Zwitterionic Photografted Coatings of Cochlear Implant Biomaterials Reduce Friction and Insertion Forces

Abstract

Hypothesis: Application of photografted zwitterionic coatings to cochlear implant (CI) biomaterials will reduce friction and insertion forces. Background: Strategies to minimize intracochlear trauma during implantation of an electrode array are critical to optimize outcomes including preservation of residual hearing. To this end, advances in thin-film zwitterionic hydrogel coatings on relevant biomaterials may show promise, in addition to the potential of these materials for decreasing the intracochlear foreign body response. Methods: Using a recently designed one-step process, thinfilm coatings derived from zwitterionic sulfobetaine methacrylate (SBMA) were photopolymerized and photografted to the surface of polydimethylsiloxane (PDMS, silastic) samples and also to CI arrays from two manufacturers. Fluorescein staining and scanning electron microscopy with energydispersive X-ray spectroscopy verified and characterized the coatings. Tribometry was used to measure the coefficient of friction between uncoated and coated PDMS and synthetic and biological tissues. Force transducer measurements were obtained during insertion of uncoated (n ¼ 9) and coated (n ¼ 9) CI electrode arrays into human cadaveric cochleae.Results: SBMA thin-film coating of PDMS resulted in >90% reduction in frictional coefficients with steel, ceramic, and dermal tissue from guinea pigs ( p < 0.0001). We employed a novel method for applying covalently bonded, durable, and uniform coating in geographically selective areas at the electrode array portion of the implant. Image analysis confirmed uniform coating of PDMS systems and the CI electrode arrays with SBMA polymer films. During insertion of electrode arrays into human cadaveric cochleae, SBMA coatings reduced maximum force by $40% during insertion ( p < 0.001), as well as decreasing force variability and the overall work of insertion. Conclusion: Thin-film SBMA photografted coatings on PDMS and electrode arrays significantly reduce frictional coefficients and insertional forces in cadaveric cochleae. These encouraging findings support that thin-film zwitterionic coating of CI electrode arrays may potentially reduce insertional trauma and thereby promote improved hearing and other longterm outcomes.

Photografted zwitterionic hydrogel coating durability for reduced foreign body response to cochlear implants

“…Disk samples were evaluated for lubricity using a pin-on-disk tribometer (TRB 3 , Anton Paar) as previously described. 26 Typically, each sample was examined for 20 cycles (∼8 minutes) at a rotational speed of 1.3 mm/s while using the tribometer liquid setting with PBS as the immersive solution, 1 Newton normal force, and a sapphire probe (representative curve in Supplemental Figure 1A). To determine longevity of samples, tribometer data were collected over 2500 cycles (∼1000 minutes) determining the coefficient of friction for coated and uncoated samples, then normalizing coated samples to the average uncoated value.…”

“…These samples were then used to cover the steel probe head prior to tribometry as illustrated previously. 26 Coefficient of friction was measured between the tissues and coated- or uncoated-PDMS surfaces. For an additional control, the coefficient of friction for dermis on dermis was measured after fixing dermis tissue to PDMS using tissue glue.…”

“…Coated and uncoated cochlear implants were inserted into human cadaveric cochleae as previously described. 26 The cochleae were mounted on a force transducer to assess the increase in force associated with an insertion run. The raw output was reported over time for each implant.…”

“…SBMA thin films were coated on cochlear implants using a previously published method. 26 In brief, cochlear implants were pretreated for one hour in an acetone solution with 50 g/L benzophenone. After removal from the solvent and drying under vacuum, the implants were inserted into rigid cylindrical sleeves of transparent PDMS (inner diameter 0.76 mm) filled with 10% crosslinker CBMA monomer solution.…”

A review of advances in tribology in 2020–2021

“…An in vivo methodology was developed to investigate the tactile friction and sensory properties between human skin and hair, and effects of hair care products/shampoos were evaluated [766]. A wide range of tribological problems were examined, including in instruments [767], urinary catheter [768], rectal sexually transmitted infections [769], pleural mesothelial cells [770], gastroscope device-esophagus interface [771], cochlear [772], etc. The effective tribological mechanisms of animals and consequent bionics designs were investigated.…”