Composite biomaterials made of biodegradable polylactic acid (PLA) and bioactive magnesium (Mg) salt are developed for orthopaedic implants or metal implant coatings. The releasing of Mg salt into the biological environment benefits the bone growth

while with the releasing of Mg salt and degradation of PLA there forms a porous scaffold for tissue engineering. The size and morphology of the salt and voids are adjustable with such preparation conditions as salt content

pH of casting solution

and the solidification rate

so that we can control the salt releasing and degradation rate of PLA. Dielectric spectroscopy is used to investigate the dispersive structures of Mg salt and voids in the polymer matrix and to monitor the

in situ

releasing of Mg salts in the simulated body fluid (SBF). The current study provides us with an orthopedic biomaterial with controllable multi-phase structures

and a tool to investigate the

in vivo

behaviors of biomaterials.