Conductive polymers have promising applications in the field of tissue engineering as tissue scaffolds. Many tissue types respond favorably to electrical stimulation, because of this conductive polymers can be used for the regeneration of damaged tissue. This review will focus on the synthesis and fabrication of conductive polymers as well as their applications in tissue engineering.
All cells exhibit some form of electrical excitability, from voltage gated ion channels to muscle contractions and heart beats electromagnetic fields are critical to the basic functions of life. Galvani famously showed in 1794 that a frog leg will contract when touched with the cut sciatic nerve of the other leg.This scientific breakthrough led to extensive research of electromagnetism within organisms. Electromagnetic fields have been found to affect a variety of biological processes including angiogenesis, cell division, cell signaling, nerve sprouting, prenatal development, and wound healing . Only in recent decades with the development of molecular and cellular technology has the link between cell biology and bioelectricity been discovered . This growth in understanding has led to the development of a variety of electrically conductive devices for uses in biomedical engineering. Devices that use electrical stimulation that have already been approved by the FDA include the pacemaker, deep brain stimulators and vagal nerve stimulators .
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Next, to determine if contraction via the EMC pathway requires extracellular or intracellular calcium, the second type of stimulus was used and the tissue was stimulated using calcium free K+-depolarising solution. The bathing solution in this experiment was calcium free solution to make sure all extracellular calcium was eliminated, as without calcium, the EMC pathway is expected to produce no response.
Figure 1. A Comparison of a CAP Recording of an Earthworm to an Intercellular Recording. The “taller” graph is a depiction of a microelectrode recording of an action potential inside a neuron. The highlighted graph is a depiction of an extracellular recording suction electrode on a giant earthworm. The dotted line represents the minimum voltage needed to depolarize an action potential. The results are obtained from a PowerLab Data Acquisition Unit and a LabChart computerized software. The data are recorded in units of milliseconds and millivolts.
Impulses will travel along the neuron pathways as the electrical charges move across each neural membrane. Ions that are moving across the membrane can cause the impulse to move along the nerve cells.
Microfluidic chips allow for the manipulation, at small quantities of neuronal cells. Further, these chips allow for precise temporal and spatial control. This model is one that can be useful in the framework of neurodegeneration. Deleglise et al (2013) fabricated a 3 chamber microfluidic chip. The chambers held one of: coritical neuron soma and dendrites, cortical axons, or striatal neurons. The chip was designed to replicate an oriented neuronal connection from the coritcal to the striatal cells. Through the use of a chemically induced axotomy, by adding fluid to the central chamber (housing the cortical axon), showed that their chip could be used to simulate a lesion in the neuronal network. An emphasis was placed on the protection of synapses, and event that in axotomy studies, traumatic injury and in many neurodegenerative disorders precedes the loss of neuronal cell soma and axons. They then showed that zVAD-fmk, a caspase inhibitor and resveratrol did not show synaptic protection, while NAD+ and Y27632, a Rho Kinase inhibitor showed significant synaptic protection, despite the mechanism not being clear. Pointing at potential therapeutic targets for neurodegeneration. This can also be further looked at from the functionality of the chip - it is a useful tool in the evaluation of drugs in the axotomy model they presented.
Polypyrrole is a conducting polymer which has non-degenerate conduction band in the ground state. The polarons and bipolarons are the dominant charge carriers in these polymers. The most widely accepted method of conductivity in these systems involve charge transport along the polymer chains, as well as hopping of carriers (holes, bipolarons). A common feature of intrinsically conducting polymers is the alternate double and single bond in the polymer backbone , referred as pi bond conjugation. The conductivity is due to four conditions namely, the existence of charge carriers, an overlap of molecular orbits to aid mobility of the carriers, mobility of pi bond and hopping of charges between polymer chains. These conducting polymers are similar to semiconductors with a filled valence band and an empty conduction band separated by energy gap. when polymers are doped new bands are created in the gap, making the paths for the electrons to move through these bands and increasing the conductivity of the materials. In the undoped form Polypyrrole is a insulator. The electronic and transport properties of the conducting polymers are mainly due to the major role of bipolarons. The positive charges commonly called as polarons created on the polymer backbone are responsible for electrical conductivity. The conductivity of polypyrrole depends on synthesis
Smooth muscle cells of the ileum spontaneously contract due to the presence of pacemaker cells, called Cajal cells (Widmaier et al., 2014d). However, these smooth muscle they are also innervated by autonomic nerves, which can be stimulated to change contraction rates by stimulating. Figure 1, shows the effect of nerve stimulation of 17volts on isolated ileum tissue. Stimulating sympathetic (sympathetic nerves was stimulated for this particular tissue), causes release of noradrenaline, which inhabits contraction of smooth muscle cells. Furthermore, according to table 1, there is a -58.83% change in contraction amplitude. It can be extrapolated that fewer smooth muscles are contracting. At lower voltages, a weaker response was observed, as voltage is increased a stronger response was observed. Increasing the voltage, means more neurons are being recruited (Widmaier et al., 2014b). In this particular experiment, stimulation of nerves around the mesenteric artery caused an inhibitory response, therefore at higher voltages, more smooth muscles are being inhibited.
Promising materials for nanofibrous scaffolds include poly (ɛ-caprolactone) (PCL) in combination with gelatin because electrospun PCL closely resembles the ECM and gelatin is a natural biopolymer with biodegradable and biocompatible properties. Previous studies in the field of tissue engineering have focused on the biological properties and biocompatibility of NGCs, but little work has been done to study the biomechanical properties of NGCs and how they compare to native peripheral nerve tissue in vivo. This is an important area of study because the NGCs must be sufficiently elastic to avoid tension at the injury site, but cannot collapse due to the patient’s movements . Designing NGCs with favorable mechanical properties is necessary for successful axonal growth and nerve regeneration. This research will provide a better understanding of the mechanical properties of peripheral nerve tissue and NGCs as well as develop a method to test the performance of NGCs in
An eel was placed in a naturalistic experimental environment with other fish and the fishes’ response to high-voltage pulses was observed. If there was a strong enough discharge, the fish was unable to move on its on accord and was captured by the eel. A pitched fish was placed behind an agar barrier, which received the same discharge as the eel directed toward earthworms placed in the same environment. In order to determine if the discharges induced the muscle movement by initiating action potentials or by activating the motor neurons in the fish, two fishes were pitched; one of the fish was injected with an AcH antagonist and the other was injected with a placebo. To test doublet and triplet discharges
Doctors implant small wire thin electrodes on both the right and left side of the brain through small holes made in the top of the skull. Each electrode has four contacts and when turned on the stimulator transmits low volts of electrical pulses along the four contacts to the nerves inside the brain
How 5-HT modulates NMDA receptor activation is a key question of interest. Despite being cation channels, NMDA receptors have non-linear, voltage-dependent conductance (Mayer and Westbrook, 1987). This property results from the voltage-dependent Mg2+ blockade of the receptor channels (Mayer et al., 1984; Nowak et al., 1984) and thus leads to the negative slope conductance in the current-voltage relationship (i.e. I-V curve; Nowak et al., 1984; Flatman et al., 1983; MacDonald et al., 1982). Because of the voltage-dependent conductance, NMDA receptor activation generates intrinsic voltage oscillations in spinal neurons of rat (Hochman et al., 1994a; Hochman et al., 1994b) and amphibian (Sillar and Simmers, 1994a; Sillar and Simmers, 1994b)
Muscles; the way we get around. With smooth muscle gripping bones, creating movement with electric current. Electrical signals flow from the brain down the spinal cord to open the calcium floodgates. With the flow of calcium, the muscles contract, and because they’re attached to bones, the flow of calcium leads to muscles pulling on the bones, which cause movement. While the contraction of muscles starts from the brain to get muscles to move from either slightly or greatly, electricity can be used instead of the brain to create movement.
In chapter three of Frances Ashcroft’s book The Spark of Life, Ashcroft details the history and discovery of nerve impulses and their role and workings in the human body. He details everything from their role in the wiring of the body to how over the years their research has developed human’s understanding of how nerves work. He incorporates many stories of examples that reveal their mechanisms and stories of scientists that researched and discovered key breakthroughs about them. He also describes how important they are for life and the many instances where death or life-threatening consequences occurred because of their disrupting. Ashcroft organizes this information into different sections with various titles that introduce these ideas.
In addition, the wires will need to conduct electrical signals received from the microphone and processor/stimulator and be flexible enough to allow navigating to and from their desired destinations. To accomplish this, a conductive material with a biocompatible coating is likely to be the most feasible approach. Currently, the wires in cochlear implants are composed of platinum conductive wires coated with silicone and this approach is used for good reason. Silicone, as previously stated, has outstanding biocompatibility, flexibility, stability, softness, water-tightness, resistance to corrosion, and acts as an insulator from electrical stimulus. While platinum is used as the conductive material because it has low chemical reactivity, is highly corrosion resistant, biocompatible, flexible, and does not display stimulus-induced corrosion resistance like most other conductive metals, meaning it should last the lifetime of the patient. These properties simply make it the greatest available conductive material for this application, and by coating it in silicone you remove any potential unwanted exposure to the surrounding
Also unlike electrical shocks, sequential light pulses can be applied repetitively, as these do not require the charging of a capacitator to generate high-voltage fields. Experimental results in mice hearts showed that 4 consecutive light pulses instead of 1 increased the termination rate of VT from 85% to