Combined Influence of Substrate Stiffness and Surface Topography on the Antiadhesive Properties of Acr-sP(EO-stat-PO) Hydrogels

Abstract

Biomaterials that prevent nonspecific protein adsorption and cell adhesion are of high relevance for diverse applications in tissue engineering and diagnostics. One of the most widely applied materials for this purpose is Poly(ethylene glycol) (PEG). We have investigated how micrometer line topography and substrate elasticity act upon the antiadhesive properties of PEG-based hydrogels. In our studies we apply bulk hydrogel cross-linked from star-shaped poly(ethylene oxide-stat-propylene oxide) macromonomers. Substrate surfaces were topographically patterned via replica molding. Additionally, the mechanical properties were altered by variations in the cross-linking density. Surface patterns with dimensions in the range of the cells' own size, namely 10 μm wide grooves, induced significant cell adhesion and spreading on the Acr-sP(EO-stat-PO) hydrogels. In contrast, there was only little adhesion to smaller and larger pattern sizes and no adhesion at all on the smooth substrates, regardless the rigidity of the gel. The effect of varied substrate stiffness on cell behavior was only manifest in combination with topography. Softer substrates with line patterns lead to significantly higher cell adhesion and spreading than stiff substrates. We conclude that the physical and mechanical surface characteristics can eliminate the nonadhesive properties of PEG-based hydrogels to a large extent. This has to be taken into account when designing surfaces for biomedical application such as scaffolds for tissue engineering which rely on the inertness of PEG.

Cell Adhesion and Spreading on an Intrinsically Anti-Adhesive PEG Biomaterial

“…10 µm wide and notably when those 10 µm wide grooves were shallow (5 µm deep). The effect of stiffness variations was only evident in combination with topography, and increased cell adhesion and spreading was observed on the softer gels (Figure 8; Schulte et al, 2010). The cells were found to adhere inside the grooves and form adhesion contacts with the side walls as well as to the bottom of the shallower grooves.…”

“…This is of high relevance for biomedical applications, as it is well known that cells feel and respond to the stiffness of the underlying substrate (Discher et al, 2005;Engler et al, 2006;Yeung et al, 2005). PEG-based hydrogels with distinctly different mechanical properties were fabricated; the resulting hydrogels from 3 different formulations are denoted as soft, intermediate and stiff (Schulte et al, 2010;Diez et al, 2011). The stiffness in the swollen state, which is obviously the most relevant for cell culture, was shown to be approximately half of that measured in the dry state, ranging from ~100 kPa for the softest to 1 MPa for the stiffest, thus covering one order of magnitude in elastic modulus (Figure 3).…”

“…No visual deformation of the hydrogels was found; the cells rather adapted their shape to fit into too narrow grooves (i.e. 5 µm wide; Schulte et al, 2010). Second, we investigated whether proteins could adsorb non-specifically to the gels and if so, if they would adsorb differently on the topographic structures, e.g.…”

Blending PEG-based polymers and their use in surface micro-patterning by the FIMIC method to obtain topographically smooth patterns of elasticity

“…We have recently discovered for instance that cells do adhere to and spread on micro-and nano-topographically patterned PEG surfaces as well as adhering to patterns of elasticity, with cells adhering preferentially to stiffer lines of PEG over softer lines. [17][18][19] This phenomenon of cells "feeling" elasticity has been shown to be crucial in directing cell migration; cells have in fact shown to migrate in the direction of increasing stiffness, a phenomenon known as durotaxis. 5,9,20,21 We believe that PEG can be utilised as an excellent substrate for the study of cell behaviour, as the modification of the surface alone influences cell adhesion and migration, be it chemical, topographical or elastic modification, with non-patterned PEG acting as the inert reference material on which the biointeraction is minimal.…”

Hybrid hierarchical patterns of gold nanoparticles and poly(ethylene glycol) microstructures

“…7,[14][15][16][17][18] Nevertheless, although reported to be highly cell repellent, when patterned topographically or elastically, cells do in fact interact with and adhere to the PEG surface, as we have recently discovered. [19][20][21] Efficient and fast crosslinking methods can be used to make PEG hydrogel networks from PEG-macromonomers. For example, photo-polymerization of polyethylene glycol diacrylate (PEGDA) liquid precursors allows not only the resulting hydrogel to be molded into any desired shape but also enables the control over crosslinking density -dependent on the amount of photoinitiator and eventual low-molecular weight crosslinker used -and therefore the stiffness of the material.…”