Ruth E. Mackay

Construction of 3D biological matrices using rapid prototyping technology

Purpose – Hydrogels with low viscosities tend to be difficult to use in constructing tissue engineering (TE) scaffolds used to replace or restore damaged tissue, due to the length of time it takes for final gelation to take place resulting in the scaffolds collapsing due to their mechanical instability. However, recent advances in rapid prototyping have allowed for a new technology called bioplotting to be developed, which aims to circumvent these inherent problems. This paper aims to present details of the process.Design/methodology/approach – The paper demonstrates how by using the bioplotting technique complex 3D geometrical scaffolds with accurate feature sizes and good pore definition can be fabriated for use as biological matrices. PEG gels containing the cell‐adhesive RGD peptide sequence were patterned using this method to produce layers of directional microchannels which have a functionalised bioactive surface. Seeding these gels with C2C12 myoblasts showed that the cells responded to the topogra...

A Simple, Low-Cost Platform for Real-Time Isothermal Nucleic Acid Amplification.

Advances in microfluidics and the introduction of isothermal nucleic acid amplification assays have resulted in a range of solutions for nucleic acid amplification tests suited for point of care and field use. However, miniaturisation of instrumentation for such assays has not seen such rapid advances and fluorescence based assays still depend on complex, bulky and expensive optics such as fluorescence microscopes, photomultiplier tubes and sensitive lens assemblies. In this work we demonstrate a robust, low cost platform for isothermal nucleic acid amplification on a microfluidic device. Using easily obtainable materials and commercial off-the-shelf components, we show real time fluorescence detection using a low cost photodiode and operational amplifier without need for lenses. Temperature regulation on the device is achieved using a heater fabricated with standard printed circuit board fabrication methods. These facile construction methods allow fabrications at a cost compatible with widespread deployment to resource poor settings.

Fabrication and mechanical properties of chitosan composite membrane containing hydroxyapatite particles

This paper described the development of chitosan composites containing precipitated hydroxyapatite particles for potential applications in orthopaedic surgery or waste water treatment. The synthetic process and morphology of hydroxyapatite were reported. The effects of hydroxyapatite content on the microstructure and mechanical properties of composites were investigated. It was found that the Young’s Modulus of the composites decreases with hydroxyapatite content while the failure strength and strain increase with the hydroxyapatite content.

Polymer micro-grippers with an integrated force sensor for biological manipulation

The development of a novel micro-system integrating SU-8 polymer micro-grippers with a tensile force sensor for handling and characterizing the mechanical properties of delicate biological materials, such as fibrils, is presented. The micro-grippers are actuated by the electro-thermal effect and have gripping forces comparable to the common ‘hot-and-cold-arm’ grippers. A robust finite element model was developed to investigate system performance and validated experimentally. A new micro-mechanical calibration method using a piezoelectric manipulator with a micro-force measurement system was successfully applied to test the structure. Both FEA simulation and micro-mechanical testing results indicated that the system could fulfil the requirements for micro-object manipulation within a biological environment.

Modular development of a prototype point of care molecular diagnostic platform for sexually transmitted infections

Highlights • A low cost, optical, POC molecular diagnostic platform.• Sample preparation using a paper membrane.• Isothermal amplification using HDA and RPA.

Chemically Roughened Solid Silver: A Simple, Robust and Broadband SERS Substrate

Surface-enhanced Raman spectroscopy (SERS) substrates manufactured using complex nano-patterning techniques have become the norm. However, their cost of manufacture makes them unaffordable to incorporate into most biosensors. The technique shown in this paper is low-cost, reliable and highly sensitive. Chemical etching of solid Ag metal was used to produce simple, yet robust SERS substrates with broadband characteristics. Etching with ammonium hydroxide (NH4OH) and nitric acid (HNO3) helped obtain roughened Ag SERS substrates. Scanning electron microscopy (SEM) and interferometry were used to visualize and quantify surface roughness. Flattened Ag wires had inherent, but non-uniform roughness having peaks and valleys in the microscale. NH4OH treatment removed dirt and smoothened the surface, while HNO3 treatment produced a flake-like morphology with visibly more surface roughness features on Ag metal. SERS efficacy was tested using 4-methylbenzenethiol (MBT). The best SERS enhancement for 1 mM MBT was observed for Ag metal etched for 30 s in NH4OH followed by 10 s in HNO3. Further, MBT could be quantified with detection limits of 1 pM and 100 µM, respectively, using 514 nm and 1064 nm Raman spectrometers. Thus, a rapid and less energy intensive method for producing solid Ag SERS substrate and its efficacy in analyte sensing was demonstrated.

Development of Micro-Tweezers for Tissue Micro-Manipulation

This paper describes the design of an integrated electro-mechanical system for small scale tissue manipulation and stimulation. Finite element modeling was applied to simulate the electro-thermal mechanism for tissue gripping. The results revealed the effects of materials, input voltage, power consumption and media on the operation of micro-tweezers.

Fabrication and Mechanical Properties of Chitosan-Montmorillonite Nano-Composite

Chitosan has found various applications in gastrointestinal stent, biomedical implants as well as an effective absorbent in waste water treatment. However, the material suffers from low strength and large shrinkage upon dehydration. The current project is aimed to develop a process to fabricate chitosan composites with the addition of functionalised montmorillonite nanoparticles and to examine the effect of ceramic content on the mechanical behavior of the composites. This paper describes the fabrication of chitosan with montmorrillonite composites and the mechanical testing of the samples and the mechanical behaviour of the composites, as well as the observations of the microstructure. The effects of composition and microstructure on the mechanical properties of the composite are investigated. The results indicate that the nanoparticles are dispersed uniformly in the matrix up to 40wt% using high speed homogeniser. The elastic modulus increases monotonically with the addition of nanoparticles, but the fracture strength drops due to the defects introduced by the nanoparticles.

Micro-gripping of Small Scale Tissues

This paper describes the design and simulation of an integrated micro-electro-mechanical system (MEMS) to be used for small scale tissue manipulation. The microgrippers are to be used to test the mechanical cell adhesion properties of the gut epithelium. In the majority of sporadic colon cancers the Adenomatous Polyopsis Coli (APC) protein is mutated or missing. Mutations of APC occur extremely early in the development of cancer, before formation of polyps. Micro-grippers were designed and finite element analysis (FEA) was used to find actuation displacements, tip temperature and stresses. Monolayers of gut epithelial tissue will be grown on collagen substrates and stretched under tensile force. Ni micro-grippers will be used to grip the substrate due to its high gripping stiffness and force resolution. SU-8 micro-grippers will be used to directly grip on cell membrane to analyze cell adhesion forces with APC present or absent. The following paper shows the design of the system and FEA of micro-grippers.

RPA using a multiplexed cartridge for low cost point of care diagnostics in the field

A point of care device utilising Lab-on-a-Chip technologies that is applicable for biological pathogens was designed, fabricated and tested showing sample in to answer out capabilities. The purpose of the design was to develop a cartridge with the capability to perform nucleic acid extraction and purification from a sample using a chitosan membrane at an acidic pH. Waste was stored within the cartridge with the use of sodium polyacrylate to solidify or gelate the sample in a single chamber. Nucleic acid elution was conducted using the RPA amplification reagents (alkaline pH). Passive valves were used to regulate the fluid flow and a multiplexer was designed to distribute the fluid into six microchambers for amplification reactions. Cartridges were produced using soft lithography of silicone from 3D printed moulds, bonded to glass substrates. The isothermal technique, RPA is employed for amplification. This paper shows the results from two separate experiments: the first using the RPA control nucleic acid, the second showing successful amplification from Chlamydia Trachomatis. Endpoint analysis conducted for the RPA analysis was gel electrophoresis that showed 143 base pair DNA was amplified successfully for positive samples whilst negative samples did not show amplification. End point analysis for Chlamydia Trachomatis samples was fluorescence detection that showed successful detection of 1 copy/μL and 10 copies/μL spiked in a MES buffer.