Enhanced Electroactivity, Mechanical Properties, and Printability through the Addition of Graphene Oxide to Photo-Cross-linkable Gelatin Methacryloyl Hydrogel

Abstract

The human tissues most sensitive to electrical activity such as neural and muscle tissues are relatively soft, and yet traditional conductive materials used to interface with them are typically stiffer by many orders of magnitude. Overcoming this mismatch, by creating both very soft and electroactive materials, is a major challenge in bioelectronics and biomaterials science. One strategy is to imbue soft materials, such as hydrogels, with electroactive properties by adding small amounts of highly conductive nanomaterials. However, electroactive hydrogels reported to date have required relatively large volume fractions (>1%) of added nanomaterial, have shown only modest electroactivity, and have not been processable via additive manufacturing to create 3D architectures. Here, we describe the development and characterization of improved biocompatible photo-cross-linkable soft hybrid electroactive hydrogels based on gelatin methacryloyol (GelMA) and large area graphene oxide (GO) flakes, which resolve each of these three limitations. The addition of very small amounts (less than a 0.07% volume fraction) of GO to a 5% w/v GelMA hydrogel resulted in a dramatic (∼35-fold) decrease in the impedance at 1 Hz compared with GelMA alone. The GelMA/GO coated indium tin oxide (ITO) electrode also showed a considerable reduction in the impedance at 1 kHz (down to 170 Ω compared with 340 Ω for the GelMA-coated ITO), while charge injection capacity increased more than 6-fold. We attribute this enhanced electroactivity to the increased electroactive surface area contributed by the GO. Despite this dramatic change in electroactivity, the GelMA/GO composite hydrogels' mechanical properties were only moderately affected. Mechanical properties increased by ∼2-fold, and therefore, the hydrogels' desired softness of <4 kPa was retained. Also, we demonstrate how light attenuation through the gel can be used to create a stiffness gradient with the exposed surface of the gel having an elastic modulus of <1.5 kPa. GO addition also enhanced the rheological properties of the GelMA composites, thus facilitating 3D extrusion printing. GelMA/GO enhanced filament formation as well as improved printability and the shape fidelity/integrity of 3D printed structures compared with GelMA alone. Additionally, the GelMA/GO 3D printed structures presented a higher electroactive behavior than nonprinted samples containing the same GelMA/GO amount, which can be attributed to the higher electroactive surface area of 3D printed structures. These findings provide new rational choices of electroactive hydrogel (EAH) compositions with broad potential applications in bioelectronics, tissue engineering, and drug delivery.

Exosomes‐Loaded Electroconductive Hydrogel Synergistically Promotes Tissue Repair after Spinal Cord Injury via Immunoregulation and Enhancement of Myelinated Axon Growth

“…[ 7 ] It has been established that NSCs exhibit poor survival in very soft (<0.1 kPa) or very hard (>100 kPa) materials and tend to differentiate into neurons in reasonably soft materials (≈0.1–1 kPa) and into glial cells in slightly stiffer materials (≈7–10 kPa). The storage moduli of GM‐based or PPy‐based electroconductive hydrogels applied in the field of myogenic differentiation, skeletal muscle regeneration, and neural tissue engineering ranges from 10 2 –10 4 Pa. [ 35,36 ] In this study, the storage moduli of the GMPE hydrogel was 1056.0 ± 133.1 Pa, which matched neural tissue mechanics (600–3000 Pa) and indicates its suitability for soft nerve tissues engineering. [ 7 ] The conductivity of GMP (1.83 × 10 −3 S cm −1 ) and GMPE (1.49 × 10 −3 S cm −1 ) hydrogels were both superior to that of the GM hydrogel.…”

Injectable, Self‐healing, and 3D Printable Dynamic Hydrogels

“…The high absorption coefficient for a 405 nm light through the graphene oxide suggested that the UV light intensity would be significantly attenuated by quenching through dark 3D printed hydrogels. [ 50 ] Therefore, the gold ion crosslinking system allowed the gold ions to diffuse into F127‐LA/AuNP/nSi to crosslink LA ligands and produce gold nanoparticles, which might benefit the electrochemical performance of conductive hydrogels. For example, reduced graphene oxide (rGO) was introduced to fabricate conductive ink.…”

3D bioprinted GelMA/GO composite induces osteoblastic differentiation

“…Some results have shown that graphene oxide (GO) enhanced the mechanical properties and improved the printability and shape integrity of 3D printed structures compared with GelMA alone. 11-13 The enhanced mechanical properties of GO are supposed to be due to the covalent interaction between GO and methacrylate groups on the GelMA chain. 12…”