Key Engineering Materials Vols. 342-343

Abstract: Fixation nail systems , such as DHS, DCS and the standard Gamma-nail, are widely applied for the 31-A2 intertrochanteric unstable fractures treatment, but which one would be of more curative effect is still remained as a disputed problem. In this work, precise femur model with 31-A2 fracture was rebuilt based on the CT data, and fixation nail models were built by CAD. By the means of finite element analysis (FEA), the biomechanical data of femur and nail systems were achieved under typical loading. The results show that under the same load, the maximal stresses on the fracture sections for DCS, DHS and Gamma nail systems are 48MPa, 24MPa and 19MPa, separately; and the directional deformation is the highest with DCS fixation systems, while lowest with Gamma nail fixation system. Considering the mechanical safety, Gamma nail is more suitable for 31-A2 intertrochanteric unstable fractures treatment.

Abstract: Sirolimus-loaded poly (lactic acid-co-glycol acid) (PLGA) films were prepared by a casting method. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to determine the optimal concentration of sirolimus for vascular smooth muscle cell (VSMC) inhibition effect. Based on the results of MTT, three samples of different weight percent loaded-sirolimus (2wt%, 6wt%, 15wt%) PLGA films were selected. The release of lactate dehydrogenase (LDH) was used to evaluate the immediate toxicity of the sirolimus-loaded PLGA films and it was shown that the three different concentrations of sirolimus-loaded films have low toxicity. Alamar blue results indicate that the sirolimus-loaded films have better antiproliferation effect than 316 stainless steel (SS). The higher the sirolimus concentration in the film is, the better is the antiproliferation effect. These films may be used for stent coating to inhibit in-stent restenosis induced by VSMC proliferation.

Abstract: Lactate dehydrogenase (LDH) and enzyme-linked immunosorbent assay (ELISA) have attracted much attention recently for the evaluation of blood compatibility of biomaterials due to their convenience and quantifiability. In this paper, the use of LDH and ELISA is described for in situ investigation of platelet behavior on biomaterial surfaces, including quantification of platelet adhesion and platelet activation, after suitable testing conditions have been established. The material samples investigated in these tests included low temperature isotropic carbon (LTIC), Ti-O films, and phosphorus- and aluminum-doped TiO2 films. The evaluation results show that the lowest platelet adhesion and activation are observed on phosphorus-doped TiO2 films while the highest platelet adhesion and activation are observed on LTIC. In addition, conventional platelet adhesion experiments were performed for comparison, and yielding similar evaluation results as LDH and ELISA. It is suggested that LDH and ELISA tests can be successfully applied to evaluate the blood compatibility of biomaterials and can show many advantages, such as quantification, reliability and objectivity, compared with conventional platelet adhesion test.

Abstract: Polyurethane foam was fabricated by ‘two-component method’ for changing cell structures. Compression force applied immediately to the polyurethane foam just after complete foam formation at the top of the mold for generation cell structure of negative Poisson effect. That is what we called pressure-controlled method. The polyurethane foam, produced by pressurecontrol method (CT), has significant higher resilience (52.3%) and similar level of shock absorption (47.5%) compared with control polyurethane foam (resilience is 21.5%, shock absorption is 54%). The PU foam with negative Poisson’s ratio showed excellent resilience with shock absorbance. The pressure-control method divided into two parts (CT0, CT1). The CT1 method is to apply compression force to the foam with time-delayed after foam formation. The PU foam produced by CT1 showed lower stress relaxation time, stress relaxation ratio, and maximum stress than CT0. Hence, CT1 foam is superior to other polyurethane foam as shock absorbing materials, such as shoes for diabetic patients.

Abstract: To prevent prolonged air leakage after lung surgery, we developed a biodegradable polyglycolic acid (PGA) sheet and compared it with an expanded polytetrafluoethylene (ePTFE). Eighteen adult mongrel dogs were used in this experiment. The airway pressures at which air first leaked at the stapled resection margins were measured immediately after surgery in group I (N=5), 2 days after surgery in group II (N=5), and 7 days after surgery in group IIII (N=5), Based on the presence of SLR, there were 3 subgroups in each group: there was no SLR in subgroup a; ePTFE in subgroup b; PGA sheet in subgroup c. The histologic examination was performed 2 months after surgery (N=3). In group I, there was a significant difference in air leakage pressures (mm Hg) between no reinforcement and SLR. We observed the same results in group II and III with statistical significance. However, there was no significant difference between the reinforcement groups. The histologic findings demonstrated more severe adhesions and biodegradation in the dogs in which the PGA sheet was used. Our PGA sheet was considered a useful reinforcement material, because it had a similar threshold for air leakage with the ePTFE with excellent biodegradation.

Abstract: Accurate measurement of the mechanical properties of artificial or cultivated cartilage is a major factor for determining successive regeneration of defective soft tissues. In this study, we developed a novel method that enabled the bulk modulus (k-modulus) to be measured nondestructively using the relationship between volume and pressure of living soft tissues. In order to validate this method we estimated the bulk modulus of soft silicone rubbers using our new method and a conventional method. The results showed a 5 ~ 10% difference between the results obtained with the two methods. Our method was used subsequently to measure the mechanical properties of cultivated cartilage samples (collagen gel type), that had been incubated for four weeks in the presence or absence of human articular chondrocytes (HACs). Our experiments showed that cultivated cartilage tissues grown in the presence of HACs had a higher bulk modulus (120 ± 20 kPa) than samples grown without HACs (90 ± 15 kPa). The results indicated that our novel method offered an effective method for measurement of volume changes in minute living soft tissues, with the measurements having a high degree of accuracy and precision. Furthermore, this method has significant advantages over conventional approaches as it can be used to rapidly and accurately evaluate the strength of soft tissues during cultivation without causing damage to the specimen.

Abstract: The purpose of this study was to evaluate the osteogenesis of tetracycline blended chitosan membranes on the calvarial critical size defect in Sprague Dawley. An 8 mm surgical defect was created with a trephine bur in the area of the midsagittal suture. Forty rats were divided into four groups: negative control group, positive control group and two experimental groups. Three types of membranes were made and a comparative study was done. One type of non-woven membrane was made by chitosan for positive control. The other two types of non-woven membranes were made by immersing non-woven chitosan into either the tetracycline solution or the chitosan-tetracycline solution. Histologic analysis was done at 2 weeks and 8 weeks of healing periods. We concluded that that the use of tetracycline blended chitosan membrane on the calvarial defects in rats has a significant effect on the regeneration of bone tissue in itself. In addition it implicates that tetracycline blended chitosan membrane may be useful for guided tissue regeneration.

Abstract: This study evaluated the combined inhibitory effects of a Curcuma xanthorrhiza extract (CXE) and Xylitol on S. mutans and A. viscosus in vitro. Three series of experiments on S. mutans and A. viscosus were carried out. In the first series, the Minimum inhibitory concentrations (MICs) of CXE, Xylitol, and CXE mixed with Xylitol (CXE+Xylitol) against S. mutans and A. viscosus were determined. Second, the antibacterial effect and the rapid effectiveness of CXE, Xylitol, and CXE+Xylitol against those bacteria was evaluated as contacting for 1, 2, 5, and 10 minutes. Finally, The saccharolytic capability of S. mutans was examined using bovine teeth that had been pretreated with CXE (1%), Xylitol (1%), CXE+Xylitol (1%), chlorhexidine (1%) and distilled water, and rinsed with distilled water. The pretreated bovine teeth were layered with soft agar containing sucrose (5%), S. mutans and phenol red, as a pH indicator, and incubated. The MICs of CXE were 5 ppm on both bacterial species. Xylitol did not inhibit either species. The MICs of CXE+Xylitol were 10 and 5 ppm against S. mutans, A. viscosus, respectively. According to the rapid effectiveness, CXE completely inhibited the growth of bacteria but Xylitol did not. CXE+Xylitol could completely inhibit the growth of bacteria. An evaluation of the saccharolytic capability of S. mutans on bovine teeth revealed that distilled water and Xylitol could not inhibit bacterial fermentation. However, the bovine teeth containing CXE, CXE+Xylitol and chlorhexidine inhibited the fermentation of bacteria. These results show that CXE and CXE+Xylitol have a strong antibacterial effect on S. mutans and A. viscosus in vitro.

Abstract: In order to prepare the enzyme electrode for sensing of chemical molecules, the Au was coated on the surface of PP film by sputter coater. Polyaniline (PANI) was polymerized on the surface of the coated Au film by electrochemical polymerization of aniline in order to use working electrode. Subsequently, horseradish peroxide (HRP) was immobilized on PANI electrode as follows: Method I. The HRP was immobilized on the surface of PANI electrode by using Au nanoparticle as linker (physical adsorption). Method II. The HRP was immobilized on the surface of PANI electrode by using 2-aminothiophenol and Au nanoparticle as linker (Self-assembling immobilization). Method III. HRP was directly immobilized with PANI electrode by using glutaric dialdehyde as linker (covalent bonding). The sensing efficiency of the prepared HRP-PANI electrode was also examined. The sensing efficiency of the HRP-PANI electrode for H2O2 was as following order; Method I > Method III > Method II..

Abstract: In order to immobilize enzyme to multi-wall nanotube (MWNT), the MWNT was coated by the electrochemical polymerization of aniline. The horseradish peroxide (HRP) was immobilized on the surface of the polyaniline (PANI)-coated MWNT (PANI-MWNT film) by using gold nanoparticle (physical immobilization). The HRP was also immobilized on the surface of PANIMWNT film by using 2-aminothiophenol and Au nanoparticle (self-assembling immobilization). HRP was immobilized on the surface of PANI-MWNT electrode by using glutaric dialdehyde (covalent immobilization). The sensing efficiency of HRP-MWNT electrodes for H2O2 was evaluated by amperometric method. The sensing efficiency of HRP-MWNT electrodes for H2O2 was as following order; physical immobilization > covalent immobilization > self-assembling immobilization.