Bipolar Electrochemical Stimulation Using Conducting Polymers for Wireless Electroceuticals and Future Directions

Electrochemistry has become a powerful strategy to modulate cellular behavior and biological activity by manipulating electrical signals. Subsequent electrical stimulus-responsive conducting polymers (CPs) have advanced traditional wired electrochemical stimulation (ES) systems and developed wireless cell stimulation systems due to their electroconductivity, biocompatibility, stability, and flexibility. Bipolar electrochemistry (BPE), i.e., wireless electrochemistry, offers an effective pathway to modify wired ES systems into a desirable contactless mode, turning out a potential technique to offer fundamental insights into neural cell stimulation and neural network formation. This review commences with a brief discussion of the BPE technique and also the advantages of a bipolar electrochemical stimulation (BPES) system compared to traditional wired ES systems and other wireless ES systems. Then, the BPES system is elucidated through four aspects: the benefits of BPES, the key factors to establish BPES platforms for cell stimulation, the limits/barriers to overcome for current rigid materials in particular metals-based systems, and a brief overview of the concept proved by CPs-based systems. Furthermore, how to refine the existing BPES system from materials/devices modification that combine CP compositions with 3D fabrication/bioprinting technologies is elaborately discussed as well. Finally, the review ends together with future research directions, picturing the potential of BPES system in biomedical applications

In vitro characterisation of 3D printed platelet lysate-based bioink for potential application in skin tissue engineering

Wounds impact millions of patients every year and represent a serious cause of morbidity and mortality worldwide, yet current treatment outcomes are far from ideal. Therapies based on delivery of multiple growth factors offer a promising approach for optimal wound management; however, their high production cost, low stability, and lack of effective delivery system limits their application in the clinic. Platelet lysate is a suitable, abundant and cost-effective source of growth factors that play an important role in the healing cascade. The aim of this current work is to develop an extrusion-based bioink consisting of platelet lysate (PL) and gelatin methacryloyl (GelMA) (PLGMA) for the fabrication of a multifunctional 3D printed dermal equivalent. This bioink meets the essential requirements of printability in terms of rheological properties and shape fidelity. Moreover, its mechanical properties can be readily tuned to achieve stiffness that is equivalent to native skin tissue. Biologically relevant factors were successfully released in a sustainable manner for up to two weeks of study. The bioavailability of those factors was demonstrated by high cell viability, good cell attachment and improved proliferation of printed dermal fibroblasts. Furthermore, growth factors upregulated ECM synthesis and deposition by dermal fibroblasts after two weeks of culture

Electrowriting of silk fibroin: Towards 3D fabrication for tissue engineering applications

Electrowriting (EW) successfully combines the principles of two widely studied biofabrication techniques; 3D printing and electrospinning, and is capable of producing complex architectures, with submicron resolutions. However, the EW process so far is limited mainly to thermoplastic polymers of synthetic origin such as poly ε-caprolactone. Herein we demonstrate the EW of silk fibroin (SF) on an in-house build setup to identify the compatibility of water-based SF ink with EW. More specifically, we optimized the SF ink composition and investigated the effect of EW process parameters including ink concentration, collector translation speed, applied voltage, and distance between nozzle and collector on filament orientation and diameter. During SF ink preparation, control over the silk degumming process and ink concentration enabled modulation of rheology and surface tension properties of SF inks. We envision that the EW of hydrophilic SF will offer a new class of material structures with biological properties akin to natural systems

Novel 3D textile structures and geometries for electrofluidics

The integration of microfluidics with electric field control, commonly referred to as electrofluidics, has led to new opportunities for biomedical analysis. The requirement for closed microcapillary channels in microfluidics, typically formed via complex microlithographic fabrication approaches, limits the direct accessibility to the separation processes during conventional electrofluidic devices. Textile structures provide an alternative and low-cost approach to overcome these limitations via providing open and surface-accessible capillary channels. Herein, we investigate the potential of different 3D textile structures for electrofluidics. In this study, 12 polyester yarns were braided around nylon monofilament cores of different diameters to produce functional 3D core–shell textile structures. Capillary electrophoresis performances of these 3D core–shell textile structures both before and after removing the nylon core were evaluated in terms of mobility and bandwidth of a fluorescence marker compound. It was shown that the fibre arrangement and density govern the inherent capillary formation within these textile structures which also impacts upon the solute analyte mobility and separation bandwidth during electrophoretic studies. Core–shell textile structures with a 0.47 mm nylon core exhibited the highest fluorescein mobility and presented a narrower separation bandwidth. This optimal textile structure was readily converted to different geometries via a simple heat-setting of the central nylon core. This approach can be used to fabricate an array of miniaturized devices that possess many of the basic functionalities required in electrofluidics while maintaining open surface access that is otherwise impractical in classical approaches

Electrofluidic control for textile-based cell culture: Identification of appropriate conditions required to integrate cell culture with electrofluidics

Electric field–driven microfluidics, known as electrofluidics, is a novel attractive analytical tool when it is integrated with low-cost textile substrate. Textile-based electrofluidics, primarily explored on yarn substrates, is in its early stages, with few studies on 3D structures. Further, textile structures have rarely been used in cellular analysis as a low-cost alternative. Herein, we investigated novel 3D textile structures and develop optimal electrophoretic designs and conditions that are favourable for direct 3D cell culture integration, developing an integrated cell culture textile-based electrofluidic platform that was optimised to balance electrokinetic performance and cell viability requirements. Significantly, there were contrasting electrolyte compositional conditions that were required to satisfy cell viability and electrophoretic mobility requiring the development of and electrolyte that satisfied the minimum requirements of both these components within the one platform. Human dermal fibroblast cell cultures were successfully integrated with gelatine methacryloyl (GelMA) hydrogel-coated electrofluidic platform and studied under different electric fields using 5 mM TRIS/HEPES/300 mM glucose. Higher analyte mobility was observed on 2.5% GelMA-coated textile which also facilitated excellent cell attachment, viability and proliferation. Cell viability also increased by decreasing the magnitude and time duration of applied electric field with good cell viability at field of up to 20 V cm−1

Catechol functionalized ink system and thrombin-free fibrin gel for fabricating cellular constructs with mechanical support and inner micro channels

The development of 3D bio printing technology has contributed to protocols for the repair and regeneration of tissues in recent years. However, it is still a great challenge to fabricate structures that mimic the complexity of native tissue, including both the biomechanics and microscale internal structure. In this study, a catechol functionalized ink system was developed to produce tough and elastic scaffolds with built-in micro channels that simulate the vascular structure. And a skin model was designed to evaluate the cytocompatibility of the scaffolds. The mechanical support stemmed from the double network based on catechol-hyaluronic acid (HACA) and alginate, the micro channels were generated using sacrificial gelatin. HACA/alginate and gelatin were firstly printed using a 3D extrusion printer. Thrombin-free fibrinogen were then mixed with human dermal fibroblasts and introduced to the printed scaffolds to induce gelation. An immortal human keratinocyte cell line was introduced on top of the cellular construct to mimic the full thickness skin structure. The printed scaffolds demonstrated high elasticity and supported the formation of a double-layered cell-laden skin like structure. The results suggest the 3D printing platform developed here provides a platform for skin regeneration and could be explored further to engineer functional skin tissue by incorporation of other types of cells

Composite Tissue Adhesive Containing Catechol-Modified Hyaluronic Acid and Poly‑l‑lysine

Commercial tissue adhesives such as fibrin, albumin-glutaraldehyde, and cyanoacrylates often suffer from the limitations of adverse inflammatory reactions, lack of bioactivity, and/or weak wet adhesion. There is a need to develop advanced tissue adhesives which possess adequate wet adhesion and appropriate biodegradability and biocompatibility. The wet adhesion of the catechol group to a variety of substrates is well-known. Further, it undergoes Michael addition with an amine or thiol group, which makes catechol-containing polymers appealing as tissue adhesives because there are abundant amine and thiol groups in native tissue. We present here a composite tissue adhesive based on a catechol-modified polymer that utilizes poly-l-lysine (PLL) as a bridging molecule to promote the interfacing with cells and tissues. Hyaluronic acid (HA) was chosen here as the polymer backbone for functionalization with catechol moieties, which is attributable to its multiple biological activities. The cross-linking conditions of catechol-functionalized HA (HACA) were optimized, and the swelling and degradation behavior of the cross-linked hydrogels were characterized. The PLL/HACA-based adhesive demonstrated good adhesion to hydrogels derived from collagen and gelatin that act as a simplified soft tissue model, and to porcine skin tissue. Moreover, the adhesive supported culture of a human umbilical vein endothelial cell line (HUV-EC-C) with high cell viability and formation of capillary-like structure. This may bring added benefit by means of promoting angiogenesis, therefore promoting the integration between host tissue and implant. Our results indicate that PLL/HACA could be a promising tissue adhesive for multiple internal uses

On demand, wireless electrochemical release of brain derived neurotrophic factor

Organic conductive polymers are prime candidates for the on demand or controlled release of neurotrophic proteins which can enhance the electrode-neural interface. In this study, bipolar electrochemistry (BPE) is employed to provide a wireless electrical stimulation that avoids the need for the direct physical connection necessary for conventional approaches. Brain-derived neurotrophic factor (BDNF) was incorporated into polypyrrole (PPy) with poly (2-methoxy-5 aniline sulfonic acid) (PMAS) as a dopant during the course of electrochemical synthesis. The synthetic PPy-PMAS-BDNF material acts as the bipolar electrode and is placed within an electric field generated by two driving electrodes. Controlled release of BDNF is demonstrated, which is wireless powered by BPE. This is likely due to the wirelessly activated redox reactions which induce gaps/channels within the structure. Quantification of the BDNF reveals significant differences in the controlled-release properties of the films driven by BPE compared to conventional wired electrochemistry. Human neuroblastoma cells (SH-SY5Y) cultured on the PPy-PMAS-BDNF electrode were subjected to one-week of wireless electrostimulation. Neurite outgrowth was significantly improved when the polymer containing BDNF and the film BPE stimulation. The data suggest that when the BPE is applied, the cells simultaneously respond to the wirelessly released BDNF and the wireless electrical stimulation through the bipolar electroactive polymer electrode. This synergistic effect promotes enhanced neurite outgrowth across the electrodes

Fabrication and Characterization of an Electro-Compacted Collagen/Elastin/Hyaluronic Acid Sheet as a Potential Skin Scaffold

The development of biomimetic structures with integrated extracellular matrix (ECM) components represents a promising approach to biomaterial fabrication. Here, an artificial ECM, comprising the structural protein collagen I and elastin (ELN), as well as the glycosaminoglycan hyaluronan (HA), is reported. Specifically, collagen and ELN are electrochemically aligned to mimic the compositional characteristics of the dermal matrix. HA is incorporated into the electro-compacted collagen-ELN matrices via adsorption and chemical immobilization, to give a final composition of collagen/ELN/HA of 7:2:1. This produces a final collagen/ELN/hyaluronic acid scaffold (CEH) that recapitulates the compositional feature of the native skin ECM. This study analyzes the effect of CEH composition on the cultivation of human dermal fibroblast cells (HDFs) and immortalized human keratinocytes (HaCaTs). It is shown that the CEH scaffold supports dermal regeneration by promoting HDFs proliferation, ECM deposition, and differentiation into myofibroblasts. The CEH scaffolds are also shown to support epidermis growth by supporting HaCaTs proliferation, differentiation, and stratification. A double-layered epidermal-dermal structure is constructed on the CEH scaffold, further demonstrating its ability in supporting skin cell function and skin regeneration

Novel Collagen Surgical Patches for Local Delivery of Multiple Drugs

Effective control of post-operative inflammation after tissue repair remains a clinical challenge. A tissue repair patch that could appropriately integrate into the surrounding tissue and control inflammatory responses would improve tissue healing. A collagen-based hybrid tissue repair patch has been developed in this work for the local delivery of an anti-inflammatory drug. Dexamethasone (DEX) was encapsulated into PLGA microspheres and then co-electrocompacted into a collagen membrane. Using a simple process, multiple drugs can be loaded into and released from this hybrid composite material simultaneously, and the ratio between each drug is controllable. Anti-inflammatory DEX and the anti-epileptic phenytoin (PHT) were co-encapsulated and released to validate the dual drug delivery ability of this versatile composite material. Furthermore, the Young’s modulus of this drug-loaded collagen patch was increased to 20 KPa using a biocompatible riboflavin (vitamin B2)-induced UV light cross-linking strategy. This versatile composite material has a wide range of potential applications which deserve exploration in further research