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

Abstract

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.

In vitro characterization of peptide-modified p(AAm-co-EG/AAc) IPN-coated titanium implants

“…At this stage in the modification, the titanium substrate was still detected (10.0 AE 1.1%), because the nominal probe depth of the 558 scan is $5 nm, and ellipsometry measurements on similarly modified SiO 2 surfaces suggest that the silane chemisorption forms a reaction site limited monolayer with a thickness of approximately 0.7 nm. 10 Photopolymerization of the p(AAm) network resulted in a sharp increase in elemental carbon and nitrogen levels of 20.5 AE 2.4% to 64.3 AE 0.4%, and 0.5 AE 0.4% to 17.6 AE 0.7%, respectively (Fig. 1), and in introduction of a strong (29 AE 1%) amide peak at 288.0 eV (Fig.…”

“…10,14 Commercially pure (Grade 2) titanium tubes (1.6/1.1 mm o.d./i.d. Â 20-mm long; Microgroup, Medway, MA) were skewered onto custom fabricated 18.5-gauge stainless steel needle supports (5.25 in.…”

“…To address this issue, an interpenetrating polymer network (IPN) of poly(acrylamideco-ethylene glycol/acrylic acid) [p(AAm-co-EG/ AAc)] was developed, which subsequently demonstrated resistance to protein fouling and nonspecific cell attachment. 10 This IPN coating has been applied to a range of different materials, and demonstrated its usefulness in encouraging biospecific interactions in complex (serum-containing) environments for a number of different applications. 11 We report here on the adaptation of previously developed methods that were employed to produce peptide-modified p(AAm-co-EG/AAc) IPN coatings on titanium implants amenable to implantation in the rat marrow ablation model.…”

Biomimetic interfacial interpenetrating polymer networks control neural stem cell behavior

“…The tether length of *3 nm between the IPN and any selected bioactive signal was specifically chosen to present the signal away from the IPN and thereby enhance cell engagement. 20 Therefore, the peptide-modified IPN ligand density (1.2-21 pmol/cm 2 ), hydrated thickness (14 nm), swelling behavior (polymer volume fraction, v 2s ¼ 0.42), shear modulus (|G*| ¼ 94 kPa), and nonfouling properties define a specific cellular microenvironment, namely by specifying the dose and mechanical context of the chemical signals presented to stem cells (see Table I). …”

Biology on a Chip: Microfabrication for Studying the Behavior of Cultured Cells

“…Cells maintained in media containing 15% fetal bovine serum (FBS) proliferated, exhibited nodule formation, and generated sheets of mineralized extracellular matrix (ECM) upon addition of β-glycerophosphate to the media. 278 RGD-modified PEG IPNs on titanium supported osteoblast attachment, spreading, and significant mineralization. 279 Stile and Healy 280,281 characterized thermo-responsive peptide-modified hydrogels consisting of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) as model scaffolds for studying cell/material interactions in 3-D.…”