Bioengineering
http://hdl.handle.net/10523/7058
2024-03-17T18:34:21ZAn Exploration of Melt-electrowriting and Fused Deposition Modelling for Tissue Engineering Blood Vessels
http://hdl.handle.net/10523/16068
An Exploration of Melt-electrowriting and Fused Deposition Modelling for Tissue Engineering Blood Vessels
2023
Thorsnes, Quinn
There are many ways in which blood vessels can be damaged, resulting in the need for replacement vessels. Traumatic injury to surrounding tissue, diseases that degrade the elasticity or other features, and life-style choices that lead to blockages are all examples of how damage can occur. Surgical treatment for damage blood vessels typically involves replacing the damaged section. Self-donated vessels guarantee compatibility with the patient, but many patients cannot self-donate. Additionally self-donating requires additional surgeries and results in impaired functionality at the donor site. The creation of multiple wounds increases the risk of infection. Synthetic grafts do exist in clinical use, but they tend to be short term solutions as a result of insufficient biocompatibility. This low biocompatibility can lead to immune rejection and may leading to the graft becoming blocked.
In this research, a potential design and manufacturing basis for tissue engineering blood vessels is explored. A novel combination of meltelectrowriting and fused deposition modelling was used to generate scaffolds via moulds. This allowed for increased scaffold design freedom not attainable with either additive manufacturing technology alone. The primary material used for these scaffolds was polycaprolactone. This is an FDA-approved synthetic polymer well-established to possess excellent compatibility with both biological systems and other materials. This compatibility with other materials allows for both the biological and material properties of scaffolds to be customised for their specific uses.
The moulds used in this study were created using a varied of materials from glass to conductive polylactic acid. This latter material, polylactic acid with graphite added to improve electrical conductivity, was found to be an excellent moulds material in its compatibility with standard fused deposition modelling to make moulds of nearly any shape while still concentrating the
electric field in melt-electrowriting and allowing the scaffolds to be removed from the mould without difficulty or residue.
This study characterised the pure polycaprolactone scaffolds both mechanically and biologically. The biological characterisation consisted of seeding the scaffolds with normal human dermal fibroblasts, similar in size to endothelial cells, and culturing them over the course of a month. This indicated that the manufacturing process did not introduce any factors that negatively impacted cell growth. Further, the mechanical characterisation, in conjunction with simulation, validated previous research and identified potential means for accurate simulation for future scaffold development.
Dynamic mechanical analysis was used to characterise the mechanical properties of the scaffolds, giving both the viscous and elastic properties of the scaffolds. The scaffolds were also physically simulated in different potential pore structures using the finite element method and theoretical values predicted by literature and observed strand sizes. The results showed that the mechanical properties of the scaffolds could be well approximated through three-dimensional Voronoi tessellation. This means that future scaffold designs made with melt-electrowriting may have their mechanical performance predicted without needing to consume materials and even when their geometries would prohibit direct testing.
2023-09-14T20:56:40ZPreliminary Development of a PPAM Actuated Pediatric Prosthetic Ankle
http://hdl.handle.net/10523/12215
Preliminary Development of a PPAM Actuated Pediatric Prosthetic Ankle
2021
McNamara-Spackman, Connor
The purpose of this research was to develop a preliminary design of a powered pediatric
prosthetic ankle. Previous research identified the health risk of improper gait cycle and the lack
of powered prosthetic ankle options for children. Costs for powered prosthetic ankles are too
high (upwards of $5000 NZD), the sizes are too large and the weight is too significant for a child
to benefit from. Current technologies for ankle joint actuation and materials for the prosthetic
structure were evaluated and a conclusion of utilizing PPAMs was chosen due to their ability to
generate the required 300 N of contraction force. CAD was used to model the structure of a
prosthetic ankle and evaluate the FOS of the different material combinations while under static
loading and fatigue simulations. HDPE and UHMWPE failed to withstand the simulations, while
the aluminum alloy and stainless steel showed minimal faults from the simulations. MatLab was
used to simulate the desired PPAM dimensions of 100 mm to determine the contraction force
and contraction percentage that can be generated by the PPAM. The smallest PPAM found in
research was 110 mm and showed promising results from their mathematical modeling. The
overall height of the prosthetic was no greater than 110 mm and the membrane length of the
PPAM was no greater than 100 mm, while successfully producing more than 300 N during
contraction. The results showed promising data that needs further development to allow the
benefits of this research to positively impact the lives of pediatric amputees.
2021-08-23T21:32:13ZThe effects of ultrasound on the spread of intramuscularly injected formulations
http://hdl.handle.net/10523/9976
The effects of ultrasound on the spread of intramuscularly injected formulations
2020
Zhang, Kuo
Context: The intramuscular (IM) injection is an important route of drug administration. Some researchers have suggested that the erratic rate of drug absorption from oil-based IM injections is due to variability in the spread of the formulations from the injection site. Recently, the application of ultrasound (US) has been investigated as a possible strategy to enhance the spread of IM injected formulations and thereby reduce variability in drug absorption.
Objective: The aim of the research reported in this thesis was to investigate the effects of US on the spread of IM injected formulations.
Methods: For in vitro experiments, transparent agarose gel was used as the matrix. Both Nile blue(aqueous) solution (0.001% w/w) and Nile red(oily) solutions (0.01% w/w) were prepared and injected into gels. The area of spread of injected formulations was photographically recorded and measured immediately after injection. US (1.1 MHz, 3 W/cm2) was then applied to the injection site using a 6 min on-off working cycle for 60 min after which the area of spread was measured again. Areas of spread determined as mean ± standard deviation before and after US treatment were compared. For in vivo experiments, three Wether lambs (6 to 8 months old, 32 kgs approx.) were subjected to IM injections post-mortem. Three different types of formulation (Lipiodol: ethyl esters of iodized fatty acid of poppy seed oil, 48% w/v iodine; oily suspension: barium sulfate in Miglyol 812, 30% w/w; and a self-emulsifying drug delivery system (SEDDS): mixture of Lipiodol, Maisine and Miglyol, 40:20:40%, w/w)) were prepared and two different injection volumes (1.5 and 4.5 mL) injected into muscle. US (1.1 MHz, 3 W/cm2, 100% working cycle) was applied for 0, 5 and 10 min at the injection site and the spread of formulations visualized by CT scan and measured before and after US application. The collected data was analysed using two-way ANOVA and Tukey test for post -hoc statistical analysis. Muscle tissue containing injected formulations was frozen in liquid nitrogen and subsequently examined by dissection.
Results: In the in vitro study, 60 minutes after injection, the spread of both aqueous and oily solutions remained unchanged after application of US. In the post-mortem study, the initial spread showed no significant difference between either type of formulation or injection volume. After application of US for 5 min, a significant increase in spread was observed for the oily suspension and SEDDS using an injection volume of 4.5 mL; after exposure to US for 10 min, significant increases in spread were found for the oily suspension and SEDDS at both 1.5 and 4.5 mL injection volumes. The subsequent dissection revealed a large amount of injected formulation outside the injected muscle bundle resulting from spread along the fat layer and into the inter-muscle space.
Conclusion: There is no effect of US on the spread of formulations injected into agarose gel. In the post-mortem study, the CT scan proved to be suitable to visualize the spread of IM injected formulations. The initial spread of the IM injected oil formulations showed high variation. US-induced spread was observed for the oil suspension and SEDDS. The mechanism behind the enhanced spread needs further investigation but could be related to the ability of applied US to reduce the viscosity of the injected formulations or to the transfer of the mechanical energy of US to surface energy.
2020-03-18T21:10:22ZSkin Tissue Regeneration: An Investigation of Melt-electrowriting with a Novel Biomaterial from Polycaprolactone and Milk Proteins
http://hdl.handle.net/10523/8228
Skin Tissue Regeneration: An Investigation of Melt-electrowriting with a Novel Biomaterial from Polycaprolactone and Milk Proteins
2018
Hewitt, Eve
In 2017, only 28% of patients awaiting tissue transplants received treatment that same year. Coupled with a growing ageing population, demand for tissue replacements is increasing rapidly. Furthermore, the treatment of dermal skin tissue wounds proves difficult due to the low regeneration capability of the innate tissue, and the physical drawbacks of current substitutes.
Polycaprolactone (PCL) is a bioresorbable and biocompatible polymer that has Food and Drug Administration approval for implantation into the human body. PCL is mechanically stable, flexible, and shows superior melt processing properties. However, PCL lacks biological functionality. Therefore, the current study sought to add bioactive milk proteins, lactoferrin (LF) and whey protein (WP), to PCL at concentrations of 0.05%, 0.1%, 0.25%, and a combination (COMB) of both LF and WP at concentrations of 0.25%. The biomaterial was used to create novel bioactive scaffolds that would encourage tissue regeneration and have the structural characteristics needed to regenerate thick dermal skin tissue. The biomaterial was processed into tissue regenerative scaffolds using a GeSiM Bioplotter equipped with an emerging 3D-bioprinting technique – melt-electrowriting (MEW).
The scaffolds were characterised, and their biological activity assessed in an in vitro model of skin tissue (using HaCaTs and Nhdf cells). Physical characterisation showed that reproducible, layered microarchitecture scaffolds (~56% porosity) could be created from the biomaterial using MEW. The biodegradability and swelling of the scaffolds was low (≤3.3% mass loss over 21 days and 24 hour swelling ratio ≤6.4%), with COMB scaffolds showing significantly higher results than PCL alone (p≤0.05). Protein release of LF and WP from scaffolds was rapid, with an initial release of >40% after 1 hour. Biological analysis showed that neat LF did not improve proliferation or migration in 2D cell culture, whereas neat WP increased cell proliferation compared to PCL in both cell lines, but only increased migration in Nhdf cells at 0.25% (p≤0.05). COMB treatment increased migration of HaCaTs, Nhdfs, and a co-culture of both cell lines. Contrastingly, cells seeded onto scaffolds (3D cell culture) showed improved biological activity in response to scaffolds containing LF (including COMB scaffolds). Cell growth, spreading, and infiltration into the scaffolds significantly increased for LF containing scaffolds compared to PCL alone and WP scaffolds (p≤0.05). Fluorescence microscopy showed a high ratio of live/dead cells attached to scaffolds. COMB scaffolds indicated a potential synergistic mechanism, showing significantly improved cell migration and growth compared to PCL alone.
These findings demonstrated that the addition of LF and WP increased the biological activity of 3D PCL scaffolds, possibly through immunomodulatory mechanisms (such as a decrease of harmful inflammation and/or production of oxidative species). These scaffolds showed promising tissue regenerative capacity and could act as suitable tissue regenerative constructs for hard-to-treat thick dermal tissue wounds. Moreover, the outcomes from this study not only illustrate the currently accepted practises for bioengineering research, as well as a validation of the GeSiM Bioplotter 3.1 for fabrication of 3D tissue regenerative constructs, but also contribute to the understanding of milk derived biomaterial-cell/tissue interaction, bioactive efficacy of WP or LF, and tissue regenerative medicine.
2018-07-17T20:46:05ZTo Investigate and Fabricate Melt Processed Biomaterials Exhibiting Shape Recovery Properties
http://hdl.handle.net/10523/7715
To Investigate and Fabricate Melt Processed Biomaterials Exhibiting Shape Recovery Properties
2017
Crake, Keegan
The purpose of this research was to produce and characterise novel hybrid biomaterials. Currently, there is a research gap in the area of producing hybrid biomaterials with shape memory properties for use in the fields of bioengineering or biomedical devices. This research will provide the initial results for a novel hybrid biomaterial that could be further researched for use in a biomedical device. In this study, melt extrusion methods were applied to the hybrid polymers. Three characterisation methods were employed within this work: mechanical (tensile) testing, shape recovery, and in vitro (trypsin) degradation. Across the three characterisation methods, PCL:PLA 30:70WT% 20% PEG-200 plasticised hybrid fibres were found to outperform the other materials reported in this thesis. Three key findings resulted from this research. The melt extrusion method used proved to be successful. PCL:PLA hybrid fibres could be produced consistently. Both glycerol and PEG-200 plasticisers used within this work were found to improve the blend properties of the hybrids. A total of 65% of tested hybrid fibres exhibited shape recovery when tested at a temperature of 37.5°C. The overall results of this study indicate that the hybrid materials produced here need to undergo further testing prior to use in biomedical applications.
2017-11-08T20:20:42ZElectrical Conductivity as an Indicator of Milk Spoilage for Use in Biosensor Technology
http://hdl.handle.net/10523/6788
Electrical Conductivity as an Indicator of Milk Spoilage for Use in Biosensor Technology
2016
Li, Xingyi
Milk is characterised as a perishable food. It is vulnerable to microbial contamination and has a limited shelf life, even when stored in a cold environment. Rapid milk spoilage is a sustained problem that restrains the shelf life of milk, and it consistently burdens the global food waste. Thus, there is a continuous interest in seeking better means of milk quality control and management. Recently, the development of biosensing technology offers a potential solution for better managing strategies of milk quality. Biosensors have been developed from growing demand for a reliable, cost-effective and rapid chemical detection tool. Many disciplines including clinical medicine, food industry, and environment monitoring employ biosensors as analytical tools. In particular, the use of electrical conductivity (EC) as a biosensing approach has frequently been studied in the dairy sector. However, its application to milk spoilage has yet to be fully explored.
The scope of this study was to investigate the use of EC as a parameter to aid in the prediction of milk spoilage. A portable conductivity meter was used to measure the EC in milk; the total bacterial count (TBC), lactic acid (LA) concentration and pH were assessed using standard plate count methods, titratable acidity and digital pH meter, respectively. Commercial pasteurized skim and whole milk were used in the study. The variations of EC, TBC, LA concentration and pH were measured over an extended storage of milk that held at either 4 or 8℃ in the trial experiment. The change in EC was comparatively examined with the change of other measured parameters, and the interrelationship between EC and parameters was analysed by correlation analysis. In addition, several laboratory-controlled model systems were used to assess the impacts of every individual parameter on the change of EC. The results of trial and model systems were compared with each other.
The trial experiment showed that EC progressively increases with an increase in TBC, LA concentration and pH during spoilage of skim and whole milk under storing at 4 and 8℃. The change in EC was found to have moderate to strong correlations with the measured parameters in spoilt milk. A statistically significant difference in EC value was observed before the complete spoilage of milk, when either the flavour defects or textural changes occurred. Moreover, the model systems revealed that the increase in EC is proportional linear to an increased LA concentration and decreased pH. By comparing the results between trial experiment and model systems, it showed that LA approximately contributed one-quarter of the total proportion of changed EC in spoiled milk. Furthermore, a number of bacteria present in milk with more than 〖10〗^7 colony forming units (CFU)/ml significantly decreased the mean EC value of milk. In addition, the ‘best before date’ (BBD) underestimated the correct shelf life of milk at both 4 and 8℃.
The fixed nature of BBD restrains its use as a suitable indicator. In comparison, EC can be a potential alternative to predict milk spoilage. Since it is a direct measurement of spoilage of milk, and changes simultaneously with the growth of bacteria, production of LA and acidity in milk held at either the optimal (4℃) or the inappropriate (8℃) temperatures. Further investigations are needed to obtain a better understanding of the interrelationship between EC and milk spoilage preceding the valid application of biosensing technology.
2016-09-23T04:53:56Z