The in situ synthesis of biphasic calcium phosphate scaffolds with controllable compositions, structures, and adjustable properties

In this study, biphasic calcium phosphate (BCP) porous scaffolds with controllable phase compositions, controllable macropore percentages, and thus adjustable properties were in situ prepared by sintering a series of composites consisted of calcium phosphate cement (CPC) and porous resin negative mold made from rapid prototyping (RP) technique. The CPC pastes were formed by mixing a powder mixture of tetracalcium phosphate and anhydrous dicalcium phosphate with liquid phase of diluted phosphate acid solution. Results show that the phase composition was easily adjustable by controlling both weight ratio of the powder mixture to the liquid phase (P/L) and concentration of the liquid phase. The macropore structure of the BCP scaffold can be regulated by using different RP negative molds. Through in vitro compressive strength (CS) and immersion tests, it was demonstrated that both macropore percentage and phase composition played important roles in the CS and also the dissolving rates of the scaffolds. As the macropore percentage of the scaffold increased, its CS decreased but the dissolving rate increased; also, as the weight ratio of hydroxyapatite to tricalcium (HA/TCP) in the scaffold increased, the CS first increased and then decreased but the dissolving rate uniformly decreased. The CS values of the BCP scaffolds with a HA/TCP weight ratio of 59:41 were 5.84 +/- 1.16 MPa for a total porosity of approximately 67.67% containing a macropore percentage of 30%, and 3.34 +/- 0.79 MPa for a total porosity of approximately 70.90% containing a macropore percentage of 50%, respectively, comparable to the corresponding levels of human cancellous bone (2-12 MPa).     

Impaction grafting with morsellised allograft and tricalcium phosphate-hydroxyapatite: incorporation within ovine metaphyseal bone defects

An ovine model was used to investigate the in vivo properties of impacted tricalcium phosphate-hydroxyapatite (TCP-HA) aggregates, varying in chemical composition (ratio of TCP to HA) and particle size distribution (8 versus 3 particle size ranges). All pellets were impacted to a standard compactive effort. Eight sheep underwent implantation of pellets in 4 metaphyseal defects in both rear limbs. Treatment groups consisted of: (1) allograft (clinical control). (2) 50/50 allograft/80% HA/20% TCP in 8 particle size ranges, (3) 50/50 allograft/80% TCP/20% HA in 8 sizes and (4) 50/50 allograft/80% HA/20% TCP in only 3 sizes of particles. Healing of defects was evaluated at 14 weeks with computed tomography, histology and histomorphometry. The computer tomography (CT) density measured in all defects containing synthetic agents was higher than in defects filled with allograft alone (p<0.01). Defects containing 8 sizes of 80% HA/ 20% TCP granules (group 2) achieved lower histological scores and contained less bone than the clinical control (p<0.05), whereas groups 3 and 4 did not differ from the control. Although all synthetic agents were osteoconductive, our results suggest that increasing the ratio of TCP over HA and limiting the number of particle size ranges to 3 instead of 8 improve the performance of impacted aggregates as graft expanders. Evaluation under loading conditions of morsellised allograft expanded with 80% TCP/20% HA (BoneSave) in 3 particle size ranges is warranted.     

A comparative study of biphasic calcium phosphate ceramics for human mesenchymal stem-cell-induced bone formation

For the repair of bone defects, a tissue engineering approach would be to combine cells capable of osteogenic (i.e. bone-forming) activity with an appropriate scaffolding material to stimulate bone regeneration and repair. Human mesenchymal stem cells (hMSCs), when combined with hydroxyapatite/beta-tricalcium phosphate (HA/TCP) ceramic scaffolds of the composition 60% HA/40% TCP (in weight %), have been shown to induce bone formation in large, long bone defects. However, full repair or function of the long bone could be limited due to the poor remodeling of the HA/TCP material. We conducted a study designed to determine the optimum ratio of HA to TCP that promoted hMSC induced bone formation yet be fully degradable. In a mouse ectopic model, by altering the composition of HA/TCP to 20% HA/80% TCP, hMSC bone induction occurred at the fastest rate in vivo over the other formulations of the more stable 100% HA, HA/TCP (76/24, 63/37, 56/44), and the fully degradable, 100% TCP. In vitro studies also demonstrated that 20/80 HA/TCP stimulated the osteogenic differentiation of hMSCs as determined by the expression of osteocalcin.     

Beta-tricalcium phosphate plugs for press-fit fixation in ACL reconstruction--a mechanical analysis in bovine bone

BACKGROUND: The goal of this study was to test fixation properties of microporous pure beta-tricalcium phosphate (TCP) plugs (porosity 40%) for press-fit fixation of the ACL graft using patellar tendons with and without bone blocks. We set out to establish whether it is possible, in this way, to obtain results comparable with those of interference screw fixation of bone-tendon-bone (BTB) grafts in terms of cyclic loading and load-to-failure. METHODS: In a bovine model 30 ACL grafts were fixed in tibial drill holes, divided into three groups: 10 BTB grafts fixed with TCP press-fit plugs (7x25 mm), 10 pure patellar tendon grafts with TCP press-fit plugs (7x25 mm), and 10 BTB grafts with metal interference screws (7x25 mm). All grafts were tested by cyclic loading (50-200 N) and loaded until failure in a tensiometer. RESULTS: Under cyclic loading one interference screw fixation failed. None of the TCP plug fixations failed. After 1500 cycles the displacement of the graft in the drill hole for BTB fixed with screws was 3.6+/-7.8 mm, for BTB/TCP plugs 1.6+/-3.4 mm, and for the pure tendon/TCP grafts 1.4+/-0.4 mm. Regarding cyclic loading the pure tendon/TCP system was significantly superior to BTB (p=0.007). The load-to-failure for the BTB/interference screw group was 908+/-539 N with a stiffness of 94+/-36 N/mm, 936+/-245 N for the BTB/TCP cylinder group with a stiffness of 98+/-12 N/mm, and 673+/-159 N for the pure tendon/TCP group with a stiffness of 117+/-9 N/mm. In terms of pull-out load the BTB/TCP system was significantly better than the pure tendon/TCP group (p=0.011). However, pure tendon/TCP grafts achieved significantly greater stiffness (p=0.002) than the BTB system. CONCLUSION: Press-fit fixation with microporous pure beta-TCP plugs of BTB grafts or patellar tendon grafts without bone blocks for ACL reconstruction leads to primary stability comparable with that achieved by fixation with metal interference screws in case of BTB grafts.     

Phase conversion of tricalcium phosphate into Ca-deficient apatite during sintering of hydroxyapatite-tricalcium phosphate biphasic ceramics

In this study, we report a new observation on the phase conversion that occurs during the sintering of hydroxyapatite (HA)-tricalcium phosphate (TCP) biphasic ceramics. During the sintering of the HA-TCP mixture powders, a large amount of TCP was converted into HA, as detected by X-ray diffraction. The amount of TCP transformed into HA was approximately 10-90% of that initially added. From the electron probe microscopy analysis, the HA transformed from TCP was found to be Ca-deficient with Ca/P ratios of 1.62-1.64. The dissolution behavior and osteoblastic responses in a series of HA-TCP biphasic ceramics (10-90% TCP) were assessed. The solubility of the HA-TCP biphasic ceramics was intermediate between that of the HA and TCP pure ceramics. However, in the case of the HA-90% TCP biphasic ceramic, the solubility was even higher than that of pure TCP. The cell proliferation and alkaline phosphatase activity of the cells on the biphasic ceramics were lower than those on pure HA, but higher than those on pure TCP. However, particularly in the HA-50% TCP biphasic composition, the cellular responses were significantly higher than those on pure HA. It is considered that the Ca-deficient apatite newly formed from the TCP may affect in some way the solubility and biological properties of the HA-TCP biphasic ceramics.     

Effect of TiO2-Ag2O additives on the formation of calcium phosphate based functionally graded bioceramics

The combined effect of titanium dioxide and silver oxide on the in situ formation of biphasic calcium phosphate ceramics was investigated. Titania (5-20 mol%) was mixed with pure hydroxyapatite (HA) or HA containing Ag2O (10-20 mol%) and was heated to 900 degrees C for 12 h. The sintered samples were found to contain tricalcium phosphate (beta-TCP) and other phases along with HA depending upon the amount as well as the type of the additives used as evidenced by X-ray powder diffraction (XRD) and fourier transform infrared (FT-IR) spectroscopic studies. Enhanced TCP formation with reduced impurity phases was observed with TiO2-Ag2O addition. In vitro solubility study in phosphate buffer at physiological conditions shows the resorbable nature of these materials. A functionally graded material (FGM) structure was formed by spreading TiO2-Ag2O mixture on the surface of the HA green compact and heating at 900 degrees C. The FGM shows gradient structure of TCP and HA from the surface to the interior of the pellet in addition to titania and silver phases.     

Diametral tensile strength and compressive strength of a calcium phosphate cement: effect of applied pressure

The diametral tensile strength (DTS) and compressive strength (CS) of a calcium phosphate cement comprised of tetracalcium phosphate and dicalcium phosphate anhydrous were studied. Cement powder and water were mixed at a powder/liquid ratio of 4.0. The resulting cement pastes were placed in molds and a pressure ranging from 0-2.8 MPa was applied for various lengths of time (0.5-24 h). DTS and CS measurements were conducted on 24-h wet samples. The strength was found to be significantly (p<0.05) affected by the pressure but not by the time. Samples prepared under a pressure of 0.7 MPa had a mean DTS value of 10.8+/-1.0 MPa (n = 5), which is comparable to the values reported in the literature for the same cement prepared under similar conditions. In contrast, the mean CS value obtained in the present study, 66.1+/-5.0 MPa (n = 5), was significantly higher than the value (51+/-4.5 MPa) previously reported. The higher CS may be attributed to an improved mold design that may reduce sample damage during demolding, and to the use of a loading device that applied a constant pressure to the sample during setting. The average standard deviation of the mean for the 19 DTS sample groups (n = 5 in each group) was 1.1 MPa, corresponding to 9.6% of the mean DTS value. The average standard deviation of the 7 CS sample groups (n = 5 in each group) was 4.5 MPa, corresponding to 7.1% of the mean CS value. Published 2000 John Wiley & Sons, Inc.     

Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: a 2-4-year follow-up study in rabbits

Biodegradation of hydroxyapatite (HA)/poly(L-lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u-HA) or calcined HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM) 2-4 years later. For u-HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u-HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross-sectional area after 4 years decreased by 23.3+/-8.4%. The mean ratio of bony ingrowth to the initial cross-sectional area around the shrunken rods was 6.7+/-1.3 %. The viscosity molecular weight of PLLA reduced from 2 x 10(5) to less than 1 x 10(3). Thus, most of the PLLA had released from the rods. The c-HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found.     

Suggested predictive indices for high altitude pulmonary oedema

A study was conducted to evaluate the responses of chemoreceptors and pulmonary vascular bed to hypoxia, on two groups of soldiers exposed to similar altitudes, one group which did not suffer from high altitude (HA) maladies (Gp A) and the other when exposed to similar altitudes suffered from HA maladies (Gp B high altitude pulmonary edema--susceptible group (HAPE-S). Aim of this study was to find out whether these two tests could be used as a screening test for soldiers and sojourners proceeding to HA. Chemoreceptor responses were evaluated by hypoxic ventilatory response (HVR) test and the pulmonary vascular responses were studied by recording pulmonary artery pressure (PAP) changes under simulated hypoxia by breathing hypoxic gas mixtures (HGM) in both the groups. It was observed that HAPE-S subjects showed a reduced HVR response and an increase in PAP (systolic, diastolic, and mean). While Gp A subjects showed an increase in ventilation of 11.39 +/- 3.36 L, the same in Gp B subjects was 3.51 +/- 2.65 L. Thus, the comparison of increase in ventilation following HVR test between the two groups was highly significant. Under hypoxic gas mixture (HGM) breathing, systolic pressure of 28.2 +/- 6.9 and 52.6 +/- 11.0 mm Hg; diastolic pressure of 11.4 +/- 3.8 and 23.6 +/- 5.8 mm Hg and mean pressure of 17.6 +/- 4.3 and 35.0 +/- 7.4 mm Hg were recorded in pulmonary arteries in Gp A and Gp B subjects, respectively. Gp B subjects showed a highly significant increase in all the three pulmonary pressures under HGM breathing.     

Contribution of hydroxyapatite to the tensile strength of the isobutyl-2-cyanoacrylate-bone bond

The bonding strength between bone and alpha-2-cyanoacrylate polymers, with or without the addition of powdered hydroxyapatite, was determined. The tensile strength of a bone-cyanoacrylate bond was measured for each polymer: 4.31 +/- 0.88 MPa (methyl-), 5.74 +/- 0.62 MPa (ethyl-), and 8.33 +/- 0.41 MPa (isobutyl-). The tensile strength of the isobutyl-2-cyanoacrylate bond increased to 12.03 +/- 0.72 MPa with the addition of 10% (w/v) hydroxyapatite before decreasing to 7.89 +/- 0.58 MPa on addition of 15% (w/v) hydroxyapatite. An optimal concentration of hydroxyapatite significantly increased the tensile strength of a bone-cyanocacrylate bond in vitro in a manner comparable to reinforced bone replacement materials.     

Nanoindentation study of interfaces between calcium phosphate and bone in an animal spinal fusion model.

Intertransverse process spinal fusion is a common surgical procedure for the treatment of spinal disorders. In the present study, a porous hydroxyapatite (HA)/beta-tricalcium phosphate (beta-TCP) ceramic was tested as graft material using a rabbit lumbar transverse process (L5-L6) fusion model. The porous ceramic blocks were implanted onto the dorsal decorticated surface of the lumbar transverse processes. The specimens were harvested at the seventh week after implantation. Histomorphological observation revealed that the integration of HA/beta-TCP with the host bone of the transverse process occurred by both cancellous bone formation and cartilage formation. Scanning electron microscopy-wavelength dispersive X-ray spectrometry examinations showed significant differences in calcium, phosphorus, and sulfur contents in the newly formed tissues and the porous HA/TCP implants. Nanoindentations were used to evaluate the intrinsic mechanical properties of the implants and the newly formed tissues. The Young's moduli of the newly formed cartilage, new cancellous bone, and HA/TCP, were 0.66 +/- 0.02 GPa, 2.36 +/- 0.50 GPa, and 10.2 +/- 1.21 GPa, respectively. Nanoindentation results revealed degradation of the porous ceramics and incomplete calcification of the new cancellous bone at the seventh week after implantation. Nanoindentation appeared to be a useful technique for assessing the mechanical status of spinal fusion in animal models.     

Correlation between compression, tensile and tearing tests on healthy and calcified aortic tissues

An anastomosis performed in calcified tissues tears up faster than in healthy tissues. This study develops and validates an in vitro non-destructive method to distinguish healthy from calcified aortic tissues. An uniaxial unconfined compression test is able to distinguish healthy from calcified aortas (p<0.01). The compressive E-modulus at a strain level of 10% is 227+/-34kPa for artificially calcified and 147+/-15kPa for healthy porcine aortic tissues. Calcified aortic tissues have a lower tensile strength than healthy porcine aortic tissues (p<0.05). The ultimate tensile strength is 1.34+/-0.18MPa and 1.55+/-0.31MPa for artificially calcified and healthy porcine aortic tissues respectively. Calcified aortic tissues have a lower resistance to tearing than healthy aortic tissues (p<0.05). The resistance to tearing is 1.78+/-0.33N/mm and 2.16+/-0.64N/mm for artificially calcified and healthy porcine aortic tissues respectively.     

Beta-CaSiO3/beta-Ca3(PO4)2 composite materials for hard tissue repair: in vitro studies

In this study, a series of beta-CaSiO(3) (CS)/beta-Ca(3)(PO(4))(2) (TCP) composites with different ratios were prepared to produce new bioactive and biodegradable biomaterials for potential bone repair. The mechanical properties of CS-TCP composites increased steadily with the increase of TCP amounts in composites. Formation of bone-like apatite on a range of CS-TCP composites with CS weight percentage ranging from 0 to 100 has been investigated in simulated body fluid (SBF). The presence of bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and fourier transform infrared reflection spectroscopy (FTIR). The results showed that the apatite formation ability of the CS-TCP composite was enhanced with increasing CS content in the composites. For composites with more than 50% CS contents, the samples were completely covered by a layer of dense bone-like apatite just after 3 days immersion. Dissolution tests in Tris-HCl buffer solution showed obvious differences with different CS contents in composites. The dissolution rate increased with the increase of CS content, which suggested that the solubility of biphasic composites could be tailored by adjusting the initial CS/TCP ratio. In vitro cell experiments showed that higher content of CS phase in composites promoted cell proliferation and differentiation. When the CS amount in the composite increased to 50%, the proliferation rate and ALP activities of osteoblast-like cells showed significant difference compared with pure TCP (p < 0.05). Results of the study suggested that the CS-TCP composites with more than 50% CS content might be promising bone repair materials.     

N-(2-mercaptopropionyl)-glycine but not allopurinol prevented cigarette smoke-induced alveolar enlargement in mouse

We investigated the possible protective effects of the Allopurinol (A), N-(2-mercaptopropionyl)-glycine (M) and N-acetylcysteine (N) against lung injury caused by long-term exposure to cigarette smoke (CS) in mouse. C57BL6 mice were exposed to 12 cigarettes a day for 60 days and concomitantly treated with either one of the antioxidant drugs diluted in saline (CS+A-50 mg/kg; CS+M-200 mg/kg/day; CS+N-200 mg/kg/day). Control groups were sham-smoked (AA). Long-term CS exposure results in extensive parenchyma destruction in CS group. Both CS+N and CS+M groups showed preserved alveolar structure and showed preserved lung function when compared to CS group. Macrophage and neutrophil counts were decreased in CS+M, and CS+N groups when compared to CS group (p<0.05). Antioxidant enzyme activities were reduced in all treated groups. CS+A showed the highest reduction in catalase activity (-25%, p<0.01). We conclude that M treatment reduced long-term CS-induced inflammatory lung parenchyma destruction and lung function, comparable to N treatment, however, antioxidant administration did not reverse CS-induced antioxidant enzyme activity reduction.     

Marrow cell induced osteogenesis in porous hydroxyapatite and tricalcium phosphate: a comparative histomorphometric study of ectopic bone formation

To investigate the bone formation ability of porous hydroxyapatite (HA) and tricalcium phosphate (TCP), ceramic discs were implanted with or without rat marrow cells into subcutaneous sites in syngeneic rats. The discs of HA and TCP had identical microstructures: pore size was 190-230 microns, porosity was 50-60%, and they were fully interconnected. Implants without marrow cells (discs themselves) did not show bone formation, whereas implants with marrow cells showed bone formation in the pores of the ceramics. The bone formation of both HA and TCP occurred initially on the surface of the ceramic and progressed towards the center of the pore. The de novo bone was quantitated from decalcified serial sections of the implants. One month after implantation with marrow cells, the percentage fractions of the pore area filled with bone for implanted HA and TCP were 16.9 and 15.1, respectively. At 2 months after implantation with marrow cells, the fractions of bone were 34.3 and 30.9, respectively. These results indicate that both HA and TCP ceramics can show comparable osteogenic ability in the presence of marrow cells.     

Ectopic osteogenesis with biphasic ceramics of hydroxyapatite and tricalcium phosphate in rabbits.

Porous calcium phosphate ceramics consisting of hydroxyapatite (HA) and tricalcium phosphate (TCP) with different HA to TCP ratio were implanted intramuscularly in rabbits for six months in order to carry out a comparative study on osteogenic activity of the ceramics. Bone formation was detected only in HT73 (HA to TCP ratio, 7-3) specimens. Other implants, HT28 (2-8) and HT010 (0-10), could not induce bone. After a six-month period of implantation, HT28 and HT010 implants showed obvious degradation of the implants changing their shape and size macro and microscopically. Microscopically, they showed aggregates of fine particles and appearance of multinucleated cells. However, HT73 implants was less degraded and could maintain their original structure macro and microscopically. This study showed that HT73 ceramics can induce bone in rabbit muscle tissue and it is considered that maintenance of porous structure, that is, degradation rate of the materials may be one of the affecting factors in ceramic-induced osteogenesis.     

Do we need synthetic osteotomy augmentation materials for opening-wedge high tibial osteotomy

High tibial osteotomy (HTO) is an increasing popular method to treat unicompartimental osteoarthritis of the knee in younger, active patients. In so doing one tries to delay the need for total or unicompartimental joint replacement. The augmentation of HTO opening gaps with supporting material is discussed controversially, especially after the introduction of locking plates, which contribute to the decline of the non-union rate. Currently, we do not recommend synthetic augmentation, when using locking plates in HTO with opening angles less than 10 degrees . In our recent randomized study we could histologically and radiologically demonstrate the complete rebuilding of lamelliform bone in patients without synthetic augmentation, whilst bony ingrowth into the hydroxyapatite/tricalcium phosphate (HA/TCP) wedge of augmented osteotomies just slowly progressed. In contrast to unaugmented osteotomies, there was no advantage in using HA/TCP wedges or the combination of HA/TCP wedges and platelet rich plasma (PRP) as supporting material after 12 months. In osteotomies where an opening angle bigger than 7.5 degrees is chosen, rigid locking plates should be used. In our opinion, autologous iliac crest graft should be used in the high-risk patients (obese, smoker, opening angle bigger than 10 degrees ). Whether synthetic augmentation combined with PRP is equal or even superior to autologous iliac crest graft in openings bigger than 10 degrees has not been proven yet.     

Electrospinning polyaniline-contained gelatin nanofibers for tissue engineering applications

Polyaniline (PANi), a conductive polymer, was blended with a natural protein, gelatin, and co-electrospun into nanofibers to investigate the potential application of such a blend as conductive scaffold for tissue engineering purposes. Electrospun PANi-contained gelatin fibers were characterized using scanning electron microscopy (SEM), electrical conductivity measurement, mechanical tensile testing, and differential scanning calorimetry (DSC). SEM analysis of the blend fibers containing less than 3% PANi in total weight, revealed uniform fibers with no evidence for phase segregation, as also confirmed by DSC. Our data indicate that with increasing the amount of PANi (from 0 to approximately 5%w/w), the average fiber size was reduced from 803+/-121 nm to 61+/-13 nm (p<0.01) and the tensile modulus increased from 499+/-207 MPa to 1384+/-105 MPa (p<0.05). The results of the DSC study further strengthen our notion that the doping of gelatin with a few % PANi leads to an alteration of the physicochemical properties of gelatin. To test the usefulness of PANi-gelatin blends as a fibrous matrix for supporting cell growth, H9c2 rat cardiac myoblast cells were cultured on fiber-coated glass cover slips. Cell cultures were evaluated in terms of cell proliferation and morphology. Our results indicate that all PANi-gelatin blend fibers supported H9c2 cell attachment and proliferation to a similar degree as the control tissue culture-treated plastic (TCP) and smooth glass substrates. Depending on the concentrations of PANi, the cells initially displayed different morphologies on the fibrous substrates, but after 1 week all cultures reached confluence of similar densities and morphology. Taken together these results suggest that PANi-gelatin blend nanofibers might provide a novel conductive material well suited as biocompatible scaffolds for tissue engineering.     

Mechanical properties of calcium sulphate/hydroxyapatite cement

Setting times, volume after setting, injectability and hardness (at 37 degrees C in contact with Ringer's solution) were determined for cements made of mixtures of calcium sulphate hemihydrate (CS) and hydroxyapatite (HA) with a range of compositions. The purpose of these experiments was to determine the behaviour of a mixture that could be used as an injectable cement for orthopaedic applications, including spinal fusion. A suitable mixture consisted of 60% CS and 40% HA by mass; a slurry was made by mixing solid (36 g) with water (15 cm(3)). The slurry had initial and final setting times of 5.7+/-1.3 min and 19.6+/-0.7 min (mean +/- standard deviation), respectively. The hardness of the cement did not systematically increase or decrease in the 72 h following the final setting time. The volume of the cement was 99.8+/-0.4% of the volume of the initial slurry, i.e. there was negligible shrinkage on setting. It was able to withstand a pressure of 7.3+/-1.2 MPa, applied by a hemispherical indenter before the onset of permanent damage, indicating adequate strength for spinal fusion.     

Preparation and characterization of biodegradable chitosan/hydroxyapatite nanocomposite rods via in situ hybridization: a potential material as internal fixation of bone fracture

A transparent and slight yellow chitosan (CS)/hydroxyapatite (HA) nanocomposite with high performed, potential application as internal fixation of bone fracture was prepared by a novel and simple in situ hybridization. The method solves the problem of the nano-sized particle aggregation in polymer matrix. XRD, TEM and SEM were used to determine component and morphology of the composite. Results indicated that nano-HA particles were dispersed well in CS matrix, which can also be proved by the transparent appearance of composite rod, and that the structure of composite is assembled by CS molecule in the order of layer-by-layer. The mechanical properties of the composite were evaluated by using bending strength and modulus, and compared with some other bone replacement materials such as PMMA and bone cement. The initial mechanical properties of bending strength and modulus of composite are 86 MPa and 3.4 GPa, respectively, which is double or triple times stronger than that of PMMA and bone cement. It was found that the bending strength and modulus of CS/HA with ratio of 100/5 (wt/wt) is slightly higher than that of pure CS rod. The addition of HA can also reduce the ratio of water absorption of composite, which postponed the retention of mechanical properties of CS/HA composite under moisture condition. The phenomenon can be predicted with the fit exponential function according the data measured.