Coating of cochlear implant electrodes with bioactive DNA-loaded calcium phosphate nanoparticles for the local transfection of stimulatory proteins

Calcium phosphate nanoparticles were loaded with nucleic acids to enhance the on-growth of tissue to a cochlear implant electrode. The nanoparticle deposition on a metallic electrode surface is possible by electrophoretic deposition (EPD) or layer-by-layer deposition (LbL). Impedance spectroscopy showed that the coating layer did not interrupt the electrical conductance at physiological frequencies and beyond (1-40,000 Hz). The transfection was demonstrated with the model cell lines HeLa and 3T3 as well as with primary explanted spiral ganglion neurons (rat) with the model protein enhanced green fluorescent protein (EGFP). The expression of the functional protein brain-derived neurotrophic factor (BDNF) was also shown. Thus, a coating of inner-ear cochlear implant electrodes with nanoparticles that carry nucleic acids will enhance the ongrowth of spiral ganglion cell axons for an improved transmission of electrical pulses.

Activity of Phosvitin in Hydroxyapatite Acid-Damage Immersion and Antimicrobial Assays

Phosvitin, the most highly phosphorylated metal-binding protein found in nature, binds more than 100 calcium ions, and has been identified as an agent that could be used to generate biomineralization scaffolds. Because of published reports describing phosvitin's affinity for calcium and potential antibiotic activity, this study was undertaken in order to evaluate phosvitin for both antibiotic activity against common microorganisms and the ability to protect hydroxyapatite surfaces from acid damage. To more clearly define its antibiotic action, the effects of phosvitin on Micrococcus luteus, P. mirabilis, B. cereus, E. coli, and S. epidermidis were evaluated. In both Kirby–Bauer tests and liquid culture growth inhibition assays, phosvitin inhibited M. luteus, a microorganism that thrives in the human mouth, but not the other bacteria tested. The MIC of phosvitin was determined to be 31.3 μg/mL when delivered in 1 mM CaCl₂ but was 0.5 mg/mL in the absence of added calcium. Expanding on the potential impacts of phosvitin on the mouth, its action was evaluated in a model of tooth decay represented by acid-damaged hydroxyapatite discs. SEM, AFM, and FAAS analyses revealed that pretreatment of discs with phosvitin modulated the damage-induced morphology and topography changes associated with acid-damaged discs.

Biomimetic multilayer coatings deliver gentamicin and reduce implant-related osteomyelitis in rats

Implant-related infections like periprosthetic joint infections (PJI) are still a challenging issue in orthopedic surgery. In this study, we present a prophylactic anti-infective approach based on a local delivery of the antibiotic gentamicin. The local delivery is achieved via a nanoscale polyelectrolyte multilayer (PEM) coating that leaves the bulk material properties of the implant unaffected while tuning the surface properties. The main components of the coating, i.e. polypeptides and sulfated glycosaminoglycans (sGAG) render this coating both biomimetic (matrix mimetic) and biodegradable. We show how adaptions in the conditions of the multilayer assembly process and the antibiotic loading process affect the amount of delivered gentamicin. The highest concentration of gentamicin could be loaded into films composed of polypeptide poly-glutamic acid when the pH of the loading solution was acidic. The concentration of gentamicin on the surface could be tailored with the number of deposited PEM layers. The resulting coatings reveal a bacteriotoxic effect on Staphylococcus cells but show no signs of cytotoxic effects on MC3T3-E1 osteoblasts. Moreover, when multilayer-coated titanium rods were implanted into contaminated medullae of rat tibiae, a reduction in the development of implant-related osteomyelitis was observed. This reduction was more pronounced for the multifunctional, matrix-mimetic heparin-based coatings that only deliver lower amounts of gentamicin.

MSC differentiation on two-photon polymerized, stiffness and BMP2 modified biological copolymers

INTRODUCTION

Bone tissue regeneration requires a three-dimensional biological setting. An ideal scaffold should enable cell proliferation and differentiation by mimicking structure and mechanical properties of the compromised defect as well as carrying growth factors. Two-photon polymerization (2PP) allows the preparation of 3D structures with a micrometric resolution.

METHODS

In this study, 2PP was applied to design scaffolds made from biocompatible methacrylated D,L-lactide-co-ε-caprolactone copolymers (LC) with a controlled porous architecture. Proliferation and differentiation of bone marrow mesenchymal stromal cells on LC was analyzed and compared to a standard inorganic urethane-dimethacrylate (UDMA) matrix. To functionalize LC and UDMA surfaces we analyzed a biomimetic, layer-by-layer coating, which could be modified in stiffness and integration of bone morphogenetic protein 2 (BMP2) and evaluated its effect on osteogenic differentiation.

RESULTS

On LC surfaces, BMSC demonstrated an optimal proliferation within pore sizes of 60-100 μm and showed a continuous expression of Vimentin. On the polyelectrolyte multilayer coating a significant increase in BMSC proliferation and differentiation as marked by Osteonectin expression was achieved using stiffness modification and BMP2 functionalization.

CONCLUSION

Combining 3D-Design with biofunctionalization, LC offers a promising approach for future regenerative applications in osteogenic differentiation of BMSCs.

Reflectometric interference spectroscopy-based sensing for evaluating biodegradability of polymeric thin films

Enzymatic degradation of poly(ε-caprolactone) (PCL) thin films was analyzed by reflectometric interference spectroscopy (RIfS)-based sensing system, and validated by attenuated total reflection infrared spectroscopy (ATR-IR) imaging. The degradation of the PCL thin film spin-coated on the silicon substrate on which 65-nm silicon nitride layer was deposited as an interference layer was easily monitored by shifting the peak bottom of reflectance spectra (Δλ) that is known to be proportional to the thickness of thin films. The Δλ values decreased with increasing the concentration of lipase from Pseudomonas cepacia, and the obtained sensorgrams were applied for kinetic analysis using a curve fitting software. ATR-IR spectra and imaging analysis on the surface of the PCL film revealed that carbonyl groups on the surface decreased with time, resulting from proceeding with the enzymatic hydrolysis, and importantly, extinction of the carbonyl group was declined with proportional to the decrease in the film thickness measured by the RIfS system. Consequently, the present RIfS-based label-free monitoring system can provide a simple and reliable way for evaluating biodegradability on synthetic materials.

STATEMENT OF SIGNIFICANCE

A RIfS-based sensing system in combination with ATR-IR measurements can be an analytical method for evaluation of biodegradability of polymeric thin films. This study demonstrates the utility of the RIfS-based sensing approach for analyzing the lipase-catalyzed degradation of PCL. Despite the RIfS is known as an inexpensive label-free detection method for biological interaction, the RIfS applications as monitoring methods for enzymatic degradation of biodegradable polymers had not been systematically explored. This study additionally demonstrated the capability of combined analysis of the biodegradation with ATR-IR spectra/imaging and RIfS measurements, which could be broadly applied towards evaluating biodegradability of various biodegradable polymers in environmental protection research.

Protein-triggered instant disassembly of biomimetic Layer-by-Layer films

Layer-by-Layer (LbL) coatings are promising tools for the biofunctionalization of biomaterials, as they allow stress-free immobilization of proteins. Here, we explore the possibility to immobilize phosvitin, a highly phosphorylated protein viewed as a model of bone phosphoproteins and, as such, a potential promotive agent of surface-directed biomineralization, into biomimetic LbL architectures. Two immobilization protocols are attempted, first, using phosvitin as the polyanionic component of phosvitin/poly-(L-lysine) films and, second, adsorbing it onto preformed chondroitin sulfate/poly-(L-lysine) films. Surprisingly, it is neither possible to embed phosvitin as the constitutive polyanion of the LbL architectures nor to adsorb it atop preformed films. Instead, phosvitin triggers instant massive film disassembly. This unexpected, incidentally detected behavior constitutes the first example of destructive interactions between LbL films and a third polyelectrolyte, a fortiori a protein, which might open a route toward new stimuli-responsive films for biosensing or drug delivery applications. Interestingly, additional preliminary results still indicate a promotive effect of phosvitin-containing remnant films on calcium phosphate deposition.