RESOURCES

Abstract
Tunicates are marine organisms renowned for their thick, leathery exoskeleton called tunic. This tunic is composed of an extracellular matrix packed with protein-cellulose complexes and sulfated polysaccharides, making it a charming biomaterial choice for cartilage tissue engineering. In this study, P.nigra tunicate was collected and processed to obtain its rich decellularized extracellular matrix (dECM). The dECM was either seeded with human mesenchymal stem cells (hMSCs) as is or underwent further processing to form a hydrogel for 3D bioprinting. The characterization of tunic dECM was achieved by FTIR, XRD, TGA, Raman spectroscopy, SEM and tensile mechanical analysis. Biological compatibility and staining were done by live/dead, alamar blue, alcian blue, safranin O and PCR gene expression. After decellularization, the tunic dECM scaffold preserved the natural honeycomb-shaped microstructure, as well as its functional cellulose and protein groups. Both the tunic dECM scaffolds and bioprinted scaffolds showed enhanced metabolic activity, cell proliferation and chondrogenic differentiation. Combining both the mechanical robustness and biocompatibility, the bioink is able to fill the elusive gap in cartilage regeneration. This study offers a new potential source of dECM scaffolds and bioinks which are both biologically compatible and mechanically stable, making it a one stop shop for cartilage tissue engineering.

Abstract
Triply periodic minimal surfaces (TPMS) are gaining popularity as scaffolds for bioapplications due to their unique structure, offering strong mechanical properties and biomorphic surfaces which enhance cell attachment and proliferation. In this work, polymer TPMS sheet lattices were printed using a well-known yet unprecedented technique of manufacturing such structures; which is material extrusion (specifically, pneumatic melt extrusion). This method offers a one step, straightforward yet reliable way to print complex porous structures while retaining design accuracy and significantly simplifying the process. Multiple primitive, gyroid and cubic structures were designed using MSLattice and Solidworks with 70% porosity and 2×2×3 unit cells. The scaffolds were printed by melt extrusion of polycaprolactone (PCL) at different parameters to establish the optimal settings. Morphological features (pore size and strut thickness) were determined using scanning electron microscopy (SEM) and the accuracy of print was determined by comparing to the design, showing high print accuracy and minimal percentage errors of less than 15% in all prints. Uniaxial compression testing was used to demonstrate the different deformation processes of the scaffolds and evaluate their mechanical properties, with primitive having the highest modulus and gyroid the highest yield strength. Finally, cell viability was quantified by alamar blue cell viability assay and visualized by SEM, displaying significant increase in cell proliferation and attachment, specifically in the primitive structure. Herein we will explain the challenges faced with design and print optimization and how we overcame them, making this work the first of its kind in material extrusion (pneumatic melt extrusion) printing of TPMS scaffolds.

Abstract
Urochordates are the closest invertebrate relative to humans and commonly referred to as tunicates, a name ascribed to their leathery outer “tunic”. The tunic is the outer covering of the organism which functions as the exoskeleton and is rich in carbohydrates and proteins. Invasive or fouling tunicates pose a great threat to the indigenous marine ecosystem and governments spend several hundred thousand dollars for tunicate management, considering the huge adverse economic impact it has on the shipping and fishing industries. In this work, the environmentally destructive colonizing tunicate species of Polyclinum constellatum was successfully identified in the coast of Abu Dhabi and methods of sustainably using it as wound-dressing materials, decellularized extra-cellular matrix (dECM) scaffolds for tissue engineering applications and bioinks for bioprinting of tissue constructs for regenerative medicine are proposed. The intricate three-dimensional nanofibrous cellulosic networks in the tunic remain intact even after the multi-step process of decellularization and lyophilization. The lyophilized dECM tunics possess excellent biocompatibility and remarkable tensile modulus of 3.85 ± 0.93 MPa compared to ∼0.1–1 MPa of other hydrogel systems. This work demonstrates the use of lyophilized tunics as wound-dressing materials, having outperformed the commercial dressing materials with a capacity of absorbing 20 times its weight in the dry state. This work also demonstrates the biocompatibility of dECM scaffold and dECM-derived bioink (3D bioprinting with Mouse Embryonic Fibroblasts (MEFs)). Both dECM scaffolds and bioprinted dECM-based tissue constructs show enhanced metabolic activity and cell proliferation over time. Sustainable utilization of dECM-based biomaterials from ecologically-destructive fouling tunicates proposed in this work helps preserve the marine ecosystem, shipping and fishing industries worldwide, and mitigate the huge cost spent for tunicate management.

Abstract
Bioprinting of nervous tissue is a major challenge in the bioprinting field due to its soft consistency and complex architecture. The first step in efficient neural bioprinting is the design and optimization of printable bioinks which favor the growth and differentiation of neural tissues by providing the mechanophysiological properties of the native tissue microenvironment. However, till date, limited studies have been conducted to make tissue specific bioinks. Here, we report a novel bioink formulation specifically designed for bioprinting and differentiation of neural stem cells (NSCs) to peripheral neurons, using a marine tunicate-derived hydrogel and Matrigel. The formulation resulted in seamless bioprinting of NSCs with minimal processing time from bioink preparation to in vitro culture. The tissues exhibited excellent post-printing viability and cell proliferation along with a precise peripheral nerve morphology on in vitro differentiation. The cultured tissues showed significant cell recovery after subjecting to a freeze-thaw cycle of −80 to 37°C, indicating the suitability of the method for developing tissues compatible for long-term storage and transportation for clinical use. The study provides a robust method to use a sustainable bioink for three-dimensional bioprinting of neural tissues for translational medicine applications.