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- ItemHighly Conductive, Stretchable, and Cell-Adhesive Hydrogel by Nanoclay Doping(Weinheim : Wiley-VCH, 2019) Tondera, Christoph; Akbar, Teuku Fawzul; Thomas, Alvin Kuriakose; Lin, Weilin; Werner, Carsten; Busskamp, Volker; Zhang, Yixin; Minev, Ivan R.Electrically conductive materials that mimic physical and biological properties of tissues are urgently required for seamless brain-machine interfaces. Here, a multinetwork hydrogel combining electrical conductivity of 26 S m-1 , stretchability of 800%, and tissue-like elastic modulus of 15 kPa with mimicry of the extracellular matrix is reported. Engineering this unique set of properties is enabled by a novel in-scaffold polymerization approach. Colloidal hydrogels of the nanoclay Laponite are employed as supports for the assembly of secondary polymer networks. Laponite dramatically increases the conductivity of in-scaffold polymerized poly(ethylene-3,4-diethoxy thiophene) in the absence of other dopants, while preserving excellent stretchability. The scaffold is coated with a layer containing adhesive peptide and polysaccharide dextran sulfate supporting the attachment, proliferation, and neuronal differentiation of human induced pluripotent stem cells directly on the surface of conductive hydrogels. Due to its compatibility with simple extrusion printing, this material promises to enable tissue-mimetic neurostimulating electrodes.
- ItemPrintability study of metal ion crosslinked PEG-catechol based inks(Cold Spring Harbor : Cold Spring Harbor Laboratory, 2019) Włodarczyk-Biegun, Malgorzata K.; Paez, Julieta I.; Villiou, Maria; Feng, Jun; del Campo, AranzazuInspired by reversible networks present in nature, we have explored the printability of catechol functionalized polyethylene glycol (PEG) based inks with metal-coordination crosslinking. Material formulations containing Al3+, Fe3+ or V3+ as crosslinking ions were tested. The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the crosslinked materials were viable, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D (bio)printing, and enables straightforward adjustment of the printable formulation to meet application-specific needs.
- ItemEffect of scanning strategy on microstructure and mechanical properties of a biocompatible Ti–35Nb–7Zr–5Ta alloy processed by laser-powder bed fusion(Berlin : Springer, 2022) Batalha, Weverson Capute; Batalha, Rodolfo Lisboa; Kosiba, Konrad; Kiminami, Claudio Shyinti; Gargarella, PiterThe influence of scanning strategy (SS) on microstructure and mechanical properties of a Ti–35Nb–7Zr–5Ta alloy processed by laser-powder bed fusion (L-PBF) is investigated for the first time. Three SSs are considered: unidirectional-Y; bi-directional with 79° rotation (R79); and chessboard (CHB). The SSs affect the type and distribution of pores. The highest relative densities and more homogeneous distribution of pores are obtained with R79 and CHB scanning strategies, whereas aligned pores are formed in the unidirectional-Y. The SSs show direct influence on the crystallographic texture with unidirectional-Y strategy showing fiber texture. The R79 strategy results in a weak texture and the CHB scanning strategy forms a randomly oriented heterogeneous grain structure. The lowest Young modulus is obtained with the unidirectional-Y strategy, whereas the R79 strategy results in the highest yield strength. It is shown that the SSs may be used for tuning the microstructure of a beta-Ti alloy in L-PBF.
- ItemDevelopment of bioactive catechol functionalized nanoparticles applicable for 3D bioprinting(Amsterdam : Elsevier, 2021) Puertas-Bartolomé, María; Włodarczyk-Biegun, Małgorzata K.; del Campo, Aránzazu; Vázquez-Lasa, Blanca; San Román, JulioEfficient wound treatments to target specific events in the healing process of chronic wounds constitute a significant aim in regenerative medicine. In this sense, nanomedicine can offer new opportunities to improve the effectiveness of existing wound therapies. The aim of this study was to develop catechol bearing polymeric nanoparticles (NPs) and to evaluate their potential in the field of wound healing. Thus, NPs wound healing promoting activities, potential for drug encapsulation and controlled release, and further incorporation in a hydrogel bioink formulation to fabricate cell-laden 3D scaffolds are studied. NPs with 2 and 29 M % catechol contents (named NP2 and NP29) were obtained by nanoprecipitation and presented hydrodynamic diameters of 100 and 75 nm respectively. These nanocarriers encapsulated the hydrophobic compound coumarin-6 with 70% encapsulation efficiency values. In cell culture studies, the NPs had a protective effect in RAW 264.7 macrophages against oxidative stress damage induced by radical oxygen species (ROS). They also presented a regulatory effect on the inflammatory response of stimulated macrophages and promoted upregulation of the vascular endothelial growth factor (VEGF) in fibroblasts and endothelial cells. In particular, NP29 were used in a hydrogel bioink formulation using carboxymethyl chitosan and hyaluronic acid as polymeric matrices. Using a reactive mixing bioprinting approach, NP-loaded hydrogel scaffolds with good structural integrity, shape fidelity and homogeneous NPs dispersion, were obtained. The in vitro catechol NPs release profile of the printed scaffolds revealed a sustained delivery. The bioprinted scaffolds supported viability and proliferation of encapsulated L929 fibroblasts over 14 days. We envision that the catechol functionalized NPs and resulting bioactive bioink presented in this work offer promising advantages for wound healing applications, as they: 1) support controlled release of bioactive catechol NPs to the wound site; 2) can incorporate additional therapeutic functions by co-encapsulating drugs; 3) can be printed into 3D scaffolds with tailored geometries based on patient requirements.
- ItemMelt Electrowriting of Scaffolds with a Porosity Gradient to Mimic the Matrix Structure of the Human Trabecular Meshwork(New York : Cold Spring Harbor Laboratory, 2022) Włodarczyk-Biegun, Małgorzata K.; Villiou, Maria; Koch, Marcus; Muth, Christina; Wang, Peixi; Ott, Jenna; del Campo, AranzazuThe permeability of the Human Trabecular Meshwork (HTM) regulates eye pressure via a porosity gradient across its thickness modulated by stacked layers of matrix fibrils and cells. Changes in HTM porosity are associated with increases in intraocular pressure and the progress of diseases like glaucoma. Engineered HTMs could help to understand the structure-function relation in natural tissues, and lead to new regenerative solutions. Here, melt electrowriting (MEW) is explored as a biofabrication technique to produce fibrillar, porous scaffolds that mimic the multilayer, gradient structure of native HTM. Poly(caprolactone) constructs with a height of 125-500 μm and fiber diameters of 10-12 μm are printed. Scaffolds with a tensile modulus between 5.6 and 13 MPa, and a static compression modulus in the range of 6-360 kPa are obtained by varying the scaffolds design, i.e., density and orientation of the fibers and number of stacked layers. Primary HTM cells attach to the scaffolds, proliferate, and form a confluent layer within 8-14 days, depending on the scaffold design. High cell viability and cell morphology close to that in the native tissue are observed. The present work demonstrates the utility of MEW to reconstruct complex morphological features of natural tissues.
- ItemPrintability study of metal ion crosslinked PEG-catechol based inks(Bristol : Institute of Physics Publishing, 2020) Włodarczyk-Biegun, M.K.; Paez, J.I.; Villiou, M.; Feng, J.; Del Campo, A.In this paper we explore the printability of reversible networks formed by catechol functionalized PEG solutions and metal cations (Al3+, Fe3+ or V3+). The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the materials crosslinked with Al3+, Fe3+ ions were viable and revealed well-spread morphologies during 7 day culture, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D bioprinting, and enables straightforward adjustment of the printable formulation to meet application-specific needs.
- ItemDesign and testing of 3D-printed micro-architectured polymer materials exhibiting a negative Poisson's ratio(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2019) Agnelli, Filippo; Constantinescu, Andrei; Nika, GrigorThis work proposes the complete design cycle for several auxetic materials where the cycle consists of three steps (i) the design of the micro-architecture, (ii) the manufacturing of the material and (iii) the testing of the material. In more precise terms, we aim to obtain domain micro-architectured materials with a prescribed elasticity tensor and Poisson's ratio. In order to reach this goal we use topology optimization via the level set method for the material design process. Specimens are manufactured using a commercial stereo-lithography Ember printer and mechanically tested. The observed displacement and strain fields during tensile testing obtained by digital image correlation match the predictions from the FE simulation.
- ItemBidirectional and Stretchable Piezoresistive Sensors Enabled by Multimaterial 3D Printing of Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites(Basel : MDPI, 2018-12-21) Christ, Josef F.; Aliheidari, Nahal; Pötschke, Petra; Ameli, AmirFabricating complex sensor platforms is still a challenge because conventional sensors are discrete, directional, and often not integrated within the system at the material level. Here, we report a facile method to fabricate bidirectional strain sensors through the integration of multiwalled carbon nanotubes (MWCNT) and multimaterial additive manufacturing. Thermoplastic polyurethane (TPU)/MWCNT filaments were first made using a two-step extrusion process. TPU as the platform and TPU/MWCNT as the conducting traces were then 3D printed in tandem using multimaterial fused filament fabrication to generate uniaxial and biaxial sensors with several conductive pattern designs. The sensors were subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. It was shown that the directional sensitivity could be tailored by the type of pattern design. A wearable glove, with built-in sensors, capable of measuring finger flexure was also successfully demonstrated where the sensors are an integral part of the system. These sensors have potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, embedding, and customizability are demanded.
- ItemPrinted Degradable Optical Waveguides for Guiding Light into Tissue(Weinheim : Wiley-VCH, 2020) Feng, Jun; Zheng, Yijun; Bhusari, Shardul; Villiou, Maria; Pearson, Samuel; del Campo, AránzazuOptogenetics and photonic technologies are changing the future of medicine. To implement light‐based therapies in the clinic, patient‐friendly devices that can deliver light inside the body while offering tunable properties and compatibility with soft tissues are needed. Here extrusion printing of degradable, hydrogel‐based optical waveguides with optical losses as low as 0.1 dB cm−1 at visible wavelengths is described. Core‐only and core‐cladding fibers are printed at room temperature from polyethylene glycol (PEG)‐based and PEG/Pluronic precursors, and cured by in situ photopolymerization. The obtained waveguides are flexible, with mechanical properties tunable within a tissue‐compatible range. Degradation times are also tunable by adjusting the molar mass of the diacrylate gel precursors, which are synthesized by linking PEG diacrylate (PEGDA) with varying proportions of DL‐dithiothreitol (DTT). The printed waveguides are used to activate photochemical and optogenetic processes in close‐to‐physiological environments. Light‐triggered migration of cells in a photoresponsive 3D hydrogel and drug release from an optogenetically‐engineered living material by delivering light across >5 cm of muscle tissue are demonstrated. These results quantify the in vitro performance, and reflect the potential of the printed degradable fibers for in vivo and clinical applications.
- ItemHigh-Throughput Production of Micrometer Sized Double Emulsions and Microgel Capsules in Parallelized 3D Printed Microfluidic Devices(Basel : MDPI, 2019) Jans, Alexander; Lölsberg, Jonas; Omidinia-Anarkoli, Abdolrahman; Viermann, Robin; Möller, Martin; De Laporte, Laura; Wessling, Matthias; Kuehne, Alexander J. C.Double emulsions are useful geometries as templates for core-shell particles, hollow sphere capsules, and for the production of biomedical delivery vehicles. In microfluidics, two approaches are currently being pursued for the preparation of microfluidic double emulsion devices. The first approach utilizes soft lithography, where many identical double-flow-focusing channel geometries are produced in a hydrophobic silicone matrix. This technique requires selective surface modification of the respective channel sections to facilitate alternating wetting conditions of the channel walls to obtain monodisperse double emulsion droplets. The second technique relies on tapered glass capillaries, which are coaxially aligned, so that double emulsions are produced after flow focusing of two co-flowing streams. This technique does not require surface modification of the capillaries, as only the continuous phase is in contact with the emulsifying orifice; however, these devices cannot be fabricated in a reproducible manner, which results in polydisperse double emulsion droplets, if these capillary devices were to be parallelized. Here, we present 3D printing as a means to generate four identical and parallelized capillary device architectures, which produce monodisperse double emulsions with droplet diameters in the range of 500 µm. We demonstrate high throughput synthesis of W/O/W and O/W/O double emulsions, without the need for time-consuming surface treatment of the 3D printed microfluidic device architecture. Finally, we show that we can apply this device platform to generate hollow sphere microgels.