Numerical modeling of bone tissue adaptation--a hierarchical approach for bone apparent density and trabecular structure.

In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone apparent density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area density. For each scale there is a material distribution problem governed by density-based design variables which at the global level can be identified with bone relative density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone apparent density as well as microstructural designs characterizing both anisotropy and bone surface area density. The bone apparent density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

Energy expenditure after 2- to 3-hour elective surgical operations.

UNLABELLED: Energy expenditure was measured by indirect calorimetry in 17 adult patients (8 women and 9 men) before surgery, 4 hours immediately after surgery, and 24 hours late after surgery in patients undergoing elective surgery of small-to-medium scope. MATERIAL AND METHODS: The total duration of surgery ranged from 2 to 3 hours. Repeated measures were performed on the same patient, so that each patient was considered to be his/her own control. All patients received a 5% dextrose solution (2000 mL/day) throughout the postoperative period. RESULTS: Men showed a reduction in CO2 production during the immediately after surgery period (257+/-42 mL/min) compared to before surgery (306+/-48 mL/min) and late after surgery (301+/-45 mL/min); this reduction was not observed in women. Energy expenditure was also lower in men during immediately after surgery (6.6 kJ/min). None of the other measurements, including substrate oxidation, showed significant differences. CONCLUSION: Therefore, elective surgery itself cannot be considered an important trauma that would result in increased energy expenditure. According to this study, it is not necessary to prescribe an energy supply exceeding basal expenditure during the immediate after-surgery period. The present results suggest that the energy supply prescribed during the postoperative period after elective surgery of small-to-medium scope should not exceed 5-7 kJ/min, so the patient does not receive a carbohydrate overload from energy supplementation.

[Comparison of methods to test the "in vitro" cytotoxicity of biocompatible materials]. / Comparação de métodos para testar a citotoxicidade "in vitro" de materiais biocompatíveis.

OBJECTIVE: A comparison of the sensitivity of the agar diffusion method with that of extraction using cell-lines RC-IAL (fibroblastic of rabbit kidney) and HeLa (epithelial carcinoma cells from the cervix uteri of the human uterus), in the in vitro evaluation of materials of medical and hospital. MATERIALS AND METHODS: Fifteen samples chosen at random, from among the already known positives and negatives in our stock, were tested and identified as cotton, form, latex, cellulose and acrylic. Besides the samples mentioned, many SDS (GIbco) concentrations were tested experimentally in RC-IAL and HeLa cell cultures. RESULTS: Of the 50 samples tested, 44(88%) were positive by both methods. However, when the SDS were compared by using the two methods, positive results were noted in the concentrations of from 0.5 to 0.05 microgram/ml in the agar diffusion ans extraction methods. A cytotoxic effect was only noted in the concentrations of up to 0.25 microgram/ml. CONCLUSION: When the SDS was used, differences favorable to the agar diffusion method were observed in the two cell lines, in two concentrations; that is, the sensitivity of this method was quantitatively greater on inspection than that of the extraction method, as well as being the simpler method to use.