Preparation, characterization and application research of a sustained dexamethasone releasing electrode coating for cochlear implantation

Oriented polyaniline/poly-l-lactic acid/gelatin nanofiber scaffolds promote outgrowth of spiral ganglion neurons

Sensorineural hearing loss (SNHL) is caused by the loss of sensory hair cells (HCs) and/or connected spiral ganglion neurons (SGNs). The current clinical conventional treatment for SNHL is cochlear implantation (CI). The principle of CI is to bypass degenerated auditory HCs and directly electrically stimulate SGNs to restore hearing. However, the effectiveness of CI is limited when SGNs are severely damaged. In the present study, oriented nanofiber scaffolds were fabricated using electrospinning technology to mimic the SGN spatial microenvironment in the inner ear. Meanwhile, different proportions of polyaniline (PANI), poly-l-lactide (PLLA), gelatin (Gel) were composited to mimic the composition and mechanical properties of auditory basement membrane. The effects of oriented PANI/PLLA/Gel biomimetic nanofiber scaffolds for neurite outgrowth were analyzed. The results showed the SGNs grew in an orientation along the fiber direction, and the length of the protrusions increased significantly on PANI/PLLA/Gel scaffold groups. The 2% PANI/PLLA/Gel group showed best effects for promoting SGN adhesion and nerve fiber extension. In conclusion, the biomimetic oriented nanofiber scaffolds can simulate the microenvironment of SGNs as well as promote neurite outgrowth in vitro, which may provide a feasible research idea for SGN regeneration and even therapeutic treatments of SNHL in future.

Preparation, characterization, and in vitro/vivo evaluation of a multifunctional electrode coating for cochlear implants

Cochlear implantation (CI) is the primary intervention for patients with sensorineural hearing loss to restore their hearing. However, approximately 90 % of CI recipients experience unexpected fibrosis around the inserted electrode arrays due to acute and chronic inflammation. This fibrosis leads to progressive residual hearing loss. Addressing this complication is crucial for enhancing CI outcomes, yet an effective treatment has not yet been found. In this study, we developed a multifunctional dexamethasone (DXM)-loaded polytrimethylene carbonate (PTMC) electrode coating to mitigate inflammatory reactions and fibrosis after CI. This thin and flexible coating could preserve the mechanical performance of the electrode and reduce the implantation resistance for CI. The in vitro release studies demonstrated the DXM-PTMC coating's efficient drug loading and sustained release capability over 90 days. DXM-PTMC also showed long-term stability, high biocompatibility, and effective anti-inflammatory effects in vitro and in vivo. Compared with the uncoated group, DXM-PTMC coating significantly inhibited the expression of inflammatory factors, such as NO, TNF-α, IL-1β, and IL-6. DXM-PTMC coating suppressed fibrosis in rat implantation models for 3 weeks by reducing both acute and chronic inflammation. Our findings suggest that DXM-PTMC coating is a novel strategy to improve the outcomes of CI.

Intratympanic injection of hydrogel nanodrug for the prevention and treatment of sensorineural hearing loss

Safe and efficient drug delivery to the inner ear has always been the focus of prevention and treatment of sensorineural deafness. The rapid development of nanodrug delivery systems based on hydrogel has provided a new opportunity. Among them, thermo-sensitive hydrogels promote the development of new dosage form for intratympanic injection. This smart biomaterial could transform to semisolid phase when the temperature increased. Thermo-sensitive hydrogel nanodrug delivery system is expected to achieve safe, efficient, and sustained inner ear drug administration. This article introduces the key techniques and the latest progress in this field.

Exploration of 2D and 2.5D Conformational Designs Applied on Epoxide/Collagen-Based Integrative Biointerfaces with Device/Tissue Heterogeneous Affinity

Collagen and multifunctional epoxides, which are respectively the common constituents of natural and polymer interfaces, were combined to fabricate integrative biointerfaces with device/tissue heterogeneous affinity. Further, the traditional 2D and advanced 2.5D conformational designs were achieved on collagen-based biointerfaces. The 2D conformational biointerfaces were formed by the self-entanglement of collagen molecules based on extensive hydrogen bonds among molecules, and the lamellar structures of 2D conformational biointerfaces could act as barriers to protect both biointerfaces and substrates from enzymes and corrosion. The unique stacking structures of 2.5D conformational biointerfaces were formed by cross-linking microaggregates that were established and connected by epoxy cross-linking bonds and provided the extra 0.5D degree of freedom on structure design and functional specialization through artificially manipulating the constituents and density of microaggregates. Besides, the intersecting channels among microaggregates gave 2.5D biointerfaces diffusion behaviors, which further brought good wettability and biodegradability. The integrative biointerfaces behaved well on cell viability and enhanced the cell adhesion strength in vitro, which could be attributed to the collaborations of collagen and epoxy groups. The subcutaneous implant model in rats was utilized to investigate soft tissue response, and the results demonstrated that the tissues around implantation areas healed well and without calcification or infection. The coating of integrative biointerfaces alleviated the fibrosis around implantation areas, and the inflammatory responses and foreign body reactions were improved.

Zwitterionic Polymer/Polydopamine Coating of Electrode Arrays Reduces Fibrosis and Residual Hearing Loss after Cochlear Implantation

Since the first surgery 50 years ago, cochlear implantation (CI) is the major treatment for patients with severe sensorineural hearing loss. However, unexpected foreign body reactions (FBRs) after surgery are reported in 90% of CI recipients, resulting in the formation of fibrosis in the cochlea and progressive residual hearing loss. Zwitterion modification is universally used to reduce bio-fouling and suppress FBRs but never for CI. In the present study, a zwitterionic coating is developed, which is composed of poly sulfobetaine methacrylate (PSB) and polydopamine (PDA) for cochlear implants. The PSB-PDA coating shows a series of characters for an ideal anti-FBRs material, including super-hydrophilicity, low protein and cell adsorption, long-term stability, and high biocompatibility. Compared to the uncoated controls, PSB-PDA coating inhibits the activation of macrophages and reduces the release of inflammatory factors (TNF-α, IL-1β, NO) and fibrosis-related factors (TGF-β1, α-SMA, collagen I). PSB-PDA coated electrode arrays suppress fibrosis completely and preserve residual hearing significantly in rat CI models. These results suggest that PSB-PDA coating is a novel strategy for anti-fibrosis to improve the outcomes of CI.

Mesoporous silica nanoparticle-modified electrode arrays of cochlear implants for delivery of siRNA-TGFβ1 into the inner ear

Cochlear implants (CI) are widely used in patients to restore hearing function. Uncontrolled fibrosis in the cochleae induced by excess secretion of TGFβ1 seriously affects the effectiveness of CIs. siRNA is a potential therapeutic strategy to downregulate TGFβ1 specifically. However, treatment with siRNA in cochleae is difficult due to the poor penetration capability and instability of siRNA and the inaccessibility and vulnerability of cochleae. To address these challenges, we developed amino-functionalized mesoporous silica nanoparticle (MSN-NH2)-modified electrode arrays to deliver siRNA-TGFβ1 into the inner ear. The shape, diameter, pore diameter, and zeta potential of MSN-NH2 were investigated. siRNA loading capability and protective effect of MSN-NH2 were determined by agarose gel electrophoresis assay. The cytotoxicity, cellular uptake assay, and TGFβ1 knockdown efficiency of MSN-NH2 were studied by CCK-8 assay, flow cytometry, and real-time PCR, respectively. MSN-NH2-siTGFβ1 nanoparticles were absorbed into the electrode arrays and worked in the cochleae. MSN-NH2-siTGFβ1-modified CI electrode arrays may be an attractive therapeutic clinical intervention strategy to inhibit cochlear implantation fibrosis.

PLLA Coating of Active Implants for Dual Drug Release

Cochlear implants, like other active implants, rely on precise and effective electrical stimulation of the target tissue but become encapsulated by different amounts of fibrous tissue. The current study aimed at the development of a dual drug release from a PLLA coating and from the bulk material to address short-term and long-lasting release of anti-inflammatory drugs. Inner-ear cytocompatibility of drugs was studied in vitro. A PLLA coating (containing diclofenac) of medical-grade silicone (containing 5% dexamethasone) was developed and release profiles were determined. The influence of different coating thicknesses (2.5, 5 and 10 µm) and loadings (10% and 20% diclofenac) on impedances of electrical contacts were measured with and without pulsatile electrical stimulation. Diclofenac can be applied to the inner ear at concentrations of or below 4 × 10⁻⁵ mol/L. Release of dexamethasone from the silicone is diminished by surface coating but not blocked. Addition of 20% diclofenac enhances the dexamethasone release again. All PLLA coatings serve as insulator. This can be overcome by using removable masking on the contacts during the coating process. Dual drug release with different kinetics can be realized by adding drug-loaded coatings to drug-loaded silicone arrays without compromising electrical stimulation.

Long-Term Release of Dexamethasone With a Polycaprolactone-Coated Electrode Alleviates Fibrosis in Cochlear Implantation

Cochlear implantation (CI) is the major treatment for severe sensorineural hearing loss. However, the fibrotic tissue forming around the electrodes reduces the treatment effectiveness of CI. Dexamethasone (DEX) is usually applied routinely in perioperative treatment of cochlear implantation (CI), but its diffusion in the inner ear after systemic administration is limited. In the present study, an electrode coated with polycaprolactone (PCL) loaded with dexamethasone was developed with a simple preparation process to maintain the stability of the electrode itself. The DEX-loaded PCL coating has good biocompatibility and does not change the smoothness, flexibility, or compliance of the implant electrode. Stable and effective DEX concentrations were maintained for more than 9 months. Compared with the pristine electrode, decreasing intracochlear fibrosis, protection of hair cells and spiral ganglion cells, and better residual hearing were observed 5 weeks after PCL-DEX electrode implantation. The PCL-DEX electrode has great potential in preventing hearing loss and fibrosis by regulating macrophages and inhibiting the expression of the fibrosis-related factors IL-1β, TNF-α, IL-4, and TGF-β1. In conclusion, the PCL-DEX electrode coating shows promising application in CI surgery.

Preparation, characterization, and in vitro/vivo evaluation of dexamethasone/poly(ε-caprolactone)-based electrode coatings for cochlear implants

With dexamethasone as the model drug and polycaprolactone (PCL) as the carrier material, a drug delivery coating for cochlear electrodes was prepared, to control cochlear fibrosis caused by cochlear implantation. A dexamethasone/poly (ε-caprolactone)-based electrode coating was prepared using the impregnation coating method. Preparation parameters were optimized, yielding 1 impregnation instance, impregnation time of 10 s, and PCL concentration of 10%. The coating was characterized in vitro using scanning electron microscopy, a universal machine, high-performance liquid chromatography, and CCK-8. The surface was porous and uniformly thick (average thickness, 48.67 µm)—with good flexibility, long-term slow drug release, and optimal drug concentration—and was biologically safe. The experimental results show that PCL is an ideal controlled-release material for dexamethasone as a drug carrier coating for cochlear implants.

Development of a rapidly made, easily personalized drug-eluting polymer film on the electrode array of a cochlear implant during surgery

OBJECTIVE

To develop a drug-eluting polymer film which can be easily personalized and rapidly made on the electrode array of a cochlear implant during surgery.

METHODS

A precursor solution was prepared with poly lactic-co-glycolic acid (PLGA) and trichloromethane. Using a dip-coating method, the silicone electrode array (HiFocus 1J, Advanced Bionics) was coated in polymer film produced from the precursor solution containing one of three drugs: dexamethasone sodium phosphate (DSP), cytosine arabinoside hydrochloride (Ara-C), or nicotinamide adenine dinucleotide (NAD), and the release of these drugs from the polymer film was studied. The drug-eluting film on the electrode array was analyzed by environmental scanning electron microscopy (ESEM). The water contact angle and the impedance of the electrode array were measured before and after coating. Drug release kinetics was evaluated in a quasi-stationary release model, using high performance liquid chromatography every 24 h for 15 days.

RESULTS

Five electrode arrays were tested with each of the three drugs in the polymer film coating. Before and after coating, ESEM studies revealed that the drug-loaded PLGA coating yielded a smooth covering with an average thickness of 1.02 ± 0.05 μm. The mass of the coated electrode increased by 1.00 ± 0.03 mg. The water contact angle decreased after coating (102 ± 0.6° vs 77 ± 1.6°, p < 0.01) but there was no significant change in the average impedance of the electrodes after coating (0.9 ± 0.22 kΩ vs 1.0 ± 0.18 kΩ, p > 0.05). An in vitro drug kinetics study revealed a faster release in the first 24 h (63.4 ± 0.6%) and a sustained release over the following 15 days (78.3 ± 1.7% in 2 days, 95.6 ± 1.0% in 7 days and 99.1 ± 0.4% in 14 days). The release rate was not affected by the drug, dose or the thickness of the coating.

CONCLUSION

The dip-coating method is feasible for rapid casting of a drug-eluting PLGA film on an electrode array during CI surgery. The coated electrode array maintained its original morphology and became more hydrophilic. The loaded drug is released in a sustained manner and is easily regulated, and so the method might represent a potential application for clinical use in cochlear implantation.