Cross-Sectional 4D-Printing: Upscaling Self-Shaping Structures with Differentiated Material Properties Inspired by the Large-Flowered Butterwort (Pinguicula grandiflora).

Extrusion-based 4D-printing, which is an emerging field within additive manufacturing, has enabled the technical transfer of bioinspired self-shaping mechanisms by emulating the functional morphology of motile plant structures (e.g., leaves, petals, capsules). However, restricted by the layer-by-layer extrusion process, much of the resulting works are simplified abstractions of the pinecone scale's bilayer structure. This paper presents a new method of 4D-printing by rotating the printed axis of the bilayers, which enables the design and fabrication of self-shaping monomaterial systems in cross sections. This research introduces a computational workflow for programming, simulating, and 4D-printing differentiated cross sections with multilayered mechanical properties. Taking inspiration from the large-flowered butterwort (Pinguicula grandiflora), which shows the formation of depressions on its trap leaves upon contact with prey, we investigate the depression formation of bioinspired 4D-printed test structures by varying each depth layer. Cross-sectional 4D-printing expands the design space of bioinspired bilayer mechanisms beyond the XY plane, allows more control in tuning their self-shaping properties, and paves the way toward large-scale 4D-printed structures with high-resolution programmability.

Codesign of Biobased Cellulose-Filled Filaments and Mesostructures for 4D Printing Humidity Responsive Smart Structures.

Hygromorphic smart structures are advantageous as passively actuated systems for generating movement, with applications ranging from weather-responsive architectural building skins to adaptive wearables and microrobotics. Four-dimensional (4D) printing is a valuable method for multiscale fabrication and physical programming of such structures. However, material limitations in terms of printability, responsiveness, and mechanical properties are major bottlenecks in achieving reliable and repeatable humidity-responsive actuation. We propose a codesign method for 4D printing hygromorphic structures through fused filament fabrication, incorporating parallel development of (1) biobased cellulose-filled filaments with varying stiffness and hygroresponsiveness, and (2) designed mesoscale structuring in printed elements. We first describe the design of a pallet of filaments produced by compounding cellulose powder in mass ratios of 0-30% within two matrix polymers with high and low stiffness. We then present the design, fabrication, and testing of a series of 4D-printed prototypes tuned to change shape, that is, open and close, in response to relative humidity (RH). The structures can fully transform in conditions of 35-90% RH, which corresponds to naturally occurring shifts in RH in daily and seasonal weather cycles. Furthermore, their motion is fast (within the range of minutes), fully reversible, and repeatable in numerous cycles. These results open new opportunities for the utilization of 4D printing and natural resources for the development of functional humidity-responsive smart structures.

Leveraging Building Material as Part of the In-Plane Robotic Kinematic System for Collective Construction.

Although collective robotic construction systems are beginning to showcase how multi-robot systems can contribute to building construction by efficiently building low-cost, sustainable structures, the majority of research utilizes non-structural or highly customized materials. A modular collective robotic construction system based on a robotic actuator, which leverages timber struts for the assembly of architectural artifacts as well as part of the robot body for locomotion is presented. The system is co-designed for in-plane assembly from an architectural, robotic, and computer science perspective in order to integrate the various hardware and software constraints into a single workflow. The system is tested using five representative physical scenarios. These proof-of-concept demonstrations showcase three tasks required for construction assembly: the ability of the system to locomote, dynamically change the topology of connecting robotic actuators and timber struts, and collaborate to transport timber struts. As such, the groundwork for a future autonomous collective robotic construction system that could address collective construction assembly and even further increase the flexibility of on-site construction robots through its modularity is laid.

Visualization for Architecture, Engineering, and Construction: Shaping the Future of Our Built World.

Our built world is one of the most important factors for a livable future, accounting for massive impact on resource and energy use, as well as climate change, but also the social and economic aspects that come with population growth. The architecture, engineering, and construction industry is facing the challenge that it needs to substantially increase its productivity, let alone the quality of buildings of the future. In this article, we discuss these challenges in more detail, focusing on how digitization can facilitate this transformation of the industry, and link them to opportunities for visualization and augmented reality research. We illustrate solution strategies for advanced building systems based on wood and fiber.

Autonomous robotic additive manufacturing through distributed model-free deep reinforcement learning in computational design environments.

The objective of autonomous robotic additive manufacturing for construction in the architectural scale is currently being investigated in parts both within the research communities of computational design and robotic fabrication (CDRF) and deep reinforcement learning (DRL) in robotics. The presented study summarizes the relevant state of the art in both research areas and lays out how their respective accomplishments can be combined to achieve higher degrees of autonomy in robotic construction within the Architecture, Engineering and Construction (AEC) industry. A distributed control and communication infrastructure for agent training and task execution is presented, that leverages the potentials of combining tools, standards and algorithms of both fields. It is geared towards industrial CDRF applications. Using this framework, a robotic agent is trained to autonomously plan and build structures using two model-free DRL algorithms (TD3, SAC) in two case studies: robotic block stacking and sensor-adaptive 3D printing. The first case study serves to demonstrate the general applicability of computational design environments for DRL training and the comparative learning success of the utilized algorithms. Case study two highlights the benefit of our setup in terms of tool path planning, geometric state reconstruction, the incorporation of fabrication constraints and action evaluation as part of the training and execution process through parametric modeling routines. The study benefits from highly efficient geometry compression based on convolutional autoencoders (CAE) and signed distance fields (SDF), real-time physics simulation in CAD, industry-grade hardware control and distinct action complementation through geometric scripting. Most of the developed code is provided open source. Supplementary Information: The online version contains supplementary material available at 10.1007/s41693-022-00069-0.

Additive Manufacturing of Large Coreless Filament Wound Composite Elements for Building Construction.

Digitization and automation are essential tools to increase productivity and close significant added-value deficits in the building industry. Additive manufacturing (AM) is a process that promises to impact all aspects of building construction profoundly. Of special interest in AM is an in-depth understanding of material systems based on their isotropic or anisotropic properties. The presented research focuses on fiber-reinforced polymers, with anisotropic mechanical properties ideally suited for AM applications that include tailored structural reinforcement. This article presents a cyber-physical manufacturing process that enhances existing robotic coreless Filament Winding (FW) methods for glass and carbon fiber-reinforced polymers. Our main contribution is the complete characterization of a feedback-based, sensor-informed application for process monitoring and fabrication data acquisition and analysis. The proposed AM method is verified through the fabrication of a large-scale demonstrator. The main finding is that implementing AM in construction through cyber-physical robotic coreless FW leads to more autonomous prefabrication processes and unlocks upscaling potential. Overall, we conclude that material-system-aware communication and control are essential for the efficient automation and design of fiber-reinforced polymers in future construction.

Development of a Material Design Space for 4D-Printed Bio-Inspired Hygroscopically Actuated Bilayer Structures with Unequal Effective Layer Widths.

(1) Significance of geometry for bio-inspired hygroscopically actuated bilayer structures is well studied and can be used to fine-tune curvatures in many existent material systems. We developed a material design space to find new material combinations that takes into account unequal effective widths of the layers, as commonly used in fused filament fabrication, and deflections under self-weight. (2) For this purpose, we adapted Timoshenko's model for the curvature of bilayer strips and used an established hygromorphic 4D-printed bilayer system to validate its ability to predict curvatures in various experiments. (3) The combination of curvature evaluation with simple, linear beam deflection calculations leads to an analytical solution space to study influences of Young's moduli, swelling strains and densities on deflection under self-weight and curvature under hygroscopic swelling. It shows that the choice of the ratio of Young's moduli can be crucial for achieving a solution that is stable against production errors. (4) Under the assumption of linear material behavior, the presented development of a material design space allows selection or design of a suited material combination for application-specific, bio-inspired bilayer systems with unequal layer widths.

Designing architectural materials: from granular form to functional granular material.

Designed granular materials are a novel class of architectural material system. Following one of the key paradigms of designed matter, material form and material function are closely interrelated in these systems. In this context, the article aims to contribute a parametric particle design model as an interface for this interrelation. A granular material is understood as an aggregation of large numbers of individual particles between which only short-range repulsive contact forces are acting. Granular materials are highly pertinent material systems for architecture. Due to the fact that they can act both as a solid and a liquid, they can be recycled and reconfigured multiple times and are thus highly sustainable. Designed granular materials have the added potential that the function of the granular material can be calibrated through the definition of the particles' form. Research on the design of granular materials in architecture is nascent. In physics they have been explored mainly with respect to different particle shapes. However, no coherent parametric particle design model of designed particle shapes for granular material systems in architecture has yet been established which considers both fabrication constraints and simulation requirements. The parametric particle design model proposed in this article has been based on a design system which has been developed through feasibility tests and simulations conducted in research and teaching. Based on this design system the parametric particle design model is developed integrating both fabrication constraints for architecture-scale particle systems and the geometric requirements of established simulation methods for granular materials. Initially the design system and related feasibility tests are presented. The parametric particle design model resulting from that is then described in detail. Directions of further research are discussed especially with respect to the integration of the parametric particle design model in 'inverse' design methods.

Programming material compliance and actuation: hybrid additive fabrication of biocomposite structures for large-scale self-shaping.

We present a hybrid approach to manufacturing a new class of large-scale self-shaping structures through a method of additive fabrication combining fused granular fabrication (FGF) and integrated hygroscopic wood actuators (HWAs). Wood materials naturally change shape with high forces in response to moisture stimuli. The strength and simplicity of this actuation make the material suitable for self-shaping architectural-scale components. However, the anisotropic composition of wood, which enables this inherent behavior, cannot be fully customized within existing stock. On the other hand, FGF allows for the design of large physical parts with multi-functional interior substructures as inspired by many biological materials. We propose to encode passively actuated movement into physical structures by integrating HWAs within 3D-printed meta-structures with functionally graded stiffnesses. By leveraging robotic manufacturing platforms, self-shaping biocomposite material systems can be upscaled with variable resolutions and at high volumes, resulting in large-scale structures capable of transforming from flat to curved simply through changes in relative humidity.

Bio-Inspired Motion Mechanisms: Computational Design and Material Programming of Self-Adjusting 4D-Printed Wearable Systems.

This paper presents a material programming approach for designing 4D-printed self-shaping material systems based on biological role models. Plants have inspired numerous adaptive systems that move without using any operating energy; however, these systems are typically designed and fabricated in the form of simplified bilayers. This work introduces computational design methods for 4D-printing bio-inspired behaviors with compounded mechanisms. To emulate the anisotropic arrangement of motile plant structures, material systems are tailored at the mesoscale using extrusion-based 3D-printing. The methodology is demonstrated by transferring the principle of force generation by a twining plant (Dioscorea bulbifera) to the application of a self-tightening splint. Through the tensioning of its stem helix, D. bulbifera exhibits a squeezing force on its support to provide stability against gravity. The functional strategies of D. bulbifera are abstracted and translated to customized 4D-printed material systems. The squeezing forces of these bio-inspired motion mechanisms are then evaluated. Finally, the function of self-tightening is prototyped in a wrist-forearm splint-a common orthotic device for alignment. The presented approach enables the transfer of novel and expanded biomimetic design strategies to 4D-printed motion mechanisms, further opening the design space to new types of adaptive creations for wearable assistive technologies and beyond.

Programming sequential motion steps in 4D-printed hygromorphs by architected mesostructure and differential hygro-responsiveness.

Through their anisotropic cellular mesostructure and differential swelling and shrinking properties, hygroscopic plant structures move in response to changes in the environment without consuming metabolic energy. When the movement is choreographed in sequential time steps, either in individual structures or with a coordinated interplay of various structural elements, complex functionalities such as dispersal and protection of seeds are achieved. Inspired by the multi-phase motion in plant structures, this paper presents a method to physically program the timescale and the sequences of shape-change in 4D-printed hygromorphic structures. Using the FDM 3D-printing method, we have developed multi-layered, multi-material functional bilayers that combine highly hygroscopic active layers (printed with hygroscopic bio-composite materials) with hydrophobic restrictive and blocking layers (printed with PLA and TPC materials). The timescale of motion is programmed through the design of the mesostructured layers and 3D-printing process parameters, including thickness (number of printed active layers), porosity (filling ratio of the active layer), and water permeability (filling ratio of the blocking layer). Through a series of experiments, it is shown that the timescale of motion can be extended by increasing the thickness of the active layer, decreasing the porosity of the active layer, or increasing the filling ratio of the hydrophobic restrictive and blocking layers. Similarly, a lower thickness of the active layer and lower filling ratio of all layers result in a faster motion. As a proof of concept, we demonstrate several prototypes that exhibit sequential motion, including an aperture with overlapping elements where each completes its movement sequentially to avoid collision, and a self-locking mechanism where defined areas of the structure are choreographed to achieve a multi-step self-shaping and locking function. The presented method extends the programmability and the functional capabilities of hygromorphic 4D-printing, allowing for novel applications across fields such as robotics, smart actuators, and adaptive architecture.

Soft Office: a human-robot collaborative system for adaptive spatial configuration.

The Soft Office project was developed in response to the rapidly changing context of commercial architecture, where accommodating fluid programmatic requirements of occupants has become key to sustainable interior space. The project is placed within a broader context of relevant research in architectural robotics, in situ robotic fabrication, and adaptive and reconfigurable architecture. It establishes a methodology for spatial configuration through the implementation of a custom collaborative robotic interior reconfiguration system. Within this system, human users and task-specific robots perform complementary tasks toward a dynamic spatial goal that is defined by a set of evaluative criteria intended to predict successful interior space configurations (Bailey et al. in Humanizing digital reality: design modeling symposium Paris 2017, Springer Singapore, Singapore, pp 337-348, 2018). Venturing beyond robotics as merely a means of construction automation, the presented research deploys an approach that critically engages future models of interaction between humans and robotic architecture, mediated by in situ, architecturally embedded machines. In contrast to a conventional collaborative robotic manufacturing process, where a human worker is executing fabrication and manufacturing tasks according to a pre-designed blueprint, the proposed approach engages the human user as the designer, the worker, and the consumer of the architectural outcome. This gives the occupant the agency to rapidly reconfigure their environment in response to changing programmatic needs as well as the ability to respond ad hoc to outside forces, such as social distancing requirements for the post-quarantine re-occupation of buildings. Furthermore, task-specificity of the presented robotic system allows us to speculate on future roles of designers in the development of architectural fabrication technology beyond the appropriation of existing hardware and to look towards systems that are architecture specific.

Computational analysis of hygromorphic self-shaping wood gridshell structures.

Bi-layered composites capable of self-shaping are of increasing relevance to science and engineering. They can be made out of anisotropic materials that are responsive to changes in a state variable, e.g. wood, which swells and shrinks by changes in moisture. When extensive bending is desired, such bilayers are usually designed as cross-ply structures. However, the nature of cross-ply laminates tends to prevent changes of the Gaussian curvature so that a plate-like geometry of the composite will be partly restricted from shaping. Therefore, an effective approach for maximizing bending is to keep the composite in a narrow strip configuration so that Gaussian curvature can remain constant during shaping. This represents a fundamental limitation for many applications where self-shaped double-curved structures could be beneficial, e.g. in timber architecture. In this study, we propose to achieve double-curvature by gridshell configurations of narrow self-shaping wood bilayer strips. Using numerical mechanical simulations, we investigate a parametric phase-space of shaping. Our results show that double curvature can be achieved and that the change in Gaussian curvature is dependent on the system's geometry. Furthermore, we discuss a novel architectural application potential in the form of self-erecting timber gridshells.

Plant Movements as Concept Generators for the Development of Biomimetic Compliant Mechanisms.

Plant movements are of increasing interest for biomimetic approaches where hinge-free compliant mechanisms (flexible structures) for applications, for example, in architecture, soft robotics, and medicine are developed. In this article, we first concisely summarize the knowledge on plant movement principles and show how the different modes of actuation, that is, the driving forces of motion, can be used in biomimetic approaches for the development of motile technical systems. We then emphasize on current developments and breakthroughs in the field, that is, the technical implementation of plant movement principles through additive manufacturing, the development of structures capable of tracking movements (tropisms), and the development of structures that can perform multiple movement steps. Regarding the additive manufacturing section, we present original results on the successful transfer of several plant movement principles into 3D printed hygroscopic shape-changing structures ("4D printing"). The resulting systems include edge growth-driven actuation (as known from the petals of the lily flower), bending scale-like structures with functional bilayer setups (inspired from pinecones), modular aperture architectures (as can be similarly seen in moss peristomes), snap-through elastic instability actuation (as known from Venus flytrap snap-traps), and origami-like curved-folding kinematic amplification (inspired by the carnivorous waterwheel plant). Our novel biomimetic compliant mechanisms highlight the feasibility of modern printing techniques for designing and developing versatile tailored motion responses for technical applications. We then focus on persisting challenges in the field, that is, how to speed-boost intrinsically slow hydraulically actuated structures and how to achieve functional resilience and robustness, before we propose the establishment of a motion design catalog in the conclusion.

4D pine scale: biomimetic 4D printed autonomous scale and flap structures capable of multi-phase movement.

We developed biomimetic hygro-responsive composite polymer scales inspired by the reversible shape-changes of Bhutan pine (Pinus wallichiana) cone seed scales. The synthetic kinematic response is made possible through novel four-dimensional (4D) printing techniques with anisotropic material use, namely copolymers with embedded cellulose fibrils and ABS polymer. Multi-phase motion like the subsequent transversal and longitudinal bending deformation during desiccation of a natural pinecone scale can be structurally programmed into such printed hygromorphs. Both the natural concept generator (Bhutan pinecone scale) and the biomimetic technical structure (4D printed scale) were comparatively investigated as to their displacement and strain over time via three-dimensional digital image correlation methods. Our bioinspired prototypes can be the basis for tailored autonomous and self-sufficient flap and scale structures performing complex consecutive motions for technical applications, e.g. in architecture and soft robotics. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.

Analysis of hygroscopic self-shaping wood at large scale for curved mass timber structures.

The growing timber manufacturing industry faces challenges due to increasing geometric complexity of architectural designs. Complex and structurally efficient curved geometries are nowadays easily designed but still involve intensive manufacturing and excessive machining. We propose an efficient form-giving mechanism for large-scale curved mass timber by using bilayered wood structures capable of self-shaping by moisture content changes. The challenge lies in the requirement of profound material knowledge for analysis and prediction of the deformation in function of setup and boundary conditions. Using time- and moisture-dependent mechanical simulations, we demonstrate the contributions of different wood-specific deformation mechanisms on the self-shaping of large-scale elements. Our results outline how to address problems such as shape prediction, sharp moisture gradients, and natural variability in material parameters in light of an efficient industrial manufacturing.

Toward a New Generation of Smart Biomimetic Actuators for Architecture.

Motile plant structures (e.g., leaves, petals, cone scales, and capsules) are functionally highly robust and resilient concept generators for the development of biomimetic actuators for architecture. Here, a concise review of the state-of-the-art of plant movement principles and derived biomimetic devices is provided. Achieving complex and higher-dimensional shape changes and passive-hydraulic actuation at a considerable time scale, as well as mechanical robustness of the motile technical structures, is challenging. For example, almost all currently available bioinspired hydraulic actuators show similar limitations due to the poroelastic time scale. Therefore, a major challenge is increasing the system size to the meter range, with actuation times of minutes or below. This means that response speed and flow rate need significant improvement for the systems, and the long-term performance degradation issue of hygroscopic materials needs to be addressed. A theoretical concept for "escaping" the poroelastic regime is proposed, and the possibilities for enhancing the mechanical properties of passive-hydraulic bilayer actuators are discussed. Furthermore, the promising aspects for further studies to implement tropistic movement behavior are presented, i.e., movement that depends on the direction of the triggering stimulus, which can finally lead to "smart building skins" that autonomously and self-sufficiently react to changing environmental stimuli in a direction-dependent manner.

Biomimetic design processes in architecture: morphogenetic and evolutionary computational design.

Design computation has profound impact on architectural design methods. This paper explains how computational design enables the development of biomimetic design processes specific to architecture, and how they need to be significantly different from established biomimetic processes in engineering disciplines. The paper first explains the fundamental difference between computer-aided and computational design in architecture, as the understanding of this distinction is of critical importance for the research presented. Thereafter, the conceptual relation and possible transfer of principles from natural morphogenesis to design computation are introduced and the related developments of generative, feature-based, constraint-based, process-based and feedback-based computational design methods are presented. This morphogenetic design research is then related to exploratory evolutionary computation, followed by the presentation of two case studies focusing on the exemplary development of spatial envelope morphologies and urban block morphologies.