ABSTRACT
Porous magnesium implants are of particular interest for application as resorbable bone substitutes, due to their mechanical strength and a Young's modulus similar to bone. The objective of the present study was to compare the biocompatibility, bone and tissue ingrowth, and the degradation behaviour of scaffolds made from the magnesium alloys LAE442 (n= 40) and Mg-La2 (n= 40)in vivo. For this purpose, cylindrical magnesium scaffolds (diameter 4 mm, length 5 mm) with defined, interconnecting pores were produced by investment casting and coated with MgF2. The scaffolds were inserted into the cancellous part of the greater trochanter ossis femoris of rabbits. After implantation periods of 6, 12, 24 and 36 weeks, the bone-scaffold compounds were evaluated usingex vivo µCT80 images, histological examinations and energy dispersive x-ray spectroscopy analysis. The La2 scaffolds showed inhomogeneous and rapid degradation, with inferior osseointegration as compared to LAE442. For the early observation times, no bone and tissue could be observed in the pores of La2. Furthermore, the excessive amount of foreign body cells and fibrous capsule formation indicates insufficient biocompatibility of the La2 scaffolds. In contrast, the LAE442 scaffolds showed slow degradation and better osseointegration. Good vascularization, a moderate cellular response, bone and osteoid-like bone matrix at all implantation periods were observed in the pores of LAE442. In summary, porous LAE442 showed promise as a degradable scaffold for bone defect repair, based on its degradation behaviour and biocompatibility. However, further studies are needed to show it would have the necessary mechanical properties required over time for weight-bearing bone defects.
Subject(s)
Alloys/chemistry , Biocompatible Materials , Lanthanum/chemistry , Magnesium/chemistry , Tissue Scaffolds/chemistry , Animals , Bone Resorption , Bone Substitutes/chemistry , Bone and Bones/metabolism , Female , Materials Testing , Microscopy, Electron, Scanning , Osseointegration , Porosity , Rabbits , Stress, Mechanical , X-Ray MicrotomographyABSTRACT
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.
Subject(s)
Absorbable Implants , Alloys/chemical synthesis , Guided Tissue Regeneration/instrumentation , Heart Ventricles/anatomy & histology , Heart-Assist Devices , Magnesium Compounds/chemical synthesis , Tissue Scaffolds , Adult , Computer Simulation , Computer-Aided Design , Equipment Failure Analysis , Female , Humans , Male , Models, Anatomic , Models, Cardiovascular , Prosthesis Design , Prosthesis Fitting/methodsABSTRACT
We have developed an experimental model to show that an additional mechanism apart from absorption by pigment epithelium is responsible for the absorption of subretinal fluid. The cause of a fast diminution of subretinal fluid after a buckling procedure is the prominence of the buckle as an obstacle to fluid movements in the eye. This results in any fluid being pushed through the retinal hole into the vitreous. When the retinal hole is closed by the buckle, the remaining part of the subretinal fluid is slowly absorbed by the pigment epithelium present. We performed a preliminary qualitative and quantitative analysis of the phenomena occurring using the finite element method of Zienkiewicz.
