Biodegradable Bone Cement Research Articles

Biodegradable polymeric bone cement formed from hydroxyapatite, poly (propylene fumerate), poly (vinyl pyrrolidone) and benzoyl peroxide

Polymeric cement is a new biocement material that is able to give immediate support to the implant area by inducing bone repair and a regeneration process through appropriate biodegradation processes. The aim of this study is to produce a polymeric cement using hydroxyapatite as absorbable filler, unsaturated polyester poly (propylene fumarate), poly (vinyl pyrrolidone) and benzoyl peroxide. The presence of hydroxyapatite is believed to enhance bioactivity. The hydroxyapatite powder used in this study was synthesised via precipitation, while poly (propylene fumarate) was synthesised using a direct esterification method. The cement was prepared, cast to form cylindrical specimens and subjected to compression testing. The crosslinking effect is achieved through the action of a mixture of poly (vinyl pyrrollidone) and benzoyl peroxide, which acted as initiator. Cement specimens were aged under simulated physiological conditions. The products were characterised using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the incorporation of bioceramic particles in biodegradable polymers rendered the cement bioactive and able to induce the formation of bonelike apatite on its surface.

Tibial plateau fracture--biodegradable bonecement-augmentation

Between October 1996 and January 1999,29 patients (f:16,m:13,age: 22-86) with fractures of the lateral tibial plateau were operated on arthroscopic,fluoroscopic control or were treated with open reduction and internal fixation. 15 of them were retrospective and 14 prospective analysed. The metaphyseal defect after elevation of the depressed fragment was augmented in 11 cases with autologous spongeous bone grafting,in 9 cases with biodegradable bone cement (Norian SRS). Augmentation was unnecessary in 9 cases. The results according to the Lysholm score and the radiological results were good or excellent. Concerning the kind of augmentation no difference was noted. In the Norian SRS-group the duration of postoperative treatment was shorter than in the other group. The duration of partial weight bearing was shorter too. The results of the present study suggest that an injectable calcium phosphate cement may be a competent material for augmentation in lateral tibial plateau fractures because of the application form and the initial high mechanical stability.

Copolymerization of photocrosslinkable anhydride monomers for use as a biodegradable bone cement

A multifunctional anhydride monomer, methacrylated sebacic anhydride (MSA), was synthesized and copolymerized with methacrylic anhydride via photoinitiated polymerization to form highly crosslinked, degradable networks. This material system was investigated as a potential degradable bone cement. Several aspects were examined, including curing characteristics, degradation rates and mechanical properties. These copolymer networks reached high double-bond conversions on clinically acceptable time scales (<5 min). Furthermore, these divinyl monomer copolymerizations exhibit features of classical crosslinking polymerizations, including autoacceleration, autodeceleration and limited double-bond conversion. Additionally, the networks degrade via a surface erosion mechanism by which the degradation rate can be controlled through varying the degree of oligomerization of the multifunctional monomer backbone, varying the copolymer precursor composition and changing the monomer backbone chemistry. Finally, the copolymer was found to have improved mechanical properties over homopolymerized MSA. Compressive strengths as high as 78 ± 5 MPa were attained with a 70/30 wt% MSA/methacrylic anhydride copolymer, which are comparable to measured (91 ± 7 MPa) and literature (approx. 100 MPa) values for conventional poly(methyl methacrylate) bone cement.

In vitro degradation of polymeric networks of poly(propylene fumarate) and the crosslinking macromer poly(propylene fumarate)-diacrylate

Polymeric networks of poly(propylene fumarate) (PPF) crosslinked with poly(propylene fumarate)-diacrylate (PPF-DA) are currently being investigated as an injectable, biodegradable bone cement. This study examined the effect of crosslinking density, medium pH, and the incorporation of a β-tricalcium phosphate ( β-TCP) filler on the in vitro degradation of PPF/PPF-DA. Cylindrical specimens were submerged in buffered saline at 37°C and the change in weight, geometry, and compressive mechanical properties were monitored over a 52-week period. All formulations showed an initial increase in modulus and yield strength over the first 12 weeks, achieving maxima of 1307±101 and 51±3 MPa, respectively, for the β-TCP composite. PPF/PPF-DA networks with the lower crosslinking density demonstrated the greatest degradation with a 17% mass loss. Samples in the lower buffer pH 5.0 compared to physiological pH 7.4 did not show any differences in mass loss, but exhibited a faster decrease in the compressive strength over time. The β-TCP composites maintained their mechanical properties at the level following their initial increase. These results show that the degradation of PPF/PPF-DA networks can be controlled by the crosslinking density, accelerated at a lower pH, and prolonged with the incorporation of the β-TCP filler.

Crosslinking characteristics of an injectable poly(propylene fumarate)/β-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement

Crosslinking characteristics of an injectable poly(propylene fumarate)/β-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement

Crosslinking Characteristics of an Injectable Poly(Propylene Fumarate)/ β-Tricalcium Phosphate Paste and Mechanical Properties of the Crosslinked Composite for Use as a Biodegradable Bone Cement

AbstractWe investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), benzoyl peroxide (BP), sodium chloride (NaCl), and β-tricalcium phosphate (β-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, heat release upon crosslinking, gel point, and the composite compressive strength and modulus. The maximum crosslinking temperature did not vary widely between formulations, with the absolute values falling between 38 and 48 °C, and was much lower than that of 94°C for poly(methyl methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF molecular weight and a decrease in N-VP/PPF ratio. The gel point was effected strongly by the PPF molecular weight, with a decrease in PPF molecular weight leading to a more rapid gel point. An increase in initiator concentration had the same effect to a lesser degree. The time frame for curing was varied from 1 -121 minutes, allowing the composite to be tailored to specific applications. The compressive strength and compressive modulus values increased with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PPF ratio. For all formulations, the compressive strength values fell between 1 and 12 MPa, and the compressive modulus values fell between 23 and 265 MPa. These data suggest that injectable PPF/β-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopaedic applications and that the mechanical properties of the cured composites are suitable for trabecular bone replacement.

Biodegradable bone cement compositions based on acrylate and epoxide terminated poly(propylene fumarate) oligomers and calcium salt compositions

The synthesis of biodegradable bone cement compositions is presented. These bone cement compositions can be applied as a putty-like mixture and harden to a strong material in a bone fracture. They degrade from the site of application to allow the ingrowth of new bone for complete healing of the bone fracture. The bone cement is composed of a solid particulate phase dispersed in an initially liquid polymeric phase, which can be hardened by cross-linking. The polymeric phase is a low-molecular-weight liquid poly(propylene fumarate) (PPF) containing double bonds available for cross-linking. The solid particulate phase consists of calcium carbonate and tricalcium phosphate. PPF oligomers of M w = 1800 and M n = 750 were prepared from the condensation of non-volatile bis(2-hydroxypropyl fumarate) and propylene-bis(hydrogen maleate) trimers. PPF terminated divinyl and diepoxide derivatives were obtained from the reactions between PPF diol and acryloyl chloride or epichlorhydrin, respectively. Putty-like cement compositions were prepared from a mixture of 30 wt% polymer phase containing benzoyl peroxide-dimethyl toluidine as polymerization catalyst and 70 wt% calcium salts. The divinyl and diepoxide terminated PPF oligomers provided a high strength composition of between 30 and 129 MPa which is suitable for bone cement applications. In vitro hydrolysis of the composites showed little weight loss with the compressive strength remaining above 20 MPa after 4 weeks in buffer solution. Compositions of the PPF oligomers cross-linked without calcium salts showed a gradual weight loss (10–65 wt% after 4 weeks) when placed in buffer solution followed by high water absorption (18–200 wt% after 4 weeks), with the epoxide terminated PPF being the least to degrade or absorb water.

Effect of Screw Diameter, Insertion Technique, and Bone Cement Augmentation of Pedicular Screw Fixation Strength

This study investigated (1) the effect of screw diameter and insertion technique in lumbar vertebrae, and insertion site in the sacrum, on the axial pullout force and transverse bending stiffness of pedicle screws, and (2) the effect of bone cement augmentation using polymethylmethacrylate (PMMA) and the biodegradable composite, poly(propylene glycol-fumarate) on axial pullout force and transverse bending stiffness of pedicle screws inserted into lumbar vertebrae. The axial pullout force and transverse bending stiffness of a 6.25-mm Steffee screw and a 6-mm Kluger screw did not differ significantly in vertebral bodies of similar equivalent bone mineral density. The axial pullout force of Schanz screws was significantly increased with a 1-mm increase in screw diameter. However, there was no significant increase in transverse bending stiffness. In the sacrum, an approach through the S1 facet produced significantly higher axial pullout forces and transverse bending stiffness than the approach described by Harrington and Dickson. PMMA and a biodegradable composite bone cement poly(propylene glycol-fumarate) both increased the axial pullout force. PMMA also increased the transverse bending stiffness.

Antibiotic release from an experimental biodegradable bone cement.

An experimental biodegradable bone cement [poly(propylene fumarate)-methylmethacrylate] (PPF-MMA) has been compared in vivo with polymethylmethacrylate (PMMA) as a carrier agent for local release of antibiotics. This approach is potentially applicable to the treatment of chronic osteomyelitis where the clinical goal is to achieve sustained high concentrations of antibiotics locally in the infected bone. In our experiments, gentamicin- and vancomycin-impregnated cylindrical PMMA and PPF-MMA cement specimens were implanted subcutaneously in rats, and blood and wound fluid samples were obtained over a 2-week period. Antibiotic levels were determined using immunoassays, and microbiologic activity was confirmed with agar diffusion techniques. The biodegradable PPF-MMA cement achieved and maintained considerably higher wound antibiotic levels than did PMMA cement. Vancomycin levels for the PPF-MMA cement were greater than 20 times those for the PMMA cement at all sampling times from 24 h to 14 days. For both cements, the serum antibiotic concentrations remained safely below maximum levels recommended for parenteral therapy. Mechanical testing of the PPF-MMA cement showed that admixture of 3% by weight of antibiotic did not adversely affect material properties. We conclude that this experimental biodegradable bone cement (PPF-MMA) can be used as a carrier to achieve high sustained local levels and low serum levels of antibiotics. Because it is biodegradable and thus does not require a secondary procedure for removal, it has special potential for use in treatment of chronic osteomyelitis.

Quantitative Histology and Mechanical Testing of a Biodegradable Bone Cement

We have developed a particulate composite bone cement consisting of a particulate phase of tricalcium phosphate (TCP) particles bound together by a polymeric matric phase (PPF). This matrix hardens through a free radical polymerization reaction in vivo within several minutes after mixing. The initial mechanical strength of our particulate composite bone cement results from the matrix, but over time this degrades and the strength is augmented by bone ingrowth and incorporation of the tricalcium phosphate particles. Possible orthopaedic applications include fixation of fractures, augmenting fixation of implants in osteoporetic bone, and temporary stabilization of bone ingrowth prostheses.