Biomaterial science studies the interactions that occur between materials and tissues in order to understand the mechanisms that lead to material integration in biological systems for medical purposes. It is a field that requires a multidisciplinary approach, integrating materials science, chemistry, biology, engineering and medicine. Its development arose out of the requirement for new materials with high performance in terms of tolerability and integration capability that can be used to replace or restore function to a body tissue. Despite advances in the biomaterials field, at this point in time a satisfactory combination between the properties of the materials (mechanical, chemical and tribological) and their biocompatibility has not yet been achieved. This is the cause of early failure of implants, which necessitates subsequent replacement of prosthetic devices, especially in young patients. Glass-ceramics are an important family of materials proposed for bone repair and substitution. They have the capability to bond with living bone by forming a hydroxyapatite layer with a composition similar to that of the mineral phase of bone [1]. The first bioglass (45S5) was discovered in 1971 by Hench at al. [2]. Afterwards many other glasses with various compositions were explored [3]. Kokubo et al. [4] developed Apatite-Wollastonite (A-W) glass-ceramics which retains a high mechanical strength in vivo for a long period and is able to bond to living bone in a short space of time. Moreover, published literature [5] shows that the preparation method, in addition to the material composition, also affects the resulting structure and, thus, the biological properties of the materials obtained. An ideal technique to prepare bioglass is the sole-gel method, a versatile synthesis technique used to produce glasses and ceramics at low temperatures. The process starts when water is added to a solution of metal alkoxide precursors in alcohol. The hydrolysis of the metal alkoxide and the polycondensation of the oligomers formed cause a transition of the system from a mostly colloidal liquid ('sol') into a solid 'gel'. By drying the obtained wet gel, it is possible to prepare xerogels (by exposure to low temperatures) or aerogels (by solvent extraction under supercritical conditions) or dense ceramic and glass by means of a further heat treatment at higher temperatures. Glasses and ceramics synthesized via the sol-gel method exhibit higher bioactivity and biocompatibility than materials with the same composition but prepared using other techniques [6]. Indeed, sol-gel-derived glasses have an inherent mesoporosity that gives them a larger surface area and degradation rates potentially more rapid than melt-derived glasses of similar composition. Moreover, the presence of -OH groups on their surface stimulates hydroxyapatite nucleation, promoting their easier Osseo integration. Sol-gel glasses and ceramics have been proposed for many biomedical applications, such as artificial dental roots, bone regenerative materials, coatings to...

Nowadays, high-strength steel structures are increasingly being used in marine or soil environments, but low attention has been paid on the corrosion and stress corrosion cracking problem. In this paper, the susceptibility to stress corrosion cracking (SCC) of butt-welding joints of Strenx® 700 (S690QL high strength steel) both in marine and acid-polluted marine atmospheres was studied, by using slow strain rate tensile (SSRT) test. The seawater corrosion environment was considered and it was prepared following the ASTM D1141. To study the influence of the environment pH, NaOH 0,1M solutions and pure H2SO4 were used to adjust the pH of the simulated seawater solution to 8 and 4, respectively. The slow strain rate tensile tests (SSRT) with a crosshead speed of 0.000017 mm/s were carried out at room temperature (approximately 25 °C). After failure, the SCC susceptibility was evaluated acquiring the elongation loss rate and the reduction-in-area loss rate. The fracture surfaces were analyzed by SEM observation.

Nowadays, approximately 1.5 million joint replacements are performed annually in Europe, while 7 million are performed in the United States. Despite the advances made in the biomaterials field over the last 50 years, today the average lifetime of an implant is still about 20 years. This entails the need for subsequent prosthetic device replacement, especially in young patients, resulting in an increase in patients’ health risks as well as clinical and economic burdens for the public health service. The failure of the implants can be caused by several reasons, such as adverse immune system reaction, biofilm formation or mechanical, chemical, tribological, surgical, manufacturing and biocompatibility problems. An alternative and useful strategy used to overcome this limitation is the modification of the implants’ surface by sol-gel coating technology. It allows for the production of coatings with a wide range of properties on substrates of different nature and shape, due to the fine control of the coating composition and microstructure. Sol-gel coatings were successfully proposed to inhibit wear, reduce corrosion and ion release, and modify the lubricity, hydrophilicity/hydrophobicity, and functionality of several substrates. Moreover, many works report the application of sol-gel coatings on bio-inert implants to improve their bioactivity and biocompatibility, leading to the enhancement of the integration process. This is ascribable to the presence of residual hydroxyl groups on coating materials’ surface, able to induce easier nucleation of the hydroxyapatite to their mesoporosity and, thus, the large specific surface area. Furthermore, the low processing temperatures allow for easy coating functionalization by embedding suitable molecules such as anti-inflammatory and antibacterial agents leading to coatings preventing biofilm formation and inflammatory pathway activation. Therefore, the application of the sol-gel coatings provides an excellent chemical modification of the materials’ surface, allowing for protective barrier layer production.

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