Novel scalable silicone elastomer and poly(2-hydroxyethyl methacrylate) (PHEMA) composite materials for tissue engineering and drug delivery applications

In recent years hydrogels have received increasing attention as potential materials for applications in regenerative medicine. They can be used for scaffold
materials providing structural integrity to tissue constructs, for controlled delivery of drugs and proteins to cell and tissues, and for support materials in tissue
growth. However, the real challenge is to obtain sufficiently good mechanical properties of the hydrogel. The present study shows the combination of two normally non-compatible materials, silicone elastomer and poly(2-hydroxyethyl methacrylate) (PHEMA), into a novel composite material with increased
hydrophilicity in regard to virgin silicone elastomer, making it suitable as a scaffold for tissue engineering and with the concomitant possibility for delivering
drug from the scaffold to the tissue.
Interpenetrating polymer networks (IPNs) of silicone elastomer and PHEMA was produced using supercritical carbon dioxide (scCO2) as the swelling agent. By removing the scCO2 an IPN of hydrogel and silicone elastomer was obtained, capable of absorbing water just like a traditional hydrogel, but with remarkably increased mechanical properties.
The biocompatibility of the IPN composite material was investigated using live/dead staining of hepatocytes (HepG2) growing on the polymer, showing
excellent viability compared to the control polystyrene. Combinations of different types of silicone elastomers and different percentages of hydrogel were also investigated.
Finally, the model drug doxycycline (a tetracycline analogue) was loaded into the hydrogel of the IPN, and the release of the doxycycline was studied using a doxycycline regulated green fluorescent reporter gene expression assay: HeLa cells grown on the IPN composite material, previously loaded with doxycycline, were transfected with the pTRE-Tight-BI-DsRed-Express plasmid, consisting of a bidirectional tetracycline sensitive promoter. The transfected HeLa cells, expressing the Tet-On transactivator, responded nicely to the release of doxycycline from the IPN composite material by the expression of green fluorescent protein. This demonstrates the potential for combined scaffold and controlled drug delivery material.