Osteogenesis Capacity of a Novel BMP／a-TCP Bioactive Composite Bone Cement

To improve the osteogenesis ability of α-trkalcium phosphate (a-TCP ) bone cement, a novel BMP/ a- TCP composite bone cement was prepared. By measuring the setting time and compressive strength, the hydration characteristic of bone cemtwnt icts eralnated. Animal experiments including histological observation, radiographic investigation as well as digital image analyses reveal the difference of osteogenesis ability among BMP, a TCP bone cetnent and BMPI a-TCP composite bone cement, Results show that a-TCP bone cement possesses excellent hydration and setting properties as well as high mechanical property, Comparison experiments show that BMPI a-TCP composite bonc cement has a stronger osteogenesis obility. The gross observation of the implant site does not exhibit any inflammation or necrosis. Histohwcal analyses reveal that the material has good osteointegration with host bone, and new bone formntion is detected within the materials, which are degrading. Strong osteogenesis ability of the composite is due to not only the excellent osteoconductive potential but also the osteoinductive potential contributed by attire BMP releasing and the material degradation . Large skull defect could be well-healed ty filling BMPl a-TCP composite bone cement. This novel material proves itself to be an absorbable and bioaetive bonecement with an osteogenesi ability.     

Hydroxyapatite/β-tricalcium Phosphate Composite for Guiding Bone Tissue Growth into a Titanium Tube in 8 mm Dog Tibia Cavity Defects

We developed a fixation method and evaluate bone regrowth in the cavities of a Ф4 mm× 8 mm titanium(Ti)tube through porous hydroxyapatite(HAP)/β-tricalcium phosphate(β-TCP)composite filling(group A),chitosan/calcium phosphate composite filling(group B),and HAP particle modification(group C).After 2 and 5 months of implantation in dog tibia defects,new bone formation in the three groups was studied by histology and histomorphometry.Group A displayed the most bone regenerated area in both 2 and 5 months post-operation.The chitosan/calcium phosphate composite in group B mostly degraded 2 months after implantation,leading to fibrous tissue invasion after 5 months.By contrast,less bone formation was observed in group C.These results indicated that filling the cavities of metalprostheses with a porous HAP/β-TCP composite can be used for stable long-term fixation in clinicalsettings.     

In vitro and in vivo characterization of homogeneous chitosan-based composite scaffolds

With a homogeneous distribution of hydroxyapatite (HAP) crystals in polymer matrix, composite scaffolds chitosan/ HAP and chitosan/collagen/HAP were fabricated in the study. XRD, SEM and EDX were used to characterize their components and structure, in vitro cell culture and in vivo animal tests were used to evaluate their biocompatibility. HAP crystals with rod-like shape embeded in chitosan scaffold, while HAP fine-granules bond with collagen/chitosan scaffold compactly. A homogenous distribution of Ca and P elements both in chitosan/HAP scaffold and chitosan/collagen/HAP scaffold was defined by EDX pattern. The presence of collagen brought a more homogenous distribution of HAP due to its higher ability to induce HAP precipitation. The results of in vitro cell culture showed that the composite’s biocompatibility was enhanced by the homogenous distribution of HAP. In vivo animal studies showed that the in vivo biodegradation was effectively improved by the addition of HAP and collagen, and was less influenced by the homogeneous distribution of HAP when compared with a concentrated distribution one. The composite scaffolds with a homogeneous HAP distribution would be excellent alternative scaffolds for bone tissue engineering.     

Preparation of filling porous osteoconduction materials and its animal experiment study

Titanium rods were processed into implant samples with cavity and groove in which was filled with HAP/β-TCP porous osteoconduction composite materials in order to increase the mechanical stability of the implant in vivo.The phase compositions of the composite was characterized by X-ray diffraction (XRD) and scanning electron microscopy(SEM).Histological evaluation showed that the biogradable composite could enhanced the ability of new bone formation.The composite can conduct new bone tissue growing into the cavities gradually after implanted into animal,and then achieve mechanical fixation.The filling biogradable compound exhibited excellent biocompatibility,which combined with the new bone tissues tightly without inflammation and loosing.     

Hydration Kinetics of Phosphorus Slag-cement Paste

Hydration characteristics of Portland cement paste with phosphorus slag powder incorporated and hydration kinetics was investigated with SEM, X-ray diffraction, DTA-TG and calorimeter Ⅱ80. Results showed that phosphorus slag powder could reduce total amount of hydration products yet had little influence on the type of hydration products. The total amount of heat of hydration was decreased by 49.11% and the final setting was postponed by 2.28 h when phosphorus slag powder substituted 35% Portland cement by m...     

Improvement of cement strength by induction method

The induction method of improriug the strength of Portland cement by adding fine slag powder,high aluminate component and hydrated poste was imestigated through determining the physical properties, hydration heat and pore size distribution, and its mechanism was discussed. The experimental results reveal that a certain content of high aluminate component,fine slag powder and hydrated paste can improve remarkably the strength of Portland cement.     

Hydration products of cement-silica fume-quartz powder mixture under different curing regimes

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement(cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes(standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.     

Modifi cation of β-TCP/PLGA Scaffold and Its Effect on Bone Regeneration in vivo

In order to look for the best proportion of β-tricalcium phosphate(β-TCP)and poly(lactideco-glycolide)(PLGA)we fabricated porous composites β-TCP/PLGA scaffold using freeze-drying method.Morphologicalcharacterization using scanning electron microscopy showed that the interconnected pore distribution was even and there was no significant difference with the increase of PLGA content.Moreover,the porosity,compressive strength and degradation in vitro were characterized.The fabricated scaffolds with increased PLGA in the composites β-TCP/PLGA scaffolds willget stronger mechanicalproperty and better appearance,furthermore,get suitable environment for cells.According to the evaluation indexes for the tissue engineering scaffold,the group of scaffold(β-TCP/PLGA=6:4)was selected to evaluate the induced celladhesion and proliferative ability of the scaffolds.Then as transplant embed into the bone criticaldefect sites on rats femur.The repairing processes of bone defect sites were characterized by X-ray analysis within 12 weeks.X-ray analysis showed that the bone defect sites alldisplayed the formation of callus obviously,In summary,our data suggest that the scaffold(β-TCP/PLGA=6:4)has a promising clinicalfuture in regeneration of bone criticaldefects.     

Microstructure and mechanical properties of calcium phosphate cement/gelatine composite scaffold with oriented pore structure for bone tissue engineering

The macroporous calcium phosphate(CPC) cement with oriented pore structure was prepared by freeze casting. SEM observation showed that the macropores in the porous calcium phosphate cement were interconnected aligned along the ice growth direction. The porosity of the as-prepared porous CPC was measured to be 87.6% by Archimede’s principle. XRD patterns of specimens showed that poorly crystallized hydroxyapatite was the main phase present in the hydrated porous calcium phosphate cement. To improve the mechanical properties of the CPC scaffold, the 15% gelatine solution was infiltrated into the pores under vacuum and then the samples were freeze dried to form the CPC/gelatine composite scaffolds. After reinforced with gelatine, the compressive strength of CPC/gelatine composite increased to 5.12 MPa, around fifty times greater than that of the unreinforced macroporous CPC scaffold, which was only 0.1 MPa. And the toughness of the scaffold has been greatly improved via the gelatine reinforcement with a much greater fracture strain. SEM examination of the specimens indicated good bonding between the cement and gelatine. Participating the external load by the deformable gelatine, patching the defects of the CPC pores wall, and crack deflection were supposed to be the reinforcement mechanisms. In conclusion, the calcium phosphate cement/gelatine composite with oriented pore structure prepared in this work might be a potential scaffold for bone tissue engineering.     

Experimental Study of Porous Beta-tricalcium Phosphate and Bone Morphogenetic Protein/porous Beta-tricalcium Phosphate Complex in Rabbit Mandibular Reconstruction

We investigated the osteogenic characteristic and biodegradation behavior of porous beta-tricalcitum phosphate （ β- TCP ） and bone morphogenetic protein/beta-tricalcium phosphate （ BMP/ β- TCP ） complex in mandibular reconstruction and evaluated the advantages of BMP / β- TCP complex in repairing bone defects. Bone defects created in the lower margin of bilateral mandible bodies in 12 rabbits were repaired with β- TCP （ control group ） and BMP/ β- TCP complex （ experimental group ） respectively. The rabbits were euthanized after 2, 4, 8 and 12 weeks and examined by macroscopy, radiography, histology, histomorphometry and image analysis. 2 weeks after surgery, ossftcation of newly-generated tissue in BMP/ β- TCP complex group appeared and after 12 weeks, massive new bone and ossification maturation were seen. However, in β- TCP group without BMP , ossification was not found until 12 weeks after operation. Image analysis showed that bone regeneration rate of BMP/ β- TCP was 30%-40% higher and the degradation rate was 20%- 30% higher than that of β- TCP. Therefore, as a reconstructive material for bone defects, BMP/ β-TCP complex is superior to β-TCP and can be used in oral and maxillofacial surgery.     

Effects of Calcination Temperature of Boron-Containing Magnesium Oxide Raw Materials on Properties of Magnesium Phosphate Cement as a Biomaterial

A new magnesium phosphate bone cement(MPBC) was prepared as a byproduct of boroncontaining magnesium oxide(B-MgO) after extracting Li_2CO_3 from salt lakes. We analyzed the elementary composition of the B-MgO raw materials and the effects of calcination temperature on the performance of MPBC. The phase composition and microstructure of the B-MgO raw materials and the hydration products(KMg PO_4·6H_2O) of MPBC were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that ionic impurities and the levels of toxic elements were sufficiently low in B-MgO raw materials to meet the medical requirements for Mg O(Chinese Pharmacopeia, 2010 Edition) and for hydroxyapatite surgical implants(GB23101.1-2008). The temperature of B-Mg O calcination had a marked influence on the hydration and hardening of MPBC pastes. Increasing calcination temperature prolonged the time required for the MPBC slurry to set, significantly decreased the hydration temperature, and prolonged the time required to reach the highest hydration temperature. However, the compressive strength of hardened MPBC did not increase with higher calcination temperatures. In the 900-1 000 ℃ temperature range, the hardened MPBC had a higher compressive strength. Imaging analysis suggested that the setting time and the highest hydration temperature of MPBC pastes were dependent on the size and crystal morphology of the B-Mg O materials. The production and microstructure compactness of KMgPO_4·6H_2O, the main hydration product, determined the compressive strength.     

Characteristics of two types of C-S-H gel in hardened complex binder pastes blended with slag

The characteristics of C-S-H gel in hardened Portland cement pastes and complex binder pastes with ground granulated blast furnace slag were investigated with nanoindentation. The composition of C-S-H gel was analysed with SEM-EDS. The obtained results showed that the volume fraction of LD C-S-H gradually reduced and the volume fraction of HD C-S-H increased with the prolongation of hydration age. Most of the C-S-H gel produced at later age was HD C-S-H. The volume fraction of HD C-S-H increased as the fraction of slag in complex binder pastes increased, suggesting that HD C-S-H was mainly in the hydration products of slag. The chemichal compositions of the two types of C-S-H gel were simlar, meaning that formation and transformation of the two types of C-S-H gel were not affected by their Ca/Si ratio.     

Preparation of a Novel Calcium Phosphate Cement Using N-methylene Phosphonic Chitosan as a Gelling Agent

A modified chitosan （ N-methylene phosphonic Chitosan, NMPC） was synthesized to improve solubility and ability to bind calcium ion. The properties of the raw material chitosan and its derivative NMPC were characterised using FTIR , ^1H- NMR . The aim of this study was to enhance the compressive CPC by reinforcing with NMPC. A formulation consisting of CPC powder , buffer solution and gelling agent was used for preparation of the CPC. CPC powder coasisted of tetracalcium phosphate（ TTCP ） and dicalcium phosphate anhydrous （ DCPA ）. NMPC which acted as the gelling ageut was dissohed into KH2PO4-Na2 HPO4 buffer solution. Each specimen in the mold was sandciched between two fritted glass sides and kept for 24 hours. Compressive strengths were determined, the setting product was identified using X-ray diffraction and scanning electron microscopy was used to investigate the hydroxyapatite particles size and porosity. The experimental results showed that the dominating influence on the compressive strengths of CPC-AMPC was the HA panicle size, its uniformity and appropriate porosity.     

Long-term Performance of Moderate Heat Portland Cement with Double-expansive Sources

The long-term performance of moderate heat Portland cement with double-expansive sources （DE cement） in the system of high MgO clinker and gypsum was studied by XRD, SEM/EDAX and test methods for strength and expansion of cement. Results indicate that the periclase particle, whose size was 5-7.5μm in DE cement clinker containing 4.8 % MgO, existed individually. The periclase hydration in hardened DE cement paste started at about 60 days and completed up to 2 000 days, and ettringite in the paste was stable from 3 days to 2 000 days. Under the conditions of 4.5%-5.0 % MgO in clinker and 2.8%-3.4 %SO3 in cement, ettringite expansion and brucite expansion in DE cement paste had a continuity, entirety and stability. At the ages of 90, 365,730 and 2 000 days the expansion of the paste reached 0.07%-0.11%, 0.16%-0.21%, 0.21%-0.27 %, and 0.29%-0.38%, respectively. The results suggest that by using this cement in mass concrete it may compensate its temperature shrinkage and autogenous shrinkage to some extent.     

Preparation, Fundamental Characteristics and Biosafety Evaluation of Compound rhBMP-2/CPC

To stndy the fundamental characteristics and biosafety of the compound bone morphogenetic protein （ BMP ） and rhBMP- 2/CPC , and to provide a theoretical basis for the compound biologically active artificial bone made of calcium phosphate cement （CPC） and bone morphogenetic protein, simplex CPC was taken as the control group, and the compound with the blending ratio of 1g CPC to 5mg rhBMP-2 was taken as the experimentation group to determine the setting time, compressive, strength, acute toxicological and sub acute toxicological properties. The osteogenic characteristic of compound rhBMP- 2/CPC was measured by making animal model of radio discontinuous defect. The setting time of the two groups meets the clinical requirements, and the compressive strength of the solidified body of bone cement increases along with increasing the immersion time. Compound rhBMP- 2/ CPC has a favorable ostengenic characteristic for animal model of radio discontinuous deject. The fundamental characteristics of the compound rhBMP- 2 phosphate bone cement are basically the same as that of CPC, and also have a favorable biosafety and osteogenesis.     

Utilization of Lithium Slag as An Admixture in Blended Cements: Physico-mechanical and Hydration Characteristics

Physical and mechanical properties variations of lithium slag were systematically investigated by three different ways such as physical, chemical activation, physical-chemical combined activation. Mechanisms of the cementitious properties and hydration process of lithium slag composite cement were studied by XRD and SEM. The results showed that specific surface area increased from 254 to 700 m2/kg while median particle size decreased from 14.97 to 8.45 um with the increase of grinding time. Physical, chemical activation and combined activation improved the strength and hydration degree of lithium slag composite cement. Compared with original lithium slag, the flexural strength and compressive strength of mortars were improved significantly with the increase of grinding time. A higher strength of the cement with the lithium slag was attained; The sample with 10% lithium slag got the highest strength when the grinding time was 10 min; the compressive strength was higher than OPC at 28 days, which increased by 12.3%. When the Na2SO4 content was 0.6%, the compressive strength increased by 1.4%; when the Al2(SO4)3·18H2O content was 0.4%, the compressive strength increased by 5.8% at 28 days. Compared with the late strength, the improving degree of early strength was larger with the incorporation of activator. The results of XRD and SEM were consistent with the results of mechanical properties; it is also evident that lithium slag composite cement hydration products were mainly AFt, Ca(OH)2, Ca SO4·2H2O, and C-S-H gel.     

Bone Formation Process of β-TCP Ceramics with Tetracycline Tracing

To stndy the new bone formation in the bone defect area after implantation, the tetracycline tracing method was used. The results show that new bone formed in 1 month, and the formation rate of new bone was very high (8.164um/day), cunsiderably faster than that of control groups ( 3.219um / day ). The new bone grew up quickly and β-TCP particles were surrounded by double fluorescence bands which became more obvious. The new bone formation rate was maximal at 2 months, and then grndually reduced. The rate was steady at 4 months, and then reduced to resembling as the normal physiologic metabolism of bone, which indicated the implanted materials were completely replaced by bone. Calcium phosphate materials had the ability of osteoconduction .     

Model Analysis of Initial Hydration and Structure Forming of Portland Cement

The auto efficiently hydration heat arrangement and the non-contacting electrical resistivity device were used to test the therrnology effect and the resistivity variation of Portland cement hydration. The structure forming model of Portland cement initial hydration was established through the systematical experiments with different cements, the amount of mixing water and the chemical admixture. The experimental results show that, the structure forming model of cement could be divided into three stages, i e, solution-solution equilibrium period, structure forming period and structure stabilizing period. Along with the increase of mixing water, the time of inflexion appeared is in advance for thermal process of cement hydration and worsened for the structure forming process. Comparison with the control specimen, adding Na2SO4 makes the minimum critical point lower, the flattening period shorter and the growing slope after stage one steeper. So the hydration and structure forming process of Portland cement could be described more exactly by applying the thermal model and the structure-forming model.     

Model Analysis of Initial Hydration and Strueture Forming of Portland Cement

The auto efficiently hydration heat arrangement and the non-contacting electrical resistivity device were used to test the thermology effect and the resistivity variation of Portland cement hydration. The structure forming model of Portland cement initial hydration was established through the systematical experiments with different cements,the amount of mixing water and the chemical admixture.The experimental results show that,the structure forming model of cement could be divided into three stages,i e,solution-solution equilibrium period,structure forming period and structure stabilizing period.Along with the increase of mixing water,the time of inflexion appeared is in advance for thermal process of cement hydration and worsened for the structure forming process.Comparison with the control specimen,adding Na_2SO_4 makes the minimum critical point lower,the flattening period shorter and the growing slope after stage one steeper.So the hydration and structure forming process of Portland cement could be described more exactly by applying thc thermal model and the structure-forming model.     

Thermodynamic Calculation and Stability of Calcium Silicate Hydrate System

Dissolution of cement clinker minerals involves a number of physical and chemical processes, and the simulation of dissolution processes helps to understand cement hydration conveniently. Dissolution model of cement clinker minerals was set up based on simulation theory of geochemical reaction equilibrium, PHREEQC simulation software provided by United States Geological Survey(USGS) was employed for thermodynamic calculation of C-S-H system. Stability of C-S-H system with low Ca/Si ratio at normal temperature was also explored. The results show that many phase assemblages coexist with the aqueous phase depending on its composition. The most stable product varies with different Ca/Si ratio of C-S-H system. Active Si O2 will consume excessive CH, so the Ca/Si ratios of C-S-H system decrease, C-S-H with low Ca/Si ratio becomes the most stable product, and this is the thermodynamic driving force of secondary pozzolanic reaction.