Maximum Polymerization Temperature Research Articles

Comparison of Methodologies for Selection of Bone Cements for Orthopaedic Surgical Procedures

Background: Poly (methyl methacrylate) (PMMA) bone cement is widely used in ortho-paedic procedures of vertebroplasty (VP) balloon kyphoplasty (BKP) and cemented total joint arthro-plasty (TJA). While only very few PMMA bone cement brands are approved (by the appropriate regulatory authority) for VP and BKP, many are approved for cemented TJA. Selection of cement for these applications must be done considering a very large number of clinically relevant properties, such as injectability, setting time, maximum polymerization temperature, polymerization rate, com-pressive strength, fracture toughness, fatigue life, and cytocompatibility. In the literature, there is a shortage of studies on methodologies for the selection of PMMA bone cement. Purpose: The present work addresses the aforementioned shortcoming of the literature. Methods: Three material selection methodologies (Desirability, Utility, and Weighted Property Index Methods) were applied to two study sets. Study Set 1 comprised three experimental types of bone cement for VP or BKP and five in vitro values of clinically-relevant cement properties and Set 2 comprised six approved antibiotic-loaded bone cement (ALBC) brands for cemented TJA and in vitro values of four clinically-relevant cement properties. Results: For each of the study sets, slight differences in the ranks of the materials were found de-pending on the selection methodology used, but when all the selection methodologies were consid-ered, there was clear differentiation in ranks. The relative attractions and challenges of the three se-lection methodologies used are highlighted. Conclusion: Decision makers in orthopaedic hospitals and clinics as well as orthopaedic surgeons, should find the results of the present study useful.

Modified Cyclodextrin Microparticles to Improve PMMA Drug Delivery Without Mechanical Loss.

Antibiotic-loaded poly(methyl methacrylate) (PMMA) cement is commonly used as a local delivery system to treat and prevent orthopedic infections associated with arthroplasties in load-bearing applications. However, these delivery systems are inefficient as release rate sharply declines to subinhibitory levels. Prior studies have shown that by adding in drug-filled cyclodextrin (CD) microparticles into PMMA cement, a more consistent release is observed, and antibiotic refilling through simulated implantation can be achieved. However, the mechanical strengths of PMMA is reduced. In order to decrease the mechanical loss, modified CD microparticles (PMMA-CD) are synthesized that contain covalently appended PMMA chains. The compressive strengths, handling characteristics, and refilling ability of PMMA cement with PMMA-CD are evaluated. Specifically, up to a 13.7% increase in compressive strength is observed when unmodified CD is substituted with PMMA-CD in PMMA samples with 10 wt% CD microparticles. Additionally, a 13.3% increase in working time, a 7.5% decrease in maximum polymerization temperature, and up to a 32.1% increase in amount of drug refilled are observed with the addition of 10 wt% CD PMMA-CD into PMMA in comparison to plain PMMA without CD microparticles.

Thermal Analysis of the Tibial Cement Interface with Modern Cementing Technique.

Background:The major cause of cemented Total Knee Arthroplasty (TKA) failure is aseptic loosening of the tibial component necessitating revision surgery. Recently, multiple techniques have been described to maximize cement penetration depth and density in the proximal tibia during TKA to potentially avoid early loosening. While cement polymerisation is an exothermic reaction, minimal investigation into the proximal tibial thermal safety margin during cement polymerisation has been undertaken. In animal models osseous injury occurs at temperatures greater than 47 °C when applied for one minute. The aim of this study was to investigate the cement bone interface temperatures in TKA using modern tibial cementing techniques with a cadaveric tibial tray model. Methods:Eight adult cadavers were obtained with the proximal tibial surface prepared by a fellowship trained arthroplasty surgeon. Third generation cementation techniques were used and temperatures during cement polymerization on cadaveric knee arthroplasty models were recorded using thermocouples. Results:The results showed that no tibial cement temperature exceeded 44 °C for more than 1 minute. Two of the eight cadaveric tibias recorded maximum temperatures greater than 44 °C for 55 seconds and 33 seconds, just less than the 60 seconds reported to cause thermal injury. Average maximum polymerization temperatures did not correlate with deeper cement penetration or tray material. Maximum mantle temperatures were not statistically different between metal and all polyethylene tibial trays. Conclusion:Our investigation suggests that modern cementing techniques result in maximum mantle temperatures that are less than previously recorded temperatures required to cause thermal osseous injury, although this thermal injury safety margin is quite narrow at an average of 4.95 °C (95% confidence interval ± 4.31).

The effect of oligo(trimethylene carbonate) addition on the stiffness of acrylic bone cement.

With the increasing elderly population an increase in the number of bony fractures associated to age-related diseases such as osteoporosis also follows. The relatively high stiffness of the acrylic bone cements used in these patients has been suggested to give raise to a suboptimal load distribution surrounding the cement in vivo, and hence contribute to clinical complications, such as additional fractures. The aim of this study was to develop a low-modulus bone cement, based on currently used, commercially available poly(methyl methacrylate) (PMMA) cements for vertebroplasty. To this end, acrylate end-functionalized oligo(trimethylene carbonate) (oTMC) was incorporated into the cements, and the resulting compressive mechanical properties were evaluated, as well as the cytotoxic and handling properties of selected formulations. Sixteen wt%oTMC was needed in the vertebroplastic cement Osteopal V to achieve an elastic modulus of 1063 MPa (SD 74), which gave a corresponding compressive strength of 46.1 MPa (SD 1.9). Cement extracts taken at 1 and 12 hours gave a reduced MG-63 cell viability in most cases, while extracts taken at 24 hours had no significant effect on cell behavior. The modification also gave an increase in setting time, from 14.7 min (SD 1.7) to 18.0 min (SD 0.9), and a decrease in maximum polymerization temperature, from 41.5°C (SD 3.4) to 30.7°C (SD 1.4). While further evaluation of other relevant properties, such as injectability and in vivo biocompatibility, remains to be done, the results presented herein are promising in terms of approaching clinically applicable bone cements with a lower stiffness.

A pair of benzoxazine isomers from o-allylphenol and 4,4′-diaminodiphenyl ether: Synthesis, polymerization behavior, and thermal properties

An allyl-containing bifunctional benzoxazine is synthesized from o-allylphenol, 4,4′-diaminodiphenyl ether, and formaldehyde, followed by isomerization in the presence of chlorotris(triphenylphosphine)rhodium(I)/triethylsilane catalytic system yielding a propenyl-containing benzoxazine, and the chemical structures of the two isomers are confirmed. In the thermal activated polymerization, both isomers undergo the oxazine ring-opening polymerization and the radical olefin polymerization with the formation of the corresponding polybenzoxazines, but only one exothermic peak is shown on each of their dynamic differential scanning calorimetry (DSC) curves. After isomerization of allyl into propenyl, the onset and maximum polymerization temperatures decrease, but the temperature range covered by the DSC exothermic peak broadens. Consequently, the structures of the resultant polybenzoxazines are different, and some properties are obviously different, for example, the storage modulus decreases, but the glass transition temperature increases, and the thermal stability is slightly enhanced.

The effect of N-acetylcysteine addition on the polymerization behavior of PMMA bone cement

N-Acetylcysteine (NAC), a well-known thiol-containing antioxidant, may alleviate the toxicity of poly (methyl methacrylate) (PMMA) bone cement through the inactivation of the monomer components in the cement by its sulfhydryl moiety. This study aimed to reveal the effects of the NAC on the polymerization heat, degree of conversion (DC), mechanical properties, and residual monomer release of PMMA bone cement. The addition of NAC (0, 0.25, 0.50, 0.75, and 1.00 wt%) to PMMA powder significantly reduced the maximum polymerization temperature and steadily delayed the setting time. The DC of all experimental PMMA bone cements reached as high as 91% after 7 days of incubation, as determined by Fourier transform infrared spectroscopy (FTIR). The experimental groups showed steady declines in flexural strength and surface hardness as a fraction of increasing NAC. Meanwhile, the mechanical properties of the experimental groups increased with the duration of time. The amount of methyl methacrylate (MMA) leached into deionized water was analyzed using high performance liquid chromatography (HPLC) and was found to increase with an immersion time up to 24 h, after which no subsequent change was observed. The results showed a linear correlation between the thermal and mechanical properties and the released MMA with the DCs of the experimental groups. The potential usefulness of NAC in developing more biocompatible PMMA bone cement for increased working performance was highlighted in this study. Open image in new window

Direct and interactive effects of three variables on properties of PMMA bone cement for vertebral body augmentation

PMMA bone cements are widely used for vertebral body augmentation procedures vertebroplasty and balloon kyphoplasty. Although there are studies in the literature on the direct effects of relevant variables on the properties of these cements, there are none on the interactive effects. In the present work, such a study was performed on both types of effects, with the variables being the concentration of initiator (benzoyl peroxide), the concentration of crosslinker (ethylene glycol dimethacrylate), and the liquid-to-powder ratio used in preparing the cement; and the properties being the compressive strength, the compressive modulus, the doughing time, the setting time, and the maximum polymerization temperature. Two additional properties obtained from the viscosity-versus-time curves, namely the time at the onset of curing, and the critical curing rate were also studied. Significant interactive effects between the amount of crosslinker and the amount of radical initiator were found to affect the doughing time and the critical curing rate. These effects were explained in terms of the reaction kinetics. It was concluded that interactive effects may exist and should be taken into account when designing bone cement formulations.

An ex vivo exothermal and mechanical evaluation of two-solution bone cements in vertebroplasty

Background context Previous ex vivo studies showed that the properties of commercial cements modified for use in vertebroplasty are not optimal and are associated with several drawbacks, including high exothermic reaction, low cement viscosity and consequent extravasation, and unpredictable wait time after cement preparation. Additionally, strength and stiffness restoration are controversial varying with the cement type, volume injected, and technique used. Purpose To investigate maximum polymerization temperatures and mechanical performance of novel two-solution bone cement (TSBC) modified by the addition of cross-linked poly(methyl methacrylate) nanospheres (η-TSBC) and microspheres (μ-TSBC) in a cadaver vertebroplasty model in comparison to a commercially available cement (KyphX). To study the viability of application of these novel cement formulations in the treatment of vertebral compression fractures. Study design/setting Ex vivo biomechanical and exothermal evaluation of TSBCs using cadaveric vertebral bodies (VBs). Methods Thirty-one cadaveric vertebrae (age, 74±2 years; T score, −1.5±0.5) were disarticulated. Thirteen vertebrae were assigned into three groups and instrumented with thermocouples positioned midbody along the intersection of the midsagittal and midcoronal axes, as well as along the intersection of the midsagittal axis and posterior VB wall. After equilibration at 37°C, 5 mL of cement was injected and temperatures were recorded for 1 hour. The groups were injected with η-TSBC, μ-TSBC, or KyphX. The remaining 18 vertebrae were biomechanically tested. After randomization into three groups, each specimen was fractured in compression and stabilized with 5 mL of each cement type. Each specimen was then retested in axial compression. Results Temperatures in the central region of the vertebrae were significantly lower (p<.05) when injected with η-TSBC (44°C) in comparison to KyphX (75°C) and μ-TSBC (64°C). A significant difference was not detected between the pre- and postcementing strength (p>.05) of the three groups. There was no significant difference between the average values of stiffness among the cements (p>.05), however there was a significant difference between intact and treated stiffness (p<.05). Conclusions The TSBC cements decreased the local temperature within the VB while providing similar mechanical strength when compared with vertebrae treated with KyphX.

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.

Biocompatibility of alendronate-loaded acrylic cement for vertebroplasty

This paper reports a biological evaluation of a non-resorbable acrylic cement loaded with alendronate for the treatment of osteoporotic vertebral compression fractures. The cement formulation was based on polymethyl methacrylate and acrylic monomers; one of these had covalently linked vitamin E residues. The same cement in the absence of alendronate was used as a control. The setting of the charged cement presented a maximum polymerization temperature of 44°C, a setting time of 24 min, a residual monomer content lower than 3 wt.%, a compressive strength of 99±10 MPa and an elastic modulus of 1.2±0.2 GPa. Cytotoxicity studies using human osteoblast cultures revealed that the leachable substances of the alendronate loaded cement collected between 1 and 7 days decreased cell viability to values lower than 80%. However, morphological changes and cellular damage in cells produced by the extracts decreased with the leak time. Cell adhesion and growth on charged cement was significantly lower than on the control. Implantation of the cement paste in the intra-femoral cavity of rabbits showed that initially the osteogenic activity was evident for the cement charged with alendronate, and the osteosynthesis process took place mainly in the trabeculae and was manifested by the presence of a non-mineralised osseous spicule. The interface between material and adjacent bone tissue was initially characterized by a variable fibrous response that in many cases it appeared reduced to thin connective tissue after a 24-week-period.

Physical and Mechanical Properties of PMMA Bone Cement Reinforced with Nano-sized Titania Fibers

X-ray contrast medium (BaSO(4) or ZrO(2)) used in commercially available PMMA bone cements imparts a detrimental effect on mechanical properties, particularly on flexural strength and fracture toughness. These lower properties facilitate the chance of implant loosening resulting from cement mantle failure. The present study was performed to examine the mechanical properties of a commercially available cement (CMW1) by introducing novel nanostructured titania fibers (n-TiO(2) fibers) into the cement matrix, with the fibers acting as a reinforcing phase. The hydrophilic nature of the n-TiO(2) fibers was modified by using a bifunctional monomer, methacrylic acid. The n-TiO(2) fiber content of the cement was varied from 0 to 2 wt%. Along with the mechanical properties (fracture toughness (K (IC)), flexural strength (FS), and flexural modulus (FM)) of the reinforced cements the following properties were investigated: complex viscosity-versus-time, maximum polymerization temperature (T (max)), dough time (t (dough)), setting time (t (set)), radiopacity, and in vitro biocompatibility. On the basis of the determined mechanical properties, the optimized composition was found at 1 wt% n-TiO(2) fibers, which provided a significant increase in K (IC) (63%), FS (20%), and FM (22%), while retaining the handling properties and in vitro biocompatibility compared to that exhibited by the control cement (CMW1). Moreover, compared to the control cement, there was no significant change in the radiopacity of any of the reinforced cements at p = 0.05. This study demonstrated a novel pathway to augment the mechanical properties of PMMA-based cement by providing an enhanced interfacial interaction and strong adhesion between the functionalized n-TiO( 2) fibers and PMMA matrix, which enhanced the effective load transfer within the cement.

Reinforcement of resin based cement with titania nanotubes

ObjectiveOne of the limitations of resin cements and flowable dental composites is their poor mechanical properties such as low flexural strength and fracture resistance under body conditions. The present study was performed to enhance the mechanical properties of commercial acrylic cement (CMW®1) by introducing novel nanostructured titania tubes (n-TiO2 tubes) into the cement matrix, with the tubes acting as a reinforcing phase. The long term objective is to add these fillers as reinforcement to dental resin cements and flowable composites in combination with existing fillers. MethodsThe surface of the n-TiO2 tubes was modified using a bi-functional monomer, methacrylic acid. The n-TiO2 tube content of the cement was varied from 0 to 2wt.%. The following cement properties were investigated: maximum polymerization temperature (Tmax), dough time (tdough), setting time (tset), complex viscosity-versus-time, radiopacity, fracture toughness (KIC), flexural strength (FS), flexural modulus (FM) and in vitro biocompatibility. ResultsBased on the determined mechanical properties, the optimized composition was found at 1wt.% n-TiO2 tubes, which provided a significant increase in KIC (73%), FS (42%) and FM (56%). However the rheology, radiopacity and biocompatibility were not different from the control (CMW®1). SignificanceEnhanced interaction and strong adhesion between the functionalized n-TiO2 tubes and polymer matrix allows external mechanical stress to be more effectively transferred through the filler-matrix interface. This novel filler in conjunction with the existing ones can be used to reinforce orthopedic and dental cements as well as flowable dental composites without altering the rheology, radiopacity and biocompatibility.

Two‐solution bone cements with cross‐linked micro and nano‐particles for vertebral fracture applications: Effects of zirconium dioxide content on the material and setting properties

The application of bone cements for the treatment of vertebral compression fracture requires radiopaque materials for adequate visualization of the flow under fluoroscopy. Besides high radiopacity, it is desirable for the cement to have relatively low viscosity, high compressive strength and appropriate curing parameters. In this study, the properties of novel two-solution bone cements composed of cross-linked poly (methyl methacrylate) PMMA microspheres or nanospheres added to the linear polymer phase were assessed for formulations with increasing concentrations of zirconium dioxide (ZrO(2)). The addition of a cross-linked phase in the standard two-solution formulation (TSBC) was observed to improve the material properties by increasing setting time and decreasing maximum polymerization temperatures and decreasing the initial viscosity in comparison to the standard cement. The properties of three formulations (TSBC, modified two-solution containing cross-linked PMMA microspheres, and nanospheres) were measured for cements prepared at 0%, 5%, 20%, and 30% ZrO(2) and compared to KyphX. Cements prepared with cross-linked particles exhibited significantly higher compressive strength than the standard-two solution cement and KyphX at increasing radiopacifier concentrations. Furthermore, cement viscosity was increased by the addition of increasing concentrations of ZrO(2) in the modified two-solution cements, whereas the maximum polymerization exotherm and setting time of these materials were decreased. This study indicates that the addition of high concentrations of ZrO(2) significantly affects the properties of two-solution cements acting as a reinforcing phase when cross-linked spheres are added. These materials were observed to be suitable for vertebroplasty applications.

Eugenol derivatives immobilized in auto-polymerizing formulations as an approach to avoid inhibition interferences and improve biofunctionality in dental and orthopedic cements

Auto-polymerizing formulations based on poly(ethyl methacrylate) (PEMA) and eugenol derivatives are reported for dental and orthopedic applications. Spherical beads of PEMA were used as the pre-polymer powder and mixed with combinations of ethyl methacrylate and eugenyl methacrylate (EgMA) or ethoxyeugenyl methacrylate (EEgMA). A range of concentrations from 10 to 30 wt.% of EgMA or EEgMA were used to impart bioactivity properties to the cements. Increasing concentrations of the eugenol derivatives decreased the maximum polymerization temperatures from 69 to 37 °C without altering the working or setting time. At concentrations of 10 and 15 wt.% of EgMA or EEgMA a noticeable increase in the compressive (8%), flexural (40%) and tensile (24%) strengths were recorded in comparison to the control cements containing PEMA/ethyl methacrylate only. In addition to the improvement in mechanical properties the cements yielded a slightly crosslinked network due to the participation of the allylic group present in the eugenol derivatives, the presence of which has an intrinsically bactericidal effect against Escherichia coli and Streptococcus mutans strains, as reported in a previous study, thus enhancing the properties of the cements.

Thermal behavior and cured products of bis(4-maleimidodiphenyl)methane, bis(isomaleimidodiphenyl)methane and 4,4?-diaminodiphenyl methane mixtures

The thermal behavior of mixtures of bis(4-maleimidophenyl) (A) with bis(4-isomaleimidophenyl)methane (C) and their mixture with 4,4′-diaminodiphenyl methane (D) were investigated by differential scanning calorimetry. The study of the binary system A/C in different proportions led us to determine an eutectic mixture at a molar fraction of C in the range of 0.7–0.9. The ternary ACD mixtures showed themselves able to participate in three principal reactions: polyaddition, ring-opening addition, and homopolymerization. In each mixture studied the addition of diamine changed the melting point and maximum polymerization temperatures in the sense of a general decrease. The properties of the networks were studied by thermal analysis and through evaluation of water absorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3547–3556, 2003

Synthesis of proton‐conducting membranes by the utilization of preirradiation grafting and atom transfer radical polymerization techniques

AbstractThe atom transfer radical polymerization (ATRP) of styrene onto poly(vinylidene fluoride)‐graft‐poly(vinylbenzyl chloride) (PVDF‐g‐PVBC) membranes was investigated. Novel membranes were designed for fuel‐cell applications. The benzyl chloride groups in the PVDF‐g‐PVBC membranes functioned as initiators, and a Cu‐based catalytic system with the general formula Cu(n)Xn/ligand [where X is Cl or Br and the ligand is 2,2′‐bipyridyl (bpy)] was employed for the ATRP. In addition, 10 vol % dimethylformamide was added for increased solubility of the catalyst complex in styrene. The system was homogeneous, except for the membrane, when the initiator/copper halide/ligand/monomer molar ratio was 1/1/3/500. As anticipated, the fastest polymerization rate of styrene was observed with the copper bromide/bpy‐based catalyst system. The reaction rate was strongly temperature‐dependent within the studied temperature interval of 100–130 °C. The degree of grafting increased linearly with time, thereby indicating first‐order kinetics, regardless of the polymerization temperature. Furthermore, 120 °C was the maximum polymerization temperature that could be used in practice because the membrane structure was destroyed at higher temperatures. The degree of styrene grafting reached 400% after 3 h at 120 °C. Such a high degree of grafting could not be reached with conventional uncontrolled radiation‐induced grafting methods because of termination reactions. On the basis of an Arrhenius plot, the activation energy for the homogeneous ATRP of styrene was 217 kJ/mol. The prepared membranes became proton‐conducting after sulfonation of the polystyrene grafts. The highest conductivity measured for the prepared membranes was 70 mS/cm, which is comparable to the values normally measured for commercial Nafion membranes. The scanning electron microscopy/energy‐dispersive X‐ray results showed that the membranes had to be grafted through the matrix with both PVBC and polystyrene to become proton‐conducting after sulfonation. In addition, PVDF‐g‐[PVBC‐g‐(styrene‐block‐tert‐butyl acrylate)] membranes were also synthesized by ATRP. © 2002 John Wiley &amp; Sons, Inc. J Polym Sci Part A: Polym Chem 40: 591–600, 2002; DOI 10.1002/pola.10146

Effects of storing initiated 2-hydroxyethyl methacrylate solutions for embedding tissues for light microscopy: some practical implications.

The effects of storing 2-hydroxyethyl methacrylate (HEMA) solutions for embedding tissues for light microscopy were studied using three commercially available HEMA embedding kits: Technovit 7100, Technovit 8100, and JB-4. These HEMA solutions were examined at various times of storage over a period of one year using a panel of physicochemical techniques including gas chromatography, titration, viscosimetry, determination of the maximum polymerization temperature and the time required to reach the maximum temperature, and detection of degradation products of HEMA monomers by histochemical procedures. The quality of the resin blocks was examined by the observation of mini-folds in sections. Data obtained from these tests showed that the release of by-products as a result of the degradation of the HEMA monomer during storage of HEMA solutions does not occur. Development of cross-linking agents by transesterification of HEMA monomer was not detected either. Gradual decrease of the inhibitor concentration during storage proved to be the main cause of the reduction of shelf-life of HEMA solutions. Inconsistent tissue infiltration after storage may be due to decreased rates of tissue penetration as a result of HEMA chain lengthening. Guidelines for safe and economical handling of HEMA mixtures are given.