Lars E. Ericson

Bone response to surface-modified titanium implants: studies on the early tissue response to machined and electropolished implants with different oxide thicknesses

The bone formation around titanium implants with varied surface properties is investigated. Machined and electropolished samples with and without thick, anodically formed surface oxides were prepared, surface characterized and inserted in the cortical bone of rabbits (1, 3 and 6 weeks). Scanning electron microscopy, scanning Auger electron spectroscopy and atomic force microscopy revealed marked differences in oxide thickness, surface topography and roughness, but no significant differences in surface chemical composition, between the different groups of implants. Light microscopic morphology and morphometry showed that all implants were in contact with bone and had a large proportion of bone within the threads at 6 weeks. The smooth, electropolished implants, irrespective of anodic oxidation, were surrounded by less bone than the machined implants after 1 week. After 6 weeks the bone volume as well as the bone-implant contact were lower for the merely electropolished implants than for the other three groups. Our study shows that a high degree of bone contact and bone formation are achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, the result with the smooth (electropolished) implants indicates that a reduction of surface roughness, in the initial phase, decreases the rate of bone formation in rabbit cortical bone.

Bone response to surface modified titanium implants: studies on electropolished implants with different oxide thicknesses and morphology

In a series of experimental studies, bone formation was analysed around systematically modified titanium implants. In the present study, machined, electropolished and anodically oxidized implants were prepared, surface characterized and inserted in the cortical bone of rabbits (7 wks and 12 wks). SEM, scanning Auger electron spectroscopy and atomic force microscopy revealed no differences in surface composition but marked differences in oxide thickness, surface topography and roughness. Light microscopic morphology and morphometry showed that all implants were in contact with bone, and had a large proportion of bone within the threads. The smooth, electropolished implants were surrounded by less bone than the machined implants with similar oxide thickness, (4-5 nm) and the anodically oxidized implants with thicker oxides (21 nm and 180 nm, respectively) after 7 wks. These studies show that a high degree of bone contact and bone formation can be achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, it appears that a reduction of surface roughness may influence the rate of bone formation in rabbit cortical bone.

Transforming growth factor-beta and epidermal growth factor synergistically stimulate epithelial to mesenchymal transition (EMT) through a MEK-dependent mechanism in primary cultured pig thyrocytes

Enhancement of tumor cell growth and invasiveness by transforming growth factor-β (TGF-β) requires constitutive activation of the ras/MAPK pathway. Here we have investigated how MEK activation by epidermal growth factor (EGF) influences the response of fully differentiated and growth-arrested pig thyroid epithelial cells in primary culture to TGF-β1. The epithelial tightness was maintained after single stimulation with EGF or TGF-β1 (both 10 ng/ml) for 48 hours. In contrast, co-stimulation abolished the transepithelial resistance and increased the paracellular flux of [3H]inulin within 24 hours. Reduced levels of the tight junction proteins claudin-1 and occludin accompanied the loss of barrier function. N-cadherin, expressed only in few cells of untreated or single-stimulated cultures, was at the same time increased 30-fold and co-localised with E-cadherin at adherens junctions in all cells. After 48 hours of co-stimulation, both E- and N-cadherin were downregulated and the cells attained a fibroblast-like morphology and formed multilayers. TGF-β1 only partially inhibited EGF-induced Erk phosphorylation. The MEK inhibitor U0126 prevented residual Erk phosphorylation and abrogated the synergistic responses to TGF-β1 and EGF. The observations indicate that concomitant growth factor-induced MEK activation is necessary for TGF-β1 to convert normal thyroid epithelial cells to a mesenchymal phenotype.

Structure of the interface between rabbit cortical bone and implants of gold, zirconium and titanium

The role of surface properties (chemical and structural) for the interaction between biomaterials and tissue is not yet understood. In the present study, implants made of titanium, zirconium (transition metals with surface oxides) and gold (metallic surface) were inserted into the rabbit tibia. Light microscopic (LM) morphometry showed that after 1 and 6 mo the gold implants had less amount of bone within the threads and a lower degree of bone-implant contact than the titanium and zirconium implants, which did not differ from each other. These quantitative differences were supported by LM and ultrastructural observations of the interface. The ultrastructural observations in addition demonstrated that the layer of non-collagenous amorphous material located between the implant and the calcified bone was appreciably thicker around zirconium than around titanium implants. The factors potentially responsible for the observed morphological differences in the bone around the different material surfaces are discussed.

Early tissue response to titanium implants inserted in rabbit cortical bone

The tissue response to screw-shaped implants of commercially pure titanium was studied 3–180 days after insertion in the rabbit tibia by means of transmission electron microscopy. Red blood cells and scattered macrophages predominated at the implant surface after 3 days. At day 7 and later intervals, multinuclear giant cells were the cell type found at the implant surface protruding into the bone marrow and in areas with no bone-titanium contact. Osteoblasts or mesenchymal cells were rarely seen at the implant surface at any time period. Two modes of mineralization could be distinguished in the interface. Firstly, the typical mineralization of osteoid seams produced by osteoblasts. Secondly, an accumulation of scattered hydroxyapatite crystals in the unmineralized collagen matrix in the interface. Mineralized tissue was observed close to the implants surface from day 14. However, the innermost 2–20 μm were poorly mineralized although scattered hydroxyapatite crystals were present. The collagen fibrils did not reach the implant surface but were separated from it by an amorphous layer, being 0.3–0.5 μm thick which did not decrease in width with time. An electron-dense lamina limitans-like line containing mineral was observed between the amorphous layer and the bone tissue.

Integration of press-fit implants in cortical bone : A study on interface kinetics

The early healing phase of hard tissue implants is important to their long-term success. Problems during this phase can result in a so-called primary biological failure. In 24 New Zealand white rabbits, the healing in cortical bone of noncoated TiAlV and cpTi cylinders and of TiAlV cylinders plasma-spray-coated with hydroxyapatite (HA) of fluorapatite (FA) was investigated histologically and histomorphometrically after 3, 7, 14, and 28 days. Histomorphometry consisted of bone contact measurements and the use of a new semi quantitative scoring system that discriminated various tissues in contact with the implant. The results demonstrated that the most important parameter in initial implant healing is the bone itself and not the characteristics of the implanted material. For all implants, healing was characterized by a sequence of hematoma formation, bone resorption, and new bone formation where the initial press-fit situation revealed more bone-implant contact than after 7 and 14 days. There were only minor differences between the implant types: the new bone formation directly on the implant surface was qualitatively histologically superior to the CaP-coated implants, but this could be confirmed with the scoring method only for the HA-coated implants. It is concluded that initial press-fit fixation in cortical bones is not an end situation; rather, what happens is that as a result of interface remodeling, early postoperatively implant integration in the bone will decrease temporarily prior to a subsequent phase of new bone formation.

Ultrastructure of the bone-titanium interface in rabbits

The interface zone between cortical bone and threaded non-alloyed titanium implants inserted in the rabbit tibia for 12 months was examined by light and electron microscopy. The implants were removeden bloc with the perfusion-fixed surrounding bone and the undecalcified specimens were, after osmification, dehydrated and embedded in plastic resin (LR White). In ground sections (about 10 µm thick) cortical bone appeared to be in direct contact with the implant surface and the implants were thus “osseointegrated”. Sections for light microscopy (1 µm thick) and electron microscopy (40 nm to 0.5 µm) were prepared by using an electropolishing technique by which the bulk part of the metal was electrochemically removed and a fracture technique by which the implant was separated from the embedded tissue before sectioning. In the electropolished specimens an unmineralized zone, 2–10 µm wide, was observed at the interface. The interface zone contained osteoid-like tissue (densely packed collagen fibrils, osteocyte canaliculi) but in general no deposits of calcium mineral. This feature of the interface could not be observed in specimens prepared by the fracture technique, indicating that the electropolishing technique had induced serious artefacts, including decalcification of the interface bone. In sections prepared by the fracture technique, mineralized bone was present very close to the implant surface. No gradient of mineral was observed. A thin layer of amorphous material (100–200 nm wide) was present peripheral to the mineralized bone. An electron dense line about 100 nm wide was formed at the border between the mineralized bone and the amorphous layer. The dense layer had the same characteristics as the lamina limitans observed around osteocyte lacunae and canaliculi or the zone between areas of bone with different degree of mineralization.Our observations suggest that mineralized bone reached close to the surface of titanium implants inserted in the rabbit tibia for 12 months but that a direct contact is not established.

Bone response to surface modified titanium implants – studies on the tissue response after 1 year to machined and electropolished implants with different oxide thicknesses

The bone formation around titanium implants with varied surface properties was investigated after 1 year in rabbits. Machined and electropolished samples with and without thick, anodically formed surface oxides were prepared, surface characterized and inserted in the cortical bone of rabbits. Scanning electron microscopy, scanning Auger electron spectroscopy and atomic force microscopy revealed marked differences in oxide thickness, surface topography and roughness, but no significant differences in surface chemical composition between the different groups of implants. Light microscopic morphology and morphometry showed that all implants were in contact with bone and had a large proportion of bone within the threads. There were no significant differences between the differently prepared implant groups. Our study shows that a high degree of bone contact and bone formation is achieved after 1 year with titanium implants which are modified with respect to oxide thickness and surface topography. There is no indication that a reduction of surface roughness, which in the initial phase decreases the rate of bone formation, had any influence on the amount of bone after 1 year in rabbit cortical bone.

Degranulation of the parafollicular cells of the rat thyroid by vitamin-D2-induced hypercalcemia.

Hypercalcemia was induced by injecting rats with high daily doses of vitamin D 2 for five days. Thyroid glands from untreated rats were used as controls. The thyroid parafollicular cells of the vitamin-treated rats differed characteristically from those of the controls, the most conspicuous feature of the former being the almost complete degranulation.

Method for ultrastructural studies of the intact tissue-metal interface

Samples were prepared for ultrastructural studies of the intact interface between metallic implants and tissue by transmission electron microscopy. The method is based on plastic embedding of implant and tissue and subsequent removal of the bulk metal by electrochemical dissolution (electropolishing), to facilitate preparation of ultrathin sections for transmission electron microscopy. Surface sensitive spectroscopy (Auger electron microscopy and X-ray photoemission spectroscopy) and transmission electron microscopy EDX results show that the method produces samples with an intact interface, containing the implant surface oxide and the adjacent tissue. Examples of application of the method on titanium, zirconium and aluminium implants in soft tissue are given.