Papers by Keyword: Resorbable

Abstract: Sometimes, in surgical procedure following an accident or illness it is necessary to use metal prostheses or implants to ensure the functionality of bones and joint systems. From time to time, at the end of the patient's healing process, it is necessary to remove the medical device used. In these cases, it would be useful to use resorbable devices to avoid further surgery. A possible solution to the problem could be to use metal alloy devices that degrade over time, while ensuring the functionality of the system. Unfortunately, the chemical compounds generated by the corrosion processes of metal alloys used in the medical field are almost always harmful to human health. The products generated by the degradation processes of some magnesium alloys, on the other hand, are not considered toxic or harmful to human health, so that a device showing controllable degradation rate can be used, guaranteeing the functionality of the implanted device. To achieve this goal, a possible solution could include the use of one or more coatings, capable of controlling the metal degradation process. To do this, we used a first coating obtained by subjecting the samples to a direct current (DC) plasma electrolytic oxidation (PEO) treatment, carried out in an alkaline solution based on silicates and sodium. Subsequently, the samples were coated with a polydopamine (PDOPA) film by dip-coating, and, at the end, a l-polylactic acid (PLLA) coating was applied on the sample by hot-pressing. The coupons were subjected to morphological characterization by Scanning Electron Spectroscopy (SEM) and to electrochemical characterization in Hank's solution at 37°C by means of electrochemical impedance spectroscopy (EIS). The experimental results obtained demonstrate that the coupling of the PEO oxide with the polydopamine and the polymeric film show properties such as to allow the creation of devices which permit the control of the metal degradation process.

Abstract: Variation of calcium excess, water content and mixing time have been taken into the parameters of the injection test of calcium phosphate paste synthesized via low temperature hydrothermal method. The result indicated that all the parameters are very prominent to influence the material injectability possible to be fully injected out the syringe. Strict control of paste synthesizing parameters has successfully overcome poor injectability of the material.

Abstract: Resorbable metallic implant of magnesium and its alloys had been studied since the 1900s. However, the excessive gas production resulted in its unpopularity after CoCr alloys and stainless steel were developed. With the advancement of alloying technologies, its use as a resorbable implant has re-emerged recently. Foreign researchers focused on the use of AZ-series and magnesium-rare earth metal alloys. However, the corrosion property of AZ-series alloys is unsatisfactory, and the effect of rare-earth metals on human is poorly studied. Therefore, we have investigated on the feasibility of using commercially available AM-series magnesium alloys. Previous researchers avoided this alloy series presumably because of the potential health effect of manganese, however our toxicological risk assessment revealed that the exposure level would be lower than the NOAEL (No Observable Adverse Effect Level), thus it is unlikely to cause any observable health effect on healthy individuals. Subcutaneous implantation of AM-series magnesium alloys into a mouse model for six months confirmed that, while all alloys tested showed slow corrosion and no observable in vivo toxicity, pitting corrosion did not occur for AM-series alloys but was frequent for AZ91D. This suggests that AM-series magnesium alloys are good candidates of resorbable metallic implants.

Abstract: In this study the setting times, compressive strengths and microstructures of cements formed using pyrophosphoric acid solution and b-tricalcium phosphate (β-TCP; Ca3(PO4)2) were compared with those of cement formed using orthophosphoric acid solution and b-TCP. It was found that cement formed using pyrophosphoric acid solution set more slowly than that formed using orthophosphoric acid and could be mixed to a higher powder to liquid ratio, facilitating the production of cement exhibiting compressive strengths, without pre-compaction, as high as 25 MPa. The use of pyrophosphoric acid as opposed to orthophosphoric acid resulted in a marked change in the microstructure of the cement.

Abstract: Tricalcium phosphate modified by silicon and zinc was synthesized as a candidate for resorbable temporal bone implant having a controlled solubility and improved biocompatibility. Since Si and Zn are essential trace elements with stimulatory effects on bone formation, Si,Znmodified tricalcium phosphate can also promote bone formation. From XRD and ICP analyses, it was shown that up to 10 mol% Si and Zn can be incorporated in the tricalcium phosphate lattice without formation of a second phase. Changes in lattice parameters and unit volume of TCP as calculated by Rietveld refinement analysis indicate that Si and Zn substitute for P and Ca respectively.

Abstract: To guarantee of the security of ceramic medical products the identification and quantification of the current degradation products is required by the ISO 10993-14 standard. Two methods - the gravimetrical registration of the mass loss and the quantitative determination of the leached ions by spectrometric methods - are planned. When checking the application of the ISO standard to calcium phosphate ceramics that can be used as implant materials a considerable difference in the results obtained with both methods was observed. It seems to be that precipitation reactions are responsible for that situation. To clear up the influence of precipitation reactions on the results the working procedure of the ISO standard was slightly modified. A first interpretation of the results is tried.