Search

Abstract: Calcium phosphate cements (CPCs) are frequently used as bone substitute material. Despite their superior clinical handling and excellent biocompatibility, they exhibit poor degradability, which limits bone ingrowth into the implant. Microspheres were prepared from poly(d,l-lactic-co-glycolic acid) (PLGA) and included in injectable CPCs as porogens in order to enhance its macroporosity after the polymeric microspheres had degraded. Upon degradation of the PLGA microspheres, acid is produced that enhances the dissolution rate of the CPC. However, the effect of the characteristics of PLGA microspheres on the degradation rate of CPCs has never been studied before. Therefore, the purpose of the current study was to investigate the dependence of CPC degradation on the chemical and morphological characteristics of incorporated PLGA microspheres. With respect to the chemical characteristics of the PLGA microspheres, the effects of both PLGA molecular weight (5, 17 and 44kDa) and end-group functionalization (acid-terminated or end-capped) were studied. In addition, two types of PLGA microspheres, differing in morphology (hollow vs. dense), were tested. The results revealed that, although both chemical parameters clearly affected the polymer degradation rate when embedded as hollow microspheres in CPC, the PLGA and CPC degradation rates were mainly dependent on the end-group functionalization. Moreover, it was concluded that dense microspheres were more efficient porogens than hollow ones by increasing the CPC macroporosity during in vitro incubation. By combining all test parameters, it was concluded that dense PLGA microspheres consisting of acid-terminated PLGA of 17kDa exhibited the highest and fastest acid-producing capacity and correspondingly the highest and fastest amount of porosity. In conclusion, the data presented here indicate that the combination of dense, acid-terminated PLGA microspheres with CPC emerges as a successful combination to achieve enhanced apatitic CPC degradation. [Copyright &y& Elsevier]

Abstract: Although extensive efforts have been devoted to the development of polymer–ceramic composites for bone repair, those developed thus far were not able to mimic the nanostructure of bone, partly because of the aggregated, microscale organization of the mineral component. As a consequence, homogenization and intermixing of organic and inorganic components remain a major engineering challenge for the development of functional, biomimetic bone-substituting composites. In the current study, various dispersants were evaluated for their potential to be used as biocompatible dispersants in the synthesis of biomimetic composites with a nanodispersed mineral phase. Based on sedimentation experiments, tribasic sodium citrate was selected as the most effective dispersant for the stabilization of calcium phosphate (CaP) suspensions. Specific adsorption of citrate anions onto CaP nanocrystals was shown to result in a strong increase in the negative surface charge of the CaP particles and consequently increased repulsive interparticle forces that were able to overcome attractive van der Waals forces. Using sodium citrate as dispersant at a CaP/citrate ratio of 4.0, CaP–gelatin nanocomposites were fabricated which displayed a nanostructured mineral phase without occurrence of microscale CaP particles. Consequently, aggregation and sedimentation of CaP mineral phase was reduced considerably. [Copyright &y& Elsevier]

Abstract: This study describes the effect of multilayered DNA coatings on (i) the formation of mineralized depositions from simulated body fluids (SBF); and (ii) osteoblast-like cell behavior with and without pretreatment in SBF. DNA coatings were generated using electrostatic self-assembly, with poly-d-lysine or poly(allylamine hydrochloride) as cationic polyelectrolytes, on titanium substrates. Coated substrates and non-coated controls were immersed in SBF with various compositions. The deposition of calcium phosphate was enhanced on multilayered DNA coatings as compared with non-coated controls, and was dependent on the type of cationic polyelectrolyte used in the build-up of the DNA coatings. Further analysis showed that the depositions consisted of carbonated apatite. Non-pretreated DNA coatings were found to have no effect on osteoblast-like cell behavior compared with titanium controls. On the other hand, SBF-pretreatment of DNA coatings affected the differentiation of osteoblast-like cells through an increased deposition of osteocalcin. The results of this study are indicative of the bone-bonding capacities of DNA coatings. Nevertheless, future animal experiments are required to provide conclusive evidence for the bioactivity of DNA coatings. [Copyright &y& Elsevier]