Role of Molecular Chemistry of Degradable pHEMA Hydrogels in Three-Dimensional Biomimetic Mineralization

Three-dimensional (3D) biomimetic mineralization is highly desired for soft biomaterials such as collagen to create useful hybrid biomaterials for orthopedic tissue engineering. Here, we apply an approach of current-mediated ion diffusion, as a feasible means of 3D biomimetic mineralization, to a series of generic, hydrolytically degradable poly(2-hydroxyethyl methacrylate) hydrogels with various molecular structures, imparted by the introduction of the comonomers, acrylic acid and 2-hydroxyethyl methacrylamide. This approach enables us to create a wide range of nanoscale single crystals of calcium phosphate within the hydrogels as characterized by high-resolution transmission electron microscopy (TEM). Molecular chemistry of the hydrogels, coupled with pH and gel strength, plays a crucial role in formation of the minerals. Both brushite (CaHPO4 center dot 2H(2)O) and octacalcium phosphate (Ca8H2(PO4)(6)center dot 5H(2)O) are observed in pHEMA homo hydrogel. Both octacalcium phosphate and monetite (CaHPO4) are seen in a copolymer hydrogel, poly(2-hydrogelethyl methacrylate-co-acrylic acid). In another copolymer hydrogel (poly(2-hydroxyethyl methacrylate-co-2-hydroxyethyl methacrylamide), both hydroxyapatite (Ca-10(PO4)(6)(OH)(2)) and monetite (CaHPO4) are observed. All these nanocrystals are essential to bone regeneration. They organize themselves primarily as nanoscale fibers, sheets, needles, and clusters. These nanoarchitectures are important to bone-cell attachment, proliferation, migration, and differentiation, and dictate the ingrowth of new bone tissues.