Ion Mixing of Pulsed Laser Deposited Hydroxylapatite (HA)
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Abstract The use of ion-beam techniques to enhance selected properties of bioactive materials, such as the adhesion of hydroxylapatite (HA) coatings on titanium-based substrates has been investigated. In this study, very thin HA films on titanium substrates were created by pulsed laser deposition techniques. Ion irradiations were carried out using 260-keV argon ions, with fluences of 0.25-50xlO0 5 ions/cm 2 , and at room temperature. Rutherford backscattering spectrometry was used to evaluate sample composition before and after irradiation. The amount of mixing was quantified by the mixing rate (the amount of atomic displacement due to an irradiation fluence). This pilot data indicates that mixing was evident after sufficient ion irradiation. The ramification of this preliminary study has provided a quantitative measure of ion mixing as a potential prosthetic biomaterial surface modification technique.
Introduction A major issue yet to be resolved in both the orthopaedic and dental implants fields is the achievement of long term fixation of load-bearing implant devices [1]. One of the more promising approaches to improve implant fixation is the use of bioactive surface coatings. Hydroxylapatite (HA) is a calcium-phosphate-bioceramic material which has drawn much attention due to its excellent biocompatibility and tissue bioactivity properties [2]. Although there are various HA coating methods possible, plasma spray is presently the only practical commercial method to date that can produce relatively thick (50-200 jim) HA coatings onto irregular shaped prostheses. However, there are several disadvantages associated with HA plasma sprayed films. Plasma sprayed HA films lack controlled microstructure which may result in suboptimal tissue responses. In addition, reports on HA coated dental and orthopaedic implants that suggest that plasma-sprayed HA coatings apparently form poor mechanical adhesion and result in their premature detachment from the implant resulting in device failure [3,4,5]. The advent of ion-implantation transformed the field of microelectronics twenty years ago [6]. This change was primarily due to the reproducibility, control, and short processing times during materials modification. Less than fifteen years ago, ion beams
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were used to modify the structure and the properties of ceramic materials [7]. Today a subgroup of ceramics, bioactive materials (e.g., HA) presents many challenges and unique opportunities for the ion-beam-modification community to resolve technological issues in biomaterials technology. Although dynamic ion mixing of HA with titanium substrates has been observed [8], the nature of that work does not allow the ready separation of conventional mixing phenomena from ion irradiation induced effects, since the porous and amorphous HA films are irradiated during deposition. Moreover our interest lies in the observation of ion mixing effects using chemically inert gas species implanted into a fully dense, polycr
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