Trends in Biotechnology
Volume 31, Issue 12, December 2013, Pages 678-687
Journal home page for Trends in Biotechnology

Review
Surface biotechnology for refining cochlear implants

https://doi.org/10.1016/j.tibtech.2013.09.001Get rights and content

Highlights

  • Surface biotechnology has successfully enhanced cochlear implant performance.

  • Surface modification, coatings, and drug delivery are promising strategies.

  • Novel surface biotechnologies minimize surgical complications.

  • Cochlear implant technology is highly transferrable to other neural implants.

The advent of the cochlear implant is phenomenal because it is the first surgical prosthesis that is capable of restoring one of the senses. The subsequent rapid evolution of cochlear implants through increasing complexity and functionality has been synchronized with the recent advancements in biotechnology. Surface biotechnology has refined cochlear implants by directly influencing the implant–tissue interface. Emerging surface biotechnology strategies are exemplified by nanofibrous polymeric materials, topographical surface modification, conducting polymer coatings, and neurotrophin-eluting implants. Although these novel developments have received individual attention in the recent literature, the time has come to investigate their collective applications to cochlear implants to restore lost hearing.

Section snippets

Cochlear implants and surface biotechnology

Implants are widely regarded as one of the greatest accomplishments of modern medicine. Very few surgical implants better exemplify the success that can be achieved through synergistic clinical and technological innovations than the cochlear implant. The cochlear implant is essentially a highly miniaturized electronic device that has become the standard of care for hearing restoration in patients with severe to profound sensorineural hearing loss (see Glossary). In less than 30 years, this

Enhancing cochlear implants: substitute biomaterials

The most convenient approach for implanting surface biotechnology is to simply substitute the current implant surface material with a distinctive and superior biomaterial.

Depending on their origins and chemical constituents, implant surface biomaterials can be synthetic or natural, organic or inorganic. Among the four types of biomaterial (synthetic organic, synthetic inorganic, natural organic, and natural inorganic), synthetic polymers undoubtedly have attracted the largest amount of

Enhancing cochlear implants: surface modification

In contrast to substituting with novel and high-performing biomaterials, modifying native implant surfaces makes it possible to engineer biofunctionality at the material–tissue interface for the purpose of modulating biological responses without altering material bulk attributes. Three types of surface modification have been explored: topographical, chemical, and biological (Box 1).

Topographical modification, the most exhaustively investigated approach, can be further divided into approaches

Enhancing cochlear implants: coating

In contrast to surface modifications, which involve alterations to the geometry, molecules, or compounds on the surface, coatings normally consist of an entirely different material from the underlying support (Box 1).

The most intensively studied coating type is synthetic organic (Table 1). Rapid progress within this field has revolved around three key emerging entities: conducting polymers, CNTs, and hydrogels. Conducting polymers have high electrical conductivity and tunable electrochemical

Enhancing cochlear implants: drug delivery

The fields of inner ear pharmacology and surface biotechnology progressed for many years in parallel with no substantial interaction, until the emergence of the cochlear implant, which opened the door to genuinely local and sustainable drug delivery.

The success of a cochlear implant largely depends on the proximity and availability of SGNs to the electrode. At least three methods have been used to reduce the distance between them. The first uses a surgical approach, in which a perimodiolar

Minimizing cochlear implantation-related complications

Not only can surface biotechnology enhance the performance of cochlear implants, it can also facilitate the minimization of surgical risks and complications (Box 3). Reducing intracochlear trauma caused by electrode insertion contributes significantly to the success of intraoperative hearing preservation and lessens subsequent degeneration of inner ear excitability. This goal can be pursued using two disparate strategies. The first decreases the insertion force, using either a less-invasive

Concluding remarks

The conspicuous trend in the advancement of implant biotechnology over the past half-decade is the merging of cochlear implantation and surface biotechnology into an auditory treatment based on the prosthesis–tissue interface. This new scientific endeavor focuses on maintaining stable long-term performance, impeding peri-electrode fibrous tissue formation, and promoting neurite outgrowth.

Future research will continue to refine current strategies and devise novel systems (Box 4). Intelligent all

Acknowledgment

MA-R and FT are supported by Science Foundation Ireland (grant no. 08/SRC/11411).

Glossary

Extracellular matrix (ECM)
tissue-specific dynamic environment that not only provides topographic architecture and mechanical support but also contains a reservoir of cell-signaling motifs and growth factors. The ECM provides the blueprint for surface biotechnology, and the balance between cell–cell and cell–ECM interactions directs auditory differentiation.
Neurotrophin family
this includes four members — brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin 3 (NT3),

References (96)

  • B.R. Prasad

    Controlling cellular activity by manipulating silicone surface roughness

    Colloids Surf. B: Biointerfaces

    (2010)
  • H. Zhou

    A simple method for amino-functionalization of carbon nanotubes and electrodeposition to modify neural microelectrodes

    J. Electroanal. Chem.

    (2013)
  • Z. Yue

    PEGylation of platinum bio-electrodes

    Electrochem. Commun.

    (2013)
  • D.V. Bax

    The linker-free covalent attachment of collagen to plasma immersion ion implantation treated polytetrafluoroethylene and subsequent cell-binding activity

    Biomaterials

    (2010)
  • D.V. Bax

    Cell patterning via linker-free protein functionalization of an organic conducting polymer (polypyrrole) electrode

    Acta Biomater.

    (2012)
  • D.V. Bax

    Directed cell attachment by tropoelastin on masked plasma immersion ion implantation treated PTFE

    Biomaterials

    (2011)
  • E. Azemi

    The surface immobilization of the neural adhesion molecule L1 on neural probes and its effect on neuronal density and gliosis at the probe/tissue interface

    Biomaterials

    (2011)
  • S-P. Lin

    On-line observation of cell growth in a three-dimensional matrix on surface-modified microelectrode arrays

    Biomaterials

    (2009)
  • Z. Yue

    Bio-functionalisation of polydimethylsiloxane with hyaluronic acid and hyaluronic acid — collagen conjugate for neural interfacing

    Biomaterials

    (2011)
  • J.E. Collazos-Castro

    Bioelectrochemical control of neural cell development on conducting polymers

    Biomaterials

    (2010)
  • X. Liu

    Conducting polymers with immobilised fibrillar collagen for enhanced neural interfacing

    Biomaterials

    (2011)
  • R.A. Green

    Cell attachment functionality of bioactive conducting polymers for neural interfaces

    Biomaterials

    (2009)
  • X. Luo

    Highly stable carbon nanotube doped poly(3,4-ethylenedioxythiophene) for chronic neural stimulation

    Biomaterials

    (2011)
  • R.A. Green

    Substrate dependent stability of conducting polymer coatings on medical electrodes

    Biomaterials

    (2012)
  • Y. Lu

    Poly(vinyl alcohol)/poly(acrylic acid) hydrogel coatings for improving electrode–neural tissue interface

    Biomaterials

    (2009)
  • H. Zhou

    Reduce impedance of intracortical iridium oxide microelectrodes by hydrogel coatings

    Sens. Actuators B: Chem.

    (2012)
  • L. Rao

    Polyethylene glycol-containing polyurethane hydrogel coatings for improving the biocompatibility of neural electrodes

    Acta Biomater.

    (2012)
  • R.A. Green

    Conducting polymers for neural interfaces: challenges in developing an effective long-term implant

    Biomaterials

    (2008)
  • Y. Lu

    Electrodeposited polypyrrole/carbon nanotubes composite films electrodes for neural interfaces

    Biomaterials

    (2010)
  • D-H. Kim

    Conducting polymers on hydrogel-coated neural electrode provide sensitive neural recordings in auditory cortex

    Acta Biomater.

    (2010)
  • M. Deng

    Electrochemical deposition of polypyrrole/graphene oxide composite on microelectrodes towards tuning the electrochemical properties of neural probes

    Sens. Actuators B: Chem.

    (2011)
  • S.S. Thanawala

    Amorphous and crystalline IrO2 thin films as potential stimulation electrode coatings

    Appl. Surf. Sci.

    (2008)
  • U. Brohede

    A novel graded bioactive high adhesion implant coating

    Appl. Surf. Sci.

    (2009)
  • R.T. Richardson

    Polypyrrole-coated electrodes for the delivery of charge and neurotrophins to cochlear neurons

    Biomaterials

    (2009)
  • B.C. Thompson

    Effect of the dopant anion in polypyrrole on nerve growth and release of a neurotrophic protein

    Biomaterials

    (2011)
  • B.C. Thompson

    Carbon nanotube biogels

    Carbon

    (2009)
  • J.A. Chikar

    The use of a dual PEDOT and RGD-functionalized alginate hydrogel coating to provide sustained drug delivery and improved cochlear implant function

    Biomaterials

    (2012)
  • R.A. Green

    Impact of co-incorporating laminin peptide dopants and neurotrophic growth factors on conducting polymer properties

    Acta Biomater.

    (2010)
  • B.C. Thompson

    Conducting polymers, dual neurotrophins and pulsed electrical stimulation — dramatic effects on neurite outgrowth

    J. Control. Release

    (2010)
  • B. Palmgren

    Survival, migration and differentiation of mouse tau-GFP embryonic stem cells transplanted into the rat auditory nerve

    Exp. Neurol.

    (2012)
  • S. Roy

    Cell-specific targeting in the mouse inner ear using nanoparticles conjugated with a neurotrophin-derived peptide ligand: potential tool for drug delivery

    Int. J. Pharm.

    (2010)
  • X. Luo

    Carbon nanotube nanoreservior for controlled release of anti-inflammatory dexamethasone

    Biomaterials

    (2011)
  • D. Rejali

    Cochlear implants and ex vivo BDNF gene therapy protect spiral ganglion neurons

    Hear. Res.

    (2007)
  • A. Warnecke

    Stable release of BDNF from the fibroblast cell line NIH3T3 grown on silicone elastomers enhances survival of spiral ganglion cells in vitro and in vivo

    Hear. Res.

    (2012)
  • F. Tan

    Cellular and transcriptomic analysis of human mesenchymal stem cell response to plasma-activated hydroxyapatite coating

    Acta Biomater.

    (2012)
  • F. Tan

    In vitro and in vivo bioactivity of CoBlast hydroxyapatite coating and the effect of impaction on its osteoconductivity

    Biotechnol. Adv.

    (2012)
  • K. Kang

    A biofunctionalization scheme for neural interfaces using polydopamine polymer

    Biomaterials

    (2011)
  • P. Roach

    Surface strategies for control of neuronal cell adhesion: a review

    Surf. Sci. Rep.

    (2010)
  • Cited by (0)

    View full text