Lasers and Long Term Implants

By: Negar Rasti

Due to the increasing demand for implanted orthopedic and dental devices, and a growth in the percentage of elderly people, the designing of reliable long term implants is vital. Therefore, a new method has been developed to improve such devices that uses laser processing, a very controlled way to modify the topographical and chemical properties of titanium and thus increase biocompatibility.

A pulsed nanosecond laser with a high intensity Gaussian beam quality is used to modify a commercial pure titanium surface. Such a laser results in the formation of microstructures, protruding from the surface of the substrate to form micro/nano roughness on the surface of the titanium and enhancing the ossointegration process. In this study, the laser processing experiments are performed in both air and hydrogen peroxide (HP) media. Laser processing in an oxide medium (Water, O2 gas) has been known to affect chemical behaviour. This is a pioneer study focuses on the effects of the laser processing of titanium in HP. This liquid-based media affects not only the micro features, developed by the irradiation of the laser beam compared to air, but also influences the chemical structure of the surface by controlling the structure of the oxide layer during laser processing under different laser parameters, or by implementing the process in different media. Of all of the titania structures (i.e., Rutile, anatase, and brookite), anatase has the best properties for medical applications. It exhibits a stronger interaction with metals, and a strong ability to absorb OH and PO4 3- , which helps the deposition of hydroxyapatite on bone.

The trend of the structure under the controlled parameters remains the same in both experiments. However the periodic space and the height of the structures created in HP is smaller than those produced in the atmosphere (Figure).

One of the main factors affecting this variation is explained by the main theory behind creation of these structures. These protruded microstructures are initiated mainly through irradiation of a short-duration high-intensity laser beam. As a result, the surface of the material reaches its vaporization temperature. Before the vaporization of the surface layer, the underlying layer attains its vapourization temperature. The pressure and temperature of the underlying layer result in the explosion of the material. With increase laser irradiation, the newly deformed asperities are accelerated away from the liquid substrate during each laser pulse, due to surface tension variation at different part of the asperities, surface. However, when the laser process is conducted in HP, the liquid media will diminish the effect of the surface tension gradient and will decrease the growth and height distribution of the structures.

The XRD results of the conditions in HP demonstrate the presence of new peaks of titanium dioxide and titanium oxide (Hongquiite) compositions. The anatase structure of titania, which improves biocompatibility, increases with laser processing especially in a hydrogen peroxide medium.

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here