Maximilian Ritter

Last Name

Ritter

First Name

Maximilian

ORCID

0000-0001-5368-2007

Organisational unit

03917 - Burgert, Ingo / Burgert, Ingo

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Publications1 - 10 of 14

Genetic Impacts on the Structure and Mechanics of Cellulose Made by Bacteria
Laurent, Julie M.; Steinacher, Mathias; Kan, Anton; et al. (2025)
Advanced Science
The synthesis of cellulose pellicles by bacteria offers an enticing strategy for the biofabrication of sustainable materials and biomedical devices. To leverage this potential, bacterial strains that overproduce cellulose are identified through directed evolution technology. While cellulose overproduction is linked with a specific genetic mutation, the effect of such mutation on the intracellular protein landscape and on the structure and mechanical properties of the cellulose pellicles is not yet understood. Here, the proteome of bacteria evolved to overproduce cellulose is studied and its effect on the structure and mechanics of the resulting cellulose pellicles is investigated. Proteomic analysis reveals that the protein landscape of the evolved bacteria shows pronounced differences from that of native microorganisms. Thanks to concerted changes in the proteome, the evolved bacteria can generate cellulose pellicles with exquisite structure and improved mechanical properties for applications in textiles, packaging, and medical implants.
Ectopic callose deposition into woody biomass modulates the nano-architecture of macrofibrils
Bourdon, Matthieu; Lyczakowski, Jan J.; Cresswell, Rosalie; et al. (2023)
Nature Plants
Plant biomass plays an increasingly important role in the circular bioeconomy, replacing non-renewable fossil resources. Genetic engineering of this lignocellulosic biomass could benefit biorefinery transformation chains by lowering economic and technological barriers to industrial processing. However, previous efforts have mostly targeted the major constituents of woody biomass: cellulose, hemicellulose and lignin. Here we report the engineering of wood structure through the introduction of callose, a polysaccharide novel to most secondary cell walls. Our multiscale analysis of genetically engineered poplar trees shows that callose deposition modulates cell wall porosity, water and lignin contents and increases the lignin–cellulose distance, ultimately resulting in substantially decreased biomass recalcitrance. We provide a model of the wood cell wall nano-architecture engineered to accommodate the hydrated callose inclusions. Ectopic polymer introduction into biomass manifests in new physico-chemical properties and offers new avenues when considering lignocellulose engineering.
Reconstructing Poplar Wood into a High-Performance Fiber-Reinforced Biocomposite
Movahedi-Rad, A. Vahid; Ritter, Maximilian; Kindler, Robert Oswin; et al. (2024)
ACS Sustainable Chemistry & Engineering
Green high-performance composite materials are in great demand thanks to the increased environmental awareness. Wood is a natural fiber-reinforced polymer composite, but its properties can hardly compete with those of artificial, much less sustainable, ones. In Central Europe, climate change-induced environmental changes will force the industrial adoption of fast-growing, drought-resistant wood species (such as poplar) with inferior mechanical properties compared to more commonly used ones (such as spruce). In response to these challenges, we describe the fabrication of a novel fully biobased high-performance composite obtained by reconstructing poplar wood. Our process is based on a combination of structure-retaining delignification, relignification, and densification, resulting in a product with superior mechanical properties and water stability. Our "reconstructed poplar" is a green composite suitable for engineering applications and an example of undervalorized wood species upcycling.
Lightweight, Strong, and Transparent Wood Films Produced by Capillary Driven Self-Densification
Chen, Feng; Ritter, Maximilian; Xu, Yifan; et al. (2024)
Small
Wood delignification and densification enable the production of high strength and/or transparent wood materials with exceptional properties. However, processing needs to be more sustainable and besides the chemical delignification treatments, energy intense hot-pressing calls for alternative approaches. Here, this study shows that additional softening of delignified wood via a mild swelling process using an ionic liquid-water mixture enables the densification of tube-line wood cells into layer-by-layer sheet structures without hot-pressing. The natural capillary force induces self-densification in a simple drying process resulting in a transparent wood film. The as-prepared films with ≈150 µm thickness possess an optical transmittance ≈70%, while maintaining optical haze >95%. Due to the densely packed sheet structure with a large interfacial area, the reassembled wood film is fivefold stronger and stiffer than the delignified wood in fiber direction. Owing to a low density, the specific tensile strength and elastic modulus are as high as 282 MPa cm³ g⁻¹ and 31 GPa cm³ g⁻¹. A facile and highly energy efficient wood nanotechnology approach are demonstrated toward more sustainable materials and processes by directly converting delignified wood into transparent wood omitting polymeric matrix infiltration or mechanical pressing.
Iron-Catalyzed Laser-Induced Graphitization Enabling Current Collector-Free Electrodes With Spatially Tunable Iron/Iron Oxide Phases
Dreimol, Christopher; Edberg, Jesper; Kürsteiner, Ronny; et al. (2025)
Advanced Materials
Iron-catalyzed laser-induced graphitization (IC-LIG) represents an eco-efficient alternative to traditional carbon electrode manufacturing. Combining a bio-based tannic acid-iron precursor ink with CO₂ laser treatment results in sheet resistance of 23.59 ± 1.2 Ω square⁻¹ on renewable substrates. Varying the tannic-acid-to-iron ratio (TA:Fe), the rheology of the precursor ink can be tuned, enabling versatile application techniques, including spray coating, screen printing, and direct-ink-writing (DIW). Subsequent laser-treatment enables the formation of functional IC-LIG electrodes for all application methods, while even thick DIW-printed layers (260 μm) result in complex, conductive electrode patterns. Laser post-treatment expands design possibilities by locally tuning iron phases, such as converting γ-iron to magnetite. The unidirectional laser-treatment results in a layered arrangement, forming a multilayer electrode with a highly graphitized top layer serving as a current collector substitute, and an underlying composite of iron-rich nanoparticles embedded in a porous graphitic foam, acting as a hybrid electrode. Electrochemical analysis reveals double-layer capacitor behavior at low TA:Fe ratios, while higher ratios demonstrate increased redox activity and pseudo-capacitive characteristics. Achieving stable capacities of 15 mF cm⁻² with a 1 M NaCl electrolyte over 5000 cycles underscores the potential of IC-LIG electrodes as a sustainable solution for advanced energy storage devices and beyond.
Piezoelectric and Photoconductive Zinc Oxide-Wood Hybrids Obtained by Atomic Layer Deposition
Ritter, Maximilian; Maćkosz, Krzysztof; Garemark, Jonas; et al. (2025)
ACS Nano
The development of sustainable functional wood-based materials for advanced photonic, optical, and energy-harvesting applications is a topic of great priority and scientific interest. Owing to its inherent piezoactivity and photoconductivity, zinc oxide (ZnO) can be of help for all these applications. While previously used for wood-based piezoelectric nanogenerators, its use for enabling wood with photoconductive properties has not yet been demonstrated. Here, we introduce an innovative method to produce ZnO-wood hybrids based on atomic layer deposition (ALD), a technique so far underrepresented in the field of wood functionalization. By a studied combination of ALD, customized sample geometry, structure-retaining delignification, and careful selection of the drying method, we obtained a homogeneous functionalization of a bulk wood scaffold with layers of nanocrystalline ZnO. This approach allowed us to achieve control over the homogeneity, distribution, and coating thickness of the oxide layer. The micro- and nanostructure of the resulting hybrids were investigated by electron microscopy as well as by X-ray diffraction and scattering. The ZnO-wood hybrids show an anisotropic piezoelectric response due to the natural structure of the wood. Moreover, we demonstrate the use of ZnO-functionalized wood for the fabrication of bulk (photo)conductive wood. Upon irradiation with UV light, a significant decrease in resistivity is observed, which increases again upon removal of UV light. Finally, we used the hybrids to fabricate a ZnO-wood replica by thermal removal of the cellulose scaffold. This treatment leaves behind a detailed inorganic wood replica down to the smallest open accessible features such as micrometer-sized wood pits.
Combined Experimental and Machine Learning Study on the Interplay between Delignification and Mechanical Properties for Improved Poplar Wood Reconstruction
Movahedi-Rad, A. Vahid; Ritter, Maximilian; Colmant, Alan; et al. (2026)
ACS Applied Materials & Interfaces
Structure-retaining delignification of wood is widely used to obtain scaffolds suitable for the preparation of high-performance biobased composites. However, this often comes at the expense of sustainability and large-scale production potential. To address these issues, we reconstructed poplar wood via room-temperature partial delignification, followed by delignification and densification. Compared to fully delignified samples, those obtained with partial delignification have superior mechanical properties at 45 degrees and 90 degrees fiber directions with respect to the loading direction, but lower ones at 0 degrees. Working at room temperature facilitated sample up-scaling and allowed reuse of the delignification solution multiple times without compromising product quality. As shown by life cycle assessment (LCA), the possibility of repeatedly reusing the delignification solution led to a significant reduction in the global warming potential (GWP) and ecosystem quality (EQ) impacts. We then developed an 'unsupervised, supervised classification, supervised regression' (USS) learning framework to accurately predict the mechanical properties of reconstructed poplar on the basis of structural and process-related features, followed by feature importance analysis to determine the key parameters influencing material performance. With our approach, we were able to estimate the mechanical performance of the reconstructed samples and gain insight into the most relevant material-fabrication parameters.
Biodegradable and Flexible Wood-Gelatin Composites for Soft Actuating Systems
Koch, Sophie; Dreimol, Christopher; Goldhahn, Christian; et al. (2024)
ACS Sustainable Chemistry & Engineering
Compliant materials are indispensable for many emerging soft robotics applications. Hence, concerns regarding sustainability and end-of-life options for these materials are growing, given that they are predominantly petroleum-based and non-recyclable. Despite efforts to explore alternative bio-derived soft materials like gelatin, they frequently fall short in delivering the mechanical performance required for soft actuating systems. To address this issue, we reinforced a compliant and transparent gelatin-glycerol matrix with structure-retained delignified wood, resulting in a flexible and entirely biobased composite (DW-flex). This DW-flex composite exhibits highly anisotropic mechanical behavior, possessing higher strength and stiffness in the fiber direction and high deformability perpendicular to it. Implementing a distinct anisotropy in otherwise isotropic soft materials unlocks new possibilities for more complex movement patterns. To demonstrate the capability and potential of DW-flex, we built and modeled a fin ray-inspired gripper finger, which deforms based on a twist-bending-coupled motion that is tailorable by adjusting the fiber direction. Moreover, we designed a demonstrator for a proof-of-concept suitable for gripping a soft object with a complex shape, i.e., a strawberry. We show that this composite is entirely biodegradable in soil, enabling more sustainable approaches for soft actuators in robotics applications.
Salt-In-Wood Piezoelectric Power Generators with Circular Materials Design for High-Performance Sustainable Energy Harvesting
Garemark, Jonas; Ritter, Maximilian; Dreimol, Christopher; et al. (2025)
Advanced Functional Materials
The nanowatt-level power density of current biobased piezoelectric energy harvesters restricts their applicative potential for the efficient conversion of biomechanical energy. A high-performing, fully renewable piezoelectric device incorporating green piezo-active Rochelle salt in a laser-drilled wood template is demonstrated to form ordered crystal pillar arrays by melt crystallization. Investigating the effect of different crystal pillar configurations on the piezoelectric response, a shearing design (45 degrees-oriented pillars) shows potential of up to 30 V and a current of 4 mu A - corresponding to a 10-fold power increase compared to single-crystalline Rochelle salt. A concept of direct laser graphitization on the crystal surfaces are demonstrated using a fully renewable ink to create electrodes of low resistance (36 Omega sq-1). The entire device can be disassembled, fully recycled, and reused. This nanogenerator outperforms state-of-the-art biobased ones and competes with conventional lead-based devices in power generation while showing a significantly lower environmental footprint, as indicated by life-cycle assessment.
Iron-Catalyzed Laser-Induced Graphitization – Multiscale Analysis of the Structural Evolution and Underlying Mechanism
Dreimol, Christopher; Kürsteiner, Ronny; Ritter, Maximilian; et al. (2024)
Small
The transition to sustainable materials and eco-efficient processes in commercial electronics is a driving force in developing green electronics. Iron-catalyzed laser-induced graphitization (IC-LIG) has been demonstrated as a promising approach for rendering biomaterials electrically conductive. To optimize the IC-LIG process and fully exploit its potential for future green electronics, it is crucial to gain deeper insights into its catalyzation mechanism and structural evolution. However, this is challenging due to the rapid nature of the laser-induced graphitization process. Therefore, multiscale preparation techniques, including ultramicrotomy of the cross-sectional transition zone from precursor to fully graphitized IC-LIG electrode, are employed to virtually freeze the IC-LIG process in time. Complementary characterization is performed to generate a 3D model that integrates nanoscale findings within a mesoscopic framework. This enabled tracing the growth and migration behavior of catalytic iron nanoparticles and their role during the catalytic laser-graphitization process. A three-layered arrangement of the IC-LIG electrode is identified including a highly graphitized top layer with an interplanar spacing of 0.343 nm. The middle layer contained gamma-iron nanoparticles encapsulated in graphitic shells. A comparison with catalyst-free laser graphitization approaches highlights the unique opportunities that IC-LIG offers and discuss potential applications in energy storage devices, catalysts, sensors, and beyond.

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Maximilian Ritter

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