Extrusion-based 3D printing of poly(propylene fumarate) scaffolds with hydroxyapatite gradients

The primary focus of this work is to present the current challenges of printing scaffolds with concentration gradients of nanoparticles with an aim to improve the processing of these scaffolds. Furthermore, we address how print fidelity is related to material composition and emphasize the importance of considering this relationship when developing complex scaffolds for bone implants. The ability to create complex tissues is becoming increasingly relevant in the tissue engineering community. For bone tissue engineering applications, this work demonstrates the ability to use extrusion-based printing techniques to control the spatial deposition of hydroxyapatite (HA) nanoparticles in a 3D composite scaffold. In doing so, we combined the benefits of synthetic, degradable polymers, such as poly(propylene fumarate) (PPF), with osteoconductive HA nanoparticles that provide robust compressive mechanical properties. Furthermore, the final 3D printed scaffolds consisted of well-defined layers with interconnected pores, two critical features for a successful bone implant. To demonstrate a controlled gradient of HA, thermogravimetric analysis was carried out to quantify HA on a per-layer basis. Moreover, we non-destructively evaluated the tendency of HA particles to aggregate within PPF using micro-computed tomography (μCT). This work provides insight for proper fabrication and characterization of composite scaffolds containing particle gradients and has broad applicability for future efforts in fabricating complex scaffolds for tissue engineering applications.

Vibrational characterization and adsorption mode on SERS-active surfaces of guanidino-(bromophenyl)methylphosphonic acid

This work presents adsorption geometry of [N-butyl-guanidino-(4-bromophenyl)methyl] phosphonic acid (4-BrPhG(n-But)P) on different SERS-active substrates (colloidal and specifically prepared Ag and Au roughened substrates). The adsorption mode is deduced from the SERS selection rules and several characteristic bands of the 4-BrPhG(n-But)P molecular fragments. The SERS spectra are compared to the experimental FT-Raman spectrum. In addition, the vibrational wavenumbers and PED's obtained for 4-BrPhG(n-But)P by using density functional theory methods with B3LYP/6-311++G(**) level of theory and PCM model is briefly presented.