Growth Of Hydroxyapatite Nanocrystals Research Articles

Biomimetically Mineralized Alginate Nanocomposite Fibers for Bone Tissue Engineering: Mechanical Properties and in Vitro Cellular Interactions.

We report herein the structural and mechanical properties and in vitro cellular response of hydroxyapatite (HAp)/alginate nanocomposite fibrous scaffolds mimicking the mineralized collagen fibrils of bone tissue. The biomimetically "engineered" nanocomposites, fabricated by electrospinning and in situ synthesis strategy, were compared with pure alginate nanofibers and micrometer-level HAp/alginate composite fibers. The tensile strength and elastic modulus of the nanocomposites increased by 79.3 and 158.4%, respectively, compared to those of alginate. The uniform nucleation and HAp nanocrystal growth on the alginate nanofibers resulted in such enhancement of the mechanical properties via a stress-transfer effect. Rat calvarial osteoblasts were stably attached and stretched more extensively on the nanocomposites' surface than on the pristine alginate. The controlled deposition of the HAp nanophase contributed to a much faster cell proliferation rate on the nanocomposites than on the others. The improved structural stability and osteoblast interactions suggest the fibrous nanocomposite scaffold's potential advantages for bone tissue regeneration.

Nucleation and growth of hydroxyapatite nanocrystals by hydrothermal method

Hydroxyapatite (HA) was synthesized by using a hydrothermal method with Ca(NO3)2·4H2O and H3PO4. We use x-ray diffraction and field-emission scanning electron microscopy to investigate how pH, reaction temperature, hydrothermal-reaction time, and calcium-ion concentration affects the microstructure and the growth of HA crystals. In addition, we discuss the growth mechanism. The results show that the crystals grow more completely and that the aspect ratio tends to increase with increasing hydrothermal-reaction time, reaction temperature, and calcium-ion concentration. The pH of the system strongly impacts the growth of HA crystals. With increasing pH, the HA crystal grain size and aspect ratio decrease significantly. By using 1 mol/L calcium-ion concentration, pH = 10, and a hydrothermal reaction at 200 °C for 8 h, we obtain high crystallinity and crystal clear of the growth polarity with hexagonal 60–100-nm-long columnar HA, 30–40 nm in diameter. The mechanisms producing this growth may be the effect of growth conditions on ion concentration, thereby changing the HA crystal growth rate along the different crystal axes.

Revealing the nanostructure of calcium phosphate coatings using HRTEM/FIB techniques

Herein, we report on the micro- and nanostructure of the calcium phosphate coating produced by pulsed laser deposition (PLD), using focused ion beam (FIB) lamella sample preparation and transmission electron microscopy (TEM) as the characterization technique. The initial selected area electron diffraction (SAED) data demonstrated the presence of hydroxyapatite (HA) over any other possible calcium phosphate crystalline structure and the polycrystalline nature of the coating. Moreover, the SAED analyses showed clear textured ring patterns coherent with the presence of a preferred orientation in the HA nano-crystal growth. The SAED data also indicated that the coating appears to be textured in the 〈002〉 crystalline direction. Dark-field images obtained using 002 as the working reflection showed a clear oriented crystal growth in columns, from bottom to top. These columns have a peculiar arrangement of nano-crystals since, in some cases, the preferred orientation appears to start at a certain distance from the substrate. Direct d-spacing measurements on high-resolution TEM images provided further proof of the presence of an HA nano-crystal structure. The reported data may be of interest in the future to adjust the microstructure of the HA coatings.

Highly dispersed nanoscale hydroxyapatite on cellulose nanofibers for bone regeneration

A successful method for fabrication of electrospun hydroxyapatite (HAp) coated cellulose nanofiber scaffold (HAp/CMC) for tissue engineering is reported. The cellulose acetate nanofibers (CANFs) were deacetylated to produce cellulose nanofibers (CNFs) which were subsequently converted to sodium carboxy methyl cellulose (Na-CMC). The Na-CMC nanofibers mat was then coated with HAp for bone regeneration applications. The FTIR results confirmed conversion of CANFs to CNFs and CNFs to Na-CMC. HAp nanocrystal growth was observed in SEM images, with crystal becoming minute and numerous upon increasing HCO3- in the simulated body fluid (SBF) solution. The proliferation of osteoblastic MC3T3-E1cells on HAp-coated CMC nanofiber mat was observed to increase with seeding time. The results confirm suitability of the HAp/CMC nanofiber mat for bone regeneration.

On the use of nanoliposomes as soft templates for controlled nucleation and growth of hydroxyapatite nanocrystals under hydrothermal conditions

Calcium phosphates are biocompatible materials with the composition closest in similarity to the mineral phase of bone. Among them, hydroxyapatite (HA) is shown to be the most promising bioactive compound widely used in bone tissue engineering applications. It has been shown that the preparation of HA with controlled morphology and size distribution may be beneficial to therapy of bone disease. In this study, a new method was developed for the synthesis of nano-HA particles in which nanoliposomes were used as nucleation sites for growth of HA crystals. Phase composition, morphology, particle size and the molecular structure of sediments were studied using X-ray diffraction techniques (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that nanoliposomes could act as carriers for the crystal growth of nano-HA particles. The powder produced from liposome encapsulation contained hexagonal bipyramidal structures of HA with nanometer dimensions, spherical shapes, dense morphologies and a mean size of about 60nm. Further investigation of the bioactivity and biocompatibility of this new class of biomaterials is being performed.

Gelatin stabilized iron oxide nanoparticles as a three dimensional template for the hydroxyapatite crystal nucleation and growth

Inspired by the structural similarity of gelatin (and collagen) linked to a mineral phase based on Ca-phosphates compounds with natural bone and increasing application of magnetic iron oxides in hyperthermia, gelatin coated iron oxide (GIO) was synthesized and hydroxyapatite (HAp) crystal nucleation and growth in the nanoparticles was explored. A series of GIO/HAp nanocomposites with various amount of GIO were synthesized by co-precipitation technique using calcium hydroxide and phosphoric acid as precursor. Various physico-chemical analysis showed that the HAp crystal nucleation and growth occurred at acidic group of gelatin, while magnetic iron oxide nanoparticles (< 8nm) were bound to the amide groups of the gelatin chain. Moreover, the growth of HAp nanocrystals in aq. GIO solution was highly influenced by the GIO contents in the solution. The mineralized composite with magnetic properties could have great scope in biomedical field as a thermoseed to kill the cancerous cell in bone side by side for the bone reinforcement.

Growth of hydroxyapatite nanocrystals on polymer particle surface

In the present paper, we describe the preparation of hybrid particles consisting of polymeric core with deposited hydroxyapatite (HAp) nanocrystals. Polystyrene submicron particles modified by β-diketone groups have been used as templates for the growth of HAp. Hybrid particles with HAp nanocrystal content between 7 and 50 wt% have been prepared. Microscopy studies indicate that hybrid particles exhibit “raspberry” morphology, and HAp nanoparticles are not homogeneously distributed on the polymer particle surface. The increase in the HAp content on the polymer particle surface reduces the colloidal stability of the hybrid particles because of the vanishing of the surface charge.

Bioinspired Growth of Hydroxyapatite Nanocrystals on PLGA- (PEG- ASP)n Scaffolds Modified with Oligopeptide Derived from BMP-2

Natural bone is a typical example of an “organic matrix-mediated” biomineralization process which constituted of hydroxyapatite(HA) nanocrystals orderly grown in intimate contact with collagen fibers. Bone morphogenetic protein 2 (BMP2) is the most powerful osteogenic factor. But it is extremely difficult to be manufactured in large scale. In previous study, we have designed a novel oligopeptide (P24) derived from BMP2 knuckle epitope and it contained abundant Asp(aspartic acid) and phosphorylated Ser(serine) which may be helpful for self-assambly biomineralization and osteogenesis. Previous In vivo experiments have shown that this novel oligopeptide had excellent osteoinductive and ectopic bone formation property which was similar to that of BMP2. In this study, PLGA-(PEG-ASP)n scaffolds were modified with P24 and a new biomimetic bone tissue engineering scaffold material with enhanced bioactivity was synthesized by a biologically inspired mineralization approach. Peptide P24 was introduced into PLGA-(PEG-ASP)n scaffolds using cross-linkers. Then the P24 modified scaffolds and the simple PLGA-(PEG-ASP)n scaffolds were incubated in modified simulated body fluid (mSBF) for 10 days. Growth of HA nanocrystals on the materials was confirmed by observation SEM and measurements EDS and XRD. SEM analysis demonstrated the well growth of bonelike HA nanocrystals on P24 modified PLGA-(PEG-ASP)n scaffolds than that of the control scaffolds. The main component of mineral of the P24 modified scaffolds was hydroxyapatite containing low crystalline nanocrystals, and the Ca/P ratio was nearly 1.60, similar to that of natural bone, while that of the control scaffolds was 1.52. The introduction of peptide P24 into PLGA- (PEG- ASP)n copolymer provides abundant active sites to mediate the nucleation and self- ssembling of HA nanocrystals in mSBF. the resulted peptide P24 modified- HA/PLGA- (PEG- ASP)n composite shows some features of natural bone both in main composition and and hierarchical microstructure. This biomimetic treatment provides a simple method for surface functionalization and subsequent biomineralization on biodegradable polymer scaffolds for tissue engineering.

Ceramic modification of N-acylated chitosan stabilized gold nanoparticles

Hydroxyapatite (HAp) [Ca10(PO4)6(OH)2] nanocrystals of controlled geometry were chemically fabricated using N-acylated chitosan stabilized gold nanoparticles (Nac-6-Au) as a matrix and characterized by various physico-chemical techniques. Results showed that the Nac-6-Au played a key role in inducing and directing the growth of HAp nanocrystals.