29. Jahrestagung der Deutschen Gesellschaft für Biomaterialien

Prof. Dr.

Chair

Development of a newly synthesized biopolymer for industrial laser-based nano-3D printing of hierarchically structured bone-cartilage implants

Additive manufacturing (e. g. 3D printing)

Tissue regeneration/regenerated medicine

Abstract text (incl. figure legends and references) Introduction Regeneration and healing of cartilage defects is naturally a difficult task and even for the human body itself hard to achieve. Objective We aimed to develop biphasic polymer-based scaffold structures for the optimal treatment of bone-cartilage defects as well as to create and synthesize a suitable material, which is biocompatible, biodegradable, and can be processed via laser-based 3D printing. Materials and Methods A protocol for the synthesis of ACM1 was developed, which serves as a substitute for the well-known reference system LCM2, as the latter leads to acidic degradation products in tissue and corresponding inflammatory reactions. Both materials are presented in figure 1 and were succesfully 3D-printed via 2-photon polymerization. The 2PP technique, as a variable 3D printing technique from the nm- to the cm-scale, in combination with an automated manufacturing process, represents the key to the targeted microstructuring of a 3D scaffold construct with optimal adjustment of the material stiffness and the bioactivity of the selected polymers. Fig. 1: Chemical structures of ACM and LCM. Results Based on the physiological conditions of bone/cartilage tissue, an osteochondral implant with suitable tissue-analogue cartilage- and bone-specific geometric, biomechanical and biochemical properties was designed and succesfully 3D-printed via 2-photon polymerization. Fig. 2: Design of the newly created biphasic scaffold. Conclusion The achieved biphasic 3D-implant represents an excellent solution to simulate the chondrogenic and osteogenic extracellular matrix (ECM) and allows the adjustment of a defined degradation rate. Acknowledgement The results are content of the project &quot;Poly-IMPLANT-Druck&quot; (funding code: 13XP5089A-F) funded by BMBF. We thank BMBF very much for the financial support. 1N. Hauptmann et al., Int. J. Mol. Sci. 2022, 23(6), 3115 2N. Hauptmann et al., Tiss. Eng. Part B: Reviews, 2019, 25(3), 167-186

Short Talk

Wet spinning of silk fibroin fibers and fiber-based additive manufacturing of 3D scaffolds for regenerative medicin

Abstract text (incl. figure legends and references) Introduction Silk ﬁbroin combines properties such as high mechanical strength, biocompatibility, and biodegradability in vivo. The possibility of using ﬁbroin in a wide variety of formats (ﬁlms, scaffolds, hydrogels, and micro- or nanoparticles for drug delivery), has led to many interesting applications in medical research. In addition, extensive effort has been focused on producing man-made silk fibers by wet spinning. However, due to degradation of fibroin molecules during isolation from cocoons only high percentage solutions of regenerated silk (13-32 % w/v) show sufficient viscosity needed for fiber spinning. Objectives The main objective was to develop a novel wet spinning process to generate silk fibers and to process those fibers into 3D open porous scaffolds applying textile fiber-based additive manufacturing. Materials &amp; methods Regenerated silk solution was isolated from Bombyx mori cocoons applying mild degumming and dissolution in ZnCl2. The resulting solution was freeze-dried and re-dissolved for wet spinning. Wet spun silk fibers were processed into staple fibers and then assembled into open porous 3D scaffolds applying fiber-based additive manufacturing. Results In contrast to all previously published spinning processes, a solvent/coagulation bath combination was developed, which enables continuously spinning of endless fibers from only 4 % (w/v) silk solution. Compared to other approaches the solid content to tensile strength ratio achieved was twice that of the highest process to date. Applying fiber-based additive manufacturing, those wet spun silk fibroin fibers were processed into 3D open porous scaffolds. Conclusion A novel process was developed enabling wet spinning of fibers from only 4 % (w/v) fibroin solution, which could be processed into 3D scaffolds with a fiber-based additive manufacturing technology. Acknowledgements This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)-437213841.

Professor

Tunable microporous scaffolds via melt electrowriting

Biofabrication

Abstract text (incl. figure legends and references) Introduction Melt electrowriting (MEW) is an electric field-assisted fiber-forming technology for the fabrication of complex scaffold architectures. However, to date MEW scaffolds are mostly macroporous, as fiber-bridging prevents defect-free printing at low interfiber distances. Therefore, MEW scaffolds need to be combined with a second biomaterial to provide a microporosity that is adequate for cellular infiltration following the in situ tissue engineering (TE) paradigm. Objectives We aim at introducing a design strategy that enables microporous scaffolds by MEW only, while avoiding fiber bridging. Methods A MATLAB algorithm creates Gcodes for polycaprolactone scaffolds via a MEW through a 23 G needle at 4.5 – 5 kV both on flat and tubular collectors. Samples were assessed via scanning electron microscopy (SEM), microcomputed tomography (µCT), and tensile testing. Ingrowth of human umbilical artery smooth muscle cells (HUASMCs) was verified via SEM and immunohistochemistry at day 3, 7, 14, and 28 after seeding. Results The design strategy is based on the superposition of angularly shifted fiber arrays with elements of controlled randomization. Modulating interfiber distance and angular shifting resulted in a large range of pore morphologies that were tunable in size and shape. Restricting angular directions of fibers introduced mechanical anisotropy, which was exemplarily tuned to match cardiovascular tissues. In contrast to electrospinning, the design strategy decoupled pore size from fiber diameter, as verified by µCT analysis for scaffolds with fiber diameters ranging from 5.1 ± 0.7 µm to 21.8 ± 1.7 µm, all with 45 µm pores. At day 3, single HUASMCs had bridged the 45 µm pores with progressing infiltration at day 7 and 14. After 28 days, scaffolds were mostly filled with neotissue. Conclusion This work enables microporous scaffolds by MEW only, which can be customized to meet the architectural and mechanical requirements of the target tissue for in situ TE.

Bioink development for multi-modal 3D-bioprinting of large tissues

Abstract text (incl. figure legends and references) 3D bioprinting shows promise in various applications, allowing for custom 3D shapes and intricate structures. Nevertheless, the challenge lies in successfully creating dense tissues. After the printing process cells require a considerable amount of time to mature and develop into functional biological tissues. Moreover, producing large-scale tissues presents another hurdle as it surpasses the diffusion limit for crucial substances necessary for survival. We present a material combination suited for multi-modal 3D-bioprinting of larger tissues. Thus, our materials are specifically tailored not only for optimal printing qualities but also to meet the unique requirements of the cells. Further, mocroextruded channels ensure long-term nutrient supply. Drop-on-demand and extrusion-based bioprinting techniques are selected based on material viscosity for ECM (polysaccharide-protein-blends) and sacrificial material (SM, gelatin) printing, respectively. Customizable bioinks are characterized by their rheological, mechanical, and surface properties. While those aspects are essential for printability, cytocompatibility and biofunctionality play a major role for cell survival and proliferation. Thus, the latter are evaluated to achieve the best results. Cytocompatible concentrations of SM regarding gel-sol transition are printed into an ECM-like material which shows cell viabilities of &gt;90 %. Further, the cell-filled ECM is printed into a custom bioreactor promoting medium flow into the channels to ensure nutrient supply to depths exceeding the oxygen diffusion limit. Matrix and SM are customized to suit both DoD and extrusion-based bioprinting methods, ensuring they fulfill the necessary criteria for creating optimal cell conditions. Looking ahead, these innovative multi-modal bioprinting techniques show immense potential for enabling large-scale fabrication of perfusable tissues, which can greatly impact areas such as drug development and personalized medicine.

Design evolution and attachment of a melt electrowritten cardiac patch to regenerate ischemic heart disease

Abstract text (incl. figure legends and references) Ischemic heart disease is the worldwide leading cause of death. Mechanical ventricular assist devices present the current standard treatment, although it is not a long-lasting solution. The BRAVꓱ project consists of a multidisciplinary consortium that aims for a biological ventricular assist device (BioVAD) as a regenerative alternative. The BioVAD is composed of two scaffold zones manufactured via Melt Electrowriting (MEW). An inner regenerative part and an outer support area that attaches to the heart and enables tissue integration. The present work outlines the BioVAD design evolution and characterisation. MEW was used to manufacture 4x6cm BioVAD scaffolds filled with fibrin hydrogel. The regenerative zone with a hexagonal pore pattern, has been shown to be favourable for cardiomyocytes. [1]. The outer support zone was tailored from a variety of design elements such as sinusoidal and straight fibres. Each scaffold architecture and its interplay were morphologically and mechanically characterised. Further testing of attachment to porcine cardiac tissue was investigated by 3D printed testing set-ups. The distinctive fibre architectures met the complex biomechanical needs of the heart. A regenerative hexagonal pore structure was successfully integrated into the surrounding support zone. Stiff areas can provide functional support to the heart by transmitting forces of the regenerative zone to the heart. The elastic zone allows stretching over the epicardium during contraction and therefore enables attachment. Scaffold manufacturing via MEW was proven to be an outstanding method to generate a clinical-size BioVAD with characteristic zonal properties. Custom-made testing set-ups allowed advanced characterisation of the BioVAD and to investigate the attachment to porcine cardiac tissue. Castilho M. et al., Adv. Funct. Mater., 28(40), 2018

A filament-based melt electrowriting approach for the fabrication of multiscale scaffolds

Abstract text (incl. figure legends and references) Introduction: Melt electrowriting (MEW) is a promising electric field-assisted biofabrication strategy for complex 3D scaffolds. However, to date, conventional MEW provides the polymer melt in a syringe and relies on highly specialized machine technology, which restricts MEW accessibility to a wider user group. Objectives: The aim is to exploit the widely used Fused Filament Fabrication (FFF) technology by retrofitting low-cost FFF systems to enable electrohydrodynamically-driven microfiber deposition. Materials &amp; Methods: We modified a FFF printer to apply a high-voltage electric field between the nozzle tip and the printing bed, by grounding the nozzle and introducing an in-house developed collector. Customized Gcodes were programmed in an Excel spreadsheet. Scaffold morphologies were evaluated via scanning electron microscopy (SEM) and mechanical testing. Human umbilical vein endothelial cells (HUVECs) were cultured on scaffolds for three days. Results: The upgrade enabled filament-based MEW (F-MEW), as validated with the MEW gold standard material polycaprolactone (PCL). We controlled fiber diameters ranging from 33.8 ± 1.4 down to 10.7 ± 0.5 μm in linear (box pores) and non-linear patterns. The melt-on-demand concept of F-MEW enabled - for the first time - direct writing of the thermo-sensitive polymer polydioxanone (PDO). HUVECs adhered and proliferated on the F-MEW microfibers. Ultimately, we hybridized the FFF with the F-MEW mode of the system to fabricate multiscale constructs both from PCL and PDO. Conclusion: This work presents a filament-based approach to MEW by building on the FFF technology ecosystem. F-MEW holds great potential to introduce electrohydrodynamic writing of polymer melts to a much wider user group and can now be easily implemented into existing FFF machines. Furthermore, combining F-MEW with FFF in the same machine brings unprecedented capabilities for multiscale additive manufacturing, de facto expanding the FFF fabrication window.

Short Talks 12
Biofabrication / Scaffolds

Appointment

Chair

Topic

Programme

Short Talks 12Biofabrication / Scaffolds

Appointment

Chair

Topic

Programme

Short Talks 12
Biofabrication / Scaffolds