Influence of Electrical Field Collector Positioning and Motion Scheme on Electrospun Bifurcated Vascular Graft Membranes.

Currently, electrospinning membranes for vascular graft applications has been limited, due to random fiber alignment, to use in mandrel-spun, straight tubular shapes. However, straight, circular tubes with constant diameters are rare in the body. This study presents a method to fabricate curved, non-circular, and bifurcated vascular grafts based on electrospinning. In order to create a system capable of electrospinning membranes to meet specific patient needs, this study focused on characterizing the influence of fiber source, electrical field collector position (inside vs. outside the mandrel), and the motion scheme of the mandrel (rotation vs. rotation and tilting) on the vascular graft membrane morphology and mechanical properties. Given the extensive use of poly(ε-caprolactone) (PCL) in tubular vascular graft membranes, the same material was used here to facilitate a comparison. Our results showed that the best morphology was obtained using orthogonal sources and collector positioning, and a well-timed rotation and tilting motion scheme. In terms of mechanical properties, our bifurcated vascular graft membranes showed burst pressure comparable to that of tubular vascular graft membranes previously reported, with values up to 5126 mmHg. However, the suture retention strength shown by the bifurcated vascular graft membranes was less than desired, not clinically viable values. Process improvements are being contemplated to introduce these devices into the clinical range.

Photopolymerizable Resins for 3D-Printing Solid-Cured Tissue Engineered Implants.

With the advent of inexpensive and highly accurate 3D printing devices, a tremendous flurry of research activity has been unleashed into new resorbable, polymeric materials that can be printed using three approaches: hydrogels for bioprinting and bioplotting, sintered polymer powders, and solid cured (photocrosslinked) resins. Additionally, there is a race to understand the role of extracellular matrix components and cell signalling molecules and to fashion ways to incorporate these materials into resorbable implants. These chimeric materials along with microfluidic devices to study organs or create labs on chips, are all receiving intense attention despite the limited number of polymer systems that can accommodate the biofabrication processes necessary to render these constructs. Perhaps most telling is the limited number of photo-crosslinkable, resorbable polymers and fabrication additives (e.g., photoinitiators, solvents, dyes, dispersants, emulsifiers, or bioactive molecules such as micro-RNAs, peptides, proteins, exosomes, micelles, or ceramic crystals) available to create resins that have been validated as biocompatible. Advances are needed to manipulate 4D properties of 3D printed scaffolds such as pre-implantation cell culture, mechanical properties, resorption kinetics, drug delivery, scaffold surface functionalization, cell attachment, cell proliferation, cell maturation, or tissue remodelling; all of which are necessary for regenerative medicine applications along with expanding the small set of materials in clinical use. This manuscript presents a review of the foundation of the most common photopolymerizable resins for solidcured scaffolds and medical devices, namely, polyethylene glycol (PEG), poly(D, L-lactide) (PDLLA), poly-ε-caprolactone (PCL), and poly(propylene fumarate) (PPF), along with methodological advances for 3D Printing tissue engineered implants (e.g., via stereolithography [SLA], continuous Digital Light Processing [cDLP], and Liquid Crystal Display [LCD]).

Influence of Controlled Cooling in Bimodal Scaffold Fabrication Using Polymers with Different Melting Temperatures.

The combination of different materials and capabilities to manufacture at several scales open new possibilities in scaffold design for bone regeneration. This work is focused on bimodal scaffolds that combine polylactic acid (PLA) melt extruded strands with polycaprolactone (PCL) electrospun fibers. This type of bimodal scaffold offers better mechanical properties, compared to the use of PCL for the extruded strands, and provides potential a means for controlled drug and/or growth factor delivery through the electrospun fibers. The technologies of fused deposition modeling (FDM) and electrospinning were combined to create 3D bimodal constructs. The system uses a controlled cooling system allowing the combination of polymers with different melting temperatures to generate integrated scaffold architecture. The thermoplastic polymers used in the FDM process enhance the mechanical properties of the bimodal scaffold and control the pore structure. Integrated layers of electrospun microfibers induce an increase of the surface area for cell culture purposes, as well as potential in situ controlled drug and/or growth factor delivery. The proposed bimodal scaffolds (PLA extruded strands and PCL electrospun fibers) show appropriate morphology and better mechanical properties when compared to the use of PCL extruded strands. On average, bimodal scaffolds with overall dimensions of 30 × 30 × 2.4 mm³ (strand diameter of 0.5 mm, strand stepover of 2.5 mm, pore size of 2 mm, and layer height of 0.3 mm) showed scaffold stiffness of 23.73 MPa and compression strength of 3.85 MPa. A cytotoxicity assay based human fibroblasts showed viability of the scaffold materials.