Stab wounds are an increasingly common cause of death or series injury and the high-risk groups in society are growing both in size and number. These facts make the study of mechanics of knife penetration more relevant than ever. The aim was to quantify the penetration force needed to inflict a certain stab wound by modelling knife penetration via the Finite Element Method. Case studies of stabbing incidents were carried out to give some insight into the nature and type of problem to be modelled. It was decided to work with an idealised stab-penetration model including a section of target tissue simulants. This stab-penetration test could yield repeatable and comparable results both experimentally and computationally. Suitable target simulants were identified by the stab-penetration test and also by uniaxial tensile tests. Pig skin was found to roughly match the mechanical properties of human skin with gelatine as a realistic flesh simulant. Computational modelling of knife penetration was attempted by use of Abaqus/Explicit, a nonlinear FEA package which features modelling of contact-impact problems. A true to scale finite element model of the stab-penetration test set-up was built including a material model of the target simulant. The computed penetration force was found highly mesh dependent for sharp blades and too high forces were predicted. Blunt penetrators were also tested both by experiments and computationally. By refining the constitutive model for skin computed values were obtained in reasonable agreement with the experiments for blunt penetrators. Mesh dependency was minimal in the computational model with blunt penetrators. It was concluded that modelling of knife penetration via finite element method is possible but analysis is time consuming due to the high mesh refinement required. Accuracy of the predicted penetration force is still too low for typical blade sharpnesses to be of practical use.

Clinical and experimental observations of foetal wound healing have led to a reappraisal of dermal wound repair. Because of the major contribution of collagen to scar tissue, the presence and role of collagen in scarless healing in foetal animal models has been a source of some controversy. The experimental work described in this thesis clearly establishes that foetal animals are able to deposit abundant collagen in traditional wound healing models. The emphasis of speculation subsequently shifted to consider the role of other matrix elements, particularly hyaluronan, which has particularly high levels in foetal wounds. Some investigators have proposed that the more 'fluid' nature of the matrix facilitates the remodelling of the deposited collagen. Experimental evidence presented in this thesis suggests, however, that while the physico-chemical properties of hyaluronan are important in influencing cell and matrix interactions, more specific and controllable interactions may be due to the action of proteins associated with the hyaluronan.

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Introduction: The difficulties in the management of the blunt chest wall trauma patient in the Emergency Department due to the development of late complications are well recognised in the literature. The first aim of this study was to investigate the risk factors for the development of complications following blunt chest wall trauma. Using these risk factors, the second aim was to develop and validate a prognostic model that can be used to assist in the management of this patient group. Methods: The risk factors for the development of late complications following blunt chest wall trauma were investigated using a number of methodologies. These included a systematic review and meta-analysis, a questionnaire study and a retrospective observational study. Following identification of the risk factors, a prognostic model was developed using multivariable logistic regression. This model was then externally validated in a prospective multi-centre study. Results: The systematic review, questionnaire study, retrospective study and development study results highlighted that the risk factors for the development of complications following blunt chest wall trauma were an increasing patient age, the existence of chronic lung disease, an increasing number of rib fractures, the use of pre-injury anti-coagulants and a decreasing oxygen saturation level on presentation to the Emergency Department. These risk factors were included in the final model. Results of the validation study indicated an overall model accuracy of 87%, a sensitivity of 75% and a specificity of 97%. A concordance index of 0.96 highlighted an excellent discriminatory ability of the model. Conclusions: The prognostic model developed in this study demonstrated good predictive capabilities in the derivation sample and excellent discrimination in the validation sample. The model demonstrates clinical usefulness as it includes risk factors not normally considered in the management of blunt chest wall trauma patients in the clinical setting.

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