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Biomedical subjects

N K Yao

Publications and source records attributed to N K Yao.

6 recordsLinked to original sources
PubMed1998

Use of a diffusion model for assessing the performance of poly(vinyl alcohol) bioartificial pancreases.

Islets of Langerhans surrounded by a semipermeable membrane to prevent an immune response by the host immunosystem is a potential way of treating type I diabetes mellitus. In this study, poly(vinyl alcohol) (PVA) tubular membranes with added polyethylene glycol to create pores in the skin layer were prepared to improve their diffusion property. In a static incubation study, islets cultured in the PVA tubular membranes still demonstrated their function of secreting insulin after 30 days. When the tubular PVA bioartificial pancreas was perifused in a small chamber with RPMI-1640 medium containing glucose at concentrations of 5.6-16.6 mmol/L, insulin release began to increase without delay. Therefore, such a membrane is an alternative potential material for a bioartificial pancreas. In addition, a mathematical mass transfer model of insulin release was developed and compared with the perifusion data. It was shown that satisfactory kinetics could be achieved with a PVA membrane. However, the model showed that the insulin output of islets cultured in the PVA tubular membrane must be increased to improve the performance significantly. These findings suggest that a bioartificial pancreas using a PVA membrane is a promising material, but the technique for seeding islets in the chamber requires further modification.

Animals↗
PubMed1997

A cell perifusion system of isolated rat islets for studies on rapid insulin-glucose dynamics.

We have developed a cell perifusion system of isolated rat islets, to improve the accuracy of controlling the medium content and the stability of the medium flow. This new system presents the following characteristics: (1) There is always a consistent flow in the perifusion chamber and only half of its volume is altered when switching the medium. (2) The medium containing test substances can be prepared and held ready in very close proximity to islets. The test glucose media are introduced to the islets immediately after a switch. (3) The environment of the islets could be repeatedly changed from one state to another in a rigorous stepwise manner. The system can provide an accurate switch of glucose concentrations both in time and quantity without introducing pressure disturbances, which makes a suitable tool for studies on rapid insulin-glucose dynamics. In experiments of perifused rat islets, our results further confirmed the observation that the amplitudes of oscillatory insulin secretions were magnified when glucose levels increased but their periods were unaffected. In addition, insulin secretions instantly increased in response to the sudden increase of glucose levels, but gradually decreased in response to the sudden decrease of glucose levels.

Animals↗
PubMed1997

Dynamic aspects for interislet synchronization of oscillatory insulin secretions.

How are the oscillatory insulin secretions from numerous islets synchronized to result in an identifiable oscillation? We postulated that a sudden increase in glucose concentration could best account for the interislet synchronization. The perifusion with two parallel chambers each containing 100 islets from the same rat was performed. The glucose concentrations of two chambers were simultaneously increased from 100 to 300 mg/dl in step function to examine the synchronizing efficacy. Synchrony and regularity of insulin oscillation were evaluated by cross-correlation and/or power spectral analysis. Although the insulin had been in stable oscillation, we found that the synchrony between two chambers and the regularity of each chamber were still significantly improved after a sudden increase in glucose level. However, the improved synchrony and regularity were transient. They gradually slid toward a less rigorous condition in a 15-h long-term perifusion. We suggested that the interislet synchronization of oscillatory insulin secretions could be improved by a sudden increase in glucose level. The insulin pulses were therefore enhanced to present their physiological effects.

Animals↗
PubMed1997

Weight bearing influence on knee joint bony contact movements: an in vivo video-fluoroscopy study.

In order to understand the effects of body weight-bearing on knee joint bony contact movements, a video-fluoroscopic digitizing system with in vivo human knee extension-flexion motions of 12 healthy adults under body weight-bearing and non-weight-bearing conditions was studied. These 12 subjects were equally separated into two groups consisting of a body weight-bearing group and a non-weight-bearing group. Video-fluoroscopic images were digitized to get three parameters from the knee joint bony geometry. These three parameters were the radius of rotation, the are length of rotation, and the contact point of the tibiofemoral joint, and they were used to decide the knee joint bony contact status of the sliding, spinning and rocking motions. The results showed that the knee bony contact movements under body weight-bearing conditions had about 4 times the incidence rate of the sliding motion under non-weight-bearing conditions. The incidence rate of the sliding motion was greatest when the knee flexion was less than 30 degrees. The knee bony contact movements under non-weight-bearing conditions had a larger spinning motion incidence rate and smaller rocking motion incidence rate than they did under weight-bearing conditions. The larger spinning motion incidence rate when the knee joint flexion was greater than 60 degrees. In conclusion, the body weight-bearing factor should be considered in studying knee joint bony contact movements.

Adult↗
PubMed1996

Evaluation of asymmetric poly(vinyl alcohol) membranes for use in artificial islets.

Islets of Langerhans surrounded by a semipermeable membrane to prevent the host immunosystem is a potential way to treat type I diabetes mellitus. In this study, a series of poly (vinyl alcohol) membranes were formed by adding polyethylene glycols to create pores in the skin layer. The permeability study showed the skin layer structure had an influence on the diffusion of low molecular weight glucose, vitamin B12 and insulin. The mass transfer coefficient was improved from 1.04 x 10(-4) to 2.16 x 10(-4) cm/ sec for glucose, from 2.84 x 10(-5) to 8.36 x 10(-5) cm/sec for vitamin B12 and from 1.45 x 10(-6) to 4.15 x 10(-6) cm/sec for insulin, whereas the passage of immunoglobulin G was completely prevented, indicating that these membranes could be effective in protecting islets from immunorejection. Thus such a membrane is an alternative potential material for artificial islets. In addition, we examined the insulin secretory response of islets separated by a poly(vinyl alcohol) membrane. We found that the insulin-secretion rate is relatively rapid compared to the permeation rate of insulin; thus, the process of the artificial islets is insulin-diffusion-controlled.

Biocompatible Materials↗