Eszter Bognár

Freeze-dried human serum albumin improves the adherence and proliferation of mesenchymal stem cells on mineralized human bone allografts

Mineralized scaffolds are widely used as bone grafts with the assumption that bone marrow derived cells colonize and remodel them. This process is slow and often unreliable so we aimed to improve the biocompatibility of bone grafts by pre‐seeding them with human mesenchymal stem cells from either bone marrow or dental pulp. Under standard cell culture conditions very low number of seeded cells remained on the surface of freeze‐dried human or bovine bone graft or hydroxyapatite. Coating the scaffolds with fibronectin or collagen improved seeding efficiency but the cells failed to grow on the surface until the 18th day. In contrast, human albumin was a very potent facilitator of both seeding and proliferation on allografts which was further improved by culturing in a rotating bioreactor. Electron microscopy revealed that cells do not form a monolayer but span the pores, emphasizing the importance of pore size and microstructure. Albumin coated bone chips were able to unite a rat femoral segmental defect, while uncoated ones did not. Micro‐hardness measurements confirmed that albumin coating does not influence the physical characteristics of the scaffold, so it is possible to introduce albumin coating into the manufacturing process of lyophilized bone allografts.

Investigation of Drug Eluting Stents

The clinical results of drug eluting stents [DESs] depend on the type of the coating, the coating technology and the dosage and efficiency of the drug. The current study shows our examinations on drug eluting stents. Different types of commercially available coronary stents were investigated. Various methods were used for these experiments, for example optical microscopy, confocal fluorescent microscopy, scanning electron microscopy and EDS analysis. The properties characterizing applicability of drug eluting stents and the changing of the coatings during expansion are shown.

Investigation of the mechanical and chemical characteristics of nanotubular and nano-pitted anodic films on grade 2 titanium dental implant materials

OBJECTIVE The objective of this study was to investigate the reproducibility, mechanical integrity, surface characteristics and corrosion behavior of nanotubular (NT) titanium oxide arrays in comparison with a novel nano-pitted (NP) anodic film. METHODS Surface treatment processes were developed to grow homogenous NT and NP anodic films on the surface of grade 2 titanium discs and dental implants. The effect of process parameters on the surface characteristics and reproducibility of the anodic films was investigated and optimized. The mechanical integrity of the NT and NP anodic films were investigated by scanning electron microscopy, surface roughness measurement, scratch resistance and screwing tests, while the chemical and physicochemical properties were investigated in corrosion tests, contact angle measurement and X-ray photoelectron spectroscopy (XPS). RESULTS AND DISCUSSION The growth of NT anodic films was highly affected by process parameters, especially by temperature, and they were apt to corrosion and exfoliation. In contrast, the anodic growth of NP film showed high reproducibility even on the surface of 3-dimensional screw dental implants and they did not show signs of corrosion and exfoliation. The underlying reason of the difference in the tendency for exfoliation of the NT and NP anodic films is unclear; however the XPS analysis revealed fluorine dopants in a magnitude larger concentration on NT anodic film than on NP surface, which was identified as a possible causative. Concerning other surface characteristics that are supposed to affect the biological behavior of titanium implants, surface roughness values were found to be similar, whereas considerable differences were revealed in the wettability of the NT and NP anodic films. CONCLUSION Our findings suggest that the applicability of NT anodic films on the surface of titanium bone implants may be limited because of mechanical considerations. In contrast, it is worth to consider the applicability of nano-pitted anodic films over nanotubular arrays for the enhancement of the biological properties of titanium implants.

Stent Fracture Analysis

Almost half of the deaths in the European Union are a consequence of cardiovascular diseases, which can be reduced significantly by dietary changes, physical activity and suitable medications. Since changing lifestyle and healthcare is a slow process, a more efficient and quicker solution is to improve medical devices. Stents are mesh-structured implants, which support arterial wall and allow dilatation of the narrowed section. The material analyses of stents removed from cadavers allow further development and improvement of these special devices. Despite of the widespread application of stents, not many publications deal with their technical analysis and most of them have a medical approach. This paper presents a technical analysis of three stents removed from cadavers. The results may promote the evaluation of the stent development. Until now these kind of feedback was missing from the improvement cycle.

Review: the potential impact of surface crystalline states of titanium for biomedical applications

Abstract In many biomedical applications, titanium forms an interface with tissues, which is crucial to ensure its long-term stability and safety. In order to exert control over this process, titanium implants have been treated with various methods that induce physicochemical changes at nano and microscales. In the past 20 years, most of the studies have been conducted to see the effect of topographical and physicochemical changes of titanium surface after surface treatments on cells behavior and bacteria adhesion. In this review, we will first briefly present some of these surface treatments either chemical or physical and we explain the biological responses to titanium with a specific focus on adverse immune reactions. More recently, a new trend has emerged in titanium surface science with a focus on the crystalline phase of titanium dioxide and the associated biological responses. In these recent studies, rutile and anatase are the major two polymorphs used for biomedical applications. In the second part of this review, we consider this emerging topic of the control of the crystalline phase of titanium and discuss its potential biological impacts. More in-depth analysis of treatment-related surface crystalline changes can significantly improve the control over titanium/host tissue interface and can result in considerable decreases in implant-related complications, which is currently a big burden on the healthcare system.

Kinking Resistance of Guidewires

The guidewire is a small diameter, steerable wire which facilitates the navigation of the interventional devices such as stent, balloon, or coil in endovascular intervention. The guidewire has an elongated flexible body and a relatively more flexible ribbon tip. The elongated body (shaft) is tapered to the ribbon tip. The composition of the helical coil formed ribbon tip is different than the elongated body. In this article we demonstrate the correlation between the material composition and the kinking resistance of guidewire. The identified metal composition of the core wire was 18-8 stainless steel and the helical coil composed of platinum-nickel alloy and the material of tip bond was tin. The kink angle which caused permanent deformation were significantly higher on the helical coil (=68,3o) due to the higher flexibility of the helical coil than that was found on the shaft portion (=55o) (p=0,00032). The remnant angel induced by 90o kinking on the helical coil was significantly lower (=15o) than that was observed on the shaft portion (=23,9o) (p=0,00046). The deformation of the helical coil was smaller due to the higher flexible properties of the platinum-nickel alloy material against the stainless steel.

Polyurethane Coating on Coronary Stents

Stents are special metallic or polymer endoprostheses of meshed structure and tube shape. Their function is to prevent restenosis in the arteries. Stents can be coated or uncoated. In the expanded part of the artery the chance of restenosis is bigger even without a stent so it is practical to coat the stents. The aim of this work is to present the results of the coating experiments made on the coronary stents. Three types of commercially available polyurethanes were used for these experiments. The coatings were produced by a dipping method. Electro-polished and non-electro-polished metallic sheets and stents were used for these experiments. Contact angle measurements were done to examine the wetting properties of the three different polyurethane coatings. The quality and the changing of the coatings were examined by different methods (stereomicroscope, scanning electron microscope and energy dispersive spectrometry).

Mechanical Behaviours of Coronary Stents

The role of the stents is to prevent restenosis. The rapid growth of stents’ application in the treatment of cardiovascular diseases resulted in the unique development of these implants. This is mainly due to the effective clinical trials, the success of which determined the use of these endoprostheses. In this study the surface properties of the coronary stents were described by using different methods (stereomicroscopy, scanning electron microscopy and energy dispersive analysis) before and after balloon expansion. Furthermore, the most frequent failures caused by the expansion were introduced. For investigating fatigue properties two high cycle fatigue test equipments were used: the first one simulates the bending stress, and the second one simulates the effect of the pulsating mechanical strain. Surface features of the stents were examined after the fatigue tests as well: macroscopic damages were not originated on the stents, and the implants were not broken down. Only small traces of fatigue occurred on the surface, which became rough; and slip lines and grain boundaries were outlined.

Determination of the Guidewire’s Visibility

The purpose of our research was the development of a new algorithm to the objective quantification of guidewire’s visibility; which is suitable for the classification and comparison of different guidewires, according to this property. The guidewire is a flexible medical device, over which the catheter or the dilator is lead into the vascular system to assist the insertion and position of these devices. During the insertion and the removal of guidewire the movement of distal end is monitored under fluoroscopy. At the beginning of our experiments two algorithms were developed and applied: the first one investigated the total distal end, while the second one investigated two parts of the distal end. Both algorithms were tested on ten guidewires made of same brand and material, so their relative visibility (the visibility of guidewire’s investigated part compared the background) were determined by both method. The average relative visibility was 19.8%±3.0% in case of algorithm for total distal end, and it was 21.5%±2.9% in case of algorithm for two part of distal end. The coefficient of variation was calculated in case of both algorithms, thus characterized by their reliability. Both coefficient of variation were low (0.15 and 0.13), so the algorithms were considered to be reliable. The two algorithm were no significant different (p=0.15), therefore the investigation of the total distal end might be replaced by the investigation of two parts.

Methods for examination an explanted coronary sinus lead stabilized with a coronary stent.

The aim of our investigation was to test the suitability of a novel method for the analysis of the integrity of an explanted pacemaker lead stabilized by a stent. A coronary sinus lead has been explanted 27 months after implantation and has been examined by optical‐, confocal‐, x‐ray‐, and scanning electron microscopy. Several surface injuries were found on the insulation. Based on the surface characteristics, it is possible to define and differentiate the source of damages as well as to measure the extent of injuries. Impedance of the explanted lead has also been measured and electronic integrity has been verified. (PACE 2013; 36:e27–e30)