Mehdi Mohammadi

In this study, we designed and developed novel poly(ε-caprolactone) (PCL)-based biomaterials, for use as bone scaffolds, through modification with both biphasic calcium phosphate (BCP), to impart bioactive/bioresorbable properties, and with silver nitrate, to provide antibacterial protection against Staphylococcus aureus, a microorganism involved in prosthetic joint infections (PJIs). Field emission scanning electron microscopy (FESEM) showed that the samples were characterized by square-shaped macropores, and energy dispersive X-ray spectroscopy analysis confirmed the presence of PCL and BCP phases, while inductively coupled plasma–mass spectrometry (ICP–MS) established the release of Ag⁺ in the medium (~0.15–0.8 wt% of initial Ag content). Adhesion assays revealed a significant (p < 0.0001) reduction in both adherent and planktonic staphylococci on the Ag-functionalized biomaterials, and the presence of an inhibition halo confirmed Ag release from enriched samples. To assess the potential outcome in promoting bone integration, preliminary tests on sarcoma osteogenic-2 (Saos-2) cells indicated PCL and BCP/PCL biocompatibility, but a reduction in viability was observed for Ag-added biomaterials. Due to their combined biodegrading and antimicrobial properties, the silver-enriched BCP/PCL-based scaffolds showed good potential for engineering of bone tissue and for reducing PJIs as a microbial anti-adhesive tool used in the delivery of targeted antimicrobial molecules, even if the amount of silver needs to be tuned to improve osteointegration.

In this work, dense, porous, and, for the first time, functionally-graded bi-layer scaffolds with a cylindrical geometry were produced from a commercially available hydroxyapatite powder using the robocasting technique. The bi-layer scaffolds were made of a dense core part attached to a surrounding porous part. Subsequently, these bi-layer robocast scaffolds were joined with an outer shell of an antibacterial porous polymer layer fabricated by solvent casting/salt leaching techniques, leading to hybrid ceramic-polymer scaffolds. The antibacterial functionality was achieved through the addition of silver ions to the polymer layer. All the robocast samples, including the bi-layer ones, were first characterized through scanning electron microscopy observations, mechanical characterization in compression and preliminary bioactivity tests. Then, the hybrid bi-layer ceramic-polymer scaffolds were characterized through antimicrobial tests. After sintering at 1300 °C for 3 h, the compressive strengths of the structures were found to be equal to 29 ± 4 MPa for dense samples and 7 ± 4 MPa for lattice structures with a porosity of 34.1%. Bioactivity tests performed at 37 °C for 4 weeks showed that the precipitated layer on the robocast samples contained octacalcium phosphate. Finally, it was evidenced that the hybrid structure was effective in releasing antibacterial Ag⁺ ions to the surrounding medium showing its potential efficiency in limiting Staphylococcus aureus proliferation during surgery.

The particle size distribution of a commercial Mg‐doped hydroxyapatite powder was tailored through two different milling procedures, carried out under wet or dry conditions. Wet milling gave rise to finer particles, with a narrower size distribution. Tailoring the particles size was the key to produce homogeneous gelcast green bodies, as well as fully dense and fine microstructures. In fact, wet‐milled samples achieved full densification and compressive strength of about 300 MPa, five times higher than the values achieved by the dry milled samples. During the calcination treatments, HA progressively decomposed into β‐ and α‐ TCP phases, promoted by the progressive Mg ²⁺ substitution inside the HA and β‐ TCP lattices. As a result, a biphasic ( HA /β‐ TCP ) calcium phosphate ceramic was successfully obtained. Gelcast macroporous materials were prepared by direct foaming, starting from both milled powders. Highly porous samples (73%‐77% porosity) with a high degree of interconnectivity within pores were successfully produced. However, dry milled‐foamed materials were characterized by a significant residual porosity within the struts, whereas in wet‐milled foams struts and pore windows were highly compact, the key to provide sufficient mechanical strength to such highly porous open‐cell foams, thus suggesting a possible use as implantable scaffolds.