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.

REINFORCEMENT OF CALCIUM PHOSPHATE CEMENTS WITH PHOSPHORYLATED CHITIN

Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by the phosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCs from monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD) and calcium hydroxide [Ca(OH)(2)] were investigated. Addition of P-chitin (M-w = 2.60 x 10(4); degree of substitution, DS = 0.68) to the liquid phase in amounts up to 3 wt.% for MCPM and CaO cements or 1.5 wt.% for DCPD and Ca(OH)(2) cements could enhance the mechanical strength considerably, while little influence on the setting time was observed. However, further addition of P-chitin will cause no setting.

In vitro and in vivo analysis of the biocompatibility of two novel and injectable calcium phosphate cements

Calcium phosphate cements(CPCs)have been widely used as bone graft substitutes for many years.The aim of this study was to evaluate the biocompatibility of two novel injectable,bioactive cements:b-tricalcium phosphate(b-TCP)/CPC and chitosan microsphere/CPC in vitro and in vivo.This was accomplished by culturing mouse pre-osteoblastic cells(MC3T3-E1)on discs and pastes of CPCs.Cell growth,adhesion,proliferation and differentiation were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and alkaline phosphatase assays as well as by scanning electron microscopy and fluorescence.The effect of CPC paste curing was also evaluated.Implantation of two materials into the muscle tissue of rabbits was also studied and evaluated by histological analysis.Cell analysis indicated good biocompatibility in vitro.The fluorescence assay suggested that the cured material discs had no obvious effect on cell growth,while the curing process did.Histological examination showed no inflammatory cell infiltration into soft tissue.These data suggest that b-TCP/CPC and chitosan microsphere/CPC composites may be promising injectable material for bone tissue engineering.

Sudoku of porous, injectable calcium phosphate cements – Path to osteoinductivity

With the increase of global population,people’s life expectancy is growing as well.Humans tend to live more active lifestyles and,therefore,trauma generated large defects become more common.Instances of tumour resection or pathological conditions and complex orthopaedic issues occur more frequently increasing necessity for bone substitutes.Composition of calcium phosphate cements(CPCs)is comparable to the chemical structure of bone minerals.Their ability to self-set and resorb in vivo secures a variety of potential applications in bone regeneration.Despite the years-long research and several products already reaching the market,finding the right properties for calcium phosphate cement to be osteoinductive and both injectable and suitable for clinical use is still a sudoku.This article is focused on injectable,porous CPCs,reviewing the latest developments on the path toward finding osteoinductive material,which is suitable for injection.

Factors influencing the drug release from calcium phosphate cements

Thanks to their biocompatibility,biodegradability,injectability and self-setting properties,calcium phosphate cements(CPCs)have been the most economical and effective biomaterials of choice for use as bone void fillers.They have also been extensively used as drug delivery carriers owing to their ability to provide for a steady release of various organic molecules aiding the regeneration of defective bone,including primarily antibiotics and growth factors.This review provides a systematic compilation of studies that reported on the controlled release of drugs from CPCs in the last 25 years.The chemical,compositional and microstructural characteristics of these systems through which the control of the release rates and mechanisms could be achieved have been discussed.In doing so,the effects of(i)the chemistry of the matrix,(ii)porosity,(iii)additives,(iv)drug types,(v)drug concentrations,(vi)drug loading methods and(vii)release media have been distinguished and discussed individually.Kinetic specificities of in vivo release of drugs from CPCs have been reviewed,too.Understanding the kinetic and mechanistic correlations between the CPC properties and the drug release is a prerequisite for the design of bone void fillers with drug release profiles precisely tailored to the application area and the clinical picture.The goal of this review has been to shed light on these fundamental correlations.

In situ magnesium calcium phosphate cements formation: From one pot powders precursors synthesis to in vitro investigations

Calcium phosphate cements are of great interest for researchers and their applications in medical practice expanded.Nevertheless,they have a number of drawbacks including the insufficient level of mechanical properties and low degradation rate.Struvite(MgNH4PO4)-based cements,which grew in popularity in recent years,despite their neutral pH and acceptable mechanical performance,release undesirable NH4+ions during their resorption.This issue could be avoided by replacement of ammonia ions in the cement liquid with sodium,however,such cements have a pH values of 9–10,leading to cytotoxicity.Thus,the main goal of this investigation is to optimize the composition of cements to achieve the combination of desirable properties:neutral pH,sufficient mechanical properties,and the absence of cytotoxicity,applying Na2HPO4-based cement liquid.For this purpose,cement powders precursors in the CaO-MgO-P2O5 system were synthesized by one-pot process in a wide composition range,and their properties were investigated.The optimal performance was observed for the cements with(Ca+Mg)/P ratio of 1.67,which are characterized by newberyite phase formation during setting reaction,pH values close to 7,sufficient compressive strength up to 22±3 MPa(for 20 mol.%of Mg),dense microstructure and adequate matrix properties of the surface.This set of features make those materials promising candidates for medical applications.

Calcium Phosphate Biomaterials: An Update

Current calcium phosphate （ CaP ） biomaterials for bone repair, substitution, augmentation and regeneration include hydroxyapatite （ HA ） from synthetic or biologic origin, beta-tricaicium phosphate （ β- TCP ）, biphasic calcium phosphate （BCP）, and are available as granules, porous blocks, components of compashes （CaP/pollymer） cements, and as coatings on orthopedic and dental implants. Experimental calcium phosphate biomaterials include CO3^- and F-substituted apatites, Mg-and Zn-substituted β-TCP, calcium phosphate glasses, This paper is a brief review of the different types of CaP biomaterials and their properties such as bioactivity , osteoconductivity , osteoinductivity.

The In-situ Reinforcement of Calcium Phosphate Cement and Its Micro-structural Analysis

Carbon nanotubes （ CNTs ） and polyacrylic acid were employed to modify the setting process and hydration products of β-TCP/TTCP calcium phosphate cement. The micro-structure of hydration product and the fashion of how additives and hydration particles interconnected were investigated. With the modification effect of CNTs , the setting particles and CNTs got winded and interconnected and thus made the composite more compact and denser.

Effect of Substitutional Sr Ion on Mechanical Properties of Calcium Phosphate Bone Cement

A novel calcium phosphate cement was developed by adding different amount of SrO to tetracalcium phosphate during the fabrication process. The experimental results show that compressive strength of cements based on tetracalcium phosphate doped with SrO significantly increases with the increase of SrO content, approximately 60 MPa, whilst the mechanical behavior of CPC slightly decreases if 0.7wt% SrO is added. X-ray diffraction measurement confirms the setting reaction of doped cements is similar to that of pure calcium phosphate cement （CPC）. Low crystalline hydroxyapatite （HA） is found to be the main constituent of set cement. A mechanical reinforcement effect is resulted from the substitution of Sr ion to Ca2＋ in tetracalcium phosphate （TTCP）, accelerating HA crystal formation and a more cross-linked cement structure. In vitro bioactivity tests showed that CPC added with 0.5wt% SrO had a more rapid degradation compared with pure CPC.

The Effect of Premixed Schedule on the Crystal Formation of Calcium Phosphate Cement-chitosan Composite with Added Tetracycline

In this study, calcium phosphate cements （CPC） were prepared by mixing cement powders of tetracalcium phosphate （TTCP） with a cement liquid of phosphate acid saline solution. Tetracycline （TTC）-CPC, chitosan-CPC and chitosan-TTC-CPC were investigated with different premixed schedule. It was demonstrate that both TTC and chitosan worked on the phase transition and crystal characteristics. TTCP mixed with phosphate acid saline solution had similar features of Fourier transform-infrared spectrometry （FT-IR） no matter it was mixed with chitosan or TTC or both. TTC premixed with cement liquid or powder had significant different features of FT-IR and 876 cm-1 seemed to be a special peak for TTC when TTC was premixed with cement liquid. This was also supported by XRD analysis, which showed that TTC premixed with cement liquid improved phase transition of TTCP to OCP. Chitosan, as organic additive, regulates the regular crystal formation and inhibits the phase transition of TTCP to OCP, except when it is mingled with cement liquid premixed with TTC in field scanning electron microscope. It was concluded that the premixed schedule influences the crystal formation and phase transition, which may be associated with its biocompatibility and bioactivities in vivo.

Microstructure and Mechanical Properties of Calcium Phosphate Cement/Gelatine Composite Scaffold with Oriented Pore Structure for Bone Tissue Engineering

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

Evaluation of Calcium Phosphate Cement As a Root Canal Sealer Filling Material

Calcium phosphate cement for root end sealing was obtained by in mixing alpha-tricalcium phosphate and additives with an aqueous solation of citric. Powder and liquid were mixed at a ratio of 1.25g/mL. The biocompatibility of this material was investigated primarily by subcutaneous implantation tests. Then calcium phosphate cement was used to fill three adult dogs' root canal, both calcium hydroxide paste and hydroxyapatite paste as control. The animals were killed at 4, 12, 20 weeks postoperatively respectively. The effects of different materials on the apical closure, restoration of periapical tissues and adaptability to the dentinal surface were examined by optical and electronic microscope. The observation at 20 weeks shows that the calcium phosphate cement has the potentialities of being a root canal sealer filling material available for pulpless teeth with open-apex and destructive periapical tissue.

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

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

Preparation and Compressive Strength of Calcium Phosphate Bone Cement Containing N,O-carboxymethyl Chitosan

N, O-carboxymethyl chitosan （ CMCTS ）, a kind of biodegradable organic substance, was added to calcium phosphate bone cement （CPC） to prodnce a composite more similar in composition to human bone. The compressive strength of the new material was inereased by 10 times compared with conventional CPC.

Injectable bone cements:What benefits the combination of calcium phosphates and bioactive glasses could bring?

Out of the wide range of calcium phosphate(CaP)biomaterials,calcium phosphate bone cements(CPCs)have attracted increased attention since their discovery in the 1980s due to their valuable properties such as bioactivity,osteoconductivity,injectability,hardening ability through a low-temperature setting reaction and moldability.Thereafter numerous researches have been performed to enhance the properties of CPCs.Nonetheless,low mechanical performance of CPCs limits their clinical application in load bearing regions of bone.Also,the in vivo resorption and replacement of CPC with new bone tissue is still controversial,thus further improvements of high clinical importance are required.Bioactive glasses(BGs)are biocompatible and able to bond to bone,stimulating new bone growth while dissolving over time.In the last decades extensive research has been performed analyzing the role of BGs in combination with different CaPs.Thus,the focal point of this review paper is to summarize the available research data on how injectable CPC properties could be improved or affected by the addition of BG as a secondary powder phase.It was found that despite the variances of setting time and compressive strength results,desirable injectable properties of bone cements can be achieved by the inclusion of BGs into CPCs.The published data also revealed that the degradation rate of CPCs is significantly improved by BG addition.Moreover,the presence of BG in CPCs improves the in vitro osteogenic differentiation and cell response as well as the tissue-material interaction in vivo.

Treatment of critical bone defects using calcium phosphate cement and mesoporous bioactive glass providing spatiotemporal drug delivery

Calcium phosphate cements (CPC) are currently widely used bone replacement materials with excellent bioactivity, but have considerable disadvantages like slow degradation. For critical-sized defects, however, an improved degradation is essential to match the tissue regeneration, especially in younger patients who are still growing. We demonstrate that a combination of CPC with mesoporous bioactive glass (MBG) particles led to an enhanced degradation in vitro and in a critical alveolar cleft defect in rats. Additionally, to support new bone formation the MBG was functionalized with hypoxia conditioned medium (HCM) derived from rat bone marrow stromal cells. HCM-functionalized scaffolds showed an improved cell proliferation and the highest formation of new bone volume. This highly flexible material system together with the drug delivery capacity is adaptable to patient specific needs and has great potential for clinical translation.

Bioactive calcium and mangnesium phosphate bone adhesive for enhanced vascularization and bone regeneration

Bone adhesive is a promising material for the treatment of bone fractures,which is helpful for the fast and effective reduction and fixation of broken bones.However,the existing adhesives bond weakly to bone tissues,and are non-absorbable,or hard to cure under wet conditions.Herein,inspired by the cement-based adhesive used in the industry field,we report a bioactive calcium and magnesium phosphate bone adhesive(MPBA)with the properties of facile preparation,robust adhesion,and bioactive.MPBA is equipped with similar strength to cancellous bones and shows reliable bonding performance for various interfaces,such as Ti6Al4V,Al2O3,and poly(ether-ether-ketone).MPBA achieves excellent bonding ability for the above interfaces with the bonding strengths of 2.28±0.47,2.32±0.15,and 1.44±0.38 MPa,respectively.Besides,it also shows reliable fixation ability for bovine bone surfaces.The bonding behavior to materials and bones suggests that MPBA could be used for both fracture treatment and implant fixation.Meanwhile,MPBA possesses good biological activity,which could promote the vascularization process and osteogenic differentiation.Finally,in vivo experiments confirmed MPBA can effectively restore bone strength and promote bone regeneration.

The Release Behavior,Biocompatibility and Physical Properties of Aid-loaded Strontium Doped Calcium Phosphate Cement

The effect of concurrent attendance of two inhibitors of bone degradation,namely Alendronate(Aid)sodium trihydrate and Strontium(Sr),on Calcium Phosphate Cement(CPC)characteristics was explored.To this aim,5 wt%Strontium and 21 mM Alendronate sodium trihydrate were used in calcium phosphate cement and setting time,ion and drug release were analyzed.RAW264.7 and G cell were cultured on cement samples and Tartrate-Resistant Acid Phosphatase(TRAP),Alkaline phosphatase(ALP)activity and MTT assay were studied.The results of structural analysis indicated that 21 mM Aid did not let the cement set.Therefore,colloidal silica was added to the cement formula and successfully decreased the setting time.In vitro tests showed Sr-loaded sample had a greater inhibitory effect on biocompatibility of G cells than Aid-loaded and Sr-Ald-loaded samples.In addition,the findings about osteoblast MTT and ALP activity indicated that Sr was more effective in osteogenic activity of G cells.The simultaneous presence of Aid and Sr in Calcium Phosphate Cement(CPC)was not as effective in its biocompatibility as the presence of Sr alone.

Local treatment of osteoporosis with alendronate-loaded calcium phosphate cement

Background A new treatment strategy is to target specific areas of the skeletal system that are prone to clinically significant osteoporotic fractures.We term this strategy as the ＂local treatment of osteoporosis＂.The study was performed to investigate the effect of alendronate-loaded calcium phosphate cement （CPC） as a novel drug delivery system for local treatment of osteoorosis.Methods An in vitro study was performed using CPC fabricated with different concentrations of alendronate （ALE,0,2,5,10 weight percent （wt％））.The microstructure,setting time,infrared spectrum,biomechanics,drug release,and biocompatibility of the composite were measured in order to detect changes when mixing CPC with ALE.An in vivo study was also performed using 30 Sprague-Dawley rats randomly divided into six groups：normal,Sham （ovariectomized （OVX） ＋ Sham）,CPC with 2％ ALE,5％ALE,and 10％ ALE groups.At 4 months after the implantation of the composite,animals were sacrificed and the caudal vertebrae （levels 4-7） were harvested for micro-CT examination and biomechanical testing.Results The setting time and strength of CPC was significantly faster and greater than the other groups.The ALE release was sustained over 21 days,and the composite showed good biocompatibility.In micro-CT analysis,compared with the Sham group,there was a significant increase with regard to volumetric bone mineral density （BMD） and trabecular number （Tb.N） in the treated groups （P ＜0.05）.Trabecular spacing （Tb.Sp） showed a significant increase in the Sham group compared to other groups （P ＜0.01）.However,trabecular thickness （Tb.Th） showed no significant difference among the groups.In biomechanical testing,the maximum compression strength and stiffness of trabecular bone in the Sham group were lower than those in the experimental groups.Conclusions The ALE-loaded CPC displayed satisfactory properties in vitro,which can reverse the OVX rat vertebral trabecular bone microarchitecture and biomechanical properties in vivo.