Stimulated in vitro bone-like apatite formation by a novel laser processing technique

Hydroxyapatite is a mineral widely studied as an artificial replacement material in dentistry and medicine due to its chemical and crystallographic resemblance to bone and tooth minerals. New trend of stimulating the hydroxyapatite formation in vitro has evolved by applying various sources of external energy. Lasers have been widely used in biomaterials area as clean and powerful sources of energy and have diverse bioapplications. They are excellent tools for creating micrometer-scale structures by precise and flexible irradiation of small and complex shapes. Using a hierarchical approach that mimics the natural material formation processes, we developed a method to produce materials with controlled physical structure at both micro- and nanometer scale. Materials organized on multiple length scales bear a closer resemblance to biological matrices than those with single scale features, and thus materials with multi-scale organization should be more advantageous in biomedical applications. In the applied laser–liquid–solid interaction method, micrometer scale architecture with precisely controlled size and shape is induced by laser irradiation of various surfaces and then nanostructured hydroxyapatite is grown preferably on the micrometer-sized areas by a biomimetic approach. The method results in an enhanced calcium phosphate formation on the materials’ surfaces which further facilitates the growth of a thicker hydroxyapatite layer. In this work we present our method and the application of optical emission spectroscopy for the in situ monitoring of the processes during the laser–liquid–solid interaction. Furthermore, tests with osteoblast-like cells reveal the biocompatibility of the hydroxyapatite layers obtained as a result of the laser–liquid–solid interaction method.