Miriam Kupková

A study of cytocompatibility and degradation of iron-based biodegradable materials.

Biodegradable metallic implants are of significant importance in the replacement of bones or the repair of bone defects. Iron-phosphate-coated carbonyl iron powder (Fe/P) was prepared by the phosphating method. Moreover, Fe/P–Mn alloy was produced by sintering the Fe/P powder mixed with manganese powder. Bare carbonyl iron samples and the Fe/P and Fe/P–Mn sintered samples were evaluated for their microstructure, cytotoxicity, and hemocompatibility. The microstructure of the sintered samples was examined using an optical microscope and scanning electron microscopic analysis. Corrosion behavior was evaluated by potentiodynamic polarization in Hank’s solution. The in vitro biocompatibilities were investigated by cytotoxicity and hemolysis tests. The results obtained demonstrate that the addition of Mn resulted in higher surface inhomogeneity, porosity and roughness as well as in increased cytotoxicity. The phosphate coating has a moderately negative effect on the cytotoxicity. The corrosion rates determined from Tafel diagrams were ordered in the following sequence: Fe/P–Mn, Fe, Fe/P from high to low. The hemocompatibility of experimental samples was ordered in the following sequence: Fe/P, Fe/P–Mn, Fe from high to low. All samples were found to be hemocompatible.

Static Corrosion Test of Porous Iron Material with Polymer Coating

Abstract At present biodegradable implants received increased attention due to their use in various fields of medicine. This work is dedicated to testing of biodegradable materials which could be used as bone implants. The samples were prepared from the carbonyl iron powder by replication method and surface polymer film was produced through sol-gel process. Corrosion testing was carried out under static conditions during 12 weeks in Hank’s solution. The quantity of corrosion products increased with prolonging time of static test as it can be concluded from the results of EDX analysis. The degradation of open cell materials with polyethylene glycol coating layer was faster compared to uncoated Fe sample. Also the mass losses were higher for samples with PEG coating. The polymer coating brought about the desired increase in degradation rate of porous iron material.

Preparation and Compaction Behaviour of Poly(methyl methacrylate) Coated Iron Microparticles

The p oly(methyl methacrylate) (PMMA) coatings onto surface of iron particles were electrochemically prepared and the efiect on both surface structure and internal structure of the resulted material after compaction was carried out. The electrochemical polymerization treatment was performed in a ∞uidized bed electrolyzer using sulphuric acid solution containing potassium persulphate and methyl methacrylate (MMA). The surface topography and the microstructure of the samples were observed by scanning electron microscopy (SEM) and optical microscopy (OM). It was found that the PMMA layer coated onto iron particles results in improvement of their compressibility compared with uncoated powders, and classical lubricants are not necessary for compacting particles coated.

The Effect of Corrosion in Hank's Solution on the Bending Stiffness of Bars from Sintered Iron-Manganese Alloys

Fe-Mn alloys represent promising degradable biomaterials for temporary implants. To investigate the effect of corrosion on their mechanical properties, iron powders were mixed with 25, 30 and 35 wt.% of a manganese powder, compressed into prismatic bars and sintered. Sintered bars were immersed in Hanks solution for 8 weeks. The bending stiffness of each bar before and after its exposure to electrolyte was examined. The higher the porosity of a bar was, the higher relative reduction in bending stiffness the bar exhibited. A likely explanation was that in a more porous bar Hank’s solution penetrated deeper and affected larger volume fraction of bar’s material.

Fe and Fe-P Foam for Biodegradable Bone Replacement Material: Morphology, Corrosion Behaviour, and Mechanical Properties

Iron and iron-phosphorus open-cell foams were manufactured by a replica method based on a powder metallurgical approach to serve as a temporary biodegradable bone replacement material. Iron foams alloyed with phosphorus were prepared with the aim of enhancing the mechanical properties and manipulating the corrosion rate. Two different types of Fe-P foams containing 0.5 wt.% of P were prepared: Fe-P(I) foams from a phosphated carbonyl iron powder and Fe-P(II) foams from a mixture of carbonyl iron and commercial Fe3P. The microstructure of foams was analyzed using scanning electron microscopy. The mechanical properties and the corrosion behaviour were studied by compression tests and potentiodynamic polarization in Hank’s solution and a physiological saline solution. The results showed that the manufactured foams exhibited an open, interconnected, microstructure similar to that of a cancellous bone. The presence of phosphorus improved the mechanical properties of the foams and decreased the corrosion rate as compared to pure iron foams.

The Effect of Graded Structure of Sintered Iron-Manganese Biomaterials on the Range and Distribution of Local Hardness Values

Powders comprised of Fe particles and 25, 30, 35wt.% of Mn particles were mixed, compacted and sintered to investigate the effect of Mn on the properties of sintered Fe-Mn alloys. It was found that the sample’s swelling, microstructure and distribution of local hardness values were strongly affected by the Mn content. The particles in Fe-25Mn and Fe-30Mn samples exhibited a distinct onion-like structure causing a considerable variability in local properties, while the particles in Fe-35Mn samples were at a glance more homogeneous, with a large volume fraction occupied by a nearly uniform material with almost constant properties.

Effect of Silver Content on Microstructure and Corrosion Behavior of Material Prepared from Silver Coated Iron Powder

Iron was considered a good material candidate for temporary implants in cardiovascular and orthopedic surgery. Mechanical properties of iron are attractive, however, a higher degradation rate is required. The contribution deals with the effect of silver content on microstructure and corrosion behavior of materials prepared from Ag coated iron powders. Using electroless deposition, Fe-powders with 0.29 and 2.1 wt.% of silver were prepared. Cylindrical specimens compacted at a pressure of 200 MPa were isothermally sintered at 1120°C for 60 min. The microstructure of the sintered specimens consisted of iron matrix with Ag-precipitates. The corrosion behaviour of sintered compacts was studied using the potentiodynamic polarization technique in Hank’s solution and complemented with SEM analysis. It was found out that corrosion resistance of material decreased with an increase in silver content.

PM Materials Prepared from Powders Consisting of Polymer Coated Iron Microparticles

A simple oxidative polymerization of pyrrole (Py) directly onto the surface of iron (Fe) microparticles was applied to increase the content of carbon in resulting material. Detection and quantification of the PPy (polypyrrole) coatings obtained were performed by means of pyrolysis gas chromatography (Py-GC). A powder consisting of such particles was compacted. The effect of PPy coating on the compressibility of coated iron powder was analysed. Namely, a set of specimens was uniaxially pressed in a steel die. Compaction pressures ranged from 50 MPa up to 600 MPa. It was found that PPy coating has a positive effect on the compaction behaviour of iron powders in the low to moderate pressure region. At higher pressures, the brittleness of PPy coating adversely affected the compressibility. Both the light and the scanning electron microscopy (LM, SEM) were used to characterize the morphology of coated powders and the microstructure of pressed samples.

On the Indentation Modulus of Sintered Materials

When the depth-sensing (nano)indentation is applied to sintered samples, measured properties, which are expected to represent the material of an individual grain, seem to depend on the overall porosity of the macroscopic sample. To understand such a result, it is assumed that while the nanoindenter penetrates into the surface grain and probes the properties of its material, the grain itself serves as another, larger indenter indenting the rest of sample and probing the properties that represent the bulk of material rather than individual grains. Load vs. displacement curve reflects the synergetic response of these two “indenters” and so it contains information about the sample’s mechanical properties at both microscopic and macroscopic scales. Obtained theoretical results agree qualitatively with the experimental data (the dependence of the indentation modulus on the porosity of sample; the indentation size effect).

The Influence of Cu-Coating versus Admixing on Mechanical Properties and Dimensional Change of Sintered Fe-Cu Parts

The differences in mechanical properties of pressed and sintered specimens made from mixtures of iron and copper powders or from copper-coated iron powders, produced by a cementation process, were studied. For this purpose different copper contents were used (3, 8 or 12wt%) and the oxygen content of the coated powders was measured. After sintering at 1120°C for 60 minutes in hydrogen flow, microgradient structures were observed. The samples were investigated by light optical microscopy and tested under bending and tensile loads. Young´s Moduli were calculated from resonance frequencies. The copper-coating of the iron powder results in an improvement of all properties, owing to a more homogeneous copper distribution and the absence of large secondary pores, compared to specimens made from mixtures of iron and copper powders. In the case of Fe-12Cu (coated), all determined properties tend to result in a maximum: highest sintered density (7,33 g/cm³), tensile strength (489 MPa), transverse rupture strength (1098 MPa) and apparent hardness (162 HV10). The Young´s Modulus (150 GPa) of coated Fe-12Cu is nearly the same as that of sintered iron (154 GPa).