Key Engineering Materials Vol. 631

Abstract: Over the last two decades, the philosophy behind an optimal fixation of orthopaedic implants progressively evolved towards “bone-conservative” solutions and, accordingly, the researchers’ attention moved from simple mechanical fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on a physico-chemical bond (surface modification) in order to minimize bone resection/loss and maximize tissue-implant integration. This research work explores the feasibility of a novel bioceramic single-piece acetabular cup for hip joint prosthesis that can be anchored to the patient’s pelvic bone by means of a bone-like trabecular coating (scaffold) able to promote implant osteointegration.

Abstract: As interface design of autotransportation materials and bioactive ceramics by supersonic treatment, human teeth-originated granules and commercial hydroxyapatite (HAp) were partially dissolved in different acid solutions, such as electrolyzed water and HNO₃ aqueous solution to control bio-absorption, adsorption-release of bone growth factor and anti-bacterial characteristics. Human teeth were pulverized with cooling, dissolved in strongly acidic electrolyzed water (pH 2.6-3.1) or 2.0% HNO₃ solution to obtain demineralized dentin matrix granules. For supersonic or stirring demineralization in the acidic electrolyzed water, dissolution efficiencies (DE) were 3-12% and dentinal tubules with 1-2μm were found, while for supersonic demineralization in the HNO₃ solution, DE was attained to the highest value of 86%. When HAp was dissolved with stirring in the acidic electrolyzed water, DE of porous ceramics was lower than that of spherical particles due to smaller specific surface area and good crystallinity. For supersonic dissolution of porous ceramics in the acidic electrolyzed water, DE was 30% and extension of grain boundary and micro-crack were observed. Concerning supersonic irradiation of the electolyzed water to parietal bone in rats by using ultrasonic scaler, enlargement and propagation of micro-crack were recognized on the hard tissues.

Abstract: The aim of this research is to develop a methodology to obtain bioactive coatings on Ti6Al4V substrates pretreated with NaOH 5M for 24 h, by an autocatalytic route using an acid bath. The autocatalytic bath was developed in order to produce bioactive coatings with a Ca/P molar ratio of 1.2 by dissolving the appropriate amounts of CaCl₂ and NaH₂PO₂ as precursors and C₄H₄Na₂O₄·6H₂O as a reducing agent in distilled water, at pH values of 5.5 and 6.0, temperatures of 80 and 90°C, and two immersion times of 60 and 180 min. It was observed that the thickness and morphology of the coating changed according to the processing conditions.

Abstract: It has been well known that bone has piezoelectric properties and these properties have been considered to be caused by the shift of the center of symmetry of the positive and negative electrical charge due to the strain of the collagen fibers included in the bone. Thus, it has long been considered that there were no piezoelectric effects in the hexagonal hydroxyapatite (HAp) which has center of symmetry of crystal. However, in recent years, the piezoelectric property of artificially synthesized HAp was reported. In the authors’ previous report, a new result which showed the piezoelectricity of the hydroxyapatite (HAp) films fabricated by the pulsed laser deposition (PLD) method was reported. In this study, the effect of poling treatment on piezoelectric constant of pulsed laser deposited HAp films was investigated.

Abstract: Dentin hypersensitivity is induced by mechanical stimuli or heat stimuli applied via dentin tubules exposed by lost of dental enamel or gingival recession. Common treatments for dentin hypersensitivity are resin coating or laser irradiation. However, these treatments have some problems such as poor biocompatibility or insufficient durability. We have been developing a treatment that creates artificial tooth enamel by attaching flexible ultrathin calcium phosphate sheet having a crystal structure similar to that of tooth enamel to seal the dentin tubules. In this study, the quantitative evaluation of dentin tubule sealing rate improved by attaching ultrathin amorphous calcium phosphate (APC) sheet on human dentin is presented. The obtained sealing-rate by APC sheet application was 70.9 ± 4.8 %.

Abstract: Once tooth decay reaches to the inside of dentin, the damage remains permanently. Therefore, the restoration of dentin is important in dental treatment. In the present study, we newly proposed a tooth restoration technique with intraoral laser ablation method. A thin layer of a-tricalcium phosphate (a-TCP) was deposited on dentin surface in the atmosphere by ablation phenomenon using an Er:YAG (Erbium: Yttrium-Aluminium-Garnet) laser irradiated to the target of a-TCP. Then, the deposited layer was hydrolyzed by dripping pure water on its surface in order to create hydroxyapatite (HAp) coating. Interface structure between the HAp coating and dentin surface was observed by a scanning electron microscope. Electron micrographs showed that the HAp layer of 10-20 mm in thickness was formed on the dentin surface. Moreover, dentinal tubules were sealed with the HAp particles. These results indicate that our newly proposed technique is useful for the treatment of dentin cavities.

Abstract: The development of open source 3D printers and the continuously growing utilization of ceramic compounds in the field of medicine among others, meet in the possibility to adapt these machines in a way to permit better controlling, high resolution, automatic, printing of scaffolds, spacers and other 3D parts not possible without this kind of machines and technology. Due to the large number of applications inside the field of medicine it is required a high capacity to create structures that can reach the needs in each case. Furthermore, the possibility to modify easily and quickly these structures as the tests are being done is also very interesting for investigation. These machines allow, thanks to its open source nature, these features and more as they are not closed to changes in order to meet the needs of its users. Therefore, the focus of the present work has been to materialize and improve a head extruder for Advanced Technical Ceramics Compounds. The tests undertaken and the results outcome demonstrate the feasibility of the technology for being applied in such mentioned cases as well as the improvement on the solutions (initial and improvements) for producing automatic casting.

Abstract: The use of rapid prototyping technologies in the manufacturing ceramic materials has been developed in recent years due to its many advantages. Studies combining rapid prototyping using biomaterials as raw material increased significantly in recent years. The inkjet printing involves using ceramic powder with binder and a fluid released onto the sample through a printhead. The effect of dispersant in conventional manufacturing of alumina-based materials was widely known. However, there are few studies dealing on this issue for rapid prototyping. This work aims to obtain pieces of alumina via a 3D printer, inkjet model, varying concentrations of dispersant and fluid in order to compare its influence. The specimens were evaluated for their apparent porosity, density and dimensions. It was concluded that 1.0% of dispersant combined with a larger amount of solvent resulted in parts with suitable dimensions and higher mechanical strength.

Abstract: Different ratios of a resorbable phosphate glass (ICEL) and a bioactive silicate glass (CEL2) were co-sintered to obtain 3D porous scaffolds by gel-cast foaming method. The scaffold morphology, crystalline phases and compressive strength were studied. All the scaffolds showed a 3D structure with highly interconnected pores. The ICEL/CEL2 co-sintering resulted in a lower shrinkage leading to higher scaffold porosity (more than 70 vol%) compared to pure ICEL and CEL2 (about 65 vol%). Tuning ICEL/CEL2 ratio allowed the modulation of the scaffold resorption rate, with weight loss ranging from 20% to 75% after soaking for 3 months in simulated body fluid. Scaffolds containing higher amount of CEL2 silicate glass, resulted in a very high bioactivity. In vitro biological test showed no toxic effect of the scaffolds on human osteoblast-like cells.

Abstract: The importance of this work is development of two methods to try to improve the bone tissue regeneration. The surface of scaffold was modified in order to favor cell interaction, through adhesion and proliferation. PLA and gelatin were used. PLA has shown in literature good results in bone tissue engineering. The gelatin is used as coating in cell culture plates to improve cell attachment for a variety of cell types, including osteoblast. Hydroxyapatite (HA) and tricalcium phosphate (TCP) were used due to its known properties in tissue engineering. It was used the polymer foam replication technique to produce the scaffolds. For characterization were used: scanning electron microscopy (SEM), optical microscopy (OP), stereoscopy, transmission electron microscopy (TEM), X-ray microtomography (Micro-CT), X-ray diffraction (XRD) and X-ray fluorescence (XRF). The scaffolds showed morphology with adequate porosity for tissue engineering and the in vitro test showed evidence of not being cytotoxic.