Review of the biological response to a novel bone cement containing poly(ethyl methacrylate) and n-butyl methacrylate

Prolonged Post-Polymerization Biocompatibility of Polymethylmethacrylate-Tri-n-Butylborane (PMMA-TBB) Bone Cement

Polymethylmethacrylate (PMMA)-based acrylic bone cement is commonly used to fix bone and metallic implants in orthopedic procedures. The polymerization initiator tri-n-butylborane (TBB) has been reported to significantly reduce the cytotoxicity of PMMA-based bone cement compared to benzoyl peroxide (BPO). However, it is unknown whether this benefit is temporary or long-lasting, which is important to establish given that bone cement is expected to remain in situ permanently. Here, we compared the biocompatibility of PMMA-TBB and PMMA-BPO bone cements over several days. Rat femur-derived osteoblasts were seeded onto two commercially-available PMMA-BPO bone cements and experimental PMMA-TBB polymerized for one day, three days, or seven days. Significantly more cells attached to PMMA-TBB bone cement during the initial stages of culture than on both PMMA-BPO cements, regardless of the age of the materials. Proliferative activity and differentiation markers including alkaline phosphatase production, calcium deposition, and osteogenic gene expression were consistently and considerably higher in cells grown on PMMA-TBB than on PMMA-BPO, regardless of cement age. Although osteoblastic phenotypes were more favorable on older specimens for all three cement types, biocompatibility increased between three-day-old and seven-day-old PMMA-BPO specimens, and between one-day-old and three-day-old PMMA-TBB specimens. PMMA-BPO materials produced more free radicals than PMMA-TBB regardless of the age of the material. These data suggest that PMMA-TBB maintains superior biocompatibility over PMMA-BPO bone cements over prolonged periods of at least seven days post-polymerization. This superior biocompatibility can be ascribed to both low baseline cytotoxicity and a further rapid reduction in cytotoxicity, representing a new biological advantage of PMMA-TBB as a novel bone cement material.

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder-based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications.

Surface functionalization of acrylic based photocrosslinkable resin for 3D printing applications

The limited number of resins, available for stereolithography applications, is one of the key drivers in research applied to rapid prototyping. In this work an acrylic photocrosslinkable resin based on methyl methacrylate (MMA), butyl methacrylate (BMA) and poly(ethylene glycol) dimethacrylate (PEGDA) was developed with different composition and characterized in terms of mechanical, thermal and biological behaviour. Two different systems have been developed using different amount of reagent. The influence of every components have been evaluated on the final characteristic of the resin in order to optimize the final composition for applications in bone tissue engineering. The crosslinked materials showed good mechanical properties and thermal stabilities and moreover cytotoxicity test confirms good biocompatibility with no cytotoxic effect on cells metabolism. Moreover two different treatments have been proposed, using fetal bovine serum (FBS) and methanol (MeOH), in order to improve cell recognition of the surfaces. Samples threatened with MeOH allow cell adhesion and survival, promoting spreading, elongation and fusion of C2C12 muscle myoblast cells.

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Photocrosslinkable biocompatible resin for application in tissue engineering.

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Surface treatment to improve materials wettability.

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Myoblast spreading and elongation on photocrosslinked modified surfaces.

Effect of thermodisinfection on mechanic parameters of cancellous bone

Revision surgery of joint replacements is increasing and raises the demand for allograft bone since restoration of bone stock is crucial for longevity of implants. Proceedings of bone grafts influence the biological and mechanic properties differently. This study examines the effect of thermodisinfection on mechanic properties of cancellous bone. Bone cylinders from both femoral heads with length 45 mm were taken from twenty-three 6-8 months-old piglets, thermodisinfected at 82.5 °C according to bone bank guidelines and control remained native. The specimens were stored at -20 °C immediately and were put into 21 °C Ringer's solution for 3 h before testing. Shear and pressure modulus were tested since three point bending force was examined until destruction. Statistical analysis was done with non-parametric Wilcoxon, t test and SPSS since p < 0.05 was significant. Shear modulus was significantly reduced by thermodisinfection to 1.02 ± 0.31 GPa from 1.28 ± 0.68 GPa for unprocessed cancellous bone (p = 0.029) since thermodisinfection reduced pressure modulus not significantly from 6.30 ± 4.72 GPa for native specimens to 4.97 ± 2.23 GPa and maximum bending force was 270.03 ± 116.68 N for native and 228.80 ± 70.49 N for thermodisinfected cancellous bone. Shear and pressure modulus were reduced by thermodisinfection around 20 % and maximum bending force was impaired by about 15 % compared with native cancellous bone since only the reduction of shear modulus reached significance. The results suggest that thermodisinfection similarly affects different mechanic properties of cancellous bone and the reduction of mechanic properties should not relevantly impair clinical use of thermodisinfected cancellous bone.

Effect of Heat Treatment on the Physical Properties of Provisional Crowns during Polymerization: An in Vitro Study

This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60 °C for evaluation of flexural strength, surface roughness, color change and marginal discrepancy. Flexural strength was determined by a three-point bending test. Surface profile was studied using atomic force microscopy. Color change was evaluated by comparing the color of the materials before and after placement in coffee. A travelling microscope helped prepare standardized crowns for assessment of marginal discrepancy. Flexural strength of all tested materials cured at 23 °C or 37 °C did not significantly change. The surface roughness and marginal discrepancy of the materials increased at 60 °C curing temperature. Marginal discrepancies, color stability, and other physical properties of materials cured at 23 °C or 37 °C did not significantly change. Flexural strength of certain provisional materials cured at 60 °C increased, but there was also an increase in surface roughness and marginal discrepancy.

Surface modification of fiber reinforced polymer composites and their attachment to bone simulating material

The purpose of this study was to investigate the effect of fiber orientation of a fiber-reinforced composite (FRC) made of poly-methyl-methacrylate (PMMA) and E-glass to the surface fabrication process by solvent dissolution. Intention of the dissolution process was to expose the fibers and create a macroporous surface onto the FRC to enhance bone bonding of the material. The effect of dissolution and fiber direction to the bone bonding capability of the FRC material was also tested. Three groups of FRC specimens (n = 18/group) were made of PMMA and E-glass fiber reinforcement: (a) group with continuous fibers parallel to the surface of the specimen, (b) continuous fibers oriented perpendicularly to the surface, (c) randomly oriented short (discontinuous) fibers. Fourth specimen group (n = 18) made of plain PMMA served as controls. The specimens were subjected to a solvent treatment by tetrahydrofuran (THF) of either 5, 15 or 30 min of time (n = 6/time point), and the advancement of the dissolution (front) was measured. The solvent treatment also exposed the fibers and created a surface roughness on to the specimens. The solvent treated specimens were embedded into plaster of Paris to simulate bone bonding by mechanical locking and a pull-out test was undertaken to determine the strength of the attachment. All the FRC specimens dissolved as function of time, as the control group showed no marked dissolution during the study period. The specimens with fibers along the direction of long axis of specimen began to dissolve significantly faster than specimens in other groups, but the test specimens with randomly oriented short fibers showed the greatest depth of dissolution after 30 min. The pull-out test showed that the PMMA specimens with fibers were retained better by the plaster of Paris than specimens without fibers. However, direction of the fibers considerably influenced the force of attachment. The fiber reinforcement increases significantly the dissolution speed, and the orientation of the glass fibers has great effect on the dissolving depth of the polymer matrix of the composite, and thus on the exposure of fibers. The glass fibers exposed by the solvent treatment enhanced effectively the attachment of the specimen to the bone modeling material.

Coronary pseudoaneurysm in a non-polymer drug-eluting stent: a rare entity

Coronary pseudoaneurysms following implantation of drug-eluting stents, although rare, are not unknown. Nearly all such cases have been reported in patients with sirolimus or paclitaxel polymer-based stents. We describe a case of coronary pseudoaneurysm developing with a non-polymer-based drug-eluting stent in a 50-year-old man who was successfully managed by coronary artery bypass grafting.

Osteoblast response to polymethyl methacrylate bioactive glass composite

Polymethylmethacrylate (PMMA) has been used in many orthopedic and dental applications since the 1960s. Biocompatibility of newly developed surface porous fiber reinforced (SPFR) PMMA based composite has not been previously proven in cell culture environment. Analysis of rat bone marrow stromal cells grown on the different test materials showed only little difference in normalized cell activity or bone sialoprotein (BSP) production between the test materials, but the osteocalcin (OC) levels remained higher (P < 0.015-0.005) through out the test with SPFR-material when compared to tissue culture poly styrene (TCPS). The cells grown on SP-FRC material also showed highest calcium depletion from the culture medium (P < 0.026-0.001) when compared to all other test substrates. SEM images of the cultured samples confirmed that all the materials enabled cell spreading and growth on their surface, but the roughened surface remarkably enhanced this process of cell attachment, division and calcified nodule formation. This study shows that the SP-FRC composite material does not elicit harmful/toxic reactions in cell cultures more than neutral TCPS and can be considered biocompatible. The material possesses good capabilities to form new mineralized tissue onto its surface, and through that a possibility to bond directly to bone. Rough surface seems to enhance osteoblast proliferation and formation of mineralized extracellular matrix.

Block copolymers for the rational design of self-forming postsurgical adhesion barriers

Post-surgical adhesions, abnormal fibrous linkages between adjacent tissue surfaces, represent one of the most common and significant complications facing surgical recovery today. Physical barriers and gels have been the most successful at limiting their formation, yet are not effective in cases where the pro-adhesive site is either unknown or difficult to reach (e.g. during laparoscopic surgery). In this work, poly(methacrylic acid-co-t-butylmethacrylate)-b-poly(ethylene glycol (M(N) = 1000) methacrylate) diblock and statistical copolymers were synthesized as a platform for designing self-forming adhesion barriers, which can attach to exposed pro-adhesive sites through binding with the positively charged extracellular matrix, basement membrane proteins and deposited fibrin. An experimental model based upon a quartz crystal microbalance with dissipation was developed to test the diblock copolymers ability (i) to adsorb to an amine-terminated self-assembled monolayer, and (ii) to inhibit subsequent protein adsorption. These results were also confirmed using an in vitro cell attachment model. As the mole fraction of methacrylic acid content increased, polymer adsorption increased. All synthesized diblock copolymers investigated provided high resistance to protein adsorption, with blockade ranging from 55% to 81%. Except for the uncharged control polymers, the ability of these materials to resist cellular attachment showed similar trends, with the suppression of attachment approaching 75%. Energy dissipation analysis and variable-angle spectroscopic ellipsometry revealed two competing adsorption mechanisms depending on the molecular properties of the polymer.

Drug-eluting stent thrombosis: the Kounis hypersensitivity-associated acute coronary syndrome revisited

The advent of drug-eluting stents (DES) has revolutionized the field of interventional cardiology. Their dramatic and persistent restenotic and target lesion revascularization advantages are unquestioned. However, concerns over the rare but potentially catastrophic risk of stent thrombosis (ST) have tempered universal acceptance of these devices. Although the precise mechanism of DES ST is undoubtedly multifactorial and as yet not fully elucidated, delayed or incomplete endothelial healing clearly plays a pivotal role. Detailed histopathological data have implicated a contributory allergic or hypersensitivity component, as verified by the Food and Drug Administration's Manufacturer and User Device Experience Center and the Research on Adverse Drug/device events And Reports (RADAR) project. These findings thus suggest a potential connection with the Kounis syndrome, the concurrence of acute coronary events with allergic, hypersensitivity, anaphylactic, or anaphylactoid reactions. Potential culprits responsible for this phenomenon include: arachidonic acid metabolites such as leukotrienes and thromboxane, proteolytic enzymes such as chymase and tryptase, histamine, cytokines, and chemokines. Additionally, inflammatory cells such as macrophages, T-lymphocytes, and mast cells are probably also contributory. Autopsy-confirmed infiltrates of various inflammatory cells including lymphocytes, plasma cells, macrophages, and eosinophils have been reported in all 3 vascular wall layers and are reminiscent of those associated with the Kounis syndrome. Although the concurrence of acute coronary syndromes with hypersensitivity reactions has been long established, the specific association with DES ST remains unproven. Potential incorporation of hypersensitivity suppressive agents might represent a promising paradigm shift from efficacy to safety in future DES designs.

Augmentation of screw fixation with injectable calcium sulfate bone cement in ovariectomized rats

The objective of this study was to determine the effect of augmenting screw fixation with an injectable calcium sulfate cement (CSC) in the osteoporotic bone of ovariectomized rats. The influence of the calcium sulfate (CS) on bone remodeling and screw anchorage in osteoporotic cancellous bone was systematically investigated using histomorphometric and biomechanical analyses. The femoral condyles of 55 Sprague-Dawley ovariectomized rats were implanted with screw augmented with CS, while the contralateral limb received a nonaugmented screw. At time intervals of 2, 4, 8, 12, and 16 weeks, 11 rats were euthanized. Six pair-matched samples were used for histological analysis, while five pair-matched samples were preserved for biomechanical testing. Histomorphometric data showed that CS augmented screws activated cancellous bone formation, evidenced by a statistically higher (p < 0.05) percentage of osteoid surface at 2, 4, and 8 weeks and a higher rate of bone mineral apposition at 12 weeks compared with nonaugmented screws. The amount of the bone-screw contact at 2, 8, and 12 weeks and of bone ingrowth on the threads at 4 and 8 weeks was greater in the CS group than in the nonaugmented group (p < 0.05), although these parameters increased concomitantly with time for both groups. The CS was resorbed completely at 8 weeks without stimulating fibrous encapsulation on the screw surface. Also, the cement significantly increased the screw pull-out force and the energy to failure at 2, 4, 8, and 12 weeks after implantation, when compared with the control group (p < 0.05). These results imply that augmentation of screw fixation with CS may have the potential to decrease the risk of implant failure in osteoporotic bone.

Surgical applications of methyl methacrylate: a review of toxicity

Methyl methacrylate (MMA) is a monomer of acrylic resin widely used in a variety of medical, dental, and industrial applications. Its extensive use in surgery, particularly for arthroplasties, has often raised concerns regarding potential human toxicity for orthopaedic surgeons, surgical nurses, and other operating-room staff who are occupationally exposed to the compound. The main toxic effects of MMA exposure appear to involve the cardiovascular system. When exposed to MMA in the work environment, surgical staff have been reported to suffer from hypersensitivity, asthmatic reactions, local neurological symptoms, irritations and local dermatological reactions. The integrity of latex gloves may also be compromised following exposure to MMA during surgical procedures. At present, MMA is not thought to be carcinogenic to humans under normal conditions of use. Nevertheless, sound occupational hygiene practices should still be used to help reduce workplace exposure to MMA during orthopaedic and other medical procedures. Surgical staff should avoid direct contact with MMA mixtures wherever possible, and room ventilation and adequate airflow should also be optimized. In the present article, the authors review studies relating to MMA toxicity in surgical practice, updating in part a previous literature review and expanding on the toxicity of MMA within the surgical setting.

New radiopaque acrylic bone cement. II. Acrylic bone cement with bromine-containing monomer

Bromine-containing methacrylate, 2-(2-bromopropionyloxy) ethyl methacrylate (BPEM), had been used in the formulation of acrylic radiopaque cements. The effect of this monomer incorporated into the liquid phase of acrylic bone cement, on the curing parameters, thermal properties, water absorption, density, compression tests and radiopacity was studied. A decrease of maximum temperature and an increase of the setting time were observed with the addition of the bromine-containing monomer in the radiolucent cement composition. Adding BPEM in radiolucent acrylic bone cements composition results in the decrease of glass transition temperature and increase of its thermal stability. Acrylic bone cements modified with bromine-containing comonomer are characterized by polymerization shrinkage lower than the radiolucent cement. Addition of bromine-containing comonomer in radiolucent acrylic bone cement composition determines the increase of compressive strength. Acrylic bone cements modified with bromine-containing comonomer proved to be radiopaque.

Biocompatibility issues with modern implants in bone - a review for clinical orthopedics

Skeletal defects may result from traumatic, infectious, congenital or neoplastic processes and are considered to be a challenge for reconstructive surgery. Although the autologous bone graft is still the "gold standard", there is continuing demand for bone substitutes because of associated disadvantages, such as limited supply and potential donor side morbidity [1]. This is not only true for indications in orthopedic and craniomaxillofacial surgeries, but also in repairing endodontic defects and in dental implantology.Before clinical use all new bone substitute materials have to be validated for their osseoconductive and - depending on the composition of the material also -inductive ability, as well as for their long-term biocompatibility in bone. Serving this purpose various bone healing models to test osteocompatibility and inflammatory potential of a novel material on one hand and, on the other hand, non-healing osseous defects to assess the healing potential of a bone substitute material have been developed. Sometimes the use of more than one implantation site can be helpful to provide a wide range of information about a new material [2].Important markers for biocompatibility and inflammatory responses are the cell types appearing after the implantation of foreign material. There, especially the role of foreign body giant cells (FBGC) is discussed controversial in the pertinent literature, such that it is not clear whether their presence marks an incompatibility of the biomaterial, or whether it belongs to a normal degradation behavior of modern, resorbable biomaterials.This publication is highlighting the different views currently existing about the function of FBGC that appear in response to biomaterials at the implantation sites. A short overview of the general classes of biomaterials, where FBGC may appear as cellular response, is added for clarity, but may not be complete.

Coronary Stents, Hypersensitivity Reactions, and the Kounis Syndrome

The use of drug-eluting stents (DES) for the treatment of coronary stenosis has increased sharply and now accounts for more than 75% of all coronary stents utilized. However, concern has been increasing that DES could be associated with stent thrombosis, paradoxical coronary vasoconstriction, and hypersensitivity reactions. Components of currently used DES have been reported to induce, either separately or synergistically, hypersensitivity reactions and possibly lead to cardiac events. DES-activated intracoronary mast cells could release histamine, arachidonic acid metabolites, proteolytic enzymes, as well as a variety of cytokines, chemokines, and platelet-activating factor (PAF) leading to local inflammation and thrombosis. These events may be more common than suspected because it is hard to document them, unless they become systemic, in which case they manifest themselves as the "Kounis syndrome," characterized by the concurrence of acute coronary events with hypersensitivity reactions. Recognition of this problem may lead to better vigilance, as well as new DES with mast cell blocking molecules that may also be disease modifying.

Vancomycin derivative photopolymerized to titanium kills S. epidermidis

Infections in the setting of orthopaedic hardware remain a serious complication. Traditional treatment modalities rely on antibiotic-loaded biomaterials and/or prolonged intravenous therapy, both of which suffer major limitations. We hypothesized a derivatized form of the glycopeptide antibiotic vancomycin could be covalently attached to a Ti-6Al-4V implant alloy to form a bactericidal surface capable of killing bacteria relevant to orthopaedic infections. First, a polymerizable poly(ethylene glycol)-acrylate derivative of vancomycin was synthesized. This monomer was characterized by liquid chromatography, 1H NMR spectroscopy, and MIC and MBC determination. The monomer was subsequently photochemically polymerized to implant grade Ti-6Al-4V alloy. The coating was bactericidal against Staphylococcus epidermidis through initial release of unattached antibiotic species followed by continued surface-contact-mediated bacterial killing by covalently tethered vancomycin. Through this surface-contact mechanism, the number of colony forming units dropped by ca. fivefold from an initial inoculum of 1 x 10(6) cfu/mL over 4 hours and by ca. 100-fold with respect to nonbactericidal control surfaces. An inoculum of 1 x 10(4) cfu/mL was reduced to undetectable levels over 17 hours. This coating method allows a loading dose several thousand times larger than that achieved with monolayer vancomycin coupling approaches and holds promise for the treatment of orthopaedic infections.

Release profiles in drug-eluting stents: issues and uncertainties

This review presents the current data on drug release from drug-eluting stents and the effects of the release profiles on animal and human data for coronary stenosis. Data for the two most important drugs, sirolimus (rapamycin) and paclitaxel, are presented, the polymers used are described and the observed release profiles are discussed for various polymer carriers. The current literature on the tissue compatibility of the polymers commonly used in drug-eluting stents is also discussed. The range of release rates from stents studied to date is limited for sirolimus, but somewhat broader for paclitaxel. Animal and human data comparing the different release profiles are limited to about 6 months for animals and 2-4 years for humans. From the data available, it appears that for both sirolimus and paclitaxel, a slow-releasing drug-eluting stent leads to slightly more favorable angiographic outcomes than more rapid release. Most of the complications arising from the use of drug-eluting stents are attributed to incomplete healing; one possible clinical consequence of this delay in healing is that anti-platelet therapy needs to be maintained over a much longer period than is the case for bare metal stents.

Biological response of new activated acrylic bone cements with antiseptic properties. Histomorphometric analysis

The biological response to an acrylic bone cement cured with 4,4'-bis-dimethylamino benzydrol (BZN) as activator of reduced cytotoxicity and antiseptic properties, has been carried out and compared with that obtained for CMW 3 cement. Histomorphometrical data (undecalcified trichromic Goldner staining) were obtained by measuring the most significant variables at the bone-cement interface. Quantitative results of tissue response revealed that newly formed bone and connective tissue were maximum at 4 weeks whereas bone marrow increased with time of implantation for both cements. Statistical analysis (p < 0.05) showed no significant differences in newly formed bone and bone marrow with time and between both groups, however, connective tissue significantly decreased between 4 weeks and 12 weeks for BZN cement, and between 12 weeks and 24 weeks for CMW3. By comparing both cements at each time, lower significant percentage of connective tissue at the bone-cement interface of the BZN cement, was obtained at 12 and 24 weeks, however, a very low amount of connective tissue was found for both cements. All the results indicate that the new activated system could be applied clinically in a relatively short time, after the corresponding preclinical study.

From Natural Products to Polymeric Derivatives of “Eugenol”: A New Approach for Preparation of Dental Composites and Orthopedic Bone Cements

Polymers with eugenol moieties covalently bonded to the macromolecular chains were synthesized for potential application in orthopedic and dental cements. First, eugenol was functionalized with polymerizable groups. The synthetic methods employed afforded two different methacrylic derivatives, where the acrylic and eugenol moieties were either directly bonded, eugenyl methacrylate (EgMA), or separated through an oxyethylene group, ethoxyeugenyl methacrylate (EEgMA). A typical Fisher esterification reaction was used for the synthesis of EgMA and EEgMA, affording the desired monomers in 80% yields. Polymerization of each of the novel monomers, at low conversion, provided soluble polymers consisting of hydrocarbon macromolecules with pendant eugenol moieties. At high conversions only cross-linked polymers were obtained, attributed to participation of the allylic double bonds in the polymerization reaction. In addition, copolymers of each eugenol derivative with ethyl methacrylate (EMA) were prepared at low conversion, with the copolymerization reaction studied by assuming the terminal model and the reactivity ratios determined according to linear and nonlinear methods. The values obtained were r(EgMA) = 1.48, r(EMA) = 0.55 and r(EEgMA) = 1.22, r(EMA) = 0.42. High molecular weight polymers and copolymers were obtained at low conversion. Analysis of thermal properties revealed a T(g) of 95 degrees C for PEgMA and of 20 degrees C for PEEgMA and an increase in the thermal stability for the eugenol derivatives polymers and copolymers with respect to that of PEMA. Water sorption of the copolymers was found to decrease with the eugenol derivative content. Both monomers EgMA and EEgMA showed antibacterial activity against Streptococcus mutans, producing inhibition halos of 7 and 21 mm, respectively. Finally, cell culture studies revealed that the copolymers did not leach any toxic eluants and showed good cellular proliferation with respect to PEMA. This study thus indicates that the eugenyl methacrylate derivatives are potentially good candidates for dental and orthopedic cements.

Deleterious tissue reaction to an alkylene bis(dilactoyl)-methacrylate bone adhesive in long-term follow up after screw augmentation in an ovine model

Biomaterials are designed to support orthopedic surgeons and once implanted they will help the body to heal itself. In this way one of the most attractive substances are biomaterials that allow gluing of bone fragments and implant fixation. Although no bone adhesive is established for practical use in clinical practice yet, there is evidence in vitro and in vivo that a new class of bone adhesives based on alkylene bis(dilactoyl)-methacrylates may meet the requirements to bridge the gap between bench and bedside. The purpose of this experimental study was to investigate the long-term biocompatibility as well as the integration in the remodeling process of a new polymer of this group of substances that was used for both fragment adaptation and implant fixation in a large-scale animal model. In 24 sheep the lateral tibial condyle was osteotomized and refixed by three cortical screws. In 12 of them overdrilling the bone thread of one screw was performed to simulate the poor mechanical properties of osteoporotic bone and the polymer was used in this setting for screw augmentation, furthermore the osteotomy surface was covered with polymer before osteosynthesis to analyze the influence of the material on bone healing. In the other 12 sheep that served as controls osteosynthesis was performed without a polymer. All animals were permitted to walk immediately after surgery under full weight bearing conditions. Six animals of the polymer group and six animals of the control group were analyzed after 6 weeks and 6 months, respectively. Bone healing and implant integration was evaluated by contact X-rays, histology and histomorphometric quantification. After 6 weeks integrity of the healing bone in the polymer group was preserved as compared to the controls, albeit signs of prolonged aseptic inflammation were observed in the polymer group, which is in line with previous reports. In sharp contrast after 6 months, extensive tissue destruction was observed in all animals of the polymer group that was attributed to a massive foreign body reaction at the histological level. These long-term results suggest that (i) short-term observation not always allow valid conclusions regarding the biocompatibility of biomaterials, (ii) that biocompatibility might vary between species, and (iii) that the polymer used in this setting, although previously attributed to be a good candidate for clinical use in patients, does not meet the necessary criteria and tremendously interferes with the physiology of skeletal repair.

Injectable and self-curing composites of acrylic/bioactive glass and drug systems. A histomorphometric analysis of the behaviour in rabbits

Injectable self-curing systems based on PMMA, phosphate-free bioactive glasses and the drug fosfosal, a phosphate derivative of salicylic acid with analgesic and moderate anti-inflammatory properties, have been tested in vivo to evaluate their biocompatibility. The model consisted of the injection of dough of cement into a defect created in the femur of rabbits, and the cure of the cement in situ after implantation. The biological response was studied in the short and long terms by macroscopic, radiological and histopathological examination, and quantitatively by histomorphometric and statistical analysis considering the most representative variables at the bone-cement interface: cement, bone marrow, newly formed bone and connective tissue. All bioactive formulations presented resorption of the cement at the end of the experiment in contrast to the control of PMMA, due to the presence of resorbable components. The presence or absence of the phosphate group added by the drug fosfosal influenced mainly on the new bone formation process. The cement formulated with bioactive glasses and in absence of fosfosal produced the maximum amount of neoformed bone at 2 weeks, and then it resorbed at 4 weeks to give a higher amount of neoformed bone at the end of the experiment, compared with the formulation containing only fosfosal. The presence of fosfosal and bioactive glass together affected the ossification process strongly. The osseous tissue was produced more gradually but it continuously increased giving rise to a more stable bone at the end of the experiment.

The tissue response to an alkylene bis(dilactoyl)-methacrylate bone adhesive

Gluing is an attractive technique to fix small bone fragments. However, to date no bone adhesive could be established successfully for all day clinical use. The purpose of this experimental study was to investigate the biocompatibility of a new bone glue based on alkylene bis(dilactoyl)-methacrylate in 36 rabbits. Monocondylar osteotomy of the distal femur was performed and bone glue was applied into the osteotomy gap in 24 rabbits. The remaining 12 animals served as controls. In all rabbits the osteotomy was subsequently stabilized by K-wire osteosynthesis. Six animals of the glue group and 3 controls were euthanized after 7, 21, 42, and 84 days, respectively. Fracture healing and degradation pattern of the glue was studied using histological, histomorphometrical, scanning electron microscopical, and radiological methods. Good resorption of the glue by mononuclear and multinucleated giant cells without prolonged inflammatory processes was observed in the glue group. Histomorphometrical analysis did not reveal any significant differences in fracture healing between the glue and control group at any time. Complete remodelling of the former osteotomy gap was found in all rabbits after 84 days. This bioresorbable bone adhesive exhibited good biocompatibility and its degradation did not interfere with physiological fracture healing.

Biocompatibility and functionality of the degradable polymer alkylene bis(dilactoyl)-methacrylate for screw augmentationin vivo

Recently, a new degradable polymer has been developed on the basis of alkylene bis(dilactoyl)-methacrylate as an alternative material for screw augmentation. The polymer has been investigated in vitro and in a short-term experiment in rabbits exhibiting promising results. The aim of the present study was to investigate its long-term biocompatibility and mechanical functionality in a large animal model. The polymer was used for screw augmentation in the cancellous bone of the femoral condyle and tibia epiphysis of 12 sheep and was compared to polymethylmethacrylate (PMMA) augmented and nonaugmented screws. After an implantation period of 6 months, bone, regional lymph nodes, and several organs were histologically evaluated. The mechanical efficacy was investigated by a biomechanical pullout test. A lot of mononuclear macrophages and multinuclear foreign body giant cells with incorporated polymer particles indicate strong inflammatory reactions. Large osteolysis zones with osteoclasts were found in the surrounding polymer. The polymer was fragmented but not substantially degraded. Polymer particles were also found in the regional lymph nodes. Lung, liver, kidney, and spleen did not show any pathological signs. The pullout force of screws augmented with the new polymer was significantly reduced in comparison to PMMA augmented and nonaugmented screws, respectively. It was concluded that the material has poor biocompatibility and cannot be recommended for clinical application as screw augmentation material.

Drug-eluting stents: caution and concerns for long-term outcome

Recent publications on drug-eluting stents (DES) report a significant reduction in restenosis rates as compared to bare metal stents in patients mostly with single vessel disease. We have recently observed however, late stent thrombosis following CYPHER DES implantation. The patient developed a hypersensitivity reaction around stent struts limited to the polymer with aneurysmal dilatation and extensive inflammation of the arterial wall in the absence of vascular healing. This incidence promotes a cautionary view and perhaps supports the use of DES only in high-risk patients.

Localized Hypersensitivity and Late Coronary Thrombosis Secondary to a Sirolimus-Eluting Stent

Background— The US Food and Drug Administration recently issued a warning of subacute thrombosis and hypersensitivity reactions to sirolimus-eluting stents (Cypher). The cause and incidence of these events have not been determined.

Methods and Results— We present findings of a 58-year-old man who died of late stent thrombosis 18 months after receiving 2 Cypher stents for unstable angina. Although angiographic and intravascular ultrasound results at 8 months demonstrated the absence of neointimal formation, vessel enlargement was present. An autopsy showed aneurysmal dilation of the stented arterial segments with a severe localized hypersensitivity reaction consisting predominantly of T lymphocytes and eosinophils.

Conclusions— The known pharmacokinetic elution profile of Cypher stents and the presence of polymer fragments surrounded by giant cells and eosinophils suggest that a reaction to the polymer may have caused late stent thrombosis. Careful long-term follow-up of patients with vessel enlargement after Cypher stent placement is recommended.

Eigenschaften und Degradation eines neuartigen bioresorbierbaren Knochenklebers / Properties and Degradation of a New Bioresorbable Bone Glue

In trauma surgery gluing is an attractive method of bonding fractured bone, which is rapid and does not require the use of screws and plates. The purpose of this study was to analyze in vitro the properties of a new bioresorbable bone glue, and in vivo its structure and degradation. The newly developed bone glue is based on alkylenbis(oligolactoyl)methacrylates and employs a two-component initiator system. Starting components for synthesis are ethylene glycol, lactic acid and methacrylic acid. In vitro the solidified glue is degraded via hydrolysis of ester bonds. Degradation products are ethylene glycol, lactic acid and oligomeres of methacrylic acid. After the first week polymer pellets (MMA, HEMALA, ELAMA) showed a weight loss of 12%. From week 2-20 a linear weight loss of 1.5% per week, that is 40% after 20 weeks, was observed. The in vivo investigations of the ultrastructure of the glue revealed a transparent and homogeneous mass with large electron-tight vacuoles. Differences in structure and degradation were not observed. Degradation of glue by hydrolysis and phagocytosis, with good biocompatibility was demonstrated.

Biocompatibility and other properties of acrylic bone cements prepared with antiseptic activators

Acrylic bone cements prepared with activators of reduced toxicity have been formulated with the aim of improving the biocompatibility of the final material. The activators used were N,N-dimethylaminobenzyl alcohol (DMOH) and 4,4'-dimethylamino benzydrol (BZN). The toxicity, cytotoxicity, and antiseptic action of these activators were first studied. DMOH and BZN presented LD50 values 3-4 times higher than DMT, were less cytotoxic against polymorphonuclear leucocytes, and possessed an antimicrobial character, with a high activity against the most representative microorganisms involved in postoperative infections. The properties of the acrylic bone cements formulated with DMOH and BZN were evaluated to determine the influence of these activators on the curing process and the physicochemical characteristics of the cements. A decrease of the peak temperature was observed for the curing with DMOH or BZN with respect to that of one commercially available formulation (CMW 3). However, residual monomer content and mechanical properties in tension and compression were comparable to those of CMW 3. The biocompatibility of acrylic bone cements containing DMOH or BZN was studied and compared with CMW 3. To that end, intramuscular and intraosseous implantation procedures were carried out and the results were obtained from the histological analysis of the surrounding tissues at different periods of time. Implantation of rods of cement into the dorsal muscle of rats showed the presence of a membrane of connective tissue, which increased in collagen fibers with time of implantation, for all formulations. The intraosseous implantation of the cements in the dough state in the femur of rabbits, revealed a higher and early osseous neoformation, with the presence of osteoid material surrounding the rest of the cured material, for the cement prepared with the activator BZN in comparison with that obtained following the implantation of the cement cured with DMOH or DMT (CMW 3).

Toxicity of methyl methacrylate in dentistry

Methyl methacrylate (MMA), a monomer of acrylic resin, has a wide variety of dental, medical and industrial applications. Concerns have been raised regarding its potential toxicity in dental use, both for the patient and also in the workplace. Dental patients are also exposed to MMA leached from some dental appliances and the effects, at least in vitro, appear toxic to cells and may cause local mucosal irritation or even an allergic reaction. When exposed to MMA in the dental clinic, dentists and other dental staff appear to occasionally suffer hypersensitivity, asthmatic reactions, local neurological symptoms, irritant and local dermatological reactions. The integrity of latex gloves may also be compromised after exposure to MMA during dental procedures. MMA is not thought to be carcinogenic to humans under normal conditions of use. Techniques should be employed to reduce patients' exposure to MMA during dental procedures in order to reduce the risks of possible complications. Dental staff should avoid direct contact with MMA and room ventilation should be optimised.

Mechanical properties of oligomer-modified acrylic bone cement

The aim of this study was to determine the mechanical properties of acrylic bone cement modified with an experimental oligomer filler, based on an amino acid of trans-4-hydroxy-L-proline synthesized in the laboratory. The test specimens were tested either dry, or after being stored in distilled water or in simulated body fluid (SBF) for 1 week and then tested in distilled water. The three-point bending test was used to measure the flexural strength and flexural modulus of the cement, and the compression tests were used to measure the compression strength and modulus. One test specimen from each group was examined under a scanning electron microscope (SEM) to determine the nature of the oligomer filler in the polymethylmethacrylate-polymethylacrylate copolymer-based (PMMA-PMA/PMMA) polymer blend. In dry conditions, the flexural strength of the test specimens tested in air was 66 MPa, and the compression strength was 93 GPa (p<0.001) for the plain bone cement. For the test specimens including 20 wt% of oligomer filler, the flexural strength was 37 MPa, and the compression strength was 102 MPa(p<0.001) in dry conditions. The storage in wet conditions (in distilled water and the SBF) decreased the flexural strength of the test specimens with 20 wt% of oligomer filler (p<0.001) by 60% and the flexural modulus by 44% compared to the plain bone cement specimens stored in the same conditions. The reduction in compression strength in wet conditions was 32%, and that of the compression modulus was 30% (p<0.001). No significant differences were found between test specimens stored in distilled water or SBF (ANOVA, p<0.001). In the SEM examinations, random voids were observed in the oligomer-PMMA-PMA/PMMA polymer blend after water or SBF storage. The results suggest that both water and SBF storage decrease the mechanical properties of the PMMA-PMA/PMMA bone cement modified with oligomer, while at the same time, there was porous formation in the bone cement structure.

Noninvasive in vivo EPR monitoring of the methyl methacrylate polymerization during the bone cement formation

The curing of poly(methyl methacrylate) (PMMA) bone cement is done by a free radical polymerization. As the amount of free radicals present is a marker of the amount of unpolymerized chains present in the polymer, it is assumed that this could be related to the mechanical properties such as strength or density. In this study, the direct observation of the free radicals produced during the PMMA bone cement formation was obtained for the first time in vivo using low-frequency EPR spectrometers (1.2 GHz). Low frequency permits measurements in live animals due to the increased microwave penetration. The amount of polymerization radicals was carried out noninvasively over days on the same animals. The decay rates obtained in vitro and in vivo were compared: the decay rates were significantly lower when the curing process occurred in vivo compared to the situation in vitro. As the kinetics are rather different in vitro and in vivo, this emphasizes the value of the present method that permits the noninvasive monitoring of the curing process directly in vivo.

Bioactive bone cement as a principal fixture for spinal burst fracture: an in vitro biomechanical and morphologic study

STUDY DESIGN

An in vitro biomechanical and radiographic study to evaluate the properties of a newly developed bioactive bone cement for stabilization of the fractured spine, suitable for minimally invasive application.

OBJECTIVES

To determine the mechanical stability of the fractured spine after injection of the newly developed bioactive bone cement under quasi-static and cyclic loading regimens.

SUMMARY OF BACKGROUND DATA

Bone cement injection has been reported as a potentially useful, minimally invasive technique for treating vertebral body fracture or stabilizing osteoporosis. However, potential problems associated with the use of polymethylmethacrylate (PMMA) have prompted the search for alternative solutions. The use of bioactive bone cement as a potential replacement for PMMA has been reported.

METHODS

Biomechanical and radiographic analyses were used to test the mechanical stability of the fractured spine. The cement used was formed from hydroxyapatite powder containing strontium and bisphenol A diglycidylether dimethacrylate (D-GMA) resin. Twenty-six fresh porcine spine specimens (T10-L1) were divided into three groups: pilot, intact, and cemented. Spinal stiffness and failure strength were recorded in the intact group with the specimens flexed at 10 degrees. Uniform injuries were created in all specimens of the cemented group, and compressive loading was applied with 10 degrees of flexion until a fracture occurred. The bone cement was injected into the fractured spine, and stiffness was evaluated after 1 hour. Failure strength was also recorded after 3000 and 20,000 fatigue load cycles. Morphology of the specimens was observed and evaluated.

RESULTS

Results from a cell biocompatibility test indicated that the new bioactive bone cement was favorable for cell growth. Spinal stiffness significantly decreased after fracture (47.5% of intact condition). Instant stiffness of the spine recovered to 107.8% of the intact condition after bone cement injection. After 3000 and 20,000 cycles of fatigue loading, stiffness of the cemented spine was found to be 93.5% and 94.4% of intact stiffness, respectively (P < 0.05). Average failure strength of the spine was 5056 N (after 3000 cycles) and 5301 N (after 20,000 cycles) after bone cement injection and fatigue loading. Radiographs and cross-sectional observations indicated a good cement-bone bonding and fracture fill.

CONCLUSIONS

A new bioactive bone cement without cytotoxic effect has been developed. Results show that minimally invasive techniques to apply this cement to porcine spines results in augmentation of mild burst fractures such that the original stiffness and strength of the vertebra are recovered. This new cement therefore shows potential as an augmentation to traditional instrumentation in the surgical management of vertebral fractures. The potential for further clinical applications is currently under investigation.

A new bioresorbable polymer for screw augmentation in the osteosynthesis of osteoporotic cancellous bone: a biomechanical evaluation

The aim of the study was to assess the mechanical efficacy of a new resorbable polymer developed on the basis of alkylene bis(dilactoyl)-methacrylate to improve the anchorage of osteosynthesis material in cancellous bone. Cancellous bone screws were inserted in bovine as well as in human vertebrae and human femoral condyles and were augmented with the new polymer or polymethylmethacrylate (PMMA), respectively. Nonaugmented screws were used as controls. A removal torque test, a dynamic fatigue test, and a pullout test were performed. Augmentation with the new polymer increased the removal torque by 84% in human femoral bone. In the dynamic fatigue test of bovine vertebrae, the removal torque after cyclic loading was 115% higher for the new polymer compared to the nonaugmented controls. In the human vertebrae, the reinforcement with the new polymer increased the removal torque after dynamic loading by 114%. The augmentation with the new polymer increased the pullout force by 88% in bovine vertebrae and by 118% in human vertebrae in comparison to nonaugmented screws. It was concluded that augmentation by the new resorbable polymer significantly enhanced the anchorage of bone screws in cancellous bone. The mechanical efficiency of the new polymer was comparable to that of PMMA cement.

The effect of implanting gentamicin-impregnated polymethylmethacrylate beads in the tarsocrural joint of the horse

OBJECTIVE

To determine the effect of intra-articular gentamicin-impregnated polymethylmethacrylate (PMMA) beads inserted in the equine tarsocrural joint on the synovial fluid, synovial lining, and cartilage, and to determine the peak and sustainable gentamicin concentrations in synovial fluid and plasma.

STUDY DESIGN

Pharmacokinetic, cytologic, and histologic study of the effect of gentamicin-impregnated PMMA on normal equine tarsocrural joints.

ANIMALS

Five healthy adult horses.

METHODS

Gentamicin-impregnated PMMA bead strands (3 strands each of 40 beads, with each strand containing 100 mg gentamicin) were surgically inserted into one radiographically normal tarsocrural joint in 5 horses. Each horse had both joints flushed with 1 L of lactated Ringer's solution before bead administration. Synovial fluid total protein concentration, white blood cell (WBC) count, gentamicin concentration, synovial histology, cartilage integrity, and cartilage glycosaminoglycan (GAG) concentrations were determined.

RESULTS

Gentamicin concentration (mean +/- SEM peak concentration, 27.9 +/- 2.27 microg/mL) occurred in the first 24 hours and remained above 2 microg/mL for 9 days. Gentamicin concentrations in control joints and the plasma remained below detectable levels. The synovial fluid WBC count for treated joints was increased compared with control joints for 72 hours, but was similar at day 6. The synovial protein concentration in gentamicin-treated joints remained increased for 21 days. Synovium in treated joints had diffuse synovitis, whereas control joints had less fibrovascular proliferation. Superficial cartilage erosion was present in all treated joints. There was no difference in the GAG content of treated and control joint cartilage.

CONCLUSIONS

Short-term implantation of gentamicin (300 mg)-impregnated PMMA beads can provide therapeutic levels of gentamicin (>2 microg/mL) in the normal tarsocrural joint for 9 days; however, gentamicin-impregnated PMMA beads induce synovitis and superficial cartilage erosion.

CLINICAL RELEVANCE

Temporary intra-articular administration of antibiotic-impregnated PMMA may be an effective way to treat septic joints that require constant high concentrations of antibiotics.