Craniofacial tendon development-Characterization of extracellular matrix morphology and spatiotemporal protein distribution.

Craniofacial (CF) tendons are often affected by traumatic injuries and painful disorders that can severely compromise critical jaw functions, such as mastication and talking. Unfortunately, tendons lack the ability to regenerate, and there are no solutions to restore their native properties or function. An understanding of jaw tendon development could inform tendon regeneration strategies to restore jaw function, however CF tendon development has been relatively unexplored. Using the chick embryo, we identified the jaw-closing Tendon of the musculus Adductor Mandibulae Externus (TmAM) and the jaw-opening Tendon of the musculus Depressor Mandibulae (TmDM) that have similar functions to the masticatory tendons in humans. Using histological and immunohistochemical (IHC) analyses, we characterized the TmAM and TmDM on the basis of cell and extracellular matrix (ECM) morphology and spatiotemporal protein distribution from early to late embryonic development. The TmAM and TmDM were detectable as early as embryonic day (d) 9 based on histological staining and tenascin-C (TNC) protein distribution. Collagen content increased and became more organized, cell density decreased, and cell nuclei elongated over time during development in both the TmAM and TmDM. The TmAM and TmDM exhibited similar spatiotemporal patterns for collagen type III (COL3), but differential spatiotemporal patterns for TNC, lysyl oxidase (LOX), and matrix metalloproteinases (MMPs). Our results demonstrate markers that play a role in limb tendon formation are also present in jaw tendons during embryonic development, implicate COL3, TNC, LOX, MMP2, and MMP9 in jaw tendon development, and suggest TmAM and TmDM possess different developmental programs. Taken together, our study suggests the chick embryo may be used as a model with which to study CF tendon extracellular matrix development, the results of which could ultimately inform therapeutic approaches for CF tendon injuries and disorders.

Developing a biomimetic tooth bud model.

A long-term goal is to bioengineer, fully functional, living teeth for regenerative medicine and dentistry applications. Biologically based replacement teeth would avoid insufficiencies of the currently used dental implants. Using natural tooth development as a guide, a model was fabricated using post-natal porcine dental epithelial (pDE), porcine dental mesenchymal (pDM) progenitor cells, and human umbilical vein endothelial cells (HUVEC) encapsulated within gelatin methacrylate (GelMA) hydrogels. Previous publications have shown that post-natal DE and DM cells seeded onto synthetic scaffolds exhibited mineralized tooth crowns composed of dentin and enamel. However, these tooth structures were small and formed within the pores of the scaffolds. The present study shows that dental cell-encapsulated GelMA constructs can support mineralized dental tissue formation of predictable size and shape. Individually encapsulated pDE or pDM cell GelMA constructs were analysed to identify formulas that supported pDE and pDM cell attachment, spreading, metabolic activity, and neo-vasculature formation with co-seeded endothelial cells (HUVECs). GelMa constructs consisting of pDE-HUVECS in 3% GelMA and pDM-HUVECs within 5% GelMA supported dental cell differentiation and vascular mineralized dental tissue formation in vivo. These studies are the first to demonstrate the use of GelMA hydrogels to support the formation of post-natal dental progenitor cell-derived mineralized and functionally vascularized tissues of specified size and shape. These results introduce a novel three-dimensional biomimetic tooth bud model for eventual bioengineered tooth replacement teeth in humans. Copyright © 2017 John Wiley & Sons, Ltd.

Maintaining dimensions and mechanical properties of ionically crosslinked alginate hydrogel scaffolds in vitro.

Ionically crosslinked alginate hydrogels are attractive scaffolds because of their biocompatibility and mild gelation reaction that allows for gentle cell incorporation. However, the instability of ionically crosslinked hydrogels in an aqueous environment is a challenge that limits their application. This report presents a novel method to control the dimensions and mechanical properties of ionically crosslinked hydrogels via control of the ionic concentration of the medium. Homogeneous calcium-alginate gels were incubated in physiological saline baths adjusted to specific calcium ion concentrations. Swelling and shrinking occurred at low and high ionic concentrations of the medium, respectively, while an "optimal" intermediate calcium ion concentration of the medium was found to maintain original size and shape of the hydrogel. This optimal calcium ion concentration was found to be a function of crosslinking density and polymer concentration of the hydrogel and chemical composition of the alginate. The effects of optimal and high calcium ion concentrations of the medium on swelling behavior, calcium content, dry weight, and mechanical properties of the immersed hydrogels were investigated. It was found that the resulting hydrogel composition and mechanical properties depended on not only the calcium concentration of the medium, but also the crosslinking density and polymer concentration of the gel. In an 8-week experiment, controlled dimensions and mechanical properties of alginate gels in an aqueous environment were demonstrated. This new technique significantly enhances the potential of alginate hydrogels for tissue engineering and other biomedical applications.

Cartilage tissue engineering: its potential and uses.

PURPOSE OF REVIEW: The prevalent nature of osteoarthritis, a cartilage degenerative disease that results in the erosion of joint surfaces and loss of mobility, underscores the importance of developing functional articular cartilage replacement. Recent research efforts have focused on tissue engineering as a promising approach for cartilage regeneration and repair. Tissue engineering is a multidisciplinary research area that incorporates both biological and engineering principles for the purpose of generating new, living tissues to replace the diseased/damaged tissue and restore tissue/organ function. This review surveys and highlights the current concepts and recent progress in cartilage tissue engineering, and discusses the challenges and potential of this rapidly advancing field of biomedical research. RECENT FINDINGS: Cartilage tissue engineering is critically dependent on selection of appropriate cells (differentiated or progenitor cells); fabrication and utilization of biocompatible and mechanically suitable scaffolds for cell delivery; stimulation with chondrogenically bioactive molecules introduced in the form of recombinant proteins or via gene transfer; and application of dynamic, mechanical loading regimens for conditioning of the engineered tissue constructs, including the design of specialized biomechanically active bioreactors. SUMMARY: Cell selection, scaffold design and biological stimulation remain the challenges of function tissue engineering. Successful regeneration or replacement of damaged or diseased cartilage will depend on future advances in our understanding of the biology of cartilage and stem cells and technological development in engineering.