Behavior Of Encapsulated Cells Research Articles

Fully synthetic, tunable poly(α-amino acids) as the base of bioinks curable by visible light

Bioinks play a crucial role in tissue engineering, influencing mechanical and chemical properties of the printed scaffold as well as the behavior of encapsulated cells. Recently, there has been a shift from animal origin materials to their synthetic alternatives. In this context, we present here bioinks based on fully synthetic and biodegradable poly(α,L-amino acids) (PolyAA) as an alternative to animal-based gelatin methacrylate (Gel-Ma) bioinks. Additionally, we first reported the possibility of the visible light photoinitiated incorporation of the bifunctional cell adhesive RGD peptide into the PolyAA hydrogel matrix. The obtained hydrogels are shown to be cytocompatible, and their mechanical properties closely resemble those of gelatin methacrylate-based scaffolds. Moreover, combining the unique properties of PolyAA-based bioinks, the photocrosslinking strategy, and the use of droplet-based printing allows the printing of constructs with high shape fidelity and structural integrity from low-viscosity bioinks without using any sacrificial components. Overall, presented PolyAA-based materials are a promising and versatile toolbox that extends the range of bioinks for droplet bioprinting.

Granular Hydrogels in Biofabrication: Recent Advances and Future Perspectives.

Granular hydrogels, which are formed by densely packing microgels, are promising materials for bioprinting due to their extrudability, porosity, and modularity. However, the multidimensional parameter space involved in granular hydrogel design makes material optimization challenging. For example, design inputs such as microgel morphology, packing density, or stiffness can influence multiple rheological properties that govern printability and the behavior of encapsulated cells. This review provides an overview of fabrication methods for granular hydrogels, and then examines how important design inputs can influence material properties associated with printability and cellular responses across multiple scales. Recent applications of granular design principles in bioink engineering are described, including the development of granular support hydrogels for embedded printing. Further, the paper provides an overview of how key physical properties of granular hydrogels can influence cellular responses, highlighting the advantages of granular materials for promoting cell and tissue maturation after the printing process. Finally, potential future directions for advancing the design of granular hydrogels for bioprinting are discussed.

Femtosecond laser induced densification within cell-laden hydrogels results in cellular alignment

The unique capabilities of ultrafast lasers to introduce user-defined microscale modifications within 3D cell-laden hydrogels have been used to investigate fundamental cellular phenomenon such as adhesion, alignment, migration and organization. In this work, we report a new material modification phenomenon coined as ‘densification’ and its influence on the behavior of encapsulated cells. Femtosecond laser writing technique was used to write densified lines of width 1–5 μm within the bulk of gelatin methacrylate (GelMA) constructs. We found that densified micro-lines within cell-laden GelMA constructs resulted in preferential and localized alignment of encapsulated human endothelial cells. Degree of cellular alignment was characterized as a function of cell-culture time and the spacing between the densified line patterns. This phenomenon was found to be true for several cell lines, including mouse fibroblasts and osteocytes, and mesenchymal stem cells derived from human induced pluripotent cells. This first report of physical densification using fs lasers can be potentially extended for investigating cell behavior within other photosensitive hydrogels.

Hybrid elastin-like polypeptide-polyethylene glycol (ELP-PEG) hydrogels with improved transparency and independent control of matrix mechanics and cell ligand density.

Hydrogels have been developed as extracellular matrix (ECM) mimics both for therapeutic applications and basic biological studies. In particular, elastin-like polypeptide (ELP) hydrogels, which can be tuned to mimic several biochemical and physical characteristics of native ECM, have been constructed to encapsulate various types of cells to create in vitro mimics of in vivo tissues. However, ELP hydrogels become opaque at body temperature because of ELP’s lower critical solution temperature behavior. This opacity obstructs light-based observation of the morphology and behavior of encapsulated cells. In order to improve the transparency of ELP hydrogels for better imaging, we have designed a hybrid ELP-polyethylene glycol (PEG) hydrogel system that rapidly cross-links with tris(hydroxymethyl) phosphine (THP) in aqueous solution via Mannich-type condensation. As expected, addition of the hydrophilic PEG component significantly improves the light transmittance. Coherent anti-Stokes Raman scattering (CARS) microscopy reveals that the hybrid ELP-PEG hydrogels have smaller hydrophobic ELP aggregates at 37 °C. Importantly, this hydrogel platform enables independent tuning of adhesion ligand density and matrix stiffness, which is desirable for studies of cell–matrix interactions. Human fibroblasts encapsulated in these hydrogels show high viability (>98%) after 7 days of culture. High-resolution confocal microscopy of encapsulated fibroblasts reveals that the cells adopt a more spread morphology in response to higher RGD ligand concentrations and softer gel mechanics.

The synergistic effects of the RGD density and the microenvironment on the behavior of encapsulated cells:In vitroandin vivodirect comparative study

The inclusion of the tripeptide RGD (Arg-Gly-Asp) in otherwise inert biomaterials employed for cell encapsulation has been observed to be an effective strategy to provide the immobilized cells with a more suitable microenvironment. However, some controversial results collected during the last years, especially in vivo, have questioned its effectiveness. Here, we have studied the behavior of C2 C12 myoblasts immobilized in alginate-poly-l-lysine-alginate microcapsules with different densities of RGD. The use of these microcapsules offer the advantage of avoiding native proteins influence permitting to establish direct comparisons between in vitro and in vivo assays. The results suggest that RGD-modified matrices provide higher dynamism, achieving therapeutically more active biosystems not only in vitro, but also in vivo. The highest functionality of the immobilized cells in vitro was obtained with the lowest RGD density. However, higher RGD densities were required in vivo to obtain the same effects observed in vitro. Altogether, these results suggest the lack of in vitro-in vivo correlation when cell behavior is evaluated within different RGD-tailored cell-loaded scaffolds.