Papers by Author: Georg Berger

Abstract: Sinus floor augmentation (SFA) has become a well-established pre-implantology procedure for alveolar ridge augmentation of the posterior maxilla. Using bioceramic bone substitutes avoids second-site surgery for autograft harvesting. Compared to the bone substitutes which are currently clinically available, there is a significant need for bone substitutes which degrade more rapidly, but still stimulate osteogenesis at the same time. This has led to the development of bioactive, rapidly resorbable calcium alkali orthophosphate (CAOP) materials, which have a greater solubility than tricalcium phosphate. In this study the biodegradability and effect of a silica containing CAOP (Si-CAOP) on osteogenesis was evaluated in human biopsies sampled 6 months after SFA and compared to that of TCP utilizing hard tissue histology, histomorphometry and immunohistochemical analysis of osteogenic marker expression. Both materials facilitated bone formation and matrix mineralization, which were still actively progressing from the sinus floor in an apical direction 6 months after SFA. With the Si-CAOP grafting material however, bone formation, the bone-biomaterial-contact, i.e. bone-bonding, and particle degradation were significantly greater compared to TCP in the apical region of the biopsies, i.e. at the largest distance from the native bone of the sinus floor. This was accompanied by greater expression of Col I, BSP and OC in the newly formed bone tissue in the Si-CAP samples compared to TCP. Six months after implantation Si-CAOP facilitated greater bone formation and biodegradability than the TCP graft material, whose excellent osteoconductive properties have been widely documented. Consequently, Si-CAOP can be regarded as excellent grafting material for SFA in a clinical setting.

Abstract: Early establishment of angiogenesis is critical for bone tissue engineering. Recently, a technique was introduced, which is based on the idea of using axial vascularization of the host tissues in engineered grafts, namely the “intrinsic angiogenesis chamber” technique, which utilizes an artery and a vein to construct an AV-Bundle. The aim of this study was to evaluate the effect of varying scaffold architecture of calcium alkali orthophosphate scaffolds (CAOP), resulting from two different fabrication procedures, namely 3D printing (RP) or a Schwarzwalder-Somers replica technique (SSM), on angiogenesis in vivo when combining a microvascular technique with bioceramic scaffolds colonized with stem cells for bone tissue engineering. 32 adult female Wistar rats, in which critical size segmental discontinuity defects 6 mm in length were created in the left femur, were divided into 4 groups, group 1 received a RP scaffold colonized with rat stem cells after 7d of dynamic cell culture and an AV-Bundle (AVB), group 2 a SSM scaffold with rat stem cells after 7d of dynamic cell culture and an AVB, group 3 a RP control scaffold (without cells and AVB), group 4 a SSM control scaffold (without cells and AVB). After 3 and 6 months, angiomicro-CT after perfusion with a contrast agent, image reconstruction, histomorphometric and immunohistochemical analysis utilizing antibodies to collagen IV, vWF and CD-31 were performed. At 6 months, a statistically significant higher blood vessel volume%, blood vessel surface/volume, blood vessel thickness, blood vessel density and blood vessel linear density was observed with RP scaffolds with cells and AVB than with the other groups. At 6 mths, RP with cells and AVB displayed the highest expression of collagen IV (score 2.75), CD31 (score 2.75) and vWF (score 2.6), which is indicative of highly dense blood vessels. Both angio-CT and immunohistochemical analysis demonstrated that AVB is an efficient technique for achieving scaffold vascularization in critical size segmental defects after 3 and 6 months of implantation.

Abstract: Over the last decade there have been increasing efforts to develop adequate 3D scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica containing calciumalkaliorthophosphate (code: GB9S14) utilizing two different fabrication processes, first a replica technique (SSM), and second 3D printing (RP). The mechanical and physical properties of the scaffolds (porosity, compressive strength, solubility) and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture prior to in vivo implantation were examined. To this end, murine osteoblastic cells (MT3T3-E1) were dynamically seeded and cultured for 7 days on both scaffold types under perfusion with two different concentrations of 1.5 and 3x10⁶ cells per ml. The amount of cells and extracellular matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. SSM scaffolds (SSMS) displayed a significantly greater total porosity (86.9%) than RP scaffolds (RPS) (50%), while RPS exhibited significantly more open micropores, greater compressive strength and silica release. RPS seeded with a 3x10⁶ cells per ml displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects.

Abstract: The paper presented here deals with the investigations of orthophosphates (Q₀) containing none or differing amounts of meta-(Q₂) and diphosphate phases (Q₁) for the use of 3-dimensional printing process in order to create porous, bioactive, nonloadbearing bone replacement scaffolds. The main ceramic phase in all cases is Ca₁₀[K/N(PO₄)₇ hereinafter called 401545(100) consisting of 99,9% Q₀ and 0,1% Q₁-phase. The other phosphate ceramics i) 401545(40) consists of 75% Q₀-phase, 22% Q₁-phase and 4% Q₂-phase ii) 401545(15) consists of 65% Q₀-phase, 33% Q₁-phase and 2% Q₂-phase iii) 401545consists of 56% Q₀-phase, 40% Q₁-phase and 4% Q₂-phase. The in-house produced ceramics where crushed and sieved to achieve particles of irregular shape in the range of 45-90µm. These powders show a quite good flowability and were used to generate cylindrical samples with a diameter of 5,5mm and a height of 11mm via 3-dimensional printing using a R1 printer from ProMetal company (USA). After drying the samples at T=125°C for 48 hours they were sintered at temperatures according to the thermal analysis results in the range of 900°C up to 1300°C. Afterwards the porosity, the linear shrinkage and the compressive strength were determined.

Abstract: 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 Α-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.

Abstract: 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 (d_course/d_small) was chosen with 7/1 and volume ratio d_course/d_small was 70/30%. For the trimodal powder mixtures the ratio in diameter (d_course/d_medium/d_small) was chosen with 70/7/1 and volume ratio d_course/d_medium/d_small 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.

Abstract: Several substituted â-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 â- 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.

Abstract: 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.

Abstract: Although autogenous bone grafts are currently the standard of care for bone reconstruction in implant dentistry, bone substitute materials are extensively studied in order to avoid harvesting autogenous bone. Recently, the use of tricalcium phosphate (TCP) and bioactive glass 45S5 particles as alloplastic bone graft materials for alveolar ridge augmentation and sinus floor elevation procedures has received increasing attention in implant dentistry. However, given the clinical findings with these current bone substitute materials there continues to be interest in bone substitute materials which degrade more rapidly, but still stimulate osteogenesis at the same time. As a result considerable efforts have been undertaken to produce rapidly resorbable bone substitute materials, which exhibit good bone bonding behaviour by stimulating enhanced bone formation at the interface in combination with a high degradation rate. This has led to the synthesis of a new series of bioactive, rapidly resorbable calcium alkali phosphate materials. These are glassy crystalline calcium alkali orthophosphates, which exhibit stable crystalline Ca₂KNa(PO₄)₂ phases. These materials have a higher solubility than TCP and therefore they are designed to exhibit a higher degree of biodegradability than TCP. On this basis, they are considered as excellent alloplastic materials for alveolar ridge augmentation. In order to evaluate the osteogenic potential in vitro, we first examined the effect of various rapidly resorbable calcium alkali orthophosphate bone grafting materials on the expression of osteogenic markers characteristic of the osteoblastic phenotype in vitro and compared this behaviour to that of the currently clinically used materials β-tricalcium phosphate (TCP) and bioactive glass 45S5. These studies showed that several calcium alkali orthophosphate materials supported osteoblast differentiation to a greater extent than TCP.

Abstract: This study describes the preparation of a composite material [1] from synthetic nano-scaled hydroxyapatite (nHA) and a gelatin matrix (80% nHA, 20% gelatin). This composite material is intended to extend the range of biological hydroxyapatite-based defect-filling materials for bone replacement. Ostim® (aqueous suspension of nHA having a crystallite size of about 20nm) was used as the inorganic component whereas porcine gelatin (type A, 180 Bloom) composed the organic part. Both components were homogenized during a spray-drying process. Cylindrical samples of the spray-dried granulate (HG 80/20) produced by pressing had adequate mechanical stability for storage, transport and handling in the surgery. The flexural strengths for the samples were determined on dry samples as well as after storing in media (distilled water, SBF solution) for 60 minutes. After staying 30 minutes in a SBF solution or in water, flexural strength dropped off about 30% while the shape of the sample was retained. Temperature treatments of both granulate and pressed samples resulted in reduction of the sample swelling from 70vol-% to 50vol-%. The sample produced by pressing can be machined (turned, drilled, milled).