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.

Asymmetric composite membranes from chitosan and tricalcium phosphate useful for guided bone regeneration.

To fulfill the properties of barrier membranes useful for guided bone tissue regeneration in the treatment of periodontitis, in this study a simple process combining lyophilization with preheating treatment to produce asymmetric barrier membranes from biodegradable chitosan (CS) and functional ß-tricalcium phosphate (TCP) was proposed. By preheating TCP/CS (3:10, w/w) in an acetic acid solution at 40°C, a skin layer that could greatly increase the mechanical properties of the membrane was formed. The asymmetric membrane with a skin layer had a modulus value almost 4-times that of the symmetric porous membrane produced only by lyophilization. This is beneficial for maintaining a secluded space for the bone regeneration, as well as to prevent the invasion of other tissues. The subsequent lyophilization at -20°C then gave the rest of material an interconnected pore structure with high porosity (83.9-90.6%) and suitable pore size (50-150 µm) which could promote the permeability and adhesiveness to bone cells, as demonstrated by the in vitro cell-culture of hFOB1.19 osteoblasts. Furthermore, the TCP particles added to CS could further increase the rigidity and the cell attachment and proliferation of hFOB1.19. The TCP/CS asymmetric composite membrane thus has the potential to be used as the barrier membrane for guided bone regeneration.

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.

Role of phase diagram of membrane formation system in controlling the crystallinity and degradation rate of PLLA membranes.

In this work, the theoretical phase diagram of membrane formation system of ethanol, methylene chloride, and poly-L-lactide (PLLA) was studied. On the basis of the phase diagram, particulate and porous membranes, dominated by crystallization and liquid-liquid demixing, respectively, were prepared. Furthermore, degradation of PLLA membranes with particulate, porous, and dense morphologies was performed in phosphate buffered solution (PBS) at 37 degrees C for 168 days and was investigated by mass loss, scanning electron microscopy (SEM), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Besides the membrane morphology, a close relationship between the phase behavior of the membrane formation system and the membrane crystallinity was found, which in turn influenced the degradation rate of these membranes significantly. In the case of dense membranes, it showed the lowest initial crystallinity and the greatest rate of mass loss and molecular weight decrease compared with particulate and porous membranes. In contrast, the particulate membranes had the highest crystallinity and the slowest degradation rate in this study. Therefore, the phase diagram of membrane formation system could not only anticipate membrane morphology, but could also control the membrane crystallinity and degradation rate simultaneously.

Preparation and antibacterial test of chitosan/PAA/PEGDA bi-layer composite membranes.

Chitosan/poly(acrylic acid)/poly(ethylene glycol) diacrylate (PEGDA) composite membranes with a bi-layer configuration were prepared and their potential application as an antibacterial material was examined. A two-step process was adopted. A dope consisting of PEGDA, acrylic acid (AA) and a photoinitiator was cast and then UV-cured on a glass substrate to form a mechanically strong, dense membrane. Subsequently, the membrane was coated with a layer of solution composed of chitosan, AA and water. As the majority of AA diffused downwards into the supporting layer underneath, chitosan coagulated with residual AA to form a nano-layer on the top surface by means of UV irradiation. Low-voltage field-emission scanning electron microscopy was used to observe the membrane morphology and to measure the thickness of the top layer. Contact angle measurements indicated a top layer mixed with chitosan and poly(acrylic acid), which was confirmed by chemical composition analysis of X-ray photon spectroscopy. The antibacterial activities of the formed membranes were tested both with respect to a Gram-negative (Escherichia coli) and a Gram-positive (Staphylococcus aureus) bacteria.