No abstract

Many studies have utilized Irgacure 2959 photopolymerized poly(ethylene glycol) (PEG) hydrogels for tissue engineering application development. Due to the limited penetration of ultraviolet light through tissue, Irgacure 2959 polymerized hydrogels are not suitable for use in tissues where material injection is desirable, such as the spinal cord. To address this, several free radical initiators (thermal initiator VA044, ammonium persulfate (APS)/TEMED reduction-oxidation reaction, and Fenton chemistry) are evaluated for their effects on the material and mechanical properties of PEG hydrogels compared with Irgacure 2959. To emulate the effects of endogenous thiols on in vivo polymerization, the effects of chain transfer agent (CTA) dithiothreitol on gelation rates, material properties, Young's and shear modulus, are examined. Mouse embryonic stem cells and human induced pluripotent stem cell derived neural stem cells were used to investigate the cytocompatibility of each polymerization. VA044 and Fenton chemistry polymerization of PEG hydrogels both had gelation rates and mechanical properties that were highly susceptible to changes in CTA concentration and showed poor cytocompatibility. APS/TEMED polymerized hydrogels maintained consistent gelation rates and mechanical properties at high CTA concentration and had a similar cytocompatibility as Irgacure 2959 when cells were encapsulated within the PEG hydrogels. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3059-3068, 2017.

Although preclinical models of spinal cord injury have shown that matrix inclusion in stem cell therapy leads to greater neurological improvements than that including cells alone, there has been insufficient matrix optimization for human cells. N-Cadherin influences the development and maintenance of neural tissue, but the effects of N-cadherin derived peptide His-Ala-Val-Asp-Ile (HAVDI) on the survival, neurite extension, and expression of neural differentiation markers in human induced pluripotent stem cell derived neural stems (hNSC) have not been widely examined. Using polyethylene glycol hydrogels containing a continuous gradient of HAVDI, this study identifies concentration dependent effects on hNSC survival and neural differentiation.

Glyceroacetonide-Oxyma [(2,2-dimethyl-1,3-dioxolan-4-yl)methyl 2-cyano-2-(hydroxyimino)acetate (1)] displayed remarkable physico-chemical properties as an additive for peptide-forming reactions. Although racemization-free amide-forming reactions have been established for N-urethane-protected α-amino acids with EDCI, 1, and NaHCO3 in water or DMF-water media, amide-forming reactions of N-acyl-protected α-amino acids and segment couplings of oligopeptides still require further development. Diethylphosphoryl-Glyceroacetonide-Oxyma (DPGOx, 3) exhibits relative stability in aprotic solvents and is an effective coupling reagent for N-acyl-protected α-amino acids and oligo peptide segments. The conditions reported here is also effective in lactam-forming reactions. Unlike most of the reported coupling reagents, simple aqueous work-up procedures can remove the reagent and by-products generated in the reactions.

are required to understand the effects of MMP driven ECM remodeling in human systems. Although polymer [7-9] and bioactive peptide signaling [10-12] selection will alter MMP activity in the matrix, the field has traditionally focused on the use of enzymatically degradable crosslinkers to increase cellular spreading and migration by increasing pore size. [13] However, enzymatically degradable cross linkers have been found to alter cellular differentiation [14] and axonal extension in 2D culture, [15,16] which implies they have greater bioactivity than previously appreciated. To incorporate ECM remodeling as a matrix design criteria, greater consideration to the effects of all matrix components on MMP activity needs to be given. Hyaluronic acid (HA) enhances neural stem cell growth, differentiation, and axon extension. [17,18] Adding laminin to HA further increases in axon extension. [19] However, HA stimulates gelatinase (MMP 2 & 9) expression. [7,8] Gelatinase promotes axonal regeneration after CNS injury, [20] but degrades laminin. [21] Revealed cryptic sites in laminin can then participate in regulating gelatinase activity and cellular behaviors. [10,22] Use of laminin derived peptide signaling, instead of whole laminin molecules, provides more consistent bioactive signaling. Not all commonly used laminin derived peptides regulate gelatinase activity. [10,23] Laminin derived Ile-Lys-Val-Ala-Val (IKVAV) promotes neural differentiation, increases axon extension, and modulates gelatinase expression. [11,24] To further manipulate cellular responses, additional peptides are often used with IKVAV. [25] Leu-Arg-Glu (LRE), another lamininderived peptide, supports adhesion, axon guidance, and other cell behaviors not stimulated by IKVAV. [26] LRE also modulates the expression of gelatinase and inhibitors of gelatinase activity by manipulating Ca 2+ flow through Cav2.2 voltage gated Ca 2+ channels. [12] IKVAV and LRE peptide signaling in HA matrices increases protease (MMP 1 & 3) and gelatinase expression in mouse embryonic stem cells, while reducing the degradation of the HA matrix. [3] The IKVAV and LRE signaling combination is capable of affecting human induced pluripotent stem cell derived neural stem cells (hNSC) behavior in 2D culture. [27] This study examines the effect of IKVAV and LRE on hNSC,