Biomedical subjects

G Khang

Publications and source records attributed to G Khang.

26 records · Page 2Linked to original sources

PubMed1996

Prevention of platelet adhesion on polysulfone porous catheter by saline solution perfusion, II. Ex vivo and in vivo investigation.

Using a custom-made PVC medical tube ateriovenous (A-V) shunt and a porous polysulfone (PSf) catheter, an ex vivo and in vivo experiment were carried out to study the effectiveness of saline solution perfusion to prevent adhesion of platelets without using anticoagulants. The critical perfusion rate for preventing adhesion of platelets onto the PSf catheter tubes is about 0.45 ml min-1 cm-2. The higher perfusion rate resulted in a lesser platelet adhesion. At the highest perfusion rate tested, 0.92 ml min-1 cm-2, the number of adhered platelets decreased by 98% in the in vivo experiment. From the results of ex vivo and in vivo canine experiments, the saline perfusion catheters can be used as a very useful clinical armamentarium to prevent platelet and blood cell adhesion without using anticoagulants.

Animals↗

PubMed1996

Radiation effects on polypropylene for sterilization.

In order to improve the resistance of gamma-radiation sterilization of polypropylene (PP), the formulations of the additives such as antioxidants, crosslinking agent, and trans-stilbene oxide (StO) have been carried out. The irradiated PP and ethylene-propylene copolymer samples with control and additives were characterized by mechanical tester, colorimetry, and Fourier transform infrared spectroscopy with total attenuated reflectance mode (FTIR-ATR). Crosslinking agent and StO formulated PP showed remarkable radiation resistance and minimum discoloration. Also, radiation resistance of ethylene-propylene copolymers with 3% of ethylene contents was better than that of PP homopolymers in the case of no additives. The proposed mechanisms of radiation stabilization with additives are also discussed.

Antioxidants↗

PubMed1996

Improved bonding strength of polyethylene/polymethylmetacrylate bone cement--a preliminary study.

The adhesion of polymethylmetacrylate (PMMA) bone cement and low density polyethylene (LDPE) substrate by means of corona discharge treatment are presented. The surfaces were characterized by water contact angle goniometer, Fourier-transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR), electron spectroscopy for chemical analysis (ESCA), and scanning electron microscopy (SEM) for surface morphology. The bonding strength between bone cement and LDPE with varying intensity of corona treatment was evaluated by a 180 degrees peel test. The water contact angles decreased with increasing treatment intensity from 95.0 +/- 1.8 to around 43.5 degrees. It was observed that the oxygen containing groups as hydroxyl, ether, carboxylic acid, ester, ketone or aldehyde groups were introduced on the LDPE surfaces by corona treatment. The peel strength steeply increased from 0 to 1.75 kgf/cm with increasing the intensity of corona treatment. The improved adhesion of bone cement onto LDPE substrate may be due to only secondary force such as hydrogen bonding between PMMA bone cement and hydrophilized LDPE substrate.

Adhesiveness↗

PubMed1995

Biocompatibility of polysulfone I. Surface modifications and characterizations.

Surface treatments by nonionic surfactant (Brij) coating and air-plasma glow discharge treatment onto polysulfone have been investigated to improve its surface properties. Surface treated samples were characterized by measurement of contact angle by a goniometer, Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR), and electron spectroscopy for chemical analysis (ESCA). The contact angles of the nonionic surfactant coated films decreased from 66.6 +/- 2.1 degrees to nearly 0 degrees due to hydrophilic polyethylene oxide (PEO) chain segment of the nonionic surfactant, and those of air-plasma treated films also decreased from 66.6 degrees to about 22 degrees with a treatment time of less than 5 s. ESCA analysis of air-plasma treated films indicates the incorporation of oxygen molecules onto polysulfone surface lowers the water contact angle. These modified techniques can be used to prevent platelet adhesion onto polysulfone surfaces.

Adsorption↗

PubMed1995

Biocompatibility of polysulfone II. Platelet adhesion and cho cell growth.

Experimental results on the platelet adhesion, and CHO cell adhesion and growth onto nonionic surfactant which is composed of a long alkyl chain (n = 12-18) as the hydrophobic part, and a polyethyleneoxide (PEO) segment (n = 10-23) as the hydrophilic part coated and air-plasma treated PSf surfaces are presented in terms of PEOs functionality and surface wettability to improved blood- and cell-compatibility of polysulfone. Platelet adhesion experiments on surface treated PSf films were carried out with platelet enriched plasma (PRP) in the parallel flow chamber in vitro. Number and morphology of adhered platelets were observed by scanning electron microscope. The number of adhered platelets on nonionic surfactant coated surfaces decreased significantly compared to the control. Also, the adhesion of platelets on to PSf substrate decreased with increasing coating concentration of nonionic surfactant. In the dry air-plasma exposed PSf sample, the adhesion of platelets decreased independently of plasma exposure time, and significant diminution of platelet adhesion was observed below about 40 degrees of the contact angle. It is believed that less platelet adhesion is preceded by less protein adsorption due to hydrophobic dehydration interaction. In Chinese hamster ovary (CHO) cell, adhesion and growth cells grew better on the air-plasma treated PSf surfaces. From these results, it can be proposed that surface wettability of PSf is very important for cell adhesion and growth.

Adsorption↗

PubMed1989

Paraplegic standing controlled by functional neuromuscular stimulation: Part I--computer model and control-system design.

We have developed a planar computer model to investigate paraplegic standing induced by functional neuromuscular stimulation. The model consists of nonlinear musculotendon dynamics (pulse train activation dynamics and musculotendon actuator dynamics), nonlinear body-segmental dynamics, and a linear output-feedback control law. The model of activation dynamics is an analytic expression that characterizes the relation between the stimulus parameters (pulse width and interpulse interval) and the muscle activation. Hill's classic two-element muscle model was modified into a musculotendon actuator model in order to account for the effects of submaximal activation and tendon elasticity on development of force by the actuator. The three body-segmental, multijoint model accounts for the anterior-posterior movements of the head and trunk, the thigh, and the shank. We modeled arm movement as an external disturbance and imposed the disturbance to the body-segmental dynamics by means of a quasistatic analysis. Linearization, and at times linear approximation of the computer model, enabled us to compute a constant, linear feedback-gain matrix, whose output is the net activation needed by a dynamical joint-torque actuator. Motivated by an assumption that minimization of energy expenditure lessens muscle fatigue, we developed an algorithm that then computes how to distribute the net activation among all the muscles crossing the joint. In part II, the combined feedback control strategy is applied to the nonlinear model of musculotendon and body-segmental dynamics to study how well the body ought to maintain balance should the feedback control strategy be employed.

Biomechanical Phenomena↗

PubMed1989

Paraplegic standing controlled by functional neuromuscular stimulation: Part II--Computer simulation studies.

We simulated two types of body motion. First, the body position is assumed to be initially perturbed from the upright position, and all muscles are assumed inactive at the initial position. The control law developed in the preceding paper drives the body segments to the standing position. Arm movements are then applied to the body to investigate how performance is affected by an external disturbance. Simulated body motion indicated that the current output-feedback control law functions well. The body can recover upright posture from a highly flexed position, and the controller can then maintain the body near the vertical during arm movements. The simulation results showed three consistent activation patterns based on energy minimization: 1) no antagonistic muscle pairs are coactivated, 2) strong muscles are recruited before weak ones, and 3) fast muscles are recruited before slow ones. The reason for the second and third observations is that energy liberation rate depends heavily on the relative amount of muscle activation. Since the current control law requires muscles to generate specific joint torques at a prescribed time, strong muscles do not have to be activated as much as weak ones, and recruiting a fast muscle at low activation level consumes less energy than recruiting a slow one at high activation level. Although the output-feedback control law functions well according to our simulation results, the static optimization process would, in practice, take too much computational time to make it practical. Based on the consistent activation patterns found in our simulations, we therefore developed a simpler (suboptimal) activation-distribution scheme that takes much less time and still gives nearly identical performance.

Biomechanical Phenomena↗

PubMedDate not supplied

Study on in vitro release patterns of fentanyl-loaded PLGA microspheres.

In order to study the development of the delivery device of long-acting local anaesthetics for post-operative analgesia and control of chronic pain of cancer patient, fentanyl loaded poly(l-lactide-co-glycolide) (PLGA, molecular weight; 5000, 8000, 20,000, and 33,000 g/mole) microspheres (FMS) were studied. FMS were prepared by an emulsion solvent-evaporation method. The influence of several preparation parameters such as initial drug loading, PLGA concentrations, emulsifier concentrations, oil phase volume and mole ratio and molecular weight has been investigated on the fentanyl release patterns. Generally, the drug showed the biphasic release patterns, with an initial diffusion followed by a lag period before the onset of the degradation phase, but there were no lag times in the device. Fentanyl was slowly released from FMS over 10 days in vitro, with a quasi-zero order property. The release rate increased with increasing drug loading as well as increasing polymer concentration with a relatively small initial burst effect. From the results, FMS may be a good formulation to deliver the anaesthesia for the treatment of chronic pain.

Analgesics↗