Relevance of microstructure for the early antibiotic release of fresh and pre-set calcium phosphate cements

Calcium phosphate cements (CPCs) have great potential as carriers for controlled release and vectoring of drugs in the skeletal system. However, a lot of work still has to be done in order to obtain reproducible and predictable release kinetics. A particular aspect that adds complexity to these materials is that they cannot be considered as stable matrices, since their microstructure evolves during the setting reaction. The aims of the present work were to analyze the effect of the microstructural evolution of the CPC during the setting reaction on the release kinetics of the antibiotic doxycycline hyclate and to assess the effect of the antibiotic on the microstructural development of the CPC. The incorporation of the drug in the CPC modified the textural and microstructural properties of the cements by acting as a nucleating agent for the heterogeneous precipitation of hydroxyapatite crystals, but did not affect its antibacterial activity. In vitro release experiments were carried out on readily prepared cements (fresh CPCs), and compared to those of pre-set CPCs. No burst release was found in any formulation. A marked difference in release kinetics was found at the initial stages; the evolving microstructure of fresh CPCs led to a two-step release. Initially, when the carrier was merely a suspension of α-TCP particles in water, a faster release was recorded, which rapidly evolved to a zero-order release. In contrast, pre-set CPCs released doxycycline following non-Fickian diffusion. The final release percentage was related to the total porosity and entrance pore size of each biomaterial.     

Controlled release of gentamicin from calcium phosphate-poly(lactic acid-co-glycolic acid) composite bone cement

Modification of a self setting bone cement with biodegradable microspheres to achieve controlled local release of antibiotics without compromising mechanical properties was investigated. Different biodegradable microsphere batches were prepared from poly(lactic-co-glycolic acid) (PLGA) using a spray-drying technique to encapsulate gentamicin crobefate varying PLGA composition and drug loading. Microsphere properties such as surface morphology, particle size and antibiotic drug release profiles were characterized. Microspheres were mixed with an apatitic calcium phosphate bone cement to generate an antibiotic drug delivery system for treatment of bone defects. All batches of cement/microsphere composites showed an unchanged compressive strength of 60 MPa and no increase in setting time. Antibiotic release increased with increasing drug loading of the microspheres up to 30% (w/w). Drug burst of gentamicin crobefate in the microspheres was abolished in cement/microsphere composites yielding nearly zero order release profiles. Modification of calcium phosphate cements using biodegradable microspheres proved to be an efficient drug delivery system allowing a broad range of 10-30% drug loading with uncompromised mechanical properties.     

骨水泥不同时相负载抗生素

背景：在人工关节置换中,骨水泥与何种抗生素配伍能起到有效预防和治疗置换后感染目前还存在争议。 目的：观察抗生素骨水泥中不同抗生素及不同混合方法对动物体内抗生素释放特性以及骨水泥力学性能的影响。 方法：36只大白兔随机抽签法分为6组,3个实验组在骨水泥固相与液相混合后分别加入2 g硫酸庆大霉素、1 g万古霉素、1.5 g头孢呋辛钠,制成负载抗生素的骨水泥,置于实验兔体内。3个对照组分别在40 g骨水泥固相与液相混合前加入2 g硫酸庆大霉素粉剂、1 g万古霉素粉剂、1.5 g头孢呋辛钠。 结果与结论：3种抗生素在兔体内持续平均释放时间均在31 d以上,骨水泥固相与液相混合后加入抗生素的3组抗生素洗提总量分别高于混合前加入抗生素的3组(P < 0.05),混合后加入万古霉素组的洗提总量高于其他各组(P < 0.05)。各组抗生素骨水泥的力学性能均优于ISO 5833国际标准,组间差异无显著性意义。提示抗生素能有效从骨水泥中释放,骨水泥中加入1.0~2.0 g抗生素不影响骨水泥的机械强度;万古霉素的洗提效果较好;骨水泥固相与液相混合后加入抗生素的混合方法更有利于抗生素的释出。     

Novel magnesium phosphate cements with high early strength and antibacterial properties

Magnesium phosphate cements (MPCs) have been extensively used as fast setting repair cements in civil engineering. They have properties that are also relevant to biomedical applications, such as fast setting, early strength acquisition and adhesive properties. However, there are some aspects that should be improved before they can be used in the human body, namely their highly exothermic setting reaction and the release of potentially harmful ammonia or ammonium ions. In this paper a new family of MPCs was explored as candidate biomaterials for hard tissue applications. The cements were prepared by mixing magnesium oxide (MgO) with either sodium dihydrogen phosphate (NaH(2)PO(4)) or ammonium dihydrogen phosphate (NH(4)H(2)PO(4)), or an equimolar mixture of both. The exothermia and setting kinetics of the new cement formulations were tailored to comply with clinical requirements by adjusting the granularity of the phosphate salt and by using sodium borate as a retardant. The ammonium-containing MPC resulted in struvite (MgNH(4)PO(4)·6H(2)O) as the major reaction product, whereas the MPC prepared with sodium dihydrogen phosphate resulted in an amorphous product. Unreacted magnesium oxide was found in all the formulations. The MPCs studied showed early compressive strengths substantially higher than that of apatitic calcium phosphate cements. The Na-containing MPCs were shown to have antibacterial activity against Streptococcus sanguinis, which was attributed to the alkaline pH developed during the setting reaction.     

Ready-to-use injectable calcium phosphate bone cement paste as drug carrier

Current developments in calcium phosphate cement (CPC) technology concern the use of ready-to-use injectable cement pastes by dispersing the cement powder in a water-miscible solvent, such that, after injection into the physiological environment, setting of cements occurs by diffusion of water into the cement paste. It has also been demonstrated recently that the combination of a water-immiscible carrier liquid combined with suitable surfactants facilitates a discontinuous liquid exchange in CPC, enabling the cement setting reaction to take place. This paper reports on the use of these novel cement paste formulations as a controlled release system of antibiotics (gentamicin, vancomycin). Cement pastes were applied either as a one-component material, in which the solid drugs were physically dispersed, or as a two-component system, where the drugs were dissolved in an aqueous phase that was homogeneously mixed with the cement paste using a static mixing device during injection. Drug release profiles of both antibiotics from pre-mixed one- and two-component cements were characterized by an initial burst release of ～7–28%, followed by a typical square root of time release kinetic for vancomycin. Gentamicin release rates also decreased during the first days of the release study, but after ～1 week, the release rates were more or less constant over a period of several weeks. This anomalous release kinetic was attributed to participation of the sulfate counter ion in the cement setting reaction altering the drug solubility. The drug-loaded cement pastes showed high antimicrobial potency against Staphylococcus aureus in an agar diffusion test regime, while other cement properties such as mechanical performance or phase composition after setting were only marginally affected.     

Gentamicin-loaded strontium-containing hydroxyapatite bioactive bone cement--an efficient bioactive antibiotic drug delivery system

Modified strontium-containing hydroxyapatite (Sr-HA) bone cement was loaded with gentamicin sulfate to generate an efficient bioactive antibiotic drug delivery system for treatment of bone defects. Gentamicin release and its antibacterial property were determined by fluorometric method and inhibition of Staphylococcus aureus (S. aureus) growth. Gentamicin was released from Sr-HA bone cement during the entire period of study and reached around 38% (w/w) cumulatively after 30 days. Antibacterial activity of the gentamicin loaded in the cements is clearly confirmed by the growth inhibition of S. aureus. The results of the amount and duration of gentamicin release suggest a better drug delivery efficiency in Sr-HA bone cement over polymethylmethacrylate bone cement. Bioactivity of the gentamicin-loaded Sr-HA bone cement was confirmed with the formation of apatite layer with 1.836 ± 0.037 μm thick on day 1 and 5.177 ± 1.355 μm thick on day 7 after immersion in simulated body fluid. Compressive strengths of the gentamicin-loaded Sr-HA cement reached 132.60 ± 10.08 MPa, with a slight decrease from the unloaded groups by 4-9%. Bending moduli of Sr-HA cements with and without gentamicin were 1.782 ± 0.072 GPa and 1.681 ± 0.208 GPa, respectively. On the contrary, unloaded Sr-HA cement obtained slightly larger bending strength of 35.48 ± 2.63 MPa comparing with 33.00 ± 1.65 MPa for loaded cement. No statistical difference was found on the bending strengths and modulus of gentamicin-loaded and -unloaded Sr-HA cements. Sr-HA bone cement loaded with gentamicin was proven to be an efficient drug delivery system with uncompromised mechanical properties and bioactivity.     

Acrylic bone cements with bismuth salicylate: Behavior in simulated physiological conditions

In a previous work, we reported the development of acrylic bone cement formulations for application in percutaneous vertebroplasty, by using bismuth salicylate (BS) as the radiopaque agent. Our objective was to obtain high radiopacity along with a therapeutical effect produced by the release of salicylic acid in situ. To follow that study, the setting kinetics and static and dynamical mechanical properties of the BS cements were studied in simulated physiological conditions. Moreover, radiopacity after various times of immersion in saline and the wettability of the cements surfaces were determined. The study finished with the analysis of the biological response. From the results, it can be concluded that physiological conditions did not affect negatively to the cements performance, since all BS-loaded cements fulfilled the ISO standard requirements. Radiopacity of the formulations was maintained over time and cements with BS were found to be biocompatible.     

A novel furanone-modified antibacterial dental glass ionomer cement

A novel furanone derivative and a polyacid constructed from it were synthesized, characterized and formulated into experimental high strength cements. The compressive strength (CS) and Streptococcus mutans viability were used to evaluate the mechanical strength and antibacterial activity of the cements. The effect of human saliva and aging were investigated. The antibacterial activity against Lactobacillus sp. and cytotoxicity to human pulp cells were also evaluated. The results show that all the formulated furanone-containing cements showed antibacterial activity, with an initial reduction in CS. The effect of the furanone derivative loading was significant. Increasing loading enhanced the antibacterial activity but reduced the initial CS of the formed cements. The derivative showed antibacterial activity against both S. mutans and Lactobacillus sp. Human saliva did not affect the antibacterial activity of the cement. The cytotoxicity study with human dental pulp cells shows that the furanone-modified cement was biocompatible. A 30 day aging study indicated that the cements may have long-lasting antibacterial activity. Within the limitations of this study it appears that the experimental cement could be a clinically attractive dental restorative due to its high mechanical strength and antibacterial function.     

High-strength resorbable brushite bone cement with controlled drug-releasing capabilities

Brushite cements differ from apatite-forming compositions by consuming a lot of water in their setting reaction whereas apatite-forming cements consume little or no water at all. Only such cement systems that consume water during setting can theoretically produce near-zero porosity ceramics. This study aimed to produce such a brushite ceramic and investigated whether near elimination of porosity would prevent a burst release profile of incorporated antibiotics that is common to prior calcium phosphate cement delivery matrices. Through adjustment of the powder technological properties of the powder reactants, that is particle size and particle size distribution, and by adjusting citric acid concentration of the liquid phase to 800mM, a relative porosity of as low as 11% of the brushite cement matrix could be achieved (a 60% reduction compared to previous studies), resulting in a wet unprecompacted compressive strength of 52MPa (representing a more than 100% increase to previously reported results) with a workable setting time of 4.5min of the cement paste. Up to 2wt.% of vancomycin and ciprofloxacin could be incorporated into the cement system without loss of wet compressive strength. It was found that drug release rates could be controlled by the adjustable relative porosity of the cement system and burst release could be minimized and an almost linear release achieved, but the solubility of the antibiotic (vancomycin>ciprofloxacin) appeared also to be a crucial factor.     

PMMA bone cement containing a quaternary amine comonomer with potential antibacterial properties

An iodinated quaternary amine dimethacrylate monomer was synthesized and incorporated as a comonomer in acrylic bone cements. Bone cement is used in orthopaedic surgery and imparting antibacterial properties to the cement can be beneficial in the lowering of bacterial infection post surgery. PMMA based bone cements were modified by copolymerising the monomer methylmethacrylate (MMA) with a quaternary amine dimethacrylate by using the redox initiator activator system as used for curing commercial bone cements. The cements were prepared using the commercial PMMA bone cement CMW and the liquid component was modified with the amine to render antimicrobial properties to the cement. The physical, mechanical, and antimicrobial properties of the modified cements were evaluated; in addition, the viability of the cement to function as a orthopaedic cement was also established, especially with an advantage of it being radiopaque, due to the inclusion of the iodine containing quaternary amine. The cytotoxicity of the modified cements were tested using a human cell model and the results indicated that the cells remained metabolically active and proliferated when placed in direct contact with the experimental cement specimens. The cements and their eluants did not evoke any cytotoxic response.     

Comparative study on the properties of acrylic bone cements prepared with either aliphatic or aromatic functionalized methacrylates

Bone cements prepared with methacrylic acid (MAA) and diethyl amino ethyl methacrylate (DEAEM) were compared with formulations employing 4-methacryloyloxybenzoic acid (MBA) and 4-diethyaminobenzyl methacrylate (DEABM) as comonomer. The influence of these new aromatic monomers on various physicochemical, setting and mechanical properties was assessed. Surface characterization demonstrated that bone cements prepared with any of the functionalized monomers exhibited increasing hydrophilicity with monomer concentration and that the aromatic monomers provided more hydrophilic cements than their aliphatic counterparts for low concentrations of the functional monomer. It was also found that bone cements prepared with high amounts of the acidic aliphatic monomer provided the highest exotherm of reaction and their setting times were shorter than MBA based cements. On the other hand, DEABM containing bone cements exhibited shorter setting times than DEAEM formulations and slightly higher peak temperatures. In general, it was found that the glass transition temperature increased with the presence of acidic comonomer and decreased when alkaline comonomers were present, especially aliphatic ones. When aromatic methacrylates were used at 0.05 molar fraction, the highest tensile and compressive strength were achieved i.e. 46 and 118 MPa for MBA and 51 and 108 MPa for DEABM formulations. A further increase in the aromatic monomer concentration led to cements of low mechanical properties due to solubility problems as revealed by SEM.     

Controlled release properties and final macroporosity of a pectin microspheres–calcium phosphate composite bone cement

The use of calcium phosphate cements (CPC) is restricted by their lack of macroporosity and poor drug release properties. To overcome these two limitations, incorporating degradable polymer microparticles into CPC is an attractive option, as polymer microparticles could help to control drug release and induce macroporosity after degradation. Although few authors have yet tested synthetic polymers, the potentiality of polysaccharides’ assuming this role has never been explored. Low-methoxy amidated pectins (LMAP) constitute valuable candidates because of their biocompatibility and ionic and pH sensitivity. In this study, the potentiality of a LMAP with a degree of esterification (DE) of 30 and a degree of amidation (DA) of 19 was explored. The aim of this study was to explore the influence of LMAP microspheres within the composite on the cement properties, drug release ability and final macroporosity after microspheres degradation. Three LMAP incorporation ratios, 2%, 4% and 6% w/w were tested, and ibuprofen was chosen as the model drug. In comparison with the CPC reference, the resulting composites presented reduced setting times and lowered the mechanical properties, which remained acceptable for an implantation in moderate-stress-bearing locations. Sustained release of ibuprofen was obtained on at least 45 days, and release rates were found to be controlled by the LMAP ratio, which modulated drug diffusion. After 4 months of degradation study, the resulting CPC appeared macroporous, with a maximum macroporosity of nearly 30% for the highest LMAP incorporation ratio, and interconnectivity between pores could be observed. In conclusion, LMAP appear as interesting candidates to generate macroporous bone cements with tailored release properties and macroporosity by adjusting the pectin content within the composites.     

Comparative study of bone cements prepared with either HA or alpha-TCP and functionalized methacrylates

The properties of bone cements prepared with both hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) and methacrylates containing acidic or basic groups are the main interest of this article. The presence of methacrylic acid or diethyl amino ethyl methacrylate as comonomers in the bone cement and both ceramic types as filler were found not to affect the amount of residual monomer, which was generally less than 4.5 wt%. In contrast, setting times, maximum temperature, and glass transition temperature were found to be composition dependent. For samples with acidic comonomer, a faster setting time, a higher maximum temperature, and higher glass transition temperatures were observed compared to those with the basic comonomer. The presence of the fillers slightly increased the setting time but did not affect the other parameters. The mechanical properties of the filled bone cements depended mainly on composition and type of testing. Both HA or alpha-TCP filled systems fulfilled the minimum compressive strength required for bone cement application, although a significantly lower value was observed for the alkaline comonomer systems. The minimum bending strength was not satisfied by any of these formulations. The tensile and shear strength of these composites ranged from 20 to 37.9 and from 18 to 27 MPa, respectively. In all cases it was higher for bone cements containing methacrylic acid. The results of this study suggest that the properties of dry unfilled bone cements prepared with MAA are comparable to CMW 3 in mechanical terms but inferior in their setting properties.     

Structure-property relationships of DEAEM-containing bone cements: effect of the substitution of a methylene group by an aromatic ring

New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoethyl methacrylate (DEAEM) by an aromatic ring at two different positions. Diethylamino benzyl methacrylate (DEABM) and N-methacryloyloxyethyl)-N-ethyl-m-toluidine (MEET) were polymerized and incorporated as co-monomers in bone cement formulations. Cements were evaluated in terms of curing and mechanical properties in addition to changes in their glass transition temperature by DSC and surface properties by contact angle measurements. The immediate effect of the presence of an aromatic ring within the amino methacrylate was that it modified the bone cements' physical appearance, as colored products were obtained. It was also observed that peak temperature increased and setting time decreased by the use of DEABM and MEET instead of DEAEM. Simultaneously, both tensile and compressive strength of bone cements were improved; this effect was related to a higher glass transition temperature. In addition, surface properties of cements were modified by the incorporation of the aromatic ring, being more hydrophilic at low molar fractions and more hydrophobic at high molar fractions. Based on these studies, it is concluded that the position of the aromatic ring within the amino methacrylate modified not only the cement's appearance, but also the setting and mechanical properties.     

纳米银缓释壳聚糖/聚乙烯醇伤口敷料的制备及表征

背景：临床上传统治疗创面感染主要使用抗生素药物敷料,但长期使用会诱导细菌耐药;同时纳米创伤敷料生物相容性差,无法降解,不宜长期覆盖创面。 目的：制备一种具有抗菌作用、生物相容性良好的伤口敷料,并表征分析其生物学性能。 方法：采用缩醛化反应制得含纳米银/聚乙二醇的壳聚糖/聚乙醇酸海绵,检测材料的物理性能、表面形貌、体外释放及抗菌性能。 结果与结论：制得的纳米银粒径小,分散性良好,体外释放实验表明纳米银粒子可持续不断地从辅料释放出来,作用于细菌。含纳米银/聚乙二醇的壳聚糖/聚乙烯醇海绵孔隙致密均匀,大小孔相互贯通;吸水性大、保湿性高、透气性适中;吸水率和透气率都随聚乙烯醇1799含量增加而增大;保湿率基本不变;对金黄色葡萄杆菌、大肠杆菌、白色念珠菌、铜绿假单胞菌、变伤寒沙门菌5种实验菌种均有良好杀菌效果。表明该敷料物理性能好,生物相容性及杀菌效果好。     

Effect of added gelatin on the properties of calcium phosphate cement

This study investigates the effect of gelatin on the setting time, compressive strength, phase evolution and microstructure of calcium phosphate cement. The composite cement powder (about 18 wt% gelatin, and 82 wt% alpha-tricalcium phosphate) was prepared from the solid compound obtained by casting a gelatin aqueous solution containing alpha-tricalcium phosphate. 5 wt% of CaHPO(4) x 2H(2)O were added to the powder before mixing with the liquid phase. Two cement formulations were prepared using two different liquid/powder ratios, and their properties compared with those of control samples, prepared without gelatin. The final setting time increases from 10 min to more than 45 min when the L/P ratio increases from 0.3 to 0.4 ml/g. The presence of gelatin accelerates the setting reaction, and improves the mechanical properties of the cements. The compressive strength increases with the setting reaction up to 10.7-14.0 MPa for the gelatin cements, whereas the control samples exhibit much lower values. The improved mechanical properties of the composite cements with respect to the controls can be related to their reduced total porosity and more compact microstructure.     

Influence of lactose addition to gentamicin-loaded acrylic bone cement on the kinetics of release of the antibiotic and the cement properties

The purpose of this study was to characterize a poly(methyl methacrylate) bone cement that was loaded with the antibiotic gentamicin sulphate (GS) and lactose, which served to modulate the release of GS from cement specimens. The release of GS when the cement specimens were immersed in phosphate-buffered saline at 37 °C was determined spectrophotometrically. The microstructure, porosity, density, tensile properties and flexural properties of the cements were determined before and after release of GS. A kinetics model of the release of GS from the cement that involved a coupled mechanism based on dissolution/diffusion processes and an initial burst effect was proposed. Dissolution assay results showed that drug elution was controlled by a diffusion mechanism which can be modulated by lactose addition. Density values and mechanical properties (tensile strength, flexural strength, elastic modulus and fracture toughness) were reduced by the increased porosity resulting from lactose addition, but maintained acceptable values for the structural functions of bone cement. The present results suggest that lactose-modified, gentamicin-loaded acrylic bone cements are potential candidates for use in various orthopaedic and dental applications.     

Adhesion enhancement of steel fibers to acrylic bone cement through a silane coupling agent

The use of a silane coupling agent (methacryloxypropyl-trichlorosilane) to improve the mechanical properties of steel fiber-reinforced acrylic bone cements was assessed. Changes to the tensile and fracture properties of bone cements reinforced with silane-coated or uncoated 316L stainless steel fibers of different aspect ratios were studied. Contact-angle measurements indicated that the coupling agent coats the metal surface through room temperature treatments in a short time (within 2 h). Push-out tests indicated that the interfacial shear strength of silane-coated 316L stainless steel rods is 141% higher than the uncoated rods. The elastic moduli, ultimate stresses, and fracture toughness of the silane-coated, steel fiber-reinforced bone cements are significantly higher than the bone cements reinforced with uncoated steel fibers. There were no differences in the tensile mechanical properties of the silane-coated or uncoated, steel fiber-reinforced cements after aging in a physiological saline solution, indicating that the bonding effectiveness is decreased by the intrusion of water at the metal-polymer interface. Because of possible biocompatibility issues with leaching of the silane coupling agent and no long-term mechanical benefit in simulated aging experiments, the use of these agents is not recommended for in vivo use.     

Setting kinetics and mechanical properties of flax fibre reinforced glass ionomer restorative materials

Regardless of the excellent properties of glass ionomer cements, their poor mechanical properties limit their applications to non-load bearing areas. This study aimed to investigate the effect of incorporated short, chopped and randomly distributed flax fibers (0, 0.5, 1, 2.5, 5 and 25 wt%) on setting reaction kinetics, and mechanical and morphological properties of glass ionomer cements. Addition of flax fibers did not significantly affect the setting reaction extent. According to their content, flax fibers increased the compressive (from 148 to 250 MPa) and flexure strength (from 20 to 42 MPa). They also changed the brittle behavior of glass ionomer cements to a plastic one. They significantly reduced the compressive (from 3 to 1.3 GPa) and flexure modulus (from 19 to 14 GPa). Accordingly, flax fiber-modified glass ionomer cements could be potentially used in high-stress bearing areas.     

Properties of an injectable low modulus PMMA bone cement for osteoporotic bone

The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening. Fractures in the adjacent vertebrae may be the consequence of this procedure. PMMA with a reduced Young's modulus may be more suitable. The goal of this study was to produce and characterize stiffness adapted PMMA bone cements. Porous PMMA bone cements were produced by combining PMMA with various volume fractions of an aqueous sodium hyaluronate solution. Porosity, Young's modulus, yield strength, polymerization temperature, setting time, viscosity, injectability, and monomer release of those porous cements were investigated. Samples presented pores with diameters in the range of 25-260 microm and porosity up to 56%. Young's modulus and yield strength decreased from 930 to 50 MPa and from 39 to 1.3 MPa between 0 and 56% porosity, respectively. The polymerization temperature decreased from 68 degrees C (0%, regular cement) to 41 degrees C for cement having 30% aqueous fraction. Setting time decreased from 1020 s (0%, regular cement) to 720 s for the 30% composition. Viscosity of the 30% composition (145 Pa s) was higher than the ones received from regular cement and the 45% composition (100-125 Pa s). The monomer release was in the range of 4-10 mg/mL for all porosities; showing no higher release for the porous materials. The generation of pores using an aqueous gel seems to be a promising method to make the PMMA cement more compliant and lower its mechanical properties to values close to those of cancellous bone.