Aqueous Preparation of Highly Dispersed Hydroxyapatite Nanorods for Colloidal Liquid Crystals

Abstract

Hydroxyapatite (HA) nanorods were synthesized using a citrate-assisted hydrothermal method. NaH₂PO₄, Na₂HPO₄, and Na₃PO₄ were used as the phosphate sources and the influences of pH value were investigated. The XRD results show that pure hexagonal HA can be synthesized using Na₃PO₄·12H₂O as the phosphate source with the citrate solution pH ranging from 5.0 to 7.6. The zeta potential evaluation demonstrates that as-synthesized HA nanorods are colloidally stable and the aqueous dispersion can be maintained homogenous without any sediment or creaming for more than at least a month. The Ca/P molar ratio of the HA nanorods is about 1.60, indicating that the HA nanorods are calcium-deficient hydroxyapatite. Besides, owing to the excellent colloidal stability and rod-like morphology with a high aspect ratio (>6), the HA aqueous dispersion undergoes a phase transition from an isotropic state to a liquid crystalline state upon increasing the particle concentration to 17wt%. The completely liquid crystalline phase forms when the particle concentration reaches above 30wt%.

Keywords

hydroxyapatite / liquid crystal / colloidal stability

References

[1] Wang L, Nancollas GH. Calcium Orthophosphates: Crystallization and Dissolution[J]. Chemical Reviews, 2008, 108(11): 4 628-4 669.

[2] Qi C, Lin J, Fu LH, et al. Calcium-based Biomaterials for Diagnosis, Treatment, and Theranostics[J]. Chemical Society Reviews, 2018, 47(2): 357-403.

[3] Hu Y, Gu XY, Yang Y, et al. Facile Fabrication of Poly(L-Lactic Acid)-grafted Hydroxyapatite/Poly(lactic-co-glycolic acid) Scaffolds by Pickering High Internal Phase Emulsion Templates[J]. ACS Applied Materials & Interfaces, 2014, 6(19): 17 166-17 175.

[4] Teotia AK, Raina DB, Singh C, et al. Nano-Hydroxyapatite Bone Substitute Functionalized with Bone Active Molecules for Enhanced Cranial Bone Regeneration[J]. ACS Applied Materials & Interfaces, 2017, 9(8): 6 816-6 828.

[5] Fernando Shanika M, Silva de RM, Silva de KMN. Synthesis, Characterization, and Application of Nano Hydroxyapatite and Nanocomposite of Hydroxyapatite with Granular Activated Carbon for the Removal of Pb²⁺ from Aqueous Solutions[J]. Applied Surface Science, 2015, 351(1): 95-103.

[6] Googerdchian F, Moheb A, Emadi R, Asgari M. Optimization of Pb(II) Ions Adsorption on Nanohydroxyapatite Adsorbents by Applying Taguchi Method[J]. Journal of Hazardous Materials, 2018, 349(5): 186-194.

[7] Chen XH, Jin XY, Tan JJ, et al. Large-scale Synthesis of Water-soluble Luminescent Hydroxyapatite Nanorods for Security Printing[J]. Journal of Colloid and Interface Science, 2016, 468(15): 300-306.

[8] Victor SP, Devi MGG, Paul W, et al. Europium Doped Calcium Deficient Hydroxyapatite as Theranostic Nanoplatforms: Effect of Structure and Aspect Ratio[J]. ACS Biomaterials Science & Engineering, 2017, 3(12): 3 588-3 595.

[9] Sun YH, Li YQ, Xu JF, et al. Interconnectivity of Macroporous Molecularly Imprinted Polymers Fabricated by Hydroxyapatite-stabilized Pickering High Internal Phase Emulsions-hydrogels for the Selective Recognition of Protein[J]. Colloids and Surfaces B: Biointerfaces, 2017, 155(1): 142-149.

[10] Li P, Li LL, Zhao YB, et al. Selective Binding and Magnetic Separation of Histidine-tagged Proteins using Fe₃O₄/Cu-apatite Nanoparticles[J]. Journal of Inorganic Biochemistry, 2016, 156: 49-54.

[11] Das P, Jana NR. Length-controlled Synthesis of Calcium Phosphate Nanorod and Nanowire and Application in Intracellular Protein Delivery[J]. ACS Applied Materials & Interfaces, 2016, 8(13): 8 710-8 720.

[12] Heng CN, Zheng XY, Liu MY, et al. Fabrication of Luminescent Hydroxyapatite Nanorods through Surface-initiated RAFT Polymerization: Characterization, Biological Imaging and Drug Delivery Applications[J]. Applied Surface Science, 2016, 386(15): 269-275.

[13] Zheng X, Liu M, Hui J, et al. Ln³-doped Hydroxyapatite Nanocrystals: Controllable Synthesis and Cell Imaging[J]. Physical Chemistry Chemical Physics, 2015, 17: 20 301-20 307.

[14] Hu YY, Rawal A, Schmidt-Rohr K. Strongly Bound Citrate Stabilizes the Apatite Nanocrystals in Bone[C]. Proceedings of the National Academy of Sciences of the United States of America, 2010, 107(52): 22 425-22 429.

[15] Wu YJ, Tseng YH, Chan JCC. Morphology Control of Fluorapatite Crystallites by Citrate Ions[J]. Crystal Growth & Design, 2010, 10(10): 4 240-4 242.

[16] Delgado-López JM, Frison R, Cervellino A, et al. Crystal Size, Morphology, and Growth Mechanism in Bio-inspired Apatite Nanocrystals[J]. Advanced Functional Materials, 2014, 24(8): 1 090-1 099.

[17] Delgado-López JM, Bertolotti F, Lyngsø J, et al. The Synergic Role of Collagen and Citrate in Stabilizing Amorphous Calcium Phosphate Precursors with Platy Morphology[J]. Acta Biomaterialia, 2016, 49: 555-562.

[18] Sandhöfer B, Meckel M, Delgado-López JM, et al. Synthesis and Preliminary in vivo Evaluation of Well-dispersed Biomimetic Nanocrystalline Apatites Labeled with Positron Emission Tomographic Imaging Agents[J]. ACS Applied Materials & Interfaces, 2015, 7(19): 10 623-10 633.

[19] Delgado-López JM, Iafisco M, Rodríguez I, et al. Crystallization of Bioinspired Citrate-functionalized Nanoapatite with Tailored Carbonate Content[J]. Acta biomaterialia, 2012, 8(9): 3 491-3 499.

[20] Yang H, Hao L, Du C, et al. A Systematic Examination of the Morphology of Hydroxyapatite in the Presence of Citrate[J]. RSC Advances, 2013, 3(45): 23 184-23 189.

[21] Tsuji T, Onuma K, Yamamoto A, et al. Direct Transformation from Amorphous to Crystalline Calcium Phosphate Facilitated by Motif-programmed Artificial Proteins[C]. Proceedings of the National Academy of Sciences, 2008, 105(44): 16 866-16 870.

[22] Jin XY, Zhuang JZ, Zhang Z, et al. Hydrothermal Synthesis of Hydroxyapatite Nanorods in the Presence of Sodium Citrate and Its Aqueous Colloidal Stability Evaluation in Neutral pH[J]. Journal of Colloid and Interface Science, 2015, 443(1): 125-130.

[23] Santos C, Almeida MM, Costa ME. Morphological Evolution of Hydroxyapatite Particles in the Presence of Different Citrate:Calcium Ratios[J]. Crystal Growth & Design, 2015, 15(9): 4 417-4 426.

[24] Jin XY, Chen XH, Cheng YT, et al. Effects of Hydrothermal Temperature and Time on Hydrothermal Synthesis of Colloidal Hydroxyapatite Nanorods in the Presence of Sodium Citrate[J]. Journal of Colloid and Interface Science, 2015, 450(15): 151-158.

[25] Yang H, Wang YJ. Morphology Control of Hydroxyapatite Microcrystals: Synergistic Effects of Citrate and CTAB[J]. Materials Science and Engineering: C, 2016, 62(1): 160-165.

[26] Jiang D, Li D, Xie J, et al. Shape-controlled Synthesis of F-substituted Hydroxyapatite Microcrystals in The Presence of Na2EDTA and Citric Acid[J]. Journal of Colloid and Interface Science, 2010, 350(1): 30-38.

[27] Martínez-Casado FJ, Iafisco M, Delgado-López JM, et al. Bioinspired Citrate-apatite Nanocrystals Doped with Divalent Transition Metal Ions[J]. Crystal Growth & Design, 2016, 16(1): 145-153.

[28] Iannotti V, Adamiano A, Ausanio G, et al. Tampieri, Fe-doping-induced Magnetism in Nano-hydroxyapatites[J]. Inorganic Chemistry, 2017, 56(8): 4 446-4 458.

[29] Yuan XY, Zhu BS, Tong GS, et al. Wet-chemical Synthesis of Mgdoped Hydroxyapatite Nanoparticles by Step Reaction and Ion Exchange Processes[J]. Journal of Materials Chemistry B, 2013, 1(47): 6 551-6 559.

[30] Fujii S, Okada M, Furuzono T. Hydroxyapatite Nanoparticles as Stimulus-responsive Particulate Emulsifiers and Building Block for Porous Materials[J]. Journal of Colloid and Interface Science, 2007, 315(1): 287-296.

[31] Sadat-Shojai M, Khorasani MT, Dinpanah-Khoshdargi E, et al. Synthesis Methods for Nanosized Hydroxyapatite with Diverse Structures[J]. Acta biomaterialia, 2013, 9(8): 7 591-7 621.

[32] Lin KL, Wu CT, Chang J. Advances in Synthesis of Calcium Phosphate Crystals with Controlled Size and Shape[J]. Acta Biomaterialia, 2014, 10(10): 4 071-4 102.

[33] Onsager L. The Effects of Shape on the Interaction of Colloidal Particles[J]. Annals of the New York Academy of Sciences, 1949, 51(4): 627-659.

[34] Gabriel JCP, Davidson P. New Trends in Colloidal Liquid Crystals based on Mineral Moieties[J]. Advanced Materials, 2000, 12(1): 9-20.

[35] Davidson P, Gabriel JCP. Mineral Liquid Crystals[J]. Current Opinion in Colloid & Interface Science, 2005, 9(6): 377-383.

[36] Lekkerkerker HNW, Vroege GJ. Liquid Crystal Phase Transitions in Suspensions of Mineral Colloids: New Life from Old Roots[C]. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013, 371: 20120263-1-20.

[37] Nakayama M, Kajiyama S, Kumamoto A, et al. Stimuli-responsive Hydroxyapatite Liquid Crystal with Macroscopically Controllable Ordering and Magneto-optical Functions[J]. Nature Communications, 2018, 9(1): 568