Interfaces in Composite Materials - Biointerfaces: Where Material Meets Biology - page 168

thorough the depth of stem cells-seeded hydrogels. Combination of a spatial
confinement and dynamic compression produced a construct with high
glycoaminoglycan accumulation in its bottom half but high collagen accu-
mulation in its top half with no signs of hypertrophy and calcification
throughout the construct. 94

d n 3 r 4 n g | 1

7.4.2 Neuromuscular Prosthesis-Tissue Interface
The electrical properties of the neural and cardiac prosthesis-tissue inter-
face have an impact on the safety, function and hence longevity of the
prosthesis. Examples of these prostheses (electrodes) include cochlea im-
plants 160 and artificial pacemakers. 161 These medical devices translate the
electrical impulses delivered by an electrode contacting the acoustic nerve or
cardiac muscle into perception of sound or regulation of the heart beat re-
spectively. The stability of the neural and cardiac electrode-tissue interface
determines the sensitivity of the electrode to small electrical signals and also
its ability to transfer the processed signals to the adjacent tissues to perform
the required function. 162 In this respect, composite multi-walled carbon
nanotube-polyelectrolytes (MWNT-PE) substantially outperformed as elec-
trodes than other state of the art interface materials [e.g., electrochemically
deposited iridium oxide (IrOx) and poly(3,4-ethylenedioxythiophene
(PEDOT)]. 162 Composites such as polypyrrole-single-walled carbon nanotube
(PPy-SWCNT) were also used as a thin film coating on the traditional plat-
inum microelectrodes. This composite coating improved the microelectrode
electrochemical interaction (by reducing its impedance while improving the
signal-to-noise ratio) 163 and neurite outgrowth pheochromocytoma cells when
implanted in the cortex of rats. 164
Understanding brain tissue responses represents the forefront of neural
engineering. Recent trends in advanced biomaterials and neural inter-
faces 165,166 involve bio-inspired exploration of new prototypes with improved
biocompatibility and lifetime while maintaining neuronal viability. Recent
advances in technology, e.g., brain activity analysis and computational al-
gorithms as well as the brain-machine interface (BMI)/brain-computer
interface (BCI) have gained importance as a strategy for improving impaired
neuromuscular systems. 166 Developing long lasting, highly selective,
implantable neural interface devices that can record the neural activity from
small, targeted groups of neurons for years with high fidelity and reliability
has been attempted. These devices are based on composite electrodes con-
sisting of a carbon-fiber core, a thin film coating based on poly(p-xylylene) as
a dielectric barrier and a recording pad based on poly(thiophene). These
devices may be used as brain-controlled prosthetic devices. They were ultra-
small (i.e., one order of magnitude smaller) but more mechanically com-
plaint with the brain tissue than the traditional recording electrodes. They
also elicited much reduced chronic reactive tissue reactions and enabled
single-neuron recording capability in acute and early chronic experiments in
rats. 167

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