Thermal analysis during bone drilling using rigid polyurethane foams: numerical and experimental methodologies

Osteotomy or bone cutting is a common procedure in orthopaedic surgery, mainly in the treatment of fractures and reconstructive surgery. However, the excessive heat produced during the bone drilling process is a problem that counters the benefits of this type of surgery, because it can result in thermal osteonecrosis, bone reabsorption and damage the osseointegration of implants. The analysis of different drilling parameters and materials can allow to decrease the temperature during the bone drilling process and contribute to a greater success of this kind of surgical interventions. The main goal of this study was to build a numerical three-dimensional model to simulate the drilling process considering the type of bone, the influence of cooling and the bone density of the different composite materials with similar mechanical properties to the human bone and generally used in experimental biomechanics. The numerical methodology was coupled with an experimental methodology. The use of cooling proved to be essential to decrease the material damage during the drilling process. It was concluded that the materials with less porosity and density present less damage in drilling process. The developed numerical model proved to be a great tool in this kind of analysis. © 2016, The Brazilian Society of Mechanical Sciences and Engineering.

Synthesis of waterborne polyurethane-urea dispersions with chain extension step in homogeneous and heterogeneous media

Hypothesis: The possibility of tailoring the final properties of environmentally friendly waterborne polyurethane and polyurethane-urea dispersions and the films they produce makes them attractive for a wide range of applications. Both the reagents content and the synthesis route contribute to the observed final properties. Experiments: A series of polyurethane-urea and polyurethane aqueous dispersions were synthesized using 1,2-ethanediamine and/or 1,4-butanediol as chain extenders. The diamine content was varied from 0 to 4.5 wt%. Its addition was carried out either by the classical heterogeneous reaction medium (after phase inversion step), or else by the alternative homogeneous medium (prior to dispersion formation). Dispersions as well as films prepared from dispersions have been later extensively characterized. Findings: 1,2-Ethanediamine addition in heterogeneous medium leads to dispersions with high particle sizes and broad distributions whereas in homogeneous medium, lower particle sizes and narrow distributions were observed, thus leading to higher uniformity and cohesiveness among particles during film formation. Thereby, stress transfer is favored adding the diamine in a homogeneous medium; and thus the obtained films presented quite higher stress and modulus values. Furthermore, the higher uniformity of films tends to hinder water molecules transport through the film, resulting, in general, in a lower water absorption capacity.