Key Engineering Materials Vols. 529-530

Abstract: Chemical modification of titanium substrate provides ability of hydroxyapatite (HAp) formation that is important property for bone-bonding capability after implantation in bony defects. Potential of the HAp-formation is occasionally reduced. In the present study, we investigated potential of the HAp-formation on titanium oxide (titania) with doped silicon or aluminum in simulated body fluid (SBF). Sol-gel processing was applied to prepare titania with doped silicon (TSx) or aluminum (TAx), in its nominal composition ranging from 0 to 10 mol%. Specific surface area of the prepared samples was gradually increased with increasing the amounts of silicon or aluminum. Zeta potential of TAx was definite changed from negative charge to positive charge with increasing aluminum amounts, but TSx slightly changed to be positive with increasing silicon amounts. The pure titania sample free from doping of silicon or aluminum showed formation of calcium phosphate precipitates, that is HAp-formation, after soaking in SBF for 14 d. In contrast, all the titania samples with doped silicon or aluminum hardly showed evidence of precipitates of calcium phosphates, although absorption of calcium and phosphate ions were detected. Especially, TAx showed remarkable adsorption of phosphate ions. Aluminum-doping in titania enhances the adsorption of phosphate ion on the surface, but reduce nucleation rate of calcium phosphates in body environment.

Abstract: The Time – Dependent Adsorptive Behavior of Biomolecules on/in Mesoporous Silica Materials (MPS) Have Been Studied by Using Transmission Electron Microscopy (TEM). Highly Ordered Hexagonal Mesoporous Silica Materials (SBA-15) Synthesized Were Immersed in Phosphate Buffer Saline (PBS) Solution Containing Cytochrome C for 2, 48, and 120 Hours at 4 °C. after that, MPS Materials Were Rinsed with PBS Solution, and then Immersed in PBS Solution without Cytochrome C. the Amount of Protein Adsorbed on/in MPS Materials Soaked for 2, 48, and 120 Hours Was 75 Mg/g, 135 Mg/g and 178 Mg/g, Respectively. the Time Profiles for Adsorption of Proteins Can Be Well Described by Intraparticle Diffusion Model. the Holes of MPS Materials Were Observed to Be Overlapped with Stained Proteins for First 2 Hours Immersion. the Stained Proteins Were Observed between Primary Particles and Partly inside the Mesoporous Channels in the MPS Material Immersed for 48 Hours. for MPS Immersed for 120 Hours, Stained Proteins Were Observed in Almost All Meso-Scale Channels of MPS. the Ratio of Desorbed Proteins from those Embedded on/in MPS Materials Was 13 % in Case of the MPS Materials Immersed in PBS Containing Cytochrome C for 2 Hours, while 8 % in Case of the MPS Materials Immersed for 48 and 120 Hours. Cytochrome C May Be Strongly Embedded on/in MPS Materials due to the Electrostatic Effect.

Abstract: Volatile sulfur compounds (VSCs) such as hydrogen sulfide (H₂S), methyl mercaptan and dimethyl sulfide produced in mouth. Some oral (Gram-negative) bacteria produce VSCs, which induces permeability of mucous membrane, cause the oral malordor, dental caries, color change of the dental fillings. Thus, material which adsorbs VSCs should be useful to keep health in mouth. Previously, we reported the H₂S adsorptive properties of zeolite and hydrotalcite materials having micro pores. The amount of H₂S adsorbed on the zeolite or hydrotalcite at room temperature was found to be around 300-400 ppm, and and 3 % of H₂S was desorbed when heated at 400 °C. The hydrotalcite, whose compositon is Mg_1-xAl_x(OH)₂A_x/n·mH₂O, where A is CO₃^2-, and x is 0.25, was heat-treated at 500 °C, and put into aqueous solution containing H₂S. In this study, the relation between heat-treatment tempearture and the sulfide adsorption on hydrotalcite in aqueous solution was investigated. The hydrotalcite materials were hydrothermally synthesized and identified by powder X-ray diffraction method. The change in concentrations of H₂S in aqueous solution was measured using FPD gas chromatography (GC). The concentrations of H₂S was decreased with time for the hydrotalcite heated at 500 °C or 600 °C, and fell to 20 % for 12 hours. But, the concentration was decreased by 40% for 12 hours for the hydrotalcite materials heated at higher temperatue. XRD and FT-IR analysis revealed that the sulfides were into or out of the hydrotalcite structure through topochemical reactions.

Abstract: Use of ready-made marine skeletons is one of the simplest possible remedies to major problems hindering the future development of regenerative orthopaedics- such as, providing a richness of framework designs and now a potentially rich, accessible source of osteopromotive analogues and biomineralisation proteins. It has already been shown that coral and marine sponge skeletons can support self-sustaining musculoskeletal tissues and that extracts of spongin collagen and nacre seashell organic matrices promote bone mineralisation. This should not be surprising given that the pivotal biomineralisation proteins, which orchestrate bone morphogenesis are also found in the earliest calcifying marine organisms. This is because they are representatives of the first molecular components established for calcification, morphogenesis and wound healing. In support of this notion, it has emerged that BMP molecules- the main cluster of bone growth factors for human bone morphogenesis- are secreted by endodermal cells into the developing skeleton. In addition, the regenerative signalling proteins, TGF-b and Wnt-prime targets in bone therapeutics- are also present in early marine sponge development and instrumental to stem cell activation in Cnidarians. Based on this match between vertebrate and invertebrate main developmental proteins, we review the nature and extent of this evolutionary relatedness and use it to support the development of a new strategy, which is to mine selected marine origin organic matrices for novel metabolic, signalling and structural proteins/peptides and protein analogues to apply in regenerative orthopaedics, particularly when using adult stem cells. To support such a proposal we show early stage evidence-gathered in our own laboratory- of the presence of fibrinogen fragments and early osteopromotive effects of a coral organic matrix extract on stem cells. In practice the discovery of new osteopromotive and osteo-accelerant protein analogues will require use of traditional chromatography techniques, osteoactivity assays to hone in on potential proteins of significance and advanced proteomic tools to provide accurate sequencing, determine the mechanisms and molecular pathways involved in osteoactivation and determine the efficiency and effectiveness of marine skeleton-derived protein modulation of the stem cell (MSC) proteome. As more analogues are discovered using proteomic tools, skeletal organic matrices may have ever increasing utility for regenerative orthopaedics.