Biomimetic inorganic-organic hybrid nanoparticles from magnesium-substituted amorphous calcium phosphate clusters and polyacrylic acid molecules

Amorphous calcium phosphate (ACP) has been widely found during bone and tooth biomineralization, but the meta-stability and labile nature limit further biomedical applications. The present study found that the chelation of polyacrylic acid (PAA) molecules with Ca²⁺ ions in Mg-ACP clusters (~2.1 ± 0.5 nm) using a biomineralization strategy produced inorganic-organic Mg-ACP/PAA hybrid nanoparticles with better thermal stability. Mg-ACP/PAA hybrid nanoparticles (~24.0 ± 4.8 nm) were pH-responsive and could be efficiently digested under weak acidic conditions (pH 5.0–5.5). The internalization of assembled Mg-ACP/PAA nanoparticles by MC3T3-E1 cells occurred through endocytosis, indicated by laser scanning confocal microscopy and cryo-soft X-ray tomography. Our results showed that cellular lipid membranes remained intact without pore formation after Mg-ACP/PAA particle penetration. The assembled Mg-ACP/PAA particles could be digested in cell lysosomes within 24 h under weak acidic conditions, thereby indicating the potential to efficiently deliver encapsulated functional molecules. Both the in vitro and in vivo results preliminarily demonstrated good biosafety of the inorganic-organic Mg-ACP/PAA hybrid nanoparticles, which may have potential for biomedical applications.

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Mg-ACP/PAA hybrid nanoparticles have been synthesized following a biomineralization strategy.

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The chelation of PAA molecules in synergy with Mg²⁺ substitution improves thermal stability of Mg-ACP/PAA nanoparticles.

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The Mg-ACP/PAA nanoparticles are pH sensitive and can be digested in cell lysosomes within 24 h.

Chlorogenic acid- loaded calcium phosphate chitosan nanogel as biofilm degradative materials

This work describes an effort to develop an antimicrobial agent (chlorogenic acid - CGA) loaded porous nanogel based on calcium phosphate-chitosan (CaPNP@Chi) nanogel with biofilm degradative properties and has potential applications in restorative dentistry. The nanogel was prepared by ionic gelation of calcium phosphate nanoparticles and chitosan in the ratio of 1.25: 1. Chlorogenic acid was loaded to the nanoparticles as an ethanolic solution and the encapsulation efficiency determined by chromatographic techniques. The particle size and morphology of CaPNP@Chi and CaPNP@Chi@CGA was determined by dynamic light scattering and scanning electron microscopic techniques. The minimum inhibitory concentration against S. aureus and K. pneumoniae was determined through the well diffusion method. The biofilm formation and biofilm decay were studied through staining assays. The toxicity, if any of the nanogel was assessed by MTT assay against HaCaT cells. All data were statistically analyzed. The composite had a CGA encapsulation efficiency of 70% and was thermally stable up to 124 °C. The zone of inhibition was found to be 18.7 mm ± 0.6 against S. aureus. CaPNP@Chi@CGA showed a 68% increase in biofilm degradation when compared with the untreated group. Results obtained in this study suggest that the positively charged nanogel interacted with the bacterial cell membrane and brought about the disruption of the cell membrane. Also, CaPNP@Chi@CGA was observed to be nontoxic up to 40 μg/mL to HaCaT cells. These results support the potential of CaPNP@Chi@CGA nanogel for biofilm degradation and its application as filling material in restorative dentistry.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based (CaXs) biomaterials including calcium phosphates, calcium carbonates, calcium silicate and calcium fluoride have been widely utilized in the biomedical field owing to their excellent biocompatibility and biodegradability. In recent years, CaXs biomaterials have been strategically integrated with imaging contrast agents and therapeutic agents for various molecular imaging modalities including fluorescence imaging, magnetic resonance imaging, ultrasound imaging or multimodal imaging, as well as for various therapeutic approaches including chemotherapy, gene therapy, hyperthermia therapy, photodynamic therapy, radiation therapy, or combination therapy, even imaging-guided therapy. Compared with other inorganic biomaterials such as silica-, carbon-, and gold-based biomaterials, CaXs biomaterials can dissolve into nontoxic ions and participate in the normal metabolism of organisms. Thus, they offer safer clinical solutions for disease theranostics. This review focuses on the state-of-the-art progress in CaXs biomaterials, which covers from their categories, characteristics and preparation methods to their bioapplications including diagnosis, treatment, and theranostics. Moreover, the current trends and key problems as well as the future prospects and challenges of CaXs biomaterials are also discussed at the end.