Developable Metamaterials

Project Brief

Initial Proposal

Proposed by Madlaina Signer, Alexandra Ion, and Olga Sorkine-Hornung, a structured material that incorporates fast fabrication technologies is designed. Utilizing the compliant smooth bends of thin sheet materials such as paper, the ruffle serves as the base unit for the developable metamaterial that is reconfigurable. The material is intended to not be stretched or compressed, but only bent, which serves as the metamaterial’s concept of developability.

Aim + Purpose of Current Study

Building off of this initial proposal, this study investigates the three-dimensional ruffle structure, which is a ruffle form controllable from x, y, and z directions. A potential implementation of this ruffle structure is then decided and studied through a series of potential design explorations, with the intention of using the ruffle structure to achieve the implemented object/structure’s original functionalities, but also improving certain aspects of the object/structure with the unique qualities that the ruffles bring.

Potential Design Implementations

Brainstorming Structures

Based on the qualities of the ruffles, a series of structural ideas are proposed in regards to focus, scale and purpose. The initial ruffle element is broken down and re-imagined with different parameters and parts from the initial 2D movements to 3D movements, which would help inform the design implementation stage later on in the process.

Structure modules explored includes reformative columns, double cones, and mobius. With a library of these parts, I moved on to developing new ideas with the 3D reconfigurable ruffle implementations.

Finalizing Design Direction

The initial proposed implementations are: Pavilion Structure, Furniture Structure, Helmet Damping Structure, and Lower Limb Prosthesis. After discussing the fabrication limitations, we've decided

The final design direction chosen after careful consideration is the lower limb prosthetic design. The prosthetic design is a more achievable implementation in comparison to the pavilion structure idea, but it is also less studied, whereas there have been many prior innovations in regards to small-scale furniture designs and helmet designs.

Foot Biomechanics Research + Existing Prosthesis

Biomechanics of Foot

Prior to the design phase, the biomechanics of the foot is studied to provide a better understanding of the human movements and gait cycle.

Study areas include the key movements of the ankle joint complex, ahis of rotation of the ankle, and motion ranges due to the difference in the individual’s daily activities, modes of living, as well as geographical and cultural differences, the ankle range of motion varies significantly. Inaddition, the forces in ankle joints are also studied. 

Existing Prosthetic Designs

In regards to ankle-foot specific prosthetic designs, the existing designs can be split into four categories: SACH/elastic keel foot; single axis/multi axis foot; dynamic response foot; and microprocessor Feet.

Each of the categories are studied and analyzed depending on their advantages and potential improvements. 

Potential Improvements of Existing Prosthetic Designs

After rounds of research and discussions, a list of three potential improvements of existing prosthetic designs is created, which are improvements that would ideally be addressed on top of using ruffles to perform prosthesis functions.

          1. Weight of the prosthesis

          2. Ankle movements: Variable directional stiffness (inversion/eversion)

          3. Sensorize the ruffles for data collection

Form Prototyping

Paper Prototypes and Initial Designs

Extending from the material considerations mentioned in the previous section, several different materials were considered and utilized throughout the process. Paper was used for initial prototyping as a brainstorming and design tool, whereas PVC sheets and spring metal sheets were used later on for more specific measurements and estimations.

With this in mind, two design directions emerged: 3D curve ruffles and mobius strip ruffles. Both the 3D curve and mobius are implemented to address the inversion/eversion aspect, whereas the regular ruffle folds would perform the predominant plantar/dorsiflexion. 

After experimenting with the three prototypes, it appears that the second design (3D curve ruffle) appears to be the most ideal and achievable design for future investigations. Thus, the models and discussions from here onwards primarily focus on the 3D curve ruffle prototype.

"Kit of Parts"

Elaborating on the kit of parts ideas with using different paper based materials, the prototype in the second image series experiments with having a “kit of parts” rather than using a single strip. Some components can be replaceable, such as the front bumper indicated in yellow, and the different parts could have varying stiffnesses according to the functionalities.

Connection & Material Exploration

Connections Testings

The paper 3d curve prototype is used to test connection points. Connections are formed by using eyelet pairs, (which would be similar to connections on the real prototype) which are indicated with colors and labels in the diagram towards the left. 

The overall form consists of 5 eyelet pairs and 1 eyelet trios. The trio (marked in orange) serves as the main body of the form, which is the 3d curve ruffle.  The connection sequence goes from top to bottom indicated on the left (pair 1, pair 2, pair 3, trio 1, pair 4, pair 5), which consists of 6 connection steps.

Material Exploration

Building off of the paper prototypes and design ideas, this section focuses specifically on the material testings (PVC and Spring steel), which is explained primarily through rough models and numeric measurements.

Full Kit Construction + Testing

Utilizing PVC material, a synthesis testing of the prototype is tested, from the assembly of kit of parts and reaction to forces as a prosthesis.

Conclusion + Future Steps

The three-dimensional ruffle structure is able to create a form that dedicates itself to perform the functionalities of the existing ankle-prosthetics, but it also has the potential to address questions that have yet to be fully answered with existing models (such as the inversion/eversion function, the detailed sensorization of the prosthetics, as well as the distributed weight of the ankle). 

However, more research, iterations, and testing with accurate numeric data need to be conducted for the prototype to be actually achieved, which would require computational implementations as well as lab studies/testing. Future work areas include: Spring Metal Prototype, Computational Implementations, and Biomechanics Studies.

This research project serves as the foundation work, and is continued by Professor Alex Ion and her Interactive Structures Team at CMU HCI Institute.