Non-connected versus interconnected macroporosity in poly(2-hydroxyethyl methacrylate) polymers. An X-ray microtomographic and histomorphometric study.

Poly(2-hydroxyethyl methacrylate) (pHEMA) has potentially broad biomedical applica- tions: it is biocompatible and has a hardness comparable to bone when bulk polymerized. Porous biomaterials allow bone integration to be increased, especially when the pores are interconnected. In this study, three types of porogens (sugar e bers, sucrose crystals, and urea beads) have been used to prepare macroporous pHEMA. The pore volume and interconnectivity parameters of the poros- ity were measured by X-ray microtomography and image analysis. Sucrose crystals, having a high volumetric mass, gave large pores that were located on the block sides. Urea beads and sugar e bers provided pores with the same star volume (2 :65 § 0:46 mm 3 and 2:48 § 0:52 mm 3 , respectively) but which differed in interconnectivity index, fractal dimension, and Euler- Poincare ' s number. Urea beads caused non-connected porosity, while sugar e bers created a dense labyrinth within the polymer. Interconnectivity was proved by carrying out surface treatment of the pHEMA (carboxymethylation in water), followed by von Kossa staining, which detected the carboxylic groups. Carboxymethy- lated surfaces were observed on the sides of the blocks and on the opened or interconnected pores. The disconnected pores were unstained. Macroporous polymers can be prepared with water-soluble porogens. X-ray microtomography appears a useful tool to measure porosity and interconnectedness.