Biomedical subjects

Jaw-Lin Wang

Publications and source records attributed to Jaw-Lin Wang.

15 recordsLinked to original sources

PubMed2007

Effects on microstrain and conversion of flowable resin composite using different curing modes and units.

The flowable resin composite, Tetric Flow, was used to measure microstrain and degree of conversion after hardening with each of three curing machines: XL3000(XL) for 10, 20, 30, and 40 s; Optilux 501 using conventional mode (OC) for 10, 20, 30, and 40 s, as well as Optilux boost (OB, 10 s) and ramp modes (OR, 20 s); and LEDemetron (LEDe) for 10, 20, 30, and 40 s. The emitted power density and spectral distribution of the three light curing units were also measured. The LEDe output energy spectrum was centralized between 425 and 490 nm, which encompasses the excited wavelength of camphorquinone. The microstrain produced by the curing process is as a second-degree polynomial for each light source. The OB microstrain was highest, while the OR microstrain was lower. The ranking in order of degree of monomer conversion was as follows: XL10 <or=<or= OC10 <or=<or= LED 10 = OR = XL 20 = OC 20 = XL 30 <or=<or= LED 20 <or=<or= OC30 = LED 40 = XL 40 = OC40 = LED 30 <or= OB. The degree of conversion cured with OB was significant higher than other curing modes except OC30, OC40, LEDe30, LEDe40, and XL40. The conversion value of XL10 was the lowest. The LEDe produced higher conversion for the same emitted energy compared to the two halogen units.

Composite Resins↗

PubMed2006

Increasing bending strength of tibial locking screws: mechanical tests and finite element analyses.

BACKGROUND: Healing of tibial fractures treated by locked nailing is threatened by locking screw failure. However, the effects of the design factors of the screws on their mechanical strength have rarely been studied. METHOD: Three-point bending tests and finite element analyses were used to investigate the bending strength of five types of commercially available tibial locking screws and two types of specially designed screws. Yielding strength and fatigue life measured in bending tests were correlated to total strain energy and maximal tensile stress computed in finite element analyses. Parametric analysis and design optimization were done according to the Taguchi method. Validation studies to assess the stress rising effect of the threads on the fatigue strength were conducted in two types of new screws made of either stainless steel or titanium alloy. FINDINGS: The yielding strength of the screws was closely related to their total strain energy, and the logarithm of the fatigue life was closely related to the maximal tensile stress with correlation coefficients of -0.95 and -0.90, respectively. Parametric studies indicated that fatigue strength of the screws was affected mainly by inner diameter (contribution, 63.8%) and root radius (27.8%). The yielding strength was determined primarily by inner diameter (88.5%). Titanium screws had a longer fatigue life than stainless steel screws, especially in screws with larger root radii. INTERPRETATION: A screw's strength is closely related to its design factors. Finite element models, which can reliably reflect the mechanical strength of screws can save time and effort during screw design. Larger root radius can effectively improve the fatigue strength, especially for titanium screws as compared with stainless steel screws.

Biomechanical Phenomena↗

PubMed2006

Multiobjective optimization of tibial locking screw design using a genetic algorithm: Evaluation of mechanical performance.

Breakage or loosening of locking screws may impair fracture fixation or bone healing in locked nailing of tibial fractures. Bending strength and bone holding power, two important design objectives of locking screws, may conflict with each other. The present study used multiobjective optimization with a genetic algorithm to investigate the optimal designs with respect to these two objectives. Three-dimensional finite element models for analyzing bending strength and bone holding power of locking screws were created first. Through use of a Taguchi L25 orthogonal array, two objective functions were developed by least-squares regression analyses. Then, the trade-off solutions between the two objectives known as Pareto optima were explored by a weighted-sum aggregating approach under geometric constraints. The objective functions, reliably reflecting the finite element results, were valid for multiobjective studies. The Pareto fronts of the screws with 4.5-mm and 5.0-mm outer diameters were similar. The "knee" region of the Pareto front, characterized by the fact that a small improvement in either objective will cause a large deterioration in the other objective, might be the favored choice of optimal designs. The commercially available locking screws compared with the Pareto optima were found to be dominated designs and could be improved. In conclusion, the multiobjective optimization with a genetic algorithm was useful for optimization of locking screw design with many variables and conflicting objectives. Choosing an optimal design requires a thorough knowledge of the inherent problems. This method could reduce the time, cost, and labor associated with the screw development process.

Algorithms↗

PubMed2006

Quantification of the pulse wave velocity of the descending aorta using axial velocity profiles from phase-contrast magnetic resonance imaging.

The pulse wave velocity (PWV) of aortic blood flow is considered a surrogate for aortic compliance. A new method using phase-contrast (PC)-MRI is presented whereby the spatial and temporal profiles of axial velocity along the descending aorta can be analyzed. Seventeen young healthy volunteers (the YH group), six older healthy volunteers (the OH group), and six patients with coronary artery disease (the CAD group) were studied. PC-MRI covering the whole descending aorta was acquired, with velocity gradients encoding the in-plane velocity. From the corrected axial flow velocity profiles, PWV was determined from the slope of an intersecting line between the presystolic and early systolic phases. Furthermore, the aortic elastic modulus (Ep) was derived from the ratio of the brachial pulse pressure to the strain of the aortic diameter. The PWV increased from YH to OH to CAD (541 +/- 94, 808 +/- 184, 1121 +/- 218 cm/s, respectively; P = 0.015 between YH and OH; P = 0.023 between OH and CAD). There was a high correlation between PWV and Ep (r = 0.861, P < 0.001). Multivariate analysis showed that age and CAD were independent risk factors for an increase in the PWV. Compared to existing methods, our method requires fewer assumptions and provides a more intuitive and objective way to estimate the PWV.

Adult↗

PubMed2006

Calculation of dynamic spinal ligament deformation.

OBJECTIVE: Previous methods to determine spinal ligament deformation have included either custom-designed transducers or computational methods using rigid body transformation of kinematic data. Goals of the present study were to describe a computational methodology to determine dynamic deformations of an arbitrarily oriented ligament in a spine specimen and its associated errors. METHODS: Calculation of ligament deformation in a spinal segment with vertebral motion tracking flags utilized digital stereophotography, lateral neutral posture radiograph, and detailed quantitative anatomy to develop geometrical relationships between flag markers and ligament attachment points. A custom jig, consisting of two flags each with four markers, was constructed to quantify errors associated with computed ligament deformation, flag marker translation, and flag rotation. RESULTS: Average error in ligament deformation was dependent upon motion direction and ranged between 0.03 mm (SD 0.45 mm) and 0.28 mm (SD 0.18 mm). Average error for flag marker translation ranged between 0.02 mm (SD 0.14 mm) and 0.11 mm (SD 0.39 mm), and for flag rotation ranged between -0.06 degrees (SD 0.17 degrees ) and 0.07 degrees (SD 0.12 degrees ). CONCLUSIONS: Accuracy of the present technique was equivalent to or greater than that of previous methods. The present technique utilized relatively cost-effective digital stereophotography, and may be used to calculate strain in ligaments not readily accessible for transducer application. The methodology has wide-spread applicability for analyses of dynamic or static spinal or other ligament strains, and may be used to determine spinal canal and intervertebral foramen narrowing and area reduction.

Biomechanical Phenomena↗

PubMed2005

Search for critical loading condition of the spine--a meta analysis of a nonlinear viscoelastic finite element model.

The relative vulnerability of spinal motion segments to different loading combinations remains unknown. The meta-analysis described here using the results of a validated L2-L3 nonlinear viscoelastic finite element model was designed to investigate the critical loading and its effect on the internal mechanics of the human lumbar spine. A Box-Behnken experimental design was used to design the magnitude of seven independent variables associated with loads, rotations and velocity of motion. Subsequently, an optimization method was used to find the primary and secondary variables that influence spine mechanical output related to facet forces, disc pressure, ligament forces, annulus matrix compressive/shear stresses and anulus fibers strain. The mechanical responses with respect to the two most-relevant variables were then regressed linearly using the response surface quadratic model. Axial force and sagittal rotation were identified as the most-relevant variables for mechanical responses. The procedure developed can be used to find the critical loading for finite element models with multi input variables. The derived meta-models can be used to predict the risk associated with various loading parameters and in setting safer load limits.

Computer Simulation↗

PubMed2005

Intervertebral neck injury criterion for prediction of multiplanar cervical spine injury due to side impacts.

OBJECTIVE: Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that dynamic three-dimensional intervertebral motion beyond physiological limits may cause multiplanar injury of cervical spine soft tissues. Goals of this study, using a biofidelic whole human cervical spine model with muscle force replication and surrogate head in simulated side impacts, were to correlate IV-NIC with multiplanar injury and determine IV-NIC injury threshold for each intervertebral level. METHODS: Using a bench-top apparatus, side impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Pre- and post-impact flexibility testing in three-motion planes measured the soft tissue injury, i.e., significant increase (p < 0.05) in neutral zone (NZ) or range of motion (RoM) at any intervertebral level, above corresponding physiological limit. RESULTS: IV-NIC in left lateral bending correlated well with total lateral bending RoM (R = 0.61, P < 0.001) and NZ (R = 0.55, P < 0.001). Additionally, the same IV-NIC correlated well with left axial rotation RoM (R = 0.50, P < 0.001). IV-NIC injury thresholds (95% confidence limits) varied among intervertebral levels and ranged between 1.5 (0.6-2.4) at C3-C4 and 4.0 (2.4-5.7) at C7-T1. IV-NIC injury threshold times were attained beginning at 84.5 ms following impact. CONCLUSIONS: Present results suggest that IV-NIC is an effective tool for determining multiplanar soft tissue neck injuries by identifying the intervertebral level, mode, time, and severity of injury.

Acceleration↗

PubMed2005

Intervertebral neck injury criterion for simulated frontal impacts.

OBJECTIVE: The Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that dynamic intervertebral motion beyond physiological limits may injure soft tissues. In contrast, the Neck Injury Criterion (NIC) hypothesizes that sudden change in spinal fluid pressure may cause neural injuries. The goals of this study, using the biofidelic whole human cervical spine model with muscle force replication, were to determine the IV-NIC injury threshold due to frontal impact at each intervertebral level, and to compare the IV-NIC and NIC in determining injury. METHODS: Using a bench-top apparatus, frontal impacts were simulated at 4, 6, 8, and 10 g horizontal accelerations of the T1 vertebra. Pre- and post-trauma flexibility testing measured the soft tissue injury; that is, a significant increase (p < 0.05) in neutral zone or range of motion at any intervertebral level, above the corresponding physiological limit. RESULTS: Results indicated that the soft tissue injury occurred due to flexion mode of injury and its threshold was 8 g. The average IV-NIC injury threshold (95% confidence interval) was 2.0 (1.2-2.8) at C4-C5 and 2.3 (1.6-3.0) at C6-C7, while the average NIC injury threshold was 18.4 (17.9-19.0) m(2)/s(2). The NIC injury threshold was reached significantly earlier than all the IV-NIC injury thresholds, demonstrating that the NIC may be unable to predict facet and soft tissue injury caused by non-physiologic inververtebral rotation. CONCLUSIONS: Present results suggest that IV-NIC is an effective tool for determining soft tissue neck injuries by identifying the intervertebral level, mode, time, and severity of injury.

Acceleration↗

PubMed2004

Increase of pullout strength of spinal pedicle screws with conical core: biomechanical tests and finite element analyses.

Screw loosening can threaten pedicle screw fixation of the spine. Conical screws can improve the bending strength, but studies of their pullout strength as compared with that of cylindrical screws have shown wide variation. In the present study, polyurethane foam with two different densities (0.32 and 0.16 gm/cm3) was used to compare the pullout strength and stripping torque among three kinds of pedicle screws with different degrees of core tapering. Three-dimensional finite element models were also developed to compare the structural performance of these screws and to predict their pullout strength. In the mechanical tests, pullout strength was consistently higher in the higher density foam and was closely related to screw insertion torque (r=0.87 and 0.81 for the high and low density foam, respectively) and stripping torque (r=0.92 and 0.78, respectively). Conical core screws with effective foam compaction had significantly higher pullout strength and insertion torque than cylindrical core screws (p<0.05). The results of finite element analyses were closely related to those of the mechanical tests in both situations with or without foam compaction. This study led to three conclusions: polyurethane foam bone yielded consistent experimental results; screws with a conical core could significantly increase pullout strength and insertion torque over cylindrical; and finite element models could reliably reflect the results of mechanical tests.

Bone Screws↗

PubMed2004

Cervical spine curvature during simulated whiplash.

OBJECTIVE: To develop a new method to describe cervical spine curvature and evaluate the potential for injury in the upper and lower cervical spine during simulated whiplash. DESIGN: A method was developed to integrate the upper and lower cervical spine rotations and describe the spine curvature. BACKGROUND: In vivo and in vitro whiplash simulations have documented the development of an S-shape curvature with simultaneous upper cervical spine flexion and lower cervical spine extension immediately following rear-impact. Investigators have hypothesized that the injury potential is highest during the S-shape phase. However, little data exist on the spine curvature during whiplash and its relation to spine injury. METHODS: A biofidelic model and a bench-top whiplash apparatus were used in an incremental rear-impact protocol (maximum 8 g) to simulate whiplash of increasing severity. To describe the spine curvature, the upper and lower cervical spine rotations were normalized to corresponding physiological limits. RESULTS: Average peak lower cervical spine extension first exceeded the physiological limits (P<0.05) at a horizontal T1 acceleration of 5 g. Average peak upper cervical spine extension exceeded the physiological limit at 8 g, while peak upper cervical spine flexion never exceeded the physiological limit. In the S-shape phase, lower cervical spine extension reached 84% of peak extension during whiplash. CONCLUSIONS: Both the upper and lower cervical spine are at risk for extension injury during rear-impact. Flexion injury is unlikely.

Aged↗

PubMed2004

Mechanical tests and finite element models for bone holding power of tibial locking screws.

OBJECTIVE: To investigate the bone holding power of tibial locking screws. DESIGN: The bone holding power was assessed by mechanical testing and finite element analysis. BACKGROUND: Screw loosening might threaten fracture fixation and bone healing. METHODS: In mechanical tests, six types of different tibial locking screws were inserted into low-density polyurethane foam tubes, which simulated osteoporotic bone. The screws were pushed out of the foam bone by an axial load, and the maximal pushout load was recorded. In finite element analysis, three-dimensional finite element models with a nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The total strain energy of the bone and total reaction force of the screws were recorded. The contribution of the design factors was analyzed by the Taguchi method. RESULTS: In the mechanical tests, foam bone was stripped by the screw threads without screw deformation. The testing results were closely related to those of finite element analysis. The Taguchi analysis showed that the descending order of contribution of the design factors was outer diameter, pitch, half angle, and inner diameter. Root radius and thread width had minimal effects. CONCLUSIONS: The bone holding power of the screws could be reliably assessed by finite element models, which could analyze the effects of all the design factors independently and were potentially applicable to screws with irregular thread patterns.

Analysis of Variance↗

PubMed2002

Radiography cannot examine disc injuries secondary to burst fracture: quantitative discomanometry validation.

STUDY DESIGN: An in vitro biomechanical study. OBJECTIVE: To examine disc integrity at levels adjacent and next adjacent to the fractured vertebra and to determine if the disc injury can be revealed by radiographs. SUMMARY OF BACKGROUND DATA: Thoracolumbar burst fracture is one of the most common spinal injuries. A fractured vertebra is easy to recognize, but the associated disc injuries are less well known. The disc injury may not be apparent in radiographic images. Quantitative discomanometry, which measures disc pressure and the injected volume, has been found to detect disc injury. METHODS: Nine specimens (T11-L3) with L1 burst fracture included adjacent discs (T12-L1 and L1-L2) and next-adjacent discs (T11-T12 and L2-L3) and were examined with radiographs and quantitative discomanometry, before and after the burst fracture. Statistical analyses were used to determine if the nine quantitative discomanometry parameters, in each of the four discs, were changed by the burst fracture and if the two next adjacent discs sustained different injuries. RESULTS: After the burst fracture both the adjacent discs were shown to be injured by both radiographic and quantitative discomanometry examinations. Whereas both next-adjacent discs were found to be uninjured by radiograph examination, the quantitative discomanometry found the lower next-adjacent disc (L2-L3) to be injured. CONCLUSIONS: Quantitative discomanometry was successful in finding disc injury, where the radiographs found none. The lower level, next adjacent disc is susceptible to injury during the burst trauma.

Adult↗

PubMed2002

Normal systolic and diastolic functions of the left ventricle and left atrium by cine magnetic resonance imaging.

Volume and phase characteristics of the left ventricle (LV) and left atrium (LA) were assessed in 31 healthy Asian adults (19 males and 12 females) using cine magnetic resonance imaging (MRI) and an automated boundary detection algorithm. Volume indexes of the LV and LA were smaller than published results obtained mostly from Westerners. Other than LV mass index and percent emptying of the LA, there was no gender difference in all LV/LA indexes. In associating LV/LA functions with the body size and heart rate (HR), we found that LV mass and the minimum LA volume correlated strongly with the body surface area, the maximum LA volume and the reservoir volume correlated strongly with the body weight, and the time to LV peak-filling rate (LVPFRt) and the time to LA peak-emptying rate (LAPERt) correlated strongly with the HR. In associating LV with LA functions, we found that LA conduit volume contributed more than 50% of the LV stroke volume, and correlated with both systolic and diastolic functions of the LV. Moreover, LVPFRt and LAPERt were virtually identical, indicating a mechanical coupling between LV and LA during diastole. In conclusion, using time-resolved, three-dimensional volume data obtained from cine MRI, we have established normative values of LV and LA functions and their functional relationships in healthy Asian adults. The imaging acquisition protocol, data analysis algorithms, and the established normative values provide the basis for the study of left heart function in patients.

Adult↗

PubMed1998

The postural stability control and gait pattern of idiopathic scoliosis adolescents.

OBJECTIVE: The static postural equilibrium and gait patterns between idiopathic scoliotic (IS) patients and normal subjects were studied to verify the best method to identify the functional disability in IS patients. DESIGN: The static stability in six postures and gait patterns among normal subjects and IS patients were compared. BACKGROUND: Postural stability control and gait analysis are non-invasive methods to identify many diseases. However, the dysfunction of IS patients in postural stability control and gait pattern is not clear. The results of this research may lead to further understanding of the etiology of idiopathic scoliosis in the postural equilibrium influencing aspects. METHODS: Thirty IS patients and fifteen normal subjects were recruited for postural stability control test and gait analysis using the force plate and 3-D motion analysis system. RESULTS: The IS patients generally produced higher sway area, lateral sway, sagittal sway, and sway radius than normal subjects. The cadence is smaller in the IS patients, but the stance phase and stride phase are similar to normal subjects. CONCLUSIONS: The IS patients are poor in postural stability control but their gait pattern is similar to that of normal subjects. Standing with trunk at full flexion is the most effective position to identify the postural stability control of IS patient.

Journal Article↗

PubMedDate not supplied

Mechanical strength, fatigue life, and failure analysis of two prototypes and five conventional tibial locking screws.

OBJECTIVE: To investigate the effects of the design and microstructure on the mechanical strength of tibial locking devices. DESIGN AND METHODS: The mechanical strength of two prototypes of specially developed locking devices (a both-ends-threaded screw and an unthreaded bolt) was tested and compared with that of five types of commercially available tibial locking screws (Synthes, Howmedica, Richards, Osteo AG, and Zimmer) with similar dimensions. The devices were inserted into a polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three-point bending test. Single-loading yielding strength and cyclic-loading fatigue life were then measured. Failure analysis of the fractured screws was performed to investigate the microstructure and potential causes of the fatigue fracture. RESULTS: Test results showed that both yielding strength and fatigue life were closely related to the section modulus of the inner diameter of screws. Among the threaded screws, the both-ends-threaded screws had a higher yielding strength and longer fatigue life than the Osteo AG, Howmedica, Richards, and Zimmer screws. The unthreaded bolts had a lower yielding strength than Synthes screws, but they demonstrated the longest fatigue life among all. In failure analysis of broken screws, no metallurgical or manufacturing defects were found except for surface microimperfections. CONCLUSIONS: The implants investigated in this study are manufactured with high-quality materials and manufacturing processes. The main cause of hardware failure was mechanical overloading. The five commercially used tibial locking screws had a relatively short fatigue life under high loading. Removing the screw threads might substantially increase the fatigue life of the locking devices. In unthreaded bolts, this increase might be tenfold to a hundredfold.

Bone Screws↗