Bio-Medical Materials and Engineering - Volume 12, issue 3

Authors: Kong, Chong‐Su | Yoon, Goan Hee | Khang, Gilson | Rhee, John M. | Lee, Hai Bang

Article Type: Research Article

Abstract: In order to investigate the fundamental data for the resistance of gamma radiation sterilization of polyvinylchloride (PVC), the formulations of the antioxidants such as commercial Irganox series and inorganic, processing aids, stabilizer aids, trans‐stilbene oxide (StO) and so on have been carried out. The control and irradiated PVC samples with 1.5, 2.5 and 4.0 Mrad were characterized by mechanical tester, colorimetry, and extractant in water. Irganox 1010 was more effective than Irganox 1076 for color changes whereas Irganox 1076 was more effective than Irganox 1010 for the change of extractant. It was also observed the significant diminution of color changes …for inorganic antioxidants as CaO and ZnO. Oxidized paraffin wax as lubricant, styrene‐methylmetacrylate copolymers as processing aids, and nontoxic debenzoylmethane as secondary stabilizer did not show good stabilization for the irradiation. The new proposed radiation stabilizer in this study, StO, showed the significant improvement of gamma radiation resistance for the plasticized PVC. The possible mechanism could be explained that an epoxy functional group stabilizes effectively the processes of dehydrogenation, the formation of hydroperoxides, and the formation of oxygen containing groups, and the synergetic effects of an epoxy compound are more notable for the prevention of radiation oxidation in the presence of an aromatic group. Show more

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 211-224, 2002

Authors: Assad, Michel | Chernyshov, Alexandr | Leroux, Michel A. | Rivard, Charles‐H.

Article Type: Research Article

Abstract: Porous titanium–nickel (PTN) alloys represent new biomaterials for long‐term implantation. Their porosity properties might confer them the capacity to trigger fluid capillarity, tissue ingrowth, as well as good tissue–implant apposition and fixation. Before PTN materials are used as long‐term implants, their biocompatibility level must be assessed. In this study, porous titanium–nickel was therefore extracted in a saline semi‐physiological solution and materials were evaluated for potential cytotoxicity and genotoxicity reactions. The cytocompatibility elution test was performed in order to determine PTN toxic potential at the in vitro cellular level: no reactivity was detected in cell layers exposed to PTN extracts or …the negative controls. In parallel, the genocompatibility of porous titanium–nickel was evaluated using three different assays in order to assess potential damage at the DNA level: the test for chemical induction of chromosome aberrations, the Salmonella typhimurium and Escherichia coli reverse mutation assay, and the mouse micronucleus test. No significant increase in the number of chromosomal aberrations, bacterian revertant colonies, or micronuclei was observed in presence of PTN extracts when compared to negative control exposition. Based on the above results, porous titanium–nickel can be considered completely cytocompatible and genocompatible, and therefore represents a good candidate for long‐term implantation. Show more

Keywords: Porous, titanium–nickel, biocompatibility, cytotoxicity testing, genotoxicity testing

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 225-237, 2002

Authors: Machen, M. Shaun | Tis, John E. | Inoue, Nozomu | Meffert, Rainer H. | Chao, Edmund Y.S. | McHale, Kathleen A.

Article Type: Research Article

Abstract: The purpose of this study was to investigate effects of low intensity pulsed ultrasound (LIPU) on distraction osteogenesis in a less‐than‐rigid biomechanical environment in a rabbit model. A less‐rigid mini‐lengthener was applied and a mid‐tibial osteotomy performed in 20 New Zealand White rabbits. After a 7 day latency period, the tibiae were distracted 0.5 mm every 12 hours for 10 days. Ten of the rabbits received LIPU for 20 min/day (ultrasound group) and 10 received sham LIPU (control group) from day 17 until sacrifice on day 37. Radiographs were taken weekly after distraction and the callus area was measured. After …sacrifice, dual‐energy X‐ray absorptiometry (DEXA), torsional testing to failure, and histomorphometry were performed. On radiographs, all the treatment tibiae displayed persistent radiolucencies; however, only one of the control tibiae displayed a radiolucent interzone. Torsional strength of the treatment group was 54% of the contralateral tibia compared to 139% in the control group (p<0.008). Bone density and callus size were not significantly different between the 2 groups; however, the ultrasound group displayed a tendency towards more cartilage and fibrous tissue formation (p<0.16) and less bone (p<0.16) than controls. In a biomechanically unstable environment, LIPU appears to stimulate more cartilage formation in regenerated callus than in controls. This callus is biomechanically inferior to unstimulated callus at the early stage of healing tested. During distraction osteogenesis a sound biomechanical environment is important to achieving anticipated results. Show more

Keywords: Ultrasound, distraction osteogenesis, rabbit model, torsional test, external fixation

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 239-247, 2002

Authors: Iwakami, Tomohiko | Imai, Toshio

Article Type: Research Article

Abstract: The effect of hydroxyapatite sol (HAm) which is composed of unheating hydroxyapatite microcrystal particle on cell proliferation and alkaline phophatase activity in osteoblastic MC3T3‐E1 cells, was examined in the presence or absence of fetal calfe serum (FCS) in the medium. In the absence of FCS, HAm inhibited the cell proliferation of MC3T3‐E1 cells in a dose‐dependent manner, but not in the presence of FCS. Inhibitory effect by HAm was observed only in directly contact with the cells. Similar inhibition effects by HAm were also observed on ALP activity of the cells. However, inhibitory effect by HAm on ALP extracted from …the cells was not observed. After HAm treatment, ALP activity in the medium was increased. HAm pretreated with FCS did not inhibit the ALP activity of the cells at all. These results suggest that serum may play an important role in the biocompatibility of HAm and osteoblastic cells. Show more

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 249-257, 2002

Authors: Lewandrowski, Kai‐Uwe | Bondre, Shrikar P. | Wise, Donald L. | Trantolo, Debra J.

Article Type: Research Article

Abstract: The tissue response of subchondral bone to a biodegradable fixation device manufactured in the shape of a screw and made of polylactide with a hydroxyapatite buffer were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. One screw was implanted per animal. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow‐up times of 8 and 16 weeks, the specimens were examined radiographically and histomorphometrically. The intact contralateral femur served as a control for comparison. Only …minimal signs of degradation of the polymer could be seen in the histologic specimens. These implant degradation sites were commonly areas of new bone formation adjacent to the screw implant. A brim of repair tissue was formed at the entrance and exit of the implant channel. The width of the repair tissue from the tissue–implant boundary towards the center of the entrance hole varied greatly between the specimens, from 80 to 750 μm. In most specimens this bridging tissue consisted of newly formed bone and undifferentiated mesenchymal tissue. Degenerative chondrocyte clustering occurred in the pre‐existing cartilage within a 400 μm wide zone from the tissue–implant interface into the recipient tissues. Some new‐bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae was only significantly higher in the screw‐implanted 16‐week specimens, when compared to the non‐operated contralateral controls. Although the bony osteotomy was invariably healed in all specimens with good implant integration, the quality and quantity of the reparative tissue of the articular cartilage near the screw hole was variable. This study showed that large polylactide implants, which are buffered with hydroxyapatite show benign tissue responses and good implant osteointegration when implanted in bone. They may be suitable for fixation of small bone fractures. However, insertion through intra‐articular surfaces may require further improvement of the implant material to avoid the degenerative repair processes seen in this study. Show more

Keywords: Bioresorbable screw, hydroxyapatite, osteotomy healing, implant osteointegration

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 259-270, 2002

Authors: Gil, F.J. | Ginebra, M.P. | Planell, J.A.

Article Type: Research Article

Abstract: This paper presents a study of the surface hardening of Ti6Al4V alloy produced by electrochemical anodizing and by different heat treatments, in addition to studying the annealing of the martensitic structure. Results of the combination of both methods produce hardening over 1300 HV and an important improvement on the tribological behaviour. These values could improve wear resistance of this alloy in applications like articular prostheses.

Keywords: Titanium, surface treatment, anodizing, microstructure

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 271-281, 2002

Authors: Puértolas, J.A. | Pérez‐García, J.M. | Juan, E. | Ríos, R.

Article Type: Research Article

Abstract: We have designed and manufacture a prototype of a new anchoring system for soft bone tissue fixation, based on the superelasticity of the Ni–Ti alloy. The anchoring capability has been observed in femoral hips by radiographs. The performance of this new anchor have been measured by tensile experiments and contrasted with finite element model. The results point out that keeping the fixation capacity, the new configuration presents advantages concerning to a minor damaged volume bone, a reduction of the manufacture cost and a simpler insertion.

Keywords: Anchors, soft tissue bone, Ni–Ti, Nitinol, shape memory alloys

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 283-289, 2002

Authors: Morita, Yusuke | Tomita, Naohide | Aoki, Hideyuki | Wakitani, Shigeyuki | Tamada, Yasushi | Suguro, Toru | Ikeuchi, Ken

Article Type: Research Article

Abstract: The mechanical properties of regenerated cartilage tissue were measured to evaluate changes in their visco‐elastic properties during cultivation. An indentation test and dynamic visco‐elasticity measurements were carried out on cartilage tissue cultured with rabbit chondrocytes that had been inoculated into the fibroin sponge. A 1.5‐mm‐diameter porous indentor was used for the indentation test, in which time‐dependent strain curves were derived from measurements taken under several loading conditions. Dynamic visco‐elasticity measurements were performed under compressive loading to evaluate the load‐bearing function of the articular cartilage. Although the amount of permanent deformation was not influenced by the duration of cartilage regeneration, the …amount of creep deformation increased with longer cultivation. The E′ value of the regenerated cartilage increased and the peak value of tan δ and the frequency at the peak became lower with longer cultivation. It is suggested that the changes in the time‐dependent strain curves and dynamic visco‐elastic properties of the regenerated cartilage were caused by maturation of the cultured cartilage tissue. Show more

Keywords: Articular cartilage, regeneration, fibroin sponge, indentation test, dynamic visco‐elasticity measurement

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 291-298, 2002

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: The values of two viscoelastic properties (storage modulus and loss angle) of four sets of ultra‐high‐molecular‐weight polyethylene specimens were obtained. Two sets comprised specimens that had been sterilized (using gamma radiation in air or ethylene oxide gas) while the other two sets comprised specimens that were sterilized and then exposed to an accelerated aging protocol that, in the literature, has been proposed as simulating 5 years of real‐time shelf aging. An analysis of the present results from the four specimen sets and those obtained, in a previous study by the present author, on specimens machined from real‐time shelf aged tibial …inserts suggests that the claim made for the accelerated aging protocol may be conservative. Show more

Keywords: Ultra‐high‐molecular‐weight polyethylene, accelerated aging, storage modulus, loss angle

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 299-308, 2002

Authors: Valdevit, Antonio | Kambic, Helen | Lilly, Deante | Graham, Scott | Parker, Richard | Bergfeld, John

Article Type: Research Article

Abstract: The Posterior Cruciate Ligament (PCL) consists of two primary bundles and is the primary restraint to posterior tibial translation. The emergence of the Posterior Tibial Inlay Technique (PTIT) has demonstrated a mechanical advantage over the commonly used Tibial Tunnel Method (TTM). This study was designed to investigate the effects on knee mechanics from both a Single‐bundle (SB) and Double‐bundle (DB) Achilles tendon PCL reconstruction using a PTIT. The investigators hypothesized that a DB graft demonstrates a mechanical advantage compared to the SB graft. A materials testing machine provided six sequential loading cycles of 100 N while total translation was measured. …The testing was conducted at 90°, 60°, 30° and 10° of flexion in neutral tibial rotation. While the mechanical advantages of the DB graft were detected, specifically at small laxity values and in the physiological range of normal gait, the additional complexity of the technique may clinically outweigh the mechanical advantages. Show more

Keywords: PCL, force, stiffness, non‐linear regression, Inlay technique

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 309-317, 2002

Authors: Ohashi, T. | Ishii, Y. | Ishikawa, Y. | Matsumoto, T. | Sato, M.

Article Type: Research Article

Abstract: Local mechanical properties were measured for bovine endothelial cells exposed to shear stress using an atomic force microscopy (AFM), and the AFM indentations were simulated using a finite element method (FEM) to determine the elastic modulus. After exposure to shear stress, the endothelial cells showed marked elongation and orientation in the flow direction, together with significant decrease in the peak cell height. The applied force–indentation depth curve was obtained at seven different locations on the major axis of the cell surface and quantitatively expressed by the quadratic equation. The elastic modulus was determined by comparison of the experimental and numerical …results. The modulus using our FEM model significantly became higher from 12.2±4.2 to 18.7±5.7 kPa with exposure to shear stress. Fluorescent images showed that stress fibers of F‐actin bundles were mainly formed in the central portion of the sheared cells. The significant increase in the modulus may be due to this remodeling of cytoskeletal structure. The moduli using the Hertz model are 0.87±0.23 and 1.75±0.43 kPa for control and sheared endothelial cells respectively. This difference can be attributable to the differences in approximation functions to determine the elastic modulus. The elastic modulus would contribute a better understanding of local mechanical properties of the cells. Show more

Keywords: Finite element method, elastic modulus, vascular endothelial cells, shear stress, cytoskeletal remodeling

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 3, pp. 319-327, 2002