Surface and interface analysis of hydroxyapatite/TiO2 biocompatible structures

Montecarlo Simulation and HAXPES Analysis of Organosilane Segregation in Titania Xerogel Films; Towards a Generic Surface Chemofunctionalization Process

The formation of xerogels implies a sequence of hydrolysis and condensation reactions, which are intricate to analyze in heteromolecular sols. We analyze by probabilistic Montecarlo methods the development of hybrid organosilane–titania xerogels and illustrate how partial charges of the reacting molecules can help estimating relative probabilities for the condensation of the molecules. Since the condensation rate of Ti alkoxides is much higher than the corresponding rate of Si alkoxides (especially if bearing a non-hydrolizable group), by imposing a fast condensation process in agreement with low pH kinetics, the process leads to a surface segregation of the organosilane. The simulation results are compared with results of characterization of thin condensates of two different organosilanes within a titanium–isopropoxide matrix. Non-destructive in-depth profiles were obtained by hard x-ray photoelectron spectroscopy, which can resolve through estimation of Si and specific moieties of the organosilane molecules the progress of the condensation. These results are relevant for the generalization of chemo-functionalization processes by kinetic demixing of organosilanes, which have myriad applications in biomedicine and biotechnology.

Osteoblast-like cell response to calcium phosphate coating chemistry and morphology on etched silicon surfaces

Being able to control the behaviour of osteoblast-like cells on a surface may provide a genuine insight into the material surface characteristics and help in creating a successful coating/cell interface. The possibility of creating a micro-environment that can induce proliferation, differentiation and mineralisation of bone cells in vitro, by successfully combining both chemistry and topography of a micro-fabricated substrate is an area that requires a multi-disciplinary approach. Utilising sputter deposition, a process that lends itself to high processability, in conjunction with photolithography allowing for the creation of highly repeatable etched surfaces, we aim to provide a successful combination of chemistry and topography. Correlating the substrate conditions with resultant osteoblast biological function and activity can ultimately be used with a view to modulating the behavior of osteoblast-like cells in vitro.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Sputter deposited bioceramic coatings: surface characterisation and initial protein adsorption studies using surface-MALDI-MS

Protein adsorption onto calcium phosphate (Ca-P) bioceramics utilised in hard tissue implant applications has been highlighted as one of the key events that influences the subsequent biological response, in vivo. This work reports on the use of surface-matrix assisted laser desorption ionisation mass spectrometry (Surface-MALDI-MS) as a technique for the direct detection of foetal bovine serum (FBS) proteins adsorbed to hybrid calcium phosphate/titanium dioxide surfaces produced by a novel radio frequency (RF) magnetron sputtering method incorporating in situ annealing between 500°C and 700°C during deposition. XRD and XPS analysis indicated that the coatings produced at 700°C were hybrid in nature, with the presence of Ca-P and titanium dioxide clearly observed in the outer surface layer. In addition to this, the Ca/P ratio was seen to increase with increasing annealing temperature, with values of between 2.0 and 2.26 obtained for the 700°C samples. After exposure to FBS solution, surface-MALDI-MS indicated that there were significant differences in the protein patterns as shown by unique peaks detected at masses below 23.1 kDa for the different surfaces. These adsorbates were assigned to a combination of growth factors and lipoproteins present in serum. From the data obtained here it is evident that surface-MALDI-MS has significant utility as a tool for studying the dynamic nature of protein adsorption onto the surfaces of bioceramic coatings, which most likely plays a significant role in subsequent bioactivity of the materials.

Characterisation of calcium phosphate/titanium dioxide hybrid coatings

The role of titanium dioxide (TiO2) as a means to engender enhanced stability into calcium phosphate (Ca-P) coatings has been well recognised. Several different methods have been used to create such Ca-P/TiO2 hybrid layers on a range of substrates. This paper reports the properties of a Ca-P/TiO2 system created by the sputter deposition of hydroxyapatite onto a titanium surface and the subsequent thermal diffusion of TiO2 through the porous Ca-P layer. The role of temperature in determining the surface contribution from TiO2 has been determined. Coatings annealed up to 600 degrees C did not exhibit any hybrid nature in the uppermost surface, however the coatings annealed to 700 degrees C did show the presence of both HA and rutile TiO2. The surfaces annealed to 800 degrees C were predominantly rutile TiO2. It was also observed that the Ca/P ratio decreased with increasing annealing temperature and that the coating annealed to 700 degrees C had a value of 1.82 +/- 0.07, which was closest to stoichiometric HA. Furthermore, the coatings that were annealed to 700 degrees C displayed a Ca-P/TiO2 hybrid nature, specifically in their uppermost surface and supported the growth and proliferation of osteoblast-like cells more readily when compared to the HA coatings or the rutile TiO2 surfaces.

Síntese de hidroxiapatita pelo método sol-gel utilizando precursores alternativos: nitrato de cálcio e ácido fosfórico

A hidroxiapatita [Ca10(PO4)6(OH)2, HA] foi sintetizada utilizando-se a rota sol-gel partindo-se de ácido fosfórico e nitrato de cálcio como precursores de cálcio e fósforo, respectivamente e como solvente utilizou-se o metanol na preparação do sol que posteriormente será utilizado na obtenção de recobrimentos de hidroxiapatita sobre substratos de ligas de titânio. O sol permaneceu estável e não ocorreu gelatinização em temperatura ambiente durante sete dias. O sol transformou-se em um gel branco somente após a remoção do solvente a 100ºC. O produto assim obtido foi calcinado em 300°C, 500°C e 700°C e caracterizou-se por DRX, FT-IR, MEV/EDS e TGA/DSC. As fases de HA sintetizada tornaram-se estáveis sem sub-produtos a 700°C. A difração de raios X mostrou que a estrutura apatita é aparente em 300°C. O tamanho do cristal e o teor de HA aumentaram com o aumento da temperatura de calcinação. A análise por MEV mostrou a presença de poros que são importantes para aplicações biomédicas, favorecendo a adesão entre o tecido ósseo neoformado e a apatita sintética, ou seja, osseointegração.