Synthesis, Properties And Applications Of One-dimensional Hydroxyapatite Micro-/nano-materials

As the main inorganic component of bone and teeth of vertebrate,hydroxyapatite has good biocompatibility.The properties and applications of hydroxyapatite are influenced by many factors,such as chemical composition,morphology,size and crystallinity.So far,hydroxyapatite with different chemical composition,morphology,size and crystallinity has been successfully synthesized including zero dimensional hydroxyapatite nanoparticles;one-dimensional hydroxyapatite Nanorods/nanowires;two-dimensional hydroxyapatite nanosheets,etc.Among hydroxyapatite materials,one dimensional hydroxyapatite micro/nano materials with high aspect ratio have attracted more and more attention.One-dimensional hydroxyapatite with high aspect ratio has excellent mechanical properties,which is easier to form 3D network structure in three-dimensional space,thus exhibit unique properties in mechanical enhancement and constructing three-dimensional bulk materials.However,the synthesis of one-dimensional hydroxyapatite micro/nano materials with long aspect ratio,high crystallinity,good dispersion,high purity and uniform size distribution are still facing some challenges,which limits the application and development of one-dimensional hydroxyapatite micro/nano materials.In this paper,one-dimensional hydroxyapatite nano/micro materials including ultralong hydroxyapatite nanowires and ultralong hydroxyapatite microtubes with long aspect ratio,high crystallinity,good dispersion,high purity and uniform size distribution have been synthesized by using calcium oleate as the precursor through hydrothermal method.Their applications in the field of bioceramics,ultralight material and mechanical enhancement have been investigated.The specific research contents of this paper are as follows:1.The preparation and application of ultralong hydroxyapatite nanowiresWith calcium oleate as precursor,ultralong hydroxyapatite nanowires with high crystallinity,high purity and uniform size distribution have been synthesized through a hydrothermal method.For the first time,ultralong hydroxyapatite?HAP?nanowires with lengths of larger than 200?m are used to fabricate highly porous HAP ceramics using palmitic acid spheres as the pore former.The effects of the aspect ratio of HAP and the addition amount of palmitic acid spheres on the formation of HAP porous ceramics are investigated and compared with the commercial HAP nanoparticles.The ultralong HAP nanowires can cross-link with each other,leading to much stronger interaction between them than HAP nanoparticles.During the sintering process,although palmitic acid spheres are decomposed at high temperatures,ultralong HAP nanowires can be well preserved and still support the whole porous structure stably,leading to the formation of highly porous HAP ceramics with high biocompatibility.The porosity of the HAP nanowire porous ceramics fabricated can be easily tuned.The as-prepared HAP nanowire porous ceramics exhibit a good biocompatibility,a good performance for cell adhesion and spreading,and cell proliferation.Thus,the as-prepared HAP nanowire porous ceramics are promising for applications in biomedical fields.Ultralong hydroxyapatite nanowire slurry with good monodisperse properties have been synthesized by using calcium oleate as the precursor through a hydrothermal method.By using the ultralong hydroxyapatite nanowire slurry,we have developed a novel kind of hydroxyapatite?HAP?nanowire-based inorganic aerogel with outstanding elasticity,which is highly porous?porosity⁹9.7%?,ultralight?density 8.54 mg/cm³,about 0.854%of water density?,and highly adiabatic?thermal conductivity 0.0387 W/m·K?.Significantly,the as-prepared HAP nanowire aerogel can be used as the highly efficient air filter with excellent PM_2.5 filtration efficiency.In addition,the HAP nanowire aerogel is also an ideal candidate for continuous oil-water separation,which can be used as a smart switch to separate oil from water continuously.Compared with organic aerogels,the as-prepared HAP nanowire aerogel is biocompatible,environmentally friendly and low-cost.Moreover,the synthetic method reported in this work may be scaled up for large-scale production,and free from the use of toxic solvents.Therefore,the as-prepared new kind of HAP nanowire aerogel is promising for the applications in various fields.2.The preparation and application of ultralong hydroxyapatite microtubesMonodisperse single-crystalline ultralong hydroxyapatite?HAP?microtubes have been successfully synthesized using a reaction system containing CaCl₂,NaOH,?NaPO₃?₆,oleic acid,water and ethanol by the solvothermal method.The formation mechanism of HAP microtubes and the effects of solvothermal temperature,pH value,molar ratio of Ca/P,and volume ratio of solvents on the product have been investigated.Owing to the unique tubular structure,the as-prepared ultralong HAP microtubes exhibit high biocompatibility and superior properties in drug loading and sustained drug release.The as-prepared HAP microtubes are promising for applications in various biomedical fields such as drug/gene delivery and bone defect repair.A novel ultralong hydroxyapatite microtubes?HMTs?-chitosan?CHS?composite scaffold has been successfully prepared.The mechanical property of the HMTs-CHS composite scaffold is greatly improved compared with the CHS-hydroxyapatite nanorod scaffold and the pure chitosan scaffold.The hydroxyapatite microtubes?HMTs?-chitosan?CHS?composite scaffold has good biomineralization ability and cell adhesion ability.By using gentamicin sulfate?GS?as the model drug,GS-loaded HMTs-CHS composite scaffold has a high drug loading capacity,sustained drug release behavior and high antibacterial activity.The as-prepared HMTs-CHS composite scaffold has promising applications in various fields such as drug delivery and bone defect repair.By using biocompatible,monodisperse,single-crystalline hydroxyapatite?HAP?microtubes as the building blocks,ultralight,strong,highly porous hydroxyapatite?HAP?ceramics have been successfully fabricated through a facile freeze drying method and subsequent sintering at 1300 ^oC for 2 h.The as-prepared ultralight,strong,highly porous HAP microtube ceramics exhibit superior properties,such as ultrahigh porosity?89%to 96%?,low density?94.1 to 347.1 mg/cm³?,high compressive strength that can withstand more than 6400 times of its own weight without any fracture and is higher than aerogels with similar densities,and ultralow thermal conductivity?0.05 W/mK?.Owing to their high porosity,ultralight,good mechanical properties and high biocompatibility,the HAP microtube ceramics reported herein are promising for applications in various fields.Dopamine-modified highly porous hydroxyapatite microtube ceramics with efficient near-infrared photothermal effect,enhanced protein adsorption and mineralization performance have been prepared through a facile method.The dopamine-modified highly porous HAP ceramics exhibit ultrahigh porosity?90.6%?,uniform pore distribution,interconnected pore structure and outstanding mechanical properties.After being modified with dopamine,the protein adsorption amount,cell attachment performance,and mineralization ability of the dopamine-modified highly porous HAP ceramic can be greatly improved.In addition,the as-prepared dopamine-modified highly porous HAP ceramics exhibit good biocompatibility,excellent near-infrared photothermal effect,and good mechanical properties.The experimental results indicate that the dopamine-modified highly porous HAP ceramics are promising for various applications.