Thermoresponsive Brushes Facilitate Effective Reinforcement of Calcium Phosphate Cements

Calcium phosphate ceramics are frequently applied to stimulate regeneration of bone in view of their excellent biological compatibility with bone tissue. Unfortunately, these bioceramics are also highly brittle. To improve their toughness, fibers can be incorporated as the reinforcing component for the calcium phosphate cements. Herein, we functionalize the surface of poly(vinyl alcohol) fibers with thermoresponsive poly(N-isopropylacrylamide) brushes of tunable thickness to improve simultaneously fiber dispersion and fiber-matrix affinity. These brushes shift from hydrophilic to hydrophobic behavior at temperatures above their lower critical solution temperature of 32 °C. This dual thermoresponsive shift favors fiber dispersion throughout the hydrophilic calcium phosphate cements (at 21 °C) and toughens these cements when reaching their hydrophobic state (at 37 °C). The reinforcement efficacy of these surface-modified fibers was almost double at 37 versus 21 °C, which confirms the strong potential of thermoresponsive fibers for reinforcement of calcium phosphate cements.

3D plotting in the preparation of newberyite, struvite, and brushite porous scaffolds: using magnesium oxide as a starting material

Calcium phosphate (CaP)-containing materials, such as hydroxyapatite and brushite, are well studied bone grafting materials owing to their similar chemical compositions to the mineral phase of natural bone and kidney calculi. In recent studies, magnesium phosphate (MgP)-containing compounds, such as newberyite and struvite, have shown promise as alternatives to CaP. However, the different ways in degradation and release of Mg²⁺ and Ca²⁺ ions in vitro may affect the biocompatibility of CaP and MgP-containing compounds. In the present paper, newberyite, struvite, and brushite 3D porous structures were constructed by 3D-plotting combining with a two-step cementation process, using magnesium oxide (MgO) as a starting material. Briefly, 3D porous green bodies fabricated by 3D-plotting were soaked in (NH₄)₂HPO₄ solution to form semi-manufactured 3D porous structures. These structures were then soaked in different phosphate solutions to translate the structures into newberyite, struvite, and brushite porous scaffolds. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were used to characterize the phases, morphologies, and compositions of the 3D porous scaffolds. The porosity, compressive strength, in vitro degradation and cytotoxicity on MC3T3-E1 osteoblast cells were assessed as well. The results showed that extracts obtained from immersing scaffolds in alpha-modified essential media induced minimal cytotoxicity and the cells could be attached merely onto newberyite and brushite scaffolds. Newberyite and brushite scaffolds produced through our 3D-plotting and two-step cementation process showed the sustained in vitro degradation and excellent biocompatibility, which could be used as scaffolds for the bone tissue engineering.

Different post-processing conditions for 3D bioprinted α-tricalcium phosphate scaffolds

The development of 3D printing hardware, software and materials has enabled the production of bone substitute scaffolds for tissue engineering. Calcium phosphates cements, such as those based on α-tricalcium phosphate (α-TCP), have recognized properties of osteoinductivity, osteoconductivity and resorbability and can be used to 3D print scaffolds to support and induce tissue formation and be replaced by natural bone. At present, however, the mechanical properties found for 3D printed bone scaffolds are only satisfactory for non-load bearing applications. This study varied the post-processing conditions of the 3D powder printing process of α-TCP cement scaffolds by either immersing the parts into binder, Ringer's solution or phosphoric acid, or by sintering in temperatures ranging from 800 to 1500 °C. The porosity, composition (phase changes), morphology, shrinkage and compressive strength were evaluated. The mechanical strength of the post-processed 3D printed scaffolds increased compared to the green parts and was in the range of the trabecular bone. Although the mechanical properties achieved are still low, the high porosity presented by the scaffolds can potentially result in greater bone ingrowth. The phases present in the scaffolds after the post-processing treatments were calcium-deficient hydroxyapatite, brushite, monetite, and unreacted α-TCP. Due to their chemical composition, the 3D printed scaffolds are expected to be resorbable, osteoinductive, and osteoconductive.

Design of an inorganic dual-paste apatite cement using cation exchange

The use of hydraulic calcium phosphate cements (CPCs) as bone substitute is impaired by their relatively poor handling due to the need to mix a powder and a liquid during surgery. The aim of the present study was to assess the possibility to design CPCs as inorganic dual-paste cements, where both pastes would be stable for years, but would react as soon as they are mixed together. Results showed that aqueous pastes of α-tricalcium phosphate (α-TCP) powder could be stabilized for up to a year at room temperature by the use of 0.1 M Mg chloride solution. Adding a calcium chloride solution in a 1:4 volume ratio activated α-TCP pastes provided the Ca/Mg ratio was larger than one. Mechanistic investigations suggest that Ca ions can displace Mg cations adsorbed at the surface of α-TCP particles to initiate α-TCP transformation to calcium-deficient hydroxyapatite and concomitant paste hardening. The compressive strength (29 MPa) was similar to that of commercial formulations (5-80 MPa). Other divalent cations (Ba, Ni, Sr) had a similar effect although with a different degree of efficacy.

Apatite bone cement reinforced with calcium silicate fibers

Several research efforts have been made in the attempt to reinforce calcium phosphate cements (CPCs) with polymeric and carbon fibers. Due to their low compatibility with the cement matrix, results were not satisfactory. In this context, calcium silicate fibers (CaSiO3) may be an alternative material to overcome the main drawback of reinforced CPCs since, despite of their good mechanical properties, they may interact chemically with the CPC matrix. In this work CaSiO3 fibers, with aspect ratio of 9.6, were synthesized by a reactive molten salt synthesis and used as reinforcement in apatite cement. 5 wt.% of reinforcement addition has increased the compressive strength of the CPC by 250% (from 14.5 to 50.4 MPa) without preventing the cement to set. Ca and Si release in samples containing fibers could be explained by CaSiO3 partial hydrolysis which leads to a quick increase in Ca concentration and in silica gel precipitation. The latter may be responsible for apatite precipitation in needle like form during cement setting reaction. The material developed presents potential properties to be employed in bone repair treatment.

Setting time and formability of calcium phosphate cements prepared using modified dicalcium phosphate anhydrous powders

Calcium phosphate cements (CPCs) were prepared using Ca4(PO4)2O (TeCP) and modified CaHPO4 (DCPA) to evaluate the effects of the powder properties for DCPA particles on the setting time and formability of the resulting CPCs. Two types of modified DCPA were prepared by milling commercially available DCPA with ethanol (to produce E-DCPA) or distilled water (to produce W-DCPA). The E-DCPA samples consisted of well-dispersed, fine primary particles, while the W-DCPA samples contained agglomerated particles, and had a smaller specific surface area. The mean particle size decreased with increased milling time in both cases. The raw CPC powders prepared using W-DCPA had a higher packing density than those prepared using E-DCPA, regardless of the mean particle size. The setting time of the CPC paste after mixing with distilled water decreased with decreases in the mean particle size and specific surface area, for both types of DCPA. The CPCs prepared using W-DCPA showed larger plasticity values compared with those prepared using E-DCPA, which contributed to the superior formability of the W-DCPA samples. The CPCs prepared using W-DCPA showed a short setting time and large plasticity values, despite the fact that only a small amount of liquid was used for the mixing of the raw CPC powders (a liquid-to-powder ratio of 0.25 g g(-1) was used). It is likely that the higher packing density of the raw CPC powders prepared using W-DCPA was responsible for the higher performance of the resulting CPCs.

Synthesis and spectral characterization of silver/magnesium co-substituted hydroxyapatite for biomedical applications

The present work is aimed at the synthesis of antibacterial and bioactive silver/magnesium co-substituted hydroxyapatite (Ag/Mg-HAP) powders. For this purpose, firstly, different concentrations (0.5, 1.5, 2.5wt.%) of silver substituted HAP (Ag-HAP) powders were prepared by ultrasonic irradiation technique and were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Secondly, magnesium (Mg) is co-substituted as secondary material into Ag-HAP to offset the potential cytotoxicity of Ag, as higher concentration of Ag is toxic. The antibacterial activity of as-synthesized powders was evaluated by Escherichia coli (E. coli) and was found to be effectively high against bacterial colonization. Also, the in vitro cell-material interaction is evaluated with human osteosarcoma MG63 (HOS MG63) cells for cell proliferation. The results showed the evidence of cytotoxic effects of the higher concentration of Ag-HAP characterized by poor cellular viability whereas, Ag/Mg-HAP showed better cell viability indicating that co-substitution of Mg in Ag-HAP effectively offset the negative effects of Ag and improve performance compared with pure HAP. Thus, the as synthesized Ag/Mg-HAP will serve as a better candidate for biomedical applications with good antibacterial property and bone bonding ability.

Development of a novel calcium phosphate cement composed mainly of calcium sodium phosphate with high osteoconductivity

Two novel calcium phosphate cements (CPC) have been developed using calcium sodium phosphate (CSP) as the main ingredient. The first of these cements, labeled CAC, contained CSP, α-tricalcium phosphate (TCP), and anhydrous citric acid, whereas the second, labeled CABC, contained CSP, α-TCP, β-TCP, and anhydrous citric acid. Biopex(®)-R (PENTAX, Tokyo, Japan), which is a commercially available CPC (Com-CPC), and OSferion(®) (Olympus Terumo Biomaterials Corp., Tokyo, Japan), which is a commercially available porous β-TCP, were used as reference controls for analysis. In vitro analysis showed that CABC set in 5.7 ± 0.3 min at 22 °C and had a compressive strength of 86.0 ± 9.7 MPa after 5 days. Furthermore, this material had a compressive strength of 26.7 ± 3.7 MPa after 2 h in physiologic saline. CAC showed a statistically significantly lower compressive strength in the presence of physiologic saline and statistically significantly longer setting times than those of CABC. CABC and CAC exhibited apatite-forming abilities in simulated body fluid that were faster than that of Com-CPC. Samples of the materials were implanted into the femoral condyles of rabbits for in vivo analysis, and subsequent histological examinations revealed that CABC exhibited superior osteoconductivity and equivalent bioresorbability compared with Com-CPC, as well as superior osteoconductivity and bioresorbability compared with CAC. CABC could therefore be used as an alternative bone substitute material.

Influence of ibuprofen addition on the properties of a bioactive bone cement

Bioactive bone cements can promote bone growth and the formation of a strong chemical bond between the implant and bone tissue increasing the lifetime of the prosthesis. This study aims at synthesizing a new bioactive bone cement with different amounts of ibuprofen (5, 10 and 20 wt%) using a low toxicity activator, and investigating its in vitro release profile. The effect of ibuprofen (IB) on the setting parameters, residual monomer and bioactivity in synthetic plasma was also evaluated. It was verified that the different IB contents do not prevent the growth of calcium phosphate aggregates on composite surfaces, confirming that the cements are potentially bioactive. A relevant advantage of these formulations was a significant improvement in their curing parameters with increasing IB amount, associated to a reduction of the peak temperature and an extension of the setting time. The investigated cements released an average of about 20 % of the total incorporated ibuprofen during 30 days test, with IB20 liberating the highest percentage of drug 20.6 %, and IB10 and IB5, respectively 19.1 and 17.6 %. This behavior was attributed to the low solubility of this drug in aqueous media and was also related with the hydrophobic character of the polymer. Regarding the therapeutic concentration sufficient to suppress inflammation, the cement with 10 % of ibuprofen achieved the required release rate for 1 week and the cement with 20 % for 2 weeks.

Injectable collagen/α-tricalcium phosphate cement: collagen-mineral phase interactions and cell response

A bone inspired material was obtained by incorporating collagen in the liquid phase of an α-tricalcium phosphate cement, either in solubilized or in fibrilized form. This material was able to set in situ, giving rise to a calcium deficient hydroxyapatite (CDHA)/collagen composite. The morphology and distribution of collagen in the composite was shown to be strongly affected by the collagen pre-treatment. The interactions between collagen and the inorganic phase were assessed by FTIR. A red shift of the amide I band was indicative of calcium chelation by the collagen carbonyl groups. The rate of CDHA formation was not affected when diluted collagen solutions (1 mg/ml) were used, whereas injectability improved. The presence of solubilized collagen, even in low amount (1 %), increased cell adhesion and proliferation on the composites. Still in the absence of osteogenic medium, significant ALP activity was detected both in the inorganic and the collagen-containing cements. The maximum ALP activity was advanced in the collagen-containing cement as compared to the inorganic cement.

Setting solution concentration effect on properties of a TTCP/DCPA-derived calcium phosphate cement

The present work was to investigate the effects of concentration of (NH(4))(2)HPO(4) (diammonium hydrogen phosphate) setting solution on properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)--derived calcium phosphate cement. Experimental results indicated that working/setting time of the cement paste decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. After being immersed in Hanks' solution for 1 day or longer, the XRD intensities of initial TTCP and DCPA phases largely decreased, while apatite phase became dominant. More residual TTCP phase was observed in the 1 day-immersed cement prepared from higher concentration setting solutions. Compressive strength of the cement immersed for 1 day was consistently higher than that immersed for 30 min or 7 days. After being immersed for 1 day, the average CS value reached a maximal value (59 MPa) as (NH(4))(2)HPO(4) concentration was increased to 0.6 M, beyond that the cement strength decreased and maintained in a relatively high range of 47-54 MPa. Cells incubated with conditioned medium of Al(2)O(3) powder and with blank medium exhibited similar average viability values (0.80 and 0.78, respectively). The OD value with extractions of cement decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. The average 0.25, 0.5 and 0.6 M--OD values were 0.78, 0.67 and 0.66, respectively. When setting solution concentration was greater than 0.6 M, the OD value sharply declined to 0.47.

Direct scaffolding of biomimetic hydroxyapatite-gelatin nanocomposites using aminosilane cross-linker for bone regeneration

Hydroxyapatite-gelatin modified siloxane (GEMOSIL) nanocomposite was developed by coating, kneading and hardening processes to provide formable scaffolding for alloplastic graft applications. The present study aims to characterize scaffolding formability and mechanical properties of GEMOSIL, and to test the in vitro and in vivo biocompatibility of GEMOSIL. Buffer Solution initiated formable paste followed by the sol-gel reaction led to a final hardened composite. Results showed the adequate coating of aminosilane, 11-19 wt%, affected the cohesiveness of the powders and the final compressive strength (69 MPa) of the composite. TGA and TEM results showed the effective aminosilane coating that preserves hydroxyapatite-gelatin nanocrystals from damage. Both GEMOSIL with and without titania increased the mineralization of preosteoblasts in vitro. Only did titania additives revealed good in vivo bone formation in rat calvarium defects. The scaffolding formability, due to cohesive bonding among GEMOSIL particles, could be further refined to fulfill the complicated scaffold processes.

Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na 2O-CaO-MgO-P 2O 5-SiO 2

Osteoconductive bioglasses, free of K(2)O and Al(2)O(3) and with content of Na(2)O lower than 10 mol%, were designed based on the ratio (SiO(2) + MgO)/(P(2)O(5) + CaO + Na(2)O) in the system Na(2)O-CaO-MgO-P(2)O(5)-SiO(2). The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12 weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.

Effect of the calcium to phosphorus ratio on the setting properties of calcium phosphate bone cements

α-Tricalcium phosphate (α-TCP) has become the main reactant of most experimental and commercial ceramic bone cements. It has calcium-to-phosphorus (Ca/P) ratio of 1.50. The present study expands and reports on the microstructures and mechanical properties of calcium phosphate (CP) cements containing sintered monolithic reactants obtained in the interval 1.29 < Ca/P < 1.77. The study focuses on their cement setting and hardening properties as well as on their microstructure and crystal phase evolution. The results showed that: (a) CP-cements made with reactants with Ca/P ratio other than 1.50 have longer setting and lower hardening properties; (b) CP-cements reactivity was clearly affected by the Ca/P ratio of the starting reactant; (c) reactants with Ca/P < 1.50 were composed of several phases, calcium pyrophosphate and α- and β-TCP. Similarly, reactants with Ca/P > 1.50 were composed of α-TCP, tetracalcium phosphate and hydroxyapatite; (d) only the reactant with Ca/P = 1.50 was monophasic and was made of α-TCP, which transformed during the setting into calcium deficient hydroxyapatite; (e) CP-cements developed different crystal microstructures with specific features depending on the Ca/P ratio of the starting reactant.

[Preparation of alpha-tricalcium phosphate/HA whisker/carboxymethyl chitosan-gelatin composite porous bone cement]

In order to investigate the effects of HA whisker and carboxymethyl chitosan-gelatin(CMC-Gel) on the mechanical properties of porous calcium phosphate cement, a series of alpha-tricalcium phosphate (alpha-TCP), HA whisker and L-sodium glutamate porogen with different mass fractions were mixed, and setting liquid was added to them to prepare alpha-TCP/HA whisker composite porous bone cement. Then, the cement was immersed in a series of CMC-Gel solutions which had different weight ratios of CMC to Gel to prepare alpha-TCP/HA whisker/CMC-Gel composite porous bone cement. The compressive strengths and microstructure of cement were characterized by mechanical testing machine and SEM. The results showed that when the mass fraction of HA whisker is 4%, the compressive strength of alpha-TCP/HA whisker composite porous bone cement reaches 2.57MPa, which is 1.81 times that of alpha-TCP bone cement. When the weight ratio of CMC to Gel is 50:50, the compressive strength of alpha-TCP/HA whisker/CMC-Gel composite porous bone cement is 3. 34MPa, which is 2.35 times that of alpha-TCP bone cement, and the toughness of the composite cement is greatly improved as well.

Apatite formation in composites of α-TCP and degradable polyesters

The objective of this study was to investigate the conversion of alpha-Ca3(PO4)2 (alpha-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the alpha-TCP filler content. Cross-linkable dimethacrylates of epsilon-caprolactone/ D,L-lactide co-polymer or of epsilon-caprolactone/glycolide co-polymer were mixed with hydroxyethylmethacrylate, a photo-initiator and alpha-TCP to obtain composites with a filler content of 80 or 40 wt% alpha-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37 degrees C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of alpha-TCP into calcium-deficient hydroxyapatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of alpha-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the alpha-TCP content of the composites. An increase of the amount of alpha-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.

Injectable PLGA microsphere/calcium phosphate cements: physical properties and degradation characteristics

Calcium phosphate (CaP) cements show an excellent biocompatibility and often have a high mechanical strength, but in general degrade relatively slow. To increase degradation rates, macropores can be introduced into the cement, e.g., by the inclusion of biodegradable microspheres into the cement. The aim of this research is to develop an injectable PLGA microsphere/CaP cement with sufficient setting/cohesive properties and good mechanical and physical properties. PLGA microspheres were prepared using a water-in-oil-in-water double-emulsion technique. The CaP-cement used was Calcibon, a commercially available hydroxyapatite-based cement. 10:90 and 20:80 dry wt% PLGA microsphere/CaP cylindrical scaffolds were prepared as well as microporous cement (reference material). Injectability, setting time, cohesive properties and porosity were determined. Also, a 12-week degradation study in PBS (37 degree C) was performed. Results showed that injectability decreased with an increase in PLGA microsphere content. Initial and final setting time of the PLGA/CaP samples was higher than the microporous sample. Porosity of the different formulations was 40.8% (microporous), 60.2% (10:90) and 69.3% (20:80). The degradation study showed distinct mass loss and a pH decrease of the surrounding medium starting from week 6 with the 10:90 and 20:80 formulations, indicating PLGA erosion. Compression strength of the PLGA microsphere/CaP samples decreased siginificantly in time, the microporous sample remained constant. After 12 weeks both PLGA/CaP samples showed a structure of spherical micropores and had a compressive strength of 12.2 MPa (10:90) and 4.3 MPa (20:80). Signs of cement degradation were also found with the 20:80 formulation. In conclusion, all physical parameters were well within workable ranges with both 10:90 and 20:80 PLGA microsphere/CaP cements. After 12 weeks the PLGA was totally degraded and a highly porous, but strong scaffold remained.

Anti-washout carboxymethyl chitosan modified tricalcium silicate bone cement: preparation, mechanical properties and in vitro bioactivity

Anti-washout CaF(2) stabilized C(3)S (F-C(3)S) bone cement was prepared by adding water-soluble carboxymethyl chitosan (CMCS) to the hydration liquid. The setting time, compressive strength and in vitro bioactivity of the CMCS modified F-C(3)S (CMCS-C(3)S) pastes were evaluated. The results indicate that CMCS-C(3)S pastes could be stable in the shaking simulated body fluid (SBF) after immediately mixed. The addition of CMCS significantly enhances the cohesion of particles, at the same time restrains the penetration of liquid, and thus endows the anti-washout ability. The setting times of the pastes increase with the increase of CMCS concentrations in the hydration liquid. Besides, the compressive strengths of CMCS-C(3)S pastes after setting for 1-28 days are lower than that of the pure F-C(3)S paste, but the sufficient strengths would be suitable for the clinical applications. The crystalline apatite deposited on the paste surface is retarded from 1 to 2 days for the addition of CMCS, but the quantities of deposited apatite are same after soaking in SBF for 3 days. As the result that pure C(3)S paste has shorter setting times than pure F-C(3)S paste, CMCS modified pure C(3)S pastes would have better anti-washout ability. Our study provides a convenient way to use C(3)S bone cement with excellent anti-washout ability when the pastes are exposed to biological fluids. The novel anti-washout CMCS-C(3)S bone cement with suitable setting times, sufficient strengths and in vitro bioactivity would have good prospects for medical application.

Low temperature fabrication of magnesium phosphate cement scaffolds by 3D powder printing

Synthetic bone replacement materials are of great interest because they offer certain advantages compared with organic bone grafts. Biodegradability and preoperative manufacturing of patient specific implants are further desirable features in various clinical situations. Both can be realised by 3D powder printing. In this study, we introduce powder-printed magnesium ammonium phosphate (struvite) structures, accompanied by a neutral setting reaction by printing farringtonite (Mg(3)(PO(4))(2)) powder with ammonium phosphate solution as binder. Suitable powders were obtained after sintering at 1100°C for 5 h following 20-40 min dry grinding in a ball mill. Depending on the post-treatment of the samples, compressive strengths were found to be in the range 2-7 MPa. Cytocompatibility was demonstrated in vitro using the human osteoblastic cell line MG63.

[Preparation and properties of calcium polyphosphate-based composite scaffold for bone tissue engineering]

Calcium polyphosphate (CPP) is a new type of degradable material for bone repair, yet it is fragile and is not so controllable in regard to degradation. For increasing biological activity and close proximity to natural bone structure, in this experiment, we chose chitosan (CS) and its derivative carboxymethyl chitosan (CMC) as the extracellular matrix structure for the organic phase. Aldehyde sodium alginate (ADA) was used as natural cross-linker. The binary (CPP/CMC) and ternary (CPP/CMC/CS) composite scaffolds were prepared by the "multiple composite-cross-linking method". The degradation laws of the two materials were investigated through the weight loss of scaffolds, the pH value of degradation solution, the compressive strength and the surface morphology characterization. The results showed that the composite scaffolds had good interface and the compressive strength increased greatly, but the organic phase of dual-phase composite scaffolds degraded quickly, while degradation controllability and mechanical properties of ternary composite scaffold were significantly improved. All the above findings show that the method of ternary complex scaffold preparation is useful for the design and preparation of bone tissue engineering materials.

Thermal preparation of highly porous calcium phosphate bone filler derived from marine algae

A sustainable marine-derived bioceramic with a unique porous structure has been developed for hard tissue repair. The conversion of alga was achieved through a novel technique, involving well controlled thermal processing followed by low pressure-temperature hydrothermal synthesis. In its preparation, a heat treatment step was required to remove the organic compounds from the algae, which reinforces the mineralised matrices. Its removal is necessary to prevent issue such as immune biocompatibility and ensure phase purity of the resultant biomaterial. This paper investigates the hydrothermal technique used for the transformation of mineralised red algae to hydroxyapatite that preserves the algae's unique structure. It specifically focuses on the effects of heat treatment on the morphology of the algae, TGA, SEM and hot stage XRD to quantity the changes.

Synthesis and characterization of poly(methyl methacrylate)-based experimental bone cements reinforced with TiO2-SrO nanotubes

In an attempt to overcome existing limitations of experimental bone cements we here demonstrate a simple approach to synthesizing strontium-modified titania nanotubes (n-SrO-TiO(2) tubes) and functionalize them using the bifunctional monomer methacrylic acid. Then, using 'grafting from' polymerization with methyl methacrylate, experimental bone cements were produced with excellent mechanical properties, radiopacity and biocompatibility. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy mapping and backscattered SEM micrographs revealed a uniform distribution of SrO throughout the titanium matrix, with retention of the nanotubular morphology. Nanocomposites were then reinforced with 1, 2, 4 and 6 wt.% of the functionalized metal oxide nanotubes. Under the mixing and dispersion regime employed in this study, 2 wt.% appeared optimal, exhibiting a more uniform dispersion and stronger adhesion of the nanotubes in the poly(methyl methacrylate) matrix, as shown by TEM and SEM. Moreover, this optimum loading provided a significant increase in the fracture toughness (K(IC)) (20%) and flexural strength (40%) in comparison with the control matrix (unfilled) at P<0.05. Examination of the fracture surfaces by SEM showed that toughening was provided by the nanotubes interlocking with the acrylic matrix and crack bridging during fracture. On modifying the n-TiO(2) tubes with strontium oxide the nanocomposites exhibited a similar radiopacity to a commercial bone cement (CMW 1), while exhibiting a significant enhancement of osteoblast cell proliferation (242%) in vitro compared with the control at P<0.05.

Properties of anti-washout-type calcium silicate bone cements containing gelatin

Novel washout-resistant bone substitute materials consisting of gelatin-containing calcium silicate cements (CSCs) were developed. The washout resistance, setting time, diametral tensile strength (DTS), morphology, and phase composition of the hybrid cements were evaluated. The results indicated that the dominant phase of beta-Ca(2)SiO(4) for the SiO(2)-CaO powders increased with an increase in the CaO content of the sols. After mixing with water, the setting times of the CSCs ranged from 10 to 29 min, increasing with a decrease in the amount of CaO in the sols. Addition of gelatin into the CSC significantly prolonged (P < 0.05) the setting time by about 2 and 8 times, respectively, for 5% and 10% gelatin. However, the presence of gelatin appreciably improved the anti-washout and brittle properties of the cements without adversely affecting mechanical strength. It was concluded that 5% gelatin-containing CSC may be useful as bioactive bone repair materials.

Evaluation of a novel radiopacifiying agent on the physical properties of surgical spineplex

Polymethlylmethacrylate (PMMA) is the most frequently used cement for percutaneous vertebroplasty and kyphoplasty. To aid visualisation during surgery cements are doped with radiopacifying agents such as Barium sulphate (Ba(2)SO(4)) or Zirconium Dioxide (ZiO(2)). Mounting research suggests that these agents may impair the biocompatibility of the cements. However, incorporating an alternative radiopacifier agent with excellent biocompatibility would be a significant step forward. Bioactive radiopaque glasses incorporating elements such as strontium (Sr) and zinc (Zn), known to have beneficial and therapeutic effects on bone, are of great interest in this respect. In this study, the Ba(2)SO(4) of the commercially available Spineplex was incrementally replaced with a radiopaque therapeutic glass composition. The resulting effects on cement setting time, peak isotherm, ultimate compressive strength, Young's modulus (up to 30 days cement maturation) and radiopacity were evaluated. The substitution lead to an increase in cement setting time from 13.1 mins for Spineplex to 16.6-18.3 mins for the glass substituted cements. The peak exotherm during curing was reduced from 74 degrees C for Spineplex to a minimum of 51 degrees C for the fully substituted cement, indicating that reduced thermal necrosis in the in vivo setting is likely with these materials. Ultimate compressive strength and Young's modulus of each formulation showed no significant deterioration due to the substitution. Finally, the radiopacity of the substituted cements were reduced by up to a maximum of 18% in comparison to the control. However, the experimental formulations still maintained radiopacity equivalent to several millimetres of aluminium. As such the substituted cements had substantial equivalence to the Spineplex control. In order to assess the clinical relevance of these findings further investigation is warranted.

Characterisation of a new bioadhesive system based on polysaccharides with the potential to be used as bone glue

Although gluing bone is in theory a very attractive alternative to classical fracture treatment, this method is not yet clinically established due to the lack of an adhesive which would meet all the necessary requirements. We therefore developed a novel two-component bioadhesive system with the potential to be used as a bone adhesive based on biocompatible and degradable biopolymers (chitosan, oxidised dextran or starch). After mixing in water, the two components covalently cross-link by forming a Schiff's base. By the same mechanism, the glue binds to any other exposed amino group such as for example those exposed in fractured bone, even in the presence of water. Modified chitosan was synthesised from commercially available chitosan by deacetylation and was then reduced in molecular weight by heating in acid. The amount of free amino groups was analysed by IR. The molecular weight was determined by viscosimetry. Starch or dextran were oxidised with periodic acid to generate aldehyde groups, which were quantified by titration. l-Dopa was conjugated to oxidised dextran or starch in analogy to the gluing mechanism of mussels. Biomechanical studies revealed that the new glue is superior to fibrin glue, but has less adhesive strength than cyanoacrylates. In vitro cell testing demonstrated excellent biocompatibility, rendering this glue a potential candidate for clinical use.

Variations of temperature of acrylic bone cements prepared by hand and vacuum mixing during their polymerization

The aim of this work was to investigate variations of temperature in acrylic bone cement SmartSet HV during its polymerization as the function of mixing technique (hand mixing and vacuum mixing) and sample thickness. The temperature of 25-mm diameter samples differing in their thickness was monitored using a parallel plate measuring system of the compact rheometer preheated to the body temperature. The curves representing the temperature measured and average values of times needed to obtain the peak temperatures of the test samples prepared by different techniques of mixing are presented and discussed. It was found that the maximum temperature and also the times of peak temperatures rose with sample thickness but at different rate for each technique of mixing.

Histological analysis of calcium phosphate bone grafts for surgically created periodontal bone defects in dogs

A calcium phosphate cement (CPC-1), prepared by mixing an equimolar mixture of tetracalcium phosphate and dicalcium phosphate anhydrous with water, has been shown to be highly biocompatible and osteoconductive. A new type of calcium phosphate cement (CPC-2), prepared by mixing a mixture of alpha-tricalcium phosphate and calcium carbonate with pH 7.4 sodium phosphate solution, was also reported to be highly biocompatible. The objective of the present study was to compare the osteoconductivities of CPC-1 and CPC-2 when implanted in surgically created defects in the jaw bones of dogs. At 1 month after surgery, implanted CPC-1 was partially replaced by new bone and converted to bone within 6 months. In comparison, at 1 month after surgery, the defect filled with CPC-2 was mostly replaced by new bone. Therefore, bone formation in CPC-2-filled pocket was more rapid than in CPC-1-filled pocket. These findings supported the hypothesis that CPC-2 converted to bone more rapidly than CPC-1.

Improved biocomposite development of poly(vinyl alcohol) and hydroxyapatite for tissue engineering scaffold fabrication using selective laser sintering

In scaffold guided tissue engineering (TE), temporary three-dimensional scaffolds are essential to guide and support cell proliferation. Selective Laser Sintering (SLS) is studied for the development of such scaffolds by eliminating pore spatial control problems faced in conventional scaffolds fabrication methods. SLS offers good user control over the scaffold's microstructures by adjusting its main processing parameters, namely the laser power, scan speed and part bed temperature. This research focuses on the improvements in the fabrication of TE scaffolds using SLS with powder biomaterials, namely hydroxyapatite (HA) and poly(vinyl alcohol) (PVA). Grinding of as-received PVA powder to varying particle sizes and two methods of mixing are investigated as the preparation process to determine a better mixing method that would enhance the mixture homogeneity. Suitable sintering conditions for the improved biocomposite are then achieved by varying the important process parameters such as laser power, scan speed and part bed temperature.SLS fabricated samples are characterized using Fourier Transform Infrared Spectrometer (FTIR) and Scanning Electron Microscope (SEM). FTIR results show that the grinding and sintering processes neither compromise the chemical composition of the PVA nor cause undue degradation. Visual analysis of the grinding, powder mixing and sintering effect are carried out with SEM. The SEM observations show improvements in the sintering effects. The favorable outcome ascertains PVA/HA biocomposite as a suitable material to be processed by SLS for TE scaffolds.

Relationship between apatite-forming ability and mechanical properties of bioactive PMMA-based bone cement modified with calcium salts and alkoxysilane

Polymethylmethacrylate (PMMA)-based bone cement is used for the fixation of artificial joints in orthopaedics. However, the fixation is liable to loosen in the body, because the cement does not bond to living bone. So-called bioactive ceramics bond directly to living bone through the apatite layer formed on their surfaces in the body. We previously revealed that modification using gamma-methacryloxypropyltrimethoxysilane (MPS) and water-soluble calcium salts such as calcium acetate and calcium hydroxide was effective for providing the PMMA-based bone cement with apatite-forming ability in a simulated body fluid (SBF, Kokubo solution) that closely reproduces the body environment. However, the effect of the chemical reaction forming the apatite on the mechanical properties of the cements has not been clarified. The present work aimed to investigate this issue from the viewpoint of the interface structure between the apatite and the cement. The surface of the cement modified with calcium acetate and MPS was fully covered with newly formed apatite after soaking in Kokubo solution within 7 days, while half of the surface area of the cement modified with calcium hydroxide and MPS was covered with the apatite. The bending strength of the modified cements decreased after soaking in Kokubo solution. Porous structure was observed in the region about 50-100 microm in depth from the top surface because of release of the Ca2+ ions by both modified cements after soaking in Kokubo solution. The decrease in bending strength of the modified cements could be attributed to the formation of the pores. In addition, the pores on the top surfaces of the cements were filled with the newly formed apatite. The apatite formation would be effective not only for bioactivity but also for decreasing the reduction of mechanical strength.

Preparation and properties of a novel bone repair composite: nano-hydroxyapatite/chitosan/carboxymethyl cellulose

Nano-hydroxyapatite/chitosan/carboxymethyl cellulose (n-HA/CS/CMC) composites with weight ratios of 70/10/20, 70/15/15 and 70/20/10 were prepared through a co-solution method. The properties of the composites were characterized by means of burn-out test, IR, XRD, TEM and universal material testing machine. The degradation and bioactivity were also investigated by in vitro test in a simulated body fluid (SBF) for 8 weeks. The results showed that n-HA particles were dispersed uniformly in organic phase, and strong chemical interactions formed among the three phases. Moreover, the composites were similar to natural bone in morphology and size. In addition, the compressive strength was improved compared with n-HA/CS composite. The biodegradation rate was controllable by altering weight ratio of the CS/CMC. Meanwhile, the composites could induce apatite particles to deposit in SBF. All the above results indicate that the novel composites of n-HA/CS/CMC have a promising prospect used for bone repair materials in view of the good mechanical property, adjustable biodegradation rate and bioactivity in SBF. Additionally, the study would provide a good guide to exploit clinical application of natural cellulose.

Effects of calcination temperature on the drug delivery behaviour of Ibuprofen from hydroxyapatite powders

The effects of heat treatment time and temperature on the delivery behaviour of Ibuprofen from hydroxyapatite particles were investigated in this study. The drug release was seen to follow Fickian diffusion for the initial period of release for all heat treatment conditions. The gradient of Fickian release increased with (1) increasing crystallite size, attributed to the decreasing amount of boundary area, and (2) with decreasing surface area, due to the reduction in porosity and hence tortuosity within the apatite particles. This study has shown that altering the heat treatment conditions used to calcine hydroxyapatite may alter its drug delivery abilities, whereby calcination temperature was noted to influence the drug release behaviour to a greater extent than calcination time.

Advantages of using glycolic acid as a retardant in a brushite forming cement

In this study we have compared the effect of using acetic, glycolic, and citric acids on the brushite cement setting reaction and the properties of the resultant cement. The cement solid phase was made by mixing beta-tricalcium phosphate (beta-TCP), monocalcium dihydrogen phosphate anhydrate (MCPA), and sodium pyrophosphate, whereas the cement liquid phase consisted of aqueous solutions of carboxy acids at concentrations ranging from 0.5 to 3.5M. Cements were prepared by mixing the solid phase with the liquid phase to form a workable paste. The cement setting time was longer for glycolic and citric acids. The best mechanical properties in dry environments were obtained using glycolic and citric acid liquid phases. In a wet environment at 37 degrees C, the cement set with glycolic acid was the strongest one. Brushite cement diametral tensile strength seems to be affected by the calcium-carboxyl phase produced in the setting reaction. The acceptable setting time and mechanical properties of cements set in glycolic acid solutions are attributed to the additional hydrophilic groups in the carboxylic acid and the low solubility in water of the calcium salt produced in the reaction. Moreover, at high concentrations, carboxylic acids add chemically to the cement matrix becoming reactants themselves.

Fabrication and mechanical testing of porous calcium phosphate bioceramic granules

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) granules were fabricated by a novel technique of vacuum impregnation of reticulated polyurethane (PU) foams with ceramic slip. The resultant granules had 5-10% interconnected porosity with controlled pore sizes necessary to allow bone ingrowth combined with good mechanical properties. Using PU foams with a different number of pores per inch (ppi), porous HA/TCP granules in the size range of 2-8 mm were successfully manufactured. Dieplunger tests were used to compare the compression and relaxation properties of the granules with those of a commercially available bone graft product, BoneSave. The results of the die-plunger testing showed that the experimental granules were stiffer than the BoneSave materials and had less of a tendency to crumble to powder after testing. This therefore suggests that these experimental granules would be useful for impaction grafting and space filling applications.

Preparation of hydroxyapatite/poly(methyl methacrylate) and calcium silicate/poly(methyl methacrylate) interpenetrating hybrid composites

Hydroxyapatite/poly(methyl methacrylate) (HAp/PMMA) and calcium silicate/poly(methyl methacrylate) (CS/PMMA) composites were prepared by interpenetrating bulk polymerization of methyl methacrylate (MMA) monomer in porous structures of HAp and CS. The porous HAp and CS templates were prepared by mixing their calcined powders with poly(vinyl alcohol) (PVA) solution, shaping by uniaxial pressing and then firing at 1,100 degrees C for HAp and 900 degrees C for CS. The templates were soaked in the solution mixture of MMA monomer and 0.1 mol% of benzoyl peroxide (BPO) for 24 h. The pre-composites were then bulk polymerized at 85 degrees C for 24 h under nitrogen atmosphere. The microstructures of the composites showed the interpenetrating of PMMA into the porous HAp and CS structures. Thermogravimetric analysis indicated that the PMMA content in the HAp/PMMA and CS/PMMA composites were 13 and 26 wt%, respectively. Weight average molecular weights (M(w)) of PMMA were about 491,000 for HAp/PMMA composites and about 348,000 for CS/PMMA composites. Compressive strengths of these composites were about 90-131 MPa in which they were significantly higher than their starting porous templates.

Vertical bone augmentation with granulated brushite cement set in glycolic acid

Brushite cements are a biocompatible materials that are resorbed in vivo. A new cement composed of a mixture of monocalcium phosphate (MCP) and beta-tricalcium phosphate (beta-TCP) that sets using glycolic acid (GA) was synthesized and characterized. After setting, the cement composition, derived from X-ray diffraction, was 83 wt % brushite and 17 wt % beta-TCP with an average brushite crystal size of about 2.6 +/- 1.4 microm. The cement has a diametral tensile strength of 2.9 +/- 0.7 MPa. Granules prepared from the set-cement were used as grafting material in bone defects on rabbit calvaria for evaluating in vivo its bone regeneration capacity. Considerable cement resorption, improvement in the bone mineral density, and bone neoformation was observed after 4 weeks of the granules' implantation.

Synthesis of TiO(2)-PMMA nanocomposite: using methacrylic acid as a coupling agent

Inorganic-polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Methacrylic acid (MA), a functionalization agent that can chemically link TiO2 nanomaterials (n-TiO2) and polymer matrix, was used to modify the surface of n-TiO2 using a Ti-carboxylic coordination bond. Then, the double bond in MA was copolymerized with methyl methacrylate (MMA) to form a n-TiO2-PMMA nanocomposite. The resulting n-TiO2-PMMA nanocomposite materials were characterized by using thermal analysis, electron microscopy, and elemental analysis. The dynamic mechanical properties (Young's and shear modulus) were measured using an ultrasonic pulse technique. The electron microscopy results showed a good distribution of the nanofillers in the polymer matrix. The glass transition temperature, thermal degradation temperature, and dynamic elastic moduli of the nanocomposites were shown to increase with an increase in the weight percentage of nanofibers in the composite. The resulting nanocomposites exhibited improved elastic properties and have potential application in dental composites and bone cements.

Factors affecting the structure and properties of an injectable self-setting calcium phosphate foam

One of the main challenges in the investigation on calcium phosphate cements (CPC) lies in the introduction of macroporosity, without loosing the self-setting ability and injectability, characteristic of the cement-type materials. The benefits of macroporosity are related to the enhancement of bone regeneration mechanisms, such as angiogenesis and tissue ingrowth. In this work, the feasibility to obtain self-setting injectable macroporous hydroxyapatite foams by the incorporation of a protein-based foaming agent to a CPC is demonstrated. Albumen is combined with an alpha-tricalcium phosphate [Ca3(PO4)2, alpha-TCP] paste, which hydrolyzes to a calcium deficient hydroxyapatite during the setting reaction. A systematic study is presented, where the effect of different processing parameters is analyzed in terms of porosity, setting properties, injectability, and compressive strength. Self-setting foams with porosities up to 70%, which maintain their porous structure after injection, are obtained. These injectable foams can be used both for direct in vivo applications and for the fabrication of low temperature tissue engineering scaffolds.

Calcium phosphate cement: review of mechanical and biological properties

PURPOSE

Calcium phosphate cement is a bioactive and biodegradable grafting material in the form of powder and liquid, which when mixed, sets as primarily hydroxyapatite, sometimes mixed with unreacted particles and other phases. This material has been extensively investigated due to its excellent biological properties, potential resorbability, molding capabilities, and easy manipulation. Because the material can potentially be replaced with bone after a period of time, it could retain the short-term biological advantages of hydroxyapatite without the long-term disadvantages. Although little is known about this material in the dental community, in vivo and in vitro studies show calcium phosphate cement as a promising material for grafting applications. In the following article, the authors review the biological and mechanical properties of calcium phosphate cement, as well as its potential use in clinical applications.

MATERIALS AND METHODS

A Medline search was performed (timeline: 1980 to 2003) using the following keywords: calcium phosphate cement, hydroxyapatite cement, HA cement, and hydroxyapatite. The search was limited to the English language. The patent literature as well as a limited number of master's theses and books were reviewed after using the electronic database search service from a dental school library.

RESULTS

Calcium phosphate cement appears to have excellent biological properties. At only 2 weeks, spicules of living bone with normal bone marrow and osteocytes can be seen. Excellent moldability is a desired clinical characteristic; however, further research is necessary in order to improve the mechanical properties of the cement. The resorption/replacement by bone capability of the cement remains controversial. Further research is needed to clarify this issue. Due to poor mechanical properties, clinical applications are currently limited to craniofacial applications. Further research is necessary to take advantage of the excellent biological properties of this cement under clinical applications.

CONCLUSION

Further research is necessary to understand and improve the behavior of this type of cement under clinical situations.

[Preparation and properties of medical calcium phosphate cement]

The preparation of tetracalcium phosphate (Ca4(PO4)2O, TTCP)was studied. Then calcium phosphate cement (CPC) was prepared. The setting time, pH value, compressive strength, X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis of CPC were studied. The results show that TTCP containing small amount of CaO can be successfully attained heated at 1 500 degrees C for 6 h in vacuum condition. The initial setting time and final setting time of CPC is 4 min and 15 min, respectively. Its compressive strength is 20 MPa after 1-day immersion and 35 MPa after 7-day immersion. The pH value of the solution changes between 6.4 and 8.9. These properties can satisfy the clinical requirements of CPC. The final product of CPC is flake-like or needle-like hydroxyapatite (Ca5(P04)3OH, HA). The continuous network structure of HA appears in the microstructure, this leads to increase the strength of the material. This CPC can be used as bone substitute material.

Surface and chemical properties of surface-modified UHMWPE powder and mechanical and thermal properties of its impregnated PMMA bone cement, IV: effect of MMA/accelerator on the surface modification of UHMWPE powder

In our previous study, we manufactured a reinforced poly(methylmethacrylate) (PMMA) bone cement with 3 wt% of the surface-modified ultra high molecular weight polyethylene (UHMWPE) powder to improve its poor mechanical and thermal properties resulting from unreacted methylmethacrylate (MMA), the generation of bubble and shrinkage, and high curing temperature. In the present study, the effect of ratios of MMA and N,N'-dimethyl-p-toluidine (DMPT) solutions in redox polymerization system was investigated for the surface modification of UHMWPE powder. We characterized physical and chemical properties of surface-modified UHMWPE powder and reinforced bone cements by a scanning electron microscope, ultimate tensile strength (UTS) and curing temperature (Tmax). It was found that UTSs (41.3-51.3 MPa) of the reinforced PMMA bone cements were similar to those (44.5 MPa) of conventional PMMA bone cement (control), as well as significantly higher (P < 0.05) than those (33.8 MPa) of 3 wt% unmodified UHMWPE powder-impregnated bone cement. In particular, the UTS of redox polymerization system using MMA/DMPT solution was better than that of radical system using MMA/xylene solution. Also, Tmax of the reinforced PMMA bone cements decreased from 103 to 72-84 degrees C. From these results, we confirmed that the surface-modified UHMWPE powder can be used as reinforcing agent to improve the mechanical and thermal properties of conventional PMMA bone cement.

Development of a nonrigid, durable calcium phosphate cement for use in periodontal bone repair

BACKGROUND

Calcium phosphate cement (CPC) hardens in situ to form hydroxyapatite and has been used in dental and craniofacial restorative applications. However, when CPC was used in periodontal osseous repair, tooth mobility resulted in the fracture and exfoliation of the brittle CPC implant. The objective of the authors' study was to develop a strong and nonrigid CPC to provide compliance for tooth mobility without fracturing the implant.

METHODS

The authors used tetracalcium phosphate, dicalcium phosphate anhydrous and biopolymer chitosan to develop a strong and nonrigid CPC. They used a powder:liquid ratio of 2:1, compared with the 1:1 ratio of a previously developed nonrigid CPC control. Specimens were characterized using a flexural test, scanning electron microscopy and powder X-ray diffraction.

RESULTS

After 28 days of immersion, the new cement had a flexural strength (mean +/- standard deviation; n = 6) of 5.2 +/- 1.0 megapascals, higher than 1.8 +/- 1.5 MPa for the control (P < .05) and overlapping the reported strengths of sintered hydroxyapatite implants and cancellous bone. This cement showed a high ductility with a strain at peak load of 6.5 +/- 1.3 percent, compared with 4.4 +/- 1.9 percent for the control; both were 20-fold higher than the 0.2 percent of the conventional CPC. Nanosized hydroxyapatite crystals, similar to those in teeth and bones, were formed in the cements.

CONCLUSIONS

The new nonrigid cement, containing nanohydroxyapatite crystals, possessed a high ductility and superior fracture resistance. This strong, tough and nonrigid CPC may be useful in periodontal repair to provide compliance for tooth mobility without fracture.

CLINICAL IMPLICATIONS

The results of this study may yield the first self-hardening and nonrigid hydroxyapatite composite with high strength and durability and large deformation capability to be useful in the regeneration of periodontal osseous defects.

Preparation, physical–chemical characterisation and cytocompatibility of calcium carbonate cements

The feasibility of calcium carbonate cements involving the recrystallisation of metastable calcium carbonate varieties has been demonstrated. Calcium carbonate cement compositions presented in this paper can be prepared straightforwardly by simply mixing water (liquid phase) with two calcium carbonate phases (solid phase) which can be easily obtained by precipitation. An original cement composition was obtained by mixing amorphous calcium carbonate and vaterite with an aqueous medium. The cement set and hardened within 2h at 37 degrees C in an atmosphere saturated with water and the final composition of the cement consisted mostly of aragonite. The hardened cement was microporous and showed poor mechanical properties. Cytotoxicity tests revealed excellent cytocompatibility of calcium carbonate cement compositions. Calcium carbonates with a higher solubility than the apatite formed for most of the marketed calcium phosphate cements might be of interest to increase biomedical cement resorption rates and to favour its replacement by bone tissue.

Dynamic void behavior in polymerizing polymethyl methacrylate cement

Cement mantle voids remain controversial with respect to survival of total hip arthroplasty. Void evolution is poorly understood, and attempts at void manipulation can only be empirical. We induced voids in a cement model simulating the constraints of the proximal femur. Intravoid pressure and temperature were recorded throughout polymerization, and the initial and final void volumes were measured. Temperature-dependent peak intravoid pressures and void volume increases were observed. After solidification, subatmospheric intravoid pressures were observed. The magnitude of these observations could not be explained by the ideal gas law. Partial pressures of the void gas at peak pressures demonstrated a dominant effect of gaseous monomer, thereby suggesting that void growth is a pressure-driven phenomenon resulting from temperature-dependent evaporation of monomer into existing trapped air voids.

[Preparation and properties of calcium silicate-phosphate composite bone cements]

In this paper, alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate (TTCP) respectively were chosen as basic compositions of phosphate bone cements. Other auxiliary materials such as hydroxyapatite (HAP), dicalcium phosphate dihydrate (DCPD), calcium carbonate (CaCO3), calcium oxide (CaO) and amorphous calcium silicate (CaSiO3) were added in the cements. Six kinds of composite bone cements were decided with 1.50 as their Ca/P ratio. Then the primary properties of them were studied. Ringer's simulated body fluid (SBF) tests were carried out for the samples. The changes of pH value in SBF and the compressive strength of the samples with the immersion time were studied. The results showed: the mixing liquid 0.25 M K2HPO4/KH2PO4 and amorphous CaSiO3 were effective for accelerating the setting of the cements; the initial setting time (It) was about 4-5.5 min and the final setting time (Ft) was about 18-19. 5 min. Amorphous calcium silicate can increase the compressive strength of the bone cements remarkably; the compressive strength of the alpha-TCP bone cement with the addition of suitable amount amorphous CaSiO3 reached 45.3 MPa after immersion in SBF for 14 days.

Surface and chemical properties of surface-modified UHMWPE powder and mechanical and thermal properties of it impregnated PMMA bone cement, III: effect of various ratios of initiator/inhibitor on the surface modification of UHMWPE powder

From our previous study, 3 wt% of ultra-high-molecular-weight polyethylene (UHMWPE) powder surface-modified by various ratios of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) solution was impregnated to improve the poor mechanical and thermal properties of conventional PMMA bone cement. In this study, various amounts of benzoyl peroxide (BPO) and hydroquinone were used for the adhesion reinforcement of UHMWPE powder with PMMA polymerized from MMA monomer (polyMMA) by the mixture of BPO and hydroquinone and ultimately to strengthen the poor mechanical and thermal properties of conventional PMMA bone cement. The tensile strengths of 3 wt% of UHMWPE powders surface-precoated with polyMMA prepared by various amounts of BPO- and hydroquinone-impregnated composite PMMA bone cements were similar to that of conventional PMMA bone cement. In particular, 3 wt% of UHMWPE powder surface precoated with polyMMA prepared with 0.75 wt% of BPO and 300 ppm of hydroquinone impregnated composite PMMA bone cement revealed the maximum tensile strength. However, no obvious significant difference was revealed, although the curing temperatures of the composite PMMA bone cements decreased from 103 degrees C to 91-97 degrees C. From these results, it was determined that the mixture of BPO and hydroquinone plays an important role in improving the poor mechanical properties of conventional PMMA bone cement. However, the thermal properties of the composite PMMA bone cements were not remarkably improved. The mechanical, chemical and thermal properties were individually confirmed using a scanning electron microscope (SEM), universal transverse mercator (UTM), Fourier transform infrared-attenuated total reflectance (FT-IR-ATR) and digital thermometer, respectively.

Vertebroplasty by use of a strontium-containing bioactive bone cement

STUDY DESIGN

A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement.

OBJECTIVES

To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements.

SUMMARY OF BACKGROUND DATA

Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications.

METHODS

Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented.

RESULTS

The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain.

DISCUSSIONS

Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.

The processing, mechanical properties and bioactivity of zinc based glass ionomer cements

The suitability of Glass Ionomer Cements (GICs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of a GIC and its absence is likely to hinder cement formation. However, zinc oxide, a bacteriocide, can act both as a network modifying oxide and an intermediate oxide in a similar fashion to alumina and so ternary systems based on zinc silicates often have extensive regions of glass formation. The purpose of this research was to produce novel GICs based on calcium zinc silicate glasses and to evaluate their rheological, mechanical and biocompatible properties with the ultimate objective of developing a new range of cements for skeletal applications. The work reported shows that GICs based on two different glasses, A and B (0.05CaO.0.53ZnO.0.42SiO2 and 0.14CaO.0.29ZnO.0.57SiO2, respectively), exhibited handling properties and flexural strengths comparable to conventional GICs. Upon immersion in simulated body fluid of a GIC based on glass B, an amorphous calcium phosphate layer nucleated on the surface of the cement indicating that these cements are bioactive in nature.

Effects of incorporation of HA/ZrO2 into glass ionomer cement (GIC)

Glass ionomer cements (GICs) are a class of bioactive cements that bond directly to bone. In this paper, a new bioactive hydroxyapatite (HA)/zirconia (ZrO(2))-filled GIC composite was developed to improve the biocompatibility and bioactivity of the GICs with the surrounding bone and connective tissues. Nano-sized HA/30 wt% ZrO(2) powders were heat treated at 700 degrees Celsius and 800 degrees Celsius for 3 h to elucidate the influence of the crystallinity of composite powders on the performance of HA/ZrO(2)-GICs. The effects of different volume percentages of HA/ZrO(2) powders (4, 12, 28 and 40 vol%) substituted within GICs were investigated based on their microhardness, compressive strength and diametral tensile strength. The HA/ZrO(2)-GICs composite was soaked in distilled water for 1 day and 1 week before subjecting the samples to mechanical testing. Results showed that the glass and HA/ZrO(2) particles were distributed uniformly in the GIC matrix. The substitution of highly crystalline HA/ZrO(2) improved the mechanical properties of the HA/ZrO(2)-GICs due to the slow resorption rate for highly crystalline powders in distilled water. The mechanical properties of HA/ZrO(2)-GICs increased with increasing soak time due to the continuous formation of aluminium salt bridges, which improved the final strength of the cements. The compositions 4 and 12 vol% HA/ZrO(2)-GICs exhibited superior mechanical properties than the original GICs. The mechanical properties of HA/ZrO(2)-GICs were found to be much better than those of HA-GICs because ZrO(2) has the attributes of high strength, high modulus, and is significantly harder than glass and HA particles. Furthermore, ZrO(2) does not dissolve with increasing soaking time.

Ionic modification of calcium phosphate cement viscosity. Part I: hypodermic injection and strength improvement of apatite cement

A broadening of the indications for which calcium phosphate cements (CPC) can be used, for example, in the field of vertebroplasty, would require injectable and higher strength materials. Unmodified CPC are not injectable due to a filter-pressing effect during injection. In this work we demonstrated that an effective method for improving the injection properties of CPC was by the use of sodium citrate solution as a liquid component. Cement consisting of tetracalcium phosphate (TTCP) and monetite (DCPA) mixed with water up to a powder:liquid ratio (P:L) of 3.3 g/ml had an injectability of approximately 60%. The use of 500 mM trisodium citrate solution instead of water decreased the viscosity of the cement paste to a point, where complete injectability (>95%) through an 800 microm diameter hypodermic needle could be achieved at low loads. The reduction in water demand of the cement effected by the use of sodium citrate enabled high P:L mixes to be formed which were 400% stronger than cements made with water. The effect was less pronounced with compacted cements such that at 9 MPa applied pressure, 58% improvement was obtained and at 50 MPa 36% improvement was measured yielding a cement with a compressive strength of 154 MPa. The liquefying effect of sodium citrate was thought to derive from a strong increase in the surface charge of both the reactants and the product as determined by zeta-potential measurement.

The chemistry of acrylic bone cements and implications for clinical use in image-guided therapy

Advances in image-guided therapy for vertebral fractures and other bone-related disorders have made acrylic bone cement an integral part of the interventional armamentarium. Unfortunately, information on the properties and chemistry of these compounds is mostly published in the biomaterial sciences literature, a source with which the interventional community is generally unfamiliar. This review focuses on the chemistry of bone cement polymerization and the properties of components in polymethylmethacrylate (PMMA)-based polymers, the most commonly used bone cements in interventional procedures such as percutaneous vertebroplasty. The effects of altering the concentration of components such as methylmethacrylate monomers, PMMA beads, benzoyl peroxide activator, N,N-dimethyl-p-toluidine (DMPT) initiator, and radiopacifiers on the setting time, polymerization temperature, and compressive strength of the cement are also considered. This information will allow interventional radiologists to manipulate bone cement characteristics for specific applications and maximize the clinical potential of image-guided interventions.