We present the first cell-attachable and visible-light-crosslinkable bioinks based on gelatin methacryloyl (GelMA) with eosin Y (EY) photoinitiation for stereolithography three-dimensional (3D) bioprinting. To develop a visible-light-crosslinkable hydrogel, we systematically studied five combinations of GelMA and EY photoinitiator with various concentrations. Their mechanical properties, microstructures, and cell viability and confluency after encapsulation were investigated rigorously to elucidate the effects of the EY and GelMA macromer concentrations on the characteristics of the hydrogel. Experimental results show that the compressive Young's modulus and pore size are positively affected by the concentration of EY, whereas the mass swelling ratio and cell viability are negatively affected. Increasing the concentration of GelMA helps in improving the compressive Young's modulus and cell attachment. We further employed the developed visible-light-based stereolithography bioprinting system to print the patterned cell-laden hydrogels to demonstrate the bioprinting applications of the developed hydrogel. We observed good cell proliferation and the formation of a 3D cellular network inside the printed pattern at day 5, which proves the great feasibility of using EY-GelMA as the bioinks for biofabrication and tissue engineering.

Gelatin methacrylate (GelMA) hydrogel is a promising bioink for biofabrication applications due to its cost-effectiveness, ease of synthesis and biocompatibility to allow cell adhesion. However, the GelMA synthesized from a widely used porcine skin gelatin has a thermal gelation problem at room temperature. Here, we present thermally stable GelMA hydrogels at room temperature while maintaining the mechanical and biological properties comparable to porcine GelMA. The novel GelMA hydrogels were synthesized from fish skin and cold soluble gelatin. We systematically characterized the properties of the GelMA hydrogels from different sources. The properties include the degree of methacrylation, compressive Young's modulus, mass swelling ratio, viscosity, and cell adhesion and proliferation in 2D and 3D microenvironments. It has been found that the cold soluble GelMA was comparable to the porcine skin GelMA but could offer low viscosity and thermal stability at room temperature. We performed a droplet generation experiment to demonstrate the benefit of using the cold soluble GelMA for biofabrication. The cold soluble GelMA showed a more reliable and stable droplet fabrication process. Taken together, the cold soluble GelMA is a promising bioink solution and may greatly benefit the research in biofabrication.

A direct laser bioprinting (DLBP) system is introduced in this work. The DLBP system applies visible-laser-induced photo-crosslinking at a wavelength of 405 nm using the photoinitiator VA-086. It is shown that such a system can fabricate vertical structures with fine features (less than 50 µm) and high cell viability (greater than 95%). Experimental characterizations and theoretical simulations are presented, and good agreement is seen between the experiments and theory. The DLBP system is applied to the fabrication of (1) cell-laden hydrogel microgrids, (2) hydrogel microwells, as well as a test of (3) cell encapsulation, and (4) cell seeding. The DLBP system is found to be a promising tool for bioprinting.

Stereolithography-based bioprinting offers advantages in resolution and rapid printing time, and thus has received major attention in recent years. However, traditional stereolithography-based bioprinting utilizes an ultraviolet light which may cause mutagenesis and carcinogenesis of cells. In this paper, we present a new visible light crosslinkable bioink that is based on cell-adhesive gelatin. The bioink consists of Eosin Y (EY) based photoinitiator and gelatin methacrylate (GelMA) pre-polymer solution. We examined the feasibility of using visible light from a commercial beam projector to pattern the EY-GelMA bioink. We measured the absorbance of bioink to characterize its sensitivity to visible light and performed bioprinting to test its ability to promote cell adhesion. It is found that the EY-GelMA bioink has an absorption peak at roughly 522 nm, and that it can be successfully crosslinked by visible light from the commercial projector. We performed the bioprinting experiments and visualized the cell morphology using nuclei/F-actin staining. Experimental results show that most of the cells attached to the EY-GelMA bioink after five days' culturing. Ultimately, the EY-GelMA bioink can support both visible light crosslinking and cell adhesion, offering great potential in bioprinting and tissue engineering.

A unified stereoselective synthesis of 4-substituted kainoids is reported. Four kainic acid analogues were obtained in 8-11 steps with up to 54% overall yields. Starting from trans-4-hydroxy-l-proline, the sequence enables a late-stage modification of C4 substituents with sp nucleophiles. Stereoselective steps include a cerium-promoted nucleophilic addition and a palladium-catalyzed reduction. A 10-step route to acid 21a was also established to enable ready functionalization of the C4 position.

A comprehensive survey of kainic acid analogs that have been tested for their biological activity is presented. Specifically, this review (1) gathers and compares over 100 kainoids according to a relative activity scale, (2) exposes structural features required to optimize affinity for kainate receptors, and (3) suggests design rules to create next-generation KA analogs. Literature SAR data are analyzed systematically and combined with the most recent crystallographic studies. In view of the renewed interest in neuroactive molecules, this review aims to help guide the efforts of organic synthesis laboratories, as well as to inform newcomers to KA/GluK research.

A fluorescent probe (2a-LP) based on an unnatural amino acid (UAA) is developed for the detection of phenylalanine ammonia lyase (PAL). In the presence of PAL, 2a-LP is catalytically deaminated to ortho-amino-transcinnamic acid (o-a-CA), which shows a remarkable “off–on” fluorescence signal. Thus, the probe 2a-LP enables direct visualization of the PAL activity in tomato under UV illumination and has potential in vitro assays.

A chemical probe (DECM-PhKA) was developed to study filopodia extension in glial cells with spatio-temporal control. Irradiating DECM-PhKA with blue light releases the neuroactive agonist phenylkainic acid with a half-lifetime of 61 seconds. The effect of rapid uncaging was demonstrated in U118-MG astrocyte cells. The agonist is released locally with high precision using an optic fiber to trigger calcium influx that leads to filopodia extension in the targeted cells. This chemical probe provides a new tool to study the contribution of kainate receptors in transduction of external signals at the single cell level using a physiologically compatible wavelength.