Jens Günster

3D-printed silicate porous bioceramics using a non-sacrificial preceramic polymer binder

Silicate bioceramics possess an excellent bioactivity; however, shaping them into complex geometries is still challenging. Therefore, this paper aims to present a new strategy for the shaping of a bioglass-ceramic with controlled geometry and properties starting from a glass powder combined with a preceramic polymer, i.e. a silicon resin, and reactive fillers. The powder-based three-dimensional (3D)-printing of wollastonite (CaSiO3)-based silicate bioceramic parts was demonstrated in this work. The resin plays a dual role, as it not only acts as a non-sacrificial binder for the filler powders in the printing process but it also reacts with the fillers to generate the desired bioceramic phases. The mechanical and physical properties, i.e. ball-on-three-balls test, density, porosity and morphology, were evaluated in 3D-printed discs. These samples possessed a total porosity around 64 vol% and a biaxial flexural strength around 6 MPa. The raw materials used in this work also enabled the 3D-printing of scaffolds possessing a designed multi-scale porosity, suitable bioceramic phase assemblage and a compressive strength of 1 MPa (for cylindrical scaffolds with total porosity ~80 vol%). Solubility in TRIS/HCl and in vitro assays, i.e. viability, cytotoxicity and apoptosis assays, were also performed. In vitro tests indicated good cell viability and no cytotoxicity effect on the cells.

Characterization of triazine derivatives on silicon wafers studied by photoelectron spectroscopy (XPS, UPS) and metastable impact electron spectroscopy (MIES)

Abstract Thin films of a diandicyanato bisphenol A (DCBA) prepolymer and thin layers of the trimer of the 2,4,6-tris-(p-cumylphenylcyanate)-1,3,5-triazine (p-CPC trimer), both deposited on silicon wafers convered by their native oxide, have been investigated by X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES). MIES as well as angle dependent XPS indicate a preferential orientation of the molecules of the first adlayer on the surface. The adsorption of the first layer is governed by the interaction of the trioxytriazine rings with the substrate surface. This adsorption model is supported by the calculated conformation of the DCBA and p-CPC trimer.

Decreased extrusion of calcium phosphate cement versus high viscosity PMMA cement into spongious bone marrow—an ex vivo and in vivo study in sheep vertebrae

BACKGROUND CONTEXT Vertebroplasty or kyphoplasty of osteoporotic vertebral fractures bears the risk of pulmonary cement embolism (3.5%-23%) caused by leakage of commonly applied acrylic polymethylmethacrylate (PMMA) cement to spongious bone marrow or outside of the vertebrae. Ultraviscous cement and specific augmentation systems have been developed to reduce such adverse effects. Rapidly setting, resorbable, physiological calcium phosphate cement (CPC) may also represent a suitable alternative. PURPOSE This study aimed to compare the intravertebral extrusion of CPC and PMMA cement in an ex vivo and in vivo study in sheep. STUDY DESIGN/SETTING A prospective experimental animal study was carried out. METHODS Defects (diameter 5 mm; 15 mm depth) were created by a ventrolateral percutaneous approach in lumbar vertebrae of female Merino sheep (2-4 years) either ex vivo (n=17) or in vivo (n=6), and injected with: (1) CPC (L3); (2) CPC reinforced with 10% poly(l-lactide-co-glycolide) (PLGA) fibers (L4); or (3) PMMA cement (L5; Kyphon HV-R). Controls were untouched (L1) or empty defects (L2). The effects of the cement injections were assessed in vivo by blood gas analysis and ex vivo by computed tomography (CT), micro-CT (voxel size: 67 µm), histology, and biomechanical testing. RESULTS Following ex vivo injection, micro-CT documented significantly increased extrusion of PMMA cement in comparison to CPC (+/- fibers) starting at a distance of 1 mm from the edge of the defect (confirmed by histology); this was also demonstrated by micro-CT following in vivo cement injection. In addition, blood gas analysis showed consistently significantly lower values for the fraction of oxygenized hemoglobin/total hemoglobin (FO2Hb) in the arterial blood until 25 minutes following injection of the PMMA cement (p ≤ .05 vs. CPC; 7, 15 minutes). Biomechanical testing following ex vivo injection showed significantly lower compressive strength and Young modulus than untouched controls for the empty defect (40% and 34% reduction, respectively) and all three cement-injected defects (21%-27% and 29%-32% reduction, respectively), without significant differences among the cements. CONCLUSIONS Because of comparable compressive strength, but significantly lower cement extrusion into spongious bone marrow than PMMA cement, physiological CPC (+/- PLGA fibers) may represent an attractive alternative to PMMA for vertebroplasty or kyphoplasty of osteoporotic vertebral fractures to reduce the frequency or severity of adverse effects.

Enhanced bone formation in sheep vertebral bodies after minimally invasive treatment with a novel, PLGA fiber-reinforced brushite cement.

BACKGROUND CONTEXT Injectable, brushite-forming calcium phosphate cements (CPC) show potential for bone replacement, but they exhibit low mechanical strength. This study tested a CPC reinforced with poly(l-lactide-co-glycolide) acid (PLGA) fibers in a minimally invasive, sheep lumbar vertebroplasty model. PURPOSE The study aimed to test the in vivo biocompatibility and osteogenic potential of a PLGA fiber-reinforced, brushite-forming CPC in a sheep large animal model. STUDY DESIGN/SETTING This is a prospective experimental animal study. METHODS Bone defects (diameter: 5 mm) were placed in aged, osteopenic female sheep, and left empty (L2) or injected with pure CPC (L3) or PLGA fiber-reinforced CPC (L4; fiber diameter: 25 µm; length: 1 mm; 10% [wt/wt]). Three and 9 months postoperation (n=20 each), the structural and functional CPC effects on bone regeneration were documented ex vivo by osteodensitometry, histomorphometry, micro-computed tomography (micro-CT), and biomechanical testing. RESULTS Addition of PLGA fibers enhanced CPC osteoconductivity and augmented bone formation. This was demonstrated by (1) significantly enhanced structural (bone volume/total volume, shown by micro-CT and histomorphometry; 3 or 9 months) and bone formation parameters (osteoid volume and osteoid surface; 9 months); (2) numerically enhanced bone mineral density (3 and 9 months) and biomechanical compression strength (9 months); and (3) numerically decreased bone erosion (eroded surface; 3 and 9 months). CONCLUSIONS The PLGA fiber-reinforced CPC is highly biocompatible and its PLGA fiber component enhanced bone formation. Also, PLGA fibers improve the mechanical properties of brittle CPC, with potential applicability in load-bearing areas.

First-time systematic postoperative clinical assessment of a minimally invasive approach for lumbar ventrolateral vertebroplasty in the large animal model sheep

BACKGROUND CONTEXT Large animal models are highly recommended for meaningful preclinical studies, including the optimization of cement augmentation for vertebral body defects by vertebroplasty/kyphoplasty. PURPOSE The aim of this study was to perform a systematic characterization of a strictly minimally invasive in vivo large animal model for lumbar ventrolateral vertebroplasty. STUDY DESIGN/ SETTING This is a prospective experimental animal study. METHODS Lumbar defects (diameter 5 mm; depth approximately 14 mm) were created by a ventrolateral percutaneous approach in aged, osteopenic, female sheep (40 Merino sheep; 6-9 years; 68-110 kg). L1 remained untouched, L2 was left with an empty defect, and L3 carried a defect injected with a brushite-forming calcium phosphate cement (CPC). Trauma/functional impairment, surgical techniques (including drill sleeve and working canula with stop), reproducibility, bone defects, cement filling, and functional cement augmentation were documented by intraoperative incision-to-suture time and X-ray, postoperative trauma/impairment scores, and ex vivo osteodensitometry, microcomputed tomography (CT), histology, static/fluorescence histomorphometry, and biomechanical testing. RESULTS Minimally invasive vertebroplasty resulted in short operation times (28±2 minutes; mean±standard error of the mean) and X-ray exposure (1.59±0.12 minutes), very limited local trauma (score 0.00±0.00 at 24 hours), short postoperative recovery (2.95±0.29 hours), and rapid decrease of the postoperative impairment score to 0 (3.28±0.36 hours). Reproducible defect creation and cement filling were documented by intraoperative X-ray and ex vivo conventional/micro-CT. Vertebral cement augmentation and osteoconductivity of the CPC was verified by osteodensitometry (CPC>control), micro-CT (CPC>control and empty defect), histology/static histomorphometry (CPC>control and empty defect), fluorescence histomorphometry (CPC>control; all p<.05 for 3 and 9 months), and compressive strength measurements (CPC numerically higher than control; 102% for 3 months and 110% for 9 months). CONCLUSIONS This first-time systematic clinical assessment of a minimally invasive, ventrolateral, lumbar vertebroplasty model in aged, osteopenic sheep resulted in short operation times, rapid postoperative recovery, and high experimental reproducibility. This model represents an optimal basis for standardized evaluation of future studies on vertebral augmentation with resorbable and osteoconductive CPC.

3-D Printed Bioactive Bone Replacement Scaffolds of Alkaline Substituted Ortho-Phosphates Containing Meta- and Di-Phosphates

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.

Powder-Bed Stabilization for Powder-Based Additive Manufacturing

The most successful additive manufacturing (AM) technologies are based on thelayer-by-layer depositionof a flowable powder. Although considered as the third industrial revolution, one factor still limiting these processes to become completely autonomous is the often necessary build-up of support structures. Besides the prevention of lateral shifts of the part during the deposition of layers, the support assures quality and stability to the built process. The loose powder itself surrounding the built object, or so-called powder-bed, does not provide this sustenance in most existent technology available. Here we present a simple but effective and economical method for stabilizing the powder-bed, preventing distortions in the geometry with no need for support structures. This effect, achieved by applying an air flow through the powder-bed, is enabling an entirely autonomous generation of parts and is a major contribution to all powder-based additive manufacturing technologies. Moreover, it makes powder-based AM independent of gravitational forces, which will facilitate crafting items in space from a variety of powdery materials.

The analysis of surface-adsorbed organic molecules by alkali-assisted MIES combined with UPS(He I)

Metastable impact electron spectroscopy (MIES) in combination with UPS(He I) is applied to the study of s-triazine and triethoxytriazine molecules adsorbed on Si(100) either alone or in combination with cesium atoms. It is demonstrated that the presence of the Cs atoms facilitates the identification of the adsorbed species considerably. It is concluded that (i) non-dissociative adsorption of the studied organic molecules occurs whereby the basal rings of the molecules lie flat on the silicon surface, in accordance with previous studies by Bu and Lin, (ii) the binding of the molecules to the surface is mainly via the lone pair orbitals of the nitrogen in the ring, and (iii) s-triazine reacts strongly with oxygen which bonds to the carbon atoms of the triazine ring.

GDF5 significantly augments the bone formation induced by an injectable, PLGA fiber-reinforced, brushite-forming cement in a sheep defect model of lumbar osteopenia

BACKGROUND CONTEXT Biodegradable calcium phosphate cement (CPC) represents a promising option for the surgical treatment of osteoporotic vertebral fractures. Because of augmented local bone catabolism, however, additional targeted delivery of bone morphogenetic proteins with the CPC may be needed to promote rapid and complete bone regeneration. PURPOSE In the present study, an injectable, poly(l-lactide-co-glycolide) acid (PLGA) fiber-reinforced, brushite-forming cement (CPC) containing the bone morphogenetic protein GDF5 was tested in a sheep lumbar osteopenia model. STUDY DESIGN/SETTING This is a prospective experimental animal study. METHODS Defined bone defects (diameter 5 mm) were placed in aged, osteopenic female sheep. Defects were treated with fiber-reinforced CPC alone (L4; CPC+fibers) or with CPC containing different dosages of GDF5 (L5; CPC+fibers+GDF5; 1, 5, 100, and 500 µg GDF5; n=5 or 6 each). The results were compared with those of untouched controls (L1). Three and 9 months postoperation, structural and functional effects of the CPC (±GDF5) were assessed ex vivo by measuring (1) bone mineral density (BMD); (2) bone structure, that is, bone volume/total volume (assessed by micro-computed tomography and histomorphometry), trabecular thickness, and trabecular number; (3) bone formation, that is, osteoid volume/bone volume, osteoid surface/bone surface, osteoid thickness, mineralized surface/bone surface, mineral apposition rate, and bone formation rate/bone surface; (4) bone resorption, that is, eroded surface/bone surface; and (5) compressive strength. RESULTS Compared with untouched controls (L1), both CPC+fibers (L4) and CPC+fibers+GDF5 (L5) numerically or significantly improved all parameters of bone formation, bone resorption, and bone structure. These significant effects were observed both at 3 and 9 months, but for some parameters they were less pronounced at 9 months. Compared with CPC without GDF5, additional significant effects of CPC with GDF5 were demonstrated for BMD and parameters of bone formation and structure (bone volume/total volume, trabecular thickness, and trabecular number, as well as mineralized surface/bone surface). The GDF5 effects were dose-dependent (predominantly in the 5-100 µg range) at 3 and 9 months. CONCLUSIONS GDF5 significantly enhanced the bone formation induced by a PLGA fiber-reinforced CPC in sheep lumbar osteopenia. The results indicated that a local dose as low as ≤100 µg GDF5 may be sufficient to augment middle to long-term bone formation. The novel CPC+GDF5 combination may thus qualify as an alternative to the bioinert, supraphysiologically stiff poly(methyl methacrylate) cement currently applied for vertebroplasty/kyphoplasty of osteoporotic vertebral fractures.

Low-dose BMP-2 is sufficient to enhance the bone formation induced by an injectable, PLGA fiber-reinforced, brushite-forming cement in a sheep defect model of lumbar osteopenia

BACKGROUND CONTEXT Bioresorbable calcium phosphate cement (CPC) may be suitable for vertebroplasty/kyphoplasty of osteoporotic vertebral fractures. However, additional targeted delivery of osteoinductive bone morphogenetic proteins (BMPs) in the CPC may be required to counteract the augmented local bone catabolism and support complete bone regeneration. PURPOSE This study aimed at testing an injectable, poly (l-lactide-co-glycolide) acid (PLGA) fiber-reinforced, brushite-forming cement (CPC) containing low-dose bone morphogenetic protein BMP-2 in a sheep lumbar osteopenia model. STUDY DESIGN/ SETTING This is a prospective experimental animal study. METHODS Bone defects (diameter 5 mm) were generated in aged, osteopenic female sheep and filled with fiber-reinforced CPC alone (L4; CPC+fibers) or with CPC containing different dosages of BMP-2 (L5; CPC+fibers+BMP-2; 1, 5, 100, and 500 µg BMP-2; n=5 or 6 each). The results were compared with those of untouched controls (L1). Three and 9 months after the operation, structural and functional effects of the CPC (±BMP-2) were analyzed ex vivo by measuring (1) bone mineral density (BMD); (2) bone structure, that is, bone volume/total volume (assessed by micro-computed tomography [micro-CT] and histomorphometry), trabecular thickness, and trabecular number; (3) bone formation, that is, osteoid volume/bone volume, osteoid surface/bone surface, osteoid thickness, mineralizing surface/bone surface, mineral apposition rate, and bone formation rate/bone surface; (4) bone resorption, that is, eroded surface/bone surface; and (5) compressive strength. RESULTS Compared with untouched controls (L1), CPC+fibers (L4) and/or CPC+fibers+BMP-2 (L5) significantly improved all parameters of bone formation, bone resorption, and bone structure. These effects were observed at 3 and 9 months, but were less pronounced for some parameters at 9 months. Compared with CPC without BMP-2, additional significant effects of BMP-2 were demonstrated for bone structure (bone volume/total volume, trabecular thickness, trabecular number) and formation (osteoid surface/bone surface and mineralizing surface/bone surface), as well as for the compressive strength. The BMP-2 effects on bone formation at 3 and 9 months were dose-dependent, with 5-100 µg as the optimal dosage. CONCLUSIONS BMP-2 significantly enhanced the bone formation induced by a PLGA fiber-reinforced CPC in sheep lumbar osteopenia. A single local dose as low as ≤100 µg BMP-2 was sufficient to augment middle to long-term bone formation. The novel CPC+BMP-2 may thus represent an alternative to the bioinert, supraphysiologically stiff polymethylmethacrylate cement presently used to treat osteoporotic vertebral fractures by vertebroplasty/kyphoplasty.