Biomedical subjects

A F Mak

Publications and source records attributed to A F Mak.

At least 19 recordsLinked to original sources

PubMed2001

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process.

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.

Apatites↗

PubMed2001

Measurement of the layered compressive properties of trypsin-treated articular cartilage: an ultrasound investigation.

An ultrasound-compression system has been developed for the study of the layered biomechanical properties of articular cartilage. Cartilage specimens harvested from the bovine patella groove, with and without trypsin digestion, were tested using this system. It was noted that a large ultrasound reflection can be detected in the interface of the trypsin digestion front. This ultrasound reflection signal was used to differentiate the deformations of different portions of the cartilage throughout its depth when a load was applied. The equilibrium compression moduli of the digested, undigested and entire portions of articular cartilage were measured. The modulus of the cartilage without any digestion was 660+/-230 kPa. After 1h digestion with 1 mg ml(-1) trypsin solution, the thickness of the digested portion was 0.50+/-0.06m, and the modulus of the entire cartilage layer changed to 125+/-42kPa. The moduli of the digested and undigested portions were 58+/-24 kPa and 470+/-31 kPa, respectively. Similar results were obtained for the cartilage with trypsin digestion for 2 h.

Animals↗

PubMed2001

Development of computer-based environment for simulating the voluntary upper-limb movements of persons with disability.

Upper-limb orthotic systems have been designed for restoring the upper-limb functions of individuals with disabilities resulting from spinal cord injury (SCI), stroke and muscular dystrophy. These systems employ either functional electrical stimulation or external power. It is proposed that, instead of time-consuming and complicated monitoring using sensors and motion analysis, a software simulator with both angular displacement and acceleration parameters can facilitate the design of a control strategy for an orthosis. Reaching movements of three cervical SCI subjects are used to verify the simulator. A motion analysis system is used to measure the range of motion and joint angles during hand reaching. Results indicate that quaternion and spline curve techniques are suitable for interpolation of the hand reaching movements. The information needed for good simulation only compress the shoulder and elbow joint angles in a few key postures. Stimulated acceleration signals on the upper-arm segment have a high correlation coefficient (> 0.9) and a small root mean squared error (< 0.11 g) with a real bi-axial accelerometer.

Arm↗

PubMed2001

Effects of knee bracing on the functional performance of patients with anterior cruciate ligament reconstruction.

OBJECTIVE: To compare the functional performance of subjects with unilateral anterior cruciate ligament (ACL) reconstruction. DESIGN: Cross-sectional comparative clinical trial. SETTING: A physical therapy outpatient department. SUBJECTS: Thirty-one subjects with unilateral ACL reconstruction for more than 5 months. INTERVENTION: Patients under 3 bracing conditions: (1) DonJoy Brace, (2) mechanical placebo brace, or (3) no brace. Running and turning 10 times on a 22-meter figure-8 runway, and running and jumping (and landing) on a semicircular path. MAIN OUTCOME MEASURES: Speed of running and turning, speed of running and jumping, and accuracy of landing after the jump. RESULTS: Subjects performed similarly in conditions 1 and 2 in all the tests, but the speeds of running and turning were significantly slower in conditions 1 and 2 than condition 3 (p =.008--.000). Results of the run and jump tests were not different among all conditions. CONCLUSION: Knee bracing may not improve functional performance of subjects 5 months after ACL reconstruction. The use of such a brace could actually slow down running and turning, irrespective of the mechanical constraints of the brace. These functional outcomes need to be noted when such a brace is used on this group of subjects.

Adult↗

PubMed2001

Effectiveness of audio-biofeedback in postural training for adolescent idiopathic scoliosis patients.

The possibility of using learned physiological responses in control of progressive adolescent idiopathic scoliosis (AIS) was investigated. Sixteen (16) AIS patients with progressing or high-risk curves (Cobb's angle between 25 degrees and 35 degrees at start and reducible by lateral bending) were fitted with a device with tone alarm for poor posture. In the first 18 months of application, 3 patients defaulted and 4 showed curve progression > 10 degrees (2 changed to rigid spinal orthoses and 2 underwent surgery). The curves for the other 9 patients were kept under control (within +/- 5 degrees of Cobb's angle) and 5 of them have reached skeletal maturity and terminated the application. The remaining 4 patients were still using the devices until skeletal maturity or curve progression. The curve control rate was 69%. A long-lasting active spinal control could be achieved through the patient's own spinal muscles. Nevertheless, before the postural training device could become a treatment modality, a long-term study for more AIS patients was necessary. This project is ongoing in the Duchess of Kent Children's Hospital, Sandy Bay, Hong Kong.

Adolescent↗

PubMed2001

Numerical simulation of streaming potentials due to deformation-induced hierarchical flows in cortical bone.

Bone is a very dynamic tissue capable of modiA,fing its composition, microstructure, and overall geometry in response to the changing biomechanical needs. Streaming potential has been hypothesized as a mechanotransduction mechanism that may allow osteocytes to sense their biomechanical environment. A correct understanding of the mechanism for streaming potential will illuminate our understanding of bone remodeling, such as the remodeling associated with exercise hypertrophy, disuse atrophy, and the bone remodeling arounid implants. In the current research, a numerical model based on the finite element discretization is proposed to simulate the fluid flows through the complicated hierarchical flow system and to calculate the concomitant stress generated potential (SGP) as a result of applied mechanical loading. The lacunae-canaliculi and the matrix microporosity are modeled together as discrete one-dimensional flow channels superposed in a biphasic poroelastic matrix. The cusplike electric potential distribution surrounding the Haversian canal that was experimentallv observed and reported in the literature earlier was successfully reproduced by the current numerical calculation.

Bone and Bones↗

PubMed2001

Stability of reconstructed paralyzed shoulders using a reflected long head biceps technique.

A new tendon transfer technique is proposed for the reconstruction of the paralyzed shoulders secondary to Brachial Plexus Injury (BPI). In this tendon transfer, the long head of the biceps tendons is utilized as a bridging tendon graft. It is reflected at the exit of the bicipital groove, passed through the deltoid and directed to the trapezius. The technique is referred to here as the Reflected Long Head Bicepts (RLHB) technique. This study evaluated the effect of this tendon transfer on the anterior, posterior, and inferior stability of the reconstructed should using cadaveric specimens. It was shown that loading of the RLHB contributed significantly to anterior stability of the reconstructed shoulder for 90 deg elevation in the scapula plane. The mean displacement was reduced by 56 percent with RLHB loaded (p<0.01), by 56 percent with the rotator cuff loaded (p <0.005), and by 67 percent with both the RLHB and the rotator cuff loaded (p<0.004). For the post-operation conditions, variation of the directions of RLHB had no significant effect on joint displacement in response to anterior loading. The RLHB tendon also contributed to the posterior and inferior stability for the low and middle elevations in the plane of scapula. Two variations of the RLHB tendon transfer procedures, namely the "Sub-Deltoid" and the "Through-Deltoid" techniques, were introduced and studied. These two techniques did not seem to have significantly different effects on the displacement of the humeral head in response to both posterior and inferior loading. The results of this study seemed to support the clinical feasibility of this tendon transfer approach as far as the biomedical stability of the reconstruction is concerned.

Adult↗

PubMed2001

[3D visualization and information interaction in biomedical applications].

3D visualization and virtual reality are important trend in the development of modern science and technology, and as well in the studies on biomedical engineering. This paper presents a computer procedure developed for 3D visualization in biomedical applications. The biomedical models are constructed in slice sequences based on polygon cells and information interaction is realized on the basis of OpenGL selection mode in particular consideration of the specialties in this field such as irregularity in geometry and complexity in material etc. The software developed has functions of 3D model construction and visualization, real-time modeling transformation, information interaction and so on. It could serve as useful platform for 3D visualization in biomedical engineering research.

Biomedical Engineering↗

PubMed2000

A histomorphometric observation of flows in cortical bone under dynamic loading.

Ferritin was used as a histological marker for interstitial fluid flows in four goats. Two transcortical pins were inserted into each tibia mediolaterally-one at the proximal side and one at the distal side of the diaphysis. For the experimental limb, dynamic loading was applied to the pins on the lateral side. The contralateral limb was used as control. Ferritin was injected into the nutrient arteries feeding the two tibiae. The goat was then euthanized immediately. Undecalcified slides of the tibial cortical bone from both the experimental and the control limbs were studied histologically. Percentages of Haversian systems marked with ferritin halos and the average radial distance of ferritin transudation away from the Haversian canals were assessed. Results for the medial and lateral sides of both the experimental and control tibiae were reported. Significant differences in the ferritin transudation distance were found between the experimental and the control tibia (P < 0.005) and between the medial and the lateral sectors (P < 0.05). The approach documented in this paper could be used to address systematically how external loading might affect the transport phenomena in cortical bone.

Animals↗

PubMed2000

Assessment of neck tissue fibrosis using an ultrasound palpation system: a feasibility study.

Fibrotic change in the soft tissue of the neck is a common side-effect after radiotherapy treatment for cancers of the head and neck region. The development of a quantitative approach for the assessment of neck tissue stiffness using an ultrasound palpation system (UPS) is reported. A testing protocol was established with the participation of eight normal subjects and four patients who had neck fibrosis after previous radiotherapy to the neck. Six reference sites were assessed on each side of the neck in each subject. Site-dependence, inter-observer variability, and intra-observer variability were further evaluated by measurement of sites 1 cm anterior, posterior, superior and inferior to two of the reference sites on each side of the neck, and by repeating measurements using a second observer on the same occasion and using the same observer one week afterwards. The mean tissue Young's modulus for normal subjects was 12.8 +/- 3.9 kPa, and that of the radiotherapy-treated patients ranged from 46.4 to 108.3 kPa. The modulus shows limited variation among anatomical sub-sites within the neck. For a confidence level of 95%, there was a variation of +/- 14.2% for site-dependence, +/- 15.2% for inter-observer, and +/- 7.2% for intra-observer tests for the group of normal subjects. The variation in the patients was +/- 13.6% for site-dependence, and +/- 13.1% for the inter-observer test.

Adult↗

PubMed2000

Biomechanical assessment of plantar foot tissue in diabetic patients using an ultrasound indentation system.

The biomechanical properties of plantar tissues were investigated for four older neuropathic diabetic patients and four healthy younger subjects. Indentation tests were performed at four high-pressure areas with three postures in each subject. The tissue thickness and effective Young's modulus were measured by an ultrasound (US) indentation system. The system comprised a pen-size probe having a US transducer at the tip and a load cell connected in series with it. Results showed that the plantar soft tissues of the elderly diabetic patients were significantly stiffer and thinner when compared with the healthy young subjects. For the diabetic subjects tested, the Young's modulus at the 1st metatarsal head was significantly larger than those at the other three sites. This site-dependence was not observed in the healthy young subjects. The plantar tissue became significantly stiffer in the healthy young subjects as a result of posture changes. This posture-dependence of the Young's modulus was not established for the elderly diabetic group.

Biomechanical Phenomena↗

PubMed2000

Adhesion formation after nerve repair: an experimental study of early protected mobilization in the rabbit.

The common peroneal nerve and its surrounding muscles were cut and repaired in 14 rabbits. The injured limb was then either immobilized for 3 weeks or passively mobilized within a "safety range" every day. At 3 weeks after operation, the "stretch test" and "peel test" showed no difference in the biomechanical features of the adhesions between the nerve repair and the surrounding soft tissues.

Animals↗

PubMed2000

Effectiveness and biomechanics of spinal orthoses in the treatment of adolescent idiopathic scoliosis (AIS).

In this prospective study, the effectiveness and biomechanical factors of spinal orthoses in the treatment of moderate adolescent idiopathic scoliosis (AIS) patients were investigated. In the first 20 months of orthotic treatment, the values of standing AP Cobb's angle, apical vertebral rotation, lumbar lordosis as well as thoracic kyphosis showed significant reduction (P<0.05), however, the angle of trunk inclination and trunk listing did not. The values of those reducible parameters reached their lowest values within the first 12 months of orthotic treatment and then the values gradually increased but they were still below the pre-brace values. The mean pressure of The pressure pads was found to be 7.09 +/- 1.77 kPa (53.2 +/- 13.3 mmHg) while the mean tension of the straps was 26.8 +/- 5.2N. The standing AP Cobb's angle strongly correlated with the pad pressure (correlation coefficient=0.931, p<(.05) and strap tension (correlation coefficient=0.914, p<0.05). The strap tension and pad pressure strongly correlated and the correlation coefficient was 0.873 (p<0.05). This suggests that in the consideration of biomechanical function of spinal orthoses, the focus may be upon how tightly the orthosis was fastened and if the location and direction of the pressure pads are the correct. Therefore, for enhancing independent standard tension should be set in each strap, and regular and close monitoring is needed.

Adolescent↗

PubMed2000

[Three-dimensional finite element analyses on the transtibial residual limb and its prosthetic socket].

This paper presents a method for developing a nonlinear finite element model to analyze the load transfer between the transtibial residual limb and its prosthetic socket. The model was developed on the basis of three-dimensional geometry of the residual limb, internal skeleton, soft liner and socket. Interface elements, were used to connect the skin and the liner to simulate the friction/slip boundary conditions. The analyses were performed in two steps to simulate the donning procedure and the load-bearing situation. The model can be used to predict the pressures, shear stresses and slip between the residual limb and its socket under different external loads. Four models with different degrees of socket rectifications were analyzed.

Artificial Limbs↗

PubMed1999

Effective elastic properties for lower limb soft tissues from manual indentation experiment.

Quantitative assessment of the biomechanical properties of limb soft tissues has become more important during the last decade because of the introduction of computer-aided design and computer-aided manufacturing (CAD/CAM) and finite element analysis to the prosthetic socket design. Because of the lack of a clinically easy-to-use apparatus, the site and posture dependences of the material properties of lower limb soft tissues have not been fully reported in the literature. In this study, an ultrasound indentation system with a pen-size hand-held probe developed earlier by the authors was used to obtain the indentation responses of lower limb soft tissues. Indentation tests were conducted on normal young subjects with four females and four males at four sites with three body postures. A linear elastic indentation solution was used to extract the effective Young's modulus from the indentation responses. The determined modulus ranged from 10.4 to 89.2 kPa for the soft tissues tested. These results were in a similar range as those reported in the literature. The thickness of the lower limb soft tissues varied slightly with body posture changes. The Young's modulus determined was demonstrated to be significantly dependent on site, posture, subject and gender. The overall mean modulus of male subjects was 40% larger than that of female subjects. No significant correlation was established between the effective Young's modulus and the thickness of entire soft tissue layers.

Adult↗

PubMed1999

Extraction of quasi-linear viscoelastic parameters for lower limb soft tissues from manual indentation experiment.

A manual indentation protocol was established to assess the quasi-linear viscoelastic (QLV) properties of lower limb soft tissues. The QLV parameters were extracted using a curve-fitting procedure on the experimental indentation data. The load-indentation responses were obtained using an ultrasound indentation apparatus with a hand-held pen-sized probe. Limb soft tissues at four sites of eight normal young subjects were tested in three body postures. Four QLV model parameters were extracted from the experimental data. The initial modulus E0 ranged from 0.22 kPa to 58.4 kPa. The nonlinear factor E1 ranged from 21.7 kPa to 547 kPa. The time constant tau ranged from 0.05 s to 8.93 s. The time-dependent materials parameter alpha ranged from 0.029 to 0.277. Large variations of the parameters were noted among subjects, sites, and postures.

Adult↗

PubMed1999

In vivo friction properties of human skin.

In vivo frictional properties of human skin and five materials, namely aluminium, nylon, silicone, cotton sock, Pelite, were investigated. Normal and untreated skin over six anatomic regions of ten normal subjects were measured under a controlled environment. The average coefficient of friction for all measurements is 0.46+/-0.15 (p<0.05). Among all measured sites, the palm of the hand has the highest coefficient of friction (0.62+/-0.22). For all the materials tested, silicone has the highest coefficient of friction (0.61+/-0.21), while nylon has the lowest friction (0.37+/-0.09).

Adult↗

PubMed1999

Objective assessment of limb tissue elasticity: development of a manual indentation procedure.

An ultrasound indentation system with a pen-size hand-held probe was developed and used to obtain the effective Young's moduli of forearm and lower limb soft tissues in 12 subjects. Since the probe is manually driven, the alignment of the probe and control of the rate of indentation are parameters upon which the results obtained depend. This paper addresses whether manual indentation tests with the probe are sufficiently acceptable and repeatable for objective biomechanical characterization of limb tissues. Forearms of three normal subjects were tested in two states of muscular contraction. Six different indentation rates, ranging from 0.75 mm/s to 7.5 mm/s, were imposed. The load-indentation responses obtained were shown to be well represented by quadratic functions. A linear elastic indentation solution was used to extract the effective Young's modulus. The material parameters extracted were repeatable and rather rate-insensitive for the range of rates used. The effective Young's modulus obtained was found to significantly increase as a result of contraction of the underlying muscles. Indentor misalignment experiments demonstrated that misalignment affects the measurement from which the effective Young's modulus of soft tissues is calculated. This effect, however, was found to decrease as the tissue thickness increased. With the investigation of the above issues, a procedure has been established for the extraction of effective Young's moduli of limb soft tissues from manual cyclic indentation responses. Tests on experimental subjects' lower limbs further demonstrated that the ultrasonic indentor is a feasible instrument for characterization of the biomechanical properties of limb soft tissues. Paired-t tests showed that the effective Young's moduli of the lower limb soft tissues of three elderly persons with transtibial amputation were significantly smaller than those of six unimpaired young subjects.

Adult↗