Effects of hydroxypropyl methylcellulose and other gelling agents on the handling properties of calcium phosphate cement

Incorporating the Antioxidant Fullerenol into Calcium Phosphate Bone Cements Increases Cellular Osteogenesis without Compromising Physical Cement Characteristics

Herein, fullerenol (Ful), a highly water-soluble derivative of C60 fullerene with demonstrated antioxidant activity, is incorporated into calcium phosphate cements (CPCs) to enhance their osteogenic ability. CPCs with added carboxymethyl cellulose/gelatin (CMC/Gel) are doped with biocompatible Ful particles at concentrations of 0.02, 0.04, and 0.1 wt v%-1 and evaluated for Ful-mediated mechanical performance, antioxidant activity, and in vitro cellular osteogenesis. CMC/gel cements with the highest Ful concentration decrease setting times due to increased hydrogen bonding from Ful's hydroxyl groups. In vitro studies of reactive oxygen species (ROS) scavenging with CMC/gel cements demonstrate potent antioxidant activity with Ful incorporation and cement scavenging capacity is highest for 0.02 and 0.04 wt v%-1 Ful. In vitro cytotoxicity studies reveal that 0.02 and 0.04 wt v%-1 Ful cements also protect cellular viability. Finally, increase of alkaline phosphatase (ALP) activity and expression of runt-related transcription factor 2 (Runx2) in MC3T3-E1 pre-osteoblast cells treated with low-dose Ful cements demonstrate Ful-mediated osteogenic differentiation. These results strongly indicate that the osteogenic abilities of Ful-loaded cements are correlated with their antioxidant activity levels. Overall, this study demonstrates exciting potential of Fullerenol as an antioxidant and proosteogenic additive for improving the performance of calcium phosphate cements in bone reconstruction procedures.

Efficacy of Silver Nanoparticles-Loaded Bone Cement against an MRSA Induced-Osteomyelitis in a Rat Model

Background and Objectives: The purpose of this study was to assess the cytotoxicity and antibacterial effects of AgNP-impregnated Tetracalcium phosphate-dicalcium phosphate dihydrate (TTCP-DCPD). Materials and Methods: Using in vitro experiments, the cytotoxicity of AgNP-impregnated TTCP-DCPD against fibroblasts and osteocytes was assessed in terms of cell viability by water-soluble tetrazolium salt assay. To assess antibacterial effects, a disc diffusion test was used; osteomyelitis was induced first in vivo, by injection of methicillin-resistant Staphylococcus aureus into the tibia of rats. AgNP-impregnated TTCP-DCPD bone cement was then applied at various silver concentrations for 3 or 12 weeks. Antibacterial effects were assessed by culturing and reverse transcription-polymerase chain reaction (RT-PCR). For histological observation, the bone tissues were stained using hematoxylin and eosin. Results: Cell viability was decreased by the impregnated bone cement but did not differ according to AgNP concentration. The diameter of the growth-inhibited zone of MRSA was between 4.1 and 13.3 mm on the disks treated with AgNP, indicating antimicrobial effects. In vivo, the numbers of bacterial colonies were reduced in the 12-week treatment groups compared to the 3-week treatment groups. The groups treated with a higher (10×) dose of AgNP (G2-G5) showed a tendency of lower bacterial colony counts compared to the group without AgNP (G1). The PCR analysis results showed a tendency of decreased bacterial gene expression in the AgNP-impregnated TTCP-DCPD groups (G2-G5) compared to the group without AgNP (G1) at 3 and 12 weeks. In the H&E staining, the degree of inflammation and necrosis of the AgNP-impregnated TTCP-DCPD groups (G2-G5) showed a tendency to be lower at 3 and 12 weeks compared to the control group. Our results suggest that AgNP-impregnated TTCP-DCPD cement has antimicrobial effects. Conclusions: This study indicates that AgNP-impregnated TTCP-DCPD bone cement could be considered to treat osteomyelitis.

Fabricating biodegradable calcium phosphate/calcium sulfate cement reinforced with cellulose: in vitro and in vivo studies

Osteoporosis is a growing public health concern worldwide. To avoid extra surgeries, developing biodegradable bone cement is critical for the treatment of osteoporosis. Herein, we designed calcium phosphate/calcium sulfate cement reinforced with sodium carboxymethyl cellulose (CMC/OPC). It presents an appropriate physicochemical performance for clinical handling. Meanwhile, CMC/OPC bone cement promotes osteogenic differentiation in vitro. Results of the immune response in vitro and in vivo confirmed that increasing the cellulose content triggered macrophage switching into the M2 phenotype and CMC/OPC exhibited significant anti-inflammation. Furthermore, in vitro and in vivo degradation demonstrated that cellulose tailors the degradation rate of composite bone cement, which achieved a linear degradation process and could degrade by more than 90% for 12 weeks. In summary, the composite bone cement CMC/OPC is a promising candidate for bone repair applications.

Development of Injectable Calcium Sulfate and Self-Setting Calcium Phosphate Composite Bone Graft Materials for Minimally Invasive Surgery

The demand of bone grafting is increasing as the population ages worldwide. Although bone graft materials have been extensively developed over the decades, only a few injectable bone grafts are clinically available and none of them can be extruded from 18G needles. To overcome the existing treatment limitations, the aim of this study is to develop ideal injectable implants from biomaterials for minimally invasive surgery. An injectable composite bone graft containing calcium sulfate hemihydrate, tetracalcium phosphate, and anhydrous calcium hydrogen phosphate (CSH/CaP paste) was prepared with different CSH/CaP ratios and different concentrations of additives. The setting time, injectability, mechanical properties, and biocompatibility were evaluated. The developed injectable CSH/CaP paste (CSH/CaP 1:1 supplemented with 6% citric acid and 2% HPMC) presented good handling properties, great biocompatibility, and adequate mechanical strength. Furthermore, the paste was demonstrated to be extruded from a syringe equipped with 18G needles and exerted a great potential for minimally invasive surgery. The developed injectable implants with tissue repairing potentials will provide an ideal therapeutic strategy for minimally invasive surgery to apply in the treatment of maxillofacial defects, certain indications in the spine, inferior turbinate for empty nose syndrome (ENS), or reconstructive rhinoplasty.

3D Printing of Calcium Phosphate/Calcium Sulfate with Alginate/Cellulose-Based Scaffolds for Bone Regeneration: Multilayer Fabrication and Characterization

Congenital abnormalities, trauma, and disease result in significant demands for bone replacement in the craniofacial region and across the body. Tetra-compositions of organic and inorganic scaffolds could provide advantages for bone regeneration. This research aimed to fabricate and characterize amorphous calcium phosphate (ACP)/calcium sulfate hemihydrate (CSH) with alginate/cellulose composite scaffolds using 3D printing. Alginate/cellulose gels were incorporated with 0%, 13%, 15%, 18%, 20%, and 23% ACP/CSH using the one-pot process to improve morphological, physiochemical, mechanical, and biological properties. SEM displayed multi-staggered filament layers with mean pore sizes from 298 to 377 μm. A profilometer revealed mean surface roughness values from 43 to 62 nm that were not statistically different. A universal test machine displayed the highest compressive strength and modulus with a statistical significance in the 20% CP/CS group. FTIR spectroscopy showed peaks in carbonate, phosphate, and sulfate groups that increased as more ACP/CSH was added. Zero percent of ACP/CSH showed the highest swelling and lowest remaining weight after degradation. The 23% ACP/CSH groups cracked after 60 days. In vitro biocompatibility testing used the mouse osteoblast-like cell line MC3T3-E1. The 18% and 20% ACP/CSH groups showed the highest cell proliferation on days five and seven. The 20% ACP/CSH was most suitable for bone cell regeneration.

In Vivo Study of Osteochondral Defect Regeneration Using Innovative Composite Calcium Phosphate Biocement in a Sheep Model

This study aimed to clarify the therapeutic effect and regenerative potential of the novel, amino acids-enriched acellular biocement (CAL) based on calcium phosphate on osteochondral defects in sheep. Eighteen sheep were divided into three groups, the treated group (osteochondral defects filled with a CAL biomaterial), the treated group with a biocement without amino acids (C cement), and the untreated group (spontaneous healing). Cartilages of all three groups were compared with natural cartilage (negative control). After six months, sheep were evaluated by gross appearance, histological staining, immunohistochemical staining, histological scores, X-ray, micro-CT, and MRI. Treatment of osteochondral defects by CAL resulted in efficient articular cartilage regeneration, with a predominant structural and histological characteristic of hyaline cartilage, contrary to fibrocartilage, fibrous tissue or disordered mixed tissue on untreated defect (p < 0.001, modified O'Driscoll score). MRI results of treated defects showed well-integrated and regenerated cartilage with similar signal intensity, regularity of the articular surface, and cartilage thickness with respect to adjacent native cartilage. We have demonstrated that the use of new biocement represents an effective solution for the successful treatment of osteochondral defects in a sheep animal model, can induce an endogenous regeneration of cartilage in situ, and provides several benefits for the design of future therapies supporting osteochondral defect healing.

Validation of the Osteomyelitis Induced by Methicillin-Resistant Staphylococcus aureus (MRSA) on Rat Model with Calvaria Defect

BACKGROUND

Osteomyelitis resulting from bacterial strains, such as methicillin-resistant Staphylococcus aureus (MRSA) that are resistant to multiple drugs, brings further clinical challenges. There is currently no model of osteomyelitis induced by MRSA using rats with calvaria defects. So, We induced osteomyelitis in rat models with the calvaria bone defect.

METHODS

The rats were randomly divided into six groups according to inoculation dose levels, which ranged from 6 × 10⁰ to 6 × 10⁵ CFU/5 µl. Bone tissues were retrieved from all rats used in the study and assessed using histology, microbiology, and radiobiology 4 weeks after surgery to evaluate the relationship between inoculation dose and infectivity.

RESULTS

In Histological results, high levels of inflammatory responses, bone necrosis, and bacteria were observed in treatment groups G3 to G5. In IHC staining, high levels of cox-2 expression were observed in treatment groups G3. Microbiological observations also indicated that significantly higher numbers of CFUs were found in G3 to G5. In radiography results, the bone mineral density in G3 to G5 was significantly higher than in the control group, G1, and G2. Our results indicate that an inoculating dose of 6 × 10³ CFU/5 μl is sufficient to induce the development of osteomyelitis in rat models.

CONCLUSION

This study suggests that the minimum dose (6 × 10³ CFU/5 µl) can induce osteomyelitis in calvaria rat model. This can offer information and ability of more accurately modeling osteomyelitis and simulating the challenge of osteomyelitis treat.

Injectable Enzymatically Hardened Calcium Phosphate Biocement

(1) Background: The preparation and characterization of novel fully injectable enzymatically hardened tetracalcium phosphate/monetite cements (CXI cements) using phytic acid/phytase (PHYT/F3P) hardening liquid with a small addition of polyacrylic acid/carboxymethyl cellulose anionic polyelectrolyte (PAA/CMC) and enhanced bioactivity. (2) Methods: Composite cements were prepared by mixing of calcium phosphate powder mixture with hardening liquid containing anionic polyelectrolyte. Phase and microstructural analysis, compressive strength, release of ions and in vitro testing were used for the evaluation of cement properties. (3) Results: The simple possibility to control the setting time of self-setting CXI cements was shown (7–28 min) by the change in P/L ratio or PHYT/F3P reaction time. The wet compressive strength of cements (up to 15 MPa) was close to cancellous bone. The increase in PAA content to 1 wt% caused refinement and change in the morphology of hydroxyapatite particles. Cement pastes had a high resistance to wash-out in a short time after cement mixing. The noncytotoxic character of CX cement extracts was verified. Moreover, PHYT supported the formation of Ca deposits, and the additional synergistic effect of PAA and CMC on enhanced ALP activity was found, along with the strong up-regulation of osteogenic gene expressions for osteopontin, osteocalcin and IGF1 growth factor evaluated by the RT-qPCR analysis in osteogenic αMEM 50% CXI extracts. (4) Conclusions: The fully injectable composite calcium phosphate bicements with anionic polyelectrolyte addition showed good mechanical and physico-chemical properties and enhanced osteogenic bioactivity which is a promising assumption for their application in bone defect regeneration.

Combination of biocompatible hydrogel precursors to apatitic calcium phosphate cements (CPCs): Influence of the in situ hydrogel reticulation on the CPC properties

In the field of bone regenerative medicine, injectable calcium phosphate cements (CPCs) are used for decades in clinics, as bone void fillers. Most often preformed polymers (e.g., hyaluronic acid, collagen, chitosan, cellulose ethers…) are introduced in the CPC formulation to make it injectable and improve its cohesion. Once the cement has hardened, the polymer is simply trapped in the CPC structure and no organic subnetwork is present. By contrast, in this work a CPC was combined with organic monomers that reticulated in situ so that a continuous biocompatible 3D polymeric subnetwork was formed in the CPC microstructure, resulting in a higher permeability of the CPC, which might allow to accelerate its in vivo degradation. Two options were investigated depending on whether the polymer was formed before the apatitic inorganic network or concomitantly. In the former case, conditions were found to reach a suitable rheology for easy injection of the composite. In addition, the in situ formed polymer was shown to strongly affect the size, density, and arrangement of the apatite crystals formed during the setting reaction, thereby offering an original route to modulate the microstructure and porosity of apatitic cements.

In vivo resorption of injectable apatitic calcium phosphate cements: Critical role of the intergranular microstructure

The in vivo resorption rate of two injectable apatitic calcium phosphate cements used in clinics (Graftys® HBS and NORIAN®) was compared, using a good laboratory practice (GLP) study based on an animal model of critical-sized bone defect. To rationalize the markedly different biological properties observed for both cements, key physical features were investigated, including permeability and water-accessible porosity, total porosity measured by mercury intrusion and gravimetry, and microstructure. Due to a different concept for creating porosity between the two cements investigated in this study, a markedly different microstructural arrangement of apatite crystals was observed in the intergranular space, which was found to significantly influence both the mechanical strength and in vivo degradation of the two calcium phosphate cements.

Improving the anti-washout property of calcium phosphate cement by introducing konjac glucomannan/κ-carrageenan blend

Anti-washout calcium phosphate cement (CPC) was prepared by dissolving water-soluble konjac glucomannan (KGM) and κ-carrageenan (KC) blend in the cement liquid. The anti-washout property, setting time, compressive strength and in vitro cytocompatibility of the CPC modified with KGM/KC blend were evaluated. The results indicated that the CPC pastes modified with KGM/KC blend exhibited excellent anti-washout property. The addition of KGM/KC blend shortened the setting time and increased the injectability of CPC. Although the introduction of KGM/KC blend reduced the compressive strength of CPC, the compressive strength still surpassed that of human cancellous bone. The optimal KGM/KC mass ratio was 2:8, with which the modified cement exhibited the most efficient washout resistance and the highest compressive strength. The introduction of KGM/KC blend obviously promoted the proliferation of mouse bone marrow mesenchymal stem cells. This anti-washout CPC modified by KGM/KC blend with excellent in vitro cytocompatibility will have good prospects for application in bone defect repair.

Improvement of anti-washout property of calcium phosphate cement by addition of konjac glucomannan and guar gum

The inferior anti-washout property of injectable calcium phosphate cement (CPC) limits its wider application in clinic. In this study, the improvement of anti-washout performance of CPC by addition of konjac glucomannan or guar gum, which was dissolved in the CPC liquid, was first studied. The influence of KGM/GG blend with different mass ratios on the anti-washout property, compressive strength and in vitro cytocompatibility of CPC was estimated. The results revealed that small amount of KGM or GG could obviously enhance the anti-washout property of CPC. Moreover, the washout resistance efficiency of KGM/GG blend was better than KGM or GG alone. The addition of KGM/GG blend slightly shortened the final setting time of CPC. Although the introduction of KGM/GG blend reduced the compressive strength of CPC, the compressive strength still reached or surpassed that of human cancellous bone. The best KGM/GG mass ratio was 5:5, which was most efficient at not only reducing CPC disintegration, but also increasing compressive strength. The addition of KGM/GG blend obviously promoted the cells proliferation on the CPC. In short, the CPC modified by KGM/GG blend exhibited excellent anti-washout property, appropriate setting time, adequate compressive strength, and good cytocompatibility, and has the potential to be used in bone defect repair. The addition of KGM/GG blend significantly improved the anti-washout property of CPC. The best KGM/GG mass ratio was 5:5, which was most efficient in reducing the CPC disintegration.

Incorporation of chitosan-alginate complex into injectable calcium phosphate cement system as a bone graft material

Calcium phosphate brushite type of cements have been used to replace bone graft materials because of their biocompatibility and other attractive features. Especially, injectability of cement allows easy handling of minimally invasive surgical techniques. New calcium phosphate cement (CPC) system, brushite based cement incorporated into polyelectrolyte complex, was developed in this study. Chitosan-alginate complex produced by an interaction between a cationic polymer (chitosan) and an anionic polymer (alginate) was loaded in the cement. This improved the functional properties and biocompatibility of the final cement. We optimized the liquid/solid (L/S) ratio of the cement components and investigated the compressive strength, setting time, pH change of CPC0 (with only citric acid) and CPC0.5, 1, and 1.5 (0.5, 1, and 1.5 v/v % chitosan-alginate complex in citric acid solution, respectively). The L/S ratio did not affect structural formation, while the addition of polymer complex showed new formation of macro-pores within CPC. However, a lower L/S ratio and higher amount of added polymer complex shortened the setting time and improved the compressive strength. The appropriate conditions for the injectable bone substitute were CPC1 with an L/S ratio of 0.45. To investigate the effect of the chitosan-alginate complex on CPC system in physiological conditions, CPC0 and CPC1 were implanted in a rabbit femoral head defect model for 1 and 3 months. Micro-computed tomography revealed improved bone formation in CPC1 compared to CPC0 3 months after implantation. Histological analysis revealed newly formed bone tissues around the peripheral sides of CPC0 and CPC1. The results indicate the potential value of the CPC system containing polymer complex as an injectable bone substitute. The study of the CPC-polymer complex system incorporating drugs or cells can be further developed into a controlled release system for faster bone regeneration.

Calcium phosphate cements for bone engineering and their biological properties

Calcium phosphate cements (CPCs) are frequently used to repair bone defects. Since their discovery in the 1980s, extensive research has been conducted to improve their properties, and emerging evidence supports their increased application in bone tissue engineering. Much effort has been made to enhance the biological performance of CPCs, including their biocompatibility, osteoconductivity, osteoinductivity, biodegradability, bioactivity, and interactions with cells. This review article focuses on the major recent developments in CPCs, including 3D printing, injectability, stem cell delivery, growth factor and drug delivery, and pre-vascularization of CPC scaffolds via co-culture and tri-culture techniques to enhance angiogenesis and osteogenesis.

Injectable, biomechanically robust, biodegradable and osseointegrative bone cement for percutaneous kyphoplasty and vertebroplasty

PURPOSE

Poly(methyl methacrylate) (PMMA) cement is widely used for percutaneous kyphoplasty and vertebroplasty (PKP and PVP) but possesses formidable shortcomings due to non-degradability. Here, a biodegradable replacement is developed.

METHODS

Calcium phosphate cement (CPC) was redesigned by incorporating starch and BaSO₄ (new cement named as CPB). The biomechanical, biocompatibility, osseointegrative and handling properties of CPB were systematically evaluated in vitro and in vivo by the models of osteoporotic sheep vertebra, rat subcutaneous implantation and rat femoral defect.

RESULTS

CPB revealed appropriate injectability and setting ability for PKP and PVP. More importantly, its biomechanical strengths measured by in vitro and in vivo models were not less than that of PMMA, while its biodegradability and osseointegrative capacities were significantly enhanced compared to PMMA.

CONCLUSIONS

CPB is injectable, biomechanically robust, biodegradable and osseointegrative, demonstrating revolutionary potential for the application in PKP and PVP.

Injectable chelate-setting hydroxyapatite cement prepared by using chitosan solution: Fabrication, material properties, biocompatibility, and osteoconductivity

An injectable chelate-setting hydroxyapatite cement (IP6-HAp), formed by chelate-bonding capability of inositol phosphate (IP6), was developed. The effects of ball-milling duration of starting HAp powder and IP6 concentration on the material properties such as injectability and mechanical strength of the cement were examined. The cement powder was prepared by ball-milling the as-synthesized HAp powder for 5 min using ZrO2 beads with a diameter of 10 mm, followed by another 60 min with ZrO2 beads with a diameter of 2 mm, and thereafter surface-modified with 5000 ppm of IP6 solution. Injectable cement was then fabricated with this HAp powder and 2.5 mass% chitosan as a mixing solution, with a setting time of 36.3 ± 4.7 min and a compressive strength of 19.0 ± 2.1 MPa. The IP6-HAp cements prepared with chitosan showed favorable biocompatibility in vitro using an osteoblast cell model, and osteoconductivity in vivo using a pig tibia model.

On the mechanical characteristics of a self-setting calcium phosphate cement

OBJECTIVE

To perform a mechanical characterization of a self-setting calcium phosphate cement in function of the immersion time in Ringer solution.

MATERIALS AND METHODS

Specimens of self-setting calcium phosphate cement were prepared from pure α-TCP powder. The residual strains developed during hardening stage were monitored using an embedded fiber Bragg grating sensor. Additionally, the evolution of the elastic modulus was obtained for the same time period by conducting low-load indentation tests. Micro-computed tomography as well as microscope-assisted inspections were employed to evaluate the porosity in the specimens. Moreover, diametral compression tests were conducted in wet and dried specimens to characterize the material strength.

RESULTS

The volume of the estimated porosity and absorbed fluid mass, during the first few minutes of the material's exposure in a wet environment, coincide. The immersion in Ringer solution lead to a noticeable increase in the moduli values. The critical value of stresses obtained from the diametral compression tests were combined with the data from uniaxial compression tests, to suggest a Mohr-Coulomb failure criterion.

CONCLUSIONS

This study presents different techniques to characterize a self-setting calcium phosphate cement and provides experimental data on porosity, mechanical properties and failure. The investigated material possessed an open porosity at its dried state with negligible residual strains and its Young's modulus, obtained from micro-indentation tests, increased with hardening time. The failure loci may be described by a Mohr-Coulomb criterion, characteristic of soil and rock materials.

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.

The Effects of S-Chitosan on the Physical Properties of Calcium Phosphate Cements

Water-soluble disodium (1→4)-2-deoxy-2-sulfoamino-β-d-glucopyranuronan (S-chitosan) was prepared from chitin by successive N-deacetylation, specific carboxylation at C-6 and sulfonation. Its structure was characterized by IR spectra and elemental analysis. The S-chitosan was added to two easily developed calcium phosphate cements (CPCs). One cement was monocalcium phosphate monohydrate (MPCM) with calcium oxide (CaO) in a 1M phosphate buffer (pH 7.4)(CPC-I); the other cement was dicalcium phosphate dihydrate (DCPD) with calcium hydroxide [Ca(OH)2] in a 1M Na2HPO4 solution (CPC-II). In vitro experiments showed that when S-chitosan where added to the liquid phases that the resulting S-chitosan containing CPCs had higher mechanical strengths and slightly prolonged setting times. The polyanion enhanced the mechanical strength of the CPCs by increasing the dissolubility of the cement start materials and binding the calcium ions strongly afterwards. An excess of the polyanion destroys the balances of the formulations of CPCs and lead to very slow setting processes or no setting at all.

Influence of polymeric additives on the cohesion and mechanical properties of calcium phosphate cements

To expand the clinical applicability of calcium phosphate cements (CPCs) to load-bearing anatomical sites, the mechanical and setting properties of CPCs need to be improved. Specifically, organic additives need to be developed that can overcome the disintegration and brittleness of CPCs. Hence, we compared two conventional polymeric additives (i.e. carboxylmethylcellulose (CMC) and hyaluronan (HA)) with a novel organic additive that was designed to bind to calcium phosphate, i.e. hyaluronan-bisphosphonate (HABP). The unmodified cement used in this study consisted of a powder phase of α-tricalcium phosphate (α-TCP) and liquid phase of 4% NaH2PO4·2H2O, while the modified cements were fabricated by adding 0.75 or 1.5 wt% of the polymeric additive to the cement. The cohesion of α-TCP was improved considerably by the addition of CMC and HABP. None of the additives improved the compression and bending strength of the cements, but the addition of 0.75% HABP resulted into a significantly increased cement toughness as compared to the other experimental groups. The stimulatory effects of HABP on the cohesion and toughness of the cements is hypothesized to derive from the strong affinity between the polymer-grafted bisphosphonate ligands and the calcium ions in the cement matrix.

A simple and effective approach to prepare injectable macroporous calcium phosphate cement for bone repair: Syringe-foaming using a viscous hydrophilic polymeric solution

In this study, we propose a simple and effective strategy to prepare injectable macroporous calcium phosphate cements (CPCs) by syringe-foaming via hydrophilic viscous polymeric solution, such as using silanized-hydroxypropyl methylcellulose (Si-HPMC) as a foaming agent. The Si-HPMC foamed CPCs demonstrate excellent handling properties such as injectability and cohesion. After hardening the foamed CPCs possess hierarchical macropores and their mechanical properties (Young's modulus and compressive strength) are comparable to those of cancellous bone. Moreover, a preliminary in vivo study in the distal femoral sites of rabbits was conducted to evaluate the biofunctionality of this injectable macroporous CPC. The evidence of newly formed bone in the central zone of implantation site indicates the feasibility and effectiveness of this foaming strategy that will have to be optimized by further extensive animal experiments.

STATEMENT OF SIGNIFICANCE

A major challenge in the design of biomaterial-based injectable bone substitutes is the development of cohesive, macroporous and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with adequate initial mechanical properties without the use of complex processing and additives. Thus, we propose a simple and effective strategy to prepare injectable macroporous CPCs through syringe-foaming using a hydrophilic viscous polymeric solution (silanized-hydroxypropyl methylcellulose, Si-HPMC) as a foaming agent, that simultaneously meets all the aforementioned aims. Evidence from our in vivo studies shows the existence of newly formed bone within the implantation site, indicating the feasibility and effectiveness of this foaming strategy, which could be used in various CPC systems using other hydrophilic viscous polymeric solutions.

Cross-linked chitosan improves the mechanical properties of calcium phosphate-chitosan cement

Calcium phosphate (CaP) cements are highly applicable and valuable materials for filling bone defects by minimally invasive procedures. The chitosan (CS) biopolymer is also considered as one of the promising biomaterial candidates in bone tissue engineering. In the present study, some key features of CaP-CS were significantly improved by developing a novel CaP-CS composite. For this purpose, CS was the first cross-linked with tripolyphosphate (TPP) and then mixed with CaP matrix. A group of CaP-CS samples without cross-linking was also prepared. Samples were fabricated and tested based on the known standards. Additionally, the effect of different powder (P) to liquid (L) ratios was also investigated. Both cross-linked and uncross-linked CaP-CS samples showed excellent washout resistance. The most significant effects were observed on Young's modulus and compressive strength in wet condition as well as surface hardness. In dry conditions, the Young's modulus of cross-linked samples was slightly improved. Based on the presented results, cross-linking does not have a significant effect on porosity. As expected, by increasing the P/L ratio of a sample, ductility and injectability were decreased. However, in the most cases, mechanical properties were enhanced. The results have shown that cross-linking can improve the mechanical properties of CaP-CS and hence it can be used for bone tissue engineering applications.

Mechanical properties of α-tricalcium phosphate-based bone cements incorporating regenerative biomaterials for filling bone defects exposed to low mechanical loads

Calcium phosphate-based cements with enhanced regenerative potential are promising biomaterials for the healing of bone defects in procedures such as percutaneous vertebroplasty. With a view to the use of such cements for low load bearing applications such as sinus augmentation or filling extraction sites. However, the inclusion of certain species into bone cement formulations has the potential to diminish the mechanical properties of the formulations and thereby reduce their prospects for clinical translation. Consequently, we have prepared α-tricalcium phosphate (α-TCP)-based bone cements including materials that we would expect to improve their regenerative potential, and describe the mechanical properties of the resulting formulations herein. Formulations incorporated α-TCP, hydroxyapatite, biopolymer-thickened wetting agents, sutures, and platelet poor plasma. The mechanical properties of the composites were composition dependent, and optimized formulations had clinically relevant mechanical properties. Such calcium phosphate-based cements have potential as replacements for cements such as those based on polymethylmethacrylate.

Fast setting and anti-washout injectable calcium–magnesium phosphate cement for minimally invasive treatment of bone defects

The fa-ICMPC exhibited potent anti-washout properties, fast setting, improved injectability, good biodegradability and osteoconductivity.

A novel injectable, cohesive and toughened Si-HPMC (silanized-hydroxypropyl methylcellulose) composite calcium phosphate cement for bone substitution

This study reports on the incorporation of the self-setting polysaccharide derivative hydrogel (silanized-hydroxypropyl methylcellulose, Si-HPMC) into the formulation of calcium phosphate cements (CPCs) to develop a novel injectable material for bone substitution. The effects of Si-HPMC on the handling properties (injectability, cohesion and setting time) and mechanical properties (Young's modulus, fracture toughness, flexural and compressive strength) of CPCs were systematically studied. It was found that Si-HPMC could endow composite CPC pastes with an appealing rheological behavior at the early stage of setting, promoting its application in open bone cavities. Moreover, Si-HPMC gave the composite CPC good injectability and cohesion, and reduced the setting time. Si-HPMC increased the porosity of CPCs after hardening, especially the macroporosity as a result of entrapped air bubbles; however, it improved, rather than compromised, the mechanical properties of composite CPCs, which demonstrates a strong toughening and strengthening effect. In view of the above, the Si-HPMC composite CPC may be particularly promising as bone substitute material for clinic application.

Calcium phosphate cements for bone substitution: chemistry, handling and mechanical properties

Since their initial formulation in the 1980s, calcium phosphate cements (CPCs) have been increasingly used as bone substitutes. This article provides an overview on the chemistry, kinetics of setting and handling properties (setting time, cohesion and injectability) of CPCs for bone substitution, with a focus on their mechanical properties. Many processing parameters, such as particle size, composition of cement reactants and additives, can be adjusted to control the setting process of CPCs, concomitantly influencing their handling and mechanical performance. Moreover, this review shows that, although the mechanical strength of CPCs is generally low, it is not a critical issue for their application for bone repair--an observation not often realized by researchers and clinicians. CPCs with compressive strengths comparable to those of cortical bones can be produced through densification and/or homogenization of the cement matrix. The real limitation for CPCs appears to be their low fracture toughness and poor mechanical reliability (Weibull modulus), which have so far been only rarely studied.

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.

The influence of different cellulose ethers on both the handling and mechanical properties of calcium phosphate cements for bone substitution

The influence of cellulose ether additives (CEAs) on the performance of final calcium phosphate cement (CPC) products is thoroughly investigated. Four CEAs were added into the liquid phase of apatitic CPCs based on the hydrolysis of α-tricalcium phosphate, to investigate the influence of both molecular weight and degree of substitution on the CPCs' properties, including handling (e.g. injectability, cohesion, washout resistance and setting time), microstructure (e.g. porosity and micromorphology) and mechanical properties (e.g. fracture toughness and compressive strength). The results showed that even a small amount of CEAs modified most of these CPCs' features, depending on the structural parameters of the CEAs. The CEAs dramatically improved the injectability, cohesion and washout resistance of the pastes, prolonged the final setting time and increased the porosity of CPCs. Moreover, the CEAs had an evident toughening effect on CPCs, and this effect become more significant with increasing molecular weight and mass fraction of CEAs, inducing a significant tolerance to damage. Overall, the molecular weight of CEAs played a major role compared to their degree of substitution in CPCs' performances.

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.

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.

Initial in vitro biocompatibility of a bone cement composite containing a poly-ε-caprolactone microspheres

The biocompatibility of a reinforced calcium phosphate injectable bone substitute (CPC-IBS) containing 30% poly-ε-caprolactone (PCL) microspheres was evaluated. The IBS consisted of a solution of chitosan and citric acid as the liquid phase and tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) powder as the solid phase with 30% PCL microspheres. The surface of the CPC-IBS was observed by SEM, and analyzed by EDX profiles. The initial setting of the sample was lower in the IBS containing 0% citric acid than in the IBS containing 10 or 20% citric acid. The compressive strength of the PCL-incorporated CPC-IBS was measured using a Universal Testing Machine. The 20% citric acid samples had the highest mechanical strength at day 12, which was dependent on both time and the citric acid concentration. The in vitro bioactivity experiments with simulated body fluid (SBF) confirmed the formation of apatite on the sample surfaces after 2, 7, and 14 days of incubation in SBF. Ca and P ion release profile by ICP method also confirmed apatite nucleation on the CPC-IBS surfaces. The in vitro biocompatibility of the CPC-IBS was evaluated by using MTT, cellular adhesion, and spreading studies. In vitro cytotoxicity tests by MTT assay showed that the 0 and 10% CPC-IBS was cytocompatible for fibroblast L-929 cells. The SEM micrograph confirmed that MG-63 cells maintained their phenotype on all of the CPC-IBS surfaces although cellular attachment was better in 0 and 10% CPC-IBS than 20% samples.

Calcium Phosphate Cements: Chemistry, Properties, and Applications

This paper reviews recent studies on self-setting calcium phosphate cements (CPC). Discussions are focused on the cement setting reactions, the products formed, those properties of the cements that contribute to their clinical efficacy, and areas of future improvements that could make CPC useful in a wider range of applications. The strengths of CPC are considerably lower than ceramic calcium phosphate biomaterials and are also lower than some of the dental cements. On the other hand, the combination of self-setting capability and high biocompatibility makes CPC a unique biomaterial. Near perfect adaptation of the cement to the tissue surfaces in a defect, and a gradual resorption followed by new bone formation are some of the distinctive advantages of CPC. In its present state CPC appears to be suitable for a number of applications. Much remains to be done to further improve its properties to meet the requirements for different applications.

Effect of Silk Fibroin on the Properties of Calcium Phosphate Cement

To improve the physicochemical properties of calcium phosphate cement (CPC), silk fibroin (SF) in the different forms were added into CPC. The structure of the composites was studied by X-ray diffraction. The setting time was investigated by ISO Cement Standard Consistency Instrument. Scanning Electron Microscope was used to observe the surface morphology. Mechanical properties of samples were tested by Instron Universal Testing Machine. The results indicated that acicular crystal of hydroxyapatite (HA) was formed in the hardening body of both CPC with SF and the pure CPC. Addition of SF had no significant effect on the structure of SF/CPC composite. The setting time of CPC with SF was significantly shorter than that of the pure CPC (30.3 mins). The setting time of CPC by adding silk fibroin powder I (SFP) and silk fibroin fiber (SFF) was greatly shortened, which was only 11.7 minutes. The setting time of CPC with SFP decreased approximately by 1/3, while the setting time of the CPC with SFF decreased nearly by 1/2. With the adding of SF, the compressive strength of CPC increased significantly. There was a distinct increase in the work-of-compressive of CPC with the adding of SFF.

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.

Evolving application of biomimetic nanostructured hydroxyapatite

By mimicking Nature, we can design and synthesize inorganic smart materials that are reactive to biological tissues. These smart materials can be utilized to design innovative third-generation biomaterials, which are able to not only optimize their interaction with biological tissues and environment, but also mimic biogenic materials in their functionalities. The biomedical applications involve increasing the biomimetic levels from chemical composition, structural organization, morphology, mechanical behavior, nanostructure, and bulk and surface chemical-physical properties until the surface becomes bioreactive and stimulates cellular materials. The chemical-physical characteristics of biogenic hydroxyapatites from bone and tooth have been described, in order to point out the elective sides, which are important to reproduce the design of a new biomimetic synthetic hydroxyapatite. This review outlines the evolving applications of biomimetic synthetic calcium phosphates, details the main characteristics of bone and tooth, where the calcium phosphates are present, and discusses the chemical-physical characteristics of biomimetic calcium phosphates, methods of synthesizing them, and some of their biomedical applications.

Osteoclastic cell behaviors affected by the α-tricalcium phosphate based bone cements

Calcium phosphate cements (CPCs) have recently gained great interest as injectable bone substitutes for use in dentistry and orthopedics. α-tricalcium phosphate (α-TCP) is a popularly used precursor powder for CPCs. When mixed with appropriate content of liquid and kept under aqueous conditions, α-TCP dissolves to form a calcium-deficient hydroxyapatite and then hardens to cement. In this study, α-TCP based cement (CP) and its composite cement with chitosan (Ch-CP) were prepared and the osteoclastic responses to the cements and their elution products were evaluated. Preliminary evaluation of the cements revealed that the CP and Ch-CP hardened within ~10 min at an appropriate powder-to-liquid ratio (PL) of 3.0. In addition, CP and Ch-CP were transformed into an apatite phase following immersion in a saline solution. Moreover, the osteoblastic cells were viable on the cements for up to 10 days. Mouse-derived bone marrow cells were isolated and activated with osteoclastic differentiation medium, and the effects of the CP and Ch-CP substrates and their ionic eluants on the osteoclastic activity were investigated. Osteoclastic cells were viable for up to 14 days on both types of cements, maintaining a higher cell growth level than the control culture dish. Multi-nucleated osteoclastic cells that were tartrate-resistant acid phosphatase (TRAP)-positive were clearly observed when cultured on the cement substrates as well as treated with the cement eluants. The TRAP activity was found to be significantly higher in cells influenced by the cement substrates and their eluants with respect to the control culture dish (Ch-CP > CP ≫ control). Overall, the osteoclastic differentiation was highly stimulated by the α-TCP based experimental cements in terms of both the substrate interaction and their elution products.

Tetracalcium phosphate: Synthesis, properties and biomedical applications

Monoclinic tetracalcium phosphate (TTCP, Ca(4)(PO(4))(2)O), also known by the mineral name hilgenstockite, is formed in the (CaO-P(2)O(5)) system at temperatures>1300 degrees C. TTCP is the only calcium phosphate with a Ca/P ratio greater than hydroxyapatite (HA). It appears as a by-product in plasma-sprayed HA coatings and shows moderate reactivity and concurrent solubility when combined with acidic calcium phosphates such as dicalcium phosphate anhydrous (DCPA, monetite) or dicalcium phosphate dihydrate (DCPD, brushite). Therefore it is widely used in self-setting calcium phosphate bone cements, which form HA under physiological conditions. This paper aims to review the synthesis and properties of TTCP in biomaterials applications such as cements, sintered ceramics and coatings on implant metals.