Custom-Made Poly(urethane) Coatings Improve the Mechanical Properties of Bioactive Glass Scaffolds Designed for Bone Tissue Engineering

The replication method is a widely used technique to produce bioactive glass (BG) scaffolds mimicking trabecular bone. However, these scaffolds usually exhibit poor mechanical reliability and fast degradation, which can be improved by coating them with a polymer. In this work, we proposed the use of custom-made poly(urethane)s (PURs) as coating materials for 45S5 Bioglass®-based scaffolds. In detail, BG scaffolds were dip-coated with two PURs differing in their soft segment (poly(ε-caprolactone) or poly(ε-caprolactone)/poly(ethylene glycol) 70/30 w/w) (PCL-PUR and PCL/PEG-PUR) or PCL (control). PUR-coated scaffolds exhibited biocompatibility, high porosity (ca. 91%), and improved mechanical properties compared to BG scaffolds (2–3 fold higher compressive strength). Interestingly, in the case of PCL-PUR, compressive strength significantly increased by coating BG scaffolds with an amount of polymer approx. 40% lower compared to PCL/PEG-PUR- and PCL-coated scaffolds. On the other hand, PEG presence within PCL/PEG-PUR resulted in a fast decrease in mechanical reliability in an aqueous environment. PURs represent promising coating materials for BG scaffolds, with the additional pros of being ad-hoc customized in their physico-chemical properties. Moreover, PUR-based coatings exhibited high adherence to the BG surface, probably because of the formation of hydrogen bonds between PUR N-H groups and BG surface functionalities, which were not formed when PCL was used.

Mechanical Reliability of Silicon Microstructures

In this article, an overview of the mechanical reliability of silicon microstructures for micro-electro-mechanical systems (MEMS) is given to clarify what we now know and what we still have to know about silicon as a high-performance mechanical material on the microscale. Focusing on the strength and fatigue properties of silicon, attempts to understand the reliability of silicon and to predict the device reliability of silicon-based microstructures are introduced. The effective parameters on the strength and the mechanism of fatigue failure are discussed with examples of measurement data to show the design guidelines for highly reliable silicon microstructures and devices.

Mechanical Reliability and Modeling of Hydroxyapatite Acaffold

Significant contributions on the improvement of the mechanical properties of hydroxyapatite (HAp) have been widely reported. However, failure analysis (mechanical reliability) and modeling are missing. This article filled the gap by conducting Two-parameter Weibull distribution assisted by modeling to investigate the mechanical reliability of HAp. The employed HAp was characterized under SEM/EDS analysis. The results revealed the characteristics of HAp and also the nature of the synthesis route employed through its irregular morphology. The Two-parameter Weibull distribution analysis was conducted on the hardness and compressive strength of HAp scaffold. The characteristic hardness and compressive strength, coupled with their corresponding bounds, failure rates, and correlation coefficients were been presented. The Weibull analysis with the assistance of modeling revealed HAp fabricated under 10 KN compaction load and sintered at 1100 oC as the most reliable sample under hardness condition, while HAp fabricated under 15 KN compaction load and sintered at 1000 oC gave the most reliable characteristic under compression. However, 15 KN compaction load and 1100 oC sintering temperature showed the best reliability on the overall mechanical (hardness and compressive strength) reliability. Future study is recommended on the reliability of HAp scaffolds considering other mechanical properties that are essential for biomedical application.