F.J. Gil

Calcium phosphate bone cements for clinical applications. Part I: solution chemistry.

Calcium phosphate cements have been the subject of many studies in the last decade because of their biocompatibility, their capacity to fill bone cavities and their hardening properties; properties which are desirable in a broad range of surgical applications. The setting and hardening of these materials are controlled by dissolution–precipitation chemical reactions at room or body temperature and involve crystalline phase transformations.

Calcium phosphate bone cements for clinical applications. Part II: Precipitate formation during setting reactions

Calcium phosphate bone cements (CPBC) have been of great interest in medicine and dentistry due to their excellent biocompatibility and bone-repair properties. In this article, a review is presented of the scientific literature concerning precipitate formation during setting reactions of CPBCs. Firstly, the available information has been classified according to the intended final product or calcium phosphate formed during setting reactions. Taking the final product into account, a second classification has been made according to the calcium phosphates present in the original powder mixture. This is the most natural classification procedure because it is based on thermodynamic reasons supported by solubility diagrams for the calcium phosphate salts. By understanding the thermodynamics of calcium phosphate salts in an aqueous solution at room or body temperature it is possible to optimize the manufacturing technology involved in the production of CPBCs. Knowledge of the limitations of this thermodynamic approach opens up new possibilities in the search for CPBCs with better in vitro and in vivo properties for clinical applications.

Formation of α-Widmanstätten structure: effects of grain size and cooling rate on the Widmanstätten morphologies and on the mechanical properties in Ti6Al4V alloy

Abstract The coarseness of the transformed β-heat treated Ti6Al4V has a strong influence on its properties. The effects of solution temperatures and cooling rate on the Widmanstatten morphologies and on mechanical properties have been determined. The α-Widmanstatten plates size increases when the cooling rate decreases and a certain decrease of α-allotromorphous phase size at the grain boundaries can be observed when the cooling rate is increased. The tensile strength can be reduced about 80 MPa with the slower cooling rate from the β annealing temperatures when comparing air cooling to water quenching for thinner section sizes.

Behaviour of normal grain growth kinetics in single phase titanium and titanium alloys

Abstract The grain growth kinetics of commercially pure Titanium, Ti–0.2Pd in the α and β phases, Ti–6Al–4V and Ni–Ti in the β phase have been studied. The perimeter, diameter and area as grain size parameters have been measured by means of the image analysis technique for different heat treatment temperatures and times. The growth exponents and activation energies have also been determined. The influence of the grain size on the mechanical properties have been evaluated and for the Ni–Ti shape memory alloy, the influence of the grain growth on the transformation temperatures, thermodynamic magnitudes and on the transformation stresses has been determined.

Shape memory alloys for medical applications

Abstract The shape memory alloys exhibit a number of remarkable properties, which open new possibilities in engineering and more specifically in biomedical engineering. The most important alloy used in biomedical applications is NiTi. This alloy combines the characeristics of the shape memory effect and superelasticity with excellent corrosion resistance, wear characteristics, mechanical properties and a good biocompatibility. These properties make it an ideal biological engineering material, especially in orthopaedic surgery and orthodontics. In this work the basis of the memory effect lies in the fact that the materials exhibiting such a property undergo a thermoelastic martensitic transformation. In order to understand even the most elementary engineering aspects of the shape memory effect it is necessary to review some basic principles of the formation and the characteristics of the martensitic phase. The different properties of shape memory, superelasticity, two-way shape memory, rubber-like behaviour and a high damping capacity are reviewed. Some applications proposed in recent years are described and classified according to different medical fields.

In vivo evaluation of micro-rough and bioactive titanium dental implants using histometry and pull-out tests

We report on the in vivo histological and mechanical performance of titanium dental implants with a new surface treatment (2Step) consisting of an initial grit-blasting process to produce a micro-rough surface, followed by a combined chemical and thermal treatment that produces a potentially bioactive surface, i.e., that can form an apatitic layer when exposed to biomimetic conditions in vitro. Our aim was to assess the short- and mid-term bone regenerative potential and mechanical retention of 2Step implants in mandible and maxilla of minipigs and compare them with micro-rough grit-blasted, micro-rough acid-etched, and smooth as-machined titanium implants. The percent of bone-to-implant contact after 2, 4, 6, and 10 weeks of implantation as well as the mechanical retention after 4, and 6 weeks of implantation were evaluated with histometric and pull-out tests, respectively, as a measure of the osseointegration of the implants. We also aimed to assess the bioactive nature of 2Step surfaces in vivo. Our results demonstrated that the 2Step treatment produced micro-rough and bioactive implants that accelerated bone tissue regeneration and increased mechanical retention in the bone bed at short periods of implantation in comparison with all other implants tested. This was mostly attributed to the ability of 2Step implants to form in vivo a layer of apatitic mineral that coated the implant and could rapidly stimulate (a) bone nucleation directly on the implant surface, and (b) bone growing from the implant surface. We also proved that roughness values of Ra≈4.5 μm favoured osseointegration of dental implants at short- and mid-term healing periods, as grit-blasted implants and 2Step implants had higher retention values than as machined and acid-etched implants. The surface quality resulting from the 2Step treatment applied on cpTi provided dental implants with a unique combination of rapid bone regeneration and high mechanical retention.

Growth of bioactive surfaces on titanium and its alloys for orthopaedic and dental implants

A simple chemical method was established for inducing bioactivity of titanium and its alloys. Recently, T. Kokubo demonstrated that an in vitro chemical-deposited bone-like apatite on Ti with bone-bonding ability could be induced. Following treatment, a dense bone-like apatite layer is formed on the surface of the titanium in simulated body fluid (SBF). Observation of the samples in wet state by means of the environmental scanning electron microscope (ESEM) enabled us to observe the calcium phosphate deposition process in situ over a number of days. One of the most important features of the study is that it was carried out on a single, unchanged titanium sample and the process was not at any stage interrupted. Moreover, it was demonstrated that human osteoblast adhesion and differentiation behaviour are better in bioactive titanium than in the titanium without the chemical treatment.

Covalent immobilization of hLf1-11 peptide on a titanium surface reduces bacterial adhesion and biofilm formation.

Bacterial infection represents a major cause of implant failure in dentistry. A common approach to overcoming this issue and treating peri-implant infection consists in the use of antibiotics. However, the rise of multidrug-resistant bacteria poses serious concerns to this strategy. A promising alternative is the use of antimicrobial peptides due to their broad-spectrum activity against bacteria and reduced bacterial resistance responses. The aim of the present study was to determine the in vitro antibacterial activity of the human lactoferrin-derived peptide hLf1-11 anchored to titanium surfaces. To this end, titanium samples were functionalized with the hLf1-11 peptide either by silanization methods or physical adsorption. X-ray photoelectron spectroscopy analyses confirmed the successful covalent attachment of the hLf1-11 peptide onto titanium surfaces. Lactate dehydrogenase assay determined that hLf1-11 peptide did not affect fibroblast viability. An outstanding reduction in the adhesion and early stages of biofilm formation of Streptococcus sanguinis and Lactobacillus salivarius was observed on the biofunctionalized surfaces compared to control non-treated samples. Furthermore, samples coated with the hLf1-11 peptide inhibited the early stages of bacterial growth. Thus, this strategy holds great potential to develop antimicrobial biomaterials for dental applications.

Effect of grain size on the martensitic transformation in NiTi alloy

The effect of grain size on the martensitic transformation in Ni42Ti shape memory alloy has been studied. The kinetics of grain growth has been evaluated and the influence of different grain sizes on the transformation temperatures and the thermodynamic magnitudes has been reported. Image analysis and flow calorimetry techniques have been used. The study shows that grain boundaries favour the martensitic transformation and at the same time obstruct retransformation. Enthalpy and entropy variations are independent of grain size, but elastic energy decreases with the grain size.

Radiopaque acrylic cements prepared with a new acrylic derivative of iodo-quinoline.

A novel iodine-containing methacrylate, 2,5-diiodo-8-quinolyl methacrylate, has been synthesized and used in the preparation of acrylic radiopaque cements. The effect of incorporation of this monomer to the self-curing resins, on the curing parameters, swelling behaviour and mechanical properties was studied. The incorporation of the radiopaque compound 2,5-diiodo-8-hydroxyquinoline to the solid phase was also carried out for comparative experiments. A decrease in the peak temperature and an increase in the setting time was observed with the addition of the radiopaque monomer, however, the curing parameters did not appreciably change with the addition of the radiopaque compound to the solid phase. Swelling of the modified cements was in the same range as that of the radiolucent cement; however, the diffusion coefficients calculated according to the Ficks law were higher for the iodine-containing materials. The addition of 5 wt% of the iodine-containing methacrylate provided a significant increase in the tensile properties with respect to either control radiolucent formulations or BaSO4-containing formulations. Biocompatibility of the modified cements was studied by implantation of rods of the cements into rats and histological analysis of the surrounding tissue.