Advanced Materials Research Vols. 47-50

Abstract: We report our observations concerning the time evolution of surface morphology occurring during the in vitro immersion of bioactive glass surfaces in contact with phosphate buffer solution. We compare regions under intentionally produced residual stresses via micro-indentation to those where no indentation was performed. The sign of the residual stress is shown to be important for predicting dissolution behaviour; compression retards dissolution, whereas tension enhances dissolution. We analyze our results with a simple model for the work of bond dissociation. We report that a highly constrained residual compressive stress state, such as in an indent, leads to a work deficit in comparison to tension, which accounts for the slower dissolution rate of compressed bioactive glass. Such a mechanochemical effect suggests that the presence of residual stresses from the manufacture of biomedical implants and devices could lead to accelerated or delayed dissolution and that careful control of residual stresses should be sought for predictable performance in dissolvable materials.

Abstract: The effect of pH value at different initial Ca/P molar ratio on the composition and crystal phase of the calcium phosphates synthesized through chemical precipitation method was studied in detail. After calcining at 900°C, the products were characterized by XRD and chemical analysis. The results showed that the composition and crystal phase of the resultant powders can be controlled by pH value at different initial Ca/P molar ratio. When Ca/P molar ratio was 1.667, pure HA was obtained at pH values of both 12.0 and 11.0. When initial Ca/P molar ratio was 1.500, pure β-TCP was obtained at pH value from 11.0 to 9.0. CPP was obtained at pH value from 6.0 to 4.0 when initial Ca/P molar ratio was 1.000.

Abstract: N-isopropylacrylamide (NIPAM)-ethylene oxide (EO) copolymer was grafted on filter paper surface to obtain paper-based adsorptive membrane. Protein adsorption on and release from the membrane was evaluated under various conditions using humanized monoclonal antibody as model protein. The results obtained indicated that amphiphilic copolymer modified filter paper could be used as a novel chromatographic membrane for protein separation/purification. Comb-block copolymers of NIPAM with N-vinylpyrrolidone (VP) were prepared through RAFT polymerization and macromonomer techniques. Surface modification of substrates, such as plastics and glass, was carried out by treatment of the substrates in aqueous solution of the amphiphilic comb-block copolymer (adsorptive coating, pre-adsorption). It was found that the adsorbed copolymer layer was stable in aqueous environment even when shear stress was applied. Protein adhesion on the material surfaces before and after the modification was investigated using lysozyme as model protein. The results obtained showed that the adsorptive coating layer on the material surfaces significantly reduced non-specific protein adhesion.

Abstract: The near-infrared (NIR) sensitive Au-Au2S nanoparticles (NPs) have shown many advantages as potential drug delivery systems. To further investigate biological safety of Au-Au2S NPs, cytotoxicity was estimated by calcein AM/EthD-1 fluorescence staining and the lactate dehydrogenase (LDH) release. The effects of NPs on apoptosis of CHL cells were determined by flow cytometry with Annexin V-FITC/PI double staining. It is evident that the Au-Au2S NPs are non-cytotoxic below IC50 dosage.

Abstract: Novel hybrid biomaterial of gelatin-siloxane nanoparticles (GS NPs), with positive surface potential and lower cytotoxicity, was synthesized through a 2-step sol-gel process. The pDNA-GS NPs complex was formulated with high encapsulation efficiency, and exhibited and efficient transfection in vitro. We thus envision that the GS NPs material could serve as non-viral gene vectors for gene therapy.

Abstract: Photonic crystals have wide applications not only in optoelectronic fields but also in bioassays. In this review, we summarized our work on colloidal photonic crystals as novel biomolecular supports in multiplex bioassays. Except for enhancing the fluorescence signal and encoding the biomolecular carriers in fluorphore labeled bioassays, photonic crystal can also encode suspended arrays. From the point view of practicality, the synthesis and self-assembly of monodispersed colloidal spheres for colloidal crystals is involved.

Abstract: Biodegradable nanofiber has become a popular candidate as tissue engineering scaffolds due to its biomimic structure as natural extracellular matrix (ECM). Certain tissue regeneration may require prolonged in vitro culture time for cellular reorganization and tissue remodeling. Therefore, long term understanding of cellular effects on scaffold degradation is needed. Although there are some degradation studies on nanofiber, degradation study of nanofibers with cell culture is rare. In our study, polyglycolide (PGA), poly(DL-lactide-co-glycolide) (PLGA), poly(L-lactide-co-ε- caprolactone) [P(LLA-CL)] were electrospun into nanofiber scaffolds. The scaffolds were cultured with porcine smooth muscle cells (PSMC) for up to 3 months to evaluate their degradation behavior and cellular response. The results showed that their degradation rates were in the order of PGA>>PLGA>P(LLA-CL). PGA nanofiber degraded in 3 weeks and only supported cell growth in the first few days. Cell culture accelerated the surface erosion of PLGA and P(LLA-CL) nanofiber while the bulk degradation remained unaffected. Furthermore, the cell culture did not significantly reduce the mechanical strength of PLGA and P(LLA-CL) during degradation.

Abstract: This paper reported a newly designed retrievable urethral stent used in treatment of urethral strictures. The spiral urethral stent is made of Poly (l-lactide) (PLLA), adding barium sulphate (BaSO4) to certain content, which can be displayed precisely under X-ray after implanted in body. The stent was clinically tested in 32 patients with recurrent urethral strictures and was left in the urethra for 5 to 12 months. The response to the effect of the stent was assessed using symptom scores, peak flow rate (Qmax), residual urine volume (RUV), stent degradation, infection and outcome. During the treatment, there were not any inflammations found. The mechanical properties of the stent are almost the same as those of the PLLA stent without BaSO4. Improvements in patient symptom score, mean Qmax and RUV were significant at the 18 month follow-up. The infection was not observed. The stent was taken out easily through urethral forceps. In no patient was the stent obstructed by incrustation for up to 1.5 years.

Abstract: Materials used to make artificial vessels and hearts can cause thrombosis, thus hindering the development of these therapeutic aids. Endothelial cells (ECs) play a key role in thrombosis, so in this study, we used human umbilical vein endothelial cells (HUVEC) and tested the hemocompatibility of different biomaterials. We then measured the signal proteins MAPK (mitogen-activated protein kinase) and Nuclear Factor- kB (NF-κB) to investigate the correlation between their expression and the degree of hemocompatibility. The results showed that ECs in the polyurethane (PU-60) group had significantly more NF-κB than the negative control (p<0.5). To identify whether the increased expression of NF-κB was induced by MAPK activation, we investigated changes in phosphorylated MAPK. We found both MAPK and NF-κB are ideal indicators for evaluating the hemocompatibility of biomaterial.

Abstract: The aim of this study was to evaluate the suitability of CaF2 doping tricalcium silicate (Ca3SiO5, C3S) as dental restorative materials. The solid state reaction method was used to prepare CaF2 doping C3S (F-C3S) using CaCO3, SiO2 and CaF2 as the starting materials. The in vitro bioactivity, the rate of heat evolution and the compressive strength were investigated. The in vitro bioactivity was examined by soaking the pastes in simulated body fluid (SBF). The FTIR and SEM results indicated the hydroxycarbonate apatite (HCA) layers of F-C3S pastes and pure C3S pastes occurred after soaking for 1 day and 3 days, respectively. The difference in bioactivity was attributed to the formation of F-substituted apatite, which has a Ksp lower than HCA. As compared with the pure C3S, the rate of heat evolution during the hydration of F-C3S was slower. This was avail to the dimensional stability of dental restorative materials. The pastes of F-C3S had a lower early compressive strength in the early stage, but a higher compressive strength in the later stage. Our results indicated that F-C3S would be bonded better to the teeth because of the earlier formation of HCA and the higher later compressive strength. F-C3S may be a progressive candidate for dental restorative materials.