Medical knowledge of the skeleton including its structures has improved constantly over the past decades. Advanced imaging methods, mechanical testing and optical techniques have revealed insights into bone architecture and composition. Most of these advancements were possible due to the ex vivo investigation of biological tissues. Investigations of fresh tissue are generally preferred over preserved or fixed samples. However, chemical fixation is sometimes inevitable due to histological procedures or logistical reasons. The aim of this study was to investigate whether short-term chemical fixation with formaldehyde affects bone quality parameters obtained from Raman spectroscopy and if these effects last for intermediate sample storage of several hours. As formaldehyde induces cross-links to the organic components in bone tissue, we hypothesized that collagen-related parameters are particularly affected. Femurs of eight 17-week-old C57BL/6 mice were extracted and divided into two groups (N = 8 / group). Samples of the first group were fixed by immersion in 4% formaldehyde (PFA-solution) for 12 h at 4°C (fixed group) while samples of the second group were left untreated (unfixed group). Raman spectroscopy was performed, and repeated after 4 h, to assess whether intermediate storage time influenced the obtained results. Based on resultant spectra, mineral-to-matrix ratio, carbonate-to-phosphate ratio, carbonate-to-amide I ratio, mineral crystallinity and collagen maturity were determined. Carbonate-to-phosphate ratio was the only parameter showing a significant difference between the first and the subsequent measurements. For both groups, ratios showed a decrease in carbonate substitution compared to the first measurement (percentage decrease: 3.1% in fixed, 4.7% in unfixed). Collagen maturity of samples, which were short-term fixed with formaldehyde, was significantly lower than of fresh, unfixed samples (percentage difference: 3.8%). Our study shows that Raman spectroscopy is able to detect changes in collagen structure initiated by formaldehyde and that changes in short-term fixed samples are minimally influencing bone material properties measured with Raman spectroscopy.
Reaching a sustainable society represents one of the key challenges of the 21st century and wood as an abundant and renewable resource has the potential to serve as one of the main materials for this transition. In this regard different concepts for the development of novel wood-based functional materials, fabricated by the in situ formation of different materials systems are shown. Another focus is laid on densified cellulose composites, a novel material concept based on delignification and densification of wood, resulting in a high performance natural fibre reinforced composite material. This approach represents a promising alternative to common glass- and fiber reinforced composites but also to other manufacturing approaches such as 3D printing.