Hydrolytically degradable poly(ethylene glycol) hydrogel scaffolds as a cell delivery vehicle: Characterization of PC12 cell response

Abstract

The central nervous system (CNS) has a low intrinsic potential for regeneration following injury and disease, yet neural stem/progenitor cell (NPC) transplants show promise to provide a dynamic therapeutic in this complex tissue environment. Moreover, biomaterial scaffolds may improve the success of NPC-based therapeutics by promoting cell viability and guiding cell response. We hypothesized that a hydrogel scaffold could provide a temporary neurogenic environment that supports cell survival during encapsulation, and degrades completely in a temporally controlled manner to allow progression of dynamic cellular processes such as neurite extension. We utilized PC12 cells as a model cell line with an inducible neuronal phenotype to define key properties of hydrolytically-degradable poly(ethylene glycol) hydrogel scaffolds that impact cell viability and differentiation following release from the degraded hydrogel. Adhesive peptide ligands (RGDS, IKVAV or YIGSR), were required to maintain cell viability during encapsulation; as compared to YIGSR, the RGDS and IKVAV ligands were associated with a higher percentage of PC12 cells that differentiated to the neuronal phenotype following release from the hydrogel. Moreover, among the hydrogel properties examined (e.g., ligand type, concentration), total polymer density within the hydrogel had the most prominent effect on cell viability, with densities above 15% w/v leading to decreased cell viability likely due to a higher shear modulus. Thus, by identifying key properties of degradable hydrogels that affect cell viability and differentiation following release from the hydrogel, we lay the foundation for application of this system towards future applications of the scaffold as a neural cell delivery vehicle.

3D in vitro modeling of the central nervous system

“…Hydrogels can be of natural or synthetic origin and include agarose (Balgude et al, 2001; Bellamkonda et al, 1995a, 1995b; Cullen et al, 2007a; Dillon et al, 1998; O'Connor et al, 2001), collagen type I (Coates and Nathan, 1987; Coates et al, 1992; Krewson et al, 1994; O'Connor et al, 2000a; O'Shaughnessy et al, 2003), hyaluronic acid (Brännvall et al, 2007, 2007; Hou et al, 2006; Pedron et al, 2013; Tian et al, 2005), N -(2-hydroxypropyl) methacrylamide (HPMA) (Woerly et al, 1990, 1991), poly(ethylene glycol) (PEG) (Pedron et al, 2013; Wang et al, 2014; Zustiak et al, 2013), chitosan (Gao et al, 2014; Leipzig et al, 2011; McKay et al, 2014), alginate (Frampton et al, 2011; Kuo and Chang, 2013; Matyash et al, 2012; Mosahebi et al, 2003), silk fibroin (Benfenati et al, 2010, 2012; Hopkins et al, 2013; Hu et al, 2013; Kim et al, 2010; Tien et al, 2013; Zhang et al, 2012) and methylcellulose (Stabenfeldt and LaPlaca, 2011; Tate et al, 2001), Table 2 .…”

Regulation of tissue ingrowth into proteolytically degradable hydrogels

“…Hydrolytically degradable scaffolds have proved beneficial as regenerative scaffolds [3,4], but an inherent and significant limitation is that the dissolution of the implant is largely dissociated from the migration and invasion of cells and rather is dependent on the intrinsic lability of the scaffold. A major advance in the design of synthetic hydrogels as extracellular matrix mimics has been the introduction of peptide sequences within the polymer backbone that renders the macromer sensitive to cellular derived proteases and therefore directly links the replacement of the scaffold to cellular proteolytic activity [5].…”

Engineering Biomaterials to Influence Oligodendroglial Growth, Maturation, and Myelin Production

“…Poly(ethylene glycol) [PEG]-based materials have been used for numerous applications in the body due to their exquisitely tunable properties. In the nervous system, PEG has been used to promote neurite growth by covalently binding bioactive sequences and taking advantage of its tunable mechanical and biochemical properties [Lampe et al, 2010b;Zustiak et al, 2013]. Throughout the literature there are substantial examples of hydrogel biomaterials used to influence differentiation into neurons, or neurite growth or branching.…”

“…Like proteins, they are typically large molecules with repeated subunits; however, synthetic polymers have an infinitely large selection of monomers from which to choose as opposed to the (relatively) limited 21 amino acids of protein polymers. While polymer hydrogels, such as those based on PEG, have been utilized ex-tensively for neural tissue engineering [Gunn et al, 2005;Burdick et al, 2006;Lampe et al, 2010b;Zustiak et al, 2013], no existing research identifies any oligodendroglial cell interactions. Working with methylcellulose and chitosan, the Shoichet and Leipzig groups have shown the importance of material stiffness on oligodendrocyte development [Leipzig and Shoichet, 2009;Wilkinson et al, 2014].…”