Alteration of titanium surfaces using hyaluronic acid coated mesoporous silica nanoparticles for local drug release

Abstract

Nosocomial infection is still an important problem for developed and developing countries as it decreases the effectiveness of the treatment as well as increases the healthcare expenses due to the prolonged stays in units. Most of these infections are biomaterial-based and caused by biofilm forming bacteria on biomaterial surfaces. Therefore, systemic drug administration is used to prevent biomaterials associated infections and to increase success of the implantation. Otherwise, revision surgery is generally required. Revision surgery means more pain for the patient, and it does not guarantee that osteointegration between the implant and surrounding tissue will be as strong as the first implementation. Local drug release using drug eluting implant materials suggests a great opportunity to prevent implant associated infections. Functional coatings containing therapeutic agents can be deposited on these surfaces by using different surface coating techniques such as layer by layer deposition (LBL), electrophoretic deposition (EPD), physical/chemical vapor deposition (CVD/PVD) etc. Local drug release from these surfaces does not only prevent implant associated infections, it also prevents the systemic toxicity. Moreover, sustained local drug release is possible with drug eluting materials. In the present study, a functional coating based on hyaluronic acid (HA) and mesoporous silica nanoparticles (MSNs) was proposed to prevent implant associated infections. For this purpose, drug loaded HA coated MSNs were prepared and deposited onto the Ti implants using EPD technique. Mesoporous silica nanoparticles (MSNs) were synthesized by the sol-gel/emulsion method and analysed using different characterization techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) and dynamic light scattering (DLS). After that, MSNs was silanized by using APTES (3- Triethoxysilylpropylamine) to form amino groups (-NH2) on the MSNs surfaces. In order to form HA coatings on MSN surfaces, HA was dissolved in MES buffer, NH2 -MSNs were added into the solution, EDC (N-(3-Dimethylaminopropyl)-N'-ethyl- carbodiimid-hydrochloride) and NHS (N-hydroxysuccinimide). Characterization of silanized (-NH2-MSNs) and HA-coated MSNs (HA-MSNs) were done by using SEM, Zeta Sizer and Fourier Transform Infrared Spectroscopy (FT-IR). SEM micrographs showed that almost homogeneous spherical MSNs ranging from 185 nm to 240 nm were synthesized. DLS analysis was showed that their sizes are ca. 8.7 μm. The cause of the difference was due to the environment MSNs exposed during characterization. SEM analysis is performed on dry nanoparticles while watery environment is used for DLS analysis. TEM analysis gave similar results with SEM for the sizes of the MSNs. Porous structure of synthesized MSNs were shown in this analysis. Moreover, characteristic peaks at 696 cm-1 and 1540 cm-1 that are attributed to –NH2 groups after silanization and peaks at 1639 cm-1 that are attributed –CH groups following the HA coating were determined in FTIR analysis. According to these results MSNs, -NH2-MSNs and HA-MSNs are synthesized and modified successfully. Ti plates were treated mechanically and chemically prior to deposit nanoparticles. Deposition onto the Ti surfaces were carried out using two different procedures. In the first procedure, HA-MSNs were dissolved in ethanol (70%) and HA coated MSNs deposited onto the Ti substrates for 1, 3 and 5 min. at 30V. In the second procedure, different ratios of MSNs and HA solution (MSNs:HA (w/w; 1:0.5, 0.5:1, 1:1)) were prepared and electrodes were then placed in this solution. Same coating parameters were applied for both coating procedures. The surfaces were analysed using SEM, FTIR and X-ray spectroscopy (EDS) to examine the surface morphology and chemical composition of the surfaces following the coating process. Characterization studies showed that both procedure 1 and procedure 2 can be used to obtain homogenous coatings on the surfaces. Neverthless, MSNs:HA should be 1:0.5 because coatings that were deposited using higher HA concentrations detached from the surfaces due to the thick film formation. In addition, SEM and EDS analysis showed that coating thickness can be increased with prolonged deposition time. The coating thicknesses were determined using mechanical profilometer and different thicknesses from 0.48 to 1.9 micrometer. were measured on the surfaces for different coating times. According to results of analysis, thickness was increased while increasing deposition time. Drug loading and release studies were carried out in PBS for free (synthesized MSNs, -NH2-MSNs, HA-MSNs) particles and coated particles (HA-MSNs) that were prepared using two different procedures. Ciprofloxacin as a model drug was used in this study, and it was both loaded into free MSNs and coated surfaces by diffusion. In accordance with the drug loading studies, drug loading efficiency was higher for HA-MSNs (ca. 80 %) when compared to HA free MSNs (ca. %40). Moreover, it was shown that drug release was possible using free MSNs for ca. 15 hours at 37 oC. Moreover, synthesized and silanized MSNs did not show sufficient drug loading and release rate like HA- MSNs. Finally, drug release from the coated Ti surfaces were examined. According to the drug release profiles, it was possible to have 10 hours drug release was determined from the Ti surfaces. In sum, HA-coated MSNs can be used as a functional coating to design a drug eluting Ti implant material and to prevent implant associated infections.