Covalent bonding of GYIGSR to EVAL membrane surface to improve migration and adhesion of cultured neural stem/precursor cells.

In the present study, we modified poly (ethylene-co-vinyl alcohol) (EVAL) membranes with the covalent bonding of the laminin-derived peptides, GYIGSR by using carbodiimidazole (CDI) to activate the hydroxyl groups on the membrane surface. The resulting GYIGSR-immobilized EVAL (EVAL-GYIGSR) membrane was analyzed in terms of the effect of immobilized peptide sequence on the behaviors of neural stem/precursor cells (NSPCs), isolated from embryonic rat cerebral cortex, in the serum-free medium. Compared to the unmodified EVAL, GYIGSR immobilized on the EVAL membrane was shown to significantly increase NSPCs migrating out of neurospheres (p<0.05). In addition, NSPCs on the EVAL-GYIGSR membrane were able to differentiate into neural lineage cells and differentiated neurons expressed functional synaptic activity. Basically, there was no significant difference between GYIGSR-immobilized and laminin-coated substrates for their ability to enhance migration and differentiation of NSPCs, suggesting that the immobilization of GYIGSR on the EVAL membrane was successful and the laminin-derived peptide YIGSR and laminin had similar effect on NSPC behaviors. However, it is non-permanent modification for coating laminin on the substrates to support cell survival after a long-term culture. In this study, differentiated neurons could still adhere to the EVAL-GYIGSR surface with functional synaptic activity after incubation for 20 days. Therefore, the bioactive EVAL-GYIGSR provided an alternative approach to improve migration and survival of NSPCs for neural tissue engineering applications.

Preparation of water-resistant antifog hard coatings on plastic substrate.

A novel water resistant antifog (AF) coating for plastic substrates was developed, which has a special hydrophilic/hydrophobic bilayer structure. The bottom layer, acting both as a mechanical support and a hydrophobic barrier against water penetration, is an organic-inorganic composite comprising colloidal silica embedded in a cross-linked network of dipentaethritol hexaacrylate (DPHA). Atop this layer, an AF coating is applied, which incorporates a superhydrophilic species synthesized from Tween-20 (surfactant), isophorone diisocyanate (coupling agent), and 2-hydroxyethyl methacrylate (monomer). Various methods, e.g., FTIR, SEM, AFM, contact angle, and steam test, were employed to characterize the prepared AF coatings. The results indicated that the size and the continuity of the hydrophilic domains on the top surface increased with increasing added amount of T20, however, at the expense of hardness, adhesiveness, and water resistivity. The optimal T20 content was found to be 10 wt %, at which capacity the resultant AF coating was transparent and wearable (5H, hardness) and could be soaked in water for 7 days at 25 °C without downgrading of its AF capability.

Efficient transfer of human adipose-derived stem cells by chitosan/gelatin blend films.

Adipose-derived stem cells (ASCs) are a potential source of abundant mesenchymal stem cells and represent a promising cell-based therapy for tissue damage or degeneration conditions. Previous investigations have demonstrated enhanced therapeutic effects of ASCs in a three-dimensional spheroid culture formulation. In this study, we hypothesize that a composite membrane made of chitosan/gelatin (C/G) is beneficial to facilitate transfer of human ASCs in spheroids. Increasing chitosan content within the blends enhanced the mechanical properties of the sample, including tensile strength and elongation-at-break ratio. Although ASC spheroids developed shortly after seeding on pure chitosan films, increasing gelatin proportion in the C/G blends promoted cell adhesion onto the membranes. We also found that ASCs did not proliferate on chitosan films, but C/G blends of different ratios supported ASC proliferation in the first 4 days of culture. However, ASCs on all C/G blends started to detach from the films to form spheroids after day 4, while ASCs on pure gelatin films remained attached and continued to grow. Gradual gelatin release from the C/G blend films, leading to enriched chitosan content in the blends, probably encouraged ASC detachment and spheroid formation. We placed porous collagen matrix on ASC-seeded C/G blends to simulate the application of ASC-seeded C/G films onto injured tissue and found that a C/G film composed of 75% chitosan could facilitate significantly more cell transfer into the overlying collagen sponge. Therefore, a blend film containing 75% chitosan and 25% gelatin showed promising results to serve as a biomaterial for human ASC-based cell therapy.

Immobilization of DNA on microporous PVDF membranes by plasma polymerization.

Microporous poly(vinylidene fluoride) (PVDF) membranes with different porous surface morphologies were prepared by immersion-precipitation from coagulation baths of different strengths. On these membranes single-strand deoxyribonucleic acid (ss-DNA) was covalently immobilized by a dual-step procedure. First, poly(glycidyl methacrylate) (PGMA) was grafted on PVDF membranes by plasma-induced free radical polymerization. Then, ss-DNA was bonded to PGMA through ring-opening reactions of epoxies with amine to form amino alcohols. The highest attainable graft yield of PGMA on PVDF membrane was 0.3 mg/cm(2), which was the case when a highly porous PVDF membrane was employed as the substrate. For immobilization of ss-DNA, the yield was found to depend significantly on the reaction temperature and pH. The maximal value was 48.5 mug/cm(2). Furthermore, adsorption tests of anti-DNA antibody were carried out on membranes with and without immobilized ss-DNA using serum obtained from systemic lupus erythematosus patients. The results indicated that the immobilized DNA could effectively adsorb the antibody in the serum.

Immobilization of L-lysine on microporous PVDF membranes for neuron culture.

Microporous poly(vinylidene fluoride) (PVDF) membranes with dense or porous surface were prepared by immersion precipitation of PVDF/TEP solutions in coagulation baths containing different amounts of water. Onto the membrane surface, poly(glycidyl methacrylate) (PGMA) was grafted by plasma-induced free radical polymerization. Then, L-lysine was covalently bonded to the as-grafted PGMA through ring-opening reactions between epoxide and amine to form amino alcohol. The highest attainable graft density of PGMA on a PVDF membrane was 0.293 mg/cm2. This was obtained when the reaction was carried out on a porous surface under an optimized reaction condition. For immobilization of L-lysine, the yield was found to depend on the reaction temperature and L-lysine concentration. The maximal yield was 0.226 mg/cm2, a value considerably higher than reported in the literature using other immobilization methods. Furthermore, neurons were cultured on L-lysine-immobilized PVDF membranes. The results indicated that these membrane surfaces were suited to the growth of neurons, with a MTT value higher than that of the standard culture dish.