@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{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{StuckensenLamoEspinosaMuinosLopezetal.2019,
  author    = {Stuckensen, Kai and Lamo-Espinosa, Jos{\´e} M. and Mui{\~n}os-L{\´o}pez, Emma and Ripalda-Cembor{\´a}in, Purificaci{\´o}n and L{\´o}pez-Mart{\´i}nez, Tania and Iglesias, Elena and Abizanda, Gloria and Andreu, Ion and Flandes-Iparraguirre, Mar{\´i}a and Pons-Villanueva, Juan and Elizalde, Reyes and Nickel, Joachim and Ewald, Andrea and Gbureck, Uwe and Pr{\´o}sper, Felipe and Groll, J{\"u}rgen and Granero-Molt{\´o}, Froil{\´a}n},
  title     = {Anisotropic cryostructured collagen scaffolds for efficient delivery of RhBMP-2 and enhanced bone regeneration},
  series = {Materials},
  volume    = {12},
  journal   = {Materials},
  number    = {19},
  issn      = {1996-1944},
  doi       = {10.3390/ma12193105},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-195966},
  year      = {2019},
  abstract  = {In the treatment of bone non-unions, an alternative to bone autografts is the use of bone morphogenetic proteins (BMPs), e.g., BMP-2, BMP-7, with powerful osteoinductive and osteogenic properties. In clinical settings, these osteogenic factors are applied using absorbable collagen sponges for local controlled delivery. Major side effects of this strategy are derived from the supraphysiological doses of BMPs needed, which may induce ectopic bone formation, chronic inflammation, and excessive bone resorption. In order to increase the efficiency of the delivered BMPs, we designed cryostructured collagen scaffolds functionalized with hydroxyapatite, mimicking the structure of cortical bone (aligned porosity, anisotropic) or trabecular bone (random distributed porosity, isotropic). We hypothesize that an anisotropic structure would enhance the osteoconductive properties of the scaffolds by increasing the regenerative performance of the provided rhBMP-2. In vitro, both scaffolds presented similar mechanical properties, rhBMP-2 retention and delivery capacity, as well as scaffold degradation time. In vivo, anisotropic scaffolds demonstrated better bone regeneration capabilities in a rat femoral critical-size defect model by increasing the defect bridging. In conclusion, anisotropic cryostructured collagen scaffolds improve bone regeneration by increasing the efficiency of rhBMP-2 mediated bone healing.},
  language  = {en}
}
@article{GrollBurdickChoetal.2019,
  author    = {Groll, J and Burdick, J A and Cho, D-W and Derby, B and Gelinsky, M and Heilshorn, S C and J{\"u}ngst, T and Malda, J and Mironov, V A and Nakayama, K and Ovsianikov, A and Sun, W and Takeuchi, S and Yoo, J J and Woodfield, T B F},
  title     = {A definition of bioinks and their distinction from biomaterial inks},
  series = {Biofabrication},
  volume    = {11},
  journal   = {Biofabrication},
  number    = {1},
  doi       = {10.1088/1758-5090/aaec52},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-253993},
  year      = {2019},
  abstract  = {Biofabrication aims to fabricate biologically functional products through bioprinting or bioassembly (Groll et al 2016 Biofabrication 8 013001). In biofabrication processes, cells are positioned at defined coordinates in three-dimensional space using automated and computer controlled techniques (Moroni et al 2018 Trends Biotechnol. 36 384-402), usually with the aid of biomaterials that are either (i) directly processed with the cells as suspensions/dispersions, (ii) deposited simultaneously in a separate printing process, or (iii) used as a transient support material. Materials that are suited for biofabrication are often referred to as bioinks and have become an important area of research within the field. In view of this special issue on bioinks, we aim herein to briefly summarize the historic evolution of this term within the field of biofabrication. Furthermore, we propose a simple but general definition of bioinks, and clarify its distinction from biomaterial inks.},
  language  = {en}
}
@unpublished{SchaeferJanzenBakircietal.2019,
  author    = {Schaefer, Natascha and Janzen, Dieter and Bakirci, Ezgi and Hrynevich, Andrei and Dalton, Paul D. and Villmann, Carmen},
  title     = {3D Electrophysiological Measurements on Cells Embedded within Fiber-Reinforced Matrigel},
  series = {Advanced Healthcare Materials},
  journal   = {Advanced Healthcare Materials},
  doi       = {10.1002/adhm.201801226},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244194},
  year      = {2019},
  abstract  = {2D electrophysiology is often used to determine the electrical properties of neurons, while in the brain, neurons form extensive 3D networks. Thus, performing electrophysiology in a 3D environment provides a closer situation to the physiological condition and serves as a useful tool for various applications in the field of neuroscience. In this study, we established 3D electrophysiology within a fiber-reinforced matrix to enable fast readouts from transfected cells, which are often used as model systems for 2D electrophysiology. Using melt electrowriting (MEW) of scaffolds to reinforce Matrigel, we performed 3D electrophysiology on a glycine receptor-transfected Ltk-11 mouse fibroblast cell line. The glycine receptor is an inhibitory ion channel associated when mutated with impaired neuromotor behaviour. The average thickness of the MEW scaffold was 141.4 ± 5.7µm, using 9.7 ± 0.2µm diameter fibers, and square pore spacings of 100 µm, 200 µm and 400 µm. We demonstrate, for the first time, the electrophysiological characterization of glycine receptor-transfected cells with respect to agonist efficacy and potency in a 3D matrix. With the MEW scaffold reinforcement not interfering with the electrophysiology measurement, this approach can now be further adapted and developed for different kinds of neuronal cultures to study and understand pathological mechanisms under disease conditions.},
  language  = {en}
}
@article{NoHolzmeisterLuetal.2019,
  author    = {No, Young Jung and Holzmeister, Ib and Lu, Zufu and Prajapati, Shubham and Shi, Jeffrey and Gbureck, Uwe and Zreiqat, Hala},
  title     = {Effect of Baghdadite Substitution on the Physicochemical Properties of Brushite Cements},
  series = {Materials},
  volume    = {12},
  journal   = {Materials},
  number    = {10},
  issn      = {1996-1944},
  doi       = {10.3390/ma12101719},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-196980},
  year      = {2019},
  abstract  = {Brushite cements have been clinically used for irregular bone defect filling applications, and various strategies have been previously reported to modify and improve their physicochemical properties such as strength and injectability. However, strategies to address other limitations of brushite cements such as low radiopacity or acidity without negatively impacting mechanical strength have not yet been reported. In this study, we report the effect of substituting the beta-tricalcium phosphate reactant in brushite cement with baghdadite (Ca\(_3\)ZrSi\(_2\)O\(_9\)), a bioactive zirconium-doped calcium silicate ceramic, at various concentrations (0, 5, 10, 20, 30, 50, and 100 wt\%) on the properties of the final brushite cement product. X-ray diffraction profiles indicate the dissolution of baghdadite during the cement reaction, without affecting the crystal structure of the precipitated brushite. EDX analysis shows that calcium is homogeneously distributed within the cement matrix, while zirconium and silicon form cluster-like aggregates with sizes ranging from few microns to more than 50 µm. X-ray images and µ-CT analysis indicate enhanced radiopacity with increased incorporation of baghdadite into brushite cement, with nearly a doubling of the aluminium equivalent thickness at 50 wt\% baghdadite substitution. At the same time, compressive strength of brushite cement increased from 12.9 ± 3.1 MPa to 21.1 ± 4.1 MPa with 10 wt\% baghdadite substitution. Culture medium conditioned with powdered brushite cement approached closer to physiological pH values when the cement is incorporated with increasing amounts of baghdadite (pH = 6.47 for pure brushite, pH = 7.02 for brushite with 20 wt\% baghdadite substitution). Baghdadite substitution also influenced the ionic content in the culture medium, and subsequently affected the proliferative activity of primary human osteoblasts in vitro. This study indicates that baghdadite is a beneficial additive to enhance the radiopacity, mechanical performance and cytocompatibility of brushite cement},
  language  = {en}
}
@article{JungstPenningsSchmitzetal.2019,
  author    = {Jungst, Tomasz and Pennings, Iris and Schmitz, Michael and Rosenberg, Antoine J. W. P. and Groll, J{\"u}rgen and Gawlitta, Debby},
  title     = {Heterotypic Scaffold Design Orchestrates Primary Cell Organization and Phenotypes in Cocultured Small Diameter Vascular Grafts},
  series = {Advanced Functional Materials},
  volume    = {29},
  journal   = {Advanced Functional Materials},
  doi       = {10.1002/adfm.201905987},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217039},
  year      = {2019},
  abstract  = {To facilitate true regeneration, a vascular graft should direct the evolution of a neovessel to obtain the function of a native vessel. For this, scaffolds have to permit the formation of an intraluminal endothelial cell monolayer, mimicking the tunica intima. In addition, when attempting to mimic a tunica media-like outer layer, the stacking and orientation of vascular smooth muscle cells (vSMCs) should be recapitulated. An integral scaffold design that facilitates this has so far remained a challenge. A hybrid fabrication approach is introduced by combining solution electrospinning and melt electrowriting. This allows a tissue-structure mimetic, hierarchically bilayered tubular scaffold, comprising an inner layer of randomly oriented dense fiber mesh and an outer layer of microfibers with controlled orientation. The scaffold supports the organization of a continuous luminal endothelial monolayer and oriented layers of vSM-like cells in the media, thus facilitating control over specific and tissue-mimetic cellular differentiation and support of the phenotypic morphology in the respective layers. Neither soluble factors nor a surface bioactivation of the scaffold is needed with this approach, demonstrating that heterotypic scaffold design can direct physiological tissue-like cell organization and differentiation.},
  language  = {en}
}
@article{BruecknerMeiningerGrolletal.2019,
  author    = {Br{\"u}ckner, Theresa and Meininger, Markus and Groll, J{\"u}rgen and K{\"u}bler, Alexander C. and Gbureck, Uwe},
  title     = {Magnesium Phosphate Cement as Mineral Bone Adhesive},
  series = {Materials},
  volume    = {12},
  journal   = {Materials},
  number    = {23},
  issn      = {1996-1944},
  doi       = {10.3390/ma12233819},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-193052},
  year      = {2019},
  abstract  = {Mineral bone cements were actually not developed for their application as bone-bonding agents, but as bone void fillers. In particular, calcium phosphate cements (CPC) are considered to be unsuitable for that application, particularly under moist conditions. Here, we showed the ex vivo ability of different magnesium phosphate cements (MPC) to adhere on bovine cortical bone substrates. The cements were obtained from a mixture of farringtonite (Mg\(_3\)(PO\(_4\))\(_2\)) with different amounts of phytic acid (C\(_6\)H\(_{18}\)O\(_{24}\)P\(_6\), inositol hexaphosphate, IP6), whereas cement setting occurred by a chelation reaction between Mg\(^{2+}\) ions and IP6. We were able to show that cements with 25\% IP6 and a powder-to-liquid ratio (PLR) of 2.0 g/mL resulted in shear strengths of 0.81 ± 0.12 MPa on bone even after 7 d storage in aqueous conditions. The samples showed a mixed adhesive-cohesive failure with cement residues on the bone surface as indicated by scanning electron microscopy and energy-dispersive X-ray analysis. The presented material demonstrated appropriate bonding characteristics, which could enable a broadening of the mineral bone cements' application field to bone adhesives},
  language  = {en}
}
@article{HettichSchierjottEppleetal.2019,
  author    = {Hettich, Georg and Schierjott, Ronja A. and Epple, Matthias and Gbureck, Uwe and Heinemann, Sascha and Mozaffari-Jovein, Hadi and Grupp, Thomas M.},
  title     = {Calcium phosphate bone graft substitutes with high mechanical load capacity and high degree of interconnecting porosity},
  series = {Materials},
  volume    = {12},
  journal   = {Materials},
  number    = {21},
  issn      = {1996-1944},
  doi       = {10.3390/ma12213471},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-193233},
  pages     = {3471},
  year      = {2019},
  abstract  = {Bone graft substitutes in orthopedic applications have to fulfill various demanding requirements. Most calcium phosphate (CaP) bone graft substitutes are highly porous to achieve bone regeneration, but typically lack mechanical stability. This study presents a novel approach, in which a scaffold structure with appropriate properties for bone regeneration emerges from the space between specifically shaped granules. The granule types were tetrapods (TEPO) and pyramids (PYRA), which were compared to porous CaP granules (CALC) and morselized bone chips (BC). Bulk materials of the granules were mechanically loaded with a peak pressure of 4 MP; i.e., comparable to the load occurring behind an acetabular cup. Mechanical loading reduced the volume of CALC and BC considerably (89\% and 85\%, respectively), indicating a collapse of the macroporous structure. Volumes of TEPO and PYRA remained almost constant (94\% and 98\%, respectively). After loading, the porosity was highest for BC (46\%), lowest for CALC (25\%) and comparable for TEPO and PYRA (37\%). The pore spaces of TEPO and PYRA were highly interconnected in a way that a virtual object with a diameter of 150 µm could access 34\% of the TEPO volume and 36\% of the PYRA volume. This study shows that a bulk of dense CaP granules in form of tetrapods and pyramids can create a scaffold structure with load capacities suitable for the regeneration of an acetabular bone defect},
  language  = {en}
}
@article{RobinsonHutmacherDalton2019,
  author    = {Robinson, Thomas M. and Hutmacher, Dietmar W. and Dalton, Paul D.},
  title     = {The next frontier in melt electrospinning: taming the jet},
  series = {Advanced Functional Materials},
  volume    = {29},
  journal   = {Advanced Functional Materials},
  doi       = {10.1002/adfm.201904664},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204819},
  pages     = {1904664},
  year      = {2019},
  abstract  = {There is a specialized niche for the electrohydrodynamic jetting of melts, from biomedical products to filtration and soft matter applications. The next frontier includes optics, microfluidics, flexible electronic devices, and soft network composites in biomaterial science and soft robotics. The recent emphasis on reproducibly direct-writing continual molten jets has enabled a spectrum of contemporary microscale 3D objects to be fabricated. One strong suit of melt processing is the capacity for the jet to solidify rapidly into a fiber, thus fixing a particular structure into position. The ability to direct-write complex and multiscaled architectures and structures has greatly contributed to a large number of recent studies, explicitly, toward fiber-hydrogel composites and fugitive inks, and has expanded into several biomedical applications such as cartilage, skin, periosteum, and cardiovascular tissue engineering. Following the footsteps of a publication that summarized melt electrowriting literature up to 2015, the most recent literature from then until now is reviewed to provide a continuous and comprehensive timeline that demonstrates the latest advances as well as new perspectives for this emerging technology.},
  language  = {en}
}