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Non-assembly 3D printed hand prosthesis

In developing countries, the accessibility to prosthetic devices is low due to the limited healthcare conditions, a general lack of technical knowledge and poorly equipped workshops. The introduction of 3D printing technologies has permitted new cheap and personalized hand prosthetic designs by bypassing many of the current manufacturing limitations of traditional prostheses. Although innovative and accepted in different settings around the world, these active 3D printed prostheses still require extra parts and assembly steps, thus reducing the overall accessibility. We have developed the first functional non-assembly prosthetic hand fabricated with the material extrusion technology; the most accessible 3D printing technique. The process is reduced to a single printing job and an extra step of support material removal. No extra parts, materials or complex assembly steps are required.

During the design process, we have also adopted ten design guidelines that led to a successful working mechanism, we encourage future designers with 3D printing to follow our non-assembly approach.



Ten Guidelines for Non-Assembly A Prosthetic Hand is 3D Printed in One Piece with No Need for Assembly

Contact: Juan Cuellar (

3D printed wasp-ovipositor replica: reverse engineering approach (CLOSED)

In nature, several species of parasitoid wasps have a thin and flexible needle-like structure, called ovipositor, which is used to deposit eggs in a host (e.g., a larva) hidden into tree trunks or fruits. The wasp ovipositor consists of three segments, called valves, longitudinally connected that can slide along each other.  The animals can drill in different substrates by actuating the valves in a reciprocal motion and steer by changing the relative positions of the valves during probing (i.e. protracting and retracting of the valves).

We are currently developing a novel steerable needle for minimally invasive interventions inspired by the wasp-ovipositor. However, the steering mechanisms used by the animal is not yet fully understood.

The project will focus on understanding how the steering mechanism works and which characteristics of the ovipositor play a relevant role.

The student will use detailed 3D images of different ovipositors to design several replicas of the wasp ovipositor in larger scale with 3D printed techniques. The prototypes will be tested with an experimental facility where motion pattern and speed can be controlled. The ovipositors will be inserted in gelatine of different concentration to study the design parameters effecting the steering mechanism.

Contact: Marta Scali,

Picture adapted from “Braconid Wasp Ovipositing” by Katja Schulz is licensed under CC BY 2.0.

Automatic design and manufacturing of upper limb prosthetic sockets for developing countries

Comfort and functionality of upper limb prosthetics is highly dependent on socket performance. Correct anatomical fit is therefore of paramount importance for prosthetic designs. We believe that the complex design process of prosthetic sockets can be achieved automatically using accurate anatomical models of the stump. With the increasing advance in smartphone technology it is possible to reconstruct digital models based on camera information. We plan to explore current technologies for generating 3D digital models from multiple 2D photos and assess such techniques to stablish a framework in which smartphone technology can be used to generate 3D computer models of upper limb stumps. Using precise geometry of the stump and current CAD technologies it is possible to create a socket design that fits accurately into the residual limb. We plan to adopt such process to build fully working prosthetic sockets using 3d printing technology for developing countries.

Contact: Juan Cuellar,

Design of an endoluminal ovipositor-device (CLOSED)

During colonoscopy procedures an endoscopic device is inserted into the patient and pushed through the colon with consequential discomfort to the patient.  Self-propelling devices that are able of moving through a lumen without the need of external push could be beneficial for these applications. Research in this topic is ongoing, but no successful solutions have yet been discovered.

At TU Delft a former master student (Perry Posthoorn) developed a self-propelled device inspired by the mechanism of the ovipositor of the wasp. The ovipositor is a needle-like structure which consists of three elements that can slide along each other. By means of a reciprocal movement of the elements the wasp is able to insert the ovipositor through a substrate. The reciprocal sliding mechanism of multiple elements has inspired the design of our ovipositor-device.

Preliminary tests have shown that the device is able to move through an ex-vivo porcine colon, although at extremely slow speed due to a sub-optimal internal construction of the device.

The aim of this graduation project  is to develop a strongly improved endoluminal device aiming at maximizing propulsion speed at minimal internal complexity with the final aim to make a revolutionary new system suited for disposable use.

For more information contact Marta Scali (

HelixFlex – Squid-like motion by helical steering

Developed in 2013-2014, diameter 5 mm, steering range: ±150º in all directions.

Nature exhibits two inherently different approaches for creating maneuverable structures: the endo- or exoskeleton approach, and the hydrostatic skeleton approach. An endo- or exoskeleton  is a rigid structure  connected by joints that enable motion, for example in our own body.  A hydrostatic skeleton, however, is a compliant structure solely contructed out of soft tissues, for example in the tentacle of a squid or in the trunk of an elephant.

Conventional steerable designs, based on rigid links and hinged mechanisms, are best comparable with nature’s endo- or exoskeleton approach. These conventional  designs have proven  to be highly effective at large dimensions, as for example in the scales of an excavator. At the smaller dimensions needed for minimally invasive surgery, however, the fabrication of such hinged structures becomes increasingly difficult.

The muscular hydrostatic skeleton in the arms of Loliginid squid consists out of differently orientated muscle layers (see Figure). Simultaneous contraction of these muscle layers results in a flexible, fluent motion. This led to the development of a new principle of steering via simultaneous actuation of multiple, differently orientated cable layers.

Inspired by nature’s hydrostatic skeleton approach, the multi-maneuvrable tip of the HelixFlex consists of a single compliant segment, and incorporates three different cable layers: one with parallel cables and two with helically-oriented cables. Simultanuous actuation of these cable layers is accomplished via a similarly shaped  joystick in the handle of the instrument. By manually controlling this joystick, the user can control the movement of HelixFlex’ tip in four Degrees of Freedom, resulting in a  fluent motion that greatly reflects the motion of squid tentacles (see movie).

To our knowledge, the HelixFlex is the first instrument that uses simultaneous actuation of parallel- and helical-routed cable layers, and therefore a patent is pending.

*Left: A section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Right: the steerable tip of HelixFlex containing multiple differently orientated cable layers.
Left: A section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Right: the steerable tip of HelixFlex containing multiple differently orientated cable layers. [1]



NWO – Ultra-Thin Steerable Needle for Solid-Organ Interventions – WASP

This research project is part of the iMIT research programme and funded by the Netherlands Organization for Scientific Research (NWO). The iMIT Program, executed by a community of Dutch Universities, university medical centers, and companies, aims to develop instruments for minimally invasive interventions. The program will result in the development of interactive Multi-Interventional Tools (iMIT)  that can adapt to their environment and integrate diagnostic and therapeutic functionalities, thus permitting effective single-procedure interventions.

The WASP project focuses on medical needles – common devices used in minimally invasive percutaneous procedures, such as localized therapeutic drug delivery or tissue sample removal (biopsy). Reaching the target with high accuracy and precision is necessary for the success of these procedures and becomes a challenge when the target is located deep inside the body. The surgeon needs a steerable flexible needle that can follow complex curved trajectories while avoiding sensitive structures, such as blood vessels, located along the trajectory between the insertion point and the target site. Looking in nature we find an interesting behavior in wasps which can be used as source of inspiration for facing this challenge. The wasp has a thin and flexible needle-like structure, called ovipositor, used for laying eggs into larvae hidden inside fruits or wood. It is composed of three longitudinal segments, called valves, that can be actuated individually and independently of each other with musculature located in the abdomen of the insect. In this way the wasp steers the ovipositor along curved trajectories inside different substrates without a need for rotatory motion or axial push.

Inspired by the anatomy and the steering mechanism of this needle-like structure we aim to develop an ultra-thin steerable needle that can follow curved paths through complex solid organs while avoiding obstacles.

Biopsy Harvester – High-Speed Tissue Cutting

Current minimally invasive laparoscopic tissue harvesting techniques for pathological purposes involve taking multiple imprecise and inaccurate biopsies, usually using a laparoscopic forceps or other assistive devices. Potential hazards, e.g. cancer spread when dealing with tumorous tissue, call for a more reliable alternative in the form of a single laparoscopic instrument capable of repeatedly taking a precise biopsy at a desired location. Therefore, the aim of this project was to design a disposable laparoscopic instrument tip, incorporating a centrally positioned glass fibre for tissue diagnostics; a cutting device for fast, accurate and reliable biopsy of a precisely defined volume and a container suitable for sample storage.

Inspired by the sea urchin’s chewing organ, Aristotle’s lantern, and its capability of rapid and simultaneous tissue incision and enclosure by axial translation, we designed a crown-shaped collapsible cutter operating on a similar basis. Based on a series of in vitro experiments indicating that tissue deformation decreases with increasing penetration speed leading to a more precise biopsy, we decided on the cutter’s forward propulsion via a spring. Apart from the embedded spring-loaded cutter, the biopsy harvester comprises a smart mechanism for cutter preloading, locking and actuation, as well as a sample container.

A real-sized biopsy harvester prototype was developed and tested in a universal tensile testing machine at TU Delft. In terms of mechanical functionality, the preloading, locking and actuation mechanism as well as the cutter’s rapid incising and collapsing capabilities proved to work successfully in vitro. Further division of the tip into a permanent and a disposable segment will enable taking of multiple biopsies, mutually separated in individual containers. We believe the envisioned laparoscopic opto-mechanical biopsy device will be a solution ameliorating time demanding, inaccurate and potentially unsafe laparoscopic biopsy procedures.