Correlation between structure and compressive strength in a reticulated glass-reinforced hydroxyapatite foam

Glass-reinforced hydroxyapatite (HA) foams were produced using reticulated foam technology using a polyurethane template with two different pore size distributions. The mechanical properties were evaluated and the structure analyzed through density measurements, image analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the mechanical properties, the use of a glass significantly improved the ultimate compressive strength (UCS) as did the use of a second coating. All the samples tested showed the classic three regions characteristic of an elastic brittle foam. From the density measurements, after application of a correction to compensate for the closed porosity, the bulk and apparent density showed a 1 : 1 correlation. When relative bulk density was plotted against UCS, a non-linear relationship was found characteristic of an isotropic open celled material. It was found by image analysis that the pore size distribution did not change and there was no degradation of the macrostructure when replicating the ceramic from the initial polyurethane template during processing. However, the pore size distributions did shift to a lower size by about 0.5 mm due to the firing process. The ceramic foams were found to exhibit mechanical properties typical of isotropic open cellular foams.     

Biomimetic synthesis of the composites of hydroxyapatite and chitosan–phosphorylated chitosan polyelectrolyte complex

A polyelectrolyte complex (PEC) composed of chitosan (CS) and phosphorylated chitosan (PCS) was used to encapsulate a calcium phosphate by a biomimetic method. An acidic CS (polycation) solution containing calcium and phosphate ions (Ca²⁺: 6 mM, Ca/P = 1.67) was added into a PCS (polyanion) solution leading to the formation of a polyelectrolyte complex (PEC) with nanoscopic carbonate-containing, low-crystallinity hydroxyapatite (HA) distributed evenly in the fibrils of the PEC by controlled crystal growth. The resulting composite material, PEC–HA, has a complicated porous structure that is expected to have high biocompatibility and that may be of use as materials for bone replacement and a carrier for controlled-release therapeutic agents.     

超顺磁性羟基磷灰石/壳聚糖棒材的制备

以壳聚糖膜为模板将磁性羟基磷灰石前驱体的壳聚糖醋酸溶液与NaOH凝固液隔离,OH^-向磁性羟基磷灰石前驱体的壳聚糖醋酸溶液内部的渗透引起pH值变化,导致质子化的壳聚糖在模板上沉积的同时无机物就地生成,原位复合制备出无机纳米颗粒分散均匀的磁性羟基磷灰石／壳聚糖（HA／CS）复合棒材．生成的超顺磁性四氧化三铁和羟基磷灰石颗粒大小均一（大约长30nm,宽20nm）,在基质中分布均匀、没有出现明显的团聚现象．     

原位增强羟基磷灰石/壳聚糖复合棒材

利用低温水溶液均相沉积法制备了磷酸钙盐微纤维; 应用原位沉析法制备了壳聚糖(CS)三维棒材及羟基磷灰石(HA*)/CS复合棒材。XRD证实应用原位沉析法制备HA*/CS复合棒材过程中, 磷酸钙盐转化为羟基磷灰石结构, 尺寸为10~60 μm, 并用SEM对晶体形貌进行了表征, 分析了转化机制。HA*/CS复合材料的微观形貌表明, HA*晶体在CS凝胶棒原位沉析的过程中析出而与CS基体形成镶嵌、 相互咬合结构, 且在基体中分散均匀, 有效地提高了HA*与CS基体的界面连接作用, 使力学性能显著提高。所制备的HA*/CS棒材随HA*含量的增大(在其饱和溶解度3.3 wt%范围内), 复合材料的弯曲性能逐渐提高, 当羟基磷灰石质量分数为3.3%时, 复合材料的弯曲强度达到159.6 MPa, 弯曲模量达到5.1 GPa, 比CS基体分别提高85.6%和54.5%。HA*/CS复合棒材的弯曲强度和弯曲模量远高于松质骨, 弯曲强度也比密质骨高。      

Synthesis and characterization of laminated hydroxyapatite/chitosan nanocomposites

Natural composite materials such as bones and seashells have been refined and perfected over millions of years of evolutionary selection. Thus they possess many advantages both on micro-structures and macroscopical performances. Inspired by the natural composites, for the first time, laminated hydroxyapatite (HAp)/chitosan (CS) nanocomposites were prepared by means of solution intercalation in this paper. Intercalated and exfoliated structures were obtained by varying CS contents. Fourier transform infrared (FTIR) result reveals that there is interaction between HAp and CS. Tensile strength test indicates that the HAp lamellae can improve the poor strength of CS evidently, especially in moist environments. The results reported here can be expanded to other HAp-polymer systems, thus may offer a new approach for fabricating biomimetic nanocomposites.     

Improvement of compressive strength of porous hydroxyapatite scaffolds by adding polystyrene to camphene-based slurries

The compressive strength of porous hydroxyapatite (HA) scaffolds was enhanced by adding polystyrene (PS) polymer as a binder to hydroxyapatite (HA)/camphene slurries. As the PS content was increased from 0 to 20 vol.% in relation to the HA content, the compressive strength was significantly increased from 1.1 ± 0.2 to 2.3 ± 0.5 MPa, while the pore size was decreased from 277 ± 47 to 170 ± 29 µm. The improvement in the compressive strength was mainly attributed to both the suppression of the cracking of the green sample during freeze drying and the mitigation of the formation of micro-pores in the HA walls.     

空心羟基磷灰石亚微球/壳聚糖可注射水凝胶的制备及表征

采用W/O/W复乳法制备空心羟基磷灰石(HAP)亚微球,将空心HAP亚微球均匀分布在壳聚糖/甘油磷酸钠(CS/GP)体系中制备可注射HAP/CS水凝胶(gel 1),同时制备可注射CS水凝胶(gel 2).用X射线衍射仪、场发射透射电镜、红外光谱、扫描电镜对空心HAP亚微球和水凝胶进行了表征,并比较分析了两种溶胶的成胶...     

Effect of hydroxyapatite nanoparticles on ibuprofen release from carboxymethyl-hexanoyl chitosan/O-hexanoyl chitosan hydrogel

In order to explore the effect of nanofiller on the regulation of the drug release behavior from microsphere-embedded hydrogel prepared by carboxymethyl-hexanoyl chitosan (HNOCC) and O-hexanoyl chitosan (OHC), the release kinetics was investigated in terms of various amounts of calcium-deficient hydroxyapatite (CDHA) nanoparticles incorporated. HNOCC is a novel chitosan-based hydrophilic matrix with a burst release profile in a highly swollen state. The drug release kinetics of the HNOCC hydrogel can be regulated by incorporation of well-dispersed CDHA nanoparticles. It was found that the release duration of ibuprofen (IBU) from HNOCC was prolonged with increasing amounts of CDHA which acts as a crosslink agent and diffusion barrier. On the contrary, the release duration of the IBU from OHC (hydrophobic phase) was shortened through increasing the CDHA amount over 5%, which is due to the hydrophilic nature of the CDHA nanoparticles destroying the intermolecular hydrophobic interaction and accelerating OHC degradation. Thus, water accessibility and molecular relaxation were enhanced, resulting in a higher release rate. In addition, sustained and sequential release behavior was achieved by embedding the OHC microspheres (hydrophobic phase) into the HNOCC (hydrophilic phase) matrix, which could significantly prolong the release duration of the HNOCC drug-loaded implant.     

Electrospun chitosan/hydroxyapatite nanofibers for bone tissue engineering

Chitosan (CS) nanofibers were prepared by an electrospinning technique and then treated with simulated body fluid (SBF) to encourage hydroxyapatite (HA) formation on their surface. The CS/HA nanofibers were subjected to scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy, and X-ray diffraction (XRD) to confirm HA formation as well as determine the morphology of the nanofibrous scaffolds. The SEM image indicated that the distribution of HA on the CS nanofibers was homogeneous. The results from EDS and XRD indicated that HA was formed on the nanofibrous surfaces after 6-day incubation in the SBF. The calcium/phosphorus ratio of deposited HA was close to that of natural bone. To determine biocompatibility, the CS/HA scaffolds were applied to the culture of rat osteosarcoma cell lines (UMR-106). The cell densities on the CS/HA nanofibers were higher than those on the CS nanofibers, the CS/HA film, and the CS film, indicating that cell proliferation on CS/HA nanofibers was enhanced. Moreover, the early osteogenic differentiation on CS/HA was also more significant, due to the differences in chemical composition and the surface area of CS/HA nanofibers. The biocompatibility and the cell affinity were enhanced using the CS/HA nanofibers. This indicates that electrospun CS/HA scaffolds would be a potential material in bone tissue engineering.     

Mechanical response and multilevel structure of biomimetic hydroxyapatite/polygalacturonic/chitosan nanocomposites

Using an in situ mineralization process that is biomimetic we have synthesized new nanocomposites of chitosan/hydroxyapatite in 50–50 ratio(ChiHAP50), polygalacturonic acid/hydroxyapatite in 50–50 ratio (PgAHAP50) and Chitosan/hydroxyapatite/Polygalacturonic acid (ChiPgAHAP50). Polygalacturonic acid (PgA) is electrostatically complementary to chitosan, and thus is expected to provide stronger interfacial interactions and improve mechanical response. Atomic force imaging of fractured and polished surfaces suggests a multilevel organization in the hydroxyapatite/biopolymer nanocomposite. The AFM images of ChiPgAHAP50 nanocomposite display presence of chitosan rich and polygalacturonic rich domains. These chitosan rich and PgA rich domains are made of smaller globular shaped particles in which, hydroxyapatite nano-particles are embedded in the biopolymer matrix. The average size of the hydroxyapatite particles in PgAHAP50, ChiHAP50 and ChiPgAHAP50 were found to be 25, 42 and 34 nm respectively. The elastic moduli determined from nanoindentation of PgAHAP50, ChiHAP50 and ChiPgAHAP50 composites are 29.81, 17.56 and 23.62 GPa respectively. Hardness values of the three composites in the same order were found to be 1.56, 0.65 and 1.14 GPa respectively. Macro-mechanical tests showed significant enhancement in elastic moduli, strain to failure and compressive strength of ChiPgAHAP50 composites over ChiHAP50 and PgAHAP50.     

原位水化法制备羟基磷灰石/壳聚糖复合支架材料

以含Ca2+和PO34-的溶液为无机相,壳聚糖(chitosan,CS)溶液为高分子相,采用原位水化法制备羟基磷灰石(hydroxyapatite,HAP)/CS复合多孔支架材料。XRD和IR的表征和分析表明水化24h后,复合支架中的钙磷盐从磷酸氢钙(dicalciumphos phate dehydrate,DCPD)转化为HAP。SEM和EDS显示15μm左右的棒状HAP颗粒均匀地分散在多孔支架的孔壁上,压缩强度的测试结果表明这种结构显著提高复合支架的力学性能。     

Novel hydroxyapatite (HA) dual-scaffold with ultra-high porosity,high surface area,and compressive strength

A novel scaffold designed for tissue engineering applications, which we refer to as a “dual-scaffold” because its structure consists of two interlaced three-dimensional (3-D) hydroxyapatite (HA) networks, was fabricated using a combination of the rapid prototyping (RP) method and dip-coating process. To accomplish this, a graphite network acting as a template was prepared using the RP method and then uniformly dip-coated with HA slurry. The resultant sample was then heat-treated at 1250 °C for 3 h in air to remove the graphite network and consolidate the HA networks. An additional 3-D channel was formed by removing the graphite network, while preserving the pre-existing channel. The unique structure of the dual-scaffold endows it with unprecedented features, such as ultra-high porosity (>85%), a high surface area and high compressive strength, as well as a tightly controlled pore structure. In addition, an excellent cellular response was observed to the fabricated HA dual-scaffold.     

Preparation of multi-layered film of hydroxyapatite and chitosan

We present flexible nacre-like multi-layered films of chitosan and hydroxyapatite using manipulation of inherited polymeric phase separation in the solidification process. Films were characterized as homogeneous dispersity, high mechanical strength, and ordered microstructure in given optimized conditions of temperature and composite ratio. It resulted that the initial solidification temperature and the composition ratio are important factors in determination of homogeneity and mechanical strength of organic/inorganic composites. These films might be suitable for further osteological applications with surgical appliances, wound dressings, and space-filling implants.     

Synthesis and characterization of hydroxyapatite/chitosan nanocomposite materials for medical engineering applications

Incorporation of hydroxyapatite (HA) with organic polymer in favor of composites would be used in biomaterial engineering. According to prior researches, because of its chemical similarity to natural bone and dental, this product could improve bioactivity and bone bonding ability. In this research, nano-hydroxyapatite/chitosan composite material was prepared via in situ Hybridization route. The surface chemical characterization on the nanocomposite was evaluated by Fourier transformed infrared (FTIR) and X-ray diffraction (XRD). Surface topography, roughness and morphology of the samples were observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The characterization results confirmed homogeneity, interaction and integration between the HA and chitosan matrix. It was indicated that composite samples consist of homogeneous aggregations around 40–100 nm, in which many HA nanocrystals align along the chitosan molecules. HA grain gradually decreased in size when amount of chitosan increased from 0 to 6 g into 100 cc solution. It can be seen that by increasing chitosan, the aggregation of nanoparticles enhance and subsequently, improve the expected compatibility among HA filler and chitosan matrix. Furthermore, the mechanical compressive testing indicated that the synthesized composites have acceptable mechanical behavior for tissue substitution. The mechanistic of the biodegradable nanocomposite systems, their preparation and characterization for medical usage are strongly discussed.     

壳聚糖/羟基磷灰石引导组织再生膜材料的制备和性能

用生物矿化交替沉积法成功在CS基质膜表面构建HA涂层,并进行了表征.结果表明,HA含量随着沉积循环数增加而增加,且在4个循环后基本达到饱和,饱和含量为8.8%;随着沉积循环数增加HA由均一颗粒状转变为无规则平板状;拉伸强度由纯CS膜的68.6 MPa降低到沉积5个循环后的46.9 MPa.控制沉积数可调控HA的含量、形貌和力学强度,以满足引导组织再生术需要.     

Antibacterial hydroxyapatite/chitosan complex coatings with superior osteoblastic cell response

Chitosan was widely used as an antibacterial component. While most antibacterial materials also possess cytotoxicities, we hypothesize that selectively destruction of bacterial cells can be achieved by controlling the material parameters of chitosan, due to its intrinsic antibacterial mechanism. In this study, porous hydroxyapatite coatings prepared by the liquid precursor plasma spraying process were used for loading the chitosan with different concentrations: 10, 20, 50, and 100 g/L, respectively. The antibacterial properties and osteoblastic cell response of the hydroxyapatite/chitosan complex coatings were studied as a function of chitosan concentration. The results indicated that the antimicrobial activity was directly proportional to the chitosan concentration, while loading of chitosan with lower concentrations (10 and 20 g/L) was even beneficial to the proliferation of osteoblastic cells. Overall, our study demonstrated that combined antibacterial activity and superior osteoblast cell response can be achieved by using hydroxyapatite/chitosan complex coatings, which have great potential in bone replacement and regeneration applications.     

Through-thickness compressive strength of a carbon/epoxy composite laminate

As carbon-fiber-reinforced composite materials are increasingly used for heavy-duty self-lubricating bearings, their through-thickness compressive strength (TTCS) has become an important parameter because the TTCS depends on the weave type and stacking sequence of laminates regardless of their tribological properties.In this work, the TTCS of a carbon/epoxy composite bearing material was measured with respect to weave type, stacking sequence, and direction of cut from the laminate. The tests showed that, for unidirectional laminate, cylindrical specimens resulted in the most reliable data of TTCS. However, for woven fabric laminate, cubic specimens with the edge length greater than twice the repeating unit gave reliable results.     

Surface modification of nanophase hydroxyapatite with chitosan

Nanophase hydroxyapatite (HAp) particles were aged in 0–2.5 wt.% chitosan acetate solutions for 30 days to evaluate the influence of chitosan on HAp surface chemistry. The HAp characterization results from Fourier transform infra-red spectroscopy (FTIR), thermal gravimetric analysis (TGA), Carbon–Hydrogen–Nitrogen (CHN) analysis, and BET N₂ adsorption revealed measurable changes in the HAp surface chemistry after aging in the chitosan acetate solutions. The TGA mass loss exhibited by HAp increased from 3.3–6.5 mass% as the chitosan acetate gel concentration increased from 0–2.5 mass%. The CHN analysis revealed an increase in C and H contents with increasing chitosan acetate concentration while the N concentration remained relatively constant (0.30–0.32 mass%). Chitosan interactions with HAp caused an increase in specific surface area from 85 m²/g up to 160 m²/g for HAp aged in 1.5 mass% chitosan acetate solution (HAp[1.5]). Chitosan exhibits strong adsorption interactions with HAp and enhances colloid stability for processing of chitosan/hydroxyapatite nanocomposites.     

Modeling and testing strain rate-dependent compressive strength of carbon/epoxy composites

A technique for testing high modulus fiber-reinforced composites in compression at different strain rates is investigated. The rate-dependent compressive behavior of unidirectional AS4/3501-6 carbon/epoxy composite is characterized by using off-axis specimens. It is found that, in the compression test, a titanium coating applied at the contact ends of the off-axis specimen can greatly reduce contact frictions, allowing a fully developed extension–shear coupling so that a state of uniform stress in the specimen can be achieved. A rate-dependent nonlinear constitutive model and a dynamic compressive strength model (fiber microbuckling model) for the unidirectional AS4/3501-6 composite are established based on the low strain rate off-axis test data. Model predictions and experimental data including high strain rate data are in very good agreement indicating that the constitutive model and compressive strength model obtained with low strain rate data are valid for high strain rates as well. A technique is also developed to extract the longitudinal compressive strength of the composite from those of the off-axis specimens.     

Measurement of the static compressive strength of carbon-fibre/epoxy laminates

This paper describes an experimental study of the compressive failure of T800/924C carbon-fibre/efoxy composite laminates. Undirectional laminates loaded parallel to the fibres have compressive strengths that are 70% of the tensile strength and fail by fibre-microbuckling. During microbuckling the fibre debonds from the matrix, and the fibres break in bending. Multidirectional [(±45/0₂)₃]_sm laminates were also tested in compression, and the critical failure mechanism observed was microbuckling of the 0° plies. The failure strain was almost the same as for the undirectional laminate, The failure strain was almost the same as for the unidirectional laminate, which indicated that the ±45° plies have no significant influence on the failure strength of the 0° plies.