No abstract

Biofabrication offers a great potential for the fabrication of three-dimensional living tissues and organs by precisely layer-by-layer placing various tissue spheroids as anatomically designed. Inkjet printing of living cell-laden bioink is one of the most promising technologies enabling biofabrication, and the bioink printability must be carefully examined for it to be a viable biofabrication technology. In this study, the cell-laden bioink droplet formation process has been studied in terms of the breakup time, droplet size and velocity, and satellite formation using a time-resolved imaging approach. The bioink has been prepared using fibroblasts and sodium alginate with four different cell concentrations: without cells, 1 × 10(6), 5 × 10(6), and 1 × 10(7) cells/mL to appreciate the effect of cell concentration on the droplet formation process. Furthermore, the bioink droplet formation process is compared with that during the inkjetting of a comparable polystyrene microbead-laden suspension under the identical operating conditions to understand the effect of particle physical properties on the droplet formation process. It is found that (1) as the cell concentration of bioink increases, the droplet size and velocity decrease, the formation of satellite droplets is suppressed, and the breakup time increases, and (2) compared to the hard bead-laden suspension, the bioink tends to have a less ejected fluid volume, lower droplet velocity, and longer breakup time.

High-performance carbon fibers (CFs) are currently produced primarily from polyacrylonitrile (PAN). However, the high cost of such CFs and the environmental concerns during its manufacturing (from PAN) are stimulating research on alternative biobased precursors and environmentally friendly processing routes. This review summarizes the recent research studies on the pathways for converting cellulose and lignin (most abundant and renewable biomass) into suitable precursor fibers and CFs. The role of various bio-based precursors, fiber spinning routes, and process conditions on the final properties of CFs is discussed. Although bio-based CFs reported in the current research studies have limited strength and modulus to be considered for high-performance aerospace applications, further progress in precursor purification and optimized fiber processing may lead to their application in less demanding structural applications such as automotive and industrial. Even in their current state, a lack of graphitic crystallinity results in a lower conductivity for the resulting CFs and makes them suitable for ultrahigh temperature insulative applications. Furthermore, the noncrystalline form of carbon obtained from bio-based precursors clearly indicates a significant potential of carbon nanofibers, mats, and activated CFs in nonstructural applications that require a large specific surface area, such as electrochemical energy storage and purification.

The sustainable solvent system acetic acid + water was used to simultaneously fractionate, solvate, and clean a softwood Kraft lignin for conversion to carbon fibers. By exploiting the novel liquid− liquid equilibrium (LLE) phase behavior exhibited by this pseudoternary system, three fractionated−solvated lignin precursors (FSLPs) of increasing molecular weight (7200, 13 800, and 28 600) were obtained via the continuous Aqueous Lignin Purification using Hot Acids (ALPHA) process. It is noteworthy that all three FSLPs, isolated as the lignin-rich liquid phase, had very low metals/ash content (230 ppm of Na and 0.07 wt % ash), in contrast to that of the bulk feed lignin (1400 ppm of Na and 0.60 wt % ash). Lignin fibers were successfully spun from the FSLPs by dry-spinning. Subsequently, the lignin fibers could be rapidly stabilized and carbonized at 1000 °C to produce carbon fibers with equivalent diameters less than 7 μm. Carbon fibers obtained from the highest molecular weight FSLP possessed an average tensile strength and modulus of 1.39 and 98 GPa, respectively, representing the highest mechanical properties ever obtained for carbon fibers derived from low-cost, chemically unmodified lignin.

No abstract