The dissolution kinetics of polymer powders as isolated grains or in beds were studied theoretically and experimentally. A simple model de®eloped for the dissolution of a dispersion of isolated grains with an arbitrary size distribution was confirmed experimentally using polysaccharides in water. Based on experimental data for the dissolution of lump-forming powder beds, modeled using a bimodal population of grains and lumps, a robust technique was de®eloped for analyzing experimental data, which is independent of the details of lump formation. A qualitati®e picture of lump formation is described, based on the idea that during the initial hydration of a powder bed a '' pore blocking'' condition quickly de®elops due to the formation of a gel layer around the dry grains.Once formed, lumps dissol®ed the same way and with the same kinetic description, as indi®idual, dispersed grains.
To support the global restart of elective surgery, data from an international prospective cohort study of 8492 patients (69 countries) was analysed using artificial intelligence (machine learning techniques) to develop a predictive score for mortality in surgical patients with SARS-CoV-2. We found that patient rather than operation factors were the best predictors and used these to create the COVIDsurg Mortality Score (https://covidsurgrisk.app). Our data demonstrates that it is safe to restart a wide range of surgical services for selected patients.
Purpose The objective of this single-center randomized single-blinded trial was to assess the hypothesis that anterior cruciate ligament reconstruction (ACLR) using a four-strand semitendinosus (ST) graft with adjustable femoral and tibial cortical fixation produced good outcomes compared to an ST/gracilis (ST/G) graft with femoral pin transfixation and tibial bioscrew fixation. Follow-up was 2 years. Methods Patients older than 16 years who underwent primary isolated ACLR included for 1 year until August 2017 were eligible. The primary outcome measures were the subjective International Knee Documentation Committee (IKDC) score, isokinetic muscle strength recovery, and return to work within 2 years. The study was approved by the ethics committee. Results Of 66 eligible patients, 60 completed the study and were included, 33 in the 4ST group and 27 in the ST/G group. Mean age was 30.5 ± 8.9 years in the 4ST group and 30.3 ± 8.5 in the ST/G group (n.s.). No significant between-group differences were found for mean postoperative subjective IKDC (4ST
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