Organising outpatient dialysis services during the COVID-19 pandemic. A simulation and mathematical modelling study.

BackgroundThis study presents two simulation modelling tools to support the organisation of networks of dialysis services during the COVID-19 pandemic. These tools were developed to support renal services in the South of England (the Wessex region caring for 650 patients), but are applicable elsewhere. MethodsA discrete-event simulation was used to model a worst case spread of COVID-19 (80% infected over three months), to stress-test plans for dialysis provision throughout the COVID-19 outbreak. We investigated the ability of the system to manage the mix of COVID-19 positive and negative patients, and examined the likely effects on patients, outpatient workloads across all units, and inpatient workload at the centralised COVID-positive inpatient unit. A second Monte-Carlo vehicle routing model estimated the feasibility of patient transport plans and relaxing the current policy of single COVID-19 patient transport to allow up to four infected patients at a time. ResultsIf current outpatient capacity is maintained there is sufficient capacity in the South of England to keep COVID-19 negative/recovered and positive patients in separate sessions, but rapid reallocation of patients may be needed (as sessions are cleared of negative/recovered patients to enable that session to be dedicated to positive patients). Outpatient COVID-19 cases will spillover to a secondary site while other sites will experience a reduction in workload. The primary site chosen to manage infected patients will experience a significant increase in outpatients and in-patients. At the peak of infection, it is predicted there will be up to 140 COVID-19 positive patients with 40 to 90 of these as inpatients, likely breaching current inpatient capacity (and possibly leading to a need for temporary movement of dialysis equipment). Patient transport services will also come under considerable pressure. If patient transport operates on a policy of one positive patient at a time, and two-way transport is needed, a likely scenario estimates 80 ambulance drive time hours per day (not including fixed drop-off and ambulance cleaning times). Relaxing policies on individual patient transport to 2-4 patients per trip can save 40-60% of drive time. In mixed urban/rural geographies steps may need to be taken to temporarily accommodate renal COVID-19 positive patients closer to treatment facilities. ConclusionsDiscrete-event simulation simulation and Monte-Carlo vehicle routing model provides a useful method for stress-testing inpatient and outpatient clinical systems prior to peak COVID-19 workloads.

Enabling Free-Standing 3D Hydrogel Microstructures with Microreactive Inkjet Printing.

Reactive inkjet printing holds great prospect as a multimaterial fabrication process because of its unique advantages involving customization, miniaturization, and precise control of droplets for patterning. For inkjet printing of hydrogel structures, a hydrogel precursor (or cross-linker) is printed onto a cross-linker (or precursor) bath or a substrate. However, the progress of patterning and design of intricate hydrogel structures using the inkjet printing technique is limited by the erratic interplay between gelation and motion control. Accordingly, microreactive inkjet printing (MRIJP) was applied to demonstrate a spontaneous 3D printing of hydrogel microstructures by using alginate as the model system. In addition, a printable window within the capillary number-Weber number for the MRIJP technique demonstrated the importance of velocity to realization of in-air binary droplet collision. Finally, systematic analysis shows that the structure and diffusion coefficient of hydrogels are important factors that affect the shape of printed hydrogels over time. Based on such a fundamental understanding of MRIJP of hydrogels, the fabrication process and the structure of hydrogels can be controlled and adapt for 2D/3D microstructure printing of any low-viscosity (<40 cP) reactive inks, with a representative tissue-mimicking structure of a ∼200 µm diameter hollow tube presented in this work.

Direct Patterning of Highly Conductive PEDOT:PSS/Ionic Liquid Hydrogel via Microreactive Inkjet Printing.

The gelation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has gained popularity for its potential applications in three dimensions, while possessing tissue-like mechanical properties, high conductivity, and biocompatibility. However, the fabrication of arbitrary structures, especially via inkjet printing, is challenging because of the inherent gel formation. Here, microreactive inkjet printing (MRIJP) is utilized to pattern various 2D and 3D structures of PEDOT:PSS/IL hydrogel by in-air coalescence of PEDOT:PSS and ionic liquid (IL). By controlling the in-air position and Marangoni-driven encapsulation, single droplets of the PEDOT:PSS/IL hydrogel as small as a diameter of ≈260 µm are fabricated within ≈600 µs. Notably, this MRIJP-based PEDOT:PSS/IL has potential for freeform patterning while maintaining identical performance to those fabricated by the conventional spin-coating method. Through controlled deposition achieved via MRIJP, PEDOT:PSS/IL can be transformed into different 3D structures without the need for molding, potentially leading to substantial progress in next-generation bioelectronics devices.