Materials Science Forum Vols. 783-786

Abstract: Layer-by-layer (LbL) is a bottom-up technique used for construction of films with self-assembly and self-organizing properties. In most cases, the fundamental driving force for the formation of these films is originated from the electrostatic interaction between oppositely charged species. The charged segments of polyelectrolytes behave as small building units and their orientation and position can be designed to target structures of great complexity. Furthermore, the technique enables the use of various materials, including natural polymers. In this work, we chose the cationic biopolymer chitosan (CHI) and the negative polyelectrolytes sodium alginate (ALG) and hyaluronic acid (HA). The aim of this study was to evaluate the effect of ionic strength (0 versus 200 mM) and pH (3 versus 5) on ALG/CHI and HA/CHI nanostructured multilayered thin films properties. From profilometry and atomic force microscopy (AFM) analyses, changes in thickness and roughness of the coatings were monitored. The presence of salt in polyelectrolyte solutions induced the polymer chains to adopt conformations with more loops and tails and this arrangement in solution was transmitted to films, resulting in rougher surfaces. Furthermore, the film thickness can be precisely controlled by adjusting the pH of the polyelectrolyte solution. The variation of these parameters shows that it is possible to molecularly control chemical and structural properties of nanostructured coatings, thus opening up new possibilities of application (e.g. cell adhesion).

Abstract: Mechanical biocompatibility, including tensile properties and Young’s modulus, of -type Ti-Mn alloys,namely, Ti-10Mn and Ti-14Mn, fabricated by the metal injection molding method were investigated. Thebone formability (biological biocompatibility) of a Ti-Mn alloy, namely, Ti-12Mn, fabricated by thearc-melting method was evaluated by means of an animal test. The tensile strength of sintered Ti-10Mn andTi-14Mn achieve a maximum value of 860 and 886 MPa, respectively. The Ti-14Mn specimen sintered at1273 K shows the lowest Young’s modulus (76 GPa) among all sintered Ti-10Mn and Ti-14Mn specimens.The tensile strength of Ti-Mn alloys is almost equal to that of Ti64 ELI; further, their Young’s modulus islower than that of Ti-6Al-4V ELI. The relative bone contact ratio of Ti-12Mn increases from 11% to 29%with increasing implantation time from 12 weeks to 52 weeks. Moreover, the relative bone contact ratio ofTi-12Mn and CP-Ti is almost constant for all implantation times.

Abstract: Titanium implant surfaces should ideally be designed to support the subsequent clinical application. Therefore temporarily used implants have to fulfill both the mechanical stabilization of the bone stock and furthermore in trauma surgery the disintegration into the bone because the implant should be removed after fracture healing. The anti-adhesive plasma-fluorocarbon-polymer (PFP) films were synthesized using two different low-pressure plasma sources, the 2.45 GHz microwave (mw) and the 13.56 MHz capacitively coupled radio-frequency (rf) discharge in a mixture of the precursor octafluoropropane (C₃F₈) and hydrogen (H₂). The film properties were characterized using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, water contact angle measurements, and abrasive strength tests. Cell adhesion and spreading of human osteoblasts were clearly reduced on these PFP surfaces. First in vivo data on the biocompatibility of the PFP films deposited in the rf-discharge demonstrate that the local inflammatory tissue response for PFP coating was comparable to controls, while a PFP coating deposited in mw plasma induced stronger tissue reactions.

Abstract: In this paper, results concerning newly developed Ti-Nb based superelastic alloys containing interstitial O or N element are presented. These elements were added because of their strong influence on the alpha” martensitic transformation and also because of their solid-solution strengthening effect. Microstructures and mechanical behavior of the alloys were investigated by different methods and compared with a binary Ti-Nb alloy taken as reference. On the other hand, in-situ synchrotron X-ray diffraction analyses during tensile tests have been specifically performed to characterize precisely the stress-induced martensitic transformation in such alloys.

Abstract: Two kinds of 3D printers were developed in our group. One is bathtub-type gel printer named SWIM-ER. The other is ink-jet-type food printer named E-CHEF NO.1. Using Meso-Decorated gels and agar, 3D printing of the soft materials was carried out. The valve of blood vessel, which is difficult to build by soft materials, is printed successfully by SWIM-ER. Their dimensions became almost the same as the designed. We also succeeded in printing food by E-CHEF NO.1, while a few bubbles are found in the sample.

Abstract: The Ti-15Mo-xNb system integrates a new class of titanium alloys without the presence of aluminum and vanadium, which exhibit cytotoxicity, and that have low elasticity modulus values (below 100 GPa). This occurs because these alloys have a beta structure, which is very attractive for use as biomaterials. In addition, Brazil has about 90% of the world’s resources of niobium, which is very important economically. It strategically invests in research on the development and processing of alloys containing this element. In this paper, a study of the influence of heat treatments on the structure and microstructure of the alloys of a Ti-15Mo-xNb system is presented. The results showed grain grown with heat treatment and elongated and irregular grains after lamination due to this processing. After quenching, there were no changes in the microstructure in relation to heat-treated and laminated conditions. These results corroborate the x-ray diffraction results, which showed the predominance of the β phase.

Abstract: Anodic oxide nanostructures (nanopores and nanotubes) were formed on a biomedical β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr alloy (TNTZ), in order to improve adhesive strength by the anchor effect of a segmented polyurethane (SPU) with soft tissue compatibility. The nanotube structure was formed beneath the nanoporous structure. The adhesive strength between the SPU coating and the nanoporous structure formed on TNTZ by anodization is more than 1.5 times that of an SPU coating on as-polished TNTZ with a mirror finish. After removal of the nanoporous structure by etching with HF solution, the adhesive strength of the SPU coating on the exposed nanotube structure is decreased.

Abstract: Most bones are anisotropically loaded and seem to be adapted to the anisotropic stress or strain field by changing the anisotropy in their microstructure. Osteocyte (OCY) is believed to play an important role as a mechanosensor and regulator of modeling and/or remodeling orchestrating osteoblast and osteoclast activity to make bone suitable to resist the mechanical environment. In general, osteocytes sense magnitude of stress (strain) applied upon the bone and then work as a trigger to change bone mass to adjust bone’s mechanical function to the stress field. This structural optimization is an important aspect of the bone functional adaptation; another inevitable optimization might be achieved through the change in intrinsic material anisotropy including the preferential c-axis orientation of biological apatite (BAp) crystal. To achieve this adaptation through material anisotropy, osteocyte needs to be a mechanosensor which can detect anisotropic stress field. In the present study, osteocyte lacunae and canaliculi in the mid-diaphysis and the distal part of the rat femur were stained by a fluorescein dye for visualization and analysis. The mid-diaphysis shows greater degree of the preferential c-axis orientation of BAp crystal than the distal part in relation to the magnitude of uni-axial stress field. It was found that the osteocytes in long bone preferentially align along the bone long axis and the degree of alignment is greater in the mid-diaphysis than in the distal region, which seems to be effective for the sensation of the site-dependent specific stress field applied on the long bone.

Abstract: Magnesium alloys are attractive for use as biodegradable materials for temporary implant applications. However, the high localized degradation of magnesium alloys in physiological conditions is a major concern, which can affect the mechanical integrity of the implant during service. Calcium phosphate (CaP) coating is a suitable method to delay the initiation of localized attack in magnesium alloys. This paper will discuss the challenges and opportunities in electrochemically coating CaP on magnesium and its magnesium alloys for biodegradable implant applications.

Abstract: In this study, effect of hydrolysis in simulated body environment on mechanical behavior oftricalcium phosphate (TCP)/Poly(L-lactic acid) (PLLA) composites were analytically characterized.In order to predict stress-strain behavior after hydrolysis, damage micromechanical analysis proposedby the authors were utilized. In this model, nonlinear behavior in stress strain relationship weresimulated considering interfacial debonding between TCP particle and PLLA matrix. For the purposeof deciding the interfacial strength, such as critical energy release rate, curve fitting was conducted onthe result of the composites with 15wt% TCP content. Theoretical results on 5wt% and 10wt%composites using the interfacial strength obtained were in good agreement with experimental results.This result indicated that interfacial strength was independent from TCP fraction.