In the fabrication of a bioprosthetic heart valve from bovine pericardial tissues, the tissues are subjected to suturing. The stress-strain response of sutured as well as unsutured strips of this tissue were examined. The stress-strain response was determined using a tensile-testing machine. It was found that suturing weakens the tissue in that sutured strips are more extensible, exhibit a lower stress at rupture and a lower final elastic modulus. In addition, it was also found that the bigger the suture/needle size used the greater the decrease in tissue strength. In all, tissue strength was observed to decrease by 22 to 59% in this study. The weakening of the tissue is attributed to the puncture holes created by the surgeon's needle which create regions of weakness. This response of bovine pericardial tissue to suturing should be given due consideration in the fabrication of a bioprosthetic heart valve using this tissue.
The response of human skin to "stress relaxation" tests at low loads in vitro was investigated. A number of behaviours, other than those already well established and documented, were observed. The significant behaviours are pure recovery and relaxation-recovery. Other behaviours observed are temporary stress recovery during the relaxation process, and momentary sudden non-linear drop in stress value followed by a second relaxation. The pure recovery and relaxation-recovery responses are repeatable. The latter represents the transitional response between the well-known behaviour of stress relaxation and the behaviour of stress recovery.
The analyses of a few tasks were carried out in an electronics factory. The main objectives are to identify the ergonomic and biomechanical hazards of problem work tasks, to analyze each task systematically in order to evaluate the workers' exposures to the risk factors of force, posture pressure and repetition and to make recommendations to reduce the risks and hazards. The methodology includes objective measures--detailed analysis by going through training manuals, job description and production records. Subjective measures include interviewing the operator and supervisors informally, the operators were also required to fill in a structured questionnaire. The paper concludes by making recommendations to reduce the ergonomic hazards by engineering solutions, redesign or administrative controls or the implementation of procedures.
A method using a texture analyzer equipment and chicken pouch as the biological tissue was investigated for measuring the bioadhesive properties of polymers under simulated buccal conditions. The method was evaluated using two polymers, namely Carbopol 974P and Methocel K4M while the instrument variables studied included the contact force, contact time and speed of withdrawal of the probe from the tissue. The parameters measured were the work of adhesion and peak detachment force. Longer contact time and faster probe speed not only gave better reproducibility of results, but also better sensitivities for both parameters measured. On the other hand, a certain level of contact force was found essential for achieving good bioadhesion, above which there was no further contribution to the bioadhesion process. When the method was applied to determine the bioadhesiveness of several polymers, the values obtained for the work of adhesion and peak detachment force were quite consistent in the ranking of the polymers. The Carbopols were found to have the highest values, followed by gelatin, sodium carboxymethyl celluloses and hydroxypropylmethyl celluloses. On the other hand, Alginic acid, Eudragit RLPO and RSPO, and Chitosan appeared to have low bioadhesive values.
To investigate the suitability of chitosan films prepared using two different solvents, acetic acid (Chitosan-AA) and lactic acid (Chitosan-LA), for wound dressing, in comparison with a commercial preparation, Omiderm.
Fracture-dislocation of the lumbo-sacral spine was an unusual injury and was divided into anterior, posterior and lateral types depending on the displacement of the cephalad portion of the spine over the caudal portion. According to the authors' knowledge, only 31 cases of traumatic fracture-dislocation of the lumbo-sacral spine were reported in the English literature. Only 3 previous reports referred to this injury with a posterior displacement, which was an even rarer injury. This was the fourth report of this type of injury.
Tarsal adhesive pads enable insects to hold on to smooth plant surfaces. Using a centrifuge technique, we tested whether a "wet adhesion" model of a thin film of liquid secreted between the pad and the surface can explain adhesive and frictional forces in Asian Weaver ants (Oecophylla smaragdina). When forces are acting parallel to the surface, pads in contact with the surface can slide smoothly. Force per unit pad contact area was strongly dependent on sliding velocity and temperature. Seemingly consistent with the effect of a thin liquid film in the contact zone, (1) frictional force linearly increased with sliding velocity, (2) the increment was greater at lower temperatures and (3) no temperature dependence was detected for low-rate perpendicular detachment forces. However, we observed a strong, temperature-independent static friction that was inconsistent with a fully lubricated contact. Static friction was too large to be explained by the contribution of other (sclerotized) body parts. Moreover, the rate-specific increase of shear stress strongly exceeded predictions derived from estimates of the adhesive liquid film's thickness and viscosity. Both lines of evidence indicate that the adhesive secretion alone is insufficient to explain the observed forces and that direct interaction of the soft pad cuticle with the surface ("rubber friction") is involved.
A study was conducted to investigate the effectiveness of freeze-dried bovine pericardium (FDBP) as a biomaterial in diaphragmatic herniorrhapy in dogs. Eight adult dogs were randomly selected and divided into two equal groups. In FDBP group, a diaphragmatic defect was induced and repaired with an identical size of FDBP. In the control group, a diaphragmatic wall was incised at three-side border creating a flap and sutured. Grossly, only mild intrathoracic adhesion was observed for most of the animals, and no herniation occured. Microscopically, the biomaterial incorporated into the host's tissue by ingrowth of young muscle fiber and massive new blood vessel formation in between the fibrous tissue.
Various blend ratios of high-density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. In the unfilled state, a blend of 50/50 (HDPE/UHMWPE) ratio by weight was found to yield optimum properties in terms of processability and mechanical properties. Hydroxyapatite (HA) was compounded with the optimum blend ratio. The effects of HA loading, varied from 0 to 50wt% for both filled and unfilled blends were tested for mechanical properties. It was found that the inclusion of HA in the blend led to a remarkable improvement of mechanical properties compared to the unfilled blend. In order to improve the bonding between the polymer blend and the filler, the HA used was chemically treated with a coupling agent known as 3-(trimethoxysiyl) propyl methacrylate and the treated HA was mixed into the blend. The effect of mixing the blend with silane-treated HA also led to an overall improvement of mechanical properties.
Linear polymers have been commonly used as dental composite. However the aim of this work is to use hyperbranched polymer in an attempt to produce dental composite. The reason is because the dendritic molecules have shown low viscosity at higher molecular weight compared to the linear counterparts. Therefore, this work attempts to substitute the linear polymer with as much of hyperbranched polymer in the dental composite that would pass the required ISO 4049:1998(E) "Dentistry - Resin-based filling material". Several formulations of dental composites were used, i.e. combinations of linear-linear and linear-hyperbranched polymers for comparison. Following this, physical and mechanical characterisation were conducted based on the ISO standards such as water sorption and water solubility. Other characterisation such as polymerisation shrinkage and Vickers hardness were also evaluated. It was found that different types of resins give different physical and mechanical properties. The maximum achievable hyperbranched polymer, which passes the required ISO standard, that can be incorporated in the linear polymer to form dental composite is 43% wt.
The aim of this study was to evaluate the effect of powder-to-liquid ratio on the glass transition temperature (Tg) and the tensile properties of denture base material prepared from poly (methyl methacrylate) (PMMA) and hydroxyapatite (HA) previously treated with 3-trimethoxysilylpropyl methacrylate (gamma-MPS). Specimens for mechanical testing were prepared by adding composites powder (PMMA, BPO and HA) to the monomer (MMA and EGDMA) followed by hand mixing as in dental laboratory description usage. The glass transition temperature was studied by using differential scanning calorimetry (DSC). It was observed that the tensile properties and the Tg were affected by the powder-to-liquid ratio. The mechanical characterization of the materials were performed by using single edge notch-tension (SEN-T) specimens; the fracture toughness was slightly higher in formulation which contained HA filler compared to commercial denture base material.
The effect of hemodialysis on the mechanical behavior of a cellulosic Hemophane ME-IOH and one Polysulfone type hollow fibers was investigated. Mechanical tests showed that the deformation of polysulfone type of hollow fibers is entirely different than that of the other dialyser for the samples used and unused in hemodialysis. All the samples exposed to the dialysis showed decreased in ductility. Fracture surface studies proved that there was some alignment on the fracture surface. XRD and DSC experiments revealed structural changes had occurred.
Treatment of articular cartilage lesions remains a clinical challenge. The uses of prosthetic joint replace allograft and/or autograft transplant carry a risk of complications due to infection, loosening of its component, immunological rejection and morbidity at the donor site. There has been an increasing interest in the management of cartilage damages, owing to the introduction of new therapeutic options. Tissue engineering as a method for tissue restoration begins to provide a potential alternative therapy for autologous grafts transplantations. We aimed to evaluate how well a tissue engineered neocartilage implant, consist of human articular chondrocytes cultured with the presence of autologous serum and mixed in a fresh fibrin derived from patient, would perform in subcutaneous implantation in athymic mice.
This finite element analysis is aimed at comparing relative stiffness of three different posterior instrumentation constructs: the Hospital Universiti Kebangsaan Malaysia Spinal Instrumentation System (HUKM-SIS), the Cotrell-Dubousset Instrumentation (CDI) and Harrington Instrumentation System (HIS), used in the treatment of adolescent idiopathic scoliosis (AIS). The constructs were tested under various loads using MSC Patran 2001 r2a. Under increasing flexion loads, there was a linearly corresponding increase in deflection magnitudes for all constructs on the load-deflection curve. The CDI was the stiffest construct under axial, forward flexion and extension loads, followed by the HUKM-SIS and HIS. Under lateral bending loads, the HUKM-SIS construct was the stiffest followed by CDI and HIS. The HUKM-SIS construct was stiffer than HIS under torsional loads. We conclude that multiple pedicle screws increase the stiffness of posterior instrumentation constructs under all loads and inter-segmental spinous processes wiring increase the stiffness against lateral bending.
Coating has been widely used in pharmaceutical manufacture either as non-functional or a functional entity. The objectives of the present study were to investigate the effect of plasticizers such as PEG400, PEG1000 and triacetin on mechanical properties, glass transition temperature and water vapor transmission of free films prepared from HPMC and/or HPMC:PVA blends, to develop suitable coating system for tablets, and to determine the release profiles of the coated tablets. The tensile strength of plasticized HPMC films was generally lower than that of control HPMC film and could be attributed to increased crystallinity and segmental chain mobility of HPMC. This effect increased as the concentration of plasticizer increased. Generally the addition of both grades of polyethylene glycol (PEG400 & PEG1000) increased the moisture permeability of HPMC films but the films containing triacetin provided a more rigid barrier to moisture compared to unplasticized HPMC films. The dissolution profiles of paracetamol tablets coated with 7% w/v HPMC coating-solutions containing PEG400, PEG1000 and triacetin, and those containing PEG400 & PVA together showed that HPMC had weak water resistance. The presence of PEG400 and 1000 in HPMC films further weakened its resistance to solubility while the presence of triacetin caused a little increase in HPMC water resistance. From the results it was concluded that HPMC at 7%w/w concentration was suitable for film-coating intended for non-functional coating. Presence of the PEG 400, PEG1000 and triacetin as well as the presence of PVA and PEG400 together improved the coating properties of HPMC films and made it more suitable as a non-functional coating material.
The last 20 years have seen a tremendous growth in mobile computing and wireless communications and services. An experimental study was conducted to explore the effect of text/background color on a laptop computing system along with variable environmental vibration on operators' data entry task performance in moving automobiles. The operators' performance was measured in terms of the number of characters entered per minute without spaces (NCEPMWS) on a laptop computing system. The subjects were divided into 3 categories, namely, Novices, Intermediates and Experts. Findings suggest a re-evaluation of existing laptop designs taking ergonomics into consideration. It appears that proper selection of text/background color on the laptop coupled with controlled vehicular speed could result in a better quality of interaction between human and laptops and it could also resolve the problem of poor data entry task performance.
This study aims at investigating the mechanical properties of the contemporary metallic bone plates determining the effect of their length, width and thickness on the properties and compares with the composite bone plates. Three-points bending test was performed over the stainless steel plates of different length, width and thickness. The test results showed that different plates had different mechanical properties. However, the properties are still much higher than that of particular bones intended to be treated. Therefore, the reported findings strongly encourage developing composite bone plates with biocompatible polymers/fibers that would have modulated properties according to the requirements.
In this study, porous hydroxyapatite (HA) samples were fabricated via sponge techniques with the aid of sago as part of the binder mixture. Development processes for the production of porous bone graft substitutes are studied using polyurethane sponge. To obtain the optimum amount of binder for successful fabrication of porous HA were done. Initially, porous HA powder was synthesized using calcium hydroxide and orthorphosphoric acid. Meanwhile, sago was mixed with PVA in a certain ratio to be used as binder for preparing the porous HA. After a series of investigative tests were conducted to characterize the sintered samples, the use of the sago and polymeric mixture was found to successfully aid the fabrication of porous HA samples. In this investigation, comparison of physical and mechanical characteristics between samples prepared using difference techniques was made.