Injectable self-curing bioactive acrylic-glass composites charged with specific anti-inflammatory/analgesic agent

Bioactive glass: A multifunctional delivery system

Bioactive glasses (BAGs) were invented five decades ago and have been widely used clinically in orthopedic and stomatology. However, in the past two decades, BAGs have been explored immensely by several researchers worldwide as a multifunctional delivery system for a multitude of therapeutics ranging from metal ions to small molecules (e.g., drugs) and macromolecules (e.g., DNA). The impetus for devising a BAG-based delivery system in the 21st century is based upon the facilitative properties it offers for entrapment of a wide range of therapeutic molecules and the tailorable controlled release kinetics to the target tissue site along with the biological activity of the ionic dissolution products in several pathological conditions such as osteoporosis, cancer, infection, and inflammation. This review comprises two parts: the first part discusses the need for a new delivery system and how the journey from melt quench progressed towards template-based sol-gel mesoporous. In the second part, we have comprehended the scientific advancements made so far, emphasizing BAGs as a delivery system ranging from therapeutic ions to phytopharmaceuticals. We have also highlighted a few loopholes that have prevented bench-to-bedside clinical translation of a plethora of elucidative researches done so far.

Multiple and Promising Applications of Strontium (Sr)-Containing Bioactive Glasses in Bone Tissue Engineering

Improving and accelerating bone repair still are partially unmet needs in bone regenerative therapies. In this regard, strontium (Sr)-containing bioactive glasses (BGs) are highly-promising materials to tackle this challenge. The positive impacts of Sr on the osteogenesis makes it routinely used in the form of strontium ranelate (SR) in the clinical setting, especially for patients suffering from osteoporosis. Therefore, a large number of silicate-, borate-, and phosphate-based BGs doped with Sr and produced in different shapes have been developed and characterized, in order to be used in the most advanced therapeutic strategies designed for the management of bone defects and injuries. Although the influence of Sr incorporation in the glass is debated regarding the obtained physicochemical and mechanical properties, the biological improvements have been found to be substantial both in vitro and in vivo. In the present study, we provide a comprehensive overview of Sr-containing glasses along with the current state of their clinical use. For this purpose, different types of Sr-doped BG systems are described, including composites, coatings and porous scaffolds, and their applications are discussed in the light of existing experimental data along with the significant challenges ahead.

Bioactive injectable polymethylmethacrylate/silicate bioceramic hybrid cements for percutaneous vertebroplasty and kyphoplasty

Polymethylmethacrylate (PMMA) cement has been widely used to fill and stabilize hard tissue defects in clinical surgery, especially in percutaneous vertebroplasty (PVP) and percutaneous kyphoplasty (PKP). However, the dense body of pure PMMA in defects has no ability to promote bone regeneration. We herein aim to fabricate novel PMMA/silicate bioceramic hybrid cements by adding bioactive calcium silicate (CS) particles into PMMA to endow PMMA/CS hybrid cements with bioactivity and biodegradability without losing the excellent mechanical strength and injectability. Following comprehensive characterization of the physicochemical properties and in vitro bioactivity study, our results showed compared with PMMA cement, the constructed PMMA/CS hybrid cements possessed significantly lower curing temperatures and simultaneously retained the acceptable mechanical strength and injectability. Moreover, obvious bioactive ion release and hydroxyapatite formation could be detected and observed after the PMMA/CS hybrid cements were soaked in simulated body fluid, indicating their pronounced bioactivity. A further in vivo study of the PMMA/CS hybrid cements on goat vertebral body defect models reflected that the PMMA/CS hybrid cements could be biodegraded well and could significantly promote new bone formation in defects 6 months of post-injection. Our results suggest that PMMA/CS hybrid cements may be promising candidates for PVP and PKP in clinic.

Anti-inflammatory drug-eluting implant model system to prevent wear particle-induced periprosthetic osteolysis

BACKGROUND

Aseptic loosening, as a consequence of an extended inflammatory reaction induced by wear particles, has been classified as one of the most common complications of total joint replacement (TJR). Despite its high incidence, no therapeutical approach has yet been found to prevent aseptic loosening, leaving revision as only effective treatment. The local delivery of anti-inflammatory drugs to modulate wear-induced inflammation has been regarded as a potential therapeutical approach to prevent aseptic-loosening.

METHODS

In this context, we developed and characterized anti-inflammatory drug-eluting TiO2 surfaces, using nanoparticles as a model for larger surfaces. The eluting surfaces were obtained by conjugating dexamethasone to carboxyl-functionalized TiO2 particles, obtained by using either silane agents with amino or mercapto moieties.

RESULTS

Zeta potential measurements, thermogravimetric analysis (TGA) and drug release results suggest that dexamethasone was successfully loaded onto the TiO2 particles. Release was pH dependent and greater amounts of drug were observed from amino route functionalized surfaces. The model-system was then tested for its cytotoxic and anti-inflammatory properties in LPS-stimulated macrophages. Dexamethasone released from amino route functionalized surfaces TiO2 particles was able to decrease LPS-induced nitric oxide (NO) and TNF-a production similarly to pure DEX at the same concentration; DEX released from mercapto route functionalized surfaces was at a too low concentration to be effective.

CONCLUSION

Dexamethasone released from amino functionalized titanium can offer the possibility of preventing asepting loosening of joint replacement devices.

Experimental study of the application of a new bone cement loaded with broad spectrum antibiotics for the treatment of bone infection

OBJECTIVES

To evaluate the in vivo behaviour of a new bone cement loaded with antibiotics, in a rabbit bone infection model.

MATERIAL AND METHODS

Sixteen New Zealand rabbits divided into 4 groups were used, depending on the cement (commercial or experimental) and the antibiotic (vancomycin or linezolid) used to control a bone infection caused by Staphylococcus aureus. The commercial cement is Palacos^® R and the experimental cement has been achieved by adding PLGA to the solid phase of Palacos^® R cement. A novel histological staging method based on bone histoarchitecture has been used. This staging allows us a global vision of bone repair capacity, in the presence of modified cement, and also allows us to correlate the damage generated with the functionality of the tissue.

RESULTS

The degree of bone destructuration found depended on the type of cement and antibiotic, and was higher in the groups with commercial cement than in the experimental group (P<.01) and in the groups with linezolid with respect to vancomycin (P=.04) The percentage of macrophages varied exclusively depending on the antibiotic used, and was higher in the vancomycin groups (P=.04).

DISCUSSION

The development of new formulations of bone cement that release more, and more prolonged, new generation antibiotics such as linezolid, present an in vivo behaviour superior to commercial cement, respecting the bone structure. This behaviour would have a clinical implication in fighting infections by increasingly resistant germs in the treatment of prosthetic infection.

β-Cyclodextrin-Functionalized Chitosan/Alginate Compact Polyelectrolyte Complexes (CoPECs) as Functional Biomaterials with Anti-Inflammatory Properties

Nowadays, the need for therapeutic biomaterials displaying anti-inflammatory properties to fight against inflammation-related diseases is continuously increasing. Compact polyelectrolyte complexes (CoPECs) represent a new class of materials obtained by ultracentrifugation of a polyanion/polycation complex suspension in the presence of salt. Here, a noncytotoxic β-cyclodextrin-functionalized chitosan/alginate CoPEC was formulated, characterized, and described as a promising drug carrier displaying an intrinsic anti-inflammatory property. This new material was successfully formed, and due to the presence of cyclodextrins, it was able to trap and release hydrophobic drugs such as piroxicam used as a model drug. The intrinsic anti-inflammatory activity of this CoPEC was analyzed in vitro using murine macrophages in the presence of lipopolysaccharide (LPS) endotoxin. In this model, it was shown that CoPEC inhibited LPS-induced TNF-α and NO release and moderated the differentiation of LPS-activated macrophages. Over time, this kind of bioactive biomaterial could constitute a new family of delivery systems and expand the list of therapeutic tools available to target inflammatory chronic diseases such as arthritis or Crohn's disease.

Preparation and characterization of injectable PMMA-strontium-substituted bioactive glass bone cement composites

In most minimally-invasive procedures used to address severe pain arising from compression fractures of the vertebral bodies, such as percutaneous vertebroplasty (PVP), a poly(methyl methacrylate) (PMMA) bone cement is used. Shortcomings of this type of cement, such as high exotherm temperature and lack of bioactivity, are well known. We prepared different formulations of a composite bone cement, whose solid constituents consisted of PMMA beads and particles of a bioactive glass (BG), where 0-20%(w/w) of the calcium component was substituted by strontium. The difference between the formulations was in the relative amounts of the solid phase constituents and in the Sr-content of BG. We determined the influence of the mixture of solid phase constituents of the cement formulation on a collection of properties, such as maximum exotherm temperature (T_max ), setting time (t_set ), and injectability (I). The selection of the PMMA beads was crucial to obtain cement composite formulations capable to be efficiently injected. Results allowed to select nine solid phase mixtures to be further tested. Then, we determined the influence of the composition of these composite bone cements on T_max , t_set , I, and cell proliferation. The results showed that the performance of various of the selected composite cements was better than that of PMMA cement reference, with lower T_max , lower t_set , and higher I. We found that incorporation of Sr-substituted BGs into these materials bestows bioactivity properties associated with the role of Sr in bone formation, leading to some composite cement formulations that may be suitable for use in PVP. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1245-1257, 2018.

Development of advanced biantibiotic loaded bone cement spacers for arthroplasty associated infections

The incidence increase of infections in patients with hip or knee implants with resistant pathogens (mainly some S. coagulase-negative and gram positive bacteria) demands advanced antibiotic loaded formulations. In this paper, we report the design of new biantibiotic acrylic bone cements for in situ delivery. They include a last generation antibiotic (daptomycin or linezolid) in combination with vancomycin and are performed based on a novel modification of the Palacos R^® acrylic bone cement, which is based on two components, a liquid (methyl methacrylate) and a solid (polymeric phase). Hence, the solid component of the experimental formulations include 45wt% of microparticles of poly(D,L-lactic-co-glycolic) acid, 55wt% of poly(methyl methacrylate) beads and supplements (10wt-% each) of antibiotics. These formulations provide a selective and excellent control of the local release of antibiotics during a long time period (up to 2 months), avoiding systemic dissemination. The antimicrobial activity of the advanced spacers tested against S. aureus shows that single doses would be enough for the control of the infection. In vitro biocompatibility of cements on human osteoblasts is ensured. This paper is mainly focused on the preparation and characterization of cements and the studies of elution kinetics and bactericidal effects. Developed formulations are proposed as spacers for the treatment of infected arthroplasties, but also, they could be applied in other antibiotic devices to treat relevant bone-related infection diseases.

Synthesis and characterization of self-curing hydrophilic bone cements for protein delivery

New formulations of acrylic bone cements for bone defect reparation, based on self-hardening methyl methacrylate (MMA)/methacrylic acid (MAA), with a high capacity for protein delivery, have been developed. The self-curing formulations were prepared by partial substitution of solid phase PMMA microparticles by newly obtained PMAA microspheres. The PMAA microspheres were prepared by inverse suspension polymerization of their monomer and were cross-linked with N,N'-methylene-bis-acrylamide (MBA) (10-15 wt %) to produce stable systems in contact with aqueous media. PMAA microspheres were loaded with hydrolyzed collagen (HC) as a model protein to simulate bone morphogenetic protein delivery useful for hard tissue reconstruction. Solid phase PMMA microparticles in the formulation were partially substituted by new PMAA-HC microspheres and were characterized to determine viability as an acrylic bone cement in minimally invasive surgery. The incorporation of PMAA-HC microspheres decreased peak temperature by 20°C, which minimized thermal necrotic risk after implantation. Mechanical compression tests revealed a behavior, under dry conditions, close to ISO 5833 standard requirements. However, a drastic drop in mechanical strength, ∼64%, was obtained after 15 days of immersion in simulated physiological conditions (37°C and pH 7.4) and was attributed to water absorption and a subsequent plasticizing effect. The increase in water uptake and retention enhanced the capability for controlled protein delivery. Finally, the biocompatibility of the cements was determined; some toxicity of the material during the first hours of culture incubation was observed. Later, toxicity was observed to decrease due to nonreacted monomer leaching, which ensured the low toxicity of the already polymerized phase.

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.

Bioglass: A novel biocompatible innovation

Advancement of materials technology has been immense, especially in the past 30 years. Ceramics has not been new to dentistry. Porcelain crowns, silica fillers in composite resins, and glass ionomer cements have already been proved to be successful. Materials used in the replacement of tissues have come a long way from being inert, to compatible, and now regenerative. When hydroxyapatite was believed to be the best biocompatible replacement material, Larry Hench developed a material using silica (glass) as the host material, incorporated with calcium and phosphorous to fuse broken bones. This material mimics bone material and stimulates the regrowth of new bone material. Thus, due to its biocompatibility and osteogenic capacity it came to be known as "bioactive glass-bioglass." It is now encompassed, along with synthetic hydroxyapatite, in the field of biomaterials science known as "bioactive ceramics." The aim of this article is to give a bird's-eye view, of the various uses in dentistry, of this novel, miracle material which can bond, induce osteogenesis, and also regenerate bone.

Combined influence of barium sulfate content and co-monomer concentration on properties of PMMA bone cements for vertebroplasty

In this work, the combined influence of barium sulfate content and co-monomer concentration on the properties of acrylic bone cement for percutaneous vertebroplasty (PVP) was investigated using a response surface methodology. Cements were prepared with methyl methacrylate (MMA) and either diethyl amino ethyl methacrylate (DEAEM) or dimethyl amino ethyl methacrylate (DMAEM) as co-monomer in the liquid phase, while variable amounts of barium sulfate were incorporated to the solid phase in order to improve the radiopacity of cements. It was found that various properties such as peak temperature, setting time, residual monomer content, mechanical properties and injectability, had an effect on the occurrence of interactions (combined effect) between the barium sulfate and DEAEM in bone cements formulations when independent variables were at their maximum.

In vitro and in vivo evaluation on the bioactivity of ZnO containing nano-hydroxyapatite/chitosan cement

A ZnO containing nano-hydroxyapatite/chitosan (n-HA/CS) cement was developed and its bone formation ability was investigated in vitro and in vivo. The physico-chemical properties of the cement were determined in terms of pH variation during and after setting, injectability and wettability. The results indicated that, the pH varied from 7.04 to 7.12 throughout the soaking of the cement in distilled water. The injectability was excellent during the first 4 min, but the cement became less injectable or even not injectable at all after 7 min setting. The static contact angle of the cement against water was 53.5 +/- 2.7 degrees . The results of immersion tests in simulated body fluid (SBF) indicated that the cement exhibited excellent bone-like apatite forming ability. In vivo studies, involving the installation of the cement of tibial-bone defects in rabbit tibia revealed an inflammatory response around the cement at 3 days of implantation. After 4 weeks, the inflammation began to disappear and the cement had bound to the surrounding host bone. Radiological examination also confirmed that the ZnO containing n-HA/CS cement significantly induced new bone formation. These results suggest that the ZnO containing n-HA/CS cement may be beneficial to enhance bone regeneration in osseous defect sites.

Ibuprofen-loaded calcium phosphate granules: combination of innovative characterization methods to relate mechanical strength to drug location

This paper studies the impact of the location of a drug substance on the physicochemical and mechanical properties of two types of calcium phosphate granules loaded with seven different contents of ibuprofen, ranging from 1.75% to 46%. These implantable agglomerates were produced by either low or high shear granulation. Unloaded Mi-Pro pellets presented higher sphericity and mechanical properties, but were slightly less porous than Kenwood granules (57.7% vs 61.2%). Nevertheless, the whole expected quantity of ibuprofen could be integrated into both types of granules. A combination of surface analysis, using near-infrared (NIR) spectroscopy coupling chemical imaging, and pellet porosity, by mercury intrusion measurements, allowed ibuprofen to be located. It was shown that, from 0% to 22% drug content, ibuprofen deposited simultaneously on the granule surface, as evidenced by the increase in surface NIR signal, and inside the pores, as highlighted by the decrease in pore volume. From 22%, porosity was almost filled, and additional drug substance coated the granule surfaces, leading to a large increase in the surface NIR signal. This coating was more regular for Mi-Pro pellets owing to their higher sphericity and greater surface deposition of drug substance. Unit crush tests using a microindenter revealed that ibuprofen loading enhanced the mechanical strength of granules, especially above 22% drug content, which was favorable to further application of the granules as a bone defect filler.

Bone tissue engineering therapeutics: controlled drug delivery in three-dimensional scaffolds

This paper provides an extensive overview of published studies on the development and applications of three-dimensional bone tissue engineering (TE) scaffolds with potential capability for the controlled delivery of therapeutic drugs. Typical drugs considered include gentamicin and other antibiotics generally used to combat osteomyelitis, as well as anti-inflammatory drugs and bisphosphonates, but delivery of growth factors is not covered in this review. In each case reviewed, special attention has been given to the technology used for controlling the release of the loaded drugs. The possibility of designing multifunctional three-dimensional bone TE scaffolds for the emerging field of bone TE therapeutics is discussed. A detailed summary of drugs included in three-dimensional scaffolds and the several approaches developed to combine bioceramics with various polymeric biomaterials in composites for drug-delivery systems is included. The main results presented in the literature are discussed and the remaining challenges in the field are summarized with suggestions for future research directions.

Comparison of three dissolution apparatuses for testing calcium phosphate pellets used as ibuprofen delivery systems

Porous calcium phosphate pellets were produced according to two granulation processes (low and high shear wet granulations) and drug loaded with five ibuprofen contents (1.75%, 7%, 12.5%, 22%, and 36%) in order to ensure both bone defect filling and local drug delivery. The drug-release kinetics from the two types of pellets was studied using three dissolution apparatuses: paddle apparatus, reciprocating cylinder, and flow-through cell. The paper compared the three dissolution methods and considered the effect of the granulation process on the ibuprofen-release kinetics. Dissolution data were analyzed using the Weibull function as well as the difference (f1) and similarity (f2) factors. Dissolution kinetics was not influenced by the granulation process, regardless of the dissolution apparatus and of the drug content. The comparison of the three dissolution devices indicated that ibuprofen was released faster from granules loaded with 36% of drug content with the reciprocating apparatus, due to the disintegration of the granules occurring during the dissolution test. For the other drug contents, dissolution profiles were not significantly different from one apparatus to another. However, the flow-through cell seemed to be more suitable for the drug-release study of implantable materials.

New injectable and radiopaque antibiotic loaded acrylic bone cements

The use of antibiotic loaded bone cements (ALBCs) has become a common clinical practice in the prevention and treatment of prosthesis-related infections. However, due to antibiotic resistance, there is a general interest in broadening the antibacterial spectrum of currently used drugs. The aim of this work is to formulate ALBCs for specific use in vertebroplasty and kyphoplasty, and to study the effect of the addition of ciprofloxacin alone and in combination with vancomycin on some properties of the cement. The cements were formulated using bismuth salicylate as the radiopacifier. The setting properties, residual monomer content, release of antibiotics, rheological behavior, injectability, and mechanical properties of these formulations were studied. They showed long setting times and low curing temperatures. From the release studies, antibacterial properties are assumed because the concentration of released antibiotic was higher than the minimum effective. Although the experimental cements had slightly reduced mechanical properties, the other alterations shown were negligible.

Characterization of new biodegradable bone cement compositions based on functional polysuccinates and methacrylic anhydride

New biodegradable poly(3-allyloxy-1,2-propylene)succinate-based materials were obtained by cross-linking poly(3-allyloxy-1,2-propylene)succinate (PSAGE) with methyl methacrylate (MMA) and methacrylic anhydride (MAAH). The aim of this study was to examine the influence of MAAH/MMA ratio and incorporation of biphasic calcium phosphate (BCP) filler on the maximum curing temperature, setting time, compressive strength and modulus of the cured materials, as well as on their hydrolytic degradation. The latter was characterized by determination of the weight loss and observation of changes in samples morphology by SEM. The maximum temperature during cross-linking was found to decrease with increasing MAAH content. The setting time was affected strongly by the concentration of double bonds and was rapidly shortened with its increase. The compressive strength and compressive modulus values increased with increasing MAAH/MMA ratio. Moreover, addition of bioactive mineral filler (BCP) improves significantly mechanical properties of these materials. On the other hand, it slows down their hydrolytic degradation.

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.

Preparation of acrylic bone cements for vertebroplasty with bismuth salicylate as radiopaque agent

One of the problems of percutaneous vertebroplasty attributed to the use of acrylic cements is related to the radiopacity of the formulation. The use of bismuth salicylate as the radiopaque agent is proposed in this work, taking into account the high radiopacity of organobismuth compounds used in dental applications and the possible analgesic effect of salicylic acid. Various cements formulated with this compound (some of them modified with polyethylene oxide) were examined. Setting parameters, mechanical properties, rheological behaviour, injectability, radiopacity and biocompatibility were studied for a variety of formulations, showing that the cement formulations containing bismuth salicylate have a higher radiopacity and better injection properties than commercial bone cement preparations and present good mechanical properties.

Anterior spinal column augmentation with injectable bone cements

A vertebral fracture, whether originating from osteoporosis or trauma, can be the cause of pain, disability, deformation and neurological deficit. The treatment of vertebral compression fractures has, for many years until the advent of vertebroplasty, consisted of bedrest and analgesics. Vertebroplasty is a percutaneous technique during which bone cement is injected in a vertebral body to provide immediate pain relief by stabilization. Inflatable bone tamps can, prior to the injection of cement, be used to create a void in the vertebral body, in which case the technique is known as balloon vertebroplasty (or kyphoplasty). The chance of extracorporal cement leakage is smaller for balloon vertebroplasty than for vertebroplasty. Some authors also claim to have gained some correction in vertebral body height or angulation. Both interventions can be used for several indications, including osteoporotic compression fractures and osteolytic lesions of the vertebral body such as myeloma, hemangioma or metastasis, and also for traumatic burst fractures in combination with pedicle screw instrumentation. Polymethyl methacrylate cement is the bone void filler that is used most frequently, although the application of calcium phosphate cements has been studied widely in vitro, in vivo and also in small-scale clinical series. The clinical results of (balloon-) vertebroplasty are favorable with 85-95% of all patients experiencing immediate and long-lasting relief of pain. Serious complications are relatively rare but include neurological deficit and pulmonary embolism. In this paper, both vertebroplasty and balloon vertebroplasty and their respective indications, techniques and results are described in relation with the application and limitations of permanent and resorbable injectable bone cements.

Influence of powder particle size distribution on complex viscosity and other properties of acrylic bone cement for vertebroplasty and kyphoplasty

For use in vertebroplasty and kyphoplasty, an acrylic bone cement should possess many characteristics, such as high radiopacity, low and constant viscosity during its application, low value of the maximum temperature reached during the polymerization process (T(max)), a setting time (t(set)) that is neither too low nor too high, and high compressive strength. The objective of this study was to investigate the influence of the powder particle distribution on various properties of one acrylic bone cement; namely, residual monomer content, T(max), t(set), complex viscosity, storage and loss moduli, injectability, and quasi-static compressive strength and modulus. It was found that the formulations that possessed the most suitable complex viscosity-versus-mixing time characteristics are those in which the ratio of the large poly(methyl methacrylate) beads (of mean diameter 118.4 microm) to the small ones (of mean diameter 69.7 microm) was at least 90% w/w. For these formulations, the values of the other properties determined were acceptable.

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.