Characteristics of Collagen-Rich Extracellular Matrix Hydrogels and Their Functionalization with Poly(ethylene glycol) Derivatives for Enhanced Biomedical Applications: A Review.

The hydrogels of natural extracellular matrix (ECM) are excellent biomaterials with promising applications in the physiological manufacture of three-dimensional (3D) constructs that replicate native tissue-like architectures and function as cargo-delivery, 3D bioprinting, or injectable systems. ECM hydrogels retain the bioactivity to trigger key cellular processes in the tissue engineering and regenerative medicine (TERM) strategies. However, they lack suitable physicochemical properties, which restricts their applications in vivo. This demand that mechanical and degradation properties of the ECM hydrogels must be balanced against biological properties. By incorporating poly(ethylene glycol) (PEG) into mammalian type I collagen-rich ECM substrates, this task can be accomplished. This review is focused on the use of PEG derivatives, widely used in formulations of pharmaceutical products or in synthesis of biomedical polyurethanes, as a strategy to modulate both physical and biological properties of natural ECM hydrogels. The processing-property relationship in decellularized ECM hydrogels, as well as the main results when used in TERM, are discussed. A comparison of the characteristics of PEG-ECM hydrogels is provided in terms of the improvement of structure, mechanics, and degradation behavior. Finally, the benefits of producing PEG-ECM hydrogels according to in vitro and in vivo performance in different proofs-of-concept of emergent biomedical technologies are overviewed.

Influence of residual composition on the structure and properties of extracellular matrix derived hydrogels.

In this work, hydrolysates of extracellular matrix (hECM) were obtained from rat tail tendon (TR), bovine Achilles tendon (TAB), porcine small intestinal submucosa (SIS) and bovine pericardium (PB), and they were polymerized to generate ECM hydrogels. The composition of hECM was evaluated by quantifying the content of sulphated glycosaminoglycans (sGAG), fibronectin and laminin. The polymerization process, structure, physicochemical properties, in vitro degradation and biocompatibility were studied and related to their composition. The results indicated that the hECM derived from SIS and PB were significantly richer in sGAG, fibronectin and laminin, than those derived from TAB and TR. These differences in hECM composition influenced the polymerization and the structural characteristics of the fibrillar gel network. Consequently, the swelling, mechanics and degradation of the hydrogels showed a direct relationship with the remaining composition. Moreover, the cytocompatibility and the secretion of transforming growth factor beta-1 (TGF-ß1) by macrophages were enhanced in hydrogels with the highest residual content of ECM biomolecules. The results of this work evidenced the role of the ECM molecules remaining after both decellularization and hydrolysis steps to produce tissue derived hydrogels with structure and properties tailored to enhance their performance in tissue engineering and regenerative medicine applications.

Improved properties of composite collagen hydrogels: protected oligourethanes and silica particles as modulators.

This paper reports the structure-property relationship of novel biomedical hydrogels derived from collagen, water-soluble oligourethanes, and silica. The molecular weight (MW) of oligourethanes, synthesized from polyoxyethylene diol and hexamethylene, l-lysine, isophorone or trimethylhexamethylene diisocyanates (P(HDI), P(LDI), P(IPDI) and P(TMDI), respectively), is determined by the chemical structure of the starting aliphatic diisocyanate. Thus, the collagen polymerization process and both the characteristics and mechanics of the formed three-dimensional (3D) network had a direct relation with the oligourethane MW. The crosslinking of collagen with oligourethanes was compatible with orthosilicate polycondensation to deposit silica particles on the fibrillar 3D network. A higher crosslinking index was found in hydrogels formulated with P(HDI) and P(LDI) in comparison with P(TMDI) and P(IPDI). In spite of similar crosslinking extensions, P(LDI) induced an enhanced water uptake and enhanced susceptibility to degradation, contrary to the impact of P(HDI). Fibroblasts and macrophages cultured for 3 days on hydrogels formulated with P(LDI) showed a metabolic activity similar to collagen only hydrogels. However, we observed the highest cell metabolic activity on hydrogels formulated with P(LDI) after 7 day culture. After this time lapse, an enhanced secretion of chemoattractant cytokines transforming growth factor-beta1 (TGF-ß1) and monocyte chemoattractant protein-1 (MCP-1 or CCL-2) was noted in macrophages cultured on hydrogels crosslinked with P(LDI). These tunable composite collagen hydrogels might be excellent candidates for holding and releasing bioactive molecules and nanomaterials intended to regulate cell behavior via their constituents and properties.