Hydroxyapatite Fibers Research Articles

Mechanically-reinforced electrospun composite silk fibroin nanofibers containing hydroxyapatite nanoparticles

Electrospun silk fibroin (SF) scaffolds provide large surface area, high porosity, and interconnection for cell adhesion and proliferation and they may replace collagen for many tissue engineering applications. Despite such advantages, electrospun SF scaffolds are still limited as bone tissue replacement due to their low mechanical strengths. While enhancement of mechanical strengths by incorporating inorganic ceramics into polymers has been demonstrated, electrospinning of a mixture of SF and inorganic ceramics such as hydroxyapatite is challenging and less studied due to the aggregation of ceramic particles within SF. In this study, we aimed to enhance the mechanical properties of electrospun SF scaffolds by uniformly dispersing hydroxyapatite (HAp) nanoparticles within SF nanofibers. HAp nanoaprticles were modified by γ-glycidoxypropyltrimethoxysilane (GPTMS) for uniform dispersion and enhanced interfacial bonding between HAp and SF fibers. Optimal conditions for electrospinning of SF and GPTMS-modified HAp nanoparticles were identified to achieve beadless nanofibers without any aggregation of HAp nanoparticles. The MTT and SEM analysis of the osteoblasts-cultured scaffolds confirmed the biocompatibility of the composite scaffolds. The mechanical properties of the composite scaffolds were analyzed by tensile tests for the scaffolds with varying contents of HAp within SF fibers. The mechanical testing showed the peak strengths at the HAp content of 20wt.%. The increase of HAp content up to 20wt.% increased the mechanical properties of the composite scaffolds, while further increase above 20wt.% disrupted the polymer chain networks within SF nanofibers and weakened the mechanical strengths.

Controlled growth of hydroxyapatite fibers precipitated by propionamide through hydrothermal synthesis

Hydroxyapatite fiber (fHA) was hydrothermally synthesized using propionamide (PA) as a pH adjusting agent. The concentrations of PA and calcium ion (Ca), as well as synthetic temperature and time, were regulated and investigated in detail to explore the formation mechanism of fHA. The results demonstrated that the morphology of fHA was susceptible to the concentrations of PA and Ca, while the composition and crystallinity were not. The morphology of fHA changed from long fibers to flowers and thorn-like bundles with increasing concentrations of PA and Ca, respectively. Higher temperature was shown to contribute to the generation of highly crystalline fHA. By further combining the theories of oriented attachment and Ostwald ripening with spiral growth mechanism, it was proposed that dicalcium phosphate (DCPA) sheets were first formed via the self-assembly of nanoplatelets derived from nucleation. The sheets were then converted into the final fHA through spiral growth.

Study on Hydroxyapatite Fibers with Strontium Reinforced Calcium Phosphate Cement

The solidification time of injectable bone cement should be fit for the clinical application. This research find out the effect of the amount of water-absorbent agent and water-retaining agent. The optimal ratio was be determined. The hydroxyapatite fibers with strontium were added into the CPC. The mechanical property, cytotoxicity test, SEM morphology, XRD and degradation performance in vitro were characterized, respectively. The results show the CPC had the solidification time of 12min when the ratio as below: β-TCP 55.5%, Ca (H2PO4)2H2O(MCPM)36%, MgHPO43H2O 5%, MgSO41%, Sodium pyrophosphate2.5%. The main components of solidify CPC were hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD). The materials had a good Anti-collapsing performance and the degradation rate up to 16.72% after 9 weeks. The mechanical property of composite materials which combined with hydroxyapatite fibers with strontium has been improved, and the cell proliferation rate is also higher than common CPC. This study shows a potentially effective method to improve the mechanical property and the biological activity of calcium phosphate cement.

RGD-bearing peptide-amphiphile-hydroxyapatite nanocomposite bone scaffold: an in vitro study

In this study, a fibrous nanocomposite scaffold was developed by combining hydroxyapatite (HA) fibers produced by electrospinning method and arginine–glycine–aspartic acid (RGD)-bearing peptide-amphiphile (PA) gel (PA-RGD) produced by self-assembly and gelation induced by calcium ions. Scanning electron microscope, transmission electron microscope and atomic force microscopy imaging confirmed the successful production of inorganic and organic components of this nanocomposite material. Within the HA, the presence of a CaCO3 phase, improving biodegradation, was shown by x-ray diffraction analysis. The in vitro effectiveness of the PA-RGD/HA scaffold was determined on MC3T3-E1 preosteoblast cultures in comparison with HA matrix and PA-RGD gel. The highest cellular proliferation was obtained on PA-RGD gel, however, alkaline phosphatase activity results denoted that osteogenic differentiation of the cells is more favorable on HA containing matrices with respect to PA-RGD itself. Microscopic observations revealed that all three matrices support cell attachment and proliferation. Moreover, cells form bridges between the HA and PA-RGD components of the nanocomposite scaffold, indicating the integrity of the biphasic components. According to the real time-polymerase chain reaction (RT-PCR) analyses, MC3T3-E1 cells expressed significantly higher osteocalcin on all matrices. Bone sialoprotein (BSP) expression level is ten-fold higher on PA-RGD/HA nanocomposite scaffolds than that of HA and PA-RGD scaffolds and the elevated expression of BSP on PA-RGD/HA nanocomposite scaffolds suggested higher mineralized matrix on this novel scaffold. Based on the results obtained in this study, the combination of HA nanofibers and PA-RGD gel takes advantage of good structural integrity during the cell culture, besides the osteoinductive and osteoconductive properties of the nanofibrous scaffold.

Kinetics and Thermodynamics of Cd(II) Sorption onto Sodium Alginate/Poly(Vinyl Alcohol)/Hydroxyapatite Composite Fiber

In this paper, the sodium alginate (SA)/poly (vinylalcohol)(PVA)/hydroxyapatite (HAp) fiber was prepared via solution spinning. The adsorption properties of SA/PVA/HAp composite fiber were studied,and the adsorption kinetics and isotherms were investigated. The experimental results showed that the adsorption process was fast, in which half-equilibrium and equilibrium was obtained in 5 and 30 minutes, respectively. The pseudo-second-order kinetic model provided a better correlation of the experimental results. Both of Langmuir isotherm and Freundlich isotherm could describe the adsorption behavior of SA/PVA/HAp composite fiber towards cadmium. The positive H° value and increased absolute value of the G° with temperature indicate that high temperature is good to the adsorption process.

Combination of simvastatin and hydroxyapatite fiber induces bone augmentation

This study evaluated the capability of hydroxyapatite fiber (HAF) as a carrier and the bone formation by blending simvastatin. The mixture of HAF and simvastatin (0.15, 0.45, 0.75 mg) was placed in 1 ml of tris-buffer and the release of simvastatin from HAF was calculated per 24 hours for 10 days. Bilateral 5 mm-diameter and 3 mm-hight Teflon chambers were fixed on calvaria of adult Japanese white rabbits and filled with 40 mg HAF which containing simvastatin (0, 0.15, 0.45, 0.75 mg). The animals were sacrificed at 4 and 8 weeks and calculated radiologically by Micro-CT. After dyeing by toluidine blue the samples were analyzed histologically. In all of the study groups approximately 25% of simvastatin was released until 10 days. The new bone volume ratio measured by Micro-CT of 4 and 8 weeks group was (22.4%, 21.3%, 41.6%, 26.3%) and (20.2%, 11.7%, 42.1%, 31.2%) in different doses respectively. The 0.45 mg group showed significantly higher new bone volume ratio than 0 mg group and 0.15 mg group. The histological measurement and observations also supported these results. In conclusion, the HAF could be used as a carrier for simvastatin. Combinations of HAF and simvastatin have the potentiality to stimulate new bone formation and approximately 0.45 mg simvastatin in 40 mg HAF is the optimal dose in rabbit chamber model.

Hydrothermal Synthesis of Hydroxyapatite Fibers Precipitated by Propionmide

Fibrous hydroxyapatite (HA) powder was successfully synthesized through hydrothermal method. Cal- cium nitrate tetrahydrate and diammonium hydrogen phosphate were added as precursors and propionamide (PA) as precipitant was used to control the degree of supersaturation of the reaction solution. XRD, FTIR, SEM and TEM were used to characterize the product. The synthesized HA powder was found to possess high crystallinity and regular morphology, as well as good dispersion. The effects of starting pH value and the concentration of precursors on the morphology, constitution, crystallinity and the growth characteristics of HA were investigated. The results show that the starting pH and concentration significantly affect the morphology at different extents, but not on the constitution and crystallinity. In fact, low starting pH controls orientation of fibrous HA while low concentration widens HA fibers.

Tailor-Made Fibrous Hydroxyapatite/Polydimethylsiloxane Composites: Insight into the Kinetics of Polymerization in the Presence of Filler and Structure–Property Relationship

A scrupulously manipulated rate acceleration of anionic ring-opening polymerization of octamethylcyclotetrasiloxane (D4), a precursor for polydimethylsiloxane (PDMS) was designed and executed using hydroxyapatite (HA) fiber surface coated with polyethyleneglycol (PEG) as the rate accelerator. Kinetics of polymerization was investigated through programmed FTIR analysis. In this paper, the beneficial role of HA as a polymerization rate promoter was investigated and hence established. In addition, PEG molecules on the filler surface acted as the activator in the polymerization reaction. Hence, a synergism of these two independent effects resulted in a momentous increase in the rate of polymerization. The rate of reaction was found to increase from 6.35 × 10–2 to 10.32 × 10–2 s–1 in the presence of 4 wt % of HA filler. A morphology–property relationship was established for these tailor-made composites to explore the diverse fields of application of these advanced materials. Although the in situ prepared sampl...

Synthesis and Preliminary Evaluation of a Polyolefin-based Core for Carrier-based Root Canal Obturation

IntroductionCarrier-based gutta-percha is an effective method of root canal obturation creating a 3-dimensional filling; however, retrieval of the plastic carrier is relatively difficult, particularly with smaller sizes. The purpose of this study was to develop composite carriers consisting of polyethylene (PE), hydroxyapatite (HA), and strontium oxide (SrO) for carrier-based root canal obturation. MethodsComposite fibers of HA, PE, and SrO were fabricated in the shape of a carrier for delivering gutta-percha (GP) using a melt-extrusion process. The fibers were characterized using infrared spectroscopy and the thermal properties determined using differential scanning calorimetry. The elastic modulus and tensile strength tests were determined using a universal testing machine. The radiographic appearance was established using digital periapical radiographs. ResultsThe composite core carrier exhibited a melting point of 111°C to 112°C, which would facilitate removal by heat application. The elastic modulus and the tensile strength were found to be lower than those of Thermafil carriers (Dentsply Tulsa Dental, Tulsa, OK). The preliminary radiographic evaluation showed that the novel composite core carrier is sufficiently radiopaque and can be distinguished from gutta-percha. ConclusionsThe PE-HA-SrO composites were successfully melt processed into composite core carriers for delivering gutta-percha into the root canal space.

Fretting behaviors of hot-pressed electrospun hydroxyapatite/poly(dl-lactide) fibrous composites as potential orthopedic implants

In situ grown composite fibers of hydroxyapatite (HA) and poly(dl-lactide) with uniaxial distribution were deposited layer-by-layer followed by hot pressing to obtain fibrous composites. The tribological profiles were clarified at low amplitude oscillatory motion as potential orthopedic implants. The inoculation of HA nanoparticles into fibrous composites lowered the coefficients of friction (COFs) and wear rates, and the hardness of HA layers and rolling effect of HA particles further improved the wear resistance. The COFs and wear rates were significantly lower when fretting along the fiber orientation than those when the slide direction was perpendicular to the fiber alignment.

Biomimetic synthesis of hierarchical crystalline hydroxyapatite fibers in large-scale

Crystalline hierarchical hydroxyapatite [Ca10(PO4)6(OH)2, HAp)] fibers were successfully synthesized via a biomimetic route by using cotton cloth as a natural bio-template. The effects of pH value, aging time, ultrasonic cleaning time, and calcination temperature on the purity and morphology of the resulting hydroxyapatite (HAp) were monitored by scanning election microscope (SEM), X-ray diffraction (XRD), and infrared spectrophotometer (IR) to obtain an optimized reaction condition, namely, pH 9, ultrasonic cleaning for 1min, aging for 24h, and calcination at 600°C for 4h. We found that the natural cellulose could not only control the morphology of HAp but also lower its phase transformation temperature. The impact of this method lies in its low cost and successful production of large-scale patterning of three-dimensional hierarchical HAp fibers.

Preparation and Characterization of Fibrous Hydroxyapatite/Chitosan Nanocomposites with High Hydroxyapatite Dosage

In this paper the hydroxyapatite fibers reinforced chitosan nanocomposites with high hydroxyapatite dosage (70~90 wt%) were synthesized by in-situ hybridization. The semi-permeable membrane was used to control the process of hybridization and morphology of hydroxyapatite. The compositional and morphological properties of nanocomposites were investigated by FTIR spectroscopy, X-ray diffraction, and transmission electron microscopy. The results showed that the hydroxyapatite were carbonated nanometer crystalline fibers with high aspect ratio (about 25) and dispersed uniformly in the nanocomposites. The high-resolution image indicated that the growth of nano-hydroxyapatite crystallites in the chitosan matrix preferred in the c-axis. The mechanical properties of these nanocomposites were enhanced dramatically and the compressive strength increases almost to 170MPa when the hydroxyapatite content is 70 wt%. The in vitro tests indicated that the composites have high bioactivity and degradation. These properties illustrated the potential application of this kind of nanocomposites for bone tissue engineering.

Preparation and Characterization of Fibrous Hydroxyapatite/Chitosan Nanocomposites with High Hydroxyapatite Dosage

In this paper the hydroxyapatite fibers reinforced chitosan nanocomposites with high hydroxyapatite dosage (70~90 wt%) were synthesized by in-situ hybridization. The semi-permeable membrane was used to control the process of hybridization and morphology of hydroxyapatite. The compositional and morphological properties of nanocomposites were investigated by FTIR spectroscopy, X-ray diffraction, and transmission electron microscopy. The results showed that the hydroxyapatite were carbonated nanometer crystalline fibers with high aspect ratio (about 25) and dispersed uniformly in the nanocomposites. The high-resolution image indicated that the growth of nano-hydroxyapatite crystallites in the chitosan matrix preferred in the c-axis. The mechanical properties of these nanocomposites were enhanced dramatically and the compressive strength increases almost to 170MPa when the hydroxyapatite content is 70 wt%. The in vitro tests indicated that the composites have high bioactivity and degradation. These properties illustrated the potential application of this kind of nanocomposites for bone tissue engineering.

Mechanism of High Fracture Strength of Bone

Scanning electron microscope (SEM) observation showed that femur bone is a kind of bioceramic composite consisting of hydroxyapatite layers and protein matters. The hydroxyapatite layers are further composed of hydroxyapatite fiber sheets. The observation also showed that the hydroxyapatite fiber sheets possess very thin fiber shape. The thickness of the hydroxyapatite fiber sheets is within nanometer scale. The mechanism of the high fracture strength of the bone was investigated based on the microstructural characteristics of the hydroxyapatite fiber sheets and the theory of fracture mechanics. The result reveals that the thin fiber shape of the hydroxyapatite fiber sheets endows the bone with high fracture strength.

Reinforcing of Porous Hydroxyapatite Ceramics with Hydroxyapatite Fibres for Enhanced Bone Tissue Engineering

Porous hydroxyapatite (HA) ceramic implants have attracted attention in bone tissue engineering due to their excellent bioactivity and biocompatibility due to their chemical similarity with the mineral component of natural bone. Unfortunately, HA when is formed into porous structures exhibits very low compression strength. In this study, fabrication of porous HA ceramic scaffolds containing HA fibers is presented. The primary aim of the study is to improve mechanical properties of the scaffold by introducing the fiber with uniform component relative to the scaffold. Scanning electron microscopy was used to observe the surface morphology and pore size of the scaffold. X-ray diffraction (XRD) was used to detect the phase composition and crystallinity of the scaffold. The compressive strength was determined using a universal material test machine. The results and the characterizations demonstrate the addition of HA fiber could enhance the uniformity of mechanical properties among samples and also the strength for a given open porosity.

Carboxymethyl Chitosan Nonwoven Scaffold for Bone Regeneration

Natural bone is a composite mainly made from nano/micro-structure of hydroxyapatite and collagen fibers. For bone regeneration by tissue engineering, it is important to synthesize three dimension nano-composites with good biocompatibility, high bioactivity and great bonding property as potentially useful scaffold. In this study, we fabricated chitosan nano-nonwoven scaffold via electrospinning and modified chitosan scaffolds by carboxymethylation (CM) to improve the osteoconductive characteristics. Results of FTIR confirmed the existence of carboxymethyl groups of CMChitosan. Moreover by employed mice osteoblast (MC3T3-E1) cell for adhesion, proliferation and differentiation assays, we found that CMChitosan appeared to have effect on the late stages of osteoblast behavior (calcium deposit).

Sub-10-micrometer toughening and crack tip toughness of dental enamel

In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R -curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip’s toughness ( K I0 , K III0 ), the crack’s closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K I0 of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K I0,Ir = 0.5 – 1.6 MPa m 0.5 (based on Irwin’s ‘near-field’ solution) and K I0,cz = 0.8 – 1.5 MPa m 0.5 (based on the cohesive zone solution of the Dugdale–Muskhelishvili (DM) crack model). The mode III crack tip toughness K III0,Ir was computed as 0.02 – 0.15 MPa m 0.5 . The crack-closure stress at the crack tip was computed as 163–770 MPa with a cohesive zone length and width 1.6 – 10.1 μ m and 24–44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified.

Fibrous growth of strontium substituted hydroxyapatite and its drug release

The effect of strontium on the crystallization of helical ribbon of hydroxyapatite (HAp) was investigated by single diffusion technique in silica gel matrix at 27°C and physiological pH. Fibers of HAp were obtained on addition of strontium. The length of the HAp fibers, were found to decrease as the strontium substitution increases. The presence of strontium ion increased the crystallinity as well as crystallite size of HAp. The strontium substituted HAp (Sr-HAp) has similar stoichiometry to that of biological apatite. Sr-HAp was found to have increased surface area (35%) compared to control. Further, strontium substitution leads to an enhancement of in vitro bioactivity. The cumulative in-vitro amoxicillin drug release in phosphate buffer solution (PBS, pH 7.2) showed a prolonged release profile for Sr-HAp.

Vancomycin release from poly( d, l-lactic acid) spray-coated hydroxyapatite fibers

The influence of the poly( d, l-lactic acid) (PDLLA) coating thickness on the in vitro vancomycin release from a hydroxyapatite (HA) carrier was studied. Microporous HA fibers with a porosity of 51 v% and an average pore diameter of 1.0 μm were fabricated by a diffusion-induced phase separation technique. They were loaded with 38 mg vancomycin hydrochloride (VH)/g HA, and their cylindrical shape enabled the application of the spray coating technique for the deposition of uniform PDLLA coating thicknesses, varying from 6.5 μm to 28 μm. The resulting in vitro VH release varied from a complete release within 14 days for 6.5 μm coatings to a release of 23% after 28 days for 28 μm coatings. It was clear that the VH release rate from a HA fiber can be adjusted by varying the PDLLA coating thickness. Microbiological tests of these fibers against a methicillin-resistant Staphylococcus aureus (MRSA) isolate pointed to the importance of the initial burst release and confirmed that the released antibiotics had the potential to interfere with S. aureus biofilm formation.

Topographical analyses of proliferation and differentiation of osteoblasts in micro‐ and macropores of apatite‐fiber scaffold

A variety of calcium phosphates have been used for bone tissue-engineering applications. We developed porous hydroxyapatite (HAp) ceramics by firing green compacts consisting of spherical carbon beads and HAp fiber. The apatite-fiber scaffold (AFS) forms a three-dimensional network of fibers with two different pore sizes (micro- and macropores). In this study, we investigated cell distribution and fine cell structure in AFS by confocal laser scanning microscopy. Osteoblastic cells were permeated homogenously throughout the scaffold under static culture conditions and grew three-dimensionally in macropores of AFS. Cells penetrated into micropores when they were capable of cell-cell formations. Cell proliferation and differentiation were also evaluated by biochemical and molecular biological approaches. The expression levels of early-phase osteogenic genes in AFS increased immediately, and those of middle-phase genes were maintained during the 2-week study period. Furthermore, the expression of late-phase markers increased gradually during the incubation period. These data indicate that macropores provide sufficient space for cell growth and proliferation and that micropores facilitate cell differentiation via cell-cell networks. This study provides evidence for the effectiveness of three-dimensional culture systems comprising AFS, which mimics the microenvironment of bone cells.