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Eingeladener Vortrag
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Plasma Spreyed Coatings of Calcium Titanium Phosphate - A New Generation of Bioactive Coatings
(1995)
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
Schwammartige glaskeramische Biowerkstoffe werden zunehmend als Knochenersatzmaterial verwendet und sind bereits im Tierversuch erprobt. Für den optimalen Einsatz dieser gut resorbierbaren Biowerkstoffe ist eine zuverlässige Charakterisierung erforderlich. Im Vordergrund stehen dabei der Herstellungsprozess, über den die offene Porosität kontrolliert eingestellt wird, sowie der Sintervorgang, der die Struktur des keramischen Gerüstmaterials entscheidend prägt. Hier werden mittels Röntgenrefraktionsanalyse und lichtoptischer Bildauswertung sowohl Porosität als auch die innere Oberflächendichte bestimmt. Während mit beiden Verfahren die Porositäten gut übereinstimmen, weichen die Oberflächendichten signifikant voneinander ab. Dieser Unterschied ist hauptsächlich auf mikrostrukturelle Defekte im keramischen Werkstoffgefüge zurückzuführen, die von der Bildanalyse quantitativ nur unvollständig erfasst werden. Dagegen ist die bildanalytische Auswertung der typischen, großporigen Hohlraumstruktur im Vergleich zur Röntgenrefraktion von Vorteil. Die Untersuchungen zeigen, dass die Kombination beider Verfahren eine geeignete Ergänzung darstellt, um die Strukturparameter verlässlich bestimmen zu können. Dies ist auch die wesentliche Voraussetzung für die Optimierung der Materialeigenschaften.
Bone development and bone structure depend on surface roughness and structure of metalic implants
(2000)
The use of biodegradable bone substitutes is advantageous for alveolar ridge augmentation, since it avoids second-site surgery for autograft harvesting. This study examines the effect of novel, rapidly resorbable calcium phosphates on the expression of bone-related genes and proteins by human bone-derived cells (HBDC) and compares this behavior to that of tricalciumphosphate (TCP). Test materials were a-TCP, and four materials which were created from ß-Rhenanite and its derivatives: R1-ß-Rhenanite (CaNaPO4); R1/M2 composed of CaNaPO4 and MgNaPO4; R1+SiO2 composed of CaNaPO4 and 9% SiO2 (wt%); and R17-Ca2KNa(PO4)2. HBDC were grown on the substrata for 3, 5, 7, 14 and 21 days, counted and probed for various mRNAs and proteins (Type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase and bone sialoprotein). All substrata supported continuous cellular growth for 21 days. At day 21, surfaces of R1+SiO2 and R17 had the highest number of HBDC. At 14 and 21 days, cells on R1 and on R1+SiO2 displayed significantly enhanced expression of all osteogenic proteins. Since all novel calcium phosphates supported cellular proliferation together with expression of bone-related proteins at least as much as TCP, these ceramics can be regarded as potential bone substitutes. R1 and R1+SiO2 had the most effect on osteoblastic differentiation, thus suggesting that these materials may possess a higher potency to enhance osteogenesis than TCP.
Calcium phosphate coated titanium and titanium alloy are widely used as dental and orthopaedic implants. This study examines the effect of novel calcium titanium and calcium titanium zirconium phosphates suitable for plasma-spraying onto titanium substrata on the expression of bone-related genes and proteins by human bone-derived cells (HBDC) and compares this behavior to that on native titanium and hydroxyapatite-coated titanium. Test materials were an acid etched and sand-blasted titanium surface (Ti-DPS), a plasma-sprayed hydroxyapatite coating (HA), and five materials which were created from CaTi4(PO4)6 (CTP) and CaZr4(PO4)6 (CZP): sintered CaTi4(PO4)6 (CTP-S1), sintered 46CaO·23TiO2·31P2O5 (CTP-S2), sintered CaTiZr3(PO4)6, (CTZP-S1), sintered 46CaO·23ZrO2·31P2O5 (CTZP-S2) and sintered 55CaO·20TiO2·31P2O5 (CTP-S3). HBDC were grown on the substrata for 3, 7, 14 and 21 d, counted and probed for various mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase and bone sialoprotein). All substrates significantly affected cellular growth and the temporal expression of an array of bone-related genes and proteins. At 14 and 21 d, cells on CTP-S3 displayed significantly enhanced expression of all osteogenic mRNAs. Surfaces of CTP-S1 and CTP-S3 had the most effect on osteoblastic differentiation inducing a greater expression of an array of osteogenic markers than recorded for cells grown on Ti-DPS and HA, suggesting that these novel materials may possess a higher potency to enhance osteogenesis.
The use of biodegradable bone substitutes is advantageous for alveolar ridge augmentation because it avoids second-site surgery for autograft harvesting. This study examines the effect of novel, rapidly resorbable calcium phosphates and a calcium phosphate bone cement on the expression of bone-related genes and proteins by human bone-derived cells (HBDCs) and compares this behavior to that of tricalciumphosphate (TCP). Test materials were -TCP, two materials with a crystalline phase Ca2KNa(PO4)2 and with a small amorphous portion containing either magnesium potassium phosphate (material denominated GB14) or silica phosphate (material denominated GB9), and a calcium phosphate bone cement (material denominated Biocement D). HBDCs were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for various mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase, and bone sialoprotein). All substrates supported continuous cellular growth for 21 days. In the presence of GB14 and Biocement D specimens cell proliferation was reduced and cell differentiation increased. At day 21, the greatest number of cells was found on GB9 expressing significantly higher levels of bone-related proteins than cells grown on all other surfaces. Because all novel materials facilitated the expression of the osteoblastic phenotype at least as much as TCP and the polystyrene control, these biomaterials can be regarded as excellent candidate bone substitute materials. GB9 induced the highest proliferation and cellular differentiation after 21 days of incubation, suggesting that this material may possess a higher potency for enhancing osteogenesis than TCP. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 145-154, 2004
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
Rapid resorbable, glassy crystalline materials on the basis of calcium alkali orthophosphates
(1995)
Neben Hydroxylapatit (HAp) findet verstärkt auch Tricalciumphosphat (TCP) Anwendung als Knochenersatzmaterial. In der Literatur finden sich widersprüchliche Angaben zur Löslichkeit von TCP. Bedingt durch unterschiedliche Darstellungsverfahren ergeben sich verschiedenartige Materialbeschaffenheiten, die sich erst nach der Implantation durch ein differenziertes Resorptions-verhalten dokumentieren (partikulärer Abbau, chemischer Lösungsprozeß). Zur Klärung derartiger Zusammenhänge in vitro wurden 2 Methoden zur Bestimmung des Lösungsverhaltens untersucht. Dafür wurden TCP-Proben aus verschiedenen Rohstoffen dargestellt, nach unterschiedlichen Temperaturregimen behandelt und/oder einer Nachbehandlung mit Phosphorsäure unterzogen.
Diese Materialien wurden vor allem mittels Röntgenpulverdiffraktometrie und Rasterelektronenmikroskopie charakterisiert. In anschließenden Löslichkeitsuntersuchungen wurden die optimalen Versuchsparameter (Lösungsmittel, Konzentration, Verhältnis Lösungsmittelmenge zur Lösungsoberfläche usw.) sowie geeignete Meßgrößen (Masseverlust, Ionenkonzentration) ermittelt. Die In-vitro-Löslichkeit erwies sich bei sorgfältiger Auswahl der Versuchsbedingungen als sehr wirkungsvolle Charakterisierungsmöglichkeit, die auf synthesebedingte chemische und morphologische Unterschiede sehr empfindlich reagiert.
Translated Abstract
Resorbable bone substitution on the basis of calcium phosphates
Besides hydroxyapatite (HAp), tricalcium phosphate is increasingly being used as bone substitution material. In literature there are contradictory claims of the TCP solubility. As a result of are contradictory claims of the TCP solubility. As a result of different manufacturing processes there are altered material properties, which are documented by different resorption behaviour especielly after implantation (particle separation, chemical solvatation). To clarify of such in vitro connections two methods for determining the solubility were investigated. Especially for this case, TCP samples prepared from different raw materials were synthesized. These samples were given different heat treatments and/or posttreatments with phosphoric acid.
The materials were characterized above all by using X-ray powder diffraction method and scanning electron microscopy. Following investigations of the solubility lead to optimized testing parameters (solvent, concentration, ratio of solvent's quantity to sample surface, etc.) as well as qualified test parameters (lost of weight, ion concentration). When the test conditions were carefully selected, the in vitro solubillity was proved to be a very effective possibility of materials characterisation which is also very sensitive regarding chemical differences caused by synthesizing or morphological differences.
Amorphous calcium phosphate cements and their transformation into calcium deficient hydroxyapatite
(1996)
This paper deals with spongiosa-like resorbable bone substitution material or scaffolds created by using Ca2KNa(PO4)6 as main crystalline phase. The material is prepared by melting, shock-cooling meanwhile the melt spontaneously crystallizes, milling to powder used to make a slip for PUR-sponge (Schwarzwalder process), and sintering. The spongiosa-like material is analyzed to characterize the pores but also the material surrounding the pores as well as the resulting internal surface by light microscopy and X-ray refraction technique, respectively. There is a big difference between the measured internal surface by the methods mentioned. Further investigations show that the differences are the result of powder particles that are not integrated in the sinter process. Introduction Ceramic scaffolds made of resorbable bone substitution material usefully have been appropriated as bone defect filling material as well as cell substrate. The spongiosa-like material was prepared using calcium phosphates consisting mainly of Ca2KNa(PO4)2 that is rapidly resorbable in comparison to tricalcium phosphate ceramics. For characterization of micro-structural parameters we used light microscopy image analysis and X-ray refraction technique. The later one enabled to determine characteristic microstructure parameters, i.e. spatially resolved internal surface densities and corresponding pore size distributions of spongiosa-like bioceramics. Methods The synthesis of glass-ceramics containing Ca2KNa(PO4)2 as the main crystalline phase has been described in detail elsewhere [1, 2].
The surface structure, in particular the surface roughness, and the surface chemistry of titanium implants influence their anchoring in bone. The aim of this study was to analyse metal-bone contact (MBC) after modification of the implant surface, using different materials for blasting. The surface modification of titanium was produced by blasting it with particles made of Al2O3 or bioceramics. The biological effects were then investigated experimentally using 27 rabbits, analysed after 7, 28 and 84 days after the implantation of titanium cylinders treated accordingly. The MBC showed a tendency for more bone after bioceramics were used as a blasting material, compared to Al2O3.
Glass-ceramics containing Ca2KNa(PO4)2 as the main crystalline phase have a solubility which is 8 times higher than that of alpha-tricalcium phosphate ceramics. When using these compositions in drug delivery systems, especially in bone, it is necessary to create a material with a high open porosity. A Ca2KNa(PO4)2-based glass-ceramic was prepared from a borosilicate glass melt. The processed material includes minor amounts of boron which are low enough for medical application. Tissue response was studied using an animal model. Particles were implanted in rabbit femurs. Bone and soft tissue development occurred at the particle interfaces. In general, most particles were enclosed in the network of trabecular bone. The advantages of using a biomaterial with high porosity (pore size of 1-3 micron), together with rapid biodegradation, bioactivity and biocompatibility, despite traces of boron, were shown. 4 refs.
The use of biodegradable bone substitutes is advantageous for alveolar ridge augmentation, since it avoids second-site surgery for autograft harvesting. This study examines the effect of novel, rapidly resorbable calcium phosphates on the expression of bone-related genes and proteins by human bone derived cells (HBDC) and compares this behavior to that of tricalciumphosphate (TCP). Test materials were -TCP, a newly synthesized chemical Ca2KNa(PO4)2 (material denominated R17), two glassy crystalline materials with a crystalline phase Ca2KNa(PO4)2 and in addition a small amorphous portion containing either magnesium potassium phosphate (material denominated GB14) or silica phosphate (material denominated GB9). HBDC was grown on the substrates for 3, 5, 7, 14 and 21 days, counted and probed for various mRNAs and proteins (collagen type I, osteocalcin, osteopontin, osteonectin, alkaline phosphatase and bone sialoprotein). All substrates supported continuous cellular growth for 21 days. At day 21, R17, GB9, TCP and GB14.
The functional expression of human bone derived cells grown on resorbable bioactive glass ceramics
(2002)
In vivo test of a high porous rapidly resorbable dicalcium potassium sodium phosphate glass-ceramics
(2002)
The surface of a titanium alloy (Ti6Al4V) implant material was covered with a bioactive calcium alkali phosphate ceramic with the aim to accelerate the healing and to form a stronger bond to living bone tissue. To fix the ceramic powder we used a femtosecond laser, which causes a thin surface melting of the metal. It is a requirement to prove that the laser irradiation would not reduce the lifetime of implants. Here we present the results of mechanical stability tests, determined by the rotating bending fatigue strength of sample rods. After describing the sample surfaces and their modifications caused by the laser treatment we give evidence for an unchanged mechanical stability. This applies not only to the ceramic fixation but also to a comparatively strong laser ablation.
Solubility and ingrowth behaviour of degradable and figuline calcium alkaline phosphate cements
(2012)
The thrust of the investigations presented here is to point out the degradation behaviour in vitro and the ingrowth behaviour in vivo of four different calcium alkaline phosphate cements. Two of the figuline and mouldable composites consist of the crystalline phase Ca2KNa(PO4)2 and two of the crystalline phase Ca10[K/Na](PO4)2 each containing 2wt% medium gel strength porcine gelatin. Furthermore A-TCP was added to both Ca10[K/Na](PO4)2 cements as a hardening supporting reactant. The testing material groups differ in small amorphous portions containing either silica phosphate (GB9), magnesium potassium phosphate (GB14) or diphosphates (401545 and 401545(70)). The respective composites show a monomodal particle size distribution (d50~7µm; span~4) and an average total porosity around 28vol%.For the solubility studies cylindrical samples (d=6mm; h=12mm) were stored in a 0.1mol TRIS buffer solution and incubated at 37°C for maximum 50 weeks. The storage solution was analysed and renewed every week. The results are plotted cumulative. For the in vivo studies critical size defects were dissected to mandibles in a sheep model in which a 1cm³ area of the bottom of the mandibles was surgically resected and replaced with the figuline cements whereas the mouldability allows the reconstruction of the original outer contour without draining off even when replacing upside down.
The paper presented here deals with rheological and hardening properties during the setting reaction, and density and compressive strength after the final setting of a figuline composite consisting of Ca2KNa(PO4)2 and 2wt% medium gel strength gelatin. Compared to the composite with monomodal particle size distribution (d50=7.18µm; span=3.9) and its properties during and after setting reaction, the goal of this work is to increase the resulting product compressive strength by mixing different particle sizes in order to obtain bi- and trimodal distributions. For the bimodal powder mixtures the ratio in diameter (dcourse/dsmall) was chosen with 7/1 and volume ratio dcourse/dsmall was 70/30%. For the trimodal powder mixtures the ratio in diameter (dcourse/dmedium/dsmall) was chosen with 70/7/1 and volume ratio dcourse/dmedium/dsmall was set to 44/28/28%.After establishing an adequate crushing and sieving process the tap density and powder density of each fraction was determined. Subsequently, the different particle sizes were mixed and the densities and the Hausner ratio were determined again. The mixtures show an increase in both densities especially the tap density increased significantly. Rheological investigations show that the graphs of storage and loss moduli of the multimodal powder mixtures respectively are similar. The characteristic setting times show a slight decrease compared with the monomodal composite but not significantly different data. When comparing the resulting compressive strength of cylindrical samples, which were stored direct after reaching the initial setting time under physiological conditions, the studies illustrated in all cases for the multimodal mixtures a significant increase in compressive strength and a higher density.
Several substituted β-tricalcium phosphates have been prepared with different cations (monovalent, divalent and trivalent) and at various levels of substitution. Structural investigations have proved that fewer than ~10% wt substitution, the substituted compounds are isostructural to β-TCP, leading to solid solutions. These samples have been characterized by infrared and Raman spectroscopies. The vibrational spectra show mainly the bands related to the vibrations of PO43- tetrahedrons present in the structure. As Raman scattering and infrared absorption are local probes, the bands are sensitive to the local environment of the distinct tetrahedrons, related to the site of substitution and to the nature of the cations.
Calcium alkaline phosphate scaffolds for bone regeneration 3D-fabricated by additive manufacturing
(2012)
Calcium alkaline phosphate granulates can be used for substitution of several bone defects but for the reconstruction of large skeletal parts in the maxillofacial and orthopaedic fields fitted scaffolds are preferable. Within the additive manufacturing methods, the 3D printing process offers exciting opportunities to generate defined porous scaffolds. We used a R1 printer from ProMetal Company, USA, for producing scaffolds directly from a ceramic powder. For this direct free form fabrication technology the powder has to possess a lot of specific properties both for the generation of a stable green body and also for the subsequent sintering preparation. For this printing process we prepared different granules in a fluidized bed process containing Ca2KNa(PO4)2 as main crystalline phase. Granules were characterized by different methods and several sieve fractions were used for preparing disc like and cylindrical parts. The suitability of granules for this printing process was determined by porosity and strength of produced bodies. Next to granules' performance both of these properties can be directly influenced by 3D printing process parameters. With knowledge of suitable process parameters scaffolds with different porosity in a respective desired design can be created. In this study, cylindrical scaffolds with graded porosity were produced for bone regeneration of segmental defects in maxillofacial surgery and dental implantology by tissue engineering.
Resorbable bioceramic coated pins: solubility behaviour in vitro and adequate reactions in vivo
(2005)
Ideally, bioactive ceramics for use in alveolar ridge augmentation should possess the ability to activate bone formation and, thus, cause the differentiation of osteoprogenitor cells into osteoblasts at their surfaces. Therefore, in order to evaluate the osteogenic potential of novel bone substitute materials, it is important to examine their effect on osteoblastic differentiation. This study examines the effect of rapidly resorbable calcium-alkali-orthophosphates on osteoblastic phenotype expression and compares this behavior to that of β-tricalcium phosphate (TCP) and bioactive glass 45S5. Test materials were three materials (denominated GB14, GB9, GB9/25) with a crystalline phase Ca2KNa(PO4)2 and with a small amorphous portion containing either magnesium potassium phosphate (GB14) or silica phosphate (GB9 and GB9/25, which also contains Ca2P2O7); and a material with a novel crystalline phase Ca10[K/Na](PO4)7 (material denominated 352i). SaOS-2 human bone cells were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for an array of osteogenic markers. GB9 had the greatest stimulatory effect on osteoblastic proliferation and differentiation, suggesting that this material possesses the highest potency to enhance osteogenesis. GB14 and 352i supported osteoblast differentiation to the same or a higher degree than TCP, whereas, similar to bioactive glass 45S5, GB9/25 displayed a greater stimulatory effect on osteoblastic phenotype expression, indicating that GB9/25 is also an excellent material for promoting osteogenesis.
Biocompatibility studies of a new bone cement using humane bone marrow cells - preliminary results
(2003)
Cool bone cement
(2003)
Bioactive ceramics used as coating materials combine the conductive properties of a bioceramic with the mechanical stability of the metal implant. We studied a calcium zirconium phosphate-containing coating material, FA-CZP [Ca5(PO4)3F, CaZr4(PO4)6], that is relatively insoluble in the biological milieu. The reaction of bone to this material was investigated histologically and histomorphometrically in an animal trial. Cylindrical Ti6Al4V specimens that had been coated with FA-CZP by plasma spraying were implanted in the femoral condyles of rabbits. The implants were left in place for 2, 4, 6, 12, and 14 weeks. FA-CZP led to impaired mineralization of the newly formed bone at the interface. Noncalcified osteoid was found throughout the whole study period. The layer seemed to become thicker with time. The mineralization disorder is evidently caused by zirconium ions. The presence of zirconium in the osteoid in contact with the implant was demonstrated by means of two different staining methods.
Osteoclastic bioresorption of biomaterials: Two- and three-dimensional imaging and quantification
(2010)
Purpose: Bioresorbable materials have been developed in the hope that the body will replace them with newly formed tissue. The first step of this remodeling process in bone is the bioresorption of the material by osteoclasts. The aim of this study was to analyze osteoclastic resorption of biomaterials in vitro using the commonly used two-dimensional methods of light-microscopy (LM) and scanning electron microscopy (SEM) in comparison with infinite focus microscopy (IFM), a recently developed imaging method allowing for three-dimensional surface analysis. Methods: Human hematopoietic stem cells were cultivated in the presence of the cytokines M-CSF and RANK-L for 4 weeks directly on dentin and a calcium phosphate cement. Osteoclast development was surveyed with standard techniques. After removal of the cells, resorption was characterized and quantified by LM, SEM and IFM. Results: Osteoclast cultures on the biomaterials presented the typical osteoclast-specific markers. On dentin samples LM, SEM as well as IFM allowed for discrimination of resorption. Quantification of the resorbed area showed a linear correlation between the results (LM vs. SEM: r=0.996, p=0.004; SEM vs. IFM: r=0.989, p=0.011; IFM vs. LM: r=0.995). It was not possible to demarcate resorption pits on GB14 using LM or SEM. With IFM, resorption on GB14 could be visualized and quantified two- and three-dimensionally.
Commonly, to determine osteoclastic resorption of biomaterials only the resorbed area is measured. The depth of the resorption pit, however, may also be important for the performance of a material. To generate such data we used two calcium phosphate ceramics (Ca10 and Ca2). The solubility of the materials was determined according to DIN EN ISO 10993-14. They were scanned three-dimensionally using infinite focus microscopy and subsequently cultivated for 4 weeks in simulated body fluid without (control) or with human osteoclasts. After this cultivation period osteoclasts number was determined and surface changes were evaluated two- and three-dimensionally. Ca10 and Ca2 showed solubilities of 11.0 ± 0.5 and 23.0 ± 2.2 mg g-1, respectively. Both materials induced a significant increase in osteoclast number. While Ca10 did not show osteoclastic resorption, Ca2 showed an increased pit area and pit volume due to osteoclastic action. This was caused by an increased average pit depth and an increased number of pits, while the average area of single pits did not change significantly. The deduced volumetric osteoclastic resorption rate (vORR) of Ca2 (0.010.02 µm3 µm-2 day-1) was lower than the remodelling speed observed in vivo (0.08 µm3 µm-2 day-1), which is in line with the observation that implanted resorbable materials remain in the body longer than originally expected. Determination of volumetric indices of osteoclastic resorption might be valuable in obtaining additional information about cellular resorption of bone substitute materials. This may help facilitate the development of novel materials for bone substitution.