Now showing 1 - 10 of 10
  • Publication
    Comparison of crystalline and amorphous versions of a magnesium-based alloy: corrosion and cell response
    (AO Research Institute Davos, 2015-08-28) ; ;
    Mg-Ca-Zn alloys have been identified as potential materials for bioresorbable orthopaedic implants –e.g. for bone fixation. It is important, however, to tailor the resorption rate of the alloy to the healing rate of the bone and the rate at which the metal ion release can be tolerated by the human body. Recent work has shown that bulk metallic glass (or amorphous) alloys corrode more slowly than their conventional crystalline counterparts1, and the rate may be more suited to orthopaedic applications. It has also indicated a slower evolution of hydrogen gas during resorption2. This paper presents an experimental study on the casting of a Mg75-Zn22-Ca5 into bulk amorphous form, and testing of the resultant material in vitrofor corrosion and cytotoxicity.
      136
  • Publication
    A Radial Clutch Needle for Facile and Safe Tissue Compartment Access
    Efficient and safe access to targeted therapeutic sites is a universal challenge in minimally invasive medical intervention. Percutaneous and transluminal needle insertion is often performed blindly and requires significant user skill and experience to avoid complications associated with the damage of underlying tissues or organs. Here, we report on the advancement of a safer needle with a radial mechanical clutch, which is designed to prevent overshoot injuries through the automatic stopping of the needle once a target cavity is reached. The stylet‐mounted clutch system is inexpensive to manufacture and compatible with standard hypodermic or endoscopic needles, and therefore can be adapted to achieve safe access in a myriad of minimally invasive procedures, including targeted drug delivery, at‐home and in‐hospital intravenous access, laparoscopic and endo‐ and trans‐luminal interventions. Here, we demonstrate the clutch needle design optimization and illustrate its potential for rapid and safe minimally invasive cannulation.
      282
  • Publication
    Development and Evaluation of 3D-Printed Dry Microneedle Electrodes for Surface Electromyography
    Surface electromyography (sEMG) allows for direct measurement of electrical muscle activity with use in fundamental research and many applications in health and sport. However, conventional surface electrode technology can suffer from poor signal quality, requires careful skin preparation, and is commonly not suited for long-term recording. These drawbacks have challenged translation of sEMG to clinical applications. In this paper, dry 3D-printed microneedle electrodes (MNEs) are proposed to overcome some of the limitations of conventional electrodes. Employing a direct-metal-laser-sintering (DMLS) 3D printing process, a two-step fabrication method is developed to produce sharp medical-grade stainless steel MNEs. The developed MNEs are compared to needle-free versions and to standard wet Ag/AgCl electrodes. Functional testing is conducted to analyze the electrode–skin impedance in healthy human volunteers and sEMG data are recorded from the biceps brachii muscle. Results show that microneedle electrodes display a greatly reduced (≈63%) electrode–skin contact impedance with respect to needle-free electrodes and record sEMG at a signal-to-noise ratio comparable to clinical-grade wet Ag/AgCl electrodes over a period of up to 6 h. Overall, a fabrication method and electrode type are presented which yield high-quality sEMG signals when evaluated in humans, highlighting the potential of MNEs as a platform for biosignal recording.
    Scopus© Citations 27  131
  • Publication
    The Effect of Powder Size and Morphology on the Sinterability of Bioresorbable Mg-Sr/Ca Alloys
    Possessing outstanding biocompatibility and bioresorbability, magnesium (Mg) alloys with strontium (Sr) and calcium (Ca) additions have shown potential to be used as temporary implants in orthopaedic applications. Having a low elastic modulus (45 GPa) close to the human bone lowers the stress shielding effects. Low temperature Additive Manufacturing (AM) techniques (e.g., Fused Deposition Modelling) have potential to be used for the fabrication of complex Mg components while avoiding safety concerns associated with high temperature AM. However, low sinterability of common Mg-alloys is the main limiting factor. The objective of this work is to investigate the effect of powder particle size / morphology on the sinterability of Mg-Ca/Sr based alloys produced via powder metallurgy. Laser Diffraction and Scanning Electron Microscopy (SEM) were used to characterize particle size and morphology. The study also focused on assessing the role of liquid phase sintering (LPS) mechanism by thermodynamic calculations and microstructural characterisation (SEM). Porosity measurements using density analysis and image processing were employed to determine the effects of powder size and morphology on sinterability of the alloys. It was found that the non-homogeneous particle size distribution with more spherical powder particles, facilitated the compaction and accordingly higher densification was obtained. This was achieved for powders milled at higher speeds (900 rpm), resulting in significantly lower porosity levels (~ 6-8 %) compared to the dry-milled state (~40-60 %).
      102
  • Publication
    Simple and customizable method for fabrication of high-aspect ratio microneedle molds using low-cost 3D printing
    We present a simple and customizable microneedle mold fabrication technique using a low-cost desktop SLA 3D printer. As opposed to conventional microneedle fabrication methods, this technique neither requires complex and expensive manufacturing facilities nor expertise in microfabrication. While most low-cost 3D-printed microneedles to date display low aspect ratios and poor tip sharpness, we show that by introducing a two-step “Print & Fill” mold fabrication method, it is possible to obtain high-aspect ratio sharp needles that are capable of penetrating tissue. Studying first the effect of varying design input parameters and print settings, it is shown that printed needles are always shorter than specified. With decreasing input height, needles also begin displaying an increasingly greater than specified needle base diameter. Both factors contribute to low aspect ratio needles when attempting to print sub-millimeter height needles. By setting input height tall enough, it is possible to print needles with high-aspect ratios and tip radii of 20–40 µm. This tip sharpness is smaller than the specified printer resolution. Consequently, high-aspect ratio sharp needle arrays are printed in basins which are backfilled and cured in a second step, leaving sub-millimeter microneedles exposed resulting microneedle arrays which can be used as male masters. Silicone female master molds are then formed from the fabricated microneedle arrays. Using the molds, both carboxymethyl cellulose loaded with rhodamine B as well as polylactic acid microneedle arrays are produced and their quality examined. A skin insertion study is performed to demonstrate the functional capabilities of arrays made from the fabricated molds. This method can be easily adopted by the microneedle research community for in-house master mold fabrication and parametric optimization of microneedle arrays.
    Scopus© Citations 151  377
  • Publication
    Development of Magnesium-Strontium/Calcium (Mg-Sr/Ca)-Based Alloys with Improved Sinterability for Next-Generation Biomedical Implants
    The use of biodegradable magnesium (Mg) alloys for bone fixation devices has potential to improve patients’ quality of life by avoiding the necessary secondary operations conducted regularly for the removal of implants fabricated from conventional non-resorbable alloys. Mg-alloys have excellent biocompatibility and biodegradability along with a low modulus of elasticity which will decrease bone-shielding effects. However, low corrosion resistance and relatively poor mechanical performance limit the use of Mg-based alloys for biomedical applications. This study focuses on the processing of Mg-Ca- and Mg-Sr-based alloys via powder metallurgical route. Thermodynamic calculations are used to predict the liquid phase fractions in order to optimise sinterability and porosity levels. Materials characterisation was conducted to validate the thermodynamic modeling results using optical and scanning electron microscopy (SEM/EDS) as well as X-ray Diffraction (XRD).
      52
  • Publication
    Towards Biofunctional Microneedles for Stimulus Responsive Drug Delivery
    (American Chemical Society, 2015) ;
    Microneedles have recently been adopted for use as a painless and safe method of transdermal therapeutic delivery through physically permeating the stratum corneum. While microneedles create pathways to introduce drugs, they can also act as conduits for biosignal sensing. Here, we explore the development of microneedles as both biosensing and drug delivery platforms. Microneedle sensors are being developed for continuous monitoring of biopotentials and bioanalytes through the use of conductive and electrochemically reactive biomaterials. The range of therapeutics being delivered through microneedle devices has diversified, while novel bioabsorbable microneedles are undergoing first-in-human clinical studies. We foresee that future microneedle platform development will focus on the incorporation of biofunctional materials, designed to deliver therapeutics in a stimulus responsive fashion. Biofunctional microneedle patches will require improved methods of attaching to and conforming to epithelial tissues in dynamic environments for longer periods of time and thus present an assortment of new design challenges. Through the evolution of biomaterial development and microneedle design, biofunctional microneedles are proposed as a next generation of stimulus responsive drug delivery systems.
    Scopus© Citations 50  1629
  • Publication
    In silico design of additively manufacturable composite synthetic vascular conduits and grafts with tuneable compliance
    (Royal Society of Chemistry, 2021-03-09) ; ; ;
    Benchtop testing of endovascular medical devices under accurately simulated physiological conditions is a critical part of device evaluation prior to clinical assessment. Currently, glass, acrylic and silicone vascular models are predominantly used as anatomical simulator test beds for in vitro testing. However, most current models lack the ability to mimic the non-linear radial compliance of native vessels and are typically limited to being compliance-matched at a single mean pressure comparison point or not at all. Hence, a degree of caution needs to be shown when analysing results from such models under simulated physiological or pathophysiological conditions. Similarly, the clinical translation of proposed biomimetic compliance-matched vascular grafts has undoubtedly been curtailed due to performance and material limitations. Here, we propose a new design for synthetic vessels where compliance can be precisely modulated across a wide physiological pressure range by customising design parameters. Building on previously demonstrated methods of 3D printing composite compliant cylindrical structures, we demonstrate proof of principle in creating composite vascular constructs designed via a finite element model. Our constructs are 3D printable and consist of a soft silicone matrix with embedded polyurethane fibres. The fibre layer consists of circumferential sinusoidal waves with an amplitude that can be altered to result in tuneable internal radial compliances of 5.2-15.9%/mmHg × 10-2 at a mean pressure of 100 mmHg. Importantly, the design presented here allows preservation of the non-linear exponentially decaying compliance curve of native arteries and veins with an increasing mean pressure. This model offers a design toolbox for 3D printable vascular models that offer biomimetic compliance. The robust nature of this model will lead to rapidly accelerating the design process for biomimetic vascular anatomical simulators, lumped parameter model flow loops, endovascular device benchtop testbeds, and compliance-matched synthetic grafts.
    Scopus© Citations 7  221
  • Publication
    Bulk metallic glasses for implantable medical devices and surgical tools
    With increasing knowledge of the materials science of bulk metallic glasses (BMGs) and improvements in their properties and processing, they have started to become candidate materials for biomedical devices. A dichotomy in the types of medical applications has also emerged, in which some families of BMGs are being developed for permanent devices whilst another family – of Mg-based alloys – is showing promise in bioabsorbable implants. The current status of these metallurgical and technological developments is summarized.
    Scopus© Citations 109  460
  • Publication
    Additive Manufacture of Composite Soft Pneumatic Actuators
    This article presents a direct additive manufacturing method for composite material soft pneumatic actuators that are capable of performing a range of programmable motions. Commonly, molding is the method used to manufacture soft fluidic actuators. This is material, labor, and time intensive and lacks the design freedom to produce custom actuators efficiently. This article proposes an alternative semiautomated method of designing and manufacturing composite soft actuators. An affordable, open-source, desktop three-dimensional (3D) printer was modified into a four-axis, combined, fused deposition modeling, and paste extrusion printer. A Grasshopper 3D algorithm was devised to implement custom actuator designs according to user inputs, resulting in a G-code print file. Bending, contracting, and twisting motion actuators were parametrically designed and subsequently additively manufactured from silicone and thermoplastic elastomer (TPE) materials. Experimental testing was completed on these actuators along with their constitutive materials. Finite element models were created to simulate the actuator's kinematic performance. Having a platform method to digitally configure and directly additively manufacture custom-motion, composite soft actuators has the potential to accelerate the development of more intricate designs and lead to potential impacts in a range of areas, including in-clinic personalization of soft assistive devices and patient-specific biomedical devices.
    Scopus© Citations 44  1458