Selective Deposition of Hard Boron-Carbon Microstructures on Silicon.

Boron-rich B-C compounds with high hardness have been recently synthesized by the chemical vapor deposition (CVD) method. In this paper, we present our successful efforts in the selective growth of microstructures of boron-carbon compounds on silicon substrates. This was achieved by combining microfabrication techniques such as maskless lithography and sputter deposition with the CVD technique. Our characterization studies on these B-C microstructures showed that they maintain structural and mechanical properties similar to that of their thin-film counterparts. The methodology presented here paves the way for the development of microstructures for microelectromechanical system (MEMS) applications which require custom hardness and strength properties. These hard B-C microstructures are an excellent choice as support structures in MEMS-based devices.

Non-equilibrium organosilane plasma polymerization for modulating the surface of PTFE towards potential blood contact applications.

We report a novel and facile organosilane plasma polymerization method designed to improve the surface characteristics of poly(tetrafluoroethylene) (PTFE). We hypothesized that the polymerized silane coating would provide an adhesive surface for endothelial cell proliferation due to a large number of surface hydroxyl groups, while the large polymer networks on the surface of PTFE would hinder platelet attachment. The plasma polymerized PTFE surfaces were then systematically characterized via different analytical techniques such as FTIR, XPS, XRD, Contact angle, and SEM. The key finding of the characterization is the time-dependent deposition of an organosilane layer on the surface of PTFE. This layer was found to provide favorable surface properties to PTFE such as a very high surface oxygen content, high hydrophilicity and improved surface mechanics. Additionally, in vitro cellular studies were conducted to determine the bio-interface properties of the plasma-treated and untreated PTFE. The important results of these experiments were rapid endothelial cell growth and decreased platelet attachment on the plasma-treated PTFE compared to untreated PTFE. Thus, this new surface modification technique could potentially address the current challenges associated with PTFE for blood contact applications, specifically poor endothelial cell growth and risk of thrombosis.

Evaluation of Viscoelastic Properties, Blood Coagulation, and Cellular Responses of a Temperature-Sensitive Gel for Hemostatic Application.

Hemorrhagic blood loss from traumatic injury is the leading cause of death in severe accidents and combat injuries. Treating and stopping blood loss in a timely and effective manner is essential for the survival of the patient. Currently, QuikClot and dry fibrin sealant dressing are well-known approaches for hemostatic treatment. However, these dressings have limitations in slowing blood loss such as being brittle, low blood absorption, and a poor sealant of the injury site. Temperature-sensitive gels may have potential as a platform for delivery of coagulation factors to improve hemostasis and wound sealing in the treatment of traumatic injuries. Here, we developed a temperature-sensitive triblock copolymer (poly ethylene oxide (PEO)-poly propylene oxide (PPO)-poly ethylene oxide (PEO)) containing fibrinogen to promote blood coagulation through gel formation at body temperature. This temperature sensitive solution-to-gel (sol-gel) transition does not require cross-linking agents or UV photoinitiation. We determined that 22 wt % (weight percent) copolymers with and without fibrinogen was the maximum concentration for sol-gel transition at body temperature. Rheology results further confirmed this sol-gel transition of 22 wt % copolymers at body temperature. We showed that fibrinogen itself promoted blood coagulation. Additionally, 22 wt % copolymer with fibrinogen successfully demonstrated stable blood coagulation within the gel compared to 22 wt % copolymer without fibrinogen. Twenty-two weight percent copolymers with and without fibrinogen also exhibited excellent biocompatibility based on cell viability, proliferation, and morphology analysis. In addition, treatment of 22 wt % copolymers did not stimulate pro-inflammatory TNF-α production from differentiated human monocytes. Our results suggest that 22 wt % of a temperature-sensitive copolymer gel containing fibrinogen has great potential as a hemostatic agent stimulating coagulation and providing immediate wound coverage for protection through a sol-gel transition at body temperature.

Non-equilibrium hybrid organic plasma processing for superhydrophobic PTFE surface towards potential bio-interface applications.

Superhydrophobic surfaces have gained increased attention due to the high water-repellency and self-cleaning capabilities of these surfaces. In the present study, we explored a novel hybrid method of fabricating superhydrophobic poly(tetrafluoroethylene) (PTFE) surfaces by combining the physical etching capability of oxygen plasma with the plasma-induced polymerization of a organic monomer methyl methacrylate (MMA). This novel hybrid combination of oxygen-MMA plasma has resulted in the generation of superhydrophobic PTFE surfaces with contact angle of 154°. We hypothesized that the generation of superhydrophobicity may be attributed to the generation of fluorinated poly(methyl methacrylate) (PMMA) moieties formed by the combined effects of physical etching causing de-fluorination of PTFE and the subsequent plasma polymerization of MMA. The plasma treated PTFE surfaces were then systematically characterized via XPS, FTIR, XRD, DSC and SEM analyses. The results have clearly shown a synergistic effect of the oxygen/MMA combination in comparison with either the oxygen plasma alone or MMA vapors alone. Furthermore, the reported new hybrid combination of Oxygen-MMA plasma has been demonstrated to achieve superhydrophobicity at lower power and short time scales than previously reported methods in the literature. Hence the reported novel hybrid strategy of fabricating superhydrophobic PTFE surfaces could have futuristic potential towards biointerface applications.

Hemopressin-Based pH-Sensitive Hydrogel: A Potential Bioactive Platform for Drug Delivery.

Peptides with proper sequences are capable of self-assembling into well-defined nanostructures, which can subsequently grow and entangle into three-dimensional nanomatrices. In this study, hemopressin, a cannabinoid receptor-modulating peptide derived from the α-chain of hemoglobin known to self-assemble into nanofibrils, was examined for its potential applicability as a gelator. The results indicated that hemopressin's gel formation was dependent on pH and salt concentration. Although hemopressin's macroscopic states showed differences, its microscopic structure remained largely unchanged in which it consisted mainly of the antiparallel ß-sheet conformation as confirmed by FTIR (C=O stretch peaks at 1630 and 1695 cm-1) and CD (ß-sheet peak at 195 nm). The major difference between the gel and sol states was displayed in the fibril length in which the gelation at pH 7.4 resulted in 4 µm fibrils, whereas the solution at pH 5.0 showed 800 nm fibrils. The pH-dependent sol-gel phase transition property was then utilized for the investigation of the pH-responsive release of FITC-dextran (4-40 kDa) from hemopressin fibrillary gel. Finally, the biocompatibility of the peptide was demonstrated by proliferation assay of cultured bone marrow mesenchymal stem cells. Altogether, the results suggested that hemopressin is a potentially promising candidate as a therapeutically active platform for drug delivery.