A.M. Vredenberg

Initial deposition of calcium phosphate ceramic on polyethylene and polydimethylsiloxane by rf magnetron sputtering deposition: the interface chemistry

Calcium phosphate (CaP) coatings are well known for their bioactive nature. CaP coated polymeric materials can be used as implant material. For this, a strong adhesion between the coating and substrate is necessary. Because the chemical structure of the interface plays an important role in the coating adhesion, we studied the interface between CaP and the polymers polyethylene (PE) and polydimethylsiloxane (PDMS/silicone rubber). Both untreated and plasma pretreated polymers were used. On PE, a low Ca/P ratio nearby the interface and a high amount of C-O bonds were found on both untreated and plasma pretreated PE. This is the result of phosphate-like groups that are able to bind to the carbon of the PE. PDMS reacts towards the plasma pretreatment by losing CH(3) side groups. Compared to PE, a low amount of C-O bonds is found nearby the interface. Besides, a low Ca/P ratio is found nearby the interface. This is the result of phosphate groups that connect to Si atoms of the PDMS, thereby replacing the CH(3) side groups. The bombardment by negatively charged oxygen ions that are accelerated from the target during the deposition process makes the chemical interaction between the coating and the substrates possible.

Radio frequency magnetron sputtering deposition of calcium phosphate coatings: the effect of resputtering on the coating composition.

Radio frequency magnetron plasma sputtering deposition is a fairly complex deposition method. Deposition of the film is influenced by the energetic bombardment of several species, like energetic electrons, neutrals, ions from the sputtering target and the plasma, and ultraviolet light. In this work we study the origin and the degree of (preferential) resputtering of species from a calcium phosphate ceramic film during the deposition process. We found that negatively charged oxygen is mostly responsible for the resputtering phenomena that occur. The degree of resputtering was determined by comparing the amount of material deposited behind and at the position of an aperture, which was positioned between the sputtering target and the substrate. The degree of resputtering can be derived, because the material behind the aperture is almost completely protected from bombardment by negatively charged oxygen. We found that at low Ar pressure, more than half of the material deposited is resputtered, preferentially ...

Radio frequency magnetron sputtering deposition of calcium phosphate coatings: Monte Carlo simulations of the deposition process and depositions through an aperture

Radio frequency magnetron sputtering deposited calcium phosphate (CaP) coatings can be applied to improve the biological performance of medical implants. However, the deposition process is rather complex. Particle ejection from the sputtering target, particle collisions with the background gas, charge state of the sputtered particles, and resputtering of the deposited film all influence the composition and structure of the film. In this work we study the deposition process of the coatings by performing depositions through an aperture. Thus an image of the sputtering target is obtained. In order to interpret these images, the deposition process is simulated using a Monte Carlo computer simulation. We found that the experimental images obtained at different gas pressures are well predicted by the simulations. The calcium and phosphorus are proven to be ejected as neutrals from the target. The particle ejection distribution could not unambiguously be derived. This was partially because the image is distorted...

Concentration and annealing effects on photoluminescence and local structure of Er-implanted silica

Abstract Extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) measurements were performed on Er-implanted silica as a function of concentration and annealing at 900°C for 30 min. Er was implanted at 5 MeV to form peaked concentration profiles, as well as at a range of energies to form nearly-flat profiles over 1.5 μm of depth. Peak concentrations ranged from 0.1 to 1.0 at.%. It is found that, for low (0.1 at.%) concentrations, local structure is unaffected by annealing, while the lifetime increases. It is suggested that the lifetime is determined by defects in the glass matrix. For higher concentrations, the ErO distance increases from 2.1 A to 2.24 A, the latter value being close to that found in bulk glasses. As a function of Er concentration and annealing, certain PL features evolve in a manner correlated with the EXAFS distances and coordination numbers. The effect of annealing becomes more pronounced at higher Er concentrations. It is suggested that some of the same structural features affect both probes.

Effect of Prenucleation of RF-Sputtered CaP Coatings on In Vitro Rat Bone Marrow Cell Behaviour

In this study we investigate the effect of prenucleating Radio F requent magnetron sputtered calcium phosphate coatings on the interface structure and ce ll respons in a Rat Bone Marrow cell culture. No differences could be observed in proliferation or differentiation of the cells between non-treated and prenucleated coatings. Non-treated coatings showe d no formation of a calcified layer up to day 8, at which the RBM-cells start diff erentiating. After 8 days, cell mediated nucleation and growth of two distinct calcified layers could be observe d, one dense and directly attached to the coating surface, and one of globular accretions associ ated w th the collagen matrix. Prenucleated samples showed imediate and continuous growth of a calcif ied layer only at the coating surface from the start of the cell culture. After cell differe ntiation, growth is enhanced by the formation of the matrix associated calcifications. Effectively , the two different forms of calcium phosphate apposition can be decoupled by the formation of surface nuclei.

Adsorption on RF-sputtered CaP coatings in SBFs

In this study ionic adsorption was investigated of Ca and PO4 from Simulated Body Fluids (SBFx) at the surface of a Radio Frequent sputtered calcium phosphate coating. The relation between adsorption and heterogeneous nucleation of calcium phosphate was studied in doubly concentrated SBF. Two types of coatings were used, one with a high Ca/P ratio (1.6 CaPhigh), and one with a low Ca/P ratio (1.0 CaPlow). Ion coverages in the adsorption layer of CaPhigh coatings were twice as high as for the CaPlow coatings. The Ca/P ratio in the adsorption layer for CaPhigh samples was 1.3, which is the same value as for the formed precipitate. CaPlow samples were found to be inert in SBF2, showing a much higher Ca/P ratio of more than 2. Also, possible desorption of coating constituents during the induction time preceding precipitation was studied. It was found that at most a few percent of the outermost ionic layer of the coating entered the solution.