Robocasting of Single and Multi-Functional Calcium Phosphate Scaffolds and Its Hybridization with Conventional Techniques: Design, Fabrication and Characterization

Abstract

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.

Novel Silver-Functionalized Poly(ε-Caprolactone)/Biphasic Calcium Phosphate Scaffolds Designed to Counteract Post-Surgical Infections in Orthopedic Applications

“…The manipulation of biomaterial surface properties to control the interaction between implants and their biological surroundings has been one of the major research topics in the biomaterials field [ 3 , 7 , 39 , 40 ]. In fact, the incorporation of stiff, bioactive inorganic materials [e.g., calcium phosphates (CaPs) such as HA and β-TCP] into a PCL polymer leads to significant enhancements in mechanical properties, bioactivity, and in vivo bone regeneration capacity [ 36 , 41 ].…”

“…Owing to these features, both HA and β-TCP and their mixtures, denoted as BCP, are commonly used as fillers in polymer-based bone substitutes. Thus, when implanted in an osseous site, bone bioactive materials provide an ideal environment for cell adhesion and colonization with high osteoconductivity (supporting bone growth and encouraging the ingrowth of surrounding bone), as well as osteoinductivity (promoting the differentiation of progenitor cells in the osteoblastic lineage) [ 3 , 39 , 44 ].…”

“…To face the problem of microbial contamination and to prevent the development of PJIs, the proposed solution is antibiotic release from the biomaterial, but it is important to appreciate that this treatment also contributes to antimicrobial resistance. Therefore, an efficient alternative to conventional methods of overcoming the growing problem of this resistance would be to incorporate inorganic antibacterial agents (such as silver, copper, or zinc ions) or natural antimicrobial compounds (chitosan, carbon-derived components) into prosthetic materials to endow them with broad antimicrobial activity against Gram-negative and Gram-positive bacteria and fungi [ 17 , 20 , 38 , 39 , 45 , 46 , 47 ]. This has been the subject of extensive research, but the desirable successful prevention or effective solution is yet to be achieved.…”

“…The antibacterial behavior of the silver-added PCL-based scaffolds was investigated by means of the inhibition halo assay in accordance with European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines (manual v 9.0; acceessed on 15 August 2021) and by a bacterial adhesion assay by applying methods used in previous papers of ours [ 39 , 46 , 75 , 76 ]. A biofilm-producing S. aureus strain (American Type Culture Collection ® , ATCC ® 29213, Manassas, VA, USA) was employed for both the tests because it is one of the main pathogens involved in PJIs.…”

“…The CFU was quantified in each sonication product by plating the pellet obtained after a centrifugation onto MHA. The number of planktonic bacteria (CFU/mL) was also determined [ 39 ]. All experiments, assayed in triplicate, were performed simultaneously for each scaffold type and repeated a minimum of three times.…”