Geometric adaption of biodegradable magnesium alloy scaffolds to stabilise biological myocardial grafts. Part I.

Synthetic patch materials currently in use have major limitations, such as high susceptibility to infections and lack of contractility. Biological grafts are a novel approach to overcome these limitations, but do not always offer sufficient mechanical durability in early stages after implantation. Therefore, a stabilising structure based on resorbable magnesium alloys could support the biological graft until its physiologic remodelling. To prevent early breakage in vivo due to stress of non-determined forming, these scaffolds should be preformed according to the geometry of the targeted myocardial region. Thus, the left ventricular geometry of 28 patients was assessed via standard cardiac magnetic resonance imaging (MRI). The resulting data served as a basis for a finite element simulation (FEM). Calculated stresses and strains of flat and preformed scaffolds were evaluated. Afterwards, the structures were manufactured by abrasive waterjet cutting and preformed according to the MRI data. Finally, the mechanical durability of the preformed and flat structures was compared in an in vitro test rig. The FEM predicted higher durability of the preformed scaffolds, which was proven in the in vitro test. In conclusion, preformed scaffolds provide extended durability and will facilitate more widespread use of regenerative biological grafts for surgical left ventricular reconstruction.

Magnesium degradation products: effects on tissue and human metabolism.

Owing to their mechanical properties, metallic materials present a promising solution in the field of resorbable implants. The magnesium metabolism in humans differs depending on its introduction. The natural, oral administration of magnesium via, for example, food, essentially leads to an intracellular enrichment of Mg(2+) . In contrast, introducing magnesium-rich substances or implants into the tissue results in a different decomposition behavior. Here, exposing magnesium to artificial body electrolytes resulted in the formation of the following products: magnesium hydroxide, magnesium oxide, and magnesium chloride, as well as calcium and magnesium apatites. Moreover, it can be assumed that Mg(2+) , OH(-) ions, and gaseous hydrogen are also present and result from the reaction for magnesium in an aqueous environment. With the aid of physiological metabolic processes, the organism succeeds in either excreting the above mentioned products or integrating them into the natural metabolic process. Only a burst release of these products is to be considered a problem. A multitude of general tissue effects and responses from the Mg's degradation products is considered within this review, which is not targeting specific implant classes. Furthermore, common alloying elements of magnesium and their hazardous potential in vivo are taken into account.

Characterization of MgNd2 alloy for potential applications in bioresorbable implantable devices.

The aim of this study is to investigate and demonstrate the mechanical and corrosive characteristics of the neodymium-containing magnesium alloy MgNd2 (Nd2), which can be used as a resorbable implant material, especially in the field of stenting applications. To determine the mechanical characteristics of Nd2, tensile and compression tests were initially carried out in the hot extruded state. Here a unique elongation ratio (~30%) of the alloy could be observed. Subsequent T5 and T6 heat treatments were arranged to reveal their effect on the alloy's strengths and elongation values. The general degradation behaviour of Nd2 in a 0.9% NaCl solution was investigated by means of polarization curves and hydrogen evolution. In addition to this, by using various in vivo parameters, a corrosion environment was established to determine the alloy's degradation in vitro. Here, the mass loss per day in (MgF(2) and Bioglass)-coated and uncoated states and the corresponding maximum forces resulting from subsequent three-point bending tests revealed slow and steady corrosion behaviour. The cell viability and proliferation tests carried out on L-929 and MSC-P5 cells also showed good results. The mechanical and corrosive characteristics determined, as well as the in vitro test results obtained within the scope of this study, led to the development and successful in vivo testing of an MgF(2)-coated Nd2 mucosa stent which was introduced as an appropriate resorbable application.

Reduction of biofilm on orthodontic brackets with the use of a polytetrafluoroethylene coating.

SUMMARY: Treatment with fixed orthodontic appliances can cause enamel demineralization by increased biofilm adhesion. The purpose of the present study was to investigate whether a polytetrafluoroethylene (PTFE) coating reduces biofilm formation on orthodontic brackets. One PTFE-coated bracket and one uncoated stainless steel bracket were bonded symmetrically on the first or second (four maxillary and nine mandibular) primary molars in 13 adolescent patients (five females and eight males, aged 11.2 +/- 2.8 years; four dropouts) for 8 weeks. Quantitative biofilm formation on brackets was analysed with the Rutherford backscattering detection (RBSD) method, a scanning electron microscopy technique. A total of five RBSD micrographs were obtained per bracket with views from the buccal, mesial, distal, cervical, and occlusal aspects. A two-sided paired t-test was used to compare data. A P-value less than 0.05 was considered significant. Total biofilm formation was 4.0 +/- 3.6 per cent of the surface on the PTFE-coated brackets and 22.2 +/- 5.4 per cent on uncoated brackets. Differences between the two groups were statistically significant (P < 0.05). Pairwise comparison of biofilm formation with respect to location (buccal, mesial, distal, cervical, and occlusal) revealed a significantly lower biofilm accumulation on PTFE-coated brackets on all surfaces. The results indicate that PTFE coating of brackets reduces biofilm adhesion to a minimum and might have the potential to reduce iatrogenic side effects, e.g. decalcification during orthodontic treatment with fixed appliances.

Analysis of supra- and subgingival long-term biofilm formation on orthodontic bands.

Insertion of fixed orthodontic appliances induces increased biofilm formation caused by a higher number of plaque-retentive sites. The purpose of the study was to perform a quantitative analysis of supra- and subgingival long-term biofilm formation on orthodontic bands. Ten patients (five females and five males, aged 18.3+/-5.4 years) who had received therapy with fixed orthodontic appliances for 24+/-9 months were enrolled in the study. Biofilm formation on 28 orthodontic bands was analyzed quantitatively with the Rutherford backscattering detection method, a scanning electron microscopy technique. The biofilm formation for the supra- and subgingival surfaces was calculated from the grey values. Statistical analysis was performed with a mixed model with the patient as the random factor. A P-value <0.05 was considered significant. A biofilm was found on 16.1+/-9.2 per cent of supragingival surfaces and on 3.6+/-4.4 per cent of subgingival surfaces. Differences in biofilm formation in supra- and subgingival surfaces were statistically significant (P<0.05) and formed a distinct demarcation line. Despite the presence of supragingival biofilm, no mature subgingival biofilm was found on the tested orthodontic bands.