When Nothing Turns Itself Inside out and Becomes Something: Coating Poly(Lactic-Co-Glycolic Acid) Spheres with Hydroxyapatite Nanoparticles vs. the Other Way Around

Abstract

To stabilize drugs physisorbed on the surface of hydroxyapatite (HAp) nanoparticles and prevent burst release, these nanoparticles are commonly coated with polymers. Bioactive HAp, however, becomes shielded from the surface of such core/shell entities, which partially defeats the purpose of using it. The goal of this study was to assess the biological and pharmacokinetic effects of inverting this classical core/shell structure by coating poly(lactic-co-glycolic acid) (PLGA) spheres with HAp nanoparticles. The HAp shell did not hinder the release of vancomycin; rather, it increased the release rate to a minor degree, compared to that from undecorated PLGA spheres. The decoration of PLGA spheres with HAp induced lesser mineral deposition and lesser upregulation of osteogenic markers compared to those induced by the composite particles where HAp nanoparticles were embedded inside the PLGA spheres. This was explained by homeostatic mechanisms governing the cell metabolism, which ensure than the sensation of a product of this metabolism in the cell interior or exterior is met with the reduction in the metabolic activity. The antagonistic relationship between proliferation and bone production was demonstrated by the higher proliferation rate of cells challenged with HAp-coated PLGA spheres than of those treated with PLGA-coated HAp. It is concluded that the overwhelmingly positive response of tissues to HAp-coated biomaterials for bone replacement is unlikely to be due to the direct induction of new bone growth in osteoblasts adhering to the HAp coating. Rather, these positive effects are consequential to more elementary aspects of cell attachment, mechanotransduction, and growth at the site of contact between the HAp-coated material and the tissue.

Antitumoral-Embedded Biopolymeric Spheres for Implantable Devices

“…Compliant with the IR data, these results confirmed the successful incorporation of HA nanoparticles withing PLGA spheres, as no secondary structures were noticed at this level. Similar results have been reported for HA/PLGA (~250 nm) and PLGA/HA (3-8 µm) spheres synthesized by the modified Pickering emulsion [88], while PLGA/HA microparticles (~250 µm) have been successfully obtained by the airflow shearing method [89]. The PLGA/HA-MTX spheres were uniformly distributed on the surface of titanium substrate, adapting to the intrinsic topography of the metallic substrate, and resulting in continuous and homogenous coatings (Figure 3b), as evidenced at structural (Figure 3c) and compositional (Figure 3d) levels.…”

“…These findings were attributed to the constituent components employed for coating fabrication, both widely used for bone tissue engineering strategies due to their biocompatibility, biodegradability, and osteogenic ability [ 92 , 93 , 94 ], and lined up to previous studies regarding the excellent biocompatibility of such composites. While preserving their drug-releasing ability to promote and support local pharmacological effects, nano-HA-modified PLGA particles exhibited osteoconductive and osteoinductive effects with respect to mesenchymal stem cells and preosteoblasts, being validated as osteogenic candidates for bone repair and regeneration [ 81 , 88 , 89 ]. Similar cellular effects have been reported for nano-HA/PLGA composite coatings proposed for improving the osseointegration of metallic implants while modulating local inflammation and infection [ 84 , 95 ].…”

Biocompatible Germanium-Doped Hydroxyapatite Nanoparticles for Promoting Osteogenic Differentiation and Antimicrobial Activity

“…Despite the sparse solubility of HAp, its ability to sustain high lattice strains and defect concentrations translates to a pronounced propensity for ion exchange. This capacity for foreign ion accommodation has led to over 60 years of application of HAp in chromatographic columns and for environmental remediation . More recently, HAp started to be doped with foreign ions in the effort to impart new properties to it .…”

Teaching Chess History to Students in Natural Sciences: How to Do It and Why

“…These changes need not be as profound and substantial as those introduced by the frameworks of, say, theory of relativity or quantum mechanics, notwithstanding that the seminal findings of these two theories illustrate well what is meant by the conceptual innovation in science. Conceptual novelties, in fact, can be more modest and take the form of, for example, reversal of the cores and shells of typical composite nanoparticle compositions used in tissue engineering and drug delivery 4 , or the reversal of the mainstream idea of controlling the differentiation of stem cells into various phenotypes by focusing instead on the conversion of differentiated primary cells to a pluripotent phenotype 5 . Conceiving of a nanoparticle modeled after an astral body 6,7 ; creating models for predicting cell fate based on the indigenous arts of African storytelling 8 and Micronesian canoe voyaging 9 ; proposing alternative biological models for assessment of material properties 10,11 and models for assessing the journey of a nanoparticle through the body 12 also count among such modest conceptual innovations in the materials science world.…”