Tunable nanoblock lasers and stretching sensors.

Reconfigurable, reliable, and robust nanolasers with wavelengths tunable in the telecommunication bands are currently being sought after for use as flexible light sources in photonic integrated circuits. Here, we propose and demonstrate tunable nanolasers based on 1D nanoblocks embedded within stretchable polydimethylsiloxane. Our lasers show a large wavelength tunability of 7.65 nm per 1% elongation. Moreover, this tunability is reconfigurable and reliable under repeated stretching/relaxation tests. By applying excessive stretching, wide wavelength tuning over a range of 80 nm (spanning the S, C, and L telecommunication bands) is successfully demonstrated. Furthermore, as a stretching sensor, an enhanced wavelength response to elongation of 9.9 nm per % is obtained via the signal differential from two nanoblock lasers positioned perpendicular to each other. The minimum detectable elongation is as small as 0.056%. Nanoblock lasers can function as reliable tunable light sources in telecommunications and highly sensitive on-chip structural deformation sensors.

A method for measuring three-dimensional mandibular kinematics in vivo using single-plane fluoroscopy.

OBJECTIVES: Accurate measurement of the three-dimensional (3D) motion of the mandible in vivo is essential for relevant clinical applications. Existing techniques are either of limited accuracy or require the use of transoral devices that interfere with jaw movements. This study aimed to develop further an existing method for measuring 3D, in vivo mandibular kinematics using single-plane fluoroscopy; to determine the accuracy of the method; and to demonstrate its clinical applicability via measurements on a healthy subject during opening/closing and chewing movements. METHODS: The proposed method was based on the registration of single-plane fluoroscopy images and 3D low-radiation cone beam CT data. It was validated using roentgen single-plane photogrammetric analysis at static positions and during opening/closing and chewing movements. RESULTS: The method was found to have measurement errors of 0.1 ± 0.9 mm for all translations and 0.2° ± 0.6° for all rotations in static conditions, and of 1.0 ± 1.4 mm for all translations and 0.2° ± 0.7° for all rotations in dynamic conditions. CONCLUSIONS: The proposed method is considered an accurate method for quantifying the 3D mandibular motion in vivo. Without relying on transoral devices, the method has advantages over existing methods, especially in the assessment of patients with missing or unstable teeth, making it useful for the research and clinical assessment of the temporomandibular joint and chewing function.

Postural responses during falling with rapid reach-and-grasp balance reaction in patients with motor complete paraplegia.

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate the kinematic, kinetic and electromyographic (EMG) aspects of postural control during falling with rapid reach-and-grasp balance reaction in thoracic cord-injured individuals wearing knee-ankle-foot orthoses (KAFOs). SETTING: Institutional Motion Analysis Laboratory. METHODS: Seven T7-T12 cord-injured subjects with complete motor loss (ASIA classes A and B) participated in this study. Subjects with KAFOs first stood steady with a modified walker and then released their hold on the walker to maintain self-supported standing until falling with grasping. The center of pressure (COP), center of mass (COM) and joint angles were measured together with EMG of the triceps (TRI), T4 paraspinal and abdominal muscles. RESULTS: After release of the walker, there was a rapid increase of COM-COP distance (that is, from 13.32+/-11.79 to 54.29+/-24.56 mm), with COM in front of COP during a forward fall, which was associated with the increases of T4 muscle activities. After the reach-and-grasp reaction, COM moved behind COP, which was associated with the increase of ankle dorsiflexion and the TRI and abdominal muscle activities. CONCLUSION: The increase of upper back extensor muscle activity might not be enough to correct postural instability during unsupported stance in thoracic spinal cord injury with complete motor loss. The rapid reach-and-grasp reaction is an alternative compensatory mechanism to prevent falling to the ground.

Cruciate ligament forces in the human knee during rehabilitation exercises.

OBJECTIVE: To determine the cruciate ligament forces occurring during typical rehabilitation exercises.Design. A combination of non-invasive measurements with mathematical modelling of the lower limb.Background. Direct measurement of ligament forces has not yet been successful in vivo in humans. A promising alternative is to calculate the forces mathematically. METHODS: Sixteen subjects performed isometric and isokinetic or squat exercises while the external forces and limb kinematics were measured. Internal forces were calculated using a geometrical model of the lower limb and the "dynamically determinate one-sided constraint" analysis procedure. RESULTS: During isokinetic/isometric extension, peak anterior cruciate ligament forces, occurring at knee angles of 35-40 degrees, may reach 0.55x body-weight. Peak posterior cruciate ligament forces are lower and occur around 90 degrees. During isokinetic/isometric flexion, peak posterior cruciate forces, which occur around 90 degrees, may exceed 4x body-weight; the anterior cruciate is not loaded. During squats, the anterior cruciate is lightly loaded at knee angles up to 50 degrees, after which the posterior cruciate is loaded. Peak posterior cruciate forces occur near the lowest point of the squat and may reach 3.5x body-weight. CONCLUSIONS: For anterior cruciate injuries, squats should be safer than isokinetic or isometric extension for quadriceps strengthening, though isokinetic or isometric flexion may safely be used for hamstrings strengthening. For posterior cruciate injuries, isokinetic extension at knee angles less than 70 degrees should be safe but isokinetic flexion and deep squats should be avoided until healing is well-advanced. RELEVANCE: Good rehabilitation is vital for a successful outcome to cruciate ligament injuries. Knowledge of ligament forces can aid the physician in the design of improved rehabilitation protocols.

Decreased diversity of hepatitis C virus quasispecies during bone marrow transplantation.

To elucidate the role of host immune status in the evolution and complexity of hepatitis C virus (HCV) quasispecies, three chronic HCV-infected patients who underwent bone marrow transplantation (BMT) were studied. The three transplanted patients' sera were sampled at pre-BMT, 3 months after BMT, and 12 months after BMT and the nucleotide diversity and substitution of the hypervariable region (HVR) of HCV quasispecies were analyzed. The nucleotide diversity was high at the pre-BMT period (28.2-43.4 x 10(-2) nucleotide difference/site). HVR of HCV quasispecies then became homogeneous in the first 3 months after BMT (0.11-6.40 x 10(-2) nucleotide difference/site). The nucleotide diversity of HVR at 12 months after BMT of all three patients was higher than that of 3 months after BMT but still lower than that of pre-BMT (2.09-6.40 x 10(-2) nucleotide difference/site). The analysis on nucleotide substitution rate showed a higher value between pre-BMT and 3 months after BMT (0.624-0.708 nucleotide difference/site per year) than that between 3 months and 12 months after BMT (0.072-0.127 nucleotide difference/site per year). HCV RNA titer decreased when the host had a low white cell count and increased accordingly. It was concluded that the evolution of HVR of HCV quasispecies related to the immune status of the host during BMT: after immunosuppression, an initial increase of viral populations was followed by the emergence of a dominant strain while the quasispecies gradually recovered as the immunity of the host gained its competence.

Bone position estimation from skin marker co-ordinates using global optimisation with joint constraints.

Widespread use of gait or motion analysis in the diagnosis of patients with locomotor pathology and the subsequent planning and assessment of treatment has been limited because of its reliability, particularly in evaluating frontal and transverse plane components. This is because spatial reconstruction of the musculoskeletal system and calculation of its kinematics and kinetics via a skin marker-based multi-link model are subject to marker skin movement artefacts. Traditional methods treat each body segment separately without imposing joint constraints, resulting in apparent dislocations at joints predominantly because of skin movement artefacts. An optimisation method for the determination of the positions and orientations of multi-link musculoskeletal models from marker co-ordinates is presented. It is based on the minimisation of the weighted sum of squared distances between measured and model-determined marker positions. The model imposes joint constraints. Numerical experiments were performed to show that the new method is capable of eliminating joint dislocations and giving more accurate model position and orientation estimations. It is suggested that, with joint constraints and a global error compensation scheme, the effects of measurement errors on the reconstruction of the musculoskeletal system and subsequent mechanical analyses can be reduced globally. The proposed method minimises errors in axial rotation and ab/adduction at the joints and may extend the applicability of gait analysis to clinical problems.

Validation of a lower limb model with in vivo femoral forces telemetered from two subjects.

A mathematical model of the human pelvis-leg system in the sagittal plane, with an anatomical model of the knee, was developed to calculate forces transmitted by the structural elements of the system. The model was used to study the influence of activity of hip flexors and extensors on the forces in the femur during isometric exercises and during level walking. Kinematic and kinetic data together with simultaneous electromyography (EMG) and in vivo axial forces transmitted along the prostheses from two patients implanted with instrumented massive proximal femoral prostheses were obtained. Comparison of the levels of the calculated axial forces in the model femur to the simultaneous telemetered forces showed good agreement for isometric tests. Interaction between the muscles and the bones during isometric tests was examined and bi-articular muscles were shown to play a major role in modulating forces in bones. The study supports the hypothesis that muscles balance the external limb moments, not only at joints but also along the limbs, decreasing the bending moments but increasing the axial compressive forces in bones. It is thus suggested that appropriate simulation of muscle force is necessary in in vitro laboratory experiments and in theoretical studies of load transmission in bones. The sagittal plane model underestimates the value of the maximum axial force in the femur during walking by about 30% but suggests that 70% was due to the action of the extensors or flexors. The results encourage further development of a three-dimensional model with anatomical models of the joints to include coronal and transverse planes for the study of adductors and abductors.

Influence of muscle activity on the forces in the femur: an in vivo study.

Experiments were performed on two patients with custom-made instrumented massive proximal femoral prostheses implanted after tumour resection. In vivo axial forces transmitted along the prostheses were telemetered during level walking, single- and double-leg stance, and isometric exercises of the hip muscles. These activities varied the lever arms available to the external loads: minimum for double-leg stance and maximum for hip isometric exercises. Kinematic, force plate, EMG and telemetered force data were recorded simultaneously. The force magnification ratio (FMR; the ratio of the telemetered axial force to the external force) was calculated. The FMRs ranged from 1.3 (during double-leg stance) to 29.8 (during abductors test), indicating that a major part of the axial force in the long bones is a response to muscle activity, the strength of which depends on the lever arms available to the external loads. From these results, it was shown that the bulk of the bending moment along limbs is transmitted by a combination of tensile forces in muscles and compressive forces in bones, so moments transmitted by the bones are smaller than the limb moments. It was concluded that appropriate simulation of muscle forces is important in experimental or theoretical studies of load transmission along bones.

Lines of action and moment arms of the major force-bearing structures crossing the human knee joint: comparison between theory and experiment.

Lines of action and moment arms in the sagittal plane of the major tension-bearing structures at the knee joint were calculated using an anatomy-based mathematical model and compared with experimental measurements reported by Herzog & Read (1993). The mobility of the model tibiofemoral joint was controlled by a sagittal plane 4-bar linkage consisting of the femur, tibia and the 2 cruciate ligaments while the knee extensor mechanism was characterised by a patellofemoral joint model. Model parameters were obtained from previous cadaveric and MRI studies. The theoretical results compare well with the published experimental measurements which suggests that, with relatively simple measurements, the model was able to reproduce major features of the natural knee joint and provide necessary information for further mechanical analysis.

Fibre recruitment and shape changes of knee ligaments during motion: as revealed by a computer graphics-based model.

A computer graphics-based model of the knee ligaments in the sagittal plane was developed for the simulation and visualization of the shape changes and fibre recruitment process of the ligaments during motion under unloaded and loaded conditions. The cruciate and collateral ligaments were modelled as ordered arrays of fibres which link attachment areas on the tibia and femur. Fibres slacken and tighten as the ligament attachment areas on the bones rotate and translate relative to each other. A four-bar linkage, composed of the femur, tibia and selected isometric fibres of the two cruciates, was used to determine the motion of the femur relative to the tibia during passive (unloaded) movement. Fibres were assumed to slacken in a Euler buckling mode when the distances between their attachments are less than chosen reference lengths. The ligament shape changes and buckling patterns are demonstrated with computer graphics. When the tibia is translated anteriorly or posteriorly relative to the femur by muscle forces and external loads, some ligament fibres tighten and are recruited progressively to transmit increasing shear forces. The shape changes and fibre recruitment patterns predicted by the model compare well qualitatively with experimental results reported in the literature. The computer graphics approach provides insight into the micro behaviour of the knee ligaments. It may help to explain ligament injury mechanisms and provide useful information to guide the design of ligament replacements.