Regulation of cell proliferation by multi-layered phospholipid polymer hydrogel coatings through controlled release of paclitaxel.

We fabricated multi-layered hydrogels on titanium alloy (Ti) surfaces by applying alternating layers of a water-soluble phospholipid polymer (PMBV) and polyvinyl alcohol (PVA). This was accomplished by a layer-by-layer (LbL) process that is based on the formation of reversible covalent bonds between the boronic acid subunits in the PMBV and the hydroxyl groups in the PVA. When placed in an aqueous medium, PMBV acquires a polymeric aggregate structure with hydrophobic domains that can effectively solubilize hydrophobic molecules such as the anticancer drug paclitaxel (PTX) used in this study. The PTX-containing PMBV layer acted as a reservoir in the multi-layered hydrogels. To obtain diverse release profiles, the PTX was loaded in either the top layer (top-type) or the bottom layer (bottom-type) of the hydrogels; additional layers of PMBV and PVA, without PTX, functioned as a diffusion-barrier. In cell culture experiments, top-type hydrogels demonstrated excessive suppression of human epidermal carcinoma A431 cell proliferation over 5 days due to the initial high concentration of released PTX. However, bottom-type hydrogels were able to maintain a constant cell number profile. The release of PTX from multi-layered hydrogels was governed by both diffusion through the diffusion-barrier and dissociation of the hydrogel through an exchange reaction of phenylboronic acid subunits with the low-molecular weight D-glucose in the cell culture medium. In the cell culture experiments, the cell cycle was arrested in S and G2/M phases, as expected following PTX-mediated growth inhibition; control hydrogels did not demonstrate any appreciable cell cycle arrest. We concluded that cell proliferation could be controlled by the concentration of PTX released from the multi-layered hydrogels prepared through the LbL process. This system when used to solubilize bioactive agents at an appropriate layer within the hydrogel has potential for localized and surface-mediated delivery of bioactive molecules from biomedical devices.