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- 309962 (1)
Mucin, a high molecular mass hydrophilic glycoprotein, is the main component of mucus that coats every wet epithelium in animals. It is thus intrinsically biocompatible, and with its protein backbone and the o-glycosidic bound oligosaccharides, it contains a plethora of functional groups which can be used for further chemical modifications. Here, chain-growth and step-growth (thiol-ene) free-radical cross-linked hydrogels prepared from commercially available pig gastric mucin (PGM) are introduced and compared as cost-efficient and easily accessible alternative to the more broadly applied bovine submaxillary gland mucin. For this, PGM is functionalized with photoreactive acrylate groups or allyl ether moieties, respectively. Whereas homopolymerization of acrylate-functionalized polymers is performed, for thiol-ene cross-linking, the allyl-ether-functionalized PGM is cross-linked with thiol-functionalized hyaluronic acid. Morphology, mechanical properties, and cell compatibility of both kinds of PGM hydrogels are characterized and compared. Furthermore, the biocompatibility of these hydrogels can be evaluated in cell culture experiments.
A novel approach, in the context of bioprinting, is the targeted printing of a defined number of cells at desired positions in predefined locations, which thereby opens up new perspectives for life science engineering. One major challenge in this application is to realize the targeted printing of cells onto a gel substrate with high cell survival rates in advanced bioinks. For this purpose, different alginate-dialdehyde—polyethylene glycol (ADA-PEG) inks with different PEG modifications and chain lengths (1–8 kDa) were characterized to evaluate their application as bioinks for drop on demand (DoD) printing. The biochemical properties of the inks, printing process, NIH/3T3 fibroblast cell distribution within a droplet and shear forces during printing were analyzed. Finally, different hydrogels were evaluated as a printing substrate. By analysing different PEG chain lengths with covalently crosslinked and non-crosslinked ADA-PEG inks, it was shown that the influence of Schiff's bases on the viscosity of the corresponding materials is very low. Furthermore, it was shown that longer polymer chains resulted in less stable hydrogels, leading to fast degradation rates. Several bioinks highly exhibit biocompatibility, while the calculated nozzle shear stress increased from approx. 1.3 and 2.3 kPa. Moreover, we determined the number of cells for printed droplets depending on the initial cell concentration, which is crucially needed for targeted cell printing approaches.
Polymers sensitive to thermal degradation include poly(lactic-co-glycolic acid) (PLGA), which is not yet processed via melt electrowriting (MEW). After an initial period of instability where mean fiber diameters increase from 20.56 to 27.37 µm in 3.5 h, processing stabilizes through to 24 h. The jet speed, determined using critical translation speed measurements, also reduces slightly in this 3.5 h period from 500 to 433 mm min\(^{−1}\) but generally remains constant. Acetyl triethyl citrate (ATEC) as an additive decreases the glass transition temperature of PLGA from 49 to 4 °C, and the printed ATEC/PLGA fibers exhibits elastomeric behavior upon handling. Fiber bundles tested in cyclic mechanical testing display increased elasticity with increasing ATEC concentration. The processing temperature of PLGA also reduces from 165 to 143 °C with increase in ATEC concentration. This initial window of unstable direct writing seen with neat PLGA can also be impacted through the addition of 10-wt% ATEC, producing fiber diameters of 14.13 ± 1.69 µm for the first 3.5 h of heating. The investigation shows that the initial changes to the PLGA direct-writing outcomes seen in the first 3.5 h are temporary and that longer times result in a more stable MEW process.
The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting
(2022)
Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period.