Nanocrystalline hydroxyapatite prepared under various pH conditions

A plant-mediated synthesis of nanostructured hydroxyapatite for biomedical applications: a review

The engineering of calcium-based phosphate materials at the nanoscale gains several unique properties compared to the bulky state. The effort to scale down, e.g., from bulky state to nanoscale in order to control the morphology and improve structural properties requires the use of varying reagents that can be detrimental to the environment. A typical example of these materials is hydroxyapatite (HAp), one of the well-known calcium phosphate materials, which has a close resemblance to human bone tissue. HAp has valuable applications in catalysis, drug delivery, bone and dental implant formation, and adsorption. Hydroxyapatite-based nanomaterials synthesized through conventional routes make use of reagents that are not environmental friendly and are very costly. Since the current research trends are geared towards producing/synthesizing nanomaterials through an eco-friendly approach, there is the need to consider the techniques and reagents involved in the synthesis of HAp. This review touches on the possible replacement of such synthetic chemical reagents, synthesis routes, and toxic capping agents with plant extracts for synthesizing HAp-based nanomaterials for multi-functional applications. The influence of biomolecules from plants on synthesized HAps and the attainable mechanism during these green approaches are discussed. Viable future modifications of the methods used to obtain extracts from plants are also studied.

Effects of polyethylene glycol content on the properties of a silk fibroin/nano-hydroxyapatite/polyethylene glycol electrospun scaffold

To study the effects of polyethylene glycol (PEG) content on the mechanical properties and degradation of silk fibroin, nano-hydroxyapatite, and PEG (SF/nHAP/PEG) electrospun scaffolds, and according to the PEG ratio in the scaffold (SF : nHAP : PEG), test groups were divided as follows: PEG-0 (10 : 2), PEG-0.5 (10 : 2 : 0.5), PEG-1 (10 : 2 : 1), and PEG-2 (10 : 2 : 2). A series of tests to determine the mechanical properties, degradation rates, and osteogenic characteristics was undertaken. PEG facilitated SF degradation (PEG-1 > PEG-0.5 > PEG-0 > PEG-2), and the mass loss of the scaffolds in PEG-1 was more than 30%, while in PEG-2 it was less than 20% after 8 days (P < 0.05). The addition of PEG strengthened the mechanical properties of the scaffold (PEG-1 > PEG-2 > PEG-0.5 > PEG-0), as the Young's modulus increased from 41.72 ± 3.40 MPa for PEG-0 to 76.12 ± 3.73 MPa for PEG-1 (P < 0.05). PEG was favorable for the osteogenic differentiation of BMSCs (PEG-0.5 > PEG-1 > PEG-2 > PEG-0). The enhancements were attributable to the increased hydrophilicity and nHAP dispersion, as well as to the secondary structure transformation of SF. The PEG content was deemed to be optimal when the SF/nHAP/PEG ratio was equal to 10 : 2 : 1.

Structural features of hydroxyapatite and carbonated apatite formed under the influence of ultrasound and microwave radiation and their effect on the bioactivity of the nanomaterials

The samples of hydroxyapatite and carbonate substituted hydroxyapatite (CHA) were obtained under the influence of physical factors, namely ultrasound (US) and microwave (MW) radiations. The results of Fourier transform infrared spectroscopy and X-ray diffraction analysis have proved the formation of the calcium deficient hydroxyapatite and B-type CHA with the Ca/P ratio in the ranges 1.62-1.87. In vitro studies have showed the increased bioactivity of the samples, synthesized under the influence of physical factors as compared to the standard ones. The samples of both groups, synthesized under the influence of 600 W MW, have shown the greatest stability in biological environment. In vivo tests confirm that obtained under US and MW radiations hydroxyapatite-based biomaterials are biocompatible, non-toxic and exhibit osteoconductive properties. The usage of US and MW radiations can significantly shorten the time (up to 5-20 min) of obtaining of calcium deficient hydroxyapatite and B-type CHA in nanopowder form, close in structure and composition to the biological hydroxyapatite.

Poly(ethylene oxide)-based block copolymers with very high molecular weights for biomimetic calcium phosphate mineralization

Ampholytic and betaine-type block copolymers are excellent growth modifiers for calcium phosphate in biologically inspired calcium phosphate mineralization.

Microwave irradiation of nanohydroxyapatite from chicken eggshells and duck eggshells

Due to similarity in composition to the mineral component of bones and human hard tissues, hydroxyapatite with chemical formula Ca₁₀(PO₄)₆(OH)₂ has been widely used in medical field. Both chicken and duck eggshells are mainly composed of calcium carbonate. An attempt has been made to fabricate nanohydroxyapatite (nHA) by chicken (CES) and duck eggshells (DES) as calcium carbonate source (CaCO₃). CES and DES were reacted with diammonium hydrogen [(NH₄)₂HPO₄] solution and subjected to microwave heating at 15 mins. Under the effect of microwave irradiation, nHA was produced directly in the solution and involved in crystallographic transformation. Sample characterization was done using by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).