Bio-Medical Materials and Engineering - Volume 9, issue 3

Authors: Lee, Hae‐Hyoung | Kon, Masayuki | Asaoka, Kenzo

Article Type: Research Article

Abstract: Thermocycling and water storage effects on fracture toughness (K_\mathrm{IC} ) of chemically or thermally tempered metal‐ceramic disks were investigated to evaluate the durability of tempering effects with regard to oral aqueous environment. Metal‐ceramic disks (\varnothing 10 mm \times 2.0 mm) consisting of opaque porcelain (0.2 mm thick), body porcelain (1.3 mm) and Ni‐Cr‐Be alloy (0.5 mm) were prepared and the porcelain surfaces were polished with 1‐\mu m diamond paste. The disks were subjected to ion exchange (potassium or rubidium) or thermal tempering treatments, then with the as‐polished or further annealed disks, thermocycled for 8000, 15,000, …and 22,000 cycles between 5^\circ C and 60^\circ C or stored in water at 37^\circ C for 33 days. After aging, K_\mathrm{IC} values of disks were determined by a Vickers indentation technique. Statistical analyses indicated that the K_\mathrm{IC} values of ion‐exchanged and annealed disks were not significantly affected by the limited number of cycles and water storage, while the thermally tempered and untreated disks revealed a significant decrease in mean K_\mathrm{IC} from even 8000 cycles and after storage. However, there was no significant difference between thermocycling and water‐storage effects on mean K_\mathrm{IC} of all surface treatment groups. Results indicate that chemical tempering (ion exchange) produced more durable residual stresses than does thermal tempering for metal‐ceramic restorations. A low‐thermal load only was unlikely to affect the apparent fracture toughness of porcelain. Show more

Keywords: Porcelain, ion exchange, thermal tempering, durability, fracture toughness

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 135-143, 1999

Authors: Mair, L.H. | Krishnan, V. Kalliyana

Article Type: Research Article

Abstract: Progressive three body wear up to 30 min for five dental composites (Concise, Heliomolar, Occlusin, P‐30, Profile, TPH) stored for 9 months at 37^{\circ} C in citrate, lactate and PBS buffers, 25 and 75% ethanol media, has been measured using a wear tester. Particle size of the filler and the storage media are found to play dominant roles in determining the extent of wear. Heliomolar, which is a microfilled composite, shows maximum wear whereas wear is least in composites containing filler particles of conventional and hybrid size such as P‐30 ({>} 1\mu m). The storage media is found …to attack and degrade glass filler particles compared to composites having quartz fillers. Show more

Keywords: Three body wear, food simulating media, dental composite

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 145-149, 1999

Authors: Rhalmi, S. | Odin, M. | Assad, M. | Tabrizian, M. | Rivard, C.H. | Yahia, L’H.

Article Type: Research Article

Abstract: Porous nickel‐titanium (NiTi) alloys have demonstrated bone attachment as well as tissue ingrowth in the past. However, very few studies have compared porous NiTi soft and hard tissue reactions, and in vitro cell response. We therefore have evaluated the general muscle and bone reaction to porous nickel‐titanium. The latter material was implanted in rabbit tibias and back muscle, and assessed after three, six and twelve weeks of implantation. Porous NiTi specimens did not cause any adverse effect regardless of both implantation site and post‐surgery recovery time. Muscle tissue exhibited thin tightly adherent fibrous capsules with fibers penetrating into implant pores. …We observed that attachment strength of the soft tissue to the porous implant seemed to increase with post‐implantation time. Bone tissue demonstrated good healing of the osteotomy. There was bone remodeling characterized by osteoclastic and osteoblastic activity in the cortex. This general good in vivo biocompatibility with muscle and bone tissue corresponded very well with the in vitro cell culture results we obtained. Fibroblasts seeded on porous nickel‐titanium sheets managed to grow into the pores and all around specimen edges showing an another interesting cytocompatibility behavior. These results indicate good biocompatibility acceptance of porous nickel‐titanium and are very promising towards eventual NiTi medical device approbation. Show more

Keywords: Nickel‐titanium, porous implant, cytocompatibity, biocompatibility, tissue ingrowth

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 151-162, 1999

Authors: Niwa, Motoo | Li, Wei | Sato, Tsutomu | Daisaku, Takehiko | Aoki, Hideo | Aoki, Hideki

Article Type: Research Article

Abstract: Hydroxyapatite is widely utilized as a component in dental hygiene agents. The ability to adsorb and remove dental plaque adhering to tooth surfaces is recognized as an important property of hydroxyapatite particles. In this study, the adsorptive ability of hydroxyapatite was evaluated based on its adsorptive amount and adsorptive strength. The adsorptive amount was determined by measuring the weight of albumin, dextran and lipids adsorbing to hydroxyapatite. The adsorptive strength was determined by measuring the weights of albumin and dextran remaining adsorbed after rinsing. Similar procedures were performed in control experiments using calcium hydrogen phosphate dihydrate, alumina and sericite. The …results showed that the weights of albumin and dextran adsorbed to hydroxyapatite were 1.4 \pm 0.13 and 1.6 \pm 0.30 times higher than that to calcium hydrogen phosphate dihydrate. The weight of lipids adsorbed to hydroxyapatite was much higher than that to alumina and sericite. The percentages of weight loss of albumin and dextran were 2.3 \pm 1.7% and 5.3 \pm 2.0% for hydroxyapatite and 27 \pm 6.8% and 19 \pm 11% for calcium hydrogen phosphate dihydrate after one rinse. It is concluded that hydroxyapatite is a better adsorbent than calcium hydrogen phosphate dihydrate, alumina and sericite with respect to adsorbing albumin, dextran and lipids. Show more

Keywords: Hydroxyapatite, albumin, dextran, lipids, adsorption

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 163-169, 1999

Authors: Djurić, Danko | Drndarević, Vujo | Vujić, Dragana

Article Type: Research Article

Abstract: A freezing device for cryopreservation of blood mononuclear cells has been developed. The device is microcontroller operated, allowing cell freezing by a fully automatic, unattended process. To ensure optimum preservation, the temperature in the cell suspension uniformly decreases from room temperature to -100^{\circ} C and then the samples are transferred to long‐term storage. The performance of the device has been tested using both physiological solution and a sample of cell suspension. The control of temperature variation of cell suspension in the entire temperature range has been realised with an accuracy better than \pm 0.1%. The viability of cells …recovered from the frozen samples was 95%. The nitrogen consumption for one cycle of cryopreservation was 1.5l. In addition to the fully automatic mode, the manual and semi‐automatic modes are available for research purposes. The device has been designed using low cost and widely used electronic components and materials, it is compact and simple to operate. Show more

Keywords: Cryopreservation, blood cells, freezing device, controlled gradient

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 171-178, 1999

Authors: Khang, Gilson | Lee, Sang Jin | Lee, Jin Ho | Kim, Yong Sik | Lee, Hai Bang

Article Type: Research Article

Abstract: Chemogradient surfaces whose properties are changed gradually along the sample length are of particular interest for the basic studies of the interaction between biological species and surfaces since the effect of a selected property can be examined in a single experiment on one surface. A wettability chemogradient on the poly(l‐lactide‐co‐glycolide) (PLGA) films by treating them in air with corona from a knife‐type electrode whose power increases gradually along the sample length. The PLGA surfaces oxidized gradually with the increasing corona power, and the wettability chemogradient was created on the surfaces as evidenced by the measurement of water contact angles and …electron spectroscopy for chemical analysis. The wettability chemogradient PLGA surfaces prepared were used to investigate the interaction of fibroblast cells in terms of the surface hydrophilicity/hydrophobicity of PLGA surface. The cells adhered and grown on the chemogradient surface along the sample length were counted and observed by scanning electron microscopy. It was observed that the cells were adhered, spread, and grown more onto positions with moderate hydrophilicity of the wettability chemogradient PLGA surface than onto the more hydrophobic or hydrophilic positions. The maximum adhesion and growth of the fibroblast cells appeared at around water contact angle of 55^\circ . It seems that the wettability plays important roles for cell adhesion, orientation, spreading and growth on the PLGA surface. It might be that this surface modification technique can be used for improving the adhesion and growth of cell onto PLGA film and scaffolds, and can be applicable in the area of the tissue engineering. Show more

Keywords: Poly(lactide‐co‐glycolide), corona treatment, wettability chemogradient, fibroblast, adhesions

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 179-187, 1999

Authors: Jones, V.C. | Barton, D.C. | Fitzpatrick, D.P. | Auger, D.D. | Stone, M.H. | Fisher, J.

Article Type: Research Article

Abstract: Current designs of mobile bearing knees have different kinematics at the tibial counterface articulation; unidirectional represented by linear tracks and rotating platform designs, and multidirectional represented by reduced constraint designs with motion of the tibial surface in A–P and M–L directions simultaneously. One fifth scale experimental models of the tibial counterface articulation have been developed with mean contact stresses of 0.6 MPa. The unidirectional model had a linear reciprocating motion with a 10 mm stroke, the multidirectional model had a reciprocating motion with a 10 mm stroke and simultaneous rotation of \pm 7.5{}^\circ . Six specimens of GUR415 …polyethylene were tested for each model, sliding on polished cobalt chrome counterfaces with Ra < 0.01 \mu m in 25% bovine serum lubricant. The mean \pm STERR wear rates were: unidirectional 0.045 \pm 0.015 mm^{3} /million cycles and multidirectional 0.44 \pm 0.15 mm^{3} /million cycles. Applying the scaling factor of 5, the predicted wear rates in actual knee prostheses were: unidirectional 0.23 mm^{3} /million cycles and multidirectional 2.2 mm^{3} /million cycles. The order of magnitude increase in wear rate was statistically significant (p={} 0.05). Show more

Citation: Bio-Medical Materials and Engineering, vol. 9, no. 3, pp. 189-196, 1999