Teoh, S.H.
Email Address
mpetsh@nus.edu.sg
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196 results
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Publication Repair of calvarial defects with customized tissue-engineered bone grafts. I. Evaluation of osteogenesis in a three-dimensional culture system(2003) Lim, T.C.; Endres, M.; Schantz, J.-T.; Teoh, S.H.; Lam, C.X.F.; Hutmacher, D.W.; SURGERY; MECHANICAL ENGINEERING; DIVISION OF BIOENGINEERINGPublication Bioreactor for growing cell or tissue cultures(2009-10-20) HUTMACHER, DIETMAR W.; TEOH, SWEE HIN; RANAWAKE, MANOJA; CHONG, WOON SHIN; TING, KENG SOON; CHUA, KAY CHIANG; MYINT, THAN; PUAH, CHUM MOK; FOO, TOON TIEN; SCHANTZ, JAN-THORSTEN; SURGERY; CTR FOR BIOMED. MATERIALS APPLNS.& TECH; MECHANICAL ENGINEERING; INSTITUTE OF MOLECULAR & CELL BIOLOGY; DIVISION OF BIOENGINEERING; NATIONAL UNIVERSITY OF SINGAPOREThe invention relates to a bioreactor comprising a chamber for containing cells or tissue cultures within a culture medium. The bioreactor also comprises a detector capable of detecting a change in one or more metabolites associated with growth of the cell or tissue cultures within the chamber and a chamber drive capable of rotating the chamber at a first speed about a first axis and a second speed about a second axis, the second axis being disposed at an angle relative to the first axis. In use, the magnitude of the first speed and the second speed are independently variable of each other.Publication Application of the model of leaf and glaskin to estimating the 3D elastic properties of knitted-fabric-reinforced composites(2000) Ramakrishna, S.; Huang, Z.M.; Teoh, S.H.; Tay, A.A.O.; Chew, C.L.; RESTORATIVE DENTISTRY; MECHANICAL & PRODUCTION ENGINEERINGThis paper presents an analytical procedure for estimating the three-dimensional (3D) elastic properties of a plain-weft-knitted-fabric-reinforced polymer-composite material. The composite material under study is assumed to have mainly reinforcement-fiber yarns and a polymer matrix. The model of Leaf and Glaskin for plain-weft-knitted fabrics is used to determine the geometrical description of the yarn in the composite. The fabric in a representative volume is considered as a series of yarn segments, which are assumed to be made of transversely isotropic unidirectional fiber-reinforced composites. A new micromechanical model is proposed to predict the elastic constants of the unidirectional-fiber-reinforced composites. The compliance/stiffness matrix of each yarn segment is then transformed from the material co-ordinate system to the global coordinate system. In contrast to the commonly used Voigt and Reuss averaging methods, a volume-averaging scheme is developed to obtain the over-all compliance/stiffness matrix of the knitted fabric composites. The predicted results are found to be in good agreement with experimental data. The effects of the fiber content and other parameters of the knitted fabric on the elastic properties of the composite material are described. © Textile Institute.Publication The effect of Rhbmp-2 on canine osteoblasts seeded onto 3D bioactive polycaprolactone scaffolds(2004) Rai, B.; Teoh, S.H.; Ho, K.H.; Chen, F.; Kamal, Y.; Hutmacher, D.; Tong, C.; ORAL AND MAXILLOFACIAL SURGERY; DENTISTRY; BIOENGINEERING; MECHANICAL ENGINEERINGThe effect of human recombinant bone morphogenetic protein-2 (rhBMP-2) on canine osteoblasts seeded onto three dimensional bioactive polycaprolactone 20% tricalcium phosphate (PCL-TCP) scaffolds was investigated. Canine osteoblasts, rhBMP-2 of various concentrations and fibrin glue were simultaneously seeded onto the top of the porous scaffolds which were placed in 24-well culture plates. It was observed that rhBMP-2 enhanced the differentiated function of canine osteoblasts in a non-dose dependent manner, which resulted in accelerated mineralization, followed by death of osteoblasts as they underwent terminal differentiation. PCL-TCP scaffolds seeded only with canine osteoblasts was found to sustain excellent osteogenic expression in vitro.Publication Fabrication of 3D chitosan-hydroxyapatite scaffolds using a robotic dispensing system(2002-05-31) Ang, T.H.; Sultana, F.S.A.; Hutmacher, D.W.; Wong, Y.S.; Fuh, J.Y.H.; Mo, X.M.; Loh, H.T.; Burdet, E.; Teoh, S.H.; BIOENGINEERING; MECHANICAL ENGINEERINGA new robotic desktop rapid prototyping (RP) system was designed to fabricate scaffolds for tissue engineering applications. The experimental setup consists of a computer-guided desktop robot and a one-component pneumatic dispenser. The dispensing material (chitosan and chitosan-hydroxyapatite (HA) dissolved in acetic acid) was stored in a 30-ml barrel and forced out through a small Teflonlined nozzle into a dispensing medium (sodium hydroxide-ethanol in ratio of 7:3). Layer-by-layer, the chitosan was fabricated with a preprogramed lay-down pattern. Neutralization of the chitosan forms a gel-like precipitate, and the hydrostatic pressure in the sodium hydroxide (NaOH) solution keeps the cuboid scaffold in shape. Comparison of the freeze-dried scaffold to the wet one showed linear and volumetric shrinkage of about 31% and 62%, respectively. A good attachment between layers allowed the chitosan matrix to form a fully interconnected channel architecture. Results of in vitro cell culture studies revealed the scaffold biocompatibility. The results of this preliminary study using the rapid prototyping robotic dispensing (RPBOD) system demonstrated its potential in fabricating three-dimensional (3D) scaffolds with regular and reproducible macropore architecture. © 2002 Elsevier Science B.V. All rights reserved.Publication TENSILE, STRESS-STRAIN AND CREEP RUPTURE PROPERTIES OF POLY(VINYL CHLORIDE)/POLY(NEOPENTYL GLYCOL ADIPATE)/POLY(VINYLIDENE FLUORIDE) BLENDS.(1988) Lau, Wayne; Swee-Hin, Teoh; Suat-Hong, Goh; CHEMICAL ENGINEERING; CHEMISTRY; MECHANICAL & PRODUCTION ENGINEERINGPoly(vinyl chloride), PVC, and poly(vinylidene fluoride), PVDF, are incompatible polymers. Poly(neopentyl glycol adipate), PDPA, is miscible with both PVC and PVDF. With PDPA acting as a compatibilizer between PVC and PVDF, compatible PVC/PDPA/PVDF blends can be formed at PVDF content of about less than 50 wt percent. Above 50 wt percent PVDF the ternary blends exist in two phases exhibiting two glass transition temperatures, T//g. PVC is the main contributor to the mechanical strength while PDPA and PVDF contribute to the elastic properties of these blends. A compatible blend of 55/22. 5/22. 5 wt percent PVC/PDPA/PVDF exhibiting one single T//g appears to show an interesting balance of the properties of the blend components.Publication Bruxing-type dental wear simulator for ranking of dental restorative materials(1998-06) Teoh, S.H.; Ong, L.F.K.L.; Yap, A.U.J.; Hastings, G.W.; RESTORATIVE DENTISTRY; MECHANICAL & PRODUCTION ENGINEERINGAn instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.Publication Bending creep rupture analysis using a non-linear energy criterion approach(1990-01) Boey, F.Y.C.; Teoh, S.H.; MECHANICAL & PRODUCTION ENGINEERINGCreep rupture analysis by simple bending induces a larger and therefore more accurately measured creep deflection. It also considers both tensile and compression behaviour simultaneously. However, the common assumption of a linear stress distribution across the cross-section of the beam leads to a nominal value for the calculated rupture stress. In this paper, the true bending rupture stresses for a wood polymer composite beam was determined using a Norton-Bailey or power creep deformation analysis. These values were then used to model the creep rupture behaviour of the material, using an energy criterion approach. The results indicated that a non-linear consideration consistently resulted in higher values for the elastic and anelastic modulus, as well as the upper and lower creep rupture stress limits. © 1990.Publication Superior osteogenic capacity for bone tissue engineering of fetal compared with perinatal and adult mesenchymal stem cells(2009) Zhang, Z.-Y.; Chong, M.S.K.; Teoh, S.-H.; Schantz, J.T.; Fisk, N.M.; Choolani, M.A.; Chan, J.; MECHANICAL ENGINEERING; OBSTETRICS & GYNAECOLOGYPublication Application of a modified strain transient dip test in the determination of the internal stresses of PVC under tension(1987-04) Teoh, S.H.; Chuan, C.L.; Poo, A.N.; MECHANICAL & PRODUCTION ENGINEERINGA modified strain transient dip test which involves the design of a load reduction apparatus to perform rapid step unloading and extrapolating to zero extension rate has been developed to measure the internal stresses (recovery and effective stress) of PVC under uniaxial tension. This simple technique appears to be consistent with other internal stress measurement techniques. It was found that the effective stress approaches a limiting value with applied strain and an extrapolated yield point could be defined. The limiting value is a function of the strain rate during the initial load application. The general increase in applied stress (at fixed applied strain) with crosshead speed was attributed to the increase in magnitude of the effective stress. The maximum peak ratio of effective over recovery stress, at each crosshead speed, could indicate that it was the energy-dissipating part of the material that played a dominant role in the early stages of the deformation while the energy-storage part dominated the latter stages. © 1987 Chapman and Hall Ltd.