COMMBINI: an experimentally-informed COmputational Model of Macrophage dynamics in the Bone INjury Immunoresponse

Bone fracture healing is a well-orchestrated but complex process that involves numerous regulations at different scales. This complexity becomes particularly evident during the inflammatory stage, as immune cells invade the healing region and trigger a cascade of signals to promote a favorable regenerative environment. Thus, the emergence of criticalities during this stage might hinder the rest of the process. Therefore, the investigation of the many interactions that regulate the inflammation has a primary importance on the exploration of the overall healing progression. In this context, an in silico model named COMMBINI (COmputational Model of Macrophage dynamics in the Bone INjury Immunoresponse) has been developed to investigate the mechano-biological interactions during the early inflammatory stage at the tissue, cellular and molecular levels. An agent-based model is employed to simulate the behavior of immune cells, inflammatory cytokines and fracture debris as well as their reciprocal multiscale biological interactions during the development of the early inflammation (up to 5 days post-injury). The strength of the computational approach is the capacity of the in silico model to simulate the overall healing process by taking into account the numerous hidden events that contribute to its success. To calibrate the model, we present an in silico immunofluorescence method that enables a direct comparison at the cellular level between the model output and experimental immunofluorescent images. The combination of sensitivity analysis and a Genetic Algorithm allows dynamic cooperation between these techniques, enabling faster identification of the most accurate parameter values, reducing the disparity between computer simulation and histological data. The sensitivity analysis showed a higher sensibility of the computer model to the macrophage recruitment ratio during the early inflammation and to proliferation in the late stage. Furthermore, the Genetic Algorithm highlighted an underestimation of macrophage proliferation by in vitro experiments. Further experiments were conducted using another externally fixated murine model, providing an independent validation dataset. The validated COMMBINI platform serves as a novel tool to deepen the understanding of the intricacies of the early bone regeneration phases. COMMBINI aims to contribute to designing novel treatment strategies in both the biological and mechanical domains.

Are elderly pedestrians allowed enough time at pedestrian crossings in Cape Town, South Africa?

A descriptive, cross-sectional analytical study was conducted to determine whether the recommended walking speed of 1.2 ms(-1) would allow elderly pedestrians to safely clear pedestrian crossings in Cape Town, South Africa. Male and female volunteers (n = 47), aged 65-93 years and resident in four homes for older persons, were recruited. Pedestrian clearance intervals at 40 traffic lights within 5-km radius of the selected homes were measured. The mean walking speed required at these traffic lights was 0.86 +/- 0.32 ms(1). The maximal walking speed over 12 m was measured without carrying any load and when carrying a predetermined weight of an average shopping bag. Participants' emotions associated with pedestrian road safety were also assessed through an interview. The mean maximal unloaded and loaded walking speeds were 1.36 +/- 0.31 ms(-1) (0.73-2.03 ms(-1)), and 1.36 +/- 0.33 ms(-1) (0.58-2.12 ms(-1)), respectively. Over 30% of the participants walked slower than the recommended walking speed of 1.2 ms(-1). Participants felt that traffic lights did not allow for sufficient time to cross roads (51.1%) and reported emotions of apprehension (44.7%), anxiety (17.0%), and fear (10.6%) when crossing. A review of traffic planning and public policy is recommended to ensure older pedestrians safely clear pedestrian crossings.

Aetiology of deafness in white children in the Cape

Two-hundred and forty White children attending special schools for the deaf have been investigated by clinical,genetic and laboratory methods in order to determine determine the aetiology of their hearing disability of these, 36% had a genetic basis for their deafness, while in a further 34% an acquired lesion was incriminated. The most important determinants of acquired deafness were maternal rubella, neonatal hyperbilirubinaemia and meningo-encephalitis. The prevention of childhood deafness is primarily dependent upon recognition of the underlying causative factor.