Tobias Jarmar

Morphological and phase stability of nickel–germanosilicide on Si1−xGex under thermal stress

Continuous and uniform Ni(Si,Ge) layers are formed on polycrystalline Si and Si0.42Ge0.58 substrate films at 500 degreesC by rapid thermal processing. The germanosilicide is identified as NiSi0.42G ...

Characterization of the surface properties of commercially available dental implants using scanning electron microscopy, focused ion beam, and high-resolution transmission electron microscopy

BACKGROUND Since osseointegration of the respective implant is claimed by all manufacturing companies, it is obvious that not just one specific surface profile including the chemistry controls bone apposition. PURPOSE The purpose was to identify and separate out a particular set of surface features of the implant surfaces that can contribute as factors in the osseointegration process. MATERIAL AND METHODS The surface properties of several commercially available dental implants were extensively studied using profilometry, scanning electron microscopy, and transmission electron microscopy. Ultrathin sections prepared with focused ion beam microscopy (FIB) provided microstructural and chemical data which have not previously been communicated. The implants were the Nobel Biocare TiUnite (Nobel Biocare AB, Göteborg, Sweden), Nobel Biocare Steri-Oss HA-coated (Nobel Biocare AB, Yorba Linda, CA, USA), Astra-Tech OsseoSpeed (Astra Tech AB, Mölndal, Sweden), Straumann SLA (Straumann AG, Waldenburg, Switzerland), and the Brånemark Integration Original Fixture implant (Brånemark Integration, Göteborg, Sweden). RESULTS It was found that their surface properties had differences. The surfaces were covered with crystalline TiO(2) (both anatase and rutile), amorphous titanium oxide, phosphorus doped amorphous titanium oxide, fluorine, titanium hydride, and hydroxyapatite, respectively. CONCLUSION This indicates that the provision of osseointegration is not exclusively linked to a particular set of surface features if the implant surface character is a major factor in that process. The studied methodology provides an effective tool to also analyze the interface between implant and surrounding bone. This would be a natural next step in understanding the ultrastructure of the interface between bone and implants.

Technique for preparation and characterization in cross-section of oral titanium implant surfaces using focused ion beam and transmission electron microscopy

The surface properties of materials are believed to control most of the biological reactions toward implanted materials. To study the surface structure, elemental distribution, and morphology, using transmission electron microscopy (TEM) techniques, thin foils of the surface (in cross-section) are needed. These have been cumbersome to produce, in particular, from the normally irregular screw-shaped metal implants. Focused ion beam (FIB) microscopy has been developed partly for TEM sample preparation, mainly within the microelectronics industry. Our study describes a method based on FIB for producing electron transparent foils/sections from a metal implant for TEM analysis. Using a screw-shaped titanium dental implant, it was demonstrated that thin foils can be prepared with submicron specificity and from almost any surface geometry. A comparison of different lift-out techniques showed that the in situ lift-out preparation technique allowed plasma cleaning and produced particularly good samples with excellent yield. The titanium oxide on the implant surface was analyzed using energy-filtered TEM (EFTEM) and high-resolution TEM (HRTEM) and the TiO(2) rutile phase being determined via the lattice parameters. This study provides the first set of data for the optimization of a new route for preparation and analysis of biomaterial surfaces and interfaces.

Forearm bone-anchored amputation prosthesis: A case study on the osseointegration

Background and purpose Bone-anchored titanium implants have been used for anchorage of amputation prostheses for more than one and a half decades. Histo-logical and ultrastructural analyses were performed on a forearm amputation prosthesis after being in use for more than 11 years. Material, methods and results The implant was retrieved from the ulnar bone after a fatigue fracture of the titanium implant, and was clinically stable at the time of removal. The histological findings showed a large amount of bone within the threads and a high degree of apposition of mineralized bone to the implant surface. Ultrastructural analysis of thin samples prepared by focused ion-beam microscopy revealed an electron-dense layer at the interface and direct apposition of crystalline hydroxyapatite at the implant surface. Interpretation Our observations in this retrieval study provide a structural correlate to the functional properties and clinical results of amputation prostheses.

Morphological instability of NiSi1-uGeu on single-crystal and polycrystalline Si1-xGex

The morphological stability of NiSi1−uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1−xGeu is studied (u can be different from x). The agglomeration of NiSi1−uGeu films on Si0.7Ge0.3 occurs at 550°C after rapid thermal processing for 30 s, independently of the crystallinity of the Si1−xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1−xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1−uGeu on sc-Si1−xGex are found to be the stored strain energy in the Si1−xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1−uGeu on poly-Si1−xGex and is not affected by the degree of crystallinity of Si1−x...

Integration Mechanisms towards Hard Tissue of Ca-Aluminate Based Biomaterials

Six mechanisms have been identified, which control how Ca-aluminate materials are integrated onto tissue; 1) Main reaction, the hydration step of CA, 2) Apatite formation in presence of phosphate ions in the biomaterial, 3) Apatite formation in the contact zone in presence of body liquid, 4) Transformation of hydrated Ca-aluminate into apatite and gibbsite, 5) Biological induced integration and ingrowth, i.e. bone formation at the contact zone, and 6) Mass increase reaction, especially important when un-hydrated CA is used as coatings or as augmentation pastes. These six mechanisms affect the integration differently depending on a) what type of tissue the biomaterial is in contact with, b) in what state (un-hydrated or hydrated) the CA is introduced, and c) what type of application is aimed at (cementation, dental fillings, endodontic fillings, sealants, coatings and augmentation products). Both a pure nanostructural mechanically controlled integration, and a chemically induced integration seem plausible.

Potential-Induced Degradation of CuIn1-xGaxSe2 Thin Film Solar Cells

The use of Na-free or low Na content glass substrates is observed to enhance the resiliency to potential-induced degradation, as compared with glass substrates with high Na content, such as soda lime glass (SLG). The results from stress tests in this study suggest that degradation caused by a combination of heat and bias across the SLG substrate is linked to increased Na concentration in the CdS and Cu(In,Ga)Se2 (CIGS) layers in CIGS-based solar cells. The degradation during the bias stress is dramatic. The efficiency drops to close to 0% after 50 h of stressing. On the other hand, cells on Na-free and low Na content substrates exhibited virtually no efficiency degradation. The degraded cells showed partial recovery by resting at room temperature without bias; thus, the degradation is nonpermanent and may be due to Na migration and accumulation rather than chemical reaction.

In Vitro Bioactivity of Atomic Layer Deposited Titanium Dioxide on Titanium and Silicon Substrates

A non-bioactive implant device can easily be changed to in vitro bioactive with a thin coating of crystalline TiO2. This crystalline coating can be deposited very thin with great step coverage at a low temperature with Atomic Layer Deposition (ALD). An anatase TiO2 coating was built up atomic layer by atomic layer using TiI4 and H2O as precursors in a hot wall furnace. Several hundreds of cycles resulted in a 10-30nm well defined TiO2 of anatase phase on both Si and Ti substrates. These coatings were shown to be bioactive when immersed in simulated body fluid in vitro, as hydroxyapatite (HA) formed on the surface. The surface roughness of the substrates affected the adhesion of the HA. The adhesion was low on the smooth Si but much better on the 100 times rougher Ti. The ALD technique is promising for coating substrates of all shapes with bioactive crystalline TiO2 at a low temperature.

Structural change of biomimetic hydroxyapatite coatings due to heat treatment

Biomimetic deposition of hydroxyapatite (HA) coatings on implants could be done for two reasons, one is to study their possible bioactivity, and one is to generate bioactive coatings on implants before implantation surgery to improve the osseointegration. Heat treatment of coated implants can be performed for several reasons, for example, to ensure coating sterility and to increase the adhesion. This paper describes the morphology and crystalline structure changes occurring due to the heat treatment of biomimetic HA coatings on rutile TiO2. Rutile TiO2 surfaces were produced on titanium (Ti) plates by heating at 800 degrees C. Afterwards, these samples were immersed in a phosphate buffer saline solution for 7 days at 37 degrees C in order to deposit HA coatings on their surfaces. These HA coatings were then either untreated or heat treated at 600 or 800 degrees C for 1 hr. The coatings microstructural changes were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cross-sectional TEM samples were produced using a sample preparation method based on focused ion beam microscopy (FIB). Rutile was found to be bioactive due to HA formation on the surface. The 600 degrees C heat treatment of the HA coating changed its morphology, increased its grain size and also increased the porosity. At 800 degrees C the coating was completely transformed to beta-TCP according to XRD. Sample preparation using FIB and TEM analysis proved to be a useful method for high-resolution analysis of biomimetic coatings in cross-section.

Injectable bone cements for Vertebroplasty studied in sheep vertebrae with electron microscopy

Vertebral compression fractures were simulated by making a hole into sheep vertebrae and by injecting a stabilizing material. The injectable bio-ceramic Xeraspine™ was evaluated together with a commercially available PMMA (Vertebroplastic™) as the reference material. The Vertebrae were harvested after 7 days and prepared for microscopy. The samples were deposited with gold on the surface and thereafter subjected to SEM and EDX analysis. It was found that the Xeraspine-bone interface was composed of a mixture of elements. The Vertebroplastic implant was embedded in a carbon containing tissue, likely a soft tissue capsule. The Xeraspine sample was subjected to high resolution analysis in the TEM combined with EDX measurements. The TEM sample was prepared with a novel technique for preparation of the tissue-material interface (FIB). In the TEM analysis it was found that the interface region consists of ZrO2 together with a mixture possibly consisting of katoite and apatite formed during setting and/or originating from the boneapatite.