Bio-Medical Materials and Engineering - Volume 12, issue 2

Authors: Hedia, H.S.

Article Type: Research Article

Abstract: The stress and strain distribution in the bone surrounding a dental implant have been analyzed using the finite element and optimization techniques. The effect of removing cancellous bone completely or not was investigated. Two models were used, the first model without cancellous bone and the second with it. The elastic modulus of the implant material and the length of the implant neck or the height of bone surrounding the implant were used as design variables in the two models. In the first model a higher level of stress in the cortical bone surrounding the neck of the implant was …found. While in the second model, it was found surrounding the tip of the implant. The result indicates that the stress concentration factor in the bone of the first model is reduced by 30% compared to the initial design. However, when the implant was surrounded by sleeve of cancellous bone (second model) the stress concentration is reduced by 16% for cortical bone and 15% for cancellous bone. This reduction help to reduce fatigue failure and bone resorption. Show more

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 111-119, 2002

Authors: Valenta, Jaroslav | Vitek, Karel | Cihak, Radomir | Konvickova, Svatava | Sochor, Miroslav | Horny, Lukas

Article Type: Research Article

Abstract: An analytical model has been used to simulate the effects of tissue aging on residual strain, constitutive relations and stiffness parameter in the main right and left (ramus circumflexus) human coronary arteries, based on experimental data. The experimental opening angle θ scatters considerably with age. The optimum angle θop ≈70°, which makes the circumferential stress uniform in the arterial wall at a normal blood pressure, is approximately constant throughout aging. Above age of the 15 years the estimated and experimental values of θ are greater than θop and therefore the mechanical load of the inner layers of the media …and the intima decreases and the adventitia is overloaded. On the basis of nonlinear regression analysis, age‐related constitutive laws of arterial wall circumferential stiffness have been determined. Above the age of 30, arterial wall hardening increases rapidly. The left coronary artery is stiffer than the right artery for groups from 35 to 45 years of age. Hyperelasticity theory has been used to identify age‐related multiaxial stress through wall thickness. A theoretical model based on the reduced Green strain provides a very good representation of the coronary artery circumferential mechanical response and predicts its nearly isotropic behavior. Bio‐composite material forms non‐homogeneous stresses and, in the course of aging, it increases the adventitia loading. In groups aged from 10 to 15 years, whose coronary artery residual strains are low, the circumferential stress distribution has a classic form. Stiffness parameter β gradually increases with age and this increase is significant above the age of 60. Parameter β tends to decrease when the opening angle θ increases. Show more

Keywords: Coronary artery, aging, residual strain, opening angle, constitutive laws, stiffness parameter

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 121-134, 2002

Authors: Khang, Gilson | Kong, Chong‐Su | 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 additives such as plasticizers of dioctylphthalate, trioctyltrimellitate and polyester, second plasticizers, Ca/Zn nontoxic metallic stabilizers with powder, paste and liquid state, and phosphite stabilizers have been carried out. The control and irradiated PVC samples with 1.5, 2.5 and 4.0 Mrads were characterized by mechanical tester, colorimetry, and extractant in water. The effect of plasticizers observed in the order of dioctylphthalate ≈ trioctyltrimellitate > polymeric plasticizer. It was observed in the order of Ca/Zn metallic stabilizers of paste > liquid …≈ powder state for the color change and liquid > paste > powder for the extractant. The mechanism of the discoloration of PVC in our experiment was predominant the formation of polyene by the dehydrochlorination rather than the formation of keton and aldehyde by the oxidation and chain dissociation by the measurement of gel permeation chromatography and mechanical property. The proposed mechanisms of stabilization and discolorization with various additives are also discussed. Show more

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 135-147, 2002

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: In this study, a determination is made of the effect of loading rate, v (0.1 mm min−1 versus 1.0 mm min−1 versus 10 mm min−1 ) on the value of the plane strain fracture toughness, KIc , of three commercial formulations of acrylic bone cement (Osteopal® , CMWTM 3, and Copal® , that are characterized as “low‐”, “medium‐”, and “high‐” viscosity brands, respectively). For all formulations, KIc increases with increase in v. However, while this trend is statistically significant for CMW3 and Copal, this is not so for Osteopal. The CMW3 and Copal results are explained in terms of changes …of the molecular relaxation transitions in the cement and the thermal state at the crack tip of the test specimen. Two implications of the findings are discussed. In the case of Osteopal, a recommendation for further study is made. Show more

Keywords: Acrylic bone cement, fracture toughness, loading rate

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 149-155, 2002

Authors: Otsuka, Makoto | Uenodan, Hiroyuki | Matsuda, Yoshihisa | Mogi, Takao | Ohshima, Hiroyuki | Makino, Kimiko

Article Type: Research Article

Abstract: Poly (lactide‐co‐glycolide or PLGA) microspheres containing 0.3% (w/w) of estradiol were prepared by a solvent evaporation method. These PLGA microspheres had a wide particle distribution between 0.5 and more than 100 μm. The average size was 76 μm. Physicochemical properties of the microspheres were characterized by X‐ray diffraction patterns, FT‐IR spectra and DSC. In vitro estradiol release was maintained at a constant rate from these PLGA microspheres for 1 month. The loaded drug was totally recovered in the collection buffer within this time period. In vivo experiments were performed on Wistar rats that had received ovariectomy. These rats were fed …with a vitamin D‐deficient and Ca‐deficient diet. The combination of ovariectomy and diet induced osteoporosis. PLGA microspheres containing either 50, 100, or 200 μg estradiol were injected into these rats. The plasma estradiol in each rat was monitored for 50 days. These in vivo drug release patterns were found to be different from the one obtained from in vitro release. The Ca‐AUC was not significant different among various dosages administered. However, bone mineral density for rats after the injection of estradiol loaded microspheres was higher than that obtained for the control. This suggested that all estradiol microspheres administration induced bone generation in osteoporosis rats. Show more

Keywords: Poly (lactide‐co‐glycolide) microsphere, drug delivery system, estradiol, osteoporosis rats, in vitro release, plasma calcium level

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 157-167, 2002

Authors: Haitao, Xiong | Kuanghu, Hu | Wanfang, Su | Shuyu, Li | Desen, Su

Article Type: Research Article

Abstract: This paper established the extracting method and algorithm for liposome images on the basis of analyzing the form feature of liposome, and its corresponding automatic analysis software. Some algorithms, such as the logical algorithms of mathematical morphology, the grayscale‐gradient co‐occurrence matrix‐based method and the image enhancement method of grayscale image, were used to restrain the noise effectively and increase the definition of image. The result on bipolysaccharide liposome indicates that the method increases the measuring speed and precision.

Keywords: Liposome, form feature extraction, mathematical morphology, grayscale‐gradient method and image enhancement

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 169-175, 2002

Authors: Ingram, Joanne | Matthews, Jane Bridget | Tipper, Joanne | Stone, Martin | Fisher, John | Ingham, Eileen

Article Type: Research Article

Abstract: This study evaluated the in vitro response of murine macrophages to clinically relevant polyethylene particles from two grades of UHMWPE at varying volume doses. Clinically relevant UHMWPE wear debris was generated in vitro using a tri‐pin‐on‐disc tribometer. The debris was observed using a scanning electron microscope and analysed by image analysis. There was no significant difference in the wear rates of the two grades of UHMWPE. Analysis of the wear debris showed that GUR 415HP produced a higher percentage of mass of debris in the submeter size range compared to GUR 1120. The wear debris was co‐cultured with C3H murine …peritoneal macrophages at particle volume (μm3 ): cell number ratios of 100 :1, 50 :1, 10 :1 and 1 :1 for both grades of UHMWPE and additionally at 0.5 :1 and 0.1 :1 for grade GUR 415HP. The secretion of TNF‐α was determined by ELISA. Significantly elevated levels of TNF‐α were secreted at 100 :1 ratio when macrophages were challenged with wear debris from GUR 1120 and at 10 :1 and 1 :1 for debris from GUR 415HP. The results suggested that the greater percentage mass of debris in the submicrometer size range from GUR 415HP lead to a substantial increase in biological activity for this grade of UHMWPE on a volume for volume basis when compared with GUR 1120. Show more

Keywords: Total joint arthroplasty, wear debris, cytokines, polyethylene, in vitro

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 177-188, 2002

Authors: Bell, J. | Tipper, J.L. | Ingham, E. | Stone, M.H. | Wroblewski, B.M. | Fisher, J.

Article Type: Research Article

Abstract: Submicrometer and micrometer‐sized UHMWPE wear particles have been associated with osteolysis and failure of total hip replacements. A previous study by Tipper et al. [16] examined the wear debris isolated from the acetabular periprosthetic tissues from 18 Charnley total hip replacements, and compared this data to the tribological variables of the prostheses. The present study aimed to isolate the UHMWPE wear debris from the femoral periprosthetic tissues from 10 of the same cohort of patients, and compare it with the debris isolated from the corresponding acetabular tissues. A variety of particle morphologies were observed, discrete submicrometer particles, along with …flakes and fibrils. The particle size distributions ranged from 0.1 to >250 μm, however, the largest particles were only found in samples when the femoral head damage was characterised as low (Rpm <0.2 μm). The mode of the frequency distribution of particles was in the range of 0.1–0.5 μm for all the femoral tissues. Considerable variations were found in the mass distributions of the wear particles as a function of size for different patients. The net mass of debris isolated from the femoral tissues was significantly lower (p<0.05, Student's t‐test) than from the corresponding acetabular tissues. This along with considerable spatial variation in the net mass of debris isolated from the different regions of the same sample of acetabular tissue, indicates that the transportation of the debris has a marked effect on the net mass of debris accumulated in different tissues. Show more

Keywords: UHMWPE, wear, wear debris, explants, total hip arthroplasty

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 189-201, 2002

Authors: Dong, Jian | Uemura, Toshimasa | Kikuchi, Masanori | Tanaka, Junzo | Tateishi, Tetsuya

Article Type: Research Article

Abstract: In this study, we hypothesize that loading more marrow‐derived mesenchymal stem cells (MSCs) into porous material by using a low‐pressure system during subculture, creating a composite which combines MSCs and a novel mechanical reinforced porous hydroxyapatite, can result in more bone tissue formation in vivo. Within 26 weeks postimplantation, we examined in vivo bone formation of the experimental group with 100 mmHg pressure applied to porous HA blocks loaded with MSCs. For in vivo testing, the 2‐week subcultured HA/MSC composites were implanted into subcutaneous sites of syngeneic rats. These implants were harvested at 13 and 26 weeks after implantation. SEM …showed that the pore surface is covered by osteoblasts as well as collagenous extracellular matrix at 13 weeks. Light microscopy revealed the quantity of bone at 26 weeks was greater than at 13 weeks. These results showed that the novel mechanical reinforced porous HA combined with MSC has more potential for bone formation at 100 mmHg, making this method very efficient for bone reconstruction. Show more

Keywords: Hydroxyapatite, mesenchymal stem cells, low‐pressure system, tissue engineering

Citation: Bio-Medical Materials and Engineering, vol. 12, no. 2, pp. 203-209, 2002