Mengyan Li

Micropatterning of three-dimensional electrospun polyurethane vascular grafts.

The uniform alignment of endothelial cells inside small-diameter synthetic grafts can be directed by surface topographies such as microgrooves and microfibers to recapitulate the flow-induced elongation and alignment of natural endothelium. These surface micropatterns may also promote directional migration and potentially improve anastomotic ingrowth of endothelial cells inside the synthetic grafts. In this paper, we developed electrospinning and spin casting techniques to pattern the luminal surface of small-diameter polyurethane (PU) grafts with microfibers and microgrooves, respectively, and evaluated endothelial cell orientation on these surface micropatterns. Tracks of circumferentially oriented microfibers were generated by electrospinning PU onto a mandrel rotated at high velocity, whereas longitudinal tracks of microgrooves were generated by spin casting PU over a rotating poly(dimethylsiloxane) mold. We found that both PU grafts possessed longitudinal Youngs moduli in the range of 0.43 ± 0.04 to 2.00 ± 0.40 MPa, comparable with values obtained from native artery. Endothelial cells seeded onto the grafts formed confluent monolayers with individual cells exhibiting elongated morphology parallel to the micropatterns. The cells were phenotypically similar to natural endothelium as assessed by the expression of the endothelial cell-specific marker, vascular endothelial cell cadherin. In addition, the cells were also responsive to stimulation with the pro-inflammatory cytokine tumor necrosis factor-α as assessed by the inducible expression of intercellular adhesion molecule-1. These results demonstrate that our micropatterned PU grafts possessed longitudinal Youngs moduli in the same range as native vascular tissue and were capable of promoting the formation of aligned and cytokine-responsive endothelial monolayers.

Alimentary ‘green’ proteins as electrospun scaffolds for skin regenerative engineering

As a potential alternative to currently available skin substitutes and wound dressings, we explored the use of bioactive scaffolds made of plant‐derived proteins. We hypothesized that ‘green’ materials, derived from renewable and biodegradable natural sources, may confer bioactive properties to enhance wound healing and tissue regeneration. We optimized and characterized fibrous scaffolds electrospun from soy protein isolate (SPI) with addition of 0.05% poly(ethylene oxide) (PEO) dissolved in 1,1,1,3,3,3‐hexafluoro‐2‐propanol, and from corn zein dissolved in glacial acetic acid. Fibrous mats electrospun from either of these plant proteins remained intact without further cross‐linking, possessing a skin‐like pliability. Soy‐derived scaffolds supported the adhesion and proliferation of cultured primary human dermal fibroblasts. Using targeted PCR arrays and qPCR validation, we found similar gene expression profiles of fibroblasts cultured for 2 and 24 h on SPI substrates and on collagen type I at both time points. On both substrates there was a pronounced time‐dependent upregulation of several genes related to ECM deposition remodelling, including MMP‐10, MMP‐1, collagen VII, integrin‐α2 and laminin‐β3, indicating that both plant‐ and animal‐derived materials induce similar responses from the cells after initial adhesion, degrading substrate proteins and depositing extracellular matrix in a ‘normal’ remodelling process. These results suggest that ‘green’ proteins, such as soy and zein, are promising as a platform for organotypic skin equivalent culture, as well as implantable scaffolds for skin regeneration. Future studies will determine specific mechanisms of their interaction with skin cells and their efficacy in wound‐healing applications. Copyright

ELECTROACTIVE AND NANOSTRUCTURED POLYMERS AS SCAFFOLD MATERIALS FOR NEURONAL AND CARDIAC TISSUE ENGINEERING

Conducting polymer, polyaniline (PANI), has been studied as a novel electroactive and electrically conductive material for tissue engineering applications. The biocompatibility of the conductive polymer can be improved by (i) covalently grafting various adhesive peptides onto the surface of prefabricated conducting polymer films or into the polymer structures during the synthesis, (ii) co-electrospinning or blending with natural proteins to form conducting nanofibers or films, and (iii) preparing conducting polymers using biopolymers, such as collagen, as templates. In this paper, we mainly describe and review the approaches of covalently attaching oligopeptides to PANI and electrospinning PANI-gelatin blend nanofibers. The employment of such modified conducting polymers as substrates for enhanced cell attachment, proliferation and differentiation has been investigated with neuronal PC-12 cells and H9c2 cardiac myoblasts. For the electrospun PANI-gelatin fibers, depending on the concentrations of PANI, H9c2 cells initially displayed different morphologies on the fibrous substrates, but after one week all cultures reached confluence of similar densities and morphologies. Furthermore, we observed, that conductive PANI, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity was decreasing over time. Preliminary data show that the application of micro-current stimulates the differentiation of PC-12 cells. All the results demonstrate the potential for using PANI as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.

Electrospun Blends of Natural and Synthetic Polymers as Scaffolds for Tissue Engineering

Engineering functional three-dimensional (3-D) tissue constructs for the replacement and/or repair of damaged native tissues using cells and scaffolds is one of the ultimate goals of tissue engineering. In this study, non-woven fibrous scaffolds were electrospun from the synthetic biodegradable polymer poly(lactic-co-glycolic acid) (PLGA) and natural proteins, gelatin (denatured collagen) and elastin. In the absence of cross-linking agent, the average PGE fiber diameter increased from 347 plusmn 103 nm to 999 plusmn 123 nm upon wetting as measured by scanning electron microscopy. Rat bone marrow stromal cells (rBMSC) were used paradigmatically to study the 3-D cell culture properties of PGE scaffolds. Consistent with the observed properties of the individual fibers, PGE scaffolds initially swelled in aqueous culture medium, however rBMSC seeded PGE scaffolds contracted to < 50% of original size. Time course histological analysis demonstrated uniform seeding of rBMSC into PGE scaffolds and complete cell penetration into the fibrous architecture over 4 weeks of in vitro culture

Designing Intelligent Polymeric Scaffolds for Tissue Engineering: Blending and Co-Electrospinning Synthetic and Natural Polymers

There is a growing interest in blending natural and synthetic polymers as biomaterials for generating complex fibrous scaffolds for tissue engineering purposes. In this talk we will report on co-electrospinning binary and tertiary blends of gelatin (denatured collagen) with either a conductive polymer, polyaniline (PANi), or with a mixture of polylactic acid / polyglycolic acid, and elastin (PGE) Finally, we will demonstrate the usefulness of elastin-based fibrous scaffolds for pulmonary tissue engineering

Nonthermal plasma bio-active liquid micro and nano-xerography

Method of biochemical patterning which allows for micro- and nano-scale resolution on nonplanar substrates is presented. Utilizing this method, bio-molecules (including DNA, proteins, and enzymes) can be delivered to charged locations on surfaces by charged water buffer droplets. Charging of water droplets is accomplished using dielectric barrier discharge (DBD) plasma. DBD was effectively stabilized in the presence of high concentration of micron-size water droplets. The concepts of the proposed method, as well as first experimental results supporting the idea are discussed in this paper.