Displaying publications 1 - 20 of 170 in total

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  1. Chasis JA, Mohandas N
    J. Cell Biol., 1986 Aug;103(2):343-50.
    PMID: 3733870
    Skeletal proteins play an important role in determining erythrocyte membrane biophysical properties. To study whether membrane deformability and stability are regulated by the same or different skeletal protein interactions, we measured these two properties, by means of ektacytometry, in biochemically perturbed normal membranes and in membranes from individuals with known erythrocyte abnormalities. Treatment with 2,3-diphosphoglycerate resulted in membranes with decreased deformability and decreased stability, whereas treatment with diamide produced decreased deformability but increased stability. N-ethylmaleimide induced time-dependent changes in membrane stability. Over the first minute, the stability increased; but with continued incubation, the membranes became less stable than control. Meanwhile, the deformability of these membranes decreased with no time dependence. Biophysical measurements were also carried out on pathologic erythrocytes. Membranes from an individual with hereditary spherocytosis and a defined abnormality in spectrin-protein 4.1 association showed decreased stability but normal deformability. In a family with hereditary elliptocytosis and an abnormality in spectrin self-association, the membranes had decreased deformability and stability. Finally, membranes from several individuals with Malaysian ovalocytosis had decreased deformability but increased stability. Our data from both pathologic membranes and biochemically perturbed membranes show that deformability and stability change with no fixed relationship to one another. These findings imply that different skeletal protein interactions regulate membrane deformability and stability. In light of these data, we propose a model of the role of skeletal protein interactions in deformability and stability.
    Matched MeSH terms: Stress, Mechanical
  2. Sulong MZ, Setchell DJ
    J Prosthet Dent, 1991 Dec;66(6):743-7.
    PMID: 1805022
    Adhesive bond strength studies for the tray adhesive of an addition vinyl polysiloxane (President) impression material were conducted with an acrylic resin, chromium-plated brass, and plastic trays. Tensile and shear stress studies were performed on the Instron Universal testing machine. Acrylic resin specimens roughened with 80-grit silicon carbide paper exhibited appreciably higher bond strengths compared with different types of tray material and methods of surface preparation.
    Matched MeSH terms: Stress, Mechanical
  3. Ibrahim WM, McCabe JF
    J Nihon Univ Sch Dent, 1993 Dec;35(4):225-9.
    PMID: 8158281
    The mean strength that has traditionally been taken as a measurement of the strength of a material does not reflect the true strength, and therefore it cannot be used as a design parameter. This explains why many brittle materials fail at unpredictable stress, either below or above the mean strength. By using Weibull statistics, the prediction and assessment of strength can be made more sensibly. The performance of a material can be predicted by considering a stress at a lower level of failure probability.
    Matched MeSH terms: Stress, Mechanical
  4. Lim KO, Cheong KC
    Med Eng Phys, 1994 Nov;16(6):526-30.
    PMID: 7858787
    In the fabrication of a bioprosthetic heart valve from bovine pericardial tissues, the tissues are subjected to suturing. The stress-strain response of sutured as well as unsutured strips of this tissue were examined. The stress-strain response was determined using a tensile-testing machine. It was found that suturing weakens the tissue in that sutured strips are more extensible, exhibit a lower stress at rupture and a lower final elastic modulus. In addition, it was also found that the bigger the suture/needle size used the greater the decrease in tissue strength. In all, tissue strength was observed to decrease by 22 to 59% in this study. The weakening of the tissue is attributed to the puncture holes created by the surgeon's needle which create regions of weakness. This response of bovine pericardial tissue to suturing should be given due consideration in the fabrication of a bioprosthetic heart valve using this tissue.
    Matched MeSH terms: Stress, Mechanical
  5. Wan Abas WA
    Biomed Mater Eng, 1994;4(7):473-86.
    PMID: 7881331
    The response of human skin to biaxial stretch tests in vivo was investigated and compared to the response to uniaxial tension. The results obtained illustrate the nonlinear, anisotropic, and viscoelastic (time-dependent) properties of skin under biaxial stretch. Preconditioning in the load-extension response was found not to be prominent. The results also suggest that the response of skin to a biaxial stretch in vivo is qualitatively similar to that in vitro. Values of the terminal stiffness and limit strain of skin under a biaxial stretch are found.
    Matched MeSH terms: Stress, Mechanical
  6. Wan Abas WA, Asseli MR
    Biomed Mater Eng, 1994;4(7):463-71.
    PMID: 7881330
    Local strains acting across an area of skin loaded uniaxially in vivo are converted to stresses using the standard elastic formulae. The stress values are compared to those obtained using the classical Bossinesq and Michell stress functions. The results indicate that these functions are capable of describing the response of the skin, both in the low load and the high load regions.
    Matched MeSH terms: Stress, Mechanical
  7. Wan Abas WA
    Biomed Mater Eng, 1995;5(2):59-63.
    PMID: 7655319
    The response of human skin to "stress relaxation" tests at low loads in vitro was investigated. A number of behaviours, other than those already well established and documented, were observed. The significant behaviours are pure recovery and relaxation-recovery. Other behaviours observed are temporary stress recovery during the relaxation process, and momentary sudden non-linear drop in stress value followed by a second relaxation. The pure recovery and relaxation-recovery responses are repeatable. The latter represents the transitional response between the well-known behaviour of stress relaxation and the behaviour of stress recovery.
    Matched MeSH terms: Stress, Mechanical
  8. Razak AA, Harrison A
    J Prosthet Dent, 1997 Apr;77(4):353-8.
    PMID: 9104710
    Dimensional accuracy of a composite inlay restoration is important to ensure an accurate fit and to minimize cementation stresses.
    Matched MeSH terms: Stress, Mechanical
  9. Alani AH, Toh CG
    Oper Dent, 1997 Jul-Aug;22(4):173-85.
    PMID: 9484158
    Matched MeSH terms: Stress, Mechanical
  10. Roychoudhury PK, Gomes J, Bhattacharyay SK, Abdulah N
    Artif Cells Blood Substit Immobil Biotechnol, 1999 Sep-Nov;27(5-6):399-402.
    PMID: 10595439
    Studies were carried out in T-flasks and bioreactor to produce urokinase enzyme using HT 1080 human kidney cell line. While growing the cell line it has been observed that the lag phase is reduced considerably in the bioreactor as compared to T-flask culture. The HT 1080 cell adhesion rate and urokinase production were observed to be the function of serum concentration in the medium. The maximum urokinase activity of 3.1 x 10(-4) unit ml(-1) was achieved in the bioreactor at around 65 h of batch culture. Since HT 1080 is an anchorage dependent cell line, therefore, the hydrodynamic effects on the cell line were investigated.
    Matched MeSH terms: Stress, Mechanical
  11. Tan YT, Peh KK, Al-Hanbali O
    AAPS PharmSciTech, 2000;1(3):E24.
    PMID: 14727910
    This study examined the mechanical (hardness, compressibility, adhesiveness, and cohesiveness) and rheological (zero-rate viscosity and thixotropy) properties of polyethylene glycol (PEG) gels that contain different ratios of Carbopol 934P (CP) and polyvinylpyrrolidone K90 (PVP). Mechanical properties were examined using a texture analyzer (TA-XT2), and rheological properties were examined using a rheometer (Rheomat 115A). In addition, lidocaine release from gels was evaluated using a release apparatus simulating the buccal condition. The results indicated that an increase in CP concentration significantly increased gel compressibility, hardness, and adhesiveness, factors that affect ease of gel removal from container, ease of gel application onto mucosal membrane, and gel bioadhesion. However, CP concentration was negatively correlated with gel cohesiveness, a factor representing structural reformation. In contrast, PVP concentration was negatively correlated with gel hardness and compressibility, but positively correlated with gel cohesiveness. All PEG gels exhibited pseudoplastic flow with thixotropy, indicating a general loss of consistency with increased shearing stress. Drug release T50% was affected by the flow rate of the simulated saliva solution. A reduction in the flow rate caused a slower drug release and hence a higher T50% value. In addition, drug release was significantly reduced as the concentrations of CP and PVP increased because of the increase in zero-rate viscosity of the gels. Response surfaces and contour plots of the dependent variables further substantiated that various combinations of CP and PVP in the PEG gels offered a wide range of mechanical, rheological, and drug-release characteristics. A combination of CP and PVP with complementary physical properties resulted in a prolonged buccal drug delivery.
    Matched MeSH terms: Stress, Mechanical
  12. Memon MS, Yunus N, Razak AA
    Int J Prosthodont, 2001 May-Jun;14(3):214-8.
    PMID: 11484567
    PURPOSE: The impact strength and the flexural properties of denture base materials are of importance in predicting their clinical performance upon sudden loading. This study compares the impact and transverse strengths and the flexural modulus of three denture base polymers.
    MATERIALS AND METHODS: The investigation included a relatively new microwave-polymerized polyurethane-based denture material processed by an injection-molding technique, a conventional microwave-polymerized denture material, and a heat-polymerized compression-molded poly(methyl methacrylate) (PMMA) denture material. Impact strength was determined using a Charpy-type impact tester. The transverse strength and the flexural modulus were assessed with a three-point bending test. The results were subjected to statistical analysis using a one-way analysis of variance and the Scheffé test for comparison.
    RESULTS: The impact strength of the microwave-polymerized injection-molded polymer was 6.3 kl/m2, while its flexural strength was 66.2 MPa. These values were lower than those shown by the two compression-molded PMMA-based polymers. The differences were statistically significant. The flexural modulus of the new denture material was 2,832 MPa, which was higher than the conventional heat-polymerized polymer but was comparable to the other microwave-polymerized PMMA-based polymer. The difference in the flexural modulus was statistically significant.
    CONCLUSION: In terms of the impact and flexural strengths, the new microwave-polymerized, injection-molded, polyurethane-based polymer offered no advantage over the existing heat- and microwave-polymerized PMMA-based denture base polymers. However, it has a rigidity comparable to that of the microwave-polymerized PMMA polymer.
    Matched MeSH terms: Stress, Mechanical
  13. Mohd Fuad D, Masbah O, Shahril Y, Jamari S, Norhamdan MY, Sahrim SH
    Med J Malaysia, 2006 Feb;61 Suppl A:27-9.
    PMID: 17042225
    Antibiotic-loaded bone cement has been used as prophylaxis against infection in total joint replacement surgery. Its effect on the mechanical strength of cement is a major concern as high dose of antibiotic was associated with a significant reduction in mechanical strength of bone cement. However, the cut-off antibiotic that weakens the mechanical strength of cement remains to be determined. This study was undertaken to observe the changes in the mechanical properties of bone cement with gradual increments of Cefuroxime antibiotic. Cefuroxime at different doses: 0, 1.5, 3.0 and 4.5gm were added to a packet of 40gm bone cement (Simplex P) and study samples were prepared by using third generation cementing technique. Mechanical impact, flexural and tensile strength were tested on each sample. Significant impact and tensile strength reduction were observed after addition of 4.5 gm of Cefuroxime. However, flexural strength was significantly reduced at a lower dose of 3.0 gm. The maximum dose of Cefuroxime to be safely added to 40mg Surgical Simplex P is 1.5gm when third generation cementing technique is used. Further study is needed to determine whether it is an effective dose as regards to microbiological parameters.
    Matched MeSH terms: Stress, Mechanical*
  14. Pingguan-Murphy B, El-Azzeh M, Bader DL, Knight MM
    J Cell Physiol, 2006 Nov;209(2):389-97.
    PMID: 16883605
    Mechanical loading modulates cartilage homeostasis through the control of matrix synthesis and catabolism. However, the mechanotransduction pathways through which chondrocytes detect different loading conditions remain unclear. The present study investigated the influence of cyclic compression on intracellular Ca2+ signalling using the well-characterised chondrocyte-agarose model. Cells labelled with Fluo4 were visualised using confocal microscopy following a period of 10 cycles of compression between 0% and 10% strain. In unstrained agarose constructs, not subjected to cyclic compression, a subpopulation of approximately 45% of chondrocytes exhibited spontaneous global Ca2+ transients with mean transient rise and fall times of 19.4 and 29.4 sec, respectively. Cyclic compression modulated global Ca2+ signalling by increasing the percentage of cells exhibiting Ca2+ transients (population modulation) and/or reducing the rise and fall times of these transients (transient shape modulation). The frequency and strain rate of compression differentially modulated these Ca2+ signalling characteristics providing a potential mechanism through which chondrocytes may distinguish between different loading conditions. Treatment with apyrase, gadolinium and the P2 receptor blockers, suramin and basilen blue, significantly reduced the percentage of cells exhibiting Ca2+ transients following cyclic compression, such that the mechanically induced upregulation of Ca2+ signalling was completely abolished. Thus cyclic compression appears to activate a purinergic pathway involving the release of ATP followed by the activation of P2 receptors causing a combination of extracellular Ca2+ influx and intracellular Ca2+ release. Knowledge of this fundamental cartilage mechanotransduction pathway may lead to improved therapeutic strategies for the treatment of cartilage damage and disease.
    Matched MeSH terms: Stress, Mechanical
  15. Al-Makramani BMA, Razak AAA, Abu-Hassan MI
    J Prosthodont, 2008 Feb;17(2):120-124.
    PMID: 18047490 DOI: 10.1111/j.1532-849X.2007.00270.x
    PURPOSE: The current study investigated the effect of different luting agents on the fracture resistance of Procera AllCeram copings.

    METHODS: Six master dies were duplicated from the prepared maxillary first premolar tooth using nonprecious metal alloy (Wiron 99). Thirty copings (Procera AllCeram) of 0.6-mm thickness were manufactured. Three types of luting media were used: zinc phosphate cement (Elite), glass ionomer cement (Fuji I), and dual-cured composite resin cement (Panavia F). Ten copings were cemented with each type. Two master dies were used for each group, and each of them was used to lute five copings. All groups were cemented according to manufacturer's instructions and received a static load of 5 kg during cementation. After 24 hours of distilled water storage at 37 degrees C, the copings were vertically compressed using a universal testing machine at a crosshead speed of 1 mm/min.

    RESULTS: ANOVA revealed significant differences in the load at fracture among the three groups (p < 0.001). The fracture strength results showed that the mean fracture strength of zinc phosphate cement (Elite), glass ionomer cement (Fuji I), and resin luting cement (Panavia F) were 1091.9 N, 784.8 N, and 1953.5 N, respectively.

    CONCLUSION: Different luting agents have an influence on the fracture resistance of Procera AllCeram copings.

    Matched MeSH terms: Stress, Mechanical
  16. Sia S, Shibazaki T, Koga Y, Yoshida N
    Am J Orthod Dentofacial Orthop, 2009 Jan;135(1):36-41.
    PMID: 19121498 DOI: 10.1016/j.ajodo.2007.01.034
    This study was designed to determine the optimum vertical height of the retraction force on the power arm that is required for efficient anterior tooth retraction during space closure with sliding mechanics.
    Matched MeSH terms: Stress, Mechanical
  17. Ooi FK, Singh R, Singh HJ, Umemura Y
    Osteoporos Int, 2009 Jun;20(6):963-72.
    PMID: 18839049 DOI: 10.1007/s00198-008-0760-6
    SUMMARY: This study determines the minimum level of exercise required to maintain 8 weeks of jumping exercise-induced bone gains in rats. It was found that the minimum level of exercise required for maintaining the different exercise-induced bone gains varied between 11% and 18% of the initial exercise intensity.

    INTRODUCTION: This study ascertains the minimum level of follow-up exercise required to maintain bone gains induced by an 8-week jumping exercise in rats.

    METHODS: Twelve groups of 12-week old rats (n = 10 rats per group) were given either no exercise for 8 (8S) or 32 weeks (32S), or received 8 weeks of standard training program (8STP) that consisted of 200 jumps per week, given at 40 jumps per day for 5 days per week, followed by 24 weeks of exercise at loads of either 40 or 20 or 10 jumps per day, for either 5, or 3, or 1 day/week. Bone mass, strength, and morphometric properties were measured in the right tibia. Data were analyzed using one-way analyses of variance.

    RESULTS: Bone mass, strength, mid-shaft periosteal perimeter and cortical area were significantly (p < 0.05) higher in the rats given 8STP than that in the 8S group. The minimal level of exercise required to maintain the bone gains was 31, 36, 25, and 21 jumps per week for mass, strength, periosteal perimeter and cortical area, respectively.

    CONCLUSIONS: Eight weeks of jumping exercise-induced bone gains could be maintained for a period of 24 weeks with follow-up exercise consisting of 11% to 18% of the initial exercise load.

    Matched MeSH terms: Stress, Mechanical
  18. Merican AM, Amis AA
    J Biomech, 2009 Jul 22;42(10):1539-1546.
    PMID: 19481211 DOI: 10.1016/j.jbiomech.2009.03.041
    The iliotibial band (ITB) has an important role in knee mechanics and tightness can cause patellofemoral maltracking. This study investigated the effects of increasing ITB tension on knee kinematics. Nine fresh-frozen cadaveric knees had the components of the quadriceps loaded with 175 N. A Polaris optical tracking system was used to acquire joint kinematics during extension from 100 degrees to 0 degrees flexion. This was repeated after the following ITB loads: 30, 60 and 90 N. There was no change with 30 N load for patellar translation. On average, at 60 and 90 N, the patella translated laterally by 0.8 and 1.4mm in the mid flexion range compared to the ITB unloaded condition. The patella became more laterally tilted with increasing ITB loads by 0.7 degrees, 1.2 degrees and 1.5 degrees for 30, 60 and 90 N, respectively. There were comparable increases in patellar lateral rotation (distal patella moves laterally) towards the end of the flexion cycle. Increased external rotation of the tibia occurred from early flexion onwards and was maximal between 60 degrees and 75 degrees flexion. The increase was 5.2 degrees, 9.5 degrees and 13 degrees in this range for 30, 60 and 90 N, respectively. Increased tibial abduction with ITB loads was not observed. The combination of increased patellar lateral translation and tilt suggests increased lateral cartilage pressure. Additionally, the increased tibial external rotation would increase the Q angle. The clinical consequences and their relationship to lateral retinacular releases may be examined, now that the effects of a tight ITB are known.
    Matched MeSH terms: Stress, Mechanical
  19. AL-Makramani BM, Razak AA, Abu-Hassan MI
    J Prosthodont, 2009 Aug;18(6):484-8.
    PMID: 19694015
    PURPOSE: This study investigated the occlusal fracture resistance of Turkom-Cerafused alumina compared to Procera AllCeram and In-Ceram all-ceramic restorations.

    MATERIALS AND METHODS: Sixmaster dies were duplicated from the prepared maxillary first premolar tooth using nonprecious metal alloy (Wiron 99). Ten copings of 0.6 mm thickness were fabricated from each type of ceramic, for a total of thirty copings. Two master dies were used for each group, and each of them was used to lute five copings. All groups were cemented with resin luting cement Panavia F according to manufacturer's instructions and received a static load of 5 kg during cementation. After 24 hours of distilled water storage at 37 degrees C, the copings were vertically compressed using a universal testing machine at a crosshead speed of 1 mm/min.

    RESULTS: The results of the present study showed the following mean loads at fracture: Turkom-Cera (2184 +/- 164 N), In-Ceram (2042 +/- 200 N), and Procera AllCeram (1954 +/- 211 N). ANOVA and Scheffe's post hoc test showed that the mean load at fracture of Turkom-Cera was significantly different from Procera AllCeram (p < 0.05). Scheffe's post hoc test showed no significant difference between the mean load at fracture of Turkom-Cera and In-Ceram or between the mean load at fracture of In-Ceram and Procera AllCeram.

    CONCLUSION: Because Turkom-Cera demonstrated equal to or higher loads at fracture than currently accepted all-ceramic materials, it would seem to be acceptable for fabrication of anterior and posterior ceramic crowns.

    Matched MeSH terms: Stress, Mechanical
  20. Shuid AN, Mehat Z, Mohamed N, Muhammad N, Soelaiman IN
    J. Bone Miner. Metab., 2010 Mar;28(2):149-56.
    PMID: 19779668 DOI: 10.1007/s00774-009-0122-2
    Recently, vitamin E has been found to promote the bone structure of nicotine-treated rats well above their baseline values, thus suggesting that vitamin E may have some anabolic action. A bone anabolic agent acts by improving the bone structure leading to stronger bone. To assess the possible anabolic action vitamin E on bone, we supplemented alpha-tocopherol (ATF) or gamma-tocotrienol (GTT) at 60 mg/kg or vehicle [normal control (NC) group] for 4 months to normal male rats and measured their bone structure and biomechanical properties. Histomorphometric analysis revealed that vitamin E-supplemented rats have better trabecular volume, thickness, number, and separation than rats receiving vehicle only. For the first time we reported that GTT improves all the parameters of bone biomechanical strength, while ATF only improved some of the parameters compared to the NC group. Vitamin E supplementation, especially with the gamma isomer, improves bone structure, which contributed to stronger bone. Therefore, vitamin E has the potential to be used as an anabolic agent to treat osteoporosis or as bone supplements for young adults to prevent osteoporosis in later years.
    Matched MeSH terms: Stress, Mechanical
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