Implantable Bioelectronic Scaffolds Laden with Therapeutic Schwann Cells for Nerve Repair

Nerve injuries can occur following physical trauma and, in severe cases, the nerve is completely severed (full transection of the axons), creating a gap that requires surgical intervention to allow regeneration. The current gold standard of treatment for severe nerve injuries is to obtain nerve tissue from elsewhere in the patient’s body and use it as a graft to bridge the gap. This presents various problems including loss of nerve function at the donor site, limited availability of donor tissue, and poor functional recovery. Electrical stimulation has shown promise in both direct applications to less severe nerve injuries¹ and to the cells responsible for nerve regeneration². This work aims to create a bioelectronic, cell laden construct that can be used to replace, and potentially surpass, the current gold standard autograft for treatment for nerve injuries.<br/><br/>The artificial bioelectronic scaffolds are comprised of a composite material of temperature controlled, templated oxidative polymerized polypyrrole (PPy) nanoparticles combined with fibrillar collagen to create a homogenous hydrogel. These gels were then processed using a technique known as gel aspiration-ejection (GAE). GAE aligns the material within the hydrogel, whilst removing the bulk of the entrapped water. Furthermore, our work investigates Schwann cells, a therapeutic cell type for nerve regeneration, and the effect of electrical stimulation through gene analysis of key repair phenotype genes.<br/><br/>This results in dense, aligned conductive scaffolds suitable for implantation in cases of severe nerve injury. An advantage of the GAE technique is that during the manufacturing process, therapeutic cells, such as Schwann cells³, can be directly incorporated and distributed throughout the composite hydrogel, creating a cell laden, bioelectronic construct.<br/><br/>Monolayer Schwann cell cultures were investigated to detect gene expression changes caused by a single application of electrical stimulation. This experiment revealed significant upregulation of pro-regenerative gene expression due to the external stimulation, and importantly, a significant upregulation of c-Jun, often cited as the key transcription factor of Schwann cell repair phenotype⁴. Furthermore, upregulation in gene expression of neurotrophic factors was also shown following electrical stimulation. Our work has shown that it is possible to create these cell laden bioelectronic scaffolds. Therapeutic cells within the constructs do not have altered viability, indicating that the material is biocompatible, and the fabrication process is suitable.<br/><br/>By developing bioelectronic cell laden tissue engineered constructs for peripheral nerve repair, we aim to enhance both the therapeutic cells within the construct, and the body’s endogenous nerve repair program. Through the process of implanting a bioelectronic scaffold, subsequent applications of electrical stimulation following surgical repair may be used throughout the regenerative process, to further augment the nerve regeneration process. Future work involves conducting the same gene analysis experiment on the therapeutic cell laden bioelectronic constructs to assess if conductive material augments the benefits shown within monolayer cultures.<br/><br/>1. Chan, K.M., Curran, M.W.T. & Gordon, T. The use of brief post-surgical low frequency electrical stimulation to enhance nerve regeneration in clinical practice. <i>J Physiol</i> <b>594</b>, 3553-3559 (2016).<br/>2. Trueman, R.P., Ahlawat, A.S. & Phillips, J. A shock to the (nervous) system: Bioelectricity within peripheral nerve tissue engineering. <i>Tissue Eng Part B Rev</i> (2021).<br/>3. Muangsanit, P. et al. Rapidly formed stable and aligned dense collagen gels seeded with Schwann cells support peripheral nerve regeneration. <i>J Neural Eng</i> <b>17</b>, 046036 (2020).<br/>4. Wagstaff, L.J. et al. Failures of nerve regeneration caused by aging or chronic denervation are rescued by restoring Schwann cell c-Jun. <i>eLife</i> <b>10</b>, e62232 (2021).