Evaluation of bone growth around bioactive glass S53P4 by scanning acoustic microscopy co-registered with optical interferometry and elemental analysis.

Bioactive glass (BAG) is a bone substitute that can be used in orthopaedic surgery. Following implantation, the BAG is expected to be replaced by bone via bone growth and gradual degradation of the BAG. However, the hydroxyapatite mineral forming on BAG resembles bone mineral, not providing sufficient contrast to distinguish the two in X-ray images. In this study, we co-registered coded-excitation scanning acoustic microscopy (CESAM), scanning white light interferometry (SWLI), and scanning electron microscopy with elemental analysis (Energy Dispersive X-ray Spectroscopy) (SEM-EDX) to investigate the bone growth and BAG reactions on a micron scale in a rabbit bone ex vivo. The acoustic impedance map recorded by the CESAM provides high elasticity-associated contrast to study materials and their combinations, while simultaneously producing a topography map of the sample. The acoustic impedance map correlated with the elemental analysis from SEM-EDX. SWLI also produces a topography map, but with higher resolution than CESAM. The two topography maps (CESAM and SWLI) were in good agreement. Furthermore, using information from both maps simultaneously produced by the CESAM (acoustic impedance and topography) allowed determining regions-of-interest related to bone formation around the BAG with greater ease than from either map alone. CESAM is therefore a promising tool for evaluating the degradation of bone substitutes and the bone healing process ex vivo.

Practical scale modification of oleogels by ultrasonic standing waves.

Lipid-based materials, such as substitutes for saturated fats (oleogels) structurally modified with ultrasonic standing waves (USW), have been developed by our group. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed. Here, we report scale-up of our procedure of structurally modifying oleogels via the use of USW by a factor of 200 compared to our previous microfluidic chamber. To this end, we compared three different USW chamber prototypes through finite element simulations (FEM) and experimental work. Imaging of the internal structure of USW-treated oleogels was used as feedback for successful development of chambers, i.e., the formation of band-like structures was the guiding factor in chamber development. We then studied the bulk mechanical properties by a uniaxial compression test of the sonicated oleogels obtained with the most promising USW chamber, and sampled local mechanical properties using scanning acoustic microscopy. The results were interpreted using a hyperelastic foam model. The stability of the sonicated oleogels was compared to control samples using automated image analysis oil-release tests. This work enabled the effective mechanical-structural manipulation of oleogels in volumes of 10-100 mL, thus paving the way for USW treatments of large-scale lipid-based materials.

CESAM-Coded excitation scanning acoustic microscope.

Scanning acoustic microscopy (SAM) finds use across many disciplines, e.g., biology, industrial quality control, and materials science, thanks to its unique ability to quantify mechanical sample properties combined with its high resolution. However, such imaging is often slow, especially if averaging is necessary. We present a Coded Excitation Scanning Acoustic Microscope (CESAM) that employs coded signals and show that it produces images of higher signal-to-noise ratios (SNRs) than the classical SAM in a comparable measurement time. The CESAM employs coded signals instead of the short bursts used in traditional SAMs, and we employ both linear and non-linear frequency modulation. Our results show that compared to the SAM approach, this modulation increases the SNR by 16.3 dB (from 39.9 to 56.2 dB) and reduces the echo duration by 26.7% when we employ a linear chirp to the transducer with a nominal bandwidth of 130-370 MHz. Driving the transducer with a broader bandwidth signal using non-linear chirps (100-450 MHz), we obtained a SNR increase of 10.3 dB and a reduced echo duration of 70.5%. The shorter echo duration increases z-resolution, whereas the lateral resolution remains limited by the wavelength. Finally, we show that by using these coded signals, one can obtain enhanced image quality relative to the standard actuation of the same measurement time. Our results have potential to invigorate the field of acoustic microscopy, especially with samples where the enhanced SNR and/or contrast-to-noise ratio is crucial for image quality.