Influence of Molecular Weight on the Enzymatic Degradation of PLA Isomer Blends by a Langmuir System

Polylactides (PLAs) and lactide copolymers are biodegradable, compostable, and derived from renewable resources, offering a sustainable alternative to petroleum-based synthetic polymers owing to their advantages of comparable mechanical properties with commodity plastics and biodegradability. Their hydrolytic stability and thermal properties can affect their potential for long-lasting applications. However, stereocomplex crystallization is a robust method between isomer PLAs that allows significant amelioration in copolymer properties, such as thermal stability, mechanical properties, and biocompatibility, through substantial intermolecular interactions amid l-lactyl and d-lactyl sequences, which have been the key approach to initial degradation rate and further PLA applications. It was demonstrated that the essential parameters affecting stereocomplexation are the mixing ratio and the chain length of each unit sequence. This study deals with the molecular weight, one of the specific interactions between isomers of PLAs. A solution polymerization method was applied to control molecular weight and chain architecture. The stereocomplexation was monitored with DSC. It was confirmed that the lower molecular weight polymer showed a higher degradation rate, as a hydrolyzed fragment having a molecular weight below a certain length dissolves into the water. To systematically explore the critical contribution of molecular weights, the Langmuir system was used to observe the stereocomplexation effect and the overall degradation rate.

Impact of discontinuing isolation in a private room for patients infected or colonized with vancomycin-resistant enterococci (VRE) on the incidence of healthcare-associated VRE bacteraemia in a hospital with a predominantly shared-room setting

BACKGROUND

Isolating patients infected or colonized with vancomycin-resistant enterococci (VRE) in a private room or cohort room to prevent hospital transmission is controversial.

AIM

To evaluate the effect of a relaxed isolation policy for VRE-infected or colonized patients on healthcare-associated (HA) VRE bacteraemia in an acute care hospital with a predominantly shared-room setting.

METHODS

The incidence of HA VRE bacteraemia was compared during a private isolation era (October 2014-September 2017), a cohort isolation era (October 2017-June 2020), and a no isolation era (July 2020-June 2022). Using Poisson regression modelling, an interrupted time-series analysis was conducted to analyse level changes and trends in incidences of HA VRE bacteraemia for each era.

FINDINGS

The proportion of VRE-infected or -colonized patients staying in shared rooms increased from 18.3% in the private isolation era to 82.6% in the no isolation era (P < 0.001). There was no significant difference in the incidences of HA VRE bacteraemia between the private isolation era and the cohort isolation era (relative risk: 1.01; 95% confidence interval: 0.52-1.98; P = 0.977) or between the cohort isolation era and the no isolation era (0.99; 0.77-1.26; P = 0.903). In addition, there was no significant slope increase in the incidence of HA VRE bacteraemia between any of the eras.

CONCLUSION

In a hospital with predominantly shared rooms, the relaxation of isolation policy did not result in increased HA VRE bacteraemia, when other infection control measures were maintained.

Muscle fatigue measured with evoked muscle vibrations

Skeletal muscle vibrates laterally during voluntary and evoked muscle contractions. We hypothesized that the vibration amplitude from evoked muscle twitches is directly related to evoked twitch force from fatiguing muscle. To test the hypothesis, vibrations produced by evoked muscle twitches were recorded during short (5-second) rest periods as the muscle was intermittently exercised with voluntary contractions. Trials were performed at 30%, 50%, and 70% of maximal voluntary contraction. Evoked muscle twitches eliminated the problems of motivation and tremor that complicate sound and vibration measurements during voluntary contractions. Results from the first dorsal interosseus hand muscle in 11 normal adult volunteers revealed that the vibration amplitude is highly correlated (r2 = 0.93, at 70% MVC, r2 = 0.97, at 50% MVC; r2 = 0.85, at 30% MVC) with force. Both potentiation and reduction of force with exercise were accompanied by parallel changes in vibration amplitude, as measured with an accelerometer. Compound muscle action potentials did not increase with exercise-induced twitch potentiation, and did not correlate as highly with force during fatigue.