Papers by Author: Michael Stiller

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: Calcium phosphates (CaPs) are synthetic bone grafting materials. CaPs are an alternative to overcome the drawbacks present with autologous bone grafting and/or xenograft materials. Among the CaPs, tricalcium phosphate (TCP) stands out as a good candidate due to its physicochemical properties. The clinical performance of β-TCP has already been proven and established. Nevertheless, the format in which TCP is delivered is also important in terms of clinical handling. This work assessed the in vivo performance of TCP-based bone grafting materials with different formats. Materials studied were a TCP paste (TCP-P), a TCP foam (TCP-F) and TCP granules (TCP-G). A sheep scapula model was used to evaluate the osteogenic performance of these bone grafting materials. All materials performed well in terms of bone regenerative capacity and material resorption. However, TCP-P and TCP-F displayed a more pronounced initial material resorption and also exhibited better handling properties compared to TCP-G. TCP-based materials with improved handling properties, such as TCP-P and TCP-F, which at the same time possess the advantageous properties of β-TCP are suitable bone substitute materials for grafting and reconstruction of bone defects in numerous clinical applications.

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: The setting behaviour, the compressive strength and the porosity of four calcium alkali orthophosphate cements were examined under laboratory conditions (dry) and under conditions similar to those during clinical application (37°C, contact with body fluid). The results showed an increase of the setting times when specimens were covered with simulated body fluid. Especially, the final setting time (FHZ) was significantly higher for three of the four cements. Furthermore, when specimens were stored in SBF for 16h, an extensive decrease of the compressive strength was noted. The porosity was more than twice as high after 16h in SBF and this may be the cause for the great decrease of the compressive strength.