Application of tertiary amines with reduced toxicity to the curing process of acrylic bone cements

Optimization of Mechanical and Setting Properties in Acrylic Bone Cements Added with Graphene Oxide

The extended use of acrylic bone cements (ABC) in orthopedics presents some disadvantages related to the generation of high temperatures during methyl methacrylate polymerization, thermal tissue necrosis, and low mechanical properties. Both weaknesses cause an increase in costs for the health system and a decrease in the patient’s quality of life due to the prosthesis’s loosening. Materials such as graphene oxide (GO) have a reinforcing effect on ABC’s mechanical and setting properties. This article shows for the first time the interactions present between the factors sonication time and GO percentage in the liquid phase, together with the percentage of benzoyl peroxide (BPO) in the solid phase, on the mechanical and setting properties established for cements in the ISO 5833-02 standard. Optimization of the factors using a completely randomized experimental design with a factorial structure resulted in selecting nine combinations that presented an increase in compression, flexion, and the setting time and decreased the maximum temperature reached during the polymerization. All of these characteristics are desirable for improving the clinical performance of cement. Those containing 0.3 wt.% of GO were highlighted from the selected formulations because all the possible combinations of the studied factors generate desirable properties for the ABC.

Sulfinates and sulfonates as high performance co-initiators in CQ based systems: Towards aromatic amine-free systems for dental restorative materials

OBJECTIVE

The aim of our study is to develop amine-free photoinitiating systems (PISs) for the polymerization of representative dental methacrylate resins under blue light irradiation. PISs based on camphorquinone (CQ)/sulfinate and CQ/sulfonate, eventually in combination with an iodonium salt, are proposed and compared to the well-established CQ/amine system. The polymerization performances of thick (1.4 mm) samples of different methacrylate blends upon exposure to a commercial blue LED centered at 477 nm under air are described. Finally, the performances of the new developed PISs are evaluated for dental composites application.

METHODS

FTIR is used to monitor the photopolymerization profiles. ESR spectroscopy and electrochemical experiments are used to identify the radicals generated. Mechanical properties measurements and color stability measurements are carried out to determine the key properties of the dental composites prepared.

RESULTS AND SIGNIFICIANCE

The performances of the new proposed PISs for the photopolymerization of thick (1.4 mm) samples of methacrylate upon exposure to a blue dental LED under air are excellent. Similar or better performances and bleaching properties are obtained with the new proposed amine-free systems compared to those reached with the CQ/amine reference system. Dental composites with excellent mechanical properties and exceptional color stability are obtained. The involved chemical mechanisms for the initiation step were also established.

Synthesis of Functional Polymer Particles from Morita-Baylis-Hillman Polymerization

Functional synthetic polymers are frequently explored for their use in the biomedical field. To fulfill the stringent demands of biodegradability and compatibility, the materials need to be versatile and tunable. Post-modification is often considered challenging for well-known degradable materials like poly(lactic acid) because of their chemical inertness. In this work a procedure is proposed to produce densely functionalized polymer particles using oligomeric precursors synthesized via the Morita-Baylis-Hillman reaction. This allows for a variety of post-modification reactions to serve bio-conjugation or tuning of the material properties. The particles are subjected to basic media and found to be degradable. Furthermore, cytotoxicity tests confirm good biocompatibility. Finally, as a proof of concept to demonstrate the versatility of the particles, post-modification reactions are carried out through the formation of imines.

Effect of the Bis-Dimethylamino Benzydrol Coinitiator on the Mechanical and Biological Properties of a Composite

To examine the effect of the alternative coinitiator 4,4'bis dimethylamino benzydrol (BZN) in degree of conversion (DC), mechanical and biological properties of experimental composites. The coinitiator BZN was used in three concentrations (0.2, 0.5 and 1.2%), and the coinitiator DMAEMA was used as control at the same concentrations as above. The molar concentration of camphorquinone (CQ) and coinitiators was kept constant (1:1). The composites were manipulated and submitted to microhardness test (VHN), flexural and compressive strength (in MPa), elastic modulus (GPa), DC (FT-IR) and in vitro cytotoxicity (against 3T3 fibroblastic cells) of the experimental resins. Data were subjected to two-way ANOVA and Tukey post-test (α=0.05). The experimental composite resin with BZN showed higher DC values compared to control DMAEMA groups. For the mechanical properties, microhardness values were higher in BZN groups; flexural strength and elastic modulus were similar between all the groups. Compressive strength for groups BZN0.5 and DMAEMA0.5 were not statistically different, being the lowest values attributed to group BZN0.2. The experimental resins with BZN and DMAEMA were considered nontoxic against 3T3 fibroblasts. The inclusion of the coinitiator BZN in experimental composites was considered nontoxic against 3T3 fibroblast cells, without compromising DC and mechanical properties.

Carboxymethylation of ulvan and chitosan and their use as polymeric components of bone cements

Ulvan, extracted from the green algae Ulva lactuca, and chitosan, extracted from Loligo forbesis squid-pen, were carboxymethylated, yielding polysaccharides with an average degree of substitution of ∼98% (carboxymethyl ulvan, CMU) and ∼87% (carboxymethyl chitosan, N,O-CMC). The carboxymethylation was confirmed by Fourier transform infrared spectroscopy and quantified by conductimetric titration and 1H nuclear magnetic resonance. The average molecular weight increased with the carboxymethylation (chitosan, Mn 145→296 kDa and Mw 227→416 kDa; ulvan, Mn 139→261 kDa and Mw 368→640 kDa), indicating successful chemical modifications. Mixtures of the modified polysaccharides were tested in the formulation of polyacrylic acid-free glass-ionomer bone cements. Mechanical and in vitro bioactivity tests indicate that the inclusion of CMU in the cement formulation, i.e. 0.50:0.50 N,O-CMC:CMU, enhances its mechanical performance (compressive strength 52.4±8.0 MPa and modulus 2.3±0.3 GPa), generates non-cytotoxic cements and induces the diffusion of Ca and/or P-based moieties from the surface to the bulk of the cements.

Influence of ibuprofen addition on the properties of a bioactive bone cement

Bioactive bone cements can promote bone growth and the formation of a strong chemical bond between the implant and bone tissue increasing the lifetime of the prosthesis. This study aims at synthesizing a new bioactive bone cement with different amounts of ibuprofen (5, 10 and 20 wt%) using a low toxicity activator, and investigating its in vitro release profile. The effect of ibuprofen (IB) on the setting parameters, residual monomer and bioactivity in synthetic plasma was also evaluated. It was verified that the different IB contents do not prevent the growth of calcium phosphate aggregates on composite surfaces, confirming that the cements are potentially bioactive. A relevant advantage of these formulations was a significant improvement in their curing parameters with increasing IB amount, associated to a reduction of the peak temperature and an extension of the setting time. The investigated cements released an average of about 20 % of the total incorporated ibuprofen during 30 days test, with IB20 liberating the highest percentage of drug 20.6 %, and IB10 and IB5, respectively 19.1 and 17.6 %. This behavior was attributed to the low solubility of this drug in aqueous media and was also related with the hydrophobic character of the polymer. Regarding the therapeutic concentration sufficient to suppress inflammation, the cement with 10 % of ibuprofen achieved the required release rate for 1 week and the cement with 20 % for 2 weeks.

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

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

Mechanical properties and drug release behavior of bioactivated PMMA cements

Septic loosening of cemented implants represents an unresolved long-term problem of total hip endoprostheses. Common treatments of infected prostheses involve the use of temporary antibiotic-loaded PMMA spacer-implants or antibiotic-loaded cements. The latter are either provided by a manufacturer or are obtained by simply mixing specific antibiotic powders according to a microbial sensitivity test with PMMA cement. This study is aimed to investigate the antibiotic release behavior and mechanical properties of novel modified PMMA cements, which were bioactivated by chemical modification of commercial cements with either 0.5% hydroxyethylmethacrylate-phosphate (HEMA-P) or 0.5% hydroxyethylmethacrylate-phosphate + calcium chloride and sodium carbonate as buffer. Tobramycin release experiments from the cements were performed statically by immersion of the drug-loaded samples in PBS buffer following liquid change after different periods of time or during cyclic mechanical loading of the cement samples. Cement modification did not significantly alter the mechanical properties of the cements, but affected the release rate from the matrix. While the unmodified cement released approximately 0.33 mg/cm(2) tobramycin after 48 h independent of the testing regime, modification with both HEMA-P and salt buffer increased the antibiotic release to 37-50 mg/cm(2) when tested under cyclical mechanical loading.

Sesamin as a co-initiator for unfilled dental restorations

A natural component, sesamin (SA), was used to replace conventional amine as co-initiator for dental composite. A combination of camphorquinone (CQ) and SA was employed to initiate the photopolymerization of 2-2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl] propane/triethylene glycol dimethacrylate (70/30wt.%). The kinetics was recorded by real-time Fourier transform infrared spectroscopy. The mechanical properties were measured by dynamic mechanical analysis, the cell toxicity was investigated by MTT assay and a mixture of CQ and ethyl 4-N,N-dimethylaminobenzoate (EDMAB) was used as control in the same photocuring condition. The results indicated that the addition of SA as co-initiator greatly improved the rate of polymerization and final double-bond conversion (DC) when compared with the system initiated by CQ alone. Compared with EDMAB, the final DC of the CQ/SA system (71%) was slightly lower than that of CQ/EDMAB (76%); SA resulted in approximately the same storage modulus at around 37 degrees C, but a slightly higher glass transition temperature. SA produced lower yellowing effect and good in vitro biocompatibility. The water sorption and solubility for two mixtures were very close and within the range of the ISO 4049 specification. These results suggest that SA is an effective alternative co-initiator to conventional amine. The natural compound characteristics of SA make it more promising than amine in dental resin formulations.

Photopolymerization of N,N-dimethylaminobenzyl alcohol as amine co-initiator for light-cured dental resins

OBJECTIVE

The present study was carried out in order to assess the suitability of N,N-dimethylaminobenzyl alcohol (DMOH) as co-initiator of camphorquinone (CQ) and 1-phenyl-1,2-propanedione (PPD) in light-cured dental resins.

METHODS

DMOH was synthesized and used as co-initiator for the photopolymerization of a model resin based on {2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane} (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA). Experimental formulations containing CQ or PPD in combination with DMOH at different concentrations were studied. The photopolymerization was carried out by means of a commercial light-emitting diode (LED) curing unit. The evolution of double bonds consumption versus irradiation time was followed by near-infrared spectroscopy (NIR). The photon absorption efficiency (PAE) of the photopolymerization process was calculated from the spectral distribution of the LED unit and the molar absorption coefficient distributions of PPD and CQ.

RESULTS

DMOH is an efficient photoreducer of CQ and PPD resulting in higher polymerization rate and higher double bond conversion compared with dimethylaminoethylmethacrylate. The PAE for PPD was higher than that for CQ. However, the polymerization initiated by PPD progressed at a lower rate and exhibited lower values of final conversion compared with the resins containing CQ. This observation indicates that the lower polymerization rate of the PPD/amine system should be explained in terms of the mechanism of generating primary radicals by PPD, which is less efficient compared with CQ.

SIGNIFICANCE

The DMOH/benzoyl peroxide redox system, has recently been proposed as a more biocompatible accelerator for the polymerization of bone cements based on poly(methyl methacrylate), because cytotoxity tests have demonstrated that DMOH possesses better biocompatibility properties compared with traditional tertiary amines. The results obtained in the present study reveal the suitability of the CQ/DMOH initiator system for the polymerization of light-cured dental composites.

A natural component as coinitiator for unfilled dental resin composites

A natural component, 1,3-benzodioxole (BDO), was used for the purpose of replacing the conventional amine for dental composite. Camphorquinone (CQ)/BDO was used to initiate the photopolymerization of urethane dimethacrylate (UDMA)/triethylene glycol dimethacrylate (TEGDMA) (70/30 wt %). The kinetics was recorded by real-time Fourier transformation infrared spectroscopy (FTIR). The mechanical properties were measured by dynamic mechanical analyzer (DMA), and CQ/ethyl 4-N,N-dimethylaminobenzoate (EDMAB) mixture was used as control in the same photocuring condition. The results indicated that, the addition of BDO as coinitiator greatly improved the rate of polymerization and final double bond conversion (DC), when compared with the system initiated by CQ alone. BDO and EDMAB were found to reach almost the same final DC (75%), though the kinetics of two systems was different. Comparing with EDMAB, BDO brought approximately the same glass transition temperature (Tg), but slightly higher storage modulus around 37 degrees C. The water sorption and solubility for two mixtures were almost the same and within the range of the ISO 4049's standards. These results suggested that BDO was an effective alternative to conventional amine for coinitiator. And the human diet characteristics of BDO made it more promising than amine in the dental resin formulations.

Development of wollastonite-poly(ethylmethacrylate co-vinylpyrrolidone) based materials for multifunctional devices

The manufacturing of a composite made of a synthetic bioactive ceramic, pseudowollastonite (psW), and a bioresorbable copolymer ethylmethacrylate-vinylpyrrolidone (EMA/VP) is presented in this article. psW porous blocks were produced by dipping an open porous polyurethane foam in a psW containing slurry. A 40/60 wt % EMA/VP monomers mixture was poured on the blocks, and free radical polymerization initiated by azobis(isobutyronitrile) at 50 degrees C. Disks of 1 mm height were obtained by cutting the composite with a diamond saw, and bioresorption and bioactivity of the specimens were tested by immersion of the disks into SBF. A ceramic/polymer weight ratio of 72/28, greater than the usually achievable ratio by polymeric solidification of slurries of monomers charged with a powdered solid component, has been obtained. The system is bioactive and does not change the pH of the medium during the degradation test.

Treatment of acne vulgaris without antibiotics: tertiary amine?benzoyl peroxide combination vs. benzoyl peroxide alone (Proactiv Solution?)

BACKGROUND

Concerns have arisen over the development of antibiotic-resistant organisms due to the prolonged use of oral and topical antibiotics in acne vulgaris. We have previously demonstrated that benzoyl peroxide used in consort with a chemical with an accessible tertiary amine, such as an allylamine, increases radical activity and biological effect.

OBJECTIVES

The purpose of this pilot study was to assess the efficacy of two nonantibiotic topical remedies for mild to moderate acne, with one of the agents being a combination of benzoyl peroxide with butenifine, an allylamine.

METHODS

In an open-label, patient-satisfaction, 8-week comparative study, 23 patients demonstrating mild to moderate facial acne were given randomly either benzoyl peroxide in Proactiv Solution or the combination of benzoyl peroxide with an allylamine.

RESULTS

The allylamine-benzoyl peroxide combination therapy outperformed Proactiv Solution during each 2-week stage of evaluation in terms of reduction of comedones, inflammatory lesions, and degree of oiliness. There was a marked preference for the allylamine-benzoyl peroxide combination in terms of patient satisfaction.

CONCLUSIONS

Benzoyl peroxide used in consort with antimicrobial agents that contain an accessible tertiary amine, such as erythromycin, has previously been shown to increase radical activity and biological effect. Trials of short duration with small numbers of patients do not adequately inform practitioners about whether the combination of allylamines with benzoyl peroxide is a viable alternative to topical antibiotic therapy for acne. Nevertheless, the higher satisfaction with the allylamine-benzoyl peroxide combination certainly warrants further investigation.

Influence of the activator in an acrylic bone cement on an array of cement properties

In all but one of the acrylic bone cement brands used in cemented arthroplasties, N,N-dimethyl-4-toluidine (DMPT) serves as the activator of the polymerization reaction. However, many concerns have been raised about this activator, all related to its toxicity. Thus, various workers have assessed a number of alternative activators, with two examples being N,N-dimethylamino-4-benzyl laurate (DMAL) and N,N-dimethylamino-4-benzyl oleate (DMAO). The results of limited characterization of cements that contain DMAL or DMAO have been reported in the literature. The present work is a comprehensive comparison of cements that contain one of these three activators, in which the values of a large array of their properties were determined. These properties range from the setting time and maximum exotherm temperature of the curing cement to the variation of the loss elastic modulus of the cured cement with frequency of the applied indenting force in dynamic nanoindentation tests. The present results, taken in conjunction with those presented in previous reports by the present authors and co-workers on other properties of these cements, indicate that both DMAL and DMPT are suitable alternatives to DMPT.

Synergistic antimicrobial activity by combining an allylamine with benzoyl peroxide with expanded coverage against yeast and bacterial species

BACKGROUND

Dermatophyte infections can be polymicrobial. Topical antifungal therapies offer limited coverage of yeasts and Gram-positive and Gram-negative bacteria. Moreover, the increased usage of these topical antimicrobial agents has resulted in the development of resistant cases. Benzoyl peroxide (BP), used in concert with antimicrobial agents containing an accessible tertiary amine, has previously been shown to increase radical activity and biological effect.

OBJECTIVES

To determine the applicability of using the tertiary amine terbinafine in concert with BP in dermatophyte and mixed skin infections by means of in vitro testing.

METHODS

In this preliminary in vitro study, the effect of BP, alone and in combination with terbinafine, was tested against Candida albicans, Pseudomonas aeruginosa and Staphylococcus aureus isolates following a checkerboard modification of the National Committee for Clinical Laboratory Standards M27-A2 and M7-A6. The individual minimum inhibitory concentrations of terbinafine, BP, and the combination, were determined against each isolate.

RESULTS

The combination of BP with terbinafine led to additive activities against the majority of Candida albicans isolates tested and additionally expanded the bacterial coverage of terbinafine.

CONCLUSIONS

The combination of antifungal agents bearing a tertiary amine with BP may have benefit in polymicrobial infections, given its wider antimicrobial coverage. Further appreciation of this mechanism of catalysis of BP radical formation by certain antimicrobials and other tertiary amine-containing compounds may lead to the discovery of improved treatments for several dermatological conditions.

Acrylic bone cements modified with beta-TCP particles encapsulated with poly(ethylene glycol)

Beta-tricalcium phosphate (beta-TCP) has been encapsulated with poly(ethylene glycol) (PEG) to improve the filler/cement interface, and it was later incorporated to a poly(methyl methacrylate) bone cement in order to obtain cements with improved stability in the long term. Size and size distribution of the agglomerates forming the initial powder was drastically changed after its dispersion in a PEG aqueous solution. Whereas the initial beta-TCP particles had a 584 microm average diameter, the treated particles (TCP-PEG) presented more than 60% of the particles in a range of 2-6 microm. The effect of adding the treated particles to an acrylic cement was evaluated in terms of curing parameters, in vitro behaviour and mechanical performance. The presence of the TCP-PEG particles did not affect either peak temperature or setting time, indicating a good homogeneity of polymerising mass in contrast to the effect observed with the plain beta-TCP particles, which gave rise to higher setting times. In vitro behaviour studies revealed hydration degree values of the modified cements comparable to that of PMMA cements. Early stages of water uptake was Fickian in nature for all the experimental formulations indicating that the water absorption followed a diffusion controlled mechanism. After 3 months of storage in SBF the experimental formulations presented values of compressive strength in the range 76-78 MPa, higher than the minimum required by ISO 5833 (70 MPa) and those of tensile strength in the range 42-48 MPa, higher than the minimum reported for commercial formulations (30 MPa), but no significant differences in the strengths and elastic modulus were observed with the treatment of the filler particles. This observation was confirmed by ESEM analysis of the tensile fracture surfaces, which revealed a rather good cohesion between the bioceramic particles with some gaps around them, independently of the type of particles. The themogravimetric analysis of dry and wet specimens showed a higher dissolution rate of the plain beta-TCP particles in comparison to the encapsulated ones, indicating that the PEG adsorbed on the surface of the TCP particles could be a way to control the resorbability of the bioceramic component.

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

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

Mechanical characterization of self-curing acrylic cements formulated with poly(methylmethacrylate)/poly(ϵ-caprolactone) beads

New acrylic-based cements were formulated by replacing a mass fraction of 20% of poly(methyl methacrylate) (PMMA) powder by PMMA/poly(epsilon-caprolactone) (PCL) beads (throughout this article all compositions are given as mass fractions, unless specified otherwise). PMMA/PCL beads containing 10 and 30% PCL were synthesized by suspension polymerization. Cements were prepared by replacing part of the PMMA powder of the formulation by an equivalent mass of PMMA/PCL particles. The influence of the PCL content in the beads on the mechanical behavior was assessed by testing the cements in flexure and compression. The addition of PMMA/PCL particles with 10% PCL content resulted in a marked increase in both flexural modulus and flexural strength related to the plain PMMA beads formulation. This improvement was attributed to a decrease in the cured material porosity. Conversely, by the incorporation of beads with 30% PCL content the flexural properties decreased. This behavior was attributed to the debonding of the particles from the matrix, which was revealed by SEM images. The observed compressive yield strength decrease with the increase of PCL content in the beads was attributed to a low degree of adhesion between the heterogeneous particles and the matrix as well as to the plasticizing effect of the PCL.

Influence of the aspect ratio of bioactive nanofillers on rheological behavior of PMMA-based orthopedic materials

In this investigation, calcium-deficient hydroxyapatite (CDHA) nanocrystals with needle-like geometry were synthesized and incorporated with Poly(methyl methacrylate), PMMA, to form CDHA-PMMA nanocomposites. Rheological behaviors of the PMMA-CDHA melting suspensions were systematically investigated in terms of solid loading and aspect ratio of the CDHA nanoparticles. The maximum solid loadings of nano-CDHA particles with aspect ratios of 7.2, 10.4, and 17 were determined to be 28, 31, and 57%, respectively. An increase in solid concentrations causes pronounced shear-thinning behavior. This result suggests that a strong interaction, including Van der Waals attraction and mechanical interlocking, between the nano-CDHA particles makes the nanocomposite mixture more non-Newtonian. Furthermore, it was found that packing efficiency and yield strength in the suspension were strongly influenced by the aspect ratio, especially above the critical value of 8.8. The obtained critical aspect ratio and solid content provide not only appropriate design in the PMMA-CDHA polymeric suspension for fabrication process but also optimal conditions for the fabrication of orthopedic devices via injection molding or extrusion.

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).

Characterization of new acrylic bone cements prepared with oleic acid derivatives

Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 C, with a setting time around 16--17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacosreg R with DMAO, a decrease of 20 C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2x10(5). PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacosreg R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials.

Organic redox-initiated polymerization process for the fabrication of hydrogels for colon-specific drug delivery

Organic-redox initiated polymerization technique based on the co-initiators system comprising benzoyl peroxide and N-phenyldiethanolamine was used at ambient temperature to fabricate pH-responsive hydrogels. The effects of changes in the concentration of the co-initiators system, the ratio in which the co-initiators combined, the type of the polymerization solvent, the pH of the hydrating medium, the concentration of the cross-linking agent based on azo-bond and the pH-sensitive cross-linking agent on the properties of the hydrogels were investigated. Increasing the concentration of the co-initiators system, decreasing the concentration of the two types of cross-linking agents, and replacing DMSO by ethanol as the polymerization solvent resulted in hydrogels with increased equilibrium swelling ratio and increased molecular weight between cross-links at pH 7.4. Increasing the concentration of N-phenyldiethanolamine while keeping the concentration of benzoyl peroxide constant gave hydrogels with increased equilibrium swelling ratios. The equilibrium swelling ratios of the hydrogels at pH 2.0 were not affected by the factors investigated. The polymerization technique may be suitable for the design of drug delivery systems containing thermolabile bioactive agents like peptides and proteins.

Injectable acrylic bone cements for vertebroplasty with improved properties

Currently commercially available acrylic bone cements lack adequate radiopacity and viscosity when they are used in percutaneous vertebroplasty (PVP). In this work improved formulations of radiopaque and injectable poly(methyl methacrylate) bone cements were prepared with different amounts (10-50 wt.%) of BaTiO3 or SrTiO3 particles as the radiopaque agent. Two sets of cements were prepared by using untreated or silanated radiopaque particles, respectively. The influence of the content and nature of the radiopaque agent as well as its silanation with 3-(trimethoxysilyl) propyl methacrylate (gamma-MPS), on the curing parameters, residual monomer content, radiopacity, mechanical properties, and injectability of the resulting materials, was examined. Doughing and setting times, maximum temperature, and compressive strength of all formulations fulfilled the requirements of standard specifications, with values of peak temperature in the range 57-72 degrees C and those of compressive strength between 114 and 135 MPa. Formulations containing at least 20 wt.% BaTiO3 or SrTiO3 had radiopacities equal to or greater than that corresponding to 2 mm of Al as required for surgical plastics. Injectability of any of the formulations provided 75-80 wt.% of the total mass manually injected through a conventional biopsy needle 4 min after mixing. Silanation of the BaTiO3 or SrTiO3 particles led to formulations with improved mechanical properties and injectability compared to those obtained with the untreated fillers.

New acrylic bone cements conjugated to vitamin E: curing parameters, properties, and biocompatibility

Acrylic bone cement formulations with antioxidant character were prepared by incorporation of a methacrylic monomer derived from vitamin E (MVE). Increasing concentrations of this monomer provided decreasing peak temperature values, ranging from 62 to 36 degrees C, and increasing setting time with values between 17 and 25 min. Mechanical properties were evaluated by compression and tension tests. Compressive strength of the new formulations were superior to 70 MPa in all cases. The cement containing 25 wt % MVE, however, showed a significant decrease in tensile properties. Biocompatibility of the new formulations was studied in vitro. The analysis of the effect of leachables from cements into the media showed continued cell proliferation and cell viability with a significant increase for the cement containing 15 wt % MVE. This formulation also showed a significant increase in cellular proliferation over a period of 7 days as indicated by the Alamar Blue test. The cells were able to differentiate and express phenotypical markers in presence of all materials. A significant increase in alkaline phosphatase activity was observed on the cements prepared in presence of 15-25 wt % MVE compared with PMMA. Morphological assessment showed that the human osteoblast (HOB) cells were able to adhere, retain their morphology, and proliferate on all the cements.

Self-curing acrylic formulations containing PMMA/PCL composites: properties and antibiotic release behavior

Partially biodegradable acrylic composites containing poly(methyl methacrylate)-poly(epsilon-caprolactone) (PMMA/PCL) systems were prepared by mixing the corresponding PMMA/PCL beads (89:11, 86:14, 83:17, and 77:23 weight ratio) used as solid phase with methyl methacrylate (MMA) (liquid phase) in a solid/liquid ratio of 1.5:1. The physical and chemical microheterogeneity of these beads influenced significantly the curing parameters, because several aspects involved in the polymerization reaction are closely related to both morphology and size distribution of the particles. In vitro behavior was studied by immersion in simulated body fluid at pH = 7.4 and 37 degrees C for more than 8 weeks and the composition was followed by 1H-nuclear magnetic resonance spectroscopy. Approximately 2% wt/wt weight loss was observed after a period of 8 weeks for the composites richest in PCL. Mechanical properties of the dry and wet specimens were evaluated by compressive and tensile tests. In all cases, the presence of PCL in the composites provided a significant decrease in both compressive strength and elastic modulus compared with plain PMMA. Tensile and compressive strength also decreased significantly after 2 weeks of immersion in simulated body fluid compared with dry specimens. The self-curing composites based on PMMA/PCL beads and loaded with 3% wt/wt vancomycin were evaluated as carriers for local release of antibiotics. The composite prepared with beads of PMMA/PCL ratio 86:14 was the most effective. It eluted 64% of the initial drug within the first 5 h, allowing progressive release of nearly the total amount of the initial drug (90%) in approximately 2 months. The results obtained suggest that the described composites can be suitable for antibiotic release in non-load bearing graft applications.

Increasing hydroxyapatite incorporation into poly(methylmethacrylate) cement increases osteoblast adhesion and response

Poly(methylmethacrylate) (PMMA) is the current standard for cement held prostheses. It forms a strong bond with the implant, but the bond between the cement and the bone is considered to be weak, with fibroblastic cells observed at the implant site, rather than direct bone contact, a contributing factor leading to implant failure. Incorporation of hydroxyapatite (HA) increases the biological response to the cement from tissue around the implant site, thus giving increased bone apposition. In this study, PMMA discs with 0, 4.6 and 8.8 vol%. HA were examined. Primary human osteoblast-like cells (HOBs) were used for the biological evaluation of the response to the cements in vitro. Morphology was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Measurement of tritiated thymidine (3H-TdR) incorporation and alkaline phosphatase (ALP) activity were used to assess proliferation and differentiation. A synergy between increasing focal contact formation, cytoskeletal organisation, cell proliferation and expression of phenotype was observed with increasing HA volume. Preferential anchorage of HOBs to HA rather than PMMA was a prominent observation.

Application of long chain amine activator in conventional acrylic bone cement

A long chain acid derivative bearing an aromatic tertiary amine group, 4-N,N-dimethylaminobenzyl laurate (DML), which acts as an activator for the curing of acrylic cements at low temperature, has been synthesized and characterized to reduce the biological adverse effects usually associated with the classical activator N,N-dimethyl-4-toluidine (DMT). The effectiveness of the activator was tested on commercial formulations (e.g., Palacos R) and on experimental bone cements based on poly (methyl methacrylate) by using different benzoyl peroxide/amine molar ratios. The exotherms of polymerization were followed at three different temperatures: 25, 30, and 37 degrees C. The DML activator was found to be more sensitive to temperature than the corresponding DMT. DML provided exotherms of polymerization with decreasing peak temperatures and increasing setting times without impairing the mechanical properties. Residual monomer content was analyzed in a range of activator concentrations by keeping the benzoyl peroxide concentration constant. In all cases the residual monomer content was lower than 5%, indicating its good efficiency in the benzoyl peroxide initiated polymerization.

Radiopaque acrylic cements prepared with a new acrylic derivative of iodo-quinoline

A novel iodine-containing methacrylate, 2,5-diiodo-8-quinolyl methacrylate, has been synthesized and used in the preparation of acrylic radiopaque cements. The effect of incorporation of this monomer to the self-curing resins, on the curing parameters, swelling behaviour and mechanical properties was studied. The incorporation of the radiopaque compound 2,5-diiodo-8-hydroxyquinoline to the solid phase was also carried out for comparative experiments. A decrease in the peak temperature and an increase in the setting time was observed with the addition of the radiopaque monomer, however, the curing parameters did not appreciably change with the addition of the radiopaque compound to the solid phase. Swelling of the modified cements was in the same range as that of the radiolucent cement; however, the diffusion coefficients calculated according to the Fick's law were higher for the iodine-containing materials. The addition of 5 wt% of the iodine-containing methacrylate provided a significant increase in the tensile properties with respect to either control radiolucent formulations or BaSO4-containing formulations. Biocompatibility of the modified cements was studied by implantation of rods of the cements into rats and histological analysis of the surrounding tissue.

ESR study of MMA polymerization by a peroxide/amine system: bone cement formation

Electron spin resonance (ESR) spectroscopy was used to gain insight at the molecular level into the curing of bone cement. Methyl methacrylate was polymerized using a N,N-dimethyl-p-toluidine (TD)/benzoyl peroxide (BPO) redox system in the presence of polymethyl methacrylate (PMMA) powder. The conventional nine-line ESR spectrum for the growing polymer radical was detected at the gel stage of polymerization. While the optimum free radical concentration was observed near the equimolar amine/BPO concentration, excess amine led to a change in the chemical structure of the trapped radical and inhibited the polymerization process. At a high amine/BPO ratio the nine-line signal disappeared and a three-line nitroxide-based radical appeared. The appearance of this nitroxide signal seems to depend on the amine/BPO molar ratio and on the presence of PMMA. An excess amount of amine with respect to BPO was found to inhibit the polymerization process. When BPO was removed, the system still polymerized but with a longer gelation time and a lower radical concentration. These results demonstrate that trapped free radicals in the bulk polymerization of MMA convert to polymeric peroxides that act as initiators in bone cement. When the accelerator 4-dimethylamino phenethyl alcohol (TDOH) was used, a higher radical concentration was observed in the polymerizing system. TDOH shows potential for being a more effective accelerator than TD for bone cement curing.

Dental materials citations: Part A, January to June 1997

OBJECTIVE

A search was conducted in biomedical journals published from January 1997 to June 1997 to identify all dental materials publications and sort them into major categories.

METHODS

Tables of contents for 79 journals for the period of January to June, 1997 were inspected and divided into 17 categories. Citations were analyzed by both frequency in journals and in categories, as well as compared to frequencies for previous years.

RESULTS

A total of 445 citations were detected in 79 journals for the period January 1997 to June 1997. Certain journals (n = 19) demonstrated a higher citation frequency (> or = 10 citations for 6 months) and represented 77.8% of all citations. The greatest number of citations continued to involve bonding (n = 97), resin-based restorative materials (composites; glass ionomers) (n = 95), prosthodontic materials (n = 51), and pulp protection/luting materials (n = 48). Frequencies by category were very similar to those for the last four years.

SIGNIFICANCE

The compiled literature citations provide a supplement for researchers and academicians seeking information in existing electronic databases.