Printability study of metal ion crosslinked PEG-catechol based inks

Printable Poly(3,4-ethylenedioxythiophene)-Based Conductive Patches for Cardiac Tissue Remodeling

Myocardial cardiopathy is one of the highest disease burdens worldwide. The damaged myocardium has little intrinsic repair ability, and as a result, the distorted muscle loses strength for contraction, producing arrhythmias and fainting, and entails a high risk of sudden death. Permanent implantable conductive hydrogels that can restore contraction strength and conductivity appear to be promising candidates for myocardium functional recovery. In this work, we present a printable cardiac hydrogel that can exert functional effects on networks of cardiac myocytes. The hydrogel matrix was designed from poly(vinyl alcohol) (PVA) dynamically cross-linked with gallic acid (GA) and the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The resulting patches exhibited excellent electrical conductivity, elasticity, and mechanical and contractile strengths, which are critical parameters for reinforcing weakened cardiac contraction and impulse propagation. Furthermore, the PVA-GA/PEDOT blend is suitable for direct ink writing via a melting extrusion. As a proof of concept, we have proven the efficiency of the patches in propagating the electrical signal in adult mouse cardiomyocytes through in vitro recordings of intracellular Ca2+ transients during cell stimulation. Finally, the patches were implanted in healthy mouse hearts to demonstrate their accommodation and biocompatibility. Magnetic resonance imaging revealed that the implants did not affect the essential functional parameters after 2 weeks, thus showing great potential for treating cardiomyopathies.

Site-specific fabrication of a melanin-like pigment through spatially confined progressive assembly on an initiator-loaded template

Melanin-like nanomaterials have emerged in surface biofunctionalization in a material-independent manner due to their versatile adhesion arising from their catechol-rich structures. However, the unique adhesive properties of these materials ironically raise difficulties in their site-specific fabrication. Here, we report a method for site-specific fabrication and patterning of melanin-like pigments, using progressive assembly on an initiator-loaded template (PAINT), different from conventional lithographical methods. In this method, the local progressive assembly could be naturally induced on the given surface pretreated with initiators mediating oxidation of the catecholic precursor, as the intermediates generated from the precursors during the progressive assembly possess sufficient intrinsic underwater adhesion for localization without diffusion into solution. The pigment fabricated by PAINT showed efficient NIR-to-heat conversion properties, which can be useful in biomedical applications such as the disinfection of medical devices and cancer therapies.

Advanced supramolecular design for direct ink writing of soft materials

The exciting advancements in 3D-printing of soft materials are changing the landscape of materials development and fabrication. Among various 3D-printers that are designed for soft materials fabrication, the direct ink writing (DIW) system is particularly attractive for chemists and materials scientists due to the mild fabrication conditions, compatibility with a wide range of organic and inorganic materials, and the ease of multi-materials 3D-printing. Inks for DIW need to possess suitable viscoelastic properties to allow for smooth extrusion and be self-supportive after printing, but molecularly facilitating 3D printability to functional materials remains nontrivial. While supramolecular binding motifs have been increasingly used for 3D-printing, these inks are largely optimized empirically for DIW. Hence, this review aims to establish a clear connection between the molecular understanding of the supramolecularly bound motifs and their viscoelastic properties at bulk. Herein, extrudable (but not self-supportive) and 3D-printable (self-supportive) polymeric materials that utilize noncovalent interactions, including hydrogen bonding, host-guest inclusion, metal-ligand coordination, micro-crystallization, and van der Waals interaction, have been discussed in detail. In particular, the rheological distinctions between extrudable and 3D-printable inks have been discussed from a supramolecular design perspective. Examples shown in this review also highlight the exciting macroscale functions amplified from the molecular design. Challenges associated with the hierarchical control and characterization of supramolecularly designed DIW inks are also outlined. The perspective of utilizing supramolecular binding motifs in soft materials DIW printing has been discussed. This review serves to connect researchers across disciplines to develop innovative solutions that connect top-down 3D-printing and bottom-up supramolecular design to accelerate the development of 3D-print soft materials for a sustainable future.

Sequential Cross-linking of Gallic Acid-Functionalized GelMA-Based Bioinks with Enhanced Printability for Extrusion-Based 3D Bioprinting

The printability of a photocross-linkable methacrylated gelatin (GelMA) bioink with an extrusion-based 3D bioprinter is highly affected by the polymer concentration and printing temperature. In this work, we developed a gallic acid (GA)-functionalized GelMA ink to improve the printability at room and physiological temperatures and to enable tissue adhesion and antioxidant properties. We introduced a sequential cross-linking approach using catechol-Fe³⁺ chelation, followed by photocross-linking. The results show that the ink formulation with 0.5% (w/v) Fe³⁺ in GelMA (30% modification) with 10% GA (GelMA30GA-5Fe) provided the optimum printability, shape fidelity, and structural integrity. The dual network inside the printed constructs significantly enhanced the viscoelastic properties. Printed cylinders were evaluated for their printing accuracy. The printed structures of GelMA30GA-5Fe provided high stability in physiological conditions over a month. In addition, the optimized ink also offered good tissue adhesion and antioxidant property. This catechol-based sequential cross-linking method could be adopted for the fabrication of other single-polymer bioinks.

A Dual-sensitive Hydrogel Based on Poly(Lactide-co-Glycolide)-Polyethylene Glycol-Poly(Lactide-co-Glycolide) Block Copolymers for 3D Printing

The thermo-sensitive hydrogel formed by triblock copolymers of polyethylene glycols and aliphatic polyesters serves as a promising candidate for bioink due to its excellent biodegradability and biocompatibility. However, the thermo-crosslinking alone cannot achieve a robust hydrogel to support the 3D printed constructs without collapse. Herein, a photo-crosslinkable group was introduced into the triblock copolymers to achieve a dual-sensitive hydrogel. A triblock copolymer poly(lactide-co-glycolide)-polyethylene glycol-poly(lactide-co-glycolide) decorated with acrylate group in the chain end was prepared. The obtained aqueous solutions of the copolymers could transform into hydrogels with excellent shear thinning properties and rapid elastic recovery properties spontaneously on the increase of temperature. The resulted thermogels also allowed for photo-crosslinking by exposure to ultraviolet radiation, with storage modulus dramatically increased to stable the printed constructs. Through a two-step crosslinking strategy, complicated tissue-like constructs with high shape fidelity can be printed using the dual-sensitive inks. Moreover, the mechanical strength, swelling ratio, and printability of the hydrogels can be tuned by varying the substitution rate of the acrylate group without compromising the inks' extrudability. We expect that the dual-sensitive hydrogels may be used as bioinks to print large constructs for applications in tissue engineering.

Mechanical Stabilization of Alginate Hydrogel Fiber and 3D Constructs by Mussel-Inspired Catechol Modification

Alginate is a representative biocompatible natural polymer with low cost for a variety of biomedical applications, such as wound dressing, drug delivery systems, tissue scaffolds, and 3D bioprinting. Particularly, the rapid and facile gelation of alginate via ionic interactions with divalent cations has been used for in situ 3D hydrogel fiber formation, which is potentially applicable to engineering cell alignment. However, challenges in enhancing the mechanical properties of alginate hydrogel fibers under physiological conditions are unresolved because of their fast dissociation by ion exchange. Herein, we report a stabilization strategy for alginate hydrogel fibers through mussel-inspired catechol chemistry, which involves inter-catechol crosslinking within a few minutes under basic conditions. The fabrication of catechol-tethered alginate hydrogel fibers through wet-spinning enabled the design of mechanically strong 3D constructs consisting of fibers. Catechol-to-quinone oxidation followed by covalent crosslinking enhanced the tensile strength of a single fiber. Additionally, the 'gluing' capability of the catechol stabilized the interface among the fibers, thus retaining the shape fidelity of the 3D constructs and encapsulating the cell density during culture. Our findings will be useful for designing bioink materials specialized in fibrous-type tissue scaffolds with mechanical stability.

Hydrogels of Polysaccharide Carboxymethyl Hydroxypropyl Guar Crosslinked by Multivalent Metal Ions

Abstract

Hydrogels of polysaccharide carboxymethyl hydroxypropyl guar crosslinked by chromium(III) ions are synthesized. The effect of crosslinker concentration on the mechanical behavior of the gels is studied, and the amount of chromium compounds able to interact with polymer chains and the amount of carboxyl groups of the polymer involved in crosslinking are compared. It is shown that the elastic modulus of the gels attains a constant value when not all but only about 10% functional groups interact with chromium compounds. At high concentrations, crosslinker molecules basically bind to one functional group; as a result, the gel recharges. This binding proceeds until all carboxyl groups are filled.

Effects of Processing Parameters of 3D Bioprinting on the Cellular Activity of Bioinks

In this review, few established cell printing techniques along with their parameters that affect the cell viability during bioprinting are considered. 3D bioprinting is developed on the principle of additive manufacturing using biomaterial inks and bioinks. Different bioprinting methods impose few challenges on cell printing such as shear stress, mechanical impact, heat, laser radiation, etc., which eventually lead to cell death. These factors also cause alteration of cells phenotype, recoverable or irrecoverable damages to the cells. Such challenges are not addressed in detail in the literature and scientific reports. Hence, this review presents a detailed discussion of several cellular bioprinting methods and their process-related impacts on cell viability, followed by probable mitigation techniques. Most of the printable bioinks encompass cells within hydrogel as scaffold material to avoid the direct exposure of the harsh printing environment on cells. However, the advantages of printing with scaffold-free cellular aggregates over cell-laden hydrogels have emerged very recently. Henceforth, optimal and favorable crosslinking mechanisms providing structural rigidity to the cell-laden printed constructs with ideal cell differentiation and proliferation, are discussed for improved understanding of cell printing methods for the future of organ printing and transplantation.