Toward 3D Bioprinting of Osseous Tissue of Predefined Shape Using Single-Matrix Cell-Bioink Constructs

Incorporation of Cross-Linked Gelatin Microparticles To Enhance Cell Attachment and Chondrogenesis in Carboxylated Agarose Bioinks for Cartilage Engineering

Due to the limited regenerative capacity of injured cartilage, surgical intervention using engineered cellular constructs or autologous cell implantation is the best accredited approach to prevent further degeneration and promote a regenerative microenvironment. Advancements in additive manufacturing present opportunities for graft customization through enhanced scaffold design. In bioprinting, an additive manufacturing process, the "bioink" serves as the medium to carry cells but also as a scaffold by imparting form and mechanical attributes to the printed object. In this study, the impact of cross-linked gelatin microparticles (GMPs) on rheological properties and printability of carboxylated agarose (CA) bioink as well as matrix deposition by human nasal chondrocytes (hNCs) was investigated. The introduction of GMPs yielded stiffer bioink formulations, with lower sol-gel transitions that retained the exceptional printability of CA. GMPs served as foci for the attachment of hNCs, improving cellular distribution and bridging the deposited extracellular matrix. After 4 weeks in chondrogenic culture, GMPs containing printed constructs showed enhanced toughness approaching that of the lower end of the spectrum of native cartilage tissue. The incorporation of proteinaceous microparticles might serve as a general concept to promote cellular function in polysaccharide-based bioinks and opens another avenue for engineering 3D-bioprinted microenvironments.

Modulation of Short-Term Delivery of Proteins from Hydrogels

For modulation of cellular behavior, systems that can provide controlled delivery of proteins (soluble signals) over a few hours to a few days are highly desirable. Conventional erosion-controlled systems are inadequate as their degradation spans days to months. Conversely, hydrogels offer quicker release but are limited by a high burst release that can lead to cytotoxicity and rapid depletion of the permeant. To avoid burst release and achieve controlled diffusion of proteins, we propose exploiting electrostatic interactions between the hydrogel matrix and proteins. Here we demonstrate this concept using two disparate hydrogel systems: (1) a chemically cross-linked protein (gelatin) matrix and (2) a physically cross-linked polysaccharide (agarose) matrix and three proteins having different isoelectric points. By introducing fixed charges into the hydrogel matrix using carboxylated agarose (CA), the precise and controlled release of BSA, lactoferrin, and FGF2 over a few hours to days is demonstrated. Using electroendosmosis, we further provide evidence for a clear role for CA in modulating the release. Our findings suggest that the paradigm presented herein has the potential to significantly enhance the design of hydrogel systems for the delivery of proteins and RNA therapeutics for vaccines and biomedical applications ranging from tissue engineering to functional coatings for medical devices.

Mesenchymal Stem Cell Spheroids: A Promising Tool for Vascularized Tissue Regeneration

BACKGROUND

Mesenchymal stem cells (MSCs) are undifferentiated cells that can differentiate into specific cell lineages when exposed to the right conditions. The ability of MSCs to differentiate into particular cells is considered very important in biological research and clinical applications. MSC spheroids are clusters of MSCs cultured in three dimensions, which play an important role in enhancing the proliferation and differentiation of MSCs. MSCs can also participate in vascular formation by differentiating into endothelial cells and secreting paracrine factors. Vascularization ability is essential in impaired tissue repair and function recovery. Therefore, the vascularization ability of MSCs, which enhances angiogenesis and accelerates tissue healing has made MSCs a promising tool for tissue regeneration. However, MSC spheroids are a relatively new research field, and more research is needed to understand their full potential.

METHODS

In this review, we highlight the importance of MSC spheroids' vascularization ability in tissue engineering and regenerative medicine while providing the current status of studies on the MSC spheroids' vascularization and suggesting potential future research directions for MSC spheroids.

RESULTS

Studies both in vivo and in vitro have demonstrated MSC spheroids' capacity to develop into endothelial cells and stimulate vasculogenesis.

CONCLUSION

MSC spheroids show potential to enhance vascularization ability in tissue regeneration. Yet, further research is required to comprehensively understand the relationship between MSC spheroids and vascularization mechanisms.