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

Abstract: 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 growthfactordeliverythroughtheelectrospunfibers. Thetechnologiesoffuseddepositionmodeling (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. Keywords: tissue engineering; bone; bimodal scaffolds; fused deposition modeling; electrospinning; hybrid manufacturing proces

Electrospinning Complexly-shaped, Resorbable, Bifurcated Vascular Grafts

The use of vascular grafts is indicated in a wide range of medical treatments. While autologous tissue is the graft of choice in most surgical bypass procedures, the next best option is the use of synthetic vascular grafts. While significant advances have been reported in the use of electrospinning for vascular grafts both at in vitro and in vivo level, most of the work is limited to straight, tubular shapes with uniform diameters. In order to generate resorbable scaffolds with curving and bifurcated tubular shapes with non-uniform diameters, this study proposes combination of directed electrical field and dynamic positioning of electrospun fibers aimed at a custom, 3D printed mandrel. The proposed approach produced a woven membrane of electrospun fibers. In this study, the fibers used were polycaprolactone. They were spun onto a 3D printed (in ABS plastic) bifurcated tubular mandrel. Preliminary mechanical testing of these bifurcated grafts is reported, with maximum indentation force between 0.7 and 2.3 N. In tension tests, the scaffolds showed an average maximum strength of 0.60 MPa (no indexing condition in the B direction) and 1.37 MPa (indexing in the B direction). © 2016 The Authors. Published by Elsevier B.V

Robotic platform and path planning algorithm for in situ bioprinting

The aim of this work is to design a robotic bioprinting platform able to fabricate a three-dimensional structure onto irregular surfaces. With respect to the limitations of current in vitro bioprinting approach, widely used in scaffold-based tissue engineering – handling difficulty, risk of contamination, shape not matching with the defect site – this robotic bioprinter can offer an innovative solution allowing in situ bioprinting, a direct dispensing of biological materials onto and into the damaged site. The robotic platform was developed starting from the 5 degrees-of-freedom open source MOVEO robot from BCN3D. The hardware and the software of the original project were re-engineered to control the robot using LinuxCNC, a path planning algorithm was developed in Matlab®, and the end-effector was equipped with a pneumatic extruder. The algorithm automatically projects any generic printing pattern on the surface on which the scaffold will be 3D bioprinted. For each point, the algorithm calculates the joint angles to keep the end effector always perpendicular to the surface. A g-code file is then exported to Linux CNC adding parameters to control the air pressure and the printing speed. The robotic platform was tested to evaluate its performances. Resolution (~200 ​μm) and repeatability were estimated and preliminary in situ bioprinting tests were performed onto different irregular surfaces, including a physiologically relevant bone model

Characterization of Soft Tooling Photopolymers and Processes for Micromixing Devices with Variable Cross-Section

In this paper, we characterized an assortment of photopolymers and stereolithography processes to produce 3D-printed molds and polydimethylsiloxane (PDMS) castings of micromixing devices. Once materials and processes were screened, the validation of the soft tooling approach in microfluidic devices was carried out through a case study. An asymmetric split-and-recombine device with different cross-sections was manufactured and tested under different regime conditions (10 < Re < 70). Mixing performances between 3% and 96% were obtained depending on the flow regime and the pitch-to-depth ratio. The study shows that 3D-printed soft tooling can provide other benefits such as multiple cross-sections and other potential layouts on a single mold

Fabrication of Multilayered Composite Nanofibers Using Continuous Chaotic Printing and Electrospinning: Chaotic Electrospinning

ChE is proposed for the creation of multi-material and multilayered nanostructures. This technology allows for the precise, continuous, and deterministic generation of internal nano-striations. The potential of ChE is shown through the fabrication of a nano-striated carbon electrode that shows a significant increase in capacitance. ChE has the potential of creating multifunctional architectures with enhanced properties for numerous applications.</p