Sean K. Powell

Improved fabrication of melt electrospun tissue engineering scaffolds using direct writing and advanced electric field control

Direct writing melt electrospinning is an additive manufacturing technique capable of the layer-by-layer fabrication of highly ordered 3d tissue engineering scaffolds from micron-diameter fibers. The utility of these scaffolds, however, is limited by the maximum achievable height of controlled fiber deposition, beyond which the structure becomes increasingly disordered. A source of this disorder is charge build-up on the deposited polymer producing unwanted coulombic forces. In this study, the authors introduce a novel melt electrospinning platform with dual voltage power supplies to reduce undesirable charge effects and improve fiber deposition control. The authors produced and characterized several 90° cross-hatched fiber scaffolds using a range of needle/collector plate voltages. Fiber thickness was found to be sensitive only to overall potential and invariant to specific tip/collector voltage. The authors also produced ordered scaffolds up to 200 layers thick (fiber spacing 1 mm and diameter 40 μm) and characterized structure in terms of three distinct zones: ordered, semiordered, and disordered. Our in vitro analysis indicates successful cell attachment and distribution throughout the scaffolds, with little evidence of cell death after seven days. This study demonstrates the importance of electrostatic control for reducing destabilizing polymer charge effects and enabling the fabrication of morphologically suitable scaffolds for tissue engineering.

Chapter 7: Quantification of articular cartilage microstructure by the analysis of the diffusion tensor

In this chapter, we present approaches to the numerical simulation of the diffusion of water molecules in fibre networks that serve as models of articular cartilage. The simulations are intended as a tool for the translation of experimental diffusion magnetic resonance imaging (MRI) data into quantitative microstructural and compositional characteristics of articular cartilage. The chapter begins with a brief introduction to diffusion nuclear magnetic resonance and diffusion imaging, focusing on diffusion tensor imaging. It discusses the current limitations of diffusion MRI in quantifying articular cartilage microstructure beyond the predominant direction of collagen fibre alignment. We then detail the construction of aligned and partially aligned networks of fibres that can serve as models of articular cartilage. We discuss the methods for the simulation of the diffusion of tracer molecules through the model networks (especially Langevin dynamics and Monte Carlo techniques), and reconstruction of the diffusion tensor from the simulated molecular trajectories. The aim of these simulations is to quantitatively link the eigenvalues and the fractional anisotropy of cartilage diffusion tensor to collagen fibre volume fraction and the degree of collagen fibre alignment. The global aim of this work is to move diffusion tensor imaging of articular cartilage beyond determination of the predominant direction of fibre alignment, and towards quantification of the fibre orientation distribution.

Effect of humidity on melt electrospun polycaprolactone scaffolds

Abstract Direct write melt electrospinning is an additive manufacturing technique used to produce 3D polymer scaffolds for tissue engineering applications. It is similar to conventional 3D printing by layering 2D patterns to build up an object, but uses a high-electric potential to draw out fibres into micron-scale diameters with great precision. Direct write melt electrospinning is related to a well-established fabrication technique, solution electrospinning, but extrudes a melted polymer in a controlled manner rather than a polymer solution. The effect of environmental conditions such as humidity has been extensively studied in the context of solution electrospinning; however, there is a lack of similar studies for direct write melt electrospinning. In this study, melt electrospun polycaprolactone scaffolds were produced with 90 degree cross-hatch architecture at three specific humidity [H2O/air (g/kg)] levels, low (0.74 g/kg), standard (8.94 g/kg), and elevated (11.26 g/kg). Micro-computed tomography and scanning electron microscopic analysis was performed on the scaffolds to investigate the degree to which humidity affects inter-layer ordering, fibre diameter consistency, and fibre surface morphology. Results indicated that humidity does not play a significant role in affecting these scaffold parameters during fabrication within the levels investigated.

Biomechanics of Synthetic Elastin: Insights from Magnetic Resonance Microimaging

We used Magnetic Resonance microimaging (MRI) to study the compressive behaviour of synthetic elastin. Compression-induced changes in the elastin sample were quantified using longitudinal and transverse spin relaxation rates (R1 and R2, respectively). Spatially-resolved maps of each spin relaxation rate were obtained, allowing the heterogeneous texture of the sample to be observed with and without compression. Compression resulted in an increase of both the mean R1 and the mean R2, but most of this increase was due to sub-locations that exhibited relatively low R1 and R2 in the uncompressed state. This behaviour can be described by differential compression, where local domains in the hydrogel with a relatively low biopolymer content compress more than those with a relatively high biopolymer content.

Aesthetic reconstruction of microtia: a review of current techniques and new 3D printing approaches

ABSTRACT Three dimensional (3D) printing and biofabrication technologies are revolutionising medicine with low-cost and novel treatments for complex medical conditions. These approaches differ from traditional treatments by using 3D scanning, computer modelling and 3D printing to automate the production of patient-specific tissue replacement or prostheses using a wide range of materials. One area impacted by this technology is the treatment of congenital maxillofacial conditions such as microtia, a condition affecting the intrauterine development of the auricle (external ear) and with a prevalence of 2.06 cases for every 10,000 births. While not life-threatening, microtia significantly impacts the emotional and psychological well-being of the affected child and their parents. Current treatments include the use of prosthetic ears or surgical methods such as autografting rib cartilage or alloplastic implants. Although current options have shown documented success, they are highly dependent on the surgeon’s skill and it has been demonstrated that poor quality solutions can further exacerbate negative psychosocial impacts. As such, higher quality, lower cost and more customised options would be welcomed by patients and parents alike. Recent advances in 3D scanning, modelling and printing techniques could significantly benefit the treatment and reconstructive options for children with microtia, leading to improved quality of life.

Comparison of three-dimensional surface scanning techniques for capturing the external ear

ABSTRACT Congenital facial anomalies, such as microtia (malformation of the external ear), lead to significant psychosocial effects starting from early childhood. Three-dimensional (3D) scanning and advanced manufacturing are being investigated as a cheaper and more personalised method of fabricating reconstructive treatments for patients compared to traditional approaches. To date, most case studies have used expensive 3D scanners, yet, there is potential for low-cost devices to provide comparable results. This study aimed to investigate these different approaches. Both ears of 16 adult participants were scanned with three devices: Artec Spider (Artec Group), Intel® RealSense™ (Intel), and the Apple iPhone® 7 (Apple Inc.) combined with photogrammetry using 90, 60 and 30 photographs. The scanning time, processing time, accuracy, completeness, resolution and repeatability of each technique were assessed using the Artec Spider as a reference scanner. Our results show that the iPhone had the longest processing time however, this decreased nine-fold when reducing the number of photos from 90 to 30. There was no significant difference in the accuracy, completeness or repeatability of the iPhone scans with 90 photographs (1.4 ± 0.6 mm, 79.9%, 1.0 ± 0.1 mm), 60 photographs (1.2 ± 0.2, 79.3%, 0.9 ± 0.2 mm) or 30 photographs (1.2 ± 0.3 mm, 74.3%, 1.0 ± 0.2 mm). The Intel RealSesne performed significantly worse in each parameter (1.8 ± 03 mm; 46.6%, 1.4 ± 0.5). Additionally, the RealSense had significantly lower resolution with not enough detail captured for the application. These results demonstrate that the ear can be accurately 3D scanned using iPhone photographs. We would recommend capturing between 30 and 60 photographs of the ear to create a scan that is accurate but without the downfall of long processing time. Using these methods we aim to provide a more comfortable setting for the patient and a lower-cost and more personalised ear prosthesis.

Smartphones for frugal three-dimensional scanning of the external ear with application to microtia⋆

Three-dimensional (3D) scanning, 3D modelling and 3D printing are disrupting healthcare with the potential to create personalised, automated and customised treatments that are superior to current approaches. One application of these technologies is the production of ear and facial prosthetics to restore aesthetics in the case of congenital defects, trauma and tumour resection. Several studies have recently investigated the potential of this approach to increase patient comfort and outcomes while decreasing labour time for prosthetists. One challenge with translating these new technologies to clinical use is the expensive cost of equipment and software and the additional training and skill required to use them. Recent studies have shown the potential for a scanning technique called photogrammetry to be used with smartphones in place of expensive industrial 3D scanners to acquire 3D craniofacial models of both adults1 and infants.2 Photogrammetry works by detecting common features within a series of photographs taken from different locations to compute the 3D spatial coordinates of each camera. Following this, patients 3D surface anatomy can be calculated. Although previous studies demonstrate the ease and accessibility of scanning with smartphones, they have not quantitatively assessed the accuracy. In this short communication, we investigate the potential of low-cost devices for 3D scanning of the external ear, and provide a quantitative comparison against a metrology rated 3D scanner. It is hoped the photogrammetry approach to 3D scanning can be used to help children born with microtia, a congenital condition which affects the formation of the external ear.

Electrofluidodynamic technologies for biomaterials and medical devices: melt electrospinning

Abstract Melt electrospinning is an electrohydrodynamic technique used to produce submicron polymer fibers. Melt electrospun fibers have applications in tissue engineering as biomaterials and medical products due to their ability to be precisely deposited to form three-dimensional scaffolds for cells, loaded with drugs for delivery, or provide reinforcement for hydrogels. In this chapter, we will explore how the process of melt electrospinning, platform design, printing and process parameters all contribute to allow the manufacture of variable fiber morphology and architecture for specific applications as a biomaterial or medical device.

Corrigendum: Diffusion tensor of water in partially aligned fibre networks (2013 J. Phys. D: Appl. Phys. 46 455401)

This is a corrigendum for the article 2013 J. Phys. D: Appl. Phys. 46 455401 ePrints 63904

The atmospheric extinction of light

An experiment is described that enables students to understand the properties of atmospheric extinction due to Rayleigh scattering. The experiment requires the use of red, green and blue lasers attached to a travelling microscope or similar device. The laser beams are passed through an artificial atmosphere, made from milky water, at varying depths, before impinging on either a light meter or a photodiode integral to a Picotech Dr. DAQ ADC. A plot of measured spectral intensity verses depth reveals the contribution Rayleigh scattering has to the extinction coefficient. For the experiment with the light meter, the extinction coefficients for red, green and blue light in the milky sample of water were 0.27, 0.36 and 0.47 cm^-1 respectively and 0.032, 0.037 and 0.092 cm^-1 for the Picotech Dr. DAQ ADC.