Porous silicon recently has been suggested for biomedical proposals. These 
applications require materials that are both biocompatible and biodegradable. Medium 
and highly porous (above 40%) silicon is known as a biodegradable material and its 
biocompatibility is highly tunable. The aim of the work is a study of the methods for 
improving its biocompatibility (up to reaching a bioactivity). As a model positive we 
investigated “in Vitro” process of deposition of hydroxyapatite (inorganic component of 
bones) form simulated body fluid SBF. In our study a surface of porous silicon materials 
was differently modified by gradual electrochemical oxidation (Si-O) or by acetylene 
(Si-C) and response produced in SBF solution was analyzed. The surface modification 
allowed for obtaining biocompatible dense hydroxyapatite layers up to 5 microns of 
thickness on the samples surfaces after one month in SBF. The results are of great interest 
for future biomedical applications of that material.