transfer along the braided stent-graft thickness direction. In this research, we provided a methodology for the vascular prostheses mass transfer evaluation. Braided stent-grafts in our former research were conducted on a self-developed testing system to investigate their blood permeability and microthrombus transfer behaviors. The pressure along wall thickness direction can be changed. Analytical models were also established based on pore parameters, making them applicative to different structures. Results revealed that the mass transfer behavior of stent-grafts was positively affected by porosity and pore diameter while negatively influenced by their thickness.