Non-decay type fast-setting calcium phosphate cement: hydroxyapatite putty containing an increased amount of sodium alginate

Design of bioresorbable calcium phosphate cement with high porosity via the addition of bioresorbable polymers

Novel calcium phosphate cements (CPCs) that can be resorbed into the human body need to be developed. One approach for improving bioresorbability is reducing the content of calcium phosphate in CPCs; however, this may induces difficulties in setting the cement and increases the risk of decay. Adding bioresorbable polymers to a liquid solution can shorten the setting time and inhibit decay during setting. A novel bioresorbable polymer, phosphorylated pullulan (PPL), was recently reported. The effect of adding PPL to α-tricalcium phosphate (α-TCP)-based CPCs was examined and compared to that of adding bioresorbable polymers such as collagen, chitosan, and alginate. Collagen did not significantly inhibit the conversion of α-TCP to hydroxyapatite (HA), and its combination with calcium phosphate decreased the setting time and suppressed decay; chitosan decreased the setting time when combined with calcium phosphate; and alginate inhibited the conversion of α-TCP to HA and contributed to suppressing the decay. In contrast, PPL slightly inhibited the conversion of α-TCP to HA; however, its combination with calcium phosphate decreased the setting time. Thus, selecting bioresorbable polymers can help effectively control the properties of CPCs.

Calcium-Enriched Nanofibrillated Cellulose/Poloxamer in-situ Forming Hydrogel Scaffolds as a Controlled Delivery System of Raloxifene HCl for Bone Engineering

PURPOSE

TEMPO-oxidized nanofibrillated cellulose (TONFC) originating from an agricultural waste (sugar cane) was utilized to prepare injectable in-situ forming hydrogel scaffolds (IHS) for regenerative medicine.

METHODS

TONFC was prepared and characterized for its morphology and chemical structure using TEM and FT-IR, respectively. The cold method was applied to prepare hydrogels. Various concentrations of poloxamer 407 were added to the prepared TONFC (0.5%w/w). Different sources of calcium, Fujicalin® (DCP) or hydroxyapatite (TCP), were used to formulate the aimed calcium-enriched raloxifene hydrochloride-loaded IHS. Gelation temperature, drug content, injectability and in-vitro drug release were evaluated along with the morphological characters. Cytocompatibility studies and tissue regeneration properties were assessed on Saos-2 cells.

RESULTS

TEM photograph of TONFC showed fibrous nanostructure. The selected formulation "Ca-IHS4" composed of TONFC+15% P407+10% TCP showed the most prolonged release pattern for 12 days with the least burst effect (about 25% within 24 h). SEM micro-photographs of the in-situ formed scaffolds showed a highly porous 3D structure. Cytocompatibility studies of formulation "Ca-IHS4" revealed the biocompatibility as well as improved cell adhesion, alkaline phosphatase enzyme activity and calcium ion deposition.

CONCLUSION

The outcomes suggest that Ca-IHS4 presents a simple, safe-line and non-invasive strategy for bone regeneration.

Biomechanical Evaluation of an Injectable Alginate / Dicalcium Phosphate Cement Composites for Bone Tissue Engineering

Biocompatible dicalcium phosphate (DCP) cements are widely used as bone repair materials. In this study, we aimed to investigate the impact of different amounts of sodium alginate (SA) on the microstructural, mechanical, and biological properties of DCP cements. Beta-tricalcium phosphate (β-TCP) was prepared using a microwave-assisted wet precipitation system. Lattice parameters of the obtained particles determined from X-ray diffraction (XRD), were in good match with a standard phase of β-TCP. Scanning electron microscopy (SEM) examination revealed that the particles were in globular shape. Furthermore, all functional groups of β-TCP were also detected using Fourier-transform infrared spectroscopy (FTIR) spectra. DCP cement (pure phase) was synthesized using monocalcium phosphate monohydrate (MCPM)/β-TCP powder mixture blended with 1.0 mL of water. SA/DCP cement composites were synthesized by dissolving different amounts of SA into water (1.0 mL) to obtain different final concentrations (0.5%, 1%, 2% and 3%). The prepared cements were characterized with XRD, SEM, FTIR and Thermogravimetric analysis (TGA). XRD results showed that pure DCP and SA/DCP cements were in a good match with Monetite phase. SEM results confirmed that addition of SA inhibited the growth of DCP particles. Setting time and injectability behaviour were significantly improved upon increasing the SA amount into DCP cements. In vitro biodegradation was evaluated using Simulated body fluid (SBF) over 21 days at 37 °C. The highest cumulative weight loss (%) in SBF was observed for 2.0% SA/DCP (about 26.52%) after 21 days of incubation. Amount of Ca²⁺ ions released in SBF increased with the addition of SA. DCP and SA/DCP cements showed the highest mechanical strength after 3 days of incubation in SBF and declined with prolonged immersion periods. In vitro cell culture experiments were conducted using Dental pulp stem cells (DPSCs). Viability and morphology of cells incubated in extract media of DCP and SA/DCP discs after 24 h incubation was studied with MTT assay and fluorescence microscopy imaging, respectively. All cements were cytocompatible and viability of cells incubated in extracts of cements was higher than observed in the control group. Based on the outcomes, SA/DCP bone cements have a promising future to be utilized as bone filler.

Enhanced antibacterial activity of calcium silicate-based hybrid cements for bone repair

Calcium silicate cement has attracted much attention for bone defect repair and regeneration due to its osteogenic properties. Biomaterial-associated infections and washout have become a common clinical problem. In order to enhance the antibacterial and washout performance of calcium silicate cement to meet clinical needs, different types of chitosan, including chitosan polysaccharide (CTS), quaternary ammonium chitosan (QTS), and chitosan oligosaccharide (COS), as a liquid phase were added to the calcium silicate powder. The physicochemical properties, in vitro bioactivity, antibacterial efficacy, and osteogenic effects (MG63 cells) of the cement were evaluated. Antibacterial activity was conducted with Gram-negative Escherichia coli (E. coli) and a Gram-positive Staphylococcus aureus (S. aureus) bacteria. The amount of intracellular reactive oxygen species (ROS) produced in the bacteria cultured with the chitosan solution was also detected. The experimental results showed that the chitosan additive did not affect the crystalline phase of calcium silicate cement, but increased the setting time and strength of the cement in a concentration-dependent manner. Within the scope of this study, CTS and QTS solutions with a concentration of not <1 wt% improved the washout resistance of the control cement, while the COS solutions failed to strengthen the cement. When soaked in simulated body fluid (SBF) for 1 day, all cement samples formed apatite spherules. As the soaking time increased, the diametral tensile strength of all cements decreased and the porosity increased. The assays of MG63 cell function showed lower osteogenic activity of osteoblastic cells grown on the surfaces of the chitosan-incorporated cements in comparison with the control cement without chitosan. At the same 1% concentration, compared with QTS and COS cement, CTS cement had lower cell attachment, proliferation, differentiation, and mineralization. Conversely, the CTS cement resulted in the highest bacteriostasis ratio among the three hybrid cements against two bacteria. The ROS production followed the order of CTS > QTS > COS at the same 1% concentration. In conclusion, calcium silicate cement with 1% QTS may be a viable candidate for bone defect repair in view of anti-washout performance, setting time, antibacterial activity, and osteogenic activity shown in this study.

Fabrication of alginate modified brushite cement impregnated with antibiotic: Mechanical, thermal, and biological characterizations

Treatment of postsurgical infections, associated with orthopedic surgeries, has been a major concern for orthopedics. Several strategies including systematic and local administration of antibiotics have been proposed to this regard. The present work focused on fabricating alginate (Alg) modified brushite (Bru) cements, which could address osteogeneration and local antibiotic demands. To find the proper method of drug incorporation, Gentamicin sulfate (Gen) was loaded into the samples in the form of solution or powder. Several characterization tests including compression test, morphology, cytotoxicity, and cell adhesion assays were carried out to determine the proper concentration of Alg as a modifier of the Bru cement. The results indicated that addition of 1 wt% Alg led to superior mechanical and biological properties of the cement. Moreover, Alg addition changed the morphology of the cement from plate and needle-like structures to petal-like structure. Fourier transform infrared spectroscopy results confirmed the successful loading of Gen on the cements, specifically when Gen solution was used, and X-Ray Diffractometer result indicated that Gen caused a decrease in crystalline size. Furthermore, thermal analysis revealed that Gen-loaded sample had more stable structure as the transformation temperature slightly shifted to a higher one. The stability study confirmed the chemical stability and adequate mechanical performance of the cements within 1 month of soaking time. Finally, the addition of Alg has a positive impact on the release behavior at low concentration of Gen solution so that 20% decrease within 2 weeks of release experiment was remarkably detected.

Sealing ability of Biodentine versus ProRoot mineral trioxide aggregate as root-end filling materials

Aim

This study evaluated the sealing ability of ProRoot MTA and Biodentine as root-end filling materials.

Method

In total, twenty (N = 20) extracted human maxillary central incisor teeth were decontaminated, cleaned and decoronated. Instrumentation was performed according to the step back technique using #50 Flex-o-file. Then the canals were flared to #70 Flex-o-file. Obturation was performed with conventional gutta percha and a resinous sealer (AH26) using the lateral condensation technique. Resection of 3 mm of apical end of each root was achieved perpendicular to the long axis of the root. Root-end cavity was prepared in each sample ultrasonically then filled with tested materials (N = 10). Fluid filtration method was used to assess the sealing ability of each tested material at three different experimental periods; one day, one week and one month after setting. All data were tabulated and statistically analyzed with a level of significance set at P ≤ .05.

Results

At each specific time interval, the leakage mean values were not consistent among the tested materials. At one day interval, ProRoot MTA samples had a higher leakage mean value than Biodentine samples. However, this difference in leakage was not statistically significant (P > .05). At one week interval, both materials showed an increased degree of leakage mean value with no significant difference (P > .05). At one month interval, ProRoot MTA samples showed a decrease in leakage mean value, while the Biodentine samples showed a further increase in leakage mean value. This difference was statistically significant (P < .05).

Conclusion

Although the sealing ability of ProRoot MTA is superior to Biodentine, Biodentine could be considered as an acceptable alternative to ProRoot MTA in peri-radicular surgeries.

Combined delivery of bone morphogenetic protein-2 and insulin-like growth factor-1 from nano-poly (γ-glutamic acid)/β-tricalcium phosphate-based calcium phosphate cement and its effect on bone regeneration in vitro

In this study, nano-doped calcium phosphate cement delivery systems (poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramics and nano (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic) were fabricated, and low doses (10 µg/g) of two growth factors, insulin-like growth factor-1 and bone morphogenetic protein-2, were encapsulated then sequentially released. We characterized the delivery systems using Fourier transform infrared spectroscopy and X-ray diffraction and measured washout resistance and compressive strength, and thus optimized the most appropriate proportioning of delivery systems for the two growth factors. One of the growth factors was absorbed by the nano-poly (γ-glutamic acid)/β-tricalcium phosphate, which was then mixed into the calcium phosphate ceramic solid phase to create a new solid phase calcium phosphate ceramic. Nano-poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic carriers were then prepared by blending the new calcium phosphate ceramic solid phase powder with a solution of the remaining growth factor. The effects of different release patterns (studying sequential behavior) of insulin-like growth factor-1 and bone morphogenetic protein-2 on osteogenic proliferation and differentiation of the MC3t3-E1 mouse osteoblast cell were investigated. This combinational delivery system provided a controlled release of the two growth factors, in which nano-doping significantly affected their release kinetics. The incorporation of dual growth factors could potentially stimulate bone healing and promoting bone ingrowth processes at a low dose.

Effects of Adding Polysaccharides and Citric Acid into Sodium Dihydrogen Phosphate Mixing Solution on the Material Properties of Gelatin-Hybridized Calcium-Phosphate Cement

We have succeeded in improving the material properties of a chelate-setting calcium-phosphate cement (CPC), which is composed of hydroxyapatite (HAp) the surface of which has been modified with inositol hexaphosphate (IP6) by adding α-tricalcium phosphate (α-TCP) powder. In order to create a novel chelate-setting CPC with sufficient bioresorbability, gelatin particles were added into the IP6-HAp/α-TCP cement system to modify the material properties. The effects of adding polysaccharides (chitosan, chondroitin sulfate, and sodium alginate) into the sodium dihydrogen phosphate mixing solution on the material properties of the gelatin-hybridized CPC were evaluated. The results of mechanical testing revealed that chondroitin sulfate would be the most suitable for fabricating the hybridized CPC with higher compressive strength. Moreover, further addition of an appropriate amount of citric acid could improve the anti-washout capability of the cement paste. In summary, a gelatin-hybridized IP6-HAp/α-TCP cement system prepared with a mixing solution containing chondroitin sulfate and citric acid is expected to be a beneficial CPC, with sufficient bioresorbability and material properties.

Preparation of hydroxyapatite/collagen injectable bone paste with an anti-washout property utilizing sodium alginate. Part 1: influences of excess supplementation of calcium compounds

The anti-washout property, viscosity, and cytocompatibility to an osteoblastic cell line, MG-63, of anti-washout pastes were investigated. Mixing a hydroxyapatite/collagen bone-like nanocomposite (HAp/Col), an aqueous solution of sodium alginate (Na-Alg), which is a paste hardening and lubricant agent, and supplementation of calcium carbonate or calcium citrate (Ca-Cit) as a calcium resource for the hardening reaction realized an injectable bone paste. Adding Ca-Cit at a concentration greater than eight times the Ca²⁺ ion concentration to Na-Alg improved the anti-washout property. Although the viscosity test indicated a gradual increase in the paste viscosity as the calcium compounds increased, pastes with excess supplementation of calcium compounds exhibited injectability through a syringe with a 1.8 mm inner diameter, realizing an injectable bone filler. Furthermore, the anti-washout pastes with Ca-Cit had almost the same cell proliferation rate as that of the HAp/Col dense body. Therefore, HAp/Col injectable anti-washout pastes composed of the HAp/Col, Na-Alg, and Ca-Cit are potential candidates for bioresorbable bone filler pastes.

Preparation, characterization and in vitro cell performance of anti-washout calcium phosphate cement modified by sodium polyacrylate

The anti-washout ability of calcium phosphate cement (CPC) is essential for its application in massive hemorrhage regions. Sodium polyacrylate (PAAS) could be used to improve the anti-washout property of CPC paste.

Novel bone wax based on poly(ethylene glycol)-calcium phosphate cement mixtures

Classic bone wax is associated with drawbacks such as the risk of infection, inflammation and hindered osteogenesis. Here, we developed a novel self-setting bone wax on the basis of hydrophilic poly(ethylene glycol) (PEG) and hydroxyapatite (HA) forming calcium phosphate cement (CPC), to overcome the problems that are linked to the use of conventional beeswax systems. Amounts of up to 10 wt.% of pregelatinized starch were additionally supplemented as hemostatic agent. After exposure to a humid environment, the PEG phase dissolved and was exchanged by penetrating water that interacted with the HA precursor (tetracalcium phosphate (TTCP)/monetite) to form highly porous, nanocrystalline HA via a dissolution/precipitation reaction. Simultaneously, pregelatinized starch could gel and supply the bone wax with liquid sealing features. The novel bone wax formulation was found to be cohesive, malleable and after hardening under aqueous conditions, it had a mechanical performance (∼2.5 MPa compressive strength) that is comparable to that of cancellous bone. It withstood systolic blood pressure conditions for several days and showed antibacterial properties for almost one week, even though 60% of the incorporated drug vancomycin hydrochloride was already released after 8h of deposition by diffusion controlled processes.

STATEMENT OF SIGNIFICANCE

The study investigated the development of alternative bone waxes on the basis of a hydroxyapatite (HA) forming calcium phosphate cement (CPC) system. Conventional bone waxes are composed of non-biodegradable beeswax/vaseline mixtures that are often linked to infection, inflammation and hindered osteogenesis. We combined the usage of bioresorbable polymers, the supplementation with hemostatic agents and the incorporation of a mineral component to overcome those drawbacks. Self-setting CPC precursors (tetracalcium phosphate (TTCP), monetite) were embedded in a resorbable matrix of poly(ethylene glycol) (PEG) and supplemented with pregelatinized starch. This formulation was found to be malleable and cohesive underwater. While immersion in an aqueous environment, CPC precursors formed highly porous, nanocrystalline HA via dissolution/precipitation reaction as water penetrated the novel wax formulation and PEG molecules simultaneously dissolved. The bone wax further withstood blood pressure conditions. After hardening, mechanical performance was comparable to that of cancellous bone and we also successfully provided the bone wax with antibacterial properties. In our opinion, the described bone wax formulation outmatches conventional bone waxes, as it circumvents the detriments being associated with the term "bone wax". Our wax has a novel composition and would broaden the application of CPC and besides, the general interest in bone waxes will increase, as they were long considered as a "first-line treatment" to avoid.

Novel bioactive nanocomposite cement formulations with potential properties: incorporation of the nanoparticle form of mesoporous bioactive glass into calcium phosphate cements

Novel calcium phosphate cements incorporated with bioactive glass nanoparticles demonstrate excellent properties for bone injectables.

Effect of tricalcium aluminate on the physicochemical properties, bioactivity, and biocompatibility of partially stabilized cements

Background/Purpose

Mineral Trioxide Aggregate (MTA) was widely used as a root-end filling material and for vital pulp therapy. A significant disadvantage to MTA is the prolonged setting time has limited the application in endodontic treatments. This study examined the physicochemical properties and biological performance of novel partially stabilized cements (PSCs) prepared to address some of the drawbacks of MTA, without causing any change in biological properties. PSC has a great potential as the vital pulp therapy material in dentistry.

Methods

This study examined three experimental groups consisting of samples that were fabricated using sol-gel processes in C3S/C3A molar ratios of 9/1, 7/3, and 5/5 (denoted as PSC-91, PSC-73, and PSC-55, respectively). The comparison group consisted of MTA samples. The setting times, pH variation, compressive strength, morphology, and phase composition of hydration products and ex vivo bioactivity were evaluated. Moreover, biocompatibility was assessed by using lactate dehydrogenase to determine the cytotoxicity and a cell proliferation (WST-1) assay kit to determine cell viability. Mineralization was evaluated using Alizarin Red S staining.

Results

Crystalline phases, which were determined using X-ray diffraction analysis, confirmed that the C3A contents of the material powder differed. The initial setting times of PSC-73 and PSC-55 ranged between 15 and 25 min; these values are significantly (p<0.05, ANOVA and post-hoc test) lower than those obtained for MTA (165 min) and PSC-91 (80.5 min). All of the PSCs exhibited ex vivo bioactivity when immersed in simulated body fluid. The biocompatibility results for all of the tested cements were as favorable as those of the negative control, except for PSC-55, which exhibited mild cytotoxicity.

Conclusion

PSC-91 is a favorable material for vital pulp therapy because it exhibits optimal compressive strength, a short setting time, and high biocompatibility and bioactivity.

Development of calcium phosphate/sulfate biphasic cement for vital pulp therapy

OBJECTIVES

Bioactive calcium phosphate cement (CPC) has been used widely to repair bone defects because of its excellent biocompatibility and bioactivity. However, the poor handling properties, low initial mechanical strength, and long setting time of CPC limit its application in vital pulp therapy (VPT). The aim of this study was to synthesize biphasic calcium phosphate/sulfate cements and evaluate the feasibility of applying these cements in VPT.

METHODS

The physical, chemical, and mechanical properties of CPC were improved by mixing the cement with various amounts of α-calcium sulfate hemihydrate (CSH). The hydration products and crystalline phases of the materials were characterized using scanning electron microscopy and X-ray diffraction analysis. In addition, the physical properties, such as the setting time, compressive strength, viscosity, and pH were determined. Water-soluble tetrazolium salt-1 and lactase dehydrogenase were used to evaluate cell viability and cytotoxicity.

RESULTS

The developed CPC (CPC/CSH cement), which contains 50wt% CSH cement, exhibited no obvious temperature increase or pH change during setting when it was used as a paste. The initial setting time of the CPC/CSH biphasic cement was substantially shorter than that of CPC, and the initial mechanical strength was 23.7±5.6MPa. The CPC/CSH cement exhibited higher viscosity than CPC and, thus, featured acceptable handling properties. X-ray diffraction analysis revealed that the relative peak intensity for hydroxyapatite increased, and the intensity for calcium sulfate dehydrate decreased as the amount of CPC was increased. The cell viability and cytotoxicity test results indicated that the CPC/CSH cement did not harm dental pulp cells.

SIGNIFICANCE

The developed CPC/CSH biphasic cement exhibits substantial potential for application in VPT.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Calcium phosphate cements as drug delivery materials

Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.

Calcium phosphate ceramic systems in growth factor and drug delivery for bone tissue engineering: a review

Calcium phosphates (CaPs) are the most widely used bone substitutes in bone tissue engineering due to their compositional similarities to bone mineral and excellent biocompatibility. In recent years, CaPs, especially hydroxyapatite and tricalcium phosphate, have attracted significant interest in simultaneous use as bone substitute and drug delivery vehicle, adding a new dimension to their application. CaPs are more biocompatible than many other ceramic and inorganic nanoparticles. Their biocompatibility and variable stoichiometry, thus surface charge density, functionality, and dissolution properties, make them suitable for both drug and growth factor delivery. CaP matrices and scaffolds have been reported to act as delivery vehicles for growth factors and drugs in bone tissue engineering. Local drug delivery in musculoskeletal disorder treatments can address some of the critical issues more effectively and efficiently than the systemic delivery. CaPs are used as coatings on metallic implants, CaP cements, and custom designed scaffolds to treat musculoskeletal disorders. This review highlights some of the current drug and growth factor delivery approaches and critical issues using CaP particles, coatings, cements, and scaffolds towards orthopedic and dental applications.

Polymeric additives to enhance the functional properties of calcium phosphate cements

The vast majority of materials used in bone tissue engineering and regenerative medicine are based on calcium phosphates due to their similarity with the mineral phase of natural bone. Among them, calcium phosphate cements, which are composed of a powder and a liquid that are mixed to obtain a moldable paste, are widely used. These calcium phosphate cement pastes can be injected using minimally invasive surgery and adapt to the shape of the defect, resulting in an entangled network of calcium phosphate crystals. Adding an organic phase to the calcium phosphate cement formulation is a very powerful strategy to enhance some of the properties of these materials. Adding some water-soluble biocompatible polymers in the calcium phosphate cement liquid or powder phase improves physicochemical and mechanical properties, such as injectability, cohesion, and toughness. Moreover, adding specific polymers can enhance the biological response and the resorption rate of the material. The goal of this study is to overview the most relevant advances in this field, focusing on the different types of polymers that have been used to enhance specific calcium phosphate cement properties.

Evaluation of cross-linked chitosan microparticles for bone regeneration

The objective of this preliminary study was to evaluate the applying of chitosan (CS)-based microparticles (MPs) in bone regeneration in vivo. The CS MPs were fabricated using our scale-up method, as previously described. Mesenchymal stem cells (MSC) were harvested from the femora and tibiae of Dark Agouti (DA) rats and seeded on CS MPs. An in vitro MSCs attachment experiment was conducted by trypsinizing the cells attached to the MPs at 5, 10, 20 and 30 h. Fluorescence images of MSCs attached to the MPs were taken at 24 and 48 h, using a LIVE/DEAD cell assay. The MSC/osteoblasts (OB) seeded on MPs were then cultured in vitro using osteogenic media and implanted into partial thickness bone defects in rat femurs. There were two groups of rats, including experimental animals and controls, for the in vivo studies. The experimental group were implanted with MSC-seeded MPs and observed at 4 and 8 weeks. The control group of rats did not receive any implant material except the stainless steel plate to support the defect. Four rats per group were used for the study. The femurs were extracted at 4 and 8 weeks post-implantation and bone formation at the defect site was analysed using radiography, microcomputed tomography (µCT) and histology. Among all groups, a significant increase in bone formation was observed in the experimental group at 8 weeks implantation. The results of this study suggested that CS MPs prove to be a successful biomaterial for bone regeneration.

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.

New processing approaches in calcium phosphate cements and their applications in regenerative medicine

The key feature of calcium phosphate cements (CPCs) lies in the setting reaction triggered by mixing one or more solid calcium phosphate salts with an aqueous solution. Upon mixture, the reaction takes place through a dissolution-precipitation process which is macroscopically observed by a gradual hardening of the cement paste. The precipitation of hydroxyapatite nanocrystals at body or room temperature, and the fact that those materials can be used as self-setting pastes, have for many years been the most attractive features of CPCs. However, the need to develop materials able to sustain bone tissue ingrowth and be capable of delivering drugs and bioactive molecules, together with the continuous requirement from surgeons to develop more easily handling cements, has pushed the development of new processing routes that can accommodate all these requirements, taking advantage of the possibility of manipulating the self-setting CPC paste. It is the goal of this paper to provide a brief overview of the new processing developments in the area of CPCs and to identify the most significant achievements.

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.

Vertical bone augmentation with fluvastatin in an injectable delivery system: a rat study

OBJECTIVES

HMG-CoA reductase inhibitors (statins) are widely used for hyperlipidemia. Previous studies demonstrate that statins stimulate bone morphogenetic protein-2 (BMP-2) expression and lead to bone formation. The aim of this study was to evaluate whether percutaneously injected statin with a novel statin delivery system achieved vertical bone augmentation.

MATERIAL AND METHODS

As experimental groups, atelocollagen-alpha-tricalcium phosphate (alphaTCP) composites containing 3.3 mg (low dose) or 6.7 mg (high dose) of fluvastatin were injected (one shot) subcutaneously over the calvarial periosteum of rats. The animals were then sacrificed 1, 2, and 4 weeks after injection. Vertically augmented bone was assessed by histomorphometric procedures, i.e., by measuring new bone thickness (NBT) and bone density (BD).

RESULTS

In control groups, no newly formed bone could be seen over the calvarial bone. In the experimental groups, in contrast, a large amount of newly formed bone could be seen over the preexisting calvarial bone. The newly formed bone was seen to be in direct contact with the preexisting bone. During the entire observation, significant NBT was observed in the experimental groups (P<0.05). At the final stage of observation (4 weeks), NBT was 66.7% (low-dose group) and 59.7% (high-dose group), while they were from 1% to 16.3% in the control groups. In the experimental groups, BD significantly increased in a time-dependent manner.

CONCLUSION

Percutaneously applied fluvastatin (one shot) with a composite of alphaTCP and collagen has great potential to augment the height of the bone.

Immersion behavior of gelatin-containing calcium phosphate cement

Calcium phosphate cements (CPCs) have many favorable properties that support their clinical use as bone defect repair. However, it is difficult to deliver to the required site and hard to compact adequately due to inherently low ductility of ceramics. The aim of this study focused on the effect of the gelatin content on properties of CPCs. The diametral tensile strength, morphology, and weight loss of gelatin cements were evaluated after immersion in physiological solution, in addition to setting time. The results indicated that the setting time significantly increased with increasing gelatin amount. The 2 wt.% gelatin could make CPCs attain the maximum strength value of 2.1 MPa at 15-day immersion, while 1.6 MPa for the cement without gelatin. It is concluded that the presence of gelatin improved mechanical properties of CPCs; in particular, 2 wt.% gelatin. CPCs containing 2 wt.% gelatin hardened in an acceptable time recommended for clinical applications.

Injectable and strong nano-apatite scaffolds for cell/growth factor delivery and bone regeneration

OBJECTIVES

Seven million people suffer bone fractures each year in the U.S., and musculoskeletal conditions cost $215 billion/year. The objectives of this study were to develop moldable/injectable, mechanically strong and in situ-hardening calcium phosphate cement (CPC) composite scaffolds for bone regeneration and delivery of osteogenic cells and growth factors.

METHODS

Tetracalcium phosphate [TTCP: Ca(4)(PO(4))(2)O] and dicalcium phosphate (DCPA: CaHPO(4)) were used to fabricate self-setting calcium phosphate cement. Strong and macroporous scaffolds were developed via absorbable fibers, biopolymer chitosan, and mannitol porogen. Following established protocols, MC3T3-E1 osteoblast-like cells (Riken, Hirosaka, Japan) were cultured on the specimens and inside the CPC composite paste carrier.

RESULTS

The scaffold strength was more than doubled via reinforcement (p<0.05). Relationships and predictive models were established between matrix properties, fibers, porosity, and overall composite properties. The cement injectability was increased from about 60% to nearly 100%. Cell attachment and proliferation on the new composite matched those of biocompatible controls. Cells were able to infiltrate into the macropores and anchor to the bone mineral-like nano-apatite crystals. For cell delivery, alginate hydrogel beads protected cells during cement mixing and setting, yielding cell viability measured via the Wst-1 assay that matched the control without CPC (p>0.1). For growth factor delivery, CPC powder:liquid ratio and chitosan content provided the means to tailor the rate of protein release from CPC carrier.

SIGNIFICANCE

New CPC scaffolds were developed that were strong, tough, macroporous and osteoconductive. They showed promise for injection in minimally invasive surgeries, and in delivering osteogenic cells and osteoinductive growth factors to promote bone regeneration. Potential applications include various dental, craniofacial, and orthopedic reconstructions.

Injectable calcium phosphate cement: effects of powder-to-liquid ratio and needle size

Calcium phosphate cement (CPC) sets in situ and forms apatite with excellent osteoconductivity and bone-replacement capability. The objectives of this study were to formulate an injectable tetracalcium phosphate-dicalcium phosphate cement (CPC(D)), and investigate the powder/liquid ratio and needle-size effects. The injection force (mean +/- SD; n = 4) to extrude the paste increased from (8 +/- 2) N using a 10-gauge needle to (144 +/- 17) N using a 21-gauge needle (p < 0.05). With the 10-gauge needle, the mass percentage of extruded paste was (95 +/- 4)% at a powder/liquid ratio of 3; it decreased to (70 +/- 12)% at powder/liquid = 3.5 (p < 0.05). A relationship was established between injection force, F, and needle lumen cross-sectional area, A: F = 5.0 + 38.7/A(0.8). Flexural strength, S, (mean +/- SD; n = 5) increased from (5.3 +/- 0.8) MPa at powder/liquid= 2 to (11.0 +/- 0.8) MPa at powder/liquid = 3.5 (p < 0.05). Pore volume fraction, P, ranged from 62.4% to 47.9%. A relationship was established: S = 47.7 x (1 - P)(2.3). The strength of the injectable CPC(D) matched/exceeded the reported strengths of sintered porous hydroxyapatite implants that required machining. The novel injectable CPC(D) with a relatively high strength may be useful in filling defects with limited accessibility such as periodontal repair and tooth root-canal fillings, and in minimally-invasive techniques such as percutaneous vertebroplasty to fill the lesions and to strengthen the osteoporotic bone.

Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures

Calcium phosphate cement (CPC) is highly promising for clinical uses due to its in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits its use to non-load-bearing applications. The objectives of this study were to develop a layered CPC structure by combining a macroporous CPC layer with a strong CPC layer, and to investigate the effects of porosity and layer thickness ratios. The rationale was for the macroporous layer to accept tissue ingrowth, while the fiber-reinforced strong layer would provide the needed early-strength. A biopolymer chitosan was incorporated to strengthen both layers. Flexural strength, S (mean+/-sd; n=6) of CPC-scaffold decreased from (9.7+/-1.2) to (1.8+/-0.3) MPa (p<0.05), when the porosity increased from 44.6% to 66.2%. However, with a strong-layer reinforcement, S increased to (25.2+/-6.7) and (10.0+/-1.4) MPa, respectively, at these two porosities. These strengths matched/exceeded the reported strengths of sintered porous hydroxyapatite implants and cancellous bone. Relationships were established between S and the ratio of strong layer thickness/specimen thickness, a/h:S=(17.6 a/h+3.2) MPa. The scaffold contained macropores with a macropore length (mean+/-sd; n=147) of (183+/-73) microm, suitable for cell infiltration and tissue ingrowth. Nano-sized hydroxyapatite crystals were observed to form the scaffold matrix of CPC with chitosan. In summary, a layered CPC implant, combining a macroporous CPC with a strong CPC, was developed. Mechanical strength and macroporosity are conflicting requirements. However, the novel functionally graded CPC enabled a relatively high strength and macroporosity to be simultaneously achieved. Such an in situ-hardening nano-apatite may be useful in moderate stress-bearing applications, with macroporosity to enhance tissue ingrowth and implant resorption.

Short-fibre reinforcement of calcium phosphate bone cement

Calcium phosphate cement (CPC) sets to form hydroxyapatite, a major component of mineral bone, and is gaining increasing interest in bone repair applications. However, concerns regarding its brittleness and tendency to fragment have limited its widespread use. In the present study, short-fibre reinforcement of an apatitic calcium phosphate has been investigated to improve the fracture behaviour. The fibres used were polypropylene (PP) fibres, 50 μm in diameter and reduced in length by cryogenic grinding. The compressive strength and fracture behaviour were examined. Fibre addition of up to 10 wt% had a significant effect on composite properties, with the energy absorbed during failure being significantly increased, although this tended to be accompanied with a slight drop in compressive strength. The fibre reinforcement mechanisms appeared to be crack bridging and fibre pull-out. The setting time of the CPC with fibre reinforcement was also investigated and was found to increase with fibre volume fraction.