@article{CastilhoHochleitnerWilsonetal.2018, author = {Castilho, Miguel and Hochleitner, Gernot and Wilson, Wouter and van Rietbergen, Bert and Dalton, Paul D. and Groll, J{\"u}rgen and Malda, Jos and Ito, Keita}, title = {Mechanical behavior of a soft hydrogel reinforced with three-dimensional printed microfibre scaffolds}, series = {Scientific Reports}, volume = {8}, journal = {Scientific Reports}, doi = {10.1038/s41598-018-19502-y}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-222280}, year = {2018}, abstract = {Reinforcing hydrogels with micro-fibre scaffolds obtained by a Melt-Electrospinning Writing (MEW) process has demonstrated great promise for developing tissue engineered (TE) constructs with mechanical properties compatible to native tissues. However, the mechanical performance and reinforcement mechanism of the micro-fibre reinforced hydrogels is not yet fully understood. In this study, FE models, implementing material properties measured experimentally, were used to explore the reinforcement mechanism of fibre-hydrogel composites. First, a continuum FE model based on idealized scaffold geometry was used to capture reinforcement effects related to the suppression of lateral gel expansion by the scaffold, while a second micro-FE model based on micro-CT images of the real construct geometry during compaction captured the effects of load transfer through the scaffold interconnections. Results demonstrate that the reinforcement mechanism at higher scaffold volume fractions was dominated by the load carrying-ability of the fibre scaffold interconnections, which was much higher than expected based on testing scaffolds alone because the hydrogel provides resistance against buckling of the scaffold. We propose that the theoretical understanding presented in this work will assist the design of more effective composite constructs with potential applications in a wide range of TE conditions.}, language = {en} } @article{RymaGencNadernezhadetal.2022, author = {Ryma, Matthias and Gen{\c{c}}, Hatice and Nadernezhad, Ali and Paulus, Ilona and Schneidereit, Dominik and Friedrich, Oliver and Andelovic, Kristina and Lyer, Stefan and Alexiou, Christoph and Cicha, Iwona and Groll, J{\"u}rgen}, title = {A Print-and-Fuse Strategy for Sacrificial Filaments Enables Biomimetically Structured Perfusable Microvascular Networks with Functional Endothelium Inside 3D Hydrogels}, series = {Advanced Materials}, volume = {34}, journal = {Advanced Materials}, number = {28}, doi = {10.1002/adma.202200653}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318532}, year = {2022}, abstract = {A facile and flexible approach for the integration of biomimetically branched microvasculature within bulk hydrogels is presented. For this, sacrificial scaffolds of thermoresponsive poly(2-cyclopropyl-2-oxazoline) (PcycloPrOx) are created using melt electrowriting (MEW) in an optimized and predictable way and subsequently placed into a customized bioreactor system, which is then filled with a hydrogel precursor solution. The aqueous environment above the lower critical solution temperature (LCST) of PcycloPrOx at 25 °C swells the polymer without dissolving it, resulting in fusion of filaments that are deposited onto each other (print-and-fuse approach). Accordingly, an adequate printing pathway design results in generating physiological-like branchings and channel volumes that approximate Murray's law in the geometrical ratio between parent and daughter vessels. After gel formation, a temperature decrease below the LCST produces interconnected microchannels with distinct inlet and outlet regions. Initial placement of the sacrificial scaffolds in the bioreactors in a pre-defined manner directly yields perfusable structures via leakage-free fluid connections in a reproducible one-step procedure. Using this approach, rapid formation of a tight and biologically functional endothelial layer, as assessed not only through fluorescent dye diffusion, but also by tumor necrosis factor alpha (TNF-α) stimulation, is obtained within three days.}, language = {en} } @article{WeiglBlumSanchoetal.2022, author = {Weigl, Franziska and Blum, Carina and Sancho, Ana and Groll, J{\"u}rgen}, title = {Correlative Analysis of Intra- Versus Extracellular Cell Detachment Events via the Alignment of Optical Imaging and Detachment Force Quantification}, series = {Advanced Materials Technologies}, volume = {7}, journal = {Advanced Materials Technologies}, number = {11}, issn = {2365-709X}, doi = {10.1002/admt.202200195}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318544}, year = {2022}, abstract = {In recent decades, hybrid characterization systems have become pillars in the study of cellular biomechanics. Especially, Atomic Force Microscopy (AFM) is combined with a variety of optical microscopy techniques to discover new aspects of cell adhesion. AFM, however, is limited to the early-stage of cell adhesion, so that the forces of mature cell contacts cannot be addressed. Even though the invention of Fluidic Force Microscopy (FluidFM) overcomes these limitations by combining the precise force-control of AFM with microfluidics, the correlative investigation of detachment forces arising from spread mammalian cells has been barely achieved. Here, a novel multifunctional device integrating Fluorescence Microscopy (FL) into FluidFM technology (FL-FluidFM) is introduced, enabling real-time optical tracking of entire cell detachment processes in parallel to the undisturbed acquisition of force-distance curves. This setup, thus, allows for entailing two pieces of information at once. As proof-of-principle experiment, this method is applied to fluorescently labeled rat embryonic fibroblast (REF52) cells, demonstrating a precise matching between identified force-jumps and visualized cellular unbinding steps. This study, thus, presents a novel characterization tool for the correlated evaluation of mature cell adhesion, which has great relevance, for instance, in the development of biomaterials or the fight against diseases such as cancer.}, language = {en} } @article{BrandForsterBoecketal.2022, author = {Brand, Jessica S. and Forster, Leonard and B{\"o}ck, Thomas and Stahlhut, Philipp and Teßmar, J{\"o}rg and Groll, J{\"u}rgen and Albrecht, Krystyna}, title = {Covalently Cross-Linked Pig Gastric Mucin Hydrogels Prepared by Radical-Based Chain-Growth and Thiol-ene Mechanisms}, series = {Macromolecular Bioscience}, volume = {22}, journal = {Macromolecular Bioscience}, number = {4}, doi = {10.1002/mabi.202100274}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318453}, year = {2022}, abstract = {Mucin, a high molecular mass hydrophilic glycoprotein, is the main component of mucus that coats every wet epithelium in animals. It is thus intrinsically biocompatible, and with its protein backbone and the o-glycosidic bound oligosaccharides, it contains a plethora of functional groups which can be used for further chemical modifications. Here, chain-growth and step-growth (thiol-ene) free-radical cross-linked hydrogels prepared from commercially available pig gastric mucin (PGM) are introduced and compared as cost-efficient and easily accessible alternative to the more broadly applied bovine submaxillary gland mucin. For this, PGM is functionalized with photoreactive acrylate groups or allyl ether moieties, respectively. Whereas homopolymerization of acrylate-functionalized polymers is performed, for thiol-ene cross-linking, the allyl-ether-functionalized PGM is cross-linked with thiol-functionalized hyaluronic acid. Morphology, mechanical properties, and cell compatibility of both kinds of PGM hydrogels are characterized and compared. Furthermore, the biocompatibility of these hydrogels can be evaluated in cell culture experiments.}, language = {en} } @article{BotheDeubelHesseetal.2019, author = {Bothe, Friederike and Deubel, Anne-Kathrin and Hesse, Eliane and Lotz, Benedict and Groll, J{\"u}rgen and Werner, Carsten and Richter, Wiltrud and Hagmann, Sebastien}, title = {Treatment of focal cartilage defects in minipigs with zonal chondrocyte/mesenchymal progenitor cell constructs}, series = {International Journal of Molecular Sciences}, volume = {20}, journal = {International Journal of Molecular Sciences}, number = {3}, issn = {1422-0067}, doi = {10.3390/ijms20030653}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-285118}, year = {2019}, abstract = {Despite advances in cartilage repair strategies, treatment of focal chondral lesions remains an important challenge to prevent osteoarthritis. Articular cartilage is organized into several layers and lack of zonal organization of current grafts is held responsible for insufficient biomechanical and biochemical quality of repair-tissue. The aim was to develop a zonal approach for cartilage regeneration to determine whether the outcome can be improved compared to a non-zonal strategy. Hydrogel-filled polycaprolactone (PCL)-constructs with a chondrocyte-seeded upper-layer deemed to induce hyaline cartilage and a mesenchymal stromal cell (MSC)-containing bottom-layer deemed to induce calcified cartilage were compared to chondrocyte-based non-zonal grafts in a minipig model. Grafts showed comparable hardness at implantation and did not cause visible signs of inflammation. After 6 months, X-ray microtomography (µCT)-analysis revealed significant bone-loss in both treatment groups compared to empty controls. PCL-enforcement and some hydrogel-remnants were retained in all defects, but most implants were pressed into the subchondral bone. Despite important heterogeneities, both treatments reached a significantly lower modified O'Driscoll-score compared to empty controls. Thus, PCL may have induced bone-erosion during joint loading and misplacement of grafts in vivo precluding adequate permanent orientation of zones compared to surrounding native cartilage.}, language = {en} } @article{HaiderAhmadYangetal.2021, author = {Haider, Malik Salman and Ahmad, Taufiq and Yang, Mengshi and Hu, Chen and Hahn, Lukas and Stahlhut, Philipp and Groll, J{\"u}rgen and Luxenhofer, Robert}, title = {Tuning the thermogelation and rheology of poly(2-oxazoline)/poly(2-oxazine)s based thermosensitive hydrogels for 3D bioprinting}, series = {Gels}, volume = {7}, journal = {Gels}, number = {3}, issn = {2310-2861}, doi = {10.3390/gels7030078}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-241781}, year = {2021}, abstract = {As one kind of "smart" material, thermogelling polymers find applications in biofabrication, drug delivery and regenerative medicine. In this work, we report a thermosensitive poly(2-oxazoline)/poly(2-oxazine) based diblock copolymer comprising thermosensitive/moderately hydrophobic poly(2-N-propyl-2-oxazine) (pPrOzi) and thermosensitive/moderately hydrophilic poly(2-ethyl-2-oxazoline) (pEtOx). Hydrogels were only formed when block length exceeded certain length (≈100 repeat units). The tube inversion and rheological tests showed that the material has then a reversible sol-gel transition above 25 wt.\% concentration. Rheological tests further revealed a gel strength around 3 kPa, high shear thinning property and rapid shear recovery after stress, which are highly desirable properties for extrusion based three-dimensional (3D) (bio) printing. Attributed to the rheology profile, well resolved printability and high stackability (with added laponite) was also possible. (Cryo) scanning electron microscopy exhibited a highly porous, interconnected, 3D network. The sol-state at lower temperatures (in ice bath) facilitated the homogeneous distribution of (fluorescently labelled) human adipose derived stem cells (hADSCs) in the hydrogel matrix. Post-printing live/dead assays revealed that the hADSCs encapsulated within the hydrogel remained viable (≈97\%). This thermoreversible and (bio) printable hydrogel demonstrated promising properties for use in tissue engineering applications.}, language = {en} } @article{RoedelTessmarGrolletal.2019, author = {R{\"o}del, Michaela and Teßmar, J{\"o}rg and Groll, J{\"u}rgen and Gbureck, Uwe}, title = {Tough and Elastic alpha-Tricalcium Phosphate Cement Composites with Degradable PEG-Based Cross-Linker}, series = {Materials}, volume = {12}, journal = {Materials}, number = {53}, doi = {10.3390/ma12010053}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226437}, pages = {1-20}, year = {2019}, abstract = {Dual setting cements composed of an in situ forming hydrogel and a reactive mineral phase combine high compressive strength of the cement with sufficient ductility and bending strength of the polymeric network. Previous studies were focused on the modification with non-degradable hydrogels based on 2-hydroxyethyl methacrylate (HEMA). Here, we describe the synthesis of suitable triblock degradable poly(ethylene glycol)-poly(lactide) (PEG-PLLA) cross-linker to improve the resorption capacity of such composites. A study with four different formulations was established. As reference, pure hydroxyapatite (HA) cements and composites with 40 wt\% HEMA in the liquid cement phase were produced. Furthermore, HEMA was modified with 10 wt\% of PEG-PLLA cross-linker or a test series containing only 25\% cross-linker was chosen for composites with a fully degradable polymeric phase. Hence, we developed suitable systems with increased elasticity and 5-6 times higher toughn ess values in comparison to pure inorganic cement matrix. Furthermore, conversion rate from alpha-tricalcium phosphate (alpha-TCP) to HA was still about 90\% for all composite formulations, whereas crystal size decreased. Based on this material development and advancement for a dual setting system, we managed to overcome the drawback of brittleness for pure calcium phosphate cements.}, language = {en} } @article{RoedelBaumannGrolletal.2018, author = {R{\"o}del, Michaela and Baumann, Katrin and Groll, J{\"u}rgen and Gbureck, Uwe}, title = {Simultaneous structuring and mineralization of silk fibroin scaffolds}, series = {Journal of Tissue Engineering}, volume = {9}, journal = {Journal of Tissue Engineering}, doi = {10.1177/2041731418788509}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226427}, pages = {1-16}, year = {2018}, abstract = {Silk fibroin is commonly used as scaffold material for tissue engineering applications. In combination with a mineralization with different calcium phosphate phases, it can also be applied as material for bone regeneration. Here, we present a study which was performed to produce mineralized silk fibroin scaffolds with controlled macroporosity. In contrast to former studies, our approach focused on a simultaneous gelation and mineralization of silk fibroin by immersion of frozen silk fibroin monoliths in acidic calcium phosphate solutions. This was achieved by thawing frozen silk fibroin monoliths in acidic calcium phosphate solution, leading to the precipitation of monocalcium phosphate within the silk fibroin matrix. In the second approach, a conversion of incorporated -tricalcium phosphate particles into brushite was successfully achieved. Furthermore, a controlled cryostructuring process of silk fibroin scaffolds was carried out leading to the formation of parallel-oriented pores with diameters of 30-50 mu m.}, language = {en} } @article{HauptsteinForsterNadernezhadetal.2022, author = {Hauptstein, Julia and Forster, Leonard and Nadernezhad, Ali and Groll, J{\"u}rgen and Teßmar, J{\"o}rg and Blunk, Torsten}, title = {Tethered TGF-β1 in a hyaluronic acid-based bioink for bioprinting cartilaginous tissues}, series = {International Journal of Molecular Sciences}, volume = {23}, journal = {International Journal of Molecular Sciences}, number = {2}, issn = {1422-0067}, doi = {10.3390/ijms23020924}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-284239}, year = {2022}, abstract = {In 3D bioprinting for cartilage regeneration, bioinks that support chondrogenic development are of key importance. Growth factors covalently bound in non-printable hydrogels have been shown to effectively promote chondrogenesis. However, studies that investigate the functionality of tethered growth factors within 3D printable bioinks are still lacking. Therefore, in this study, we established a dual-stage crosslinked hyaluronic acid-based bioink that enabled covalent tethering of transforming growth factor-beta 1 (TGF-β1). Bone marrow-derived mesenchymal stromal cells (MSCs) were cultured over three weeks in vitro, and chondrogenic differentiation of MSCs within bioink constructs with tethered TGF-β1 was markedly enhanced, as compared to constructs with non-covalently incorporated TGF-β1. This was substantiated with regard to early TGF-β1 signaling, chondrogenic gene expression, qualitative and quantitative ECM deposition and distribution, and resulting construct stiffness. Furthermore, it was successfully demonstrated, in a comparative analysis of cast and printed bioinks, that covalently tethered TGF-β1 maintained its functionality after 3D printing. Taken together, the presented ink composition enabled the generation of high-quality cartilaginous tissues without the need for continuous exogenous growth factor supply and, thus, bears great potential for future investigation towards cartilage regeneration. Furthermore, growth factor tethering within bioinks, potentially leading to superior tissue development, may also be explored for other biofabrication applications.}, language = {en} } @article{HaiderAhmadGrolletal.2021, author = {Haider, Malik Salman and Ahmad, Taufiq and Groll, J{\"u}rgen and Scherf-Clavel, Oliver and Kroiss, Matthias and Luxenhofer, Robert}, title = {The Challenging Pharmacokinetics of Mitotane: An Old Drug in Need of New Packaging}, series = {European Journal of Drug Metabolism and Pharmacokinetics}, volume = {46}, journal = {European Journal of Drug Metabolism and Pharmacokinetics}, number = {5}, issn = {2107-0180}, doi = {10.1007/s13318-021-00700-5}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-270476}, pages = {575-593}, year = {2021}, abstract = {Adrenocortical carcinoma (ACC) is a malignant tumor originating from the adrenal gland cortex with a heterogeneous but overall dismal prognosis in advanced stages. For more than 50 years, mitotane has remained a cornerstone for the treatment of ACC as adjuvant and palliative therapy. It has a very poor aqueous solubility of 0.1 mg/l and high partition coefficient in octanol/water (log P) value of 6. The commercially available dosage form is 500 mg tablets (Lysodren®). Even at doses up to 6 g/day (12 tablets in divided doses) for several months, > 50\% patients do not achieve therapeutic plasma concentration > 14 mg/l due to poor water solubility, large volume of distribution and inter/intra-individual variability in bioavailability. This article aims to give a concise update of the clinical challenges associated with the administration of high-dose mitotane oral therapy which encompass the issues of poor bioavailability, difficult-to-predict pharmacokinetics and associated adverse events. Moreover, we present recent efforts to improve mitotane formulations. Their success has been limited, and we therefore propose an injectable mitotane formulation instead of oral administration, which could bypass many of the main issues associated with high-dose oral mitotane therapy. A parenteral administration of mitotane could not only help to alleviate the adverse effects but also circumvent the variable oral absorption, give better control over therapeutic plasma mitotane concentration and potentially shorten the time to achieve therapeutic drug plasma concentrations considerably. Mitotane as tablet form is currently the standard treatment for adrenocortical carcinoma. It has been used for 5 decades but suffers from highly variable responses in patients, subsequent adverse effects and overall lower response rate. This can be fundamentally linked to the exceedingly poor water solubility of mitotane itself. In terms of enhancing water solubility, a few research groups have attempted to develop better formulations of mitotane to overcome the issues associated with tablet dosage form. However, the success rate was limited, and these formulations did not make it into the clinics. In this article, we have comprehensively reviewed the properties of these formulations and discuss the reasons for their limited utility. Furthermore, we discuss a recently developed mitotane nanoformulation that led us to propose a novel approach to mitotane therapy, where intravenous delivery supplements the standard oral administration. With this article, we combine the current state of knowledge as a single piece of information about the various problems associated with the use of mitotane tablets, and herein we postulate the development of a new injectable mitotane formulation, which can potentially circumvent the major problems associated to mitotane's poor water solubility.}, language = {en} }