Bone has a special structure that is both stiff and elastic, and the composition of bone confers it with an exceptional mechanical property. However, bone substitute materials that are made of the same hydroxyapatite (HA) and collagen do not offer the same mechanical properties. It is important for bionic bone preparation to understand the structure of bone and the mineralization process and factors. In this paper, the research on the mineralization of collagen is reviewed in terms of the mechanical properties in recent years. Firstly, the structure and mechanical properties of bone are analyzed, and the differences of bone in different parts are described. Then, different scaffolds for bone repair are suggested considering bone repair sites. Mineralized collagen seems to be a better option for new composite scaffolds. Last, the paper introduces the most common method to prepare mineralized collagen and summarizes the factors influencing collagen mineralization and methods to analyze its mechanical properties. In conclusion, mineralized collagen is thought to be an ideal bone substitute material because it promotes faster development. Among the factors that promote collagen mineralization, more attention should be given to the mechanical loading factors of bone.

Purpose: This research was to reveal the thermal characteristics of a water-cooled microwave ablation antenna in phantom, and the influence of cooling water velocity on ablation pattern by numerical method. In addition, by comparing the numerical results with experimental results, the experimentally obtained SAR was proven to be correct. Methods: The temperature distribution in ablations was simulated by the finite element method. In the FEM, the cooling effect in the region of the water-cooled antenna was introduced by applying the convective coefficient to the related boundaries, and the experimental determined SAR in phantom was applied as heat generation of microwave generator. To study the effect of water flow rate on ablation pattern, three different water velocities were chosen. In addition, the phantom thermal properties changes were considered in simulation when the heating temperature was above 80°C. Results: The ablation pattern could be identified as a pear shape. The temperatures of monitoring points which were located near the antenna could rise more rapidly, and they were more likely to achieve steady heat transfer state within a short time compared with those far away from the antenna. The cooling water effectively decreased the temperature near the antenna, an under-temperature occurred in the cooling region, and the different cooling water flow rate did not affect significantly the ablation pattern. Conclusions: The numerical results compared reasonably well with the experimental results in both heating pattern and temperature of individual monitoring point over the same heating duration. The SAR measured by our previous experiment was also confirmed by this numerical simulation. This method could be employed to study combination thermal field of multi-antennas in future work.

The objective of this research was to reveal the thermal characteristics of microwave ablations in the vicinity of an arterial bifurcation. The temperature distribution after microwave heating of a liver-like material in the close proximity of an arterial bifurcation was simulated using the finite element method. Coupled fluid flow and solid heat transfer were taken into consideration and a three-dimensional analysis was performed. An experimentally determined SAR (specific absorption rate) generated by the absorption of microwaves in liver-like material was used in the analysis instead of utilizing electromagnetic calculations. Several different tests of time-controlled ablations with varying distances between the microwave antenna and the bifurcation were performed and detailed temperature distributions near the bifurcation were obtained. The interaction between the recirculation flow in the bifurcation and the heat transfer in the surrounding tissue makes the temperature distribution near the bifurcation complicated. Most importantly, after a period of continuous heating with constant microwave output power, the maximum temperatures caused by the ablation did not always increase with the distance between the antenna and the bifurcation. It can be concluded that inadequate ablations can be the result not only from a close proximity between the antenna and the blood vessel, but also from a complicated blood flow in large vessels whose structure causes recirculation flow.