Glial cells influence cardiac permittivity as evidenced through in vitro and in silico models.

Excitation-contraction (EC) coupling in the heart has, until recently, been solely accredited to cardiomyocytes. The inherent complexities of the heart make it difficult to examine non-muscle contributions to contraction in vivo, and conventional in vitro models fail to capture multiple features and cellular heterogeneity of the myocardium. Here, we report on the development of a 3D cardiac μTissue to investigate changes in the cellular composition of native myocardium in vitro. Cells are encapsulated within micropatterned gelatin-based hydrogels formed via visible light photocrosslinking. This system enables spatial control of the microarchitecture, perturbation of the cellular composition, and functional measures of EC coupling via video microscopy and a custom algorithm to quantify beat frequency and degree of coordination. To demonstrate the robustness of these tools and evaluate the impact of altered cell population densities on cardiac μTissues, contractility and cell morphology were assessed with the inclusion of exogenous non-myelinating Schwann cells (SCs). Results demonstrate that the addition of exogenous SCs alter cardiomyocyte EC, profoundly inhibiting the response to electrical pacing. Computational modeling of connexin-mediated coupling suggests that SCs impact cardiomyocyte resting potential and rectification following depolarization. Cardiac μTissues hold potential for examining the role of cellular heterogeneity in heart health, pathologies, and cellular therapies

000524692.pdf

The field of tissue engineering has benefited greatly from the broad  development of natural and synthetic polymers. Extensive work in neural  engineering has demonstrated the value of conductive materials to  improve spontaneous neuron activity as well as lowering the necessary  field parameters for exogenous electrical stimulation. Further, cell  fate is directly coupled to the mechanical properties of the cell  culture substrate. Increasing the conductivity of hydrogel materials  often necessitates the addition of dopant materials that facilitate  electron mobility. However, very little electron transfer is observed in  native cell signaling and most of these materials are opaque, severely  limiting microscopy applications commonly employed to assess cell  culture morphology and function. To overcome these shortcomings, the  inclusion of an ionic liquid, choline acrylate, into the backbone of a  modified collagen polymer increases the bulk conductivity 5-fold at a  1:1 ratio while maintaining optical transmission of visible light. Here,  we explore how the inclusion of choline acrylate influences bulk  material properties including the mechanical, swelling, and optical  properties of our hydrogels, referred to as Gel-Amin hydrogels, as a  material for tissue culture.  Despite an increase in swelling over  traditional GelMA materials, the conductive hydrogels support whole  dorsal root ganglia encapsulation and outgrowth. Our results indicate  that our Gel-Amin system holds potential for neural engineering  applications and lowering the required charge injection for the  application of exogenous electrical stimulation. This is this first time  an ionic liquid-hydrogel system has been used to culture and support  primary neurons in vitro.</p

Electrical stimuli in the central nervous system microenvironment

Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue

Bioactive Organic Rosette Nanotubes Support Sensory Neurite Outgrowth

Regardless of the intervention for peripheral nerve repair, slow rates of axonal regeneration often result in poor clinical outcomes. Thus, using new materials such as biologically inspired, biocompatible, organic rosette nanotubes (RNTs) could provide a tailorable scaffold to modulate neurite extension and attachment for improved nerve repair. RNTs are obtained through the spontaneous self-assembly of a synthetic DNA base analogue featuring the hydrogen bond triads of both guanine and cytosine, the G∧C base. Here, we investigated the potential of RNTs functionalized with lysine and Arg-Gly-Asp-Ser-Lys (<u>RGD</u>SK) peptide to support neural growth. We hypothesized that (a) due to their dimensions, the RNTs would support neuron attachment, and (b) their conjugation to the integrin-binding peptide <u>RGD</u>SK would further enhance neurite outgrowth compared to unfunctionalized RNT. Neurite extension was examined on a variety of RNT structures, including RNT with a lysine side chain (K1), a mixture of the K1 and a free RGDS peptide, RNT alone, an RGDSK-functionalized RNT, in addition to poly-d-lysine and laminin controls. Both whole dorsal root ganglion (DRG) and single dissociated DRG neurons were seeded onto RNT-coated substrates containing various ratios of peptides. Analysis of neuron morphometrics showed that RNT blends support DRG neuron attachment and neurite extension, with RGDS presentation increasing neurite outgrowth from whole DRG by up to 47% over a 7-day period compared to K1 alone (<i>p</i> < 0.013). In addition, while RNTs increased the sprouting of primary neurites extending from dissociated DRG neurons, the total neurite outgrowth per neuron remained the same. These results show that functionalized biomimetic RNTs provide a support for neurite growth and extension and have the ability to modulate neuronal morphology. These results also pave the way for the design of injectable RNT-based nanomaterials that support guided neural regeneration following traumatic injury

Electroconductive Gelatin Methacryloyl-PEDOT:PSS Composite Hydrogels: Design, Synthesis, and Properties

Electroconductive hydrogels are used in a wide range of biomedical applications, including electrodes for patient monitoring and electrotherapy, or as biosensors and electrochemical actuators. Approaches to design electroconductive hydrogels are often met with low biocompatibility and biodegradability, limiting their potential applications as biomaterials. In this study, composite hydrogels were prepared from a conducting polymer complex, poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) dispersed within a photo-crosslinkable naturally derived hydrogel, gelatin methacryloyl (GelMA). To determine the impact of PEDOT:PSS loading on physical and microstructural properties and cellular responses, the electrical and mechanical properties, electrical properties, and biocompatibility of hydrogels loaded with 0–0.3% (w/v) PEDOT:PSS were evaluated and compared to GelMA control. Our results indicated that the properties of the hydrogels, such as mechanics, degradation, and swelling, could be tuned by changing the concentration of PEDOT:PSS. In particular, the impedance of hydrogels decreased from 449.0 kOhm for control GelMA to 281.2 and 261.0 kOhm for hydrogels containing 0.1% (w/v) and 0.3% (w/v) PEDOT:PSS at 1 Hz frequency, respectively. In addition, an <i>ex vivo</i> experiment demonstrated that the threshold voltage to stimulate contraction in explanted abdominal tissue connected by the composite hydrogels decreased from 9.3 ± 1.2 V for GelMA to 6.7 ± 1.5 V and 4.0 ± 1.0 V for hydrogels containing 0.1% (w/v) and 0.3% (w/v) PEDOT:PSS, respectively. <i>In vitro</i> studies showed that composite hydrogels containing 0.1% (w/v) PEDOT:PSS supported the viability and spreading of C2C12 myoblasts, comparable to GelMA controls. These results indicate the potential of our composite hydrogel as an electroconductive biomaterial

Photocrosslinkable Gelatin/Tropoelastin Hydrogel Adhesives for Peripheral Nerve Repair.

Suturing peripheral nerve transections is the predominant therapeutic strategy for nerve repair. However, the use of sutures leads to scar tissue formation, hinders nerve regeneration, and prevents functional recovery. Fibrin-based adhesives have been widely used for nerve reconstruction, but their limited adhesive and mechanical strength and inability to promote nerve regeneration hamper their utility as a stand-alone intervention. To overcome these challenges, we engineered composite hydrogels that are neurosupportive and possess strong tissue adhesion. These composites were synthesized by photocrosslinking two naturally derived polymers, gelatin-methacryloyl (GelMA) and methacryloyl-substituted tropoelastin (MeTro). The engineered materials exhibited tunable mechanical properties by varying the GelMA/MeTro ratio. In addition, GelMA/MeTro hydrogels exhibited 15-fold higher adhesive strength to nerve tissue ex vivo compared to fibrin control. Furthermore, the composites were shown to support Schwann cell (SC) viability and proliferation, as well as neurite extension and glial cell participation in vitro, which are essential cellular components for nerve regeneration. Finally, subcutaneously implanted GelMA/MeTro hydrogels exhibited slower degradation in vivo compared with pure GelMA, indicating its potential to support the growth of slowly regenerating nerves. Thus, GelMA/MeTro composites may be used as clinically relevant biomaterials to regenerate nerves and reduce the need for microsurgical suturing during nerve reconstruction