Comprehensive biocompatibility testing of a new PMMA-HA bone cement versus conventional PMMA cement in vitro

For more than 50 years PMMA bone cements have been used in orthopaedic surgery. In this study attempts were made to show whether cultured human bone marrow cells (HBMC) show an osteogenetic response resulting in new bone formation, production of extracellular matrix (ECM) and cell differentiation when they were cultured onto polymerized polymethylmethacrylate (PMMA)-hydroxyapatite (HA), conventional PMMA bone cement being taken as reference. Biocompatibility parameters were collagen-I and -III synthesis, the detection of the osteoblast markers alkaline phosphatase (ALP) and osteocalcin, the number of adherent cells and the cytodifferentiation of immunocompetent cells. Cement surface structure, HA stability in culture medium and chemical element analysis of specimens were considered. Fresh marrow cells were obtained from the human femora during hip replacement. Incubation time was up to ten weeks. We used atomic forced microscopy (AFM) and scanning electron microscopy (SEM) for cement specimen analysis. Fluorescent activated cell sorter (FACS), immunohistochemical staining, SEM and light microscopy (LM) served us to judge the cellular morphology. Products of the extracellular matrix were analyzed by protein dot blot analysis, SEM energy dispersive X-ray analysis (SEM-EDX) and Ca²⁺/PO₄ ^3- detection. HA particles increased the osteogenetic potential of PMMA bone cement regarding the cellular production of collagen, alkaline phosphatase (AP), the number of osteoblasts and the cellular differentiation pattern in vitro. Both tested cements showed good biocompatibility in a human long-term bone marrow cell-culture system.     

Extensive H(+) release by bone substitutes affects biocompatibility in vitro testing

Bone substitutes are widespread in orthopedic and trauma surgery to restore critical bony defects and/or promote local bone healing. Cell culture systems have been used for many years to screen biomaterials for their toxicity and biocompatibility. This study applies a human bone marrow cell culture system to evaluate the toxic in vitro effects of soluble components of different bone substitutes, which are already in clinical use. Different specimens of tricalcium phosphates (TCP) (Vitoss, Cerasorb), nondecalcified bovine bone (Lubboc), demineralized human bone matrices (DBM) (Grafton Flex/Putty), and collagen I/III matrix (ACI-Maix) were tested in Dulbecco's modified Eagle's medium (DMEM) and MesenCult culture solution and compared with a biomaterial-free cell culture. Biocompatibility parameters were cell viability evaluated by phase-contrast microscopy and laser flow cytometry, morphology, and the local H(+) release by bone substitutes. There were significant differences (p < 0.05) between the tested biomaterials and culture solutions. Collagen I/III, non-demineralized bovine bone, and TCP materials showed advantages for cell survival over other tested biomaterials (average values of vital cells/mL MesenCult/DMEM: Collagen I/III: 1090/1083; Vitoss: 893/483; Cerasorb: 471/523; Lubboc: 815/410; Grafton Putty: 61/44; Grafton Flex: 149/57). Especially the DBM materials lead to a significant decrease of pH, which is considered to be a major factor for cell death. DMEM culture solution supports cell survival for those bone substitutes that induce an alkaline reaction, whereas MesenCult media promotes cell vitality in biomaterials, which leads to an acidification of culture solution.     

Free radical decay kinetics in PMMA bone cement

Electron-spin resonance has been used to measure the decay of the concentration of polymerization radicals in polymethyl methacrylate (PMMA) bone cement and the kinetics of the decay determined. Thermal annealing at various temperatures has shown that the logarithm of the concentration of radicals varies linearly with time, but with a nonzero intercept. These results have been analyzed by including both first- and second-order decay processes. The first-order process has an activation energy of 39 +/- 2 kcal/mol and is probably due to a diffusion-limited termination. The second-order process has an activation energy of 36 +/- 5 kcal/mol and is probably due to bimolecular termination.     

Leaching of tobramycin from PMMA bone cement beads

The in vitro leaching characteristics of tobramycin from acrylic resin (PMMA) bone cement beads have been determined by a radioimmune assay. Tobramycin was incorporated at two concentrations into bone cement beads fabricated from three commercial brands of acrylic resin. Antibiotic leaching followed a curvilinear relationship of the form X . Y = A . X + B . Y. All beads showed similar tobramycin leaching rates over time but the initial amount of leached material differed with the amount of tobramycin incorporated in the bead and the source of the PMMA bone cement. The data indicate that tobramycin-impregnated PMMA beads permit antibiotic leaching at a controlled rate compatible with possible clinical application.     

Repair of segmental bone defects using bioactive bone cement: comparison with PMMA bone cement.

We developed a bioactive bone cement (BABC) that consists of apatite and wollastonite containing glass ceramic (AW-GC) powder and bisphenol-A-glycidyl dimethacrylate (Bis-GMA) based resin. In the present study, the effectiveness of the BABC for repair of segmental bone defects under load-bearing conditions was examined using a rabbit tibia model. Polymethylmethacrylate (PMMA) bone cement was used as a control. A 15-mm length of bone was resected from the middle of the shaft of the tibia, and the tibia was fixed by two Kirschner wires. The defects were replaced by cement. Each cement was used in 12 rabbits; six rabbits were sacrificed at 12 and 25 weeks after surgery, and the tibia containing the bone cement was excised and tension tested. At both the intervals studied, the failure loads of the BABC were significantly higher than those of the PMMA cement. The BABC was in direct contact with bone, whereas soft tissue was observed between the cement and bone in all PMMA cement specimens. Results indicated that the BABC was useful as a bone substitute under load-bearing conditions.     

Low-modulus PMMA bone cement modified with castor oil

Some of the current clinical and biomechanical data suggest that vertebroplasty causes the development of adjacent vertebral fractures shortly after augmentation. These findings have been attributed to high injection volumes as well as high Young's moduli of PMMA bone cements compared to that of the osteoporotic cancellous bone. The aim of this study was to evaluate the use of castor oil as a plasticizer for PMMA bone cements. The Young's modulus, yield strength, maximum polymerization temperature, doughing time, setting time and the complex viscosity curves during curing, were determined. The cytotoxicity of the materials extracts was assessed on cells of an osteoblast-like cell line. The addition of up to 12 wt% castor oil decreased yield strength from 88 to 15 MPa, Young's modulus from 1500 to 446 MPa and maximum polymerization temperature from 41.3 to 25.6°C, without affecting the setting time. However, castor oil seemed to interfere with the polymerization reaction, giving a negative effect on cell viability in a worst-case scenario.     

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.     

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.     

Attachment of PMMA cement to bone: force measurements in rats

The attachment of an implant material to bone relates to surface roughness and surface chemistry. There is a relatively low chemical bonding strength of so-called bioactive surfaces. Hydroxyapatite interfaces typically have an interfacial tensile strength of 0.15-1.5 MPa. An attachment force similar to that of bioactive surfaces might also be reached through mechanical interlock with ordinary bone cement. This study measured bone cement interfacial tensile strength for polished (R(a) 0.5 microm) and regular (R(a) 4.8 microm) vacuum mixed PMMA bone cement. Bone bonding was evaluated by a detachment test. We used unloaded cement surfaces, which could be detached from the bone. Titanium plates were developed such that a cement fill was contained within a plate, which was contained within a titanium holder. The cement surface came into contact with traumatized bone only, and the rest of the plate had no contact with tissue. The cement surface was either polished or left untreated after conventional preparation. Four weeks later, the plates were detached from the bone by a perpendicular force. The detaching load of the polished cement surface never exceeded 0.07 MPa, whereas for unpolished cement there was a load up to 0.9 MPa. The results suggest that surface irregularities and microinterlock enable an attachment that can resist tension between bone and a cement surface.     

Effect of vacuum-treatment on deformation properties of PMMA bone cement

Deformation behavior of polymethyl methacrylate (PMMA) bone cement is explored using microindentation. Two types of PMMA bone cement were prepared. Vacuum treated samples were subjected to the degassing of the material under vacuum of 270 mbar for 35 s, followed by the second degassing under vacuum of 255 mbar for 35 s. Air-cured samples were left in ambient air to cool down and harden. All samples were left to age for 6 months before the test. The samples were then subjected to the indentation fatigue test mode, using sharp Vickers indenter. First, loading segment rise time was varied in order to establish time-dependent behavior of the samples. Experimental data showed that viscous part of the deformation can be neglected under the observed test conditions. The second series of microindentation tests were realized with variation of number of cycles and indentation hardness and modulus were obtained. Approximate hardness was also calculated using analysis of residual impression area. Porosity characteristics were analyzed using CellC software. Scanning electron microscopy (SEM) analysis showed that air-cured bone cement exhibited significant number of large voids made of aggregated PMMA beads accompanied by particles of the radiopaque agent, while vacuum treated samples had homogeneous structure. Air-cured samples exhibited variable hardness and elasticity modulus throughout the material. They also had lower hardness values (approximately 65-100 MPa) than the vacuum treated cement (approximately 170 MPa). Porosity of 5.1% was obtained for vacuum treated cement and 16.8% for air-cured cement. Extensive plastic deformation, microcracks and craze whitening were produced during indentation of air-cured bone cement, whereas vacuum treated cement exhibited no cracks and no plastic deformation.     

Pressurization of bioactive bone cement in vitro

We have developed a bioactive bone cement consisting of MgO-CaO-SiO2-P2O5-CaF2 glass-ceramic powder (AW glass-ceramic powder), silica glass powder as an inorganic filler, and bisphenol-a-glycidyl methacrylate (bis-GMA) based resin as an organic matrix. The efficacy of this bioactive bone cement was investigated by evaluating its pressurization in a 5-mm hole and small pores using a simulated acetabular cavity. Two types of acetabular components were used (flanged and unflanged sockets) and a commercially available polymethylmethacrylate (PMMA) bone cement (CMW 1 Radiopaque Bone Cement) was selected as a comparative control. Bioactive bone cement exerted greater intrusion volume in 5-mm holes than PMMA bone cement in both the flanged and unflanged sockets 10 minutes after pressurization (p < 0.05). In the small pores the bioactive and PMMA bone cements exerted almost identical intrusion volumes in flanged and unflanged sockets 10 min after pressurization. The intrusion volume in the flanged socket 10 minutes after pressurization was greater than that in the unflanged socket in all groups (p < 0.05). These results show that bioactive bone cement intrudes deeper into anchor holes than PMMA bone cement.     

Influence of mixing technique on some properties of PMMA bone cement

PMMA bone cements (Refobacin-Palacos R, Sulfix 6, AKZ, and CMW bone cement, types I and II), from six different clinics, were investigated in three stages. In the first stage, studies of density, hardness, flexural strength, and compressive strength were made, as well as molecular weight measurements and microscopic investigations. These studies reflected the current state of techniques of application used in operating theaters. They revealed wide variations in the properties of the materials studied. Secondly, a comprehensive study of the process-technology in the laboratory was performed. The following variables were investigated or discussed: mixing vessel, order of the individual components, mixing time, rate of mixing, pressure application on the mixed bone cement, kneading, cement thickness, pouring into the syringe, contact force during polymerization, and preparation quantity. The third stage involved the development and clinical testing of an improved mixing technique. Using this improved mixing technique, all three selected clinics achieved far better results with reduced variability. A comparison between a centrifuging technique after mixing and our improved, but conventional, mixing technique, displays advantages for the latter. The question regarding a correlation between cement specimens of high porosity and early implant loosening could not be answered on the basis of the 43 PMMA bone cement explants investigated (implanted 6 months to 15 years). In some cases, the studies revealed that the bone cement manufacturers should be required to revise and quantify existing instructions for use. The users, on the other hand, should give more consideration to the mixing technique and its consequences.     

Preliminary study of interfacial shear strength between PMMA precoated UHMWPE acetabular cup and PMMA bone cement

Followed by successful demonstration of high interfacial tensile strength in a new design of cemented all-polyethylene acetabular cup, interfacial shear strength was investigated in this study, with the use of canine-size prototypes of polymethylmethacrylate (PMMA) precoated UHMWPE acetabular cups. In addition to the PMMA precoated prototypes, three different types of controls were also prepared and tested: grooved UHMWPE cups, PMMA (bone cement) cups, and noncoated, plain UHMWPE cups. The interfacial shear strength of the precoated prototypes was 10.1 +/- 0.69 MPa (n = 6), whereas it was 24.3 +/- 0.78 MPa (n = 2) for the PMMA cup, 6.95 +/- 0.21 MPa (n = 2) for the grooved UHMWPE cup, and 0.34 +/- 0.47 MPa (n = 2) for the UHMWPE cup. These results indicate benefits of the PMMA precoating to stabilize the polyethylene acetabular cup securely when applied with bone cement in simulated clinical applications. Analysis of the failed PMMA precoated UHMWPE prototype cups suggested that the chemically induced bonds between precoated PMMA layer and bone cement played a key role in developing high shear strength. After the interfacial shear test of the PMMA precoated prototypes, major disruptions at the interface between treated UHMWPE and precoated PMMA layer were observed by scanning electron microscopy (SEM), which was a unique failure pattern, not found with other prototypes.     

New bioactive glass-ceramic: synthesis and application in PMMA bone cement composites

In present study, a new composition of glass-ceramic was synthesized based on the Na2O-CaO-SiO2-P2O5 glass system. Heat treatment of glass powder was carried out in 2 stages: 600 °C as the nucleation temperature and different temperature on crystallization at 850, 950 and 1000 °C. The glass-ceramic heat-treated at 950 °C was selected as bioactive filler in commercial PMMA bone cement; (PALACOS? LV) due to its ability to form 2 high crystallization phases in comparison with 850 and 1000 °C. The results of this newly glass-ceramic filled PMMA bone cement at 0-16 wt% of filler loading were compared with those of hydroxyapatite (HA). The effect of different filler loading on the setting properties was evaluated. The peak temperature during the polymerization of bone cement decreased when the liquid to powder (L/P) ratio was reduced. The setting time, however, did not show any trend when filler loading was increased. In contrast, dough time was observed to decrease with increased filler loading. Apatite morphology was observed on the surface of the glass-ceramic and selected cement after bioactivity test.     

Evaluation of the biocompatibility of polymers implanted into bone using titanium mosaic on bone cement

A method for high-resolution study of the interaction of bone and polymeric materials is described. By creating a 'mosaic' surface of polymer and pure titanium, using the titanium as an internal control, the tissue influence of the polymer surface can be deduced.     

Bone bonding ability and handling properties of a titania-polymethylmethacrylate (PMMA) composite bioactive bone cement modified with a unique PMMA powder

One of the challenges of using bioactive bone cements is adjusting their handling properties for clinical application. To resolve the poorer handling properties of bioactive bone cements we developed a novel bioactive bone cement containing a unique polymethylmethacrylate (PMMA) powder, termed SPD-PMMA (40 μm in diameter), composed of cohered minute particles of PMMA (0.5 μm). The present study aimed to examine the mechanical and handling properties and the in vivo bone bonding strength of this cement. The titania content of the cement varied from 10 to 30 wt.% (Ts10, Ts20, and Ts30). The mechanical and thermal properties of Ts10 and Ts20 exceeded those of commercially available PMMA cements (PMMAc). The setting properties of Ts20, including a shorter dough time and a working time that was comparable with that of PMMAc, were adequate for clinical application. Hardened cylindrical cement specimens were inserted into rabbit femurs and the interfacial shear strengths were measured by a push-out test at 6, 12, and 26 weeks after the operation. The interfacial shear strength values (in Newtons per square millimeter) of Ts10, Ts20, and Ts30 at 12 weeks and those of Ts20 and Ts30 at 26 weeks were significantly higher than that of PMMAc (P < 0.05). These results show that a bioactive titania–PMMA composite bone cement modified by SPD-PMMA particles possesses adequate mechanical and handling properties, as well as osteoconductivity and in vivo bone bonding ability, and can be used for prosthesis fixation.     

The water jet as a new tool for endoprosthesis revision surgery--an in vitro study on human bone and bone cement

In revision surgeries of endoprostheses, the interface between implant and bone cement or bone must be loosened. Conventional tools have many disadvantages because of their size and limited range. Taking advantage of the selective and athermic cutting process, a plain water jet is already used in order to cut soft tissues. This study investigates the possibilities of both a plain and an abrasive water jet as cutting tools for revision surgery. Samples of the mid-diaphysis of human femora and bone cement (CMW3) were cut with a plain water jet (PWJ) and an abrasive water jet (AWJ) at two different jet-to-surface angles (30 degrees,90 degrees ) and at five different pressure levels (30, 40, 50, 60, 70 MPa). For a PWJ a selective pressure range was identified, where only bone cement was cut. Injecting a bio-compatible abrasive (lactose) to the jet stream resulted in significantly higher cut depths in both materials. Material removal in bone was significantly less at the smaller jet-to-surface angle for both techniques. No clear selectivity between bone and bone cement was observed for application of the AWJ. However, the material removal rate was significantly higher for bone cement than for bone at all pressure levels. The results indicate that an AWJ might be an alternative tool for cement removal. The possibility for localised cutting at interfaces could be an advantage for revision of a non-cemented prosthesis.     

Intraocular PMMA lenses modified with surface-immobilized heparin: evaluation of biocompatibility in vitro and in vivo

Intraocular lenses (IOL) were surface modified with covalently linked heparin. The surface-bound heparin could not be removed by incubation in solutions known to be effective in breaking non-covalent bonds, nor by incubation in a solution of proteinase K and only to a limited extent by incubation with heparinase. In vitro studies demonstrated improved biocompatibility by the heparin surface-modified lens with respect to outgrowth of fibroblasts and macrophages, activation of granulocytes and adhesion of platelets. These results were subsequently verified in vivo in terms of less inflammatory cells on the lens surface and fewer incidences of synechiae after 3 and 6 wk IOL implantation in the rabbit eye.     

Biocompatibility of a new radiopaque iodine-containing acrylic bone cement

Radiopacity in the vast majority of the commercially available acrylic bone cements that are used clinically is provided by particles of either BaSO(4) or ZrO(2). Literature reports have shown these agents to have a detrimental effect on some mechanical properties of the cements as well as on its biological response. We, therefore, have developed a new type of bone cement, for which radiopacity results from the presence of an iodine-containing methacrylic copolymer. The focus of the present work was the comparison of the biocompatibility of this new cement and a commercially available cement that contains barium sulfate. In vitro experiments show that both cements are cytocompatible materials, for which no toxic leachables are found. Implantation of the cements in a rabbit for three months resulted in the occasional presence of a thin fibrous tissue at the cement-bone interface, which is common for acrylic bone cements. Consideration of all the results led to the conclusion that the new cement is as biocompatible as the BaSO(4)-containing one.