Influence of surface modification on the apatite formation and corrosion behavior of Ti and Ti-15Mo alloy for biomedical applications

Commercially pure Ti and Ti-15Mo specimens were subjected to alkali-hydrogen peroxide and subsequent heat treatment to produce a nanoporous titanate gel layer with anatase phase. The surface morphology of the untreated, alkali-hydrogen peroxide treated and alkali-hydrogen peroxide heat treated specimens before and after 7 days of immersion in simulated body fluid was characterized using X-ray Diffractometer (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). The formation of nanoporous titanate gel layer and the growth of apatite layer over the surface modified specimens after 7 days of immersion in simulated body fluid were confirmed. Further, the electrochemical corrosion behavior of all the specimens was examined using potentiodynamic polarization and electrochemical impedance spectroscopic techniques.     

Novel silica/bis(3-aminopropyl) polyethylene glycol inorganic/organic hybrids by sol–gel chemistry

Biomaterials are needed for tissue regeneration applications that provide control of mechanical properties and enhanced toughness compared to conventional bioceramics. New sol–gel hybrids were developed with interpenetrating networks of silica and bis(3-aminopropyl) polyethylene glycol. Covalent coupling between the organic and the inorganic components was used to control mechanical properties of the hybrids. The objective was to synthesise and characterise a bis(3-aminopropyl) polyethylene glycol silica hybrid material with 35 wt% organic and 65 wt% inorganic and covalent coupling between the components. A coupling agent, 3-glycidopropyltrimethoxysilane (GPTMS) was used to form the covalent links. The hypothesis was that the epoxy ring of the GPTMS would react with the polymer, leaving a polymer functionalised with siloxane groups. In a sol of hydrolysed tetraethyl orthosilicate (TEOS) the siloxanes from the GPTMS form –Si–O–Si– bonds between the functionalised polymer and the silica network. Bis(3-aminopropyl) polyethylene glycol contains two terminal amino groups available for the covalent functionalisation with the epoxy group of GPTMS. Hybrids with 35 wt% organic and 65 wt% inorganic with a ratio of GPTMS:PEG of 1:4 were proven to have an excellent balance between strain to failure (10%) and compressive strength (20 MPa). However, the functionalisation of the polymer was followed by liquid NMR as a function of the aging time and temperature and the expected reaction of nucleophilic attack of the epoxy ring by the amino group of the polymer did not happen until the water was removed from the system during drying. Increasing the amount of GPTMS decreased rate of weight loss during immersion in TRIS buffer solution.     

Fabrication of porous bioactive glass particles by one step sintering

In this study, we reported a facile method to prepare porous bioactive glass microparticles. Porous particles were synthesized by sintering hollow bioactive glass microspheres obtained using a sol-gel co-template technology. The results showed that porous bioactive glass particles possessed a narrow particle size distribution, a relatively porous surface morphology and a hollow structure. It is worth to say that the resulting microparticles present an amorphous structure although the sintering temperature was improved compared to hollow microspheres. The presence of macropore on the shell may provide an efficient method to carry drugs in the hollow cores. Considering the high deposit rate of nanoscale apatite for bioactive glass materials, the porous microparticles should have potential applications in drug and bioactive molecules delivery, in addition to bone tissue regeneration.     

Modulation of nanotube formation in apatite single crystal via organic molecule incorporation

Hydroxyapatite materials are potentially useful for biomedical application, especially as vehicles for functional molecules. Structural control of bulk apatite materials, such as in the fabrication of hollow microspheres or porous structures, has been studied for this purpose. However, control of the internal structure of the source apatite crystal itself is still a challenge. Here, we show that small organic molecules incorporated in apatite crystals act as porogens which control the porous structure of apatite single crystal. The presence of amino acid under apatite synthesis conditions leads to firm bindings and encapsulation of the amino acid in apatite single crystals. Amino acid elimination by heating or electron beam irradiation enhances the pore formation in apatite single crystal. Moreover, incorporation of an acidic amino acid in apatite induces peapod like nanotubes in apatite single crystals. This study suggests the potential of using small organics for nano-structural control of apatite single crystals which would be valuable for enhancing drug loadings or modulating material digestion in vivo.     

Synthesis and in vitro bioactivity of a borate-based bioglass

A bioactive borate glass was synthesized through normal melting-derived route in this letter. The degradation and bioactivity of the glass were studied by the immersion of glass microspheres in a dilute K₂HPO₄ solution. The cell growth inhibition rate of the borate glass was examined by MTT assay. The conversion product of the borate glass was identified by XRD, SEM. It was confirmed that the borate glass had a rapid degradation rate, comparing with the silicate-based bioglass, 45S5 glass. HA formed from the borate glass, that is an indication of bioactive potential in vivo. MTT assay results demonstrate that the inhibition effect of B ions released from the borate glass on cell proliferation can be alleviated by diluting extract solution to a certain concentration (v/v ratio: 1:4, [B] < 1.792 mM). It is believed that the borate glass could be a desirable biomaterial for preparing scaffold of tissue engineering.     

A novel wet polymeric precipitation synthesis method for monophasic β-TCP

β-Tricalcium phosphate (β-Ca₃(PO₄)₂, β-TCP) powders were synthesized using wet polymeric precipitation method for the first time to our best knowledge. The results of X-ray diffraction analysis showed the formation of almost single a Ca-deficient hydroxyapatite (CDHA) phase of a poor crystallinity already at room temperature. With continuously increasing the calcination temperature up to 800 °C the crystalline β-TCP was obtained as the main phase. It was demonstrated that infrared spectroscopy is very effective method to characterize the formation of β-Ca₃(PO₄)₂. The SEM results showed that β-Ca₃(PO₄)₂ solids were homogeneous having a small particle size distribution. The β-TCP powders consisted of spherical particles varying in size from 100 to 300 nm. Fabricated β-TCP specimens were placed to the bones of the rats and maintained for 1–2 months. The histological properties of these samples will be also investigated.     

Surface Modification of Biomaterials in Hard Tissue Applications

Surface modification technologies are quite common in the biomedical field to improve the mechanical,chemical, physical and biological properties of implants such as artificial joint and cardiovascular devices. In this paper, recent progress in the investigation of the bioactivity and biocompatibility enhancement of implants using plasma spraying and plasmabased ion implantation (PIII) is described. Plasma sprayed hydroxyapatite (HA) coatings are commonly used as bioactive coatings but the relatively poor adhesion between the coatings and titanium is one of main disadvantages which have limited their biomedical applications. In our recent studies, novel bioactive coatings, such as wollastonite and dicalcium silicate, were deposited onto titanium to enhance the surfaces bioactivity and biocompatibility. Our results indicate that plasma sprayed wollastonite and dicalcium silicate coatings possess excellent bioactivity as well as relatively high bonding strength. Plasma immersion ion implantation was also employed to improve the anti-corrosion and biological properties of implants.