Key Engineering Materials Vols. 361-363

Abstract: β-tricalcium phosphate (β-TCP) based cement features unique biodegradability and mild temperature rise as a material for bone reconstruction. However, the bone cement often raises a shelf life issue and therefore study was made focusing on the temperature and humidity during storage. With the increase of storing days, the density and compressive strength of hardened cement were found to drastically decrease for the cement powder stored in a mixed state. In addition, the setting property was finally lost at the same time. Such a degradation was more evident at higher temperature and was the result of the formation of dicalcium phosphate anhydrous (DCP) instead of dicalcium phosphate dehydrate (DCPD) during the storage. On the contrary, for the cement stored in an unmixed state, very slight changes were detected in density, compressive strength and setting time with the increase of storing days even if the powders were kept in a humid environment. In the unmixed ones, DCP was not precipitated regardless of the storing temperature. Discussion was made on the condition for precipitating either DCPD or DCP in terms of the amount of water supplied during setting. Practically the work suggested that the β-TCP based cement needs to be conserved at lower temperature and in dry environment as possible to effectively increase the shelf life.

Abstract: It is well known that calcium phosphate compounds are widely used as bone substitute due to their biocompatibility and bioactivity. Furthermore, recent studies have shown that slight changes in morphology or crystal structure can lead to several in vivo behaviours. Therefore, the purpose of this study was to investigate two different β-TCP synthesis routes (solid state reaction and aqueous solution precipitation) and their consequences on the final cement properties. It was found out that both routes are equivalent as there were no significant differences on their cement properties, except for mechanical resistance. The latter difference can also be attributed to the difference on the particle size distributions of the obtained β-TCP. These facts indicate that solid state reaction route is more interesting given its simplicity and yield.

Abstract: Injectable calcium phosphate (CaP) biomaterial is considered as an injectable bone substitute (IBS). It was developed to minimize invasive surgery in various applications in orthopedic and dental surgery. The IBS considered of a polymer solution mixed with biphasic calcium phosphate (BCP) ceramic particles. Two particle sizes of BCP (40-80 and 80-200μm) were used and the weight ratio was 40%. This study investigated the influence of polymer solution on the BCP particles stability. Effects of particles size and limiting viscosity of polymer on the sedimentation were studied. The polymer concentration and particles size can be adapted to provide the best stability and storage of IBS.

Abstract: Two different injectable materials, intended for use in vertebroplasty (VP) treatments of fractured vertebras, were tested in an in vitro bone model. The materials tested were an experimental bioceramic material based on calcium aluminate manufactured by Doxa AB, and Vertebroplastic, a PMMA based material manufactured by DePuy Acromed. The model was earlier developed by others and has been found valid for testing of materials intended for PVP. The model offers alternative data to traditional compressive and diametral tensile testing by adding the infiltration of material into synthetic cancellous bone. Five different synthetic bones with different porosity and pore structure were tested. The results show that for the PMMA the infiltration pattern of the different bones tested seems to have no influence. The material deforms plastically and displays about the same strength in all bones tested. For the bioceramic, linear elastic, material however there is a difference. In the more porous bones, where the material infiltrate the pores and creates a test body with a large amount of crack initiation points, the material displays lower strength compared to that of the more solid bones.

Abstract: Vertebral compression fractures were simulated by making a hole into sheep vertebrae and by injecting a stabilizing material. The injectable bio-ceramic Xeraspine™ was evaluated together with a commercially available PMMA (Vertebroplastic™) as the reference material. The Vertebrae were harvested after 7 days and prepared for microscopy. The samples were deposited with gold on the surface and thereafter subjected to SEM and EDX analysis. It was found that the Xeraspine-bone interface was composed of a mixture of elements. The Vertebroplastic implant was embedded in a carbon containing tissue, likely a soft tissue capsule. The Xeraspine sample was subjected to high resolution analysis in the TEM combined with EDX measurements. The TEM sample was prepared with a novel technique for preparation of the tissue-material interface (FIB). In the TEM analysis it was found that the interface region consists of ZrO2 together with a mixture possibly consisting of katoite and apatite formed during setting and/or originating from the boneapatite.

Abstract: We performed vertebroplasty on goat model by injecting a new macroporous calcium phosphate cement MCPC®. The mechanical property of the cement is about 12MPa after 24 hours (compression test). The cement matrix is totally transformed into poorly crystallized apatite in 48 hours. This study demonstrates that MCPC cement was suitable and efficient for a spine application. Its injectability allows to be used in mini invasive surgery and its mechanical properties are compatible to support spine strength. In addition, a bone ingrowth onto the BCP granules occurred with time.

Abstract: Calcium alkyl phosphates and their strontium and magnesium analogues were synthesised by the reaction of aqueous metal salts with a range of alkyl phosphates of varying chain length and were characterised by X-ray diffraction, thermogravimetric and FTIR analyses. These hybrid structures are based on alternating organic/metal phosphate regions and were found to exhibit a linear increase in interlayer separation upon increasing the length of the alkyl chain. Our analysis suggests a general formula for these phases of M(ROPO3).nH2O (where M = Ca, Sr, Mg and R = alkyl group), containing alkyl bilayers reminiscent of phospholipid bilayers found in biological membranes.

Abstract: A comparative study of the in situ interactions between different maleic anhydride based copolymers and calcium phosphates is presented in this paper. The ability of functional groups of the organic polymers to form under high pressure and low temperatures chemical bonds with the inorganic phase leading to improved properties of hybrid nanostructured material is discussed. The open challenges of new hybrid nanocomposites in the field of biomedical materials are evaluated. The challenge to use these nanostructured materials in medical field was evaluated by mapping the interface reactions between hybrid active layers and cells.

Abstract: Pure calcium sulfate (CS) is an excellent bone graft material because it is biocompatible, completely biodegradable, osteoconductive, safe, nontoxic and angiogenic. It also has barrier properties. However, its rapid degradation limits its use as a bone graft material. A nanocomposite of CS and poly (l lactic acid) (PLLA) in a ratio of 96:4 was developed to overcome this problem. This composite underwent slower degradation. It took 16 weeks for complete degradation whereas pure CS takes only 4 weeks. When implanted in bone defects in rabbits, it underwent complete degradation and stimulated vigorous bone formation.