While the ability to form a chemically-bonded interface with bone remains a key characteristic of bioactive materials, research has shown that certain materials, such as 45S5 glass, can not only support bone regeneration, but also have the potential to stimulate the growth and repair of soft tissues like skin, cardiac, and nerve tissues . Thus, the term "bioactivity" now encompasses a broader range of applications that are not limited only to the bone bonding. Therefore, the formation of nonorganic crystals precipitating form SBF on PBS-DLS copolymers surface was observed and analyzed with the use of SEM and EDX. Figure and 13 demonstrate the SEM images along with the EDX analysis of PBS-DLS (70-30) and PBS-DLS (60-40) copolymers surface, respectively (Figure and Figure ) modified with PEG (Figure and Figure ) after immersing samples in SBF for 28 days. The results showed the formation of agglomerated calcium phosphate crystals on the surface of all copolymers. The observed process can be described by the mechanism observed for other polymeric materials : when the copolymers are immersed in SBF solution, the negative charge density on the polymer surface is increasing by ionization of the -OH bond at the end group of the copolymers, causing the absorption of Ca 2+ ions from the SBF solution. This leads to the formation of a positive charge density layer of calcium on the surface of the copolymers, which attracted the negatively charged phosphate ions (PO 4 3-) from SBF solution, thus resulting in the formation of hydroxyapatite (HA) . HA is the bone mineral and contains calcium (Ca) and phosphorus (P) with a Ca/P ratio of 1.667 . Therefore, in our work, the EDX analysis was applied along with SEM to analyze the type and the amount of the elements precipitating on the surface of copolymers. The EDX results indicated the presence of four elements in significant amount, including C (from the copolymers), Cr (from the sample coating for SEM), Ca, and P, with the last two being the main constituents of HA. The Ca/P ratio of the samples containing higher amount of hard segments (70 wt.%) (Figure ) revealed C/P ratio of 1.31 -1.35 which is close to tricalcium phosphate (TCP), while in case of lower hard segments content (60 wt.%) (Figure ) the C/P ratio was 1.8 -1.6 which is close to the stoichiometric value of HA (1.667).