Synthesis of Graphene-Hydroxyapatite Nanocomposites for Potential Use in Bone Tissue Engineering

Summary

Novel nanocomposites of graphene nanoribbons and hydroxyapatite nanoparticles were prepared using solution-phase synthesis. These hybrids when employed in bioactive scaffolds can exhibit potential applications in tissue engineering and bone regeneration.

Abstract

Developing novel materials for bone tissue engineering is one of the most important thrust areas of nanomedicine. Several nanocomposites have been fabricated with hydroxyapatite to facilitate cell adherence, proliferation, and osteogenesis. In this study, hybrid nanocomposites were successfully developed using graphene nanoribbons (GNRs) and nanoparticles of hydroxyapatite (nHAPs), that when employed in bioactive scaffolds may potentially improve bone tissue regeneration. These nanostructures can be biocompatible. Here, two approaches were used for preparing the novel materials. In one approach, a co-functionalization strategy was used where nHAP was synthesized and conjugated to GNRs simultaneously, resulting in nanohybrids of nHAP on GNR surfaces (denoted as nHAP/GNR). High-resolution transmission electron microscopy (HRTEM) confirmed that the nHAP/GNR composite is comprised of slender, thin structures of GNRs (maximum length of 1.8 µm) with discrete patches (150-250 nm) of needle-like nHAP (40-50 nm in length). In the other approach, commercially available nHAP was conjugated with GNRs forming GNR-coated nHAP (denoted as GNR/nHAP) (i.e., with an opposite orientation relative to the nHAP/GNR nanohybrid). The nanohybrid formed using the latter method exhibited nHAP nanospheres with a diameter ranging from 50 nm to 70 nm covered with a network of GNRs on the surface. Energy dispersive spectra, elemental mapping, and Fourier transform infrared (FTIR) spectra confirmed the successful integration of nHAP and GNRs in both nanohybrids. Thermogravimetric analysis (TGA) indicated that the loss at elevated heating temperatures due to the presence of GNRs was 0.5% and 0.98% for GNR/nHAP and nHAP/GNR, respectively. The nHAP-GNR nanohybrids with opposite orientations represent significant materials for use in bioactive scaffolds to potentially promote cellular functions for improving bone tissue engineering applications.

Introduction

Graphene has sheet-like two-dimensional structures composed of sp-hybridized carbon. Several other allotropes can be attributed to the extended honeycomb network of graphene (e.g., the stacking of graphene sheets forms 3D graphite while rolling off the same material results in the formation of 1D nanotubes¹). Likewise, 0D fullerenes are formed due to wrapping². Graphene has attractive physicochemical and optoelectronic properties that include an ambipolar field-effect and a quantum Hall effect at room temperature^3,4. Detection of single-molecule adsorption events....

Protocol

1. Synthesis of nHAP by precipitation

1. Synthesize the pristine nHAP using 50 mL of the reaction mixture containing 1 M Ca(NO₃)₂∙4H₂O and 0.67 M (NH₄)H₂PO₄ followed by the dropwise addition of NH₄OH (25%) to maintain a pH around 10¹⁸.
2. Thereafter, agitate the reaction mixture by ultrasound irradiation (UI) for 30 min (500 W power and 20 kHz ultrasound frequency).
3. Allow the resulting solution to mature for 120 h at room temperature until the white precipitate of nHAP settles out. Recover the nHAP by centrifugation at 1....

Results

HRTEM analysis
Individually, GNRs were slender bamboo-like structures with some bends at some distance as observed in Figure 2. The longest GNR was 1.841 µm while the smallest bent GNR was 497 nm. The nanoribbons often showed a visible variation in width that might be attributed to twisting to form helical configurations in many places. Such unidirectional alignment of GNRs may help to obtain attractive features such as magnetic properties, conductivity, or heat transpor.......

Discussion

Although various metals, polymers, ceramics, and their combinations have been researched as orthopedic implants and fixation accessories, HAP is considered to be one of the most preferable materials due to its chemical similarity to the bone itself and consequent high cytocompatibility^20,21,22. In this study, the orientation of HAP was varied, which can have a significant impact on its unique properties, such as promotion of ost.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ammonium phosphate monobasic	Sigma-Aldrich	216003-100G	Synthesis
Calcium nitrate tetrahydrate	Sigma-Aldrich	237124	Synthesis
Centrifuge	Hettich	EBA 200S	Recovery
Fourier transform infrared spectrometer	Brucker	Vertex 70	Characterization
Graphene nanoribbon	Sigma-Aldrich	922714	Synthesis
High resolution transmission electron microscope	Thermo Fisher Scientific	Themis Titan 300	Characterization
Magnetic stirrer	IKA	C-MAG HS7 S68	Functionalization
Micropipettes	TreffLab	06H35687	Reagent preparation
pH meter	Eutech pH5+	ECPH503PLUSK	Reagent preparation
Thermogravimetric analyzer	TA Instruments	SDT Q600	Characterization
Ultrasonic bath	Bandelin	DT100	Functionalization
Universal Oven	Memmert	UF55	Functionalization
Weighing balance	Precisa	XB220A	Reagent preparation
X-ray diffractometer	Brucker	D8-Advanced	Characterization