@article{GeffersGrollGbureck2015,
  author    = {Geffers, Martha and Groll, J{\"u}rgen and Gbureck, Uwe},
  title     = {Reinforcement strategies for load-bearing calcium phosphate biocements},
  series = {Materials},
  volume    = {8},
  journal   = {Materials},
  doi       = {10.3390/ma8052700},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-148636},
  pages     = {2700-2717},
  year      = {2015},
  abstract  = {Calcium phosphate biocements based on calcium phosphate chemistry are well-established biomaterials for the repair of non-load bearing bone defects due to the brittle nature and low flexural strength of such cements. This article features reinforcement strategies of biocements based on various intrinsic or extrinsic material modifications to improve their strength and toughness. Altering particle size distribution in conjunction with using liquefiers reduces the amount of cement liquid necessary for cement paste preparation. This in turn decreases cement porosity and increases the mechanical performance, but does not change the brittle nature of the cements. The use of fibers may lead to a reinforcement of the matrix with a toughness increase of up to two orders of magnitude, but restricts at the same time cement injection for minimal invasive application techniques. A novel promising approach is the concept of dual-setting cements, in which a second hydrogel phase is simultaneously formed during setting, leading to more ductile cement-hydrogel composites with largely unaffected application properties.},
  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{SeifertGruberGburecketal.2021,
  author    = {Seifert, Annika and Gruber, Julia and Gbureck, Uwe and Groll, J{\"u}rgen},
  title     = {Morphological control of freeze-structured scaffolds by selective temperature and material control in the ice-templating process},
  series = {Advanced Engineering Materials},
  volume    = {24},
  journal   = {Advanced Engineering Materials},
  number    = {3},
  doi       = {10.1002/adem.202100860},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256330},
  year      = {2021},
  abstract  = {Herein, it is aimed to highlight the importance of the process parameter choice during directional solidification of polymer solutions, as they have a significant influence on the pore structure and orientation. Biopolymer solutions (alginate and chitosan) are directionally frozen, while systematically varying parameters such as the external temperature gradient, the temperature of the overall system, and the temperatures of the cooling surfaces. In addition, the effect of material properties such as molecular weight, solution concentration, or viscosity on the sample morphology is investigated. By selecting appropriate temperature gradients and cooling surface temperatures, aligned pores ranging in size between (50 ± 22) μm and (144 ± 56) μm are observed in the alginate samples, whereas the pore orientation is influenced by altering the external temperature gradient. As this gradient increases, the pores are increasingly oriented perpendicular to the sample surface. This is also observed in the chitosan samples. However, if the overall system is too cold, that is, using temperatures of the lower cooling surface down to -60 °C combined with low temperatures of the upper cooling surface, control over pore orientation is lost. This is also found when viscosity of chitosan solutions is above ≈5 Pas near the freezing point.},
  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{HolzmeisterWeichholdGrolletal.2021,
  author    = {Holzmeister, Ib and Weichhold, Jan and Groll, J{\"u}rgen and Zreiqat,, Hala and Gbureck, Uwe},
  title     = {Hydraulic reactivity and cement formation of baghdadite},
  series = {Journal of the American Ceramic Society},
  volume    = {104},
  journal   = {Journal of the American Ceramic Society},
  number    = {7},
  doi       = {10.1111/jace.17727},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-259457},
  pages     = {3554-3561},
  year      = {2021},
  abstract  = {In this study, the hydraulic reactivity and cement formation of baghdadite (Ca\(_{3}\)ZrSi\(_{2}\)O\(_{9}\)) was investigated. The material was synthesized by sintering a mixture of CaCO\(_{3}\), SiO\(_{2}\), and ZrO\(_{2}\) and then mechanically activated using a planetary mill. This leads to a decrease in particle and crystallite size and a partial amorphization of baghdadite as shown by X-ray powder diffraction (XRD) and laser diffraction measurements. Baghdadite cements were formed by the addition of water at a powder to liquid ratio of 2.0 g/ml. Maximum compressive strengths were found to be ~2 MPa after 3-day setting for a 24-h ground material. Inductively coupled plasma mass spectrometry (ICP-MS) measurements showed an incongruent dissolution profile of set cements with a preferred dissolution of calcium and only marginal release of zirconium ions. Cement formation occurs under alkaline conditions, whereas the unground raw powder leads to a pH of 11.9 during setting, while prolonged grinding increased pH values to approximately 12.3.},
  language  = {en}
}
@article{GoetzHoleczekGrolletal.2021,
  author    = {G{\"o}tz, Lisa-Marie and Holeczek, Katharina and Groll, J{\"u}rgen and J{\"u}ngst, Tomasz and Gbureck, Uwe},
  title     = {Extrusion-Based 3D Printing of Calcium Magnesium Phosphate Cement Pastes for Degradable Bone Implants},
  series = {Materials},
  volume    = {14},
  journal   = {Materials},
  number    = {18},
  issn      = {1996-1944},
  doi       = {10.3390/ma14185197},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-246110},
  year      = {2021},
  abstract  = {This study aimed to develop printable calcium magnesium phosphate pastes that harden by immersion in ammonium phosphate solution post-printing. Besides the main mineral compound, biocompatible ceramic, magnesium oxide and hydroxypropylmethylcellulose (HPMC) were the crucial components. Two pastes with different powder to liquid ratios of 1.35 g/mL and 1.93 g/mL were characterized regarding their rheological properties. Here, ageing over the course of 24 h showed an increase in viscosity and extrusion force, which was attributed to structural changes in HPMC as well as the formation of magnesium hydroxide by hydration of MgO. The pastes enabled printing of porous scaffolds with good dimensional stability and enabled a setting reaction to struvite when immersed in ammonium phosphate solution. Mechanical performance under compression was approx. 8-20 MPa as a monolithic structure and 1.6-3.0 MPa for printed macroporous scaffolds, depending on parameters such as powder to liquid ratio, ageing time, strand thickness and distance.},
  language  = {en}
}
@article{SchmitzJannaschWeigeletal.2020,
  author    = {Schmitz, Tobias and Jannasch, Maren and Weigel, Tobias and Moseke, Claus and Gbureck, Uwe and Groll, J{\"u}rgen and Walles, Heike and Hansmann, Jan},
  title     = {Nanotopographical Coatings Induce an Early Phenotype-Specific Response of Primary Material-Resident M1 and M2 Macrophages},
  series = {Materials},
  volume    = {13},
  journal   = {Materials},
  number    = {5},
  issn      = {1996-1944},
  doi       = {10.3390/ma13051142},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-203378},
  year      = {2020},
  abstract  = {Implants elicit an immunological response after implantation that results in the worst case in a complete implant rejection. This biomaterial-induced inflammation is modulated by macrophages and can be influenced by nanotopographical surface structures such as titania nanotubes or fractal titanium nitride (TiN) surfaces. However, their specific impact on a distinct macrophage phenotype has not been identified. By using two different levels of nanostructures and smooth samples as controls, the influence of tubular TiO2 and fractal TiN nanostructures on primary human macrophages with M1 or M2-phenotype was investigated. Therefore, nanotopographical coatings were either, directly generated by physical vapor deposition (PVD) or by electrochemical anodization of titanium PVD coatings. The cellular response of macrophages was quantitatively assessed to demonstrate a difference in biocompatibility of nanotubes in respect to human M1 and M2-macrophages. Depending on the tube diameter of the nanotubular surfaces, low cell numbers and impaired cellular activity, was detected for M2-macrophages, whereas the impact of nanotubes on M1-polarized macrophages was negligible. Importantly, we could confirm this phenotypic response on the fractal TiN surfaces. The results indicate that the investigated topographies specifically impact the macrophage M2-subtype that modulates the formation of the fibrotic capsule and the long-term response to an implant.},
  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{SeifertGrollWeichholdetal.2021,
  author    = {Seifert, Annika and Groll, J{\"u}rgen and Weichhold, Jan and Boehm, Anne V. and M{\"u}ller, Frank A. and Gbureck, Uwe},
  title     = {Phase Conversion of Ice-Templated α-Tricalcium Phosphate Scaffolds into Low-Temperature Calcium Phosphates with Anisotropic Open Porosity},
  series = {Advanced Engineering Materials},
  volume    = {23},
  journal   = {Advanced Engineering Materials},
  number    = {5},
  doi       = {10.1002/adem.202001417},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256311},
  year      = {2021},
  abstract  = {The current study aims to extend the material platform for anisotropically structured calcium phosphates to low-temperature phases such as calcium-deficient hydroxyapatite (CDHA) or the secondary phosphates monetite and brushite. This is achieved by the phase conversion of highly porous α-tricalcium phosphate (α-TCP) scaffolds fabricated by ice-templating into the aforementioned phases by hydrothermal treatment or incubation in phosphoric acid. Prior to these steps, α-TCP scaffolds are either sintered for 8 h at 1400 °C or remain in their original state. Both nonsintered and sintered α-TCP specimens are converted into CDHA by hydrothermal treatment, while a transformation into monetite and brushite is achieved by incubation in phosphoric acid. Hydrothermal treatment for 72 h at 175 °C increases the porosity in nonsintered samples from 85\% to 88\% and from 75\% to 88\% in the sintered ones. An increase in the specific surface area from (1.102 ± 0.005) to (9.17 ± 0.01) m2 g-1 and from (0.190 ± 0.004) to (2.809 ± 0.002) m2 g-1 due to the phase conversion is visible for both the nonsintered and sintered samples. Compressive strength of the nonsintered samples increases significantly from (0.76 ± 0.11) to (5.29 ± 0.94) MPa due to incubation in phosphoric acid.},
  language  = {en}
}