---

Aims: In bone tissue engineering, the scaffold as a supportive structure, plays a vital role. Putting the scaffold in dynamic cell culture, such as perfusion bioreactor, makes the role of mechanical parameters such as shear stress and hydrodynamic pressure more important. On the other hand, these mechanical parameters are influenced by scaffold architecture. In this study, the effects of bone scaffold architecture on mechanical stimuli have been analyzed and their effects on the mesenchymal stem cell fate have been predicted.
Material & Methods: Using the tools of computer simulation, five bone scaffolds (Gyroid, high porous Gyroid, Diamond, IWP, and gradient architecture Gyroid) based on mathematical functions of minimal surfaces were designed and exposed in a simulated dynamic cell culture under the inlet velocities of 1, 10, 25, 50, and 100μm/s. Cell accumulation on the inner part of the scaffold was considered as an 8.5-micron layer. This layer was designed for Gyroid and IWP scaffolds.
Findings: Based on the results, Diamond scaffold showed the most efficient performance from the homogeneity of stresses point of view. In the presence of the cell layer, the von Mises stress was reported as 60 and 50 mPa on the Gyroid and IWP scaffolds, respectively which eases osteogenic differentiation.
Conclusion: In gradient architecture scaffolds under dynamic conditions, there is a gradient in shear stress that causes various signaling in different positions of theses scaffold and facilitates multi-differentiation of the cells on the same scaffold.

---

Since one of the main problems in bone tissue repair is the bacterial infections, recently the development of drug-eluting nanocomposite scaffolds for bone regenerative medicine applications has attracted significant attention. In this study Polycaprolactone (PCL)-based composite scaffolds containing 10vol% of titanium dioxide nanoparticles (~21nm), and bioactive glass particles (~6µm), were prepared without drug and also loaded by Tetracycline hydrochloride (TCH) antibiotic (0.57, 1.15 mg/mL) through solvent casting method for bone tissue engineering applications. Structural characterizations based on Scanning Electron Microscopy (SEM), and FTIR analysis were utilized to study the chemical bonds of glass/ceramic particles, and antibiotic crystals on the surface. In addition, in vitro cytotoxicity, and antibacterial analysis were performed by MTT, and Agar well-diffusion assays, respectively. In this study polymeric and composite scaffolds were fabricated with TCH clusters decorated on the surface. It was shown that the bioactive glass/PCL scaffolds loaded by 0.57 mg/mL of TCH revealed significant antibacterial effect, despite the acceptable cell viability. These scaffolds seem to be of interest as a potential candidate in drug-eluting scaffolds for bone tissue engineering applications.

 

---

Objective: Biodegradable polycaprolactone/starch composites can be used for bone tissue engineering applications. The effect of the ratio of components on composite properties is of tremendous importance. Methods: Polycaprolactone/starch composite of 80/20 and 70/30 ratios were fabricated by dissolving them in chloroform followed by evaporation of the solvent. Results: The composites were characterized by fourier transform infrared spectroscopy. Their bioactivity was evaluated by studying the apatite formation ability after immersing the specimens in simulated body fluid. The results of compressive test on samples showed that the composite’s modulus and strength approximated that of human trabecular bone. Mass loss in distilled water and starch degradation rate in PBS was evaluated, which showed that the starch ratio was effective in composite degradation. MTT analysis and alkaline phosphatase levels showed that this composite had no toxicity and could increase G-299 cell line osteoblastic activities. Conclusion: The increase in cellular osteoblastic activities and the ability for apatite formation on the composite surface, in addition to the polycaprolactone/starch samples' mechanical properties shows their capability to be used as substitutes for bone. Because this composite degradation rate is controlled by changing the starch ratio, it has the potential for use in bone tissue engineering applications. Samples that have a 70/30 ratio are considered optimal due to their enhanced cellular response and better mechanical properties.

---

The use of porous scaffolds for repairing the damaged bone tissues has been increased in recent years. As exploration of the mechanical properties of the scaffolds on the basis of experiments is time consuming and uneconomic, mathematical models are increasingly being introduced into the field, but most of them rely on finite element method and theoretical studies are rarely found in the literature. In this paper, different micromechanical models are presented for obtaining the effective elastic properties of bone scaffolds. Using these models, the mechanical properties of different scaffolds, including ceramic and composite bone scaffolds, are investigated. Single scale and multi-scale modeling approaches are used to simulate the ceramic and composite scaffolds, respectively. Furthermore, because of the wide application of hydroxyapatite in fabrication of bone scaffolds, the mechanical properties of hydroxyapatite scaffolds in different porosities are obtained in the current study by means of the presented methods. Results show that Dewey, self-consistent and differential schemes are the best methods in calculation of the value of Young’s modulus of these scaffolds in porosity ranges of less than 30 %, 30 to 60 % and more than 60 %, respectively. Moreover, self-consistent scheme gives good estimation of the value of Poisson’s ratio of hydroxyapatite scaffolds in different porosities. By obtaining the values of the mechanical properties of the scaffolds in different porosities by these models and using the statistical analysis, the mathematical relationship between the porosity and the mechanical properties of this kind of scaffolds (Young’s modulus and Poisson’s ratio) is obtained.