Simon J. Leigh

Fabrication of 3-dimensional cellular constructs via microstereolithography using a simple, three-component, poly(ethylene glycol) acrylate-based system.

A novel method for the production of inhibitor- and solvent-free resins suitable for three-dimensional (3D) microstereolithography is reported. Using an exemplar poly(ethylene glycol)-based resin, the control of features in the X, Y, and Z planes is demonstrated such that complex structures can be manufactured. Human mesenchymal stem cells cultured on the manufactured scaffolds remained viable during the 7 day assessment period, with proliferation rates comparable to those observed on tissue culture polystyrene. These data suggest that this novel, yet simple, method is suitable for the production of 3D scaffolds for tissue engineering and regenerative medicine applications.

Using a magnetite/thermoplastic composite in 3D printing of direct replacements for commercially available flow sensors

Flow sensing is an essential technique required for a wide range of application environments ranging from liquid dispensing to utility monitoring. A number of different methodologies and deployment strategies have been devised to cover the diverse range of potential application areas. The ability to easily create new bespoke sensors for new applications is therefore of natural interest. Fused deposition modelling is a 3D printing technology based upon the fabrication of 3D structures in a layer-by-layer fashion using extruded strands of molten thermoplastic. The technology was developed in the late 1980s but has only recently come to more wide-scale attention outside of specialist applications and rapid prototyping due to the advent of low-cost 3D printing platforms such as the RepRap. Due to the relatively low-cost of the printers and feedstock materials, these printers are ideal candidates for wide-scale installation as localized manufacturing platforms to quickly produce replacement parts when components fail. One of the current limitations with the technology is the availability of functional printing materials to facilitate production of complex functional 3D objects and devices beyond mere concept prototypes. This paper presents the formulation of a simple magnetite nanoparticle-loaded thermoplastic composite and its incorporation into a 3D printed flow-sensor in order to mimic the function of a commercially available flow-sensing device. Using the multi-material printing capability of the 3D printer allows a much smaller amount of functional material to be used in comparison to the commercial flow sensor by only placing the material where it is specifically required. Analysis of the printed sensor also revealed a much more linear response to increasing flow rate of water showing that 3D printed devices have the potential to at least perform as well as a conventionally produced sensor.

A microstereolithography resin based on thiol-ene chemistry: towards biocompatible 3D extracellular constructs for tissue engineering

A new class of degradable aliphatic poly(carbonate) resins for use in microstereolithographic process is described. Using a biologically inert photo-inhibiting dye, exemplar 3-dimensional structures were produced using thiol-ene chemistry via microstereolithography. Fabricated constructs demonstrated good biological compatibility with cells and had tensile properties that render them suitable for use as tissue engineering scaffolds.

Fabrication of patterned surfaces by photolithographic exposure of DNA hairpins carrying a novel photolabile group

This article demonstrates a method for the fabrication of patterned surfaces using hairpin oligonucleotides carrying a novel photolabile group at the apex of the loop. Photolysis of surfaces carrying photolabile hairpin oligonucleotides results in the formation of areas carrying single-stranded DNA sequences that direct the deposition of the complementary sequence at the photolysed sites. The non-photolysed areas carrying the intact hairpin do not bind to complementary sequences due to the presence of the more stable intramolecular hairpin duplex. The photolithographic process was performed on silicon wafers and followed by atomic force microscopy and epi-fluorescent microscopy. The method described offers an attractive option for the fabrication of biologically interfaced patterned surfaces with specific recognition properties with potential uses in electronics and as biosensors.

Polymer composites for 3D printing of functional sensors and transducers

This paper represents a review of the recent work undertaken in the Digital and Materials Technology Laboratory at the University of Warwick on the theme of Additive Manufacturing (AM)/3D printing technology with polymer composites to carry out the manufacture of functional sensors and transducers. Examples of devices for acoustic, flow, electronic and chemical sensing are presented. Each sensor system utilizes a composite material developed in order to achieve functional sensing. This collection of examples demonstrates the viability of AM technology in the manufacture of bespoke sensor devices.

High-resolution acoustic imaging at low frequencies using 3D-printed metamaterials

An acoustic metamaterial has been constructed using 3D printing. It contained an array of air-filled channels, whose size and shape could be varied within the design and manufacture process. In this paper we analyze both numerically and experimentally the properties of this polymer metamaterial structure, and demonstrate its use for the imaging of a sample with sub-wavelength dimensions in the audible frequency range.

Rapid manufacture of monolithic micro-actuated forceps inspired by echinoderm pedicellariae

The concept of biomimetics and bioinspiration has been used to enhance the function of materials and devices in fields ranging from healthcare to renewable energy. By developing advanced design and manufacturing processes, researchers are rapidly accelerating their ability to mimic natural systems. In this paper we show how micro-actuated forceps inspired by echinoderm pedicellarie have been produced using the rapid manufacturing technology of micro-stereolithography. The manufactured monolithic devices are composed of sets of jaws on the surface of thin polymer resin membranes, which serve as musculature for the jaws. The membranes are suspended above a pneumatic chamber with the jaws opened and closed through pneumatic pressure changes exerted by a simple syringe. The forceps can be used for tasks such as grasping of microparticles. Furthermore, when an object is placed in the centre of the membrane, the membrane flexes and the jaws of the device close and grasp the object in a responsive manner. When uncured liquid photopolymer is used to actuate the devices hydraulically instead of pneumatically, the devices exhibit self-healing behaviour, sealing the damaged regions and maintaining hydraulic integrity. The manufactured devices present exciting possibilities in fields such as micromanipulation and micro-robotics for healthcare.

Rapid prototyping technologies for ultrasonic beam focussing in NDE

This paper describes a technique where ultrasonic beam-modifying elements (acoustic lenses) have been designed in CAD, and then fabricated using rapid-prototyping techniques. An example of such a lens (resembling a miniature Schmidt-Cassegrain telescope) has been fabricated, and has been successfully used with a standard, commercially available ultrasonic transducer for imaging. Examples of images taken of a coin are given. Details of the design, build, performance and analysis of this focusing system are described.

Fabrication and analysis of cylindrical resin AFM microcantilevers

In this paper a new method of fabricating cylindrical resin microcantilevers using the Direct Digital Manufacturing (DDM) technique of Micro-stereolithography (MSL) is described. The method is rapid and commercially viable, allowing the fabrication of atomic force microscope (AFM) cantilevers which exhibit much larger spring constants than those currently commercial available. This allows for experimentation in a force regime orders of magnitude higher than currently possible using the AFM. This makes these cantilevers ideally suited for AFM-based depth sensing indentation. Due to their geometry, the assumptions used in the standard Euler-Bernoulli beam theory usually used to analyse AFM cantilevers may no longer be valid. Therefore approximate analytical solutions based on Timoshenko beam theory have been derived for the stiffness and resonant frequency of these cantilevers. Prototypes of the cantilevers have been fabricated and tested. Results show good agreement between experiment and theory.

Design and characterization of 3D-printed phononic crystals for sub-MHz ultrasound manipulation

Additive manufacturing (3D printing) has been used to construct phononic crystals that operate in the 100 kHz - 1MHz frequency range. These were in the form of regular arrays and columns of steel spheres, embedded within a polymer matrix. Experimental measurements using coded waveforms in a water tank were able to demonstrate that focusing effects were present at certain frequencies, as expected from a phononic crystal structure.