Materials Science Forum Vols. 539-543

Abstract: The basic principles behind human tissue response to artificial surface implantation may be developed under its biological aspect, it is necessary for a medical use to study the mechanical limits of every biomaterials to predict the tissue and the body's response according to the composition, the structure and the design of a biomedical material. To promote a stable and functional direct connection between bone and implant, titanium implants can be coated with materials based on calcium phosphate ceramics such as hydroxyapatite (HAp)(Ca10(P04)6(OH)2). The preferred orientation of HAp crystallites at the interface bone-implant in sheep tibia bones has been measured with the neutron 2-axis diffractometer D20 at the Institut Max von Laue-Paul Langevin (ILL), extracted 60 days after implantation. The implant has two faces, one coated and one non-coated with plasma-sprayed HAp (80 .m). We probed the samples with a spatial resolution of 0.5 mm started from the interface in order to inspect the reorganisation of the HAp crystallite’s distribution after implantation.

Abstract: Calcium carbonate (vaterite)-containing poly(lactic acid) (PLA) composites (CCPCs) were prepared for novel biomaterials that are expected to exhibit high bioresorbability and osteoconductivity. CCPC containing 30% vaterite showed bending strengths of 40~50 MPa. 13C CP/MAS-NMR spectrum of CCPC suggested the formation of a bond between Ca2+ ion and COOgroup. The bond may play an important role in the improvement of the mechanical properties. On the surface of CCPC containing 30 % vaterite, ~10-μm-thick hydroxycarbonate apatite (HCA) formed after 1 day of soaking in SBF at 37oC. After 1-week incubation of human osteoblasts (HOBs) on the HCA-coated CCPC, numerous HOBs attached. The adhesion of cells on the composite was greater than that on PLA. After 3-week culture of HOBs on HA-coated CCPC, numerous bone nodules could be seen on the surface. CCPC is believed to be one of the most promising materials for bone repair. A novel CCPC containing polysiloxane was also prepared using aminopropyltriethoxysilane (APTES). Polysiloxane partially assembled in the membrane and a molecular chain of PLA was bonded at the end of an organic chain in APTES through the amide bond formed between carboxy groups in PLA and amino groups in APTES. The composite formed HA on its surface after 3 days of soaking in SBF. The HA layer included Si with Ca and P. The composite coated with silicon-containing HCA had higher cell-proliferation ability than that without HA. The existence of silicon-containing HCA may be apt to stimulate the proliferation.

Abstract: The formation of plasma-polymerized materials made from organic molecules is a technologically attractive way to obtain films with unique properties for life science applications. Surface properties like bio-compatibility, wettability, etc., can be adjusted by tailoring the chemical functionalization. It is well known that after deposition these films undergo post-plasma reactions, especially when they are exposed to ambient atmosphere. Most often, in applications these films are not used immediately after their deposition – they are usually stored for a certain time. Therefore there is a need for a development of analytical procedures enabling studies of ageing phenomena of plasma chemically deposited films. With the help of these studies a better understanding of basic post-plasma reaction phenomena as well as relevant empiric information for practical applications can be obtained. However, a detailed chemical characterization of plasma chemically deposited films is a great challenge for the analysts because of the co-existence of a number of different chemical species. We investigated r.f. plasma-polymerized organic films by using photoelectron spectroscopy for chemical analysis (ESCA), spectroscopy of the near edge X-ray absorption fine structures (NEXAFS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Ethylene, styrene, allyl alcohol and allyl amine were used as monomers. A dedicated plasma preparation chamber was designed and added to the main analysis chamber of the respective spectrometer. This approach offers the possibility to study plasma-polymerized films in situ and, subsequently, the influence of post-plasma reactions. The important effect of air exposure of the film, in terms of plasma technology denominated as “ageing”, can be studied subsequentially step by step by this unique approach.

Abstract: This paper presents a methodology for assessing the in-vivo degradation mechanisms of articular components of total hip replacement (THR) prostheses of Charnley type. The experimental procedure revealed that common features can be observed even if the clinical cases under investigation were quite different with regard to the demographic data. It particularly emphasises the detrimental effects of foreign bodies on the damage of the articulating surfaces. These foreign bodies can migrate into the joint space before embedding definitely into the Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular cup surface where they further participate to a third body wear mechanism accelerated by a progressive increase of the femoral head roughness. Our experimental results underline, from a practical point of view, the need for careful manufacturing and clinical handling of porous surfaces, advocate for a systematic assessment of retrieved components, particularly when changed because of unexplained wear, and make questionable the clinical use of multifilament trochanteric cables.

Abstract: The development of an efficient targeted gene delivery system into cells is an important strategy for the advancement of gene therapy. The targeted gene delivery system is especially important in non-viral gene transfer which shows the relative low transfection efficiency. And it also opens the possibility of selective delivery of therapeutic plasmids to specific tissues. Chitosan has been considered to be a good candidate for gene delivery system, since it is already known as a biocompatible, biodegradable, and low toxic material with high cationic potential. However, low specificity and low transfection efficiency of chitosan need to be overcome prior to clinical trial. In this study, we focused on the chemical modification of chitosan for enhancement of cell specificity and transfection efficiency.

Abstract: Microstructures and mechanical properties including elastic modulus were investigated in terms of ternary alloying elements Si addition, Nb content variations and tensile test. Martensite structure with α'(hcp) or α"(orthorhombic) was observed in Ti-xNb-1.5at.%Si, where x=10-20at.%. The crystal structure of martensite formed from water quenching process was largely dependent upon Nb content but does not on Si content. On the basis of experimental results obtained, it is suggested that Si has an effective role to suppress the precipitation of ω phase leading to reduction in elastic modulus in the metastable β phase region. Metastable β phase region was superior to reduce the elastic modulus than stable β phase region in the present alloy system. The minimum value of elastic modulus was measured to 48GPa. We have found that stress-induced martensitic transformation takes place during the deformation in the present alloys. Within the alloys having β(bcc) phase studied Nb-poor region appeared to exhibit a dominant behavior for stress-induced martensitic transformation than Nb-rich region. This result suggests that metastable β phase is superior to stable β phase for the occurrence of stress-induced martensitic transformation in the present alloy system.

Abstract: For commercialized dental implants, to enhance the bone bonding of the artificial tooth roots, several kinds of surface modification techniques, such as hydroxy-apatite coating, anodic oxidation and sand-blasting, have been developed. Apart from the surface modification, it is known that the bone growth is accelerated by electric stimulations in the living body. In the present study, the galvanic current between titanium substrate and gold coating partially on the titanium implants was applied to enhance calcium phosphate precipitation in a pseudo-body fluid namely Hanks’ solution. The galvanic current between titanium specimens and gold electrode jumped up approximately 0.2 s after put into Hanks’ solution and the current has decreased asymptotically. With such consideration, the desirable conditions of surface modification by gold coating were presented to provide suitable galvanic current density enhancing calcium phosphate precipitation.

Abstract: In the last few years, clinical procedures undergone huge modifications. Among them, mini-invasive surgery has modified the clinical practice and the quality of life of patients. Shape Memory Polymers (SMPs), a class of stimuli-responsive materials, can be considered ideal candidates for the design of devices for mini-invasive surgical procedures. Such a device can be inserted in a packed in, temporary shape and later can expand at body temperature. A bone defect could be filled by a SMP porous structure, that improves the tissue integration and healing. In this work, two different processing techniques to obtain porous shape memory polymer scaffolds from Calo MER™ and MM-4520, two SMPs, are presented. Porous structures were obtained by micro-extrusion with different chemical foaming agents or with sodium chloride, or by solvent casting/particulate leaching. The morphology, the thermo-mechanical and the shape recovery properties of the SMP porous samples were investigated. Tridimensional porous structures showed a well interconnected morphology, with a pore size in the range aimed for bone interaction applications. The shape memory properties were not significantly affected by the transformation processes: a good ability of recovering the original shape was verified. Therefore, the porous structures, obtained from these SMP materials, appear adequate for an use as bone filler.