ICMCTF2012 Session D2-1: Coatings for Biomedical Implants

Friday, April 27, 2012 8:00 AM in Room Sunset
Friday Morning

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8:00 AM Invited D2-1-1 Functional plasma polymer films engineered at the nanoscale for biomaterial applications
Krasimir Vasilev (University of South Australia, Australia)

Functional coatings presenting a variety of functional chemical groups can be readily prepared by plasma polymerisation in an easy one-step process. Applications of such films span over a range of fields from modification of biomaterials to protective coatings.

In my talk, I will present recent developments from our group on various biomaterial coatings prepared by plasma polymerisation which include chemical and biomolecular gradients, and antibacterial coatings based on silver nanoparticles and conventional antibiotics.

Surface gradients have become important tools for studying and guiding cellular responses such as migration, adhesion, differentiation, etc. We generate gradients of various surface chemistries via plasma co-polymerisation over a moving mask. We used these chemical gradients to direct differentiation of kidney (KSC) and embryonic stem cells. We found that KSC express proximal tubule markers at medium amine group surface concentration and adapt a podocyte-like morphology at high.We extended these surface chemical gradients to density gradients of bound ligands, proteins and nanoparticles. We developed gradients of two proteins because gradients of single protein (employed in cell studies up to now) are probably too simplistic to mimic natural biological processes. We also developed density gradients of nanoparticles to use as a tool to study the effect of nanoscale surface features on cell behaviour.

Antibacterial coatings are important for many biomedical applications. We developed unique coatings based on silver nanoparticles which allow control over the rate of release of silver ions. As we show, the rate of silver release can be tuned such that it allows normal adhesion and spreading of mammalian cell and preserves the antibacterial properties of the coatings. We also developed two platforms for release of conventional antibiotics such as vancomycin and levofloxacin. Delicate control over the rate of release was achieved by a plasma polymer overlayer of a controlled thickness.

References:

K. Vasilev et al “Tunable antibacterial coatings that support mammalian cell growth” Nano Lett 10 (1), 202–207 (2010)

K. Vasilev et al “A PEG-density gradient to control protein binding: creating gradients of two proteins”, Biomaterials 31, 392–397 (2010)

S. Simovic, D. Losic and K Vasilev “Controlled drug release from mesoporous materials by plasma polymer deposition” Chem Commun 46, 1317 - 1319 (2010)

R.V. Goreham, R. D. Short and K. Vasilev “A Novel Method for the Generation of Surface-Bound Nanoparticle Density Gradients” J Phys Chem C 115 (8), 3429-3433 (2011)

8:40 AM D2-1-3 Effect of the surface atom ordering on the protein adsorption
Phaedra Silva-Bermudez, Lazaro Huerta, Sandra Rodil (Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de Mexico, México)

The study of the protein adsorption is relevant to understand the interactions biological media–foreign material since the adsorbed protein layer on the material surface mediates the interactions cell-material, greatly determining the biological response. The protein adsorption on solid surfaces is mainly driven by the surface properties; different studies have shown that properties such as hydrophobicity or roughness influence protein adsorption. Also, certain crystalline phases of a material have been mentioned as to induce a more biocompatible response than other crystalline or amorphous phases of the same material. However, this is not fully understood and more studies are needed to get a deeper understanding of the processes occurring when surfaces of the same material but with different atom ordering interact with biological media.

In the present study titanium oxide, a potential material for biocompatible cotaings for orthopaedic and dental implants, was chosen as the model material to study the influence of surface atom ordering on protein adsorption. Albumin (BSA) and Fibrinogen (Fib) were chosen as the model proteins. Quasi-amorphous and polycrystalline titanium oxide thin films (qa-TiO2 and pc-TiO2) were deposited on Si(100) substrates by Reactive Magnetron Sputtering. The atom ordering, wettability, surface energy, roughness, optical properties and chemical composition of the films were characterized. The films were immersed in BSA and Fib solutions and the protein adsorption was studied in-situ using dynamic and spectroscopic ellipsometry. Then, after 2400 s of immersion the adsorbed protein layer was studied ex-situ in a dried ambient using Atomic Force Microscopy and X-Ray Photoelectron Spectroscopy (XPS).

The results showed that the film roughness decreased with atom ordering; however, their water contact angle increased from 74° for qa-TiO2 to 85° for pc-TiO2. For both proteins a higher adsorption rate was observed on pc-TiO2 characterized for a total Δ change 3 degrees higher compared to that one for qa-TiO2. The surface mass density of the adsorbed protein layer was higher on pc-TiO2. The N at. % calculated form XPS after protein adsorption evidenced a slightly higher protein adsorption on pc-TiO2; for BSA adsorption on pc-TiO2 the N at. % was ≈ 5.3 while on qa-TiO2 it was ≈ 4.7%. For Fib adsorption the difference was more notorious with a N at. % ≈ 8.2 on q-aTiO2 and ≈ 28% on pc-TiO2. The Differences observed in the protein adsorption on the two films might be related to the changes in the films hydrophobicity induced by the different surface atom ordering.

Acknowledgments to the financial funding from the CONACyT project # 152995
9:00 AM D2-1-4 Nanodiamond/DLC Composite Coating Deposited on Ti6Al4V for Orthopaedic Joint Applications
Chunzi Zhang, Qiaoqin Yang, Yongji Tang, Yuanshi Li (University of Saskatchewan, Canada)

Researches show that 90% of the population over the age of 40 suffers from some degree of degenerative joint disease. Surgeries to repair or replace damaged joints are increasingly needed in recent years. However, current artificial joints made of Ti6Al4V have limited service lifetime due to their low wear resistance. The debris caused by wear results in tissue inflammation, osteolysis, and loosening of the implants, which is the main failure mechanism of artificial joints. Diamond-like carbon (DLC) coatings exhibit low friction coefficient, high wear resistance, and excellent biocompatibility and thus they are very promising protective coatings for artificial joints to prolong their service lifetime. However, DLC often suffers from high internal stress and poor adhesion on Ti6Al4V due to their thermal expansion mismatch.

In this research, nanodiamond/DLC composite coatings were deposited on Ti6Al4V substrates. Initially, nanocrystalline diamond particles were deposited on Ti6Al4V substrates by microwave plasma enhanced chemical vapor deposition to enhance adhesion and wear resistance of DLC. DLC thin film was then deposited on the predeposited substrate by ion beam deposition. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction were used to characterize the microstructure of the Diamond/DLC composite. Nanoindentation and scratch tests were used to study the hardness and adhesion property of the films. The friction and wear tests were conducted using both ball- and pin- on-disc techniques. The results show that the nanocrystalline diamond particles can significantly enhance the adhesion between DLC thin film and Ti6Al4V substrate as well as the hardness and wear resistance of DLC.

9:20 AM D2-1-5 Effects of argon plasma treatment on controlling the drug release rate from biocompatible polymers
Katsuya Hagiwara (Keio University, Japan); Terumitsu Hasebe (Toho University Sakura Medical center, Japan); Tetsuya Suzuki, Atsushi Hotta (Keio University, Japan)

Argon plasma surface treatment was introduced for the modification of the surface of drug-eluting stent (DES) coated with polymers in order to prevent the initial burst release of the drug. Currently, the implantation of DES is the most powerful way to treat coronary artery disease. DES elutes anti-proliferative drugs that suppress the proliferation of smooth muscle cells in the stented segment of the artery. Despite the impressive reduction in restenosis, DES still has a disadvantage for not preventing restenosis at the implant site due to the relatively vast drug release from the stent surface in the early stage of the release.

To solve the problem, we focused on argon plasma treatment. Argon gas is an inert gas without the risk of damaging the surface of the stent by surface treatment. In this experiment, polymers were used as drug-reservoir materials, where it was necessary to achieve the controllable and sustainable drug release from the polymers. Three biocompatible polymer films were selected as base drug-reservoir materials: hydrophilic 2-metacryloyloxyethyl phosphorylcholine (MPC), hydrophobic poly (ethylene-co-vinyl acetate) (EVA), and less hydrophobic polyurethane (PU). Structural analyses were carried out using scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle measurements, and X-ray photon spectroscopy (XPS). By changing processing time of argon plasma from 5 sec to 45 sec, it was found that the initial burst release of drug, especially with EVA and PU films, was suppressed. These experimental results of the plasma treatment could provide a new and alternative approach to a controllable and sustainable drug release system.

9:40 AM D2-1-6 In vitro biological response of plasma electrolytically oxidised and sprayed hydroxyapatite coatings on Ti6Al4V alloy
Wing Yeung, Aleksey Yerokhin, Gwendolen Reilly, Allan Matthews (University of Sheffield, UK)
Plasma electrolytic oxidation (PEO) is a new branch of surface modification to attain bioactivity of Ti alloy implants, compared to conventional plasma spray method. Enhanced interfacial bonding between the PEO coating and the metal substrate reduces risk of coating delamination, which is highly desired for long term orthopaedic implants. The aim of this study is compare surface characteristics and biological effects of PEO and plasma spray coatings on human osteoscarcoma cells (MG-63). The coating characteristics were examined by XRD, EDX, SEM, surface profilometry and wettability tests. The biological properties were determined by cell viability, calcium and collagen synthesis assays. PEO coatings showed a different morphology than the plasma sprayed coating. The results show that the PEO coatings are more hydrophilic and have a lower surface roughness than the plasma sprayed coating. At the same time, cellular behaviour is strongly dependent on the phase composition and surface distribution of elements in the PEO coatings. Thus MG-63 cell viability for the TiO2-based PEO coating containing amorphous calcium phosphates it is significantly less than that for the coating containing crystalline hydroxyapatite as well as for the plasma sprayed coating. However, the collagen synthesis on both PEO coatings is significantly higher than the plasma sprayed coating after 14 days.
10:00 AM D2-1-7 Biocompatibility and Anti-Microbial Properties of Silver Modified Amorphous Carbon Films
Argelia Almaguer-Flores (Universidad Nacional Autónoma de México, Mexico); René Olivares-Navarrete (Georgia Tech, US); Giovanni Ramirez (Universidad Nacional Autónoma de México, Mexico); Sandra Rodil (Universidad Nacional Autónoma de Mexico, Mexico)
Microbial infection on implant surfaces has a strong influence on healing and long-term outcome of implants. The prevention and control of biofilms can be achieved by reducing the initial bacterial adhesion on the surfaces of modified metallic implants. Amorphous carbon (a-C) films have been studied as a surface modification for implant materials. These films could be interesting due to the biocompatibility, corrosion resistance and antibacterial properties that have been reported. In this work, we proposed the modification of the a-C films by inclusions of silver nanoparticles in small percentages to prevent device-associated infections, since in a previous study our results showed no inhibition of the bacterial adhesion on a-C films. The a-C:Ag films were deposited by dual co-sputtering using graphite and silver targets under an Argon plasma, varying the power applied to the Ag target. The biocompatibility of the a-C:Ag samples containing up to 6 at% Ag was evaluated using osteoblast-like cells (MG63). The biological tests showed that a-C:Ag films allowing the osteoblast to proliferate and produce osteogenic local factors, demonstrating that the biocompabitilty and the osteoinduction properties of the surfaces were not modified by the addition of small percentages of silver. Having this information, we evaluate the antibacterial properties of the a-C:Ag samples with Ag concentrations ranging from 0 to about 10 at%. The bacterial adhesion at 24 hours (counting the number of colony forming units) and the biofilm formation (observed by scanning electron microscopy, SEM and fluorescence microscopy) during incubation periods of 1, 3 and 5 days were evaluated for three bacterial strains: Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The results shows a decrease in the number on bacteria found in samples with a-C:Ag films comparing with the samples in which no silver were added. The microstructure and composition of the a-C:Ag films was characterized by X-ray Diffraction, Energy Dispersive spectroscopy(EDS), Atomic Force Microscopy (AFM) and SEM.
10:20 AM D2-1-8 Corrosion Resistance and Biocompatibility of Titanium Coated with Tantalum Pentoxide
Ying-Sui Sun, Her-Hsiung Huang (National Yang-Ming University, Taiwan)
Titanium (Ti) is commonly used as dental implanterial because of its good corrosion resistance and biocompatibility. Nevertheless, corrosion process might still happen when Ti metal is implanted in the human body for long-term application. The tantalum pentoxide (Ta2O5) has superior corrosion resistance than the titanium dioxide (TiO2) spontaneously formed on Ti surface. In this study, the Ta2O5 coating was produced on Ti surface using hydrolysis-condensation process. Surface characteristics, including chemical composition, microstructure, topography, wettability and substrate adhesion, of the coating were analyzed. The corrosion resistance of the test specimens was evaluated using potentiodynamic polarization curve measurement in simulated blood plasma. The in vitro biocompatibility, in terms of protein adsorption and cell adhesion, was evaluated. Experimental data were analyzed using Student’s t-test with a=0.05. Results showed that the Ta2O5 coating was successfully produced on Ti surface using a simple hydrolysis-condensation process. TheTa2O5 coating showed a good adhesion to Ti substrate, and enhanced the corrosion resistance (i.e. decreased the corrosion rate and anodic current) and biocompatibility (i.e. improved the protein adsorption and cell adhesion) of Ti surface. We would conclude that the Ta2O5 coating could be easily produced on Ti surface using a simple hydrolysis-condensation process. The Ta2O5 coating provided the Ti surface with better corrosion resistance and in vitro biocompatibility.
10:40 AM D2-1-9 Mechanical Properties of Fluorinated DLC and Si Interlayer on a Ti Biomedical Alloy
Chau-Chang Chou, Yi-Yang Wu (National Taiwan Ocean University, Taiwan); Jyh-Wei Lee (Ming Chi University of Technology, Taiwan); Jen-Ching Huang (Tungnan University, Taiwan); C.H. Yeh (Keelung Chang Gung Memorial Hospital,Taiwan)
Fluorinated diamond-like carbon (F-DLC) films were deposited on Ti6Al4V substrates by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique using a mixture of methane (CH4) and tetrafluoromethane (CF4) gases. A 100 nm Si interlayer was coated in advance by physical vapor deposition (PVD) process to improve the adhesion between F-DLC and Ti alloy. The structure and surface properties of F-DLC coatings, prepared by various fluorine flow ratios, were investigated by using Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The mechanical properties were evaluated by nano-indentation and the adhesion, by nano-scratch. As CF4 flow ratio is promoted in the mixture, CFx group and sp2 carbon clusters in the amorphous microstructure increase. However, the etching mechanism attributed to the fluorine species in the plasma becomes significant when the CF4/CH4 ratio was higher than 4 in this study. F-DLC film’s Young’s modulus and hardness were reduced by the increased fluorine content, but the critical load from the scratch test revealed that the film’s thickness is the only factor that determines its adhesion strength. The results showed that a moderate incorporation of the fluorine content in the DLC films can still maintain acceptable mechanical properties, which, on the other hand, obtains remarkable benefits of biomedical application.
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