Florin Miculescu

Characterization and In Vitro and In Vivo Assessment of a Novel Cellulose Acetate-Coated Mg-Based Alloy for Orthopedic Applications

Despite their good biocompatibility and adequate mechanical behavior, the main limitation of Mg alloys might be their high degradation rates in a physiological environment. In this study, a novel Mg-based alloy exhibiting an elastic modulus E = 42 GPa, Mg-1Ca-0.2Mn-0.6Zr, was synthesized and thermo-mechanically processed. In order to improve its performance as a temporary bone implant, a coating based on cellulose acetate (CA) was realized by using the dipping method. The formation of the polymer coating was demonstrated by FT-IR, XPS, SEM and corrosion behavior comparative analyses of both uncoated and CA-coated alloys. The potentiodynamic polarization test revealed that the CA coating significantly improved the corrosion resistance of the Mg alloy. Using a series of in vitro and in vivo experiments, the biocompatibility of both groups of biomaterials was assessed. In vitro experiments demonstrated that the media containing their extracts showed good cytocompatibility on MC3T3-E1 pre-osteoblasts in terms of cell adhesion and spreading, viability, proliferation and osteogenic differentiation. In vivo studies conducted in rats revealed that the intramedullary coated implant for fixation of femur fracture was more efficient in inducing bone regeneration than the uncoated one. In this manner, the present study suggests that the CA-coated Mg-based alloy holds promise for orthopedic aplications.

In Vitro Biocompatibility of Human Endothelial Cells with Collagen-Doxycycline Matrices

The aim of this study was to test the biocompatibility between collagen-doxycycline matrices with various porosities and human endothelial cells. Collagen matrices were prepared by freeze-drying process. The crosslinking degree of collagen matrices was evaluated by FT-IR spectroscopy, the matrices morphology by SEM microscopy. The biocompatibility of collagen matrices with endothelial cells was monitored byfluorescence and transmission electron microscopy. We found that the three-dimensional structures of matrix with 1.2% collagen, 0.2% doxycycline crosslinked with 0.25% glutaraldehyde was optimal in terms of biodegradability, morphology and endothelial cells biocompatibility indicating the use of these scaffolds in tissueengineering.

Effect of micron sized silver particles concentration on the adhesion induced by sintering and antibacterial properties of hydroxyapatite microcomposites

Abstract In this paper, silver microparticles were proposed as an additive (wetting agent) in the sintering of bovine bone-derived hydroxyapatite, and their well-known antibacterial properties were evaluated for the newly-developed materials. Hydroxyapatite was prepared by thermal processing of bovine bones, followed by milling and sorting. After silver addition, the samples were tested as precursors, green compacts and adhered particles-sintered compacts, using complementary morphological, compositional and structural evaluation techniques (scanning electron microscopy coupled with energy dispersive spectrometry, Fourier infrared spectroscopy, X-ray diffraction). The antibacterial effect was assessed on bacterial strains popular for their association with post-implantation infections. The study was designed to evaluate the precursors, investigate the surface, morphology and/or structure changes during forming and adhesion by sintering, and explore the relationship between the silver concentration and the antibacterial effect of the material. The results confirmed the benefits of adding silver as a wetting agent in sintering bovine bone-derived hydroxyapatite as well as its antibacterial effect (with best results at 2 wt%Ag). In spite of the great potential as a wetting agent and antibacterial factor in hydroxyapatite, the proper evaluation of these results requires extensive testing for elevating the control level in designing the material properties, and for establishing optimal concentrations of silver in order to achieve proper antibacterial and biocompatible behaviours.

Modification of titanium surface with collagen and doxycycline as a new approach in dental implants

In this work, we investigate for the first time several issues involved in bio-adhesion process for a new type of chemically modified titanium surfaces (in their initial form and after collagen deposition), in order to assess their potential in dental implant surface modification. For this purpose, we studied the following: collagen adhesion, cytotoxicity, osteoblast cytomorphology, cell adhesion and proliferation, doxycycline embedding and modifications in the collagen film deposed on the metal surfaces, drug release from the collagen films. The improvement of adhesion between collagen film and titanium substrate, when hydroxyl and amino functional groups are assisting the surfaces was presented, all materials showing no cytotoxic effects as revealed by lactate dehydrogenase-based assay. The drug release from titanium–coll–doxy systems offers a dual mechanism of the delivery profile (burst release followed by moderate discharge of the antibiotic), with perspectives in soft tissue recovery postoperative stage.

Synergistic effect of carbon nanotubes and graphene for high performance cellulose acetate membranes in biomedical applications

Comparative evaluation of innovative combinations of three types of carbon nanomaterial (CNM) highlighted membranes with important potential for biomedical applications. Non-solvent induced phase separation coupled with ultrasound technique was used to generate membranes comprised of (i) cellulose acetate/ammonia functionalized carbon nanotubes (CA/CNT), (ii) cellulose acetate/ammonia functionalized graphene oxide (CA/GO), and (iii) cellulose acetate/CNT-GO. Structural, topographical and thermal features as well as water and ethanol permeation, bovine serum albumin (BSA) and haemoglobin (Hb) rejection were evaluated. Biocompatibility in terms of cytotoxicity, cell proliferation and adhesion were explored using a 3T3E1 cell line. The formation of amorphous structures, within which the CNMs were well dispersed, facilitated the development of smoother topographies. Addition of CNMs generated morphological changes influencing a decrease in water and ethanol fluxes. Furthermore, CNMs concentrated within the membrane skin layer exhibited repellent effects against BSA and Hb molecules and excellent cytocompatibility.

The Influence of Classical and Modern Manufacturing Technologies on the Properties of Metal Dental Bridges

This paper aims to characterize two dental bridges made from Co-Cr alloy, the first one obtained by the conventional method (casting) and the second one by Selective Laser Sintering technique (SLS). The elemental composition, microstructure, hardness and corrosion behavior in artificial saliva were investigated, allowing a parallel analysis of this two samples obtained with the two methods mentioned above.

Production and characterization of cellulose acetate – titanium dioxide nanotubes membrane fraxiparinized through polydopamine for clinical applications

The present paper introduces a study on the preparation and characterization of cellulose acetate - TiO2 nanotubes membrane. In order to be used as a hemodialysis membrane, fraxiparinized nanotubes have been incorporated into the cellulose matrix. Fraxiparine embedding was performed via strong binding ability of dopamine. Composite membrane was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and water contact angle measurement. Electrochemical impedance spectroscopy was used to correlate the morphology of composite membrane with its electrochemical properties. Mott-Schottky test proved titanium dioxide semiconductor incorporation in composite membrane. Permeation test was made to determine pure water flux. The obtained results showed that addition of nanotubes had a positive impact on membrane permeation compared with a control polymeric membrane.

Optimized silicon reinforcement of carbon coatings by pulsed laser technique for superior functional biomedical surfaces fabrication

We report on the fabrication of silicon-reinforced carbon (C:Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No micro-cracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of a C to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp3 hybridization of up to 80% at 40-48 mm apart from the edge with higher C content. Si addition was demonstrated to significantly increase C:Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 mN m-1. In certain cases, the Si-reinforced C coatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C:Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.

Effect of Calcium Content on the Microstructure and Degradation of Mg-Ca Binary Alloys Potentially Used as Orthopedic Biomaterials

The effect of calcium addition in modifying the microstructural aspects and corrosion behavior was investigated on two different biodegradable magnesium alloys type Mg-xCa binary alloys (x = 0.8, 1.8 wt. (%)). Systematic microstructure investigations was made using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray. Following these experimental investigations, in the microstructure of the investigated Mg-Ca alloys a notable refinement was observed occurred with increasing the calcium content. The evaluation of corrosion resistance was performed both using electrochemical measurements and hydrogen release in simulated body fluid (SBF), as proposed by Kokubo and his colleagues, maintaining the temperature at 37°C. The results showed a lower corrosion resistance when the calcium content was increased, due to the increased Mg2Ca intermetallic phase in grain boundaries. Consequently, our preliminary results showed that MgCa0.8 alloy having a minimal amount of Mg2Ca appear to be a promising alloy to be used as a biomaterial for orthopedic implants.

Failure Analysis of some Retrieved Orthopedic Implants Based on Materials Characterization

The aim of this paper is to determine causes of failure of orthopedic implants like intramedullary nail based on explants analysis and materials characterization. The clinical performance, corrosion characteristics and metallurgical properties of some retrieved titanium femoral nails have been examined. The macroscopic and the microscopic investigation of explants help us to describe the breaking mechanism and to identify the potential causes that led to implant failure.