Key Engineering Materials Vols. 361-363

Abstract: Molluscan shell possesses excellent strength, stiffness and fracture toughness that are closely related to its exquisite microstructure. SEM observation of a clam’ shell showed that the shell is a kind of bioceramic composite consisting of aragonite and protein layers parallel with the surface of the shell. The observation also showed that the aragonite layers are composed of long and thin aragonite sheets. Many aragonite sheets are of curving shape at the center of the shell. The higher fracture toughness of the shell was analyzed based on the representative model of the curving aragonite sheets and the concept of the maximum pullout force that is related to the fracture toughness of the shell. The analytical result showed that the maximum pullout force of the curving aragonite sheet is larger than that of straight aragonite sheets, which may effectively enhance the fracture toughness of the shell.

Abstract: Bone possesses excellent mechanical properties, which are closely related to its favorable microstructures optimized by nature through many centuries. In this work, a scanning electron microscope (SEM) was used to observe the microstructures of a cannon bone. It showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The hydroxyapatite layers are composed of long and thin hydroxyapatite sheets. The hydroxyapatite sheets in different hydroxyapatite layers distribute along different orientations, which composes a kind of cross microstructure. The maximum pullout force of the cross microstructure was investigated and compared with that of the 0° microstructure with their representative models. The result indicated that the maximum pullout force of the cross microstructure is markedly larger than that of the 0° microstructure.

Abstract: A novel hybrid material of chitosan/nano-sized SiO2/hydroxyapatite (HAp) composite was prepared through a biomimetic approach. HAp deposited in situ on the surface of chitosan/ nano-sized SiO2 composite film in simulate body fluid (SBF) solution at 36.5°C. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to study composition and morphological characteristics of the HAp crystal. The results indicated that nano-sized SiO2 dispersed in the chitosan film provided initial nucleation sites for the growth of the HAp in SBF solution by adsorbing further PO4 3−, Ca2+ due to the induction of HAp formed. The strength of the composite was largely improved because of the addition of nano-sized SiO2.

Abstract: Titanium oxide/ titanium/ plastic composite implants were formed by coating commercially pure titanium thin films on the surfaces of plastic cylinders by DC magnetron sputtering method. The composite is uniformly formed and the surface of the composite implant is smooth. The implants in rat tibias were not broken and the films on the surfaces of the samples did not decompose. The samples with bone were able to cut by diamond knife and observations between bone and titanium oxide on titanium by TEM succeeded. Therefore, the composite is useful for implants or observations the interactions between titanium oxide and bone in detail.

Abstract: The poly(methyl methacrylate)/silica nano-composite made from trimethoxysilyl functionalized poly(methyl methacrylate) and dimethyl diethoxysilane was newly prepared and its apatite-forming ability and mechanical properties were evaluated comparing to poly(methyl methacrylate)/silica nano-composite made from trimethoxysilyl functionalized poly(methyl methacrylate) and tetraethyl orthosilicate. Its apatite-forming ability was similar to that of poly(methyl methacrylate)/silica nano-composite using tetraethyl orthosilicate but its fracture toughness was much improved. Its high fracture toughness might come from the less quantity of siloxane linkages in its structure because dimethyl diethoxysilane had only two ethoxysilane groups while tetraethyl orthosilicate had four ethoxysilane groups. From the results, it can be concluded that it has a possibility to be used as bioactive bone cement.

Abstract: Composites of calcinated bovine bone derived hydroxyapatite (BHA) doped with 5 wt% and 10 wt% machineable fluorapatite glass (MFG) were prepared by sintering. Microstructure observations and measurements of density, compression strength and microhardness indicated a positive effect of MFG-doping to BHA. The highest compression strength (59.7 MPa) was achieved after sintering at 1300°C for 5% MFG. In the light of results of earlier similar studies, the paper discusses the features of the potential of BHA-MFG composites in biomedical practice.

Abstract: A new in situ precipitation technique was developed to promote high-affinity nucleation and growth of calcium phosphate in the polymer hydrogel. Gelatine/poly(acrylic acid)/hydroxyapatite (HA) composite has been prepared using template-driven reaction. Nano-sized hydroxyapatite particles were distributed within organic template homogenously, furthermore, inorganic particles were fine and uniform. During the composite process, 3D network of organic matrices and homogenous distributed nucleation sites played an important role in the superfine interaction of HA and hydrogel. This method provides an efficient approach toward inorganic/organic nanocomposites with high-uniformity decentralization for biomimetic replant applications. This paper discussed the mechanism of the reaction, and the concept of in situ precipitation in gel was brought forward.

Abstract: Silk fibroin hydrogels were prepared and their potential to deposit calcium phosphates in vitro was observed. Pristine and lyophilized samples were tested in 1xSBF and 1.5xSBF. The results showed that silk fibroin hydrogels can induce calcium phosphate deposits both in the pristine and lyophilized form. However, the pristine silk fibroin hydrogel after calcification presented a fragile structure making it difficult to handle, while the lyophilized samples presented better resistance to handling. Calcium phosphates deposits were intense in samples submitted to tests in 1.5xSBF, however, few and isolated deposits were observed on samples submitted to tests in 1xSBF. The 3-D porous structure and the ability to deposit calcium phosphates, turn silk fibroin hydrogel a potential material suitable to use in biomimetic processes.

Abstract: This paper addresses the determination of aldehyde group (% of dialdehyde units) in dialdehyde cellulose (DACs) oxidized from bacterial cellulose (BC). With 4 determination methods, the oxidation degrees of DACs were studied: Automatic potential titration method through Schiff base reaction, Acid-base titration in Cannizzaro reaction, Metaperiodate consumption determination, and Measurement of amino nitrogen content in DAC derivatives. By comparing determination results of these methods, we found out the proper way suitable for this metaperiodate oxidation system of BC to measure the dialdehyde unit content of the DACs.

Abstract: Cattle bone-based hydroxyapatite (HA) powders were prepared. Three types of silane coupling agents, i.e. γ-aminopropyl triethoxysilane (APES), methyl trimethoxysilane (MTMS), and γ-glycidoxypropyl trimethoxysilane (GPMS) were used to modify the HA surface. Untreated HA powders and silane-treated HA powders were utilized to produce HA/polypropylene (PP) composites containing a 60% (w/w) of HA content. Effect of filler surface modification on properties of HA/PP composites were investigated. The results suggested that treating HA surface with a silane coupling agent enhances interaction at HA-PP interface. Among the silane coupling agents used in this study, APES is, on average, the most effective agent for enhancing stiffness of HA/PP composites.