Cholecalciferol as Bioactive Plasticizer of High Molecular Weight Poly(D,L-Lactic Acid) Scaffolds for Bone Regeneration.

Synthetic thermoplastic polymers are a widespread choice as material candidates for scaffolds for tissue engineering (TE), thanks to their ease of processing and tunable properties with respect to biological polymers. These features made them largely employed in melt-extrusion-based additive manufacturing, with particular application in hard-TE. In this field, high molecular weight (Mw) polymers ensuring entanglement network strength are often favorable candidates as scaffold materials because of their enhanced mechanical properties compared with lower Mw grades. However, this is accompanied by high viscosities once processed in molten conditions, which requires driving forces not always accessible technically or compatible with often chemically nonstabilized biomedical grades. When possible, this is circumvented by increasing the operating temperature, which often results in polymer chain scission and consequent degradation of properties. In addition, synthetic polymers are mostly considered bioinert compared with biological materials, and additional processing steps are often required to make them favorable for tissue regeneration. In this study, we report the plasticization of a common thermoplastic polymer with cholecalciferol, the metabolically inactive form of vitamin D3 (VD3). Plasticization of the polymer allowed us to reduce its melt viscosity, and therefore the energy requirements (mechanical [torque] and heat [temperature]) for extrusion, limiting ultimately polymer degradation. In addition, we evaluated the effect of cholecalciferol, which is more easily available than its active counterpart, on the osteogenic differentiation of human mesenchymal stromal cells (hMSCs). Results indicated that cholecalciferol supported osteogenic differentiation more than the osteogenic culture medium, suggesting that hMSCs possess the enzymatic toolbox for VD3 metabolism. Impact statement Limitations in mechanical and biological performances of scaffolds manufactured through melt deposition may result from material thermal degradation during processing and inherent bioinertness of synthetic polymers. Current approaches involve the incorporation of chemical additives to reduce the extent of thermal degradation, which are often nonbiocompatible or may lead to uncontrolled modifications to the polymer structure. Lack of polymer bioactivity is tackled by postfunctionalization methods that often involve extra processes extending scaffold production time. Therefore, new methods to improve scaffolds performances should consider preserving the integrity of the molecular structure and improving biological responsiveness of the material while keeping the process as straightforward as possible.

Light Cross-Linkable Marine Collagen for Coaxial Printing of a 3D Model of Neuromuscular Junction Formation.

Collagen is a major component of the extracellular matrix (ECM) that modulates cell adhesion, growth, and migration, and has been utilised in tissue engineering applications. However, the common terrestrial sources of collagen carry the risk of zoonotic disease transmission and there are religious barriers to the use of bovine and porcine products in many cultures. Marine based collagens offer an attractive alternative and have so far been under-utilized for use as biomaterials for tissue engineering. Marine collagen can be extracted from fish waste products, therefore industry by-products offer an economical and environmentally sustainable source of collagen. In a handful of studies, marine collagen has successfully been methacrylated to form collagen methacrylate (ColMA). Our work included the extraction, characterization and methacrylation of Red Snapper collagen, optimisation of conditions for neural cell seeding and encapsulation using the unmodified collagen, thermally cross-linked, and the methacrylated collagen with UV-induced cross-linking. Finally, the 3D co-axial printing of neural and skeletal muscle cell cultures as a model for neuromuscular junction (NMJ) formation was investigated. Overall, the results of this study show great potential for a novel NMJ in vitro 3D bioprinted model that, with further development, could provide a low-cost, customizable, scalable and quick-to-print platform for drug screening and to study neuromuscular junction physiology and pathogenesis.

One-Step Photoactivation of a Dual-Functionalized Bioink as Cell Carrier and Cartilage-Binding Glue for Chondral Regeneration.

Cartilage defects can result in pain, disability, and osteoarthritis. Hydrogels providing a chondroregeneration-permissive environment are often mechanically weak and display poor lateral integration into the surrounding cartilage. This study develops a visible-light responsive gelatin ink with enhanced interactions with the native tissue, and potential for intraoperative bioprinting. A dual-functionalized tyramine and methacryloyl gelatin (GelMA-Tyr) is synthesized. Photo-crosslinking of both groups is triggered in a single photoexposure by cell-compatible visible light in presence of tris(2,2'-bipyridyl)dichlororuthenium(II) and sodium persulfate as initiators. Neo-cartilage formation from embedded chondroprogenitor cells is demonstrated in vitro, and the hydrogel is successfully applied as bioink for extrusion-printing. Visible light in situ crosslinking in cartilage defects results in no damage to the surrounding tissue, in contrast to the native chondrocyte death caused by UV light (365-400 nm range), commonly used in biofabrication. Tyramine-binding to proteins in native cartilage leads to a 15-fold increment in the adhesive strength of the bioglue compared to pristine GelMA. Enhanced adhesion is observed also when the ink is extruded as printable filaments into the defect. Visible-light reactive GelMA-Tyr bioinks can act as orthobiologic carriers for in situ cartilage repair, providing a permissive environment for chondrogenesis, and establishing safe lateral integration into chondral defects.