Biomolecular modification of p(AAm-co-EG/AA) IPNs supports osteoblast adhesion and phenotypic expression

Interpenetrating polymer networks (IPNs) were designed to resist materials fouling caused by non-specific protein adsorption, and indiscriminate cell or bacterial adhesion. These IPNs were thin adherent films (approximately 20 nm) comprised of acrylamide (AAm), ethylene glycol (EG), and acrylic acid (AA) grafted to either silicon waters or quartz substrates via photoinitiated free radical polymerization. These networks were further modified to promote specific cell adhesion by tethering bioactive groups such as peptides that mimic cell-binding domains found on extracellular matrix molecules. As a specific example of biomolecular surface engineering, peptides from the cell-binding domain of bone sialoprotein were tethered to a p(AAm-co-EG/AA) IPN to control cell behavior at the surface. The networks were characterized by contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy to convey information on IPN wettability, thickness, and chemistry. The surface characterization data supported the theory that the PEG/AA layer formed an IPN with the underlying p(AAm) network, and after graft modification of this IPN with diamino PEG (PEG(NH2)2), the PEG(NH2)2 chains were enriched at the surface. Rat calvarial osteoblasts attached to Arg-Gly-Asp (RGD) modified IPNs at levels significantly greater than on clean quartz, Arg-Gly-Glu (RGE) modified, or the PEG(NH2)2 modified IPN, with or without serum in the media. Cells maintained in media containing 15% fetal bovine serum (FBS) proliferated, exhibited nodule formation, and generated sheets of mineralized extracellular matrix (ECM) with the addition on beta-glycerophosphate to the media. Cell adhesion and mineralized ECM formation were specifically dependent on the peptide sequence present at the surface.