Key Engineering Materials Vols. 361-363

Abstract: Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of these bioceramics with the flexibility of polymers. In previous work hybrid foams with 80% bioactive glass and 20% polyvinyl alcohol (PVA) were prepared by the sol-gel process for application as scaffold for bone tissue engineering. In this work it was evaluated the effect of increasing the PVA content of the hybrids on structural characteristics and mechanical properties of hybrid foams produced by this method. The hybrids were prepared with inorganic phase composition of 70%SiO2-30%CaO and PVA fractions of 20 to 60% by the sol-gel method. The structural and mechanical characterization of the obtained foams was done by FTIR, SEM, Helium Picnometry, and compression tests. To reduce the acidic character of the hybrids due to the catalysts added, different neutralization solutions were tested. The immersion of hybrids in a calcium acetate solution was the most adequate neutralization method, avoiding calcium loss while maintaining pH nearly 7,0 and low PVA loss. The foams presented porosity of 60-85% and pore diameters of 100-500μm with interconnected structure. The pore structure varied with the polymer content in the hybrid. The compression tests showed that an increase of PVA fraction in the hybrids improved their mechanical properties.

Abstract: Natural bone is a kind of organic-inorganic hybrid composed of collagen and apatite crystals with a structure that provides specific mechanical properties such as high fracture toughness and flexibility. Materials exhibiting both high flexibility and bioactivity similar to natural bone are required for novel bone-repairing materials in medical fields. We expect that we can design such materials by mimicking the bone structure. Biomimetic process has been paid much attention where bone-like apatite is deposited on organic polymers in simulated body fluid (SBF). In this study, we investigated influence of cross-linking agents on apatite-forming ability of pectin gels. Pectin is a polysaccharide abundant in carboxyl group. Pectin gels were prepared by cross-linking of pectin aqueous solutions with calcium ions or divinylsulfone (DVS). Apatite-forming ability of the gels was examined in SBF. The citrus-derived pectin showed tendency to form the largest amount of the apatite independent on a kind of cross-linking agents in SBF.

Abstract: The characteristics and properties of bacterial cellulose and dialdehyde celluloses from bacterial cellulose were studied by XRD, TG-IR and adsorption capacity testing. The crystal cell parameters of BC were calculated and approximated to that of monocline crystal cell model. The XRD profiles showed that the crystallinity degree of BC was 66%, and that of the DACs (12% aldehyde) was 56%. The optimal adsorption capacities of pure water on dried BC and DAC were 12 g/g and 3.1 g/g respectively, and that of iron ion on dried BC and DAC were 11 mg/g and 6.9 mg/g respectively. And the optimal adsorption capacity of hexanediamine on DAC was 700 mg/g, and that of n-phenylene diamine on DAC was 490 mg/g. The IR result showed that the adsorption of hexanediamine on DAC was physical adsorption, not chemical reaction under the experimental conditions.

Abstract: So-called bioactive ceramics are used for bone-repairing owing to attractive features such as direct bone-bonding in living body. However, there is limitation on clinical applications due to their inappropriate mechanical properties performances such as higher brittleness and lower fracture toughness than natural bone. To overcome this problem, hybrid materials have been developed by modification of calcium silicate, that is basic component of bioactive ceramics, with organic polymer. It is known that bioactive ceramics bond to bone through bone-like apatite layer which is formed on their surfaces by chemical reaction with body fluid. We attempted preparation of bioactive organic-inorganic hybrids from Glucomannan that is a kind of complex polysaccharide, and calcium silicate. Hybrids were prepared from glucomannan and tetraethoxysilane (TEOS). They were treated with 1M (=mol·m-3) CaCl2 aqueous solution for 24 hours. Then ability of apatite formation on the hybrids was examined in vitro using simulated body fluid (SBF, Kokubo solution). Surface structure of the specimens was examined by thin-film X-ray diffraction (TF-XRD), scanning electron microscopic (SEM) observation. The hybrids with TEOS:Glucomannan= 1:1 to 4:1 in mass ratio formed the apatite in SBF within 3 or 7 d, when they were previously treated with CaCl2 solution.

Abstract: We have performed and evaluated a composite combining PL DLLA and PCa able to have a better control of the hydrolysis and maintain of the mechanical property on time, until wound healing was achieved. Bioabsorbable osteoconductive composite is devoted to the development of resorbable osteosynthesis for spine and osteoarticular surgeries. Such resorbable osteosynthesis will be associated to new bone substitute having high osteogenic property but without initial mechanical property. The purpose of this study was to evaluate the resorption kinetic of a composite using PL DLLA (Poly [L-Lactide-co-D,L-Lactide] acide) charged with PCa granules and the interaction with injectable bioceramic without self hardening. MBCP gel® is a composite associating a mineral phase of an intimate nanoscale melting of hydroxyapatite and beta tri calcium phosphate and an aqueous phase containing a synthetic polymer derived from cellulose HPMC (hydroxyl propyl methyl cellulose).

Abstract: A new biodegradable adhesive(LYDEX) which is based on Schiff base formation had developed. LYDEX is easy to control the setting time and degradation speed and it has no risk of infection. In the previous study, LYDEX showed high bonding strength and low cytotoxicity in vitro[1]. In the present study, good bone repair was seen in rat bone defect models, especially in rapidly degrading type. On the other hand, slowly degrading type kept its shape longer without excessive inflammation. In rabbit critical defect model with hydroxyapatite granules (HAs), more newly formed bone was seen in rapidly degrading group and hydroxyapatite group, in 3weeks. In 6weeks, more new bone was seen in slowly degrading type group, whereas, almost no new bone was seen in deep area of the fibrin group, in 12weeks. Direct bonding between HAs and bone was seen in HA group and LYDEX groups. These findings suggest that LYDEX with hydroxyapatite granules can be a promising bone substitute.

Abstract: In order to study method for preparing bioactive titanium metal, calcium ions were attempted to be incorporated into the surface of the titanium metal by ion exchange method. Titanium metal was soaked in 5M NaOH solution and 100mMCaCl2 solution and subjected to heat treatment. About 5 atom% of Na was incorporated into the surface of the titanium metal by the NaOH treatment This Na was completely replaced with calcium ion by the CaCl2 treatment and maintained even after the heat treatment. Critical detaching strength of the surface layer to the substrate of NaOH-treated titanium metal was a little increased by the CaCl2 treatment and remarkably increased by the heat treatment. Apatite-forming ability of the NaOH-treated titanium metal in SBF was increased by the CaCl2 treatment, but decreased by the subsequent heat treatment.

Abstract: Topography of the surface plays an important role in cellular responses. A novel method, called template-assisted electrohydrodynamic atomization (TAEA) spraying, was developed to create surface topography of hydroxyapatite (HA) on metallic surfaces. In this work, by varying the core process parameters (e.g. flow rate, applied voltage and distance between substrate and needle), the optimization and development of the TAEA process with nanoHA suspension is investigated with the aim of preparing a nanostructured HA coating with patterning of high resolution for biomedical applications.

Abstract: Protein thin films were prepared by electrostatic spray deposition (ESD) from aqueous solutions of the enzyme alkaline phosphatase (ALP). ALP thin films with preserved functional properties were successfully deposited using the ESD technique. The biological activity of the deposited ALP films was investigated in vitro by immersing the ESD-coated titanium substrates in both simulated body fluid (SBF) and cell-culture medium. Mineral deposition occurred on substrates immersed in both SBF and medium. Various analytical techniques (SEM,XRD,FTIR,EDS) showed that the calcium phosphate layers deposited in SBF and medium differ in both crystallinity and morphology. The results demonstrated that ESD is a successful method for the deposition of biomedical coatings with enhanced functionality.

Abstract: Two different glasses, one biocompatible but with a low bioactivity index (G1) and the other with an higher bioactivity index (G2), the ceramic version of the second glass and a titanium alloy (Ti6Al4V) have been functionalizated by anchoring alkaline phosphatase (ALP) on their surfaces. The enzyme has been chosen because it is involved in mineralization processes of hard tissues and is a model for more complex ones. ALP has been grafted on glasses and glass-ceramics surfaces both with and without samples silanization and on metallic surfaces with and without tresyl chloride activation. Samples have been analyzed at each step of the functionalization process in order to verify it.