Hydrogels for Cardiac Restorative Support: Relevance of Gelation Mechanisms for Prospective Clinical Use

PURPOSE OF REVIEW

Cardiac tissue regenerative strategies have gained much traction over the years, in particular those utilizing hydrogels. With our review, and with special focus on supporting post-myocardial infarcted tissue, we aim to provide insights in determining crucial design considerations of a hydrogel and the implications these could have for future clinical use.

RECENT FINDINGS

To date, two hydrogel delivery strategies are being explored, cardiac injection or patch, to treat myocardial infarction. Recent advances have demonstrated that the mechanism by which a hydrogel is gelated (i.e., physically or chemically cross-linked) not only impacts the biocompatibility, mechanical properties, and chemical structure, but also the route of delivery of the hydrogel and thus its effect on cardiac repair. With regard to cardiac regeneration, various hydrogels have been developed with the ability to function as a delivery system for therapeutic strategies (e.g., drug and stem cells treatments), as well as a scaffold to guide cardiac tissue regeneration following myocardial infarction. However, these developments remain within the experimental and pre-clinical realm and have yet to transition towards the clinical setting.

The chondrogenic differentiation potential of dental pulp stem cells

Dental pulp stem cells (DPSCs) are particularly promising for tissue engineering (TE) due to the ease of their isolation procedure, great expansion potential and capability to differentiate towards several cell types of the mesodermal, ectodermal and endodermal lineages. Although several studies hint that DPSCs exhibit potential for cartilage tissue formation, the chondrogenic potential of DPSCs has only been marginally explored. Thus, the aim of the present study was to closely investigate the chondrogenic differentiation capacity of DPSCs for TE applications. More specifically, the potential of DPSCs for engineering hyaline and fibrous cartilage was determined. DPSCs obtained from 7 human molars were expanded and chondrogenically differentiated in a 3D pellet culture model. After 21 d of differentiation with chondrogenic stimuli, DPSCs displayed glycosaminoglycan, aggrecan and limited collagen type II deposition. Cells presented an elongated morphology and produced a collagen-rich extracellular matrix, with a predominance of collagen type I in most of the samples, a characteristic of fibrous cartilage tissue. Variations in the administration periods of several chondro-inductive growth factors, including transforming growth factor beta 3, bone morphogenetic protein-2, -6, -7 and insulin-like growth factor-1, did not increase glycosaminoglycan or collagen type II deposition, typical markers of hyaline cartilage tissue. Furthermore, DPSCs could not be stimulated to go into hypertrophic chondrogenesis. These results indicated that under a large variety of chondro-inductive culture conditions, DPSCs could form fibrocartilaginous tissues but not hyaline cartilage. Thus, DPSCs represent a valuable cell source for the regeneration of fibrocartilage in joints.