Cellulose phosphates as biomaterials. In vitro biocompatibility studies

Grafting of phosphate groups has been investigated as a means to render biomedical polymers able to induce the formation of an apatite layer. In the present investigation, regenerated cellulose hydrogels were surface modified by phosphorylation using a previously reported method. The in vitro biocompatibility of materials with varying phosphate contents was evaluated in cultured human bone marrow stromal cells (HBMSC), in terms of cytotoxicity, cell attachment, proliferation and immunohistochemistry. Negatively charged cellulose phosphates were neutralized in the form of the calcium salt before contact with cells. Cellulose phosphates were not cytotoxic, independently of the phosphate content. Unmodified regenerated cellulose hydrogels showed good rates of HBMSC attachment and proliferation. On the contrary, negatively charged, highly hydrophilic, phosphorylated surfaces showed poor HBMSC attachment and proliferation, as well as poor alkaline phosphatase-specific activity and expression of osteocalcin and type I collagen. Differences found are discussed in terms of surface chemical functionality, hydrophilicity and charge.