Three-dimensional porous silk tumor constructs in the approximation of in vivo osteosarcoma physiology.

The lack of good preclinical models has hampered anticancer drug discovery. Standard preclinical protocols require the growth of cells in high throughput two-dimensional (2D) culture systems. However, such in vitro drug testing methods yield drug efficacy results that differ greatly from animal models. Conversely, it is much more difficult and expensive to use animal models for large-scale molecular biology research. It is conceivable that three-dimensional (3D) growth may be responsible for some of these changes. Porous silk sponges were fabricated through freeze drying and seeded with 143.98.2 osteosarcoma cells. Molecular profiles were obtained by carrying out real-time polymerase chain reaction for angiogenic growth factors and proliferation markers for osteosarcoma cells grown under 2D, 3D, and SCID mouse xenograft conditions. The angiogenic factor expression profiles for cells grown in 2D differed greatly from the 3D silk scaffold model (P < 0.05 for bFGF, HIF-1α, IL-8, and VEGF-A), whereas 3D tumor model profiles were found to be able to approximate that for the in vivo tumor better with no statistically different expression of HIF-1α and VEGF-A between the two. Immunohistochemistry staining for HIF-1α, VEGF-A, and VEGF receptor on osteosarcoma cells grown on the scaffolds validated the results obtained with the gene expression profiles. The results suggest that 3D tumor models could be used to bridge the gap between in vitro and in vivo tumor studies, and aid in the study of mechanisms activated during tumorigenesis for the development of novel targeted chemotherapy.

Characterization of a novel polymeric scaffold for potential application in tendon/ligament tissue engineering.

Unlike braided fabrics, knitted scaffolds have been proven to favor deposition of collagenous connective tissue matrix, which is crucial for tendon/ligament reconstruction. But cell seeding of such scaffolds often requires a gel system, which is unstable in a dynamic situation, especially in the knee joint. This study developed a novel, biodegradable nano-microfibrous polymer scaffold by electrospinning PLGA nanofibers onto a knitted PLGA scaffold in order to provide a large biomimetic surface for cell attachment. Porcine bone marrow stromal cells were seeded onto either the novel scaffolds by pipetting a cell suspension (Group I) or the knitted PLGA scaffolds by immobilizing in fibrin gel (Group II). Cell attachment at 36 hours, cell proliferation and extracellular matrix synthesis at 1 week, and mechanical properties over 2 weeks were investigated. Cell attachment was comparable and cell proliferation was faster in Group I. Moreover, cellular function was more actively exhibited in Group I, as evident by the higher expression of collagen I, decorin, and biglycan genes. Thus, this novel scaffold, facilitating cell seeding and promoting cell proliferation, function, and differentiation, could be applied with promise in tissue engineering of tendon/ligament.

Development of an integrated CAD-FEA process for below-knee prosthetic sockets.

BACKGROUND: Computer-aided design and manufacturing has been successfully used in prosthetic applications since 1980s. It simplifies the socket rectification process and improves reproducibility but does not introduce any new principle into socket design. Integrating finite element analysis to CAD will provide a more objective assessment of socket fit and improve the chance of a successful first fitting. METHODS: Current study aims to establish a finite element model generation technique directly from geometrical information of commercial prosthetic CAD workstation. A program developed in-house automatically performs meshing of the stump geometry and assigns suitable material properties, load and boundary conditions to the model. The model was validated by comparing predicted pressure with experimentally measured values for one amputee subject. FINDINGS: The predicted pressure distribution has an root-mean-square error of 8.8 kPa compared to experimental values at 10%, 25% and 50% of the gait cycle. INTERPRETATION: Current method was able to develop a finite element model to predict interface pressure reasonably well and can be integrated with prosthetic CAD system to provide quantitative feedback to the prosthetist in an automated process.

Pattern of third molar impaction in a Singapore Chinese population: a retrospective radiographic survey.

One thousand orthopantomograms (OPGs) of patients 20-40 years old were examined. Where impacted third molars were present, the angle and depth of impaction were recorded. Results were analysed using the Pearson chi2 test. 68.6% of OPGs showed at least one impacted third molar. The frequency was three-fold higher in the mandible (1024/1079=90%) than in the maxilla (306/1077=28%), with a significantly higher frequency (P<0.05) in females (56%) than males (44%). The mesioangular impaction was the most common, and 80% of all impacted third molars were partially buried in bone. Of the 429 bilateral occurrence of impacted third molars, 423 were in the mandible. It was concluded that the frequency of impacted third molars in the Singapore Chinese population studied was generally two to three times that reported in races of the Caucasian stock. There was also double the frequency of impacted third molars when compared to a previous study in a Chinese population published in 1932 with females being more frequently affected than males.

Effects of dietary oil contamination and absence of prophylaxis on orthodontic bonding.

The effect of contamination by dietary oil on acid etching has not been reported in the literature. If dietary oil adversely affects acid etching, then a decrease in bond strength is expected. This in vitro study investigated the bond strength of brackets bonded to tooth surfaces that had been contaminated with dietary oil and on which prophylaxis was not carried out. The mean shear bond strengths for the control, teeth with oil contamination and teeth with oil contamination but no prophylaxis undertaken were 53.33 +/- 14.31 (SD), 61.76 +/- 19.32 and 64.12 +/- 17.90 N, respectively. An analysis of variance (ANOVA) test showed that there was no significant difference between the three groups. The power of the ANOVA was calculated for the minimum clinical change that would be worth detecting and was found to be approximately 1.0. It can therefore be concluded that the presence of dietary oil on the tooth surface does not adversely affect shear bond strength, even if prophylaxis is not carried out. Bond failures for all three groups occurred mainly at the tooth-adhesive interface.

Multiple-image shearography: a direct method to determine curvatures.

We present a modified method of shearography, known herein as multiple-image shearography, whereby the curvatures of an object can be measured directly from the resulting fringes. It employs an image-shearing camera that produces three sheared images simultaneously to interfere with each other in the image plane. When film is doubly exposed before and after an object is deformed, three sets of fringes are observed of which one set would depict the second-order derivatives of surface displacement.The theory of the multiple-image shearography technique and its application to curvature measurements in plate bending are presented.

Whole-field determination of surface roughness by speckle correlation.

A whole-field method of double-exposure speckle photography is employed to determine metal surface roughness by correlation between two speckle patterns. A movable rectangular aperture that is mounted before an image lens is shifted between the exposures, which results in a decrease in the contrast of the reconstructed Young's fringes with increasing roughness. The technique permits evaluation of the roughness of particular points on a surface as well as the average roughness of an entire surface. Four sets of random surfaces that were prepared by different machine-finishing processes and with roughnesses ranging from 0.6 to 13 µm have been tested. Different methods have been carried out to process the test data, and a practical method for the evaluation of surface roughness is proposed.

Bending stiffness of two aesthetic orthodontic archwires: an in vitro comparative study.

The aims of the study were to quantify the transverse stiffness of two aesthetic orthodontic archwires (0018 inch Teflon-coated stainless steel and 0017 inch Optiflex) in a simulated clinical setting and to assess the influence of deflection direction on the bending stiffness. The aesthetic archwires were randomly divided into three equal groups: group 1, lingual deflection; group 2, labial deflection; and group 3, occlusal deflection. Each group consisted of six archwires of the same type. The control group consisting of eighteen 0014 inch stainless steel archwires were also subjected to the same grouping. A total of 54 archwires were tested in the study. The deflection of the archwires was measured with a travelling microscope and the load measured with a calibrated strain gauge ring transducer. The mean stiffnesses of the archwires in the lingual, labial and occlusal deflection groups were found to be 29, 08 and 25 mN/mm respectively for 0017 inch Optiflex (r = 09, P less than 0001), 132, 105 and 245 mN/mm respectively for 0018 inch Teflon-coated stainless steel (r = 09, P less than 0001) and 266, 164 and 323 mN/mm respectively for the control (r = 09, P less than 0001). Springback was found to be poor for Optiflex and the archwire remained bent upon deactivation. ANOVA showed that the influence of arch curvature on the bending stiffness was significantly different for Optiflex (P less than 005), Teflon-coated stainless steel (P less than 0005) and the control group (P <0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Fatigue testing of energy storing prosthetic feet.

This paper describes a simple approach to the fatigue testing of prosthetic feet. A fatigue testing machine for prosthetic feet was designed as part of the programme to develop an energy storing prosthetic foot (ESPF). The fatigue tester does not simulate the loading pattern on the foot during normal walking. However, cyclic vertical loads are applied to the heel and forefoot during heel-strike and toe-off respectively, for 500,000 cycles. The maximum load applied was chosen to be 1.5 times that applied by the bodyweight of the amputee and the test frequency was chosen to be 2 Hz to shorten the test duration. Four prosthetic feet were tested: two Lambda feet (a newly developed ESPF), a Kingsley SACH foot and a Proteor SACH foot. It was found that the Lambda feet have very good fatigue properties. The Kingsley SACH foot performed better than the Proteor model, with no signs of wear at the heel. The results obtained using the simple approach was found to be comparable to the results from more complex fatigue machines which simulate the load pattern during normal walking. This suggests that simple load simulating machines, which are less costly and require less maintenance, are useful substitutes in studying the fatigue properties of prosthetic feet.

Analysis of shearogram reconstruction.

The high-pass Fourier filtering technique with an opaque stopper is commonly used for the reconstruction of shearograms. We believe that no analysis of this technique as applied to the shearogram reconstruction has been described. We present here a theoretical analysis of this reconstruction system taking into account the stopper that blocks the low-frequency region in the Fourier transform plane. The results show that the light-intensity distribution after reconstruction is different from that of the original shearogram. High fringe visibility is obtained with high-pass filtering.

Biofeedback device for patients on axillary crutches.

The axillary crutch is commonly prescribed as an ambulatory aid to patients with temporal or permanent disability in the lower extremity. When fitting the axillary crutch, it is important that the user be instructed not to bear excessive weight on the axillary bar. Excessive weight bearing on the axillary bar can result in a sevenfold increase in the reaction force under the armpit. This force may be a contributory factor to crutch paralysis or thrombosis of the axillobrachial artery. In order to prevent this occurrence an electronic biofeedback device was designed and developed for use in the training of 3-point swing-through axillary crutch ambulation. It detects excessive weight bearing on the axillary bar during crutch ambulation and produces an audible signal which prompts the patient to make necessary adjustment to relieve load bearing on the axillary bar. The design and development of the biofeedback device is discussed in this paper.

Biomechanical study on axillary crutches during single-leg swing-through gait.

This paper describes a kinetic and kinematic study on axillary crutches during one-leg swing-through gait. The primary objective is to evaluate the interplay of forces at the crutch and body interfaces and to relate them in the understanding of problems associated with the use of axillary crutches. Ten normal adult male subjects with simulated left leg impairment participated in the study. For data acquisition, the VICON kinematic system, a Kistler force plate and an instrumented crutch (with force transducers at the two upper struts close to the axillary bar and one near the crutch tip) were used. Results showed that the peak ground reaction force on the weight-bearing leg during lower limb stance increased by 21.6 percent bodyweight. The peak reaction force transmitted to the arm during crutch stance was 44.4 percent bodyweight. These increased loadings could be detrimental to patients with unsound weight-bearing leg and upper extremities respectively. When the crutches were used incorrectly, 34 percent bodyweight was carried by the underarm. This could cause undue pressure over the neurovascular structures at the axillary region.