Marian Miculescu

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.

Metallurgical Characterization of some Magnesium Alloys for Medical Applications

The magnesium alloys has been intensively studied for their suitable mechanical properties, excellent biocompatibility and their ability to biodegrade in biological environments. Although magnesium biodegradable implants possess many desirable properties, it is important that the alloy is able to be tolerated by the body- the constitutional elements of magnesium-based alloys should be toxic free. In this study two binary magnesium alloys Mg-Ca0,8 and Mg-Ca1,8 were experimentally obtained by casting and was characterized in order to investigate the microstructure, mechanical properties and how alloying elements influenced the characteristics of this new alloys potentially used for orthopedic implants.

PCBs thermophysical properties in lead-free assembling process assessment

As elements of interconnection structures at level two in electronic packaging, the pads could be considered as a particular solution into a virtual space defined by the materials, geometry, surface finishes and substrate [1, 2]. The assembling processes emphasize the substrate contribution over thermal mass and heat transfer [3]. Each of the pad particular solution defined in the design stage will have unique values of thermophysical properties (THP) [2]. In the paper it will be presented the results of the THP measurements for different types of PCBs having particular solutions defined by the pad finishes, geometry and substrate materials using ANTER equipments (FlashLine 3000 thermal diffusivity system and Unitherm1161V dilatometer type). Finally, scientific and practical conclusions shall be drawn in order to improve the quality, reliability and increase the energetic efficiency of the reflow soldering process.

Synthesis and Characterization of Jellified Composites from Bovine Bone-Derived Hydroxyapatite and Starch as Precursors for Robocasting

Hydroxyapatite–starch composites solidify rapidly via jellification, making them suitable candidates for robocasting. However, many aspects related to hydroxyapatite powder characteristics, hydroxyapatite–starch interaction, and composites composition and properties need to be aligned with robocasting requirements to achieve a notable improvement in the functionality of printed scaffolds intended for bone regeneration. This article presents a preliminary evaluation of hydroxyapatite–starch microcomposites. Thermal analysis of the starting powders was performed for predicting composites’ behavior during heat-induced densification. Also, morphology, mechanical properties, and hydroxyapatite–starch interaction were evaluated for the jellified composites and the porous bodies obtained after conventional sintering, for different starch additions, and for ceramic particle size distributions. The results indicate that starch could be used for hydroxyapatite consolidation in limited quantities, whereas the composites shall be processed under controlled temperature. Due to a different mechanical behavior induced by particle size and geometry, a wide particle size distribution of hydroxyapatite powder is recommended for further robocasting ink development.

Morphologic Characterization of Ceramic-Ceramic Dental Systems Failure

Sintered ceramics and ceramic glasses are frequently used as biomaterials for dental restorations, usually for inlays, onlays, veneers, crowns or bridges. In this study we analyzed several types of ceramic-ceramic type prosthetic restorations in order to assess the types of defects that can lead to their failure. The research aim is to morphologically identify by scanning electron microscopy the main types of defects that lead to failure over time of ceramic-ceramic prostheses type. The type of failure registered were fracture of plating material (feldspatic porcelain) and fracture of entire structure (zirconia and feldspatic porcelain).

Biological Reactions to Dental Implants

Generally, the cells’ isolated systems are more sensitive than the tissues of the body at the contact with material outside the natural system. Although, the research by applying some viable methods in vitro is constantly growing, because the cellular mechanism of the toxicity assessment materials can be described through some simple and cheep experiments, that could represent viable alternatives for testing in vivo on animals bio bases and, finally, on people. Using these testing methods, the materials can be classified according to their degree of toxicity and chosen, if necessary, for further testing in vivo. To appreciate the materials’ biocompatibility for implantation in human body and to provide their functionality in vivo in the maximum safety for the patient represent a rigorous complex process, with two important distinct steps (Black, 1992): conducting preliminary assessment tests such as cytotoxicity, awareness, the irritant potential, intracutaneous reactivity, systemic toxicity (acute), subchronic toxicity (subacute), genotoxicity, implantation, hemocompatibility, or conducting tests for complementary evaluation, that consist in testing the chronic toxicity, the carcinogenicity, the toxicity of reproduction and development (growth) and the biodegradation. Through the process of testing in vitro the biomaterials can be assessed in a number of functions and characteristics of cells, as: integrity of membrane, cytoskeleton, viability, proliferation, proteins synthesis, oxidative response, mobility, secretion, response to growth factors, cell-cell interactions. To prepare the materials for testing the cytotoxicity has a great importance, because those physical and chemical properties strongly influence the cells response and the entire experimental system. Testing standards and how to prepare samples for testing in vitro are present at all professional bodies, including International Organization for Standardization (ISO), Ente Nazionale Italiano di Unificazione (UNI), British Standards Institute (BSI), Deutsches Institut fur Normung (DIN), Swiss Association for Standardization (SNN), Association Francaise de Normalisation (AFNOR), American Society for Testing and Materials (ASTM), American Dental Association (ADA). In such a standard are presented the requirements for physical and chemical form of materials, sterilization procedures, form and size of samples and any treatment required to obtain a sample suitable for cytotoxicity testing. The adoption of these specifications is recommended when pursued some comparisons between different laboratories or when

Dental Plating Efficiency of Metal Base Dental Alloys by Thermal Diffusivity Study

The need for reliable data on thermophysical properties of materials has increased continuously in the last period. The existing data, except for some pure elements or alloys and compounds, often unreliable, and in many cases the need for accurate and acceptable data, can only be achieved by measuring a given property. This paper focuses on elements of the used test methods associated with the description of the newly introduced parameter (effectiveness of dental coating). The selected method was the “pulse method” for determining thermal diffusivity (the method allows simultaneous determination of thermal diffusivity, specific heat capacity and thermal conductivity) directly applicable in the study of the thermal compatibility of metal-ceramic systems in dental applications.

Cooling Conditions Influence on Cortical Bovine Bones Derived Hydroxyapatite

The aim of the study is to highlight the influence of the cooling conditions on cortical bovine bones derived hydroxyapatite. Bone samples with thicknes of 50 mm were cut from the central part of the bovine femur with a jigsaw. Then, they were processed in order to remove all the proteins and collagen traces by boiling for 4 hours and heating and holding them at 450°C for 2 hours. They were heat treated at temperatures ranging from 1000° to 1300°C, being held for 3 hours and then rapidly cooled in air atmosphere or ice-water. A natural fracture of the samples appeared after the applied heat treatments, which allowed us to analyse the fragments without a further preparation. The morphological changes that occurred during the sample processing were highlighted using the scanning electron microscopy (SEM) techniques. The morphological changes occurred not only between the heat treated samples at different temperature, but also in samples cooled in different environments. Also, it was noticed that crystals sizes proportionaly increased with temperature, while the porosity considerably decreased and also a condensation of the porous matrix/structure appeared.

Corrosion Behavior of Ti and Ti Based Alloys Used as Implants-Supported Mandibular Overdentures

In the present study, four different types of the commercial dental implants used as support for total/partial dental prosthesis have been investigated. Pure Ti and Ti6Al4V alloy, provided by four different manufactures, were chosen because these were the most used in dentistry market. The corrosion resistance was evaluated by using linear polarization technique, after recording the open circuit curves in Fusayama Meyer artificial saliva for 240 minutes. The corrosion tests in artificial saliva with pH 5.2 have shown that pure Ti exhibited a better behavior than the Ti alloy. This result can be explained by a higher stability of the passive thin layer of titanium oxide than the complex oxide layer formed on the Ti alloy surface.

Micro-Analytical Comparison on Elemental Composition of Nonstoichiometric Bovine Bone Derived Hydroxyapatite

Hydroxyapatite (HA) is one of the most common ceramic materials used for bone substitutions or reconstructions [1]. HA synthesis from natural sources is convenient relative to synthetic HA preparation while ensuring a similarity with viable bone tissue in terms of chemical composition and some other properties. One of the most important markers used for hydroxyapatite identification and differentiation from other calcium phosphates is the Ca/P ratio [2]. In order to perform a proper identification, this ratio should be evaluated with high accuracy, which involves a correct determination of the elemental concentrations. This study was made on a series of samples, derived from bovine osseous tissue, thermaly treated at 1000, 1100 and 1200°C. Establishing the influence of sample preparation on the Ca/P ratio assessment from the energy dispersion spectrometry (EDS) coupled with scanning electron microscopy determinations was intended. The samples were prepared by two completely different methods: mechanical fracture (without further preparation) and milling followed by homogenization. Regardless the sample preparation method, the analytical results represents the five measurements average performed on different spots.The EDS results showed that, within the same group, the compositional dissimilarities between the samples treated at different temperatures do not exceed 10% regardless of the sample preparation technique. For the same thermal treatment temperature, slight differences between the elemental chemical compositions of differently prepared samples were observed. The most important effect was a 20% decrease of the average Ca/P ratio for the samples prepared by milling and homogenization in regard to the mechanical fractured ones. Thereby, heat treated bovine bone samples’ milling and further homogenization for performing semi quantitative EDS analysis allows the Ca/P ratio assessment with a better accuracy.