Abteilung für Funktionswerkstoffe der Medizin und der Zahnheilkunde
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- Abteilung für Funktionswerkstoffe der Medizin und der Zahnheilkunde (171)
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Sonstige beteiligte Institutionen
- Department of Cellular Therapies, University of Navarra, Pamplona, Spain (1)
- Department of X-ray Microscopy, University of Würzburg, Würzburg, Germany (1)
- Experimental Physics V, University of Wuerzburg (1)
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- Lehrstuhl für Biotechniologie und Biophysik am Biozentrum der Universität Würzburg (1)
Six different magnesium-containing mineral bone cement formulations (based on struvite, K-struvite, dittmarite, newberyite, magnesium oxychloride or an amorphous magnesium phosphate cement) were developed in the present thesis with the aim to improve material degradability, particularly in comparison to clinically established hydroxyapatite (HA) cements. Ideally, a rapid degradation supports simultaneous new bone formation and enables a full replacement of the implanted material by newly formed bone within several months.
All compositions were characterized and optimized in vitro regarding handling, mechanical stability, and phase composition. Additionally, porosity and passive degradation was investigated. Four formulations (struvite, K-struvite, newberyite, magnesium oxychloride) exhibited a higher in vitro weight loss (1%, 8%, 1%, 37%) and cumulative ion release after 18 days in phosphate buffered saline (Mg: 10 µmol, 7 µmol, 12 µmol, 67 µmol) compared to the HA control cement (-0.4%, Ca: 0.5 µmol), indicating a higher passive solubility. HA is mainly resorbed by osteoclasts in vivo, which limits the resorption to the cement surface and results in a very slow degradation in vivo. Only for the amorphous magnesium phosphate cement, which is based on trimagnesium phosphate and sodium hydrogen phosphate, no weight loss during storage in PBS and a similarly low ion release compared to HA was observed. The in vitro degradation of the prefabricated dittmarite cement was not investigated, because it is expected to be similar to struvite-forming cements, due to the chemical resemblance of the two minerals. The most promising cement compositions (struvite, K-struvite, newberyite and dittmarite) were implanted in an established ovine bone defect model by our cooperation partners and degradation and new bone formation were quantified histomorphometrically. The cement area reduction 4 months after implantation was for all compositions (25%, 63%, 18%, 37%) noticeably higher compared to the HA reference cement (<5%), which had been already implanted in the very same defect model in a predecessor study. Furthermore, all compositions demonstrated a high biocompatibility and the degraded material was replaced by new bone.
The prefabricated dittmarite cement, which allows the storage of the viscous paste and a direct application during surgery, proved to be the most promising cement composition, with an observed in vivo cement area reduction of 37% at 4 months after implantation (control HA: <5%). By using a trimodal particle size distribution, including diammonium hydrogen phosphate and trimagnesium phosphate with two different particle sizes, the injection force was reduced from 72 to 25 N. The high porosity of the set cement (52%) likely promoted the rapid degradation, but also decreased the compressive strength to 9-14 MPa. By contrast, the non-prefabricated struvite cement, exhibiting 12% porosity, reached a compressive strength of 36 MPa. For future clinical use, the storage stability would be important to address, because an increase of injection force from 25 N to 113 N was observed after a storage time of 4 weeks, caused by a strong viscosity increase.
Apart from bone cement formulations, granules are a commonly used application form of bone replacement materials, particularly in maxillofacial surgery. Here, three different magnesium-mineral based granules (struvite, K-struvite, farringtonite) were fabricated with an emulsion process and compared to the clinically established material ß-TCP. For farringtonite and ß-TCP, new process routes for the granule fabrication were developed. Thereby, farringtonite and ß-TCP contents of 97% and 90%, respectively, were achieved. After the in vivo implantation in drill hole bone defects in a sheep model, also conducted by our cooperation partners, struvite granules exhibited a similar, and farringtonite granules a slightly improved degradation and new bone formation compared to ß-TCP granules. The remaining granule area after 4 months was 29%, 18% and 30% for struvite, farringtonite and ß-TCP, respectively. Only the K-struvite granules degraded too rapidly, with a relative granule area of 2% at 4 months after implantation.
In conclusion, particularly magnesium ammonium phosphate cement pastes (struvite, dittmarite) appear to be a very promising advancement of mineral bone cements, enabling a rapid resorption of the material in vivo and replacement by newly formed bone.
Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.
Background:
Copper-containing biomaterials are increasingly applied for bone regeneration due to their pro-angiogenetic, pro-osteogenetic and antimicrobial properties. Therefore, the effect of Cu2+ on osteoclasts, which play a major role in bone remodeling was studied in detail.
Methods:
Human primary osteoclasts, differentiated from human monocytes were differentiated or cultivated in the presence of Cu2+. Osteoclast formation and activity were analyzed by measurement of osteoclast-specific enzyme activities, gene expression analysis and resorption assays. Furthermore, the glutathione levels of the cells were checked to evaluate oxidative stress induced by Cu2+.
Results:
Up to 8 µM Cu2+ did not induce cytotoxic effects. Activity of tartrate-resistant acid phosphatase (TRAP) was significantly increased, while other osteoclast specific enzyme activities were not affected. However, gene expression of TRAP was not upregulated. Resorptive activity of osteoclasts towards dentin was not changed in the presence of 8 µM Cu2+ but decreased in the presence of extracellular bone matrix. When Cu2+ was added to mature osteoclasts TRAP activity was not increased and resorption decreased only moderately. The glutathione level of both differentiating and mature osteoclasts was significantly decreased in the presence of Cu2+.
Conclusions:
Differentiating and mature osteoclasts react differently to Cu2+. High TRAP activities are not necessarily related to high resorption.
The present work deals with the preparation of hydrogels in different size scales for various applications. Thus, macroscopic bulk hydrogels were prepared from differently modified pig gastric mucin (PGM), microgels were made from PGM in combination with hyaluronic acid (HA), as well as from gelatin in combination with poly(ethylene glycol) (PEG), and nanogels were fabricated from poly(glycidol) (PG). According to their size, each hydrogels have different applications. First, it was investigated whether previously existing studies involving the preparation of covalently crosslinked hydrogels via free radical polymerization from bovine submaxillary gland mucin (BSM) could also be carried out with the much cheaper alternative PGM. After this was successfully demonstrated and the hydrogels were systematically investigated for their mechanical properties and biocompatibility, a second hydrogel system was established. Here, PGM was functionalized with allyl glycidyl ether (AGE) and crosslinked in combination with thiolated HA via thiol-ene reaction. These hydrogels were also systematically evaluated and compared with the hydrogels prepared via free radical polymerization. It was confirmed that the more random free radical polymerization leads to more disordered networks than the thiol-ene reaction. In both systems, biocompatibility was demonstrated with both L929 CCL1 murine fibroblasts and human mesenchymal stem cells (hMSCs). Using this knowledge as background and the request to make mucin printable, microgels were prepared via the emulsion technique using the previously established thiol-ene hydrogel precursor solution. Here, applying the recently used photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2- methylpropiophenone (Irgacure 2959), which is more soluble in oil than in water, was challenging and did not result in well-crosslinked microgels. Therefore, a third hydrogel system was established, which was based on thiol-ene crosslinked AGE functionalized pig gastric mucin (PGM-AGE)-thiolated hyaluronic acid (HASH) hydrogels and with lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP) being used as photoinitiator. Hereby, stably crosslinked microgels could be prepared via the emulsion technique. After the jamming process, which means the extraction of the microgel solution by vacuum, the resulting so-called granular ink could be successfully printed via extrusion-based printing. The widely known challenge of printing living cells was also successfully managed. Cells were encapsulated in the microgels during microgel synthesis. Here, the stirring velocity had to be adjusted to avoid harming the cells during the manufacturing process. The cell-loaded microgels were successfully printed in the same way as the empty microgels in multiple layers resulting in dimensionally stable constructs. Live/dead experiments verified that many viable cells were printable after 24 hours. In the next part of this thesis, microgels were prepared from AGE-functionalized gelatin and thiol-functionalized PEG by the same procedure. Again, cells were incorporated and printed by extrusion-based printing. After the addition of hydroxypropyl-methylcellulose, the right conditions for viable cells and stable constructs were found. The printed constructs were further secondarily crosslinked by immersion in initiator solution after the printing process followed by re-irradiating with light. Hereafter, a strongly increased stability of the constructs could be observed. Microgels for use as cell sensor particles were produced as part of this thesis. Here, microfluidic was applied to prepare microgels with a monodisperse size distribution. After adjusting the oil phase, as well as optimizing the manufacturing parameters to the mucin hydrogel system, the microfluidic setup established by Ilona Paulus in this research group could be used. By setting very fast flow rates, microgels in the size range of cells could be obtained. Furthermore, various parameters affecting the stiffness of the particles were varied. This laid the foundation for follow-up studies within the framework of the SFB TRR225 to be able to produce cellmimicking particles. Further follow-up experiments could include the investigation of hydrogels being based only on mucin, like a crosslinking of thiolated mucin and mucin modified with an allyl function such as the PGM-AGE. Furthermore, the granular mucin ink could serve as a supporting material for other microgels or less stable inks during the printing process and thus expand the field of applicable materials for three dimensional (3D) printing.
The mechanisms underlying the cellular response to extracellular matrices (ECMs) that consist of multiple adhesive ligands are still poorly understood. Here, we address this topic by monitoring specific cellular responses to two different extracellular adhesion molecules – the main integrin ligand fibronectin and galectin-8, a lectin that binds β-galactoside residues − as well as to mixtures of the two proteins. Compared with cell spreading on fibronectin, cell spreading on galectin-8-coated substrates resulted in increased projected cell area, more-pronounced extension of filopodia and, yet, the inability to form focal adhesions and stress fibers. These differences can be partially reversed by experimental manipulations of small G-proteins of the Rho family and their downstream targets, such as formins, the Arp2/3 complex and Rho kinase. We also show that the physical adhesion of cells to galectin-8 was stronger than adhesion to fibronectin. Notably, galectin-8 and fibronectin differently regulate cell spreading and focal adhesion formation, yet act synergistically to upregulate the number and length of filopodia. The physiological significance of the coherent cellular response to a molecularly complex matrix is discussed.
This article has an associated First Person interview with the first author of the paper.
The electrohydrodynamic stabilization of direct-written fluid jets is explored to design and manufacture tissue engineering scaffolds based on their desired fiber dimensions. It is demonstrated that melt electrowriting can fabricate a full spectrum of various fibers with discrete diameters (2–50 µm) using a single nozzle. This change in fiber diameter is digitally controlled by combining the mass flow rate to the nozzle with collector speed variations without changing the applied voltage. The greatest spectrum of fiber diameters was achieved by the simultaneous alteration of those parameters during printing. The highest placement accuracy could be achieved when maintaining the collector speed slightly above the critical translation speed. This permits the fabrication of medical-grade poly(ε-caprolactone) into complex multimodal and multiphasic scaffolds, using a single nozzle in a single print. This ability to control fiber diameter during printing opens new design opportunities for accurate scaffold fabrication for biomedical applications.
One challenge in biofabrication is to fabricate a matrix that is soft enough to elicit optimal cell behavior while possessing the strength required to withstand the mechanical load that the matrix is subjected to once implanted in the body. Here, melt electrowriting (MEW) is used to direct-write poly(ε-caprolactone) fibers “out-of-plane” by design. These out-of-plane fibers are specifically intended to stabilize an existing structure and subsequently improve the shear modulus of hydrogel–fiber composites. The stabilizing fibers (diameter = 13.3 ± 0.3 µm) are sinusoidally direct-written over an existing MEW wall-like structure (330 µm height). The printed constructs are embedded in different hydrogels (5, 10, and 15 wt% polyacrylamide; 65% poly(2-hydroxyethyl methacrylate) (pHEMA)) and a frequency sweep test (0.05–500 rad s−1, 0.01% strain, n = 5) is performed to measure the complex shear modulus. For the rheological measurements, stabilizing fibers are deposited with a radial-architecture prior to embedding to correspond to the direction of the stabilizing fibers with the loading of the rheometer. Stabilizing fibers increase the complex shear modulus irrespective of the percentage of gel or crosslinking density. The capacity of MEW to produce well-defined out-of-plane fibers and the ability to increase the shear properties of fiber-reinforced hydrogel composites are highlighted.
The development of alternatives to vascular bone grafts, the current clinical standard for the surgical repair of large segmental bone defects still today represents an unmet medical need. The subcutaneous formation of transplantable bone has been successfully achieved in scaffolds axially perfused by an arteriovenous loop (AVL) and seeded with bone marrow stromal cells or loaded with inductive proteins. Although demonstrating clinical potential, AVL-based approaches involve complex microsurgical techniques and thus are not in widespread use. In this study, 3D-printed microporous bioceramics, loaded with autologous total bone marrow obtained by needle aspiration, are placed around and next to an unoperated femoral vein for 8 weeks to assess the effect of a central flow-through vein on bone formation from marrow in a subcutaneous site. A greater volume of new bone tissue is observed in scaffolds perfused by a central vein compared with the nonperfused negative control. These analyses are confirmed and supplemented by calcified and decalcified histology. This is highly significant as it indicates that transplantable vascularized bone can be grown using dispensable vein and marrow tissue only. This is the first report illustrating the capacity of an intrinsic vascularization by a single vein to support ectopic bone formation from untreated marrow.
This study approaches the accurate continuous direct-writing onto a cylindrical collector from a mathematical perspective, taking into account the winding angle, cylinder diameter and length required for the final 3D printed tube. Using an additive manufacturing process termed melt electrowriting (MEW), porous tubes intended for tissue engineering applications are fabricated from medical-grade poly(ε-caprolactone) (PCL), validating the mathematically-derived method. For the fabricated tubes in this study, the pore size, winding angle and printed length can all be planned in advance and manufactured as designed. The physical dimensions of the tubes matched theoretical predictions and mechanical testing performed demonstrated that variations in the tubular morphology have a direct impact on their strength. MEWTubes, the web-based application developed and described here, is a particularly useful tool for planning the complex continuous direct writing path required for MEW onto a rotating, cylindrical build surface.
Here, the formation of high surface area microscale assemblies of nanocarbon through phosphate and ultrasound cavitation treatment is reported. Despite high conductivity and large surface area, potential health and safety concerns limit the use of nanocarbon and add challenges to handling. Previously, it is shown that phosphate ultrasonic bonding is ineffective for organic materials but in this study, it is found that by a preliminary oxidizing treatment, several carbons can be readily assembled from xerogels. Assembling nanocarbon into microparticles can usually require a binder or surfactants, which can reduce surface area or conductivity and generate a low microsphere yield. Carbon nanotube microspheres are nitrogen-doped and flower-like nanostructured Pt deposited on their surface, and finally showcased as efficient cathode electrocatalysts for the oxygen reduction reaction (half-wave potential 0.78 V vs reversible hydrogen electrode) and methanol oxidation (417 mA mg−1). In particular, no significant degradation of the catalysts is detected after 12 000 cycles (26.6 h). These results indicate the potential of this multimaterial assembly method and open a new way to improve handling of nanoscale materials.