Electrospinning of composite biomaterials: incorporation of bioactive agents and formation of hierarchical nanostructures

This PhD focused on promotion of bioactivity of electrospun fibres. Two methods were used to achieve this objective: using antimicrobial agents and, creating hierar-chical structures.Antimicrobial agents, essential oils and zinc oxide nanoparticles, were encapsulat-ed in polymer nanofibres to promote antimicrobial properties. Tea tree and Manuka essential oils were encapsulated in poly (lactic acid) (PLA) by dissolving in their common solvent acetone and then electrospin. Plasticising effect of essential oils was observed in differential scanning calorimetry (DSC)test. Glass transition temperature of PLA fibres decreased with increasing essential oil concen-tration. This corresponded with mechanical results. Manuka/PLA fibres showed successful result in inhibition of E. coli in antimicrobial test.Zinc oxide nanoparticles have previously been used in electrospun fibres for anti-microbial purpose. To my knowledge, previous studies have only achieved to en-capsulate zinc oxide nanoparticles directly in electrospun fibres. In this thesis, for the first time, zinc oxide nanoparticles were first in-situ synthesised in polyethylene-imine (PEI) and then combined with zein to electrospin fibres. Resulting fibres showed better mechanical properties when compared to pure electrospun zein fi-bres.The second method, creating hierarchical structure, was achieved by phase separa-tion. An unique dual-porosity structure of electrospun poly(ethyl cyanoacry-late)/polycaprolactone (PECA/PCL) was demonstrated. Composition of fibres was confirmed by Fourier-transform infrared spectroscopy (FTIR). Hierarchical structures are believed to favour cell attachment and proliferation by increasing fibre surface roughness and surface-to-volume ratio.</div

Phase separation events induce the coexistence of distinct nanofeatures in electrospun fibres of poly(ethyl cyanoacrylate) and polycaprolactone

© 2018 Elsevier Ltd Here we show that thermodynamic instabilities during electrospinning of polymer blends of poly(ethyl cyanoacrylate) (PECA) and polycaprolactone (PCL) in a ternary solvent system (acetone/chloroform/acetonitrile) induce the formation of hierarchical composite fibres with dual porosity. The analysis of the surface and cross-section of the PECA-PCL fibres reveals that, differently from previous works, the electrospun fibres are formed of two distinct morphologies: half of the fibre exhibits parallel and elongated grooves; whereas the other half has near-circular shaped pores. Porosity is present throughout the fibre volume with some regions being hollow. The occurrence of this novel architecture is investigated using different solvent systems and a dual phase separation mechanism is proposed. Porous fibres with a hierarchical porous structure are beneficial in many fields, including biomedical, environmental and energy related applications

Electrospun nanofibres containing antimicrobial plant extracts

Over the last 10 years great research interest has been directed toward nanofibrous architectures produced by electrospinning bioactive plant extracts. The resulting structures possess antimicrobial, anti-inflammatory, and anti-oxidant activity, which are attractive for biomedical applications and food industry. This review describes the diverse approaches that have been developed to produce electrospun nanofibres that are able to deliver naturally-derived chemical compounds in a controlled way and to prevent their degradation. The efficacy of those composite nanofibres as wound dressings, scaffolds for tissue engineering, and active food packaging systems will be discussed

On the Properties of Kullback-Leibler Divergence Between Multivariate Gaussian Distributions

Kullback-Leibler (KL) divergence is one of the most important divergence measures between probability distributions. In this paper, we prove several properties of KL divergence between multivariate Gaussian distributions. First, for any two $n$-dimensional Gaussian distributions $\mathcal{N}_1$ and $\mathcal{N}_2$, we give the supremum of $KL(\mathcal{N}_1||\mathcal{N}_2)$ when $KL(\mathcal{N}_2||\mathcal{N}_1)\leq \varepsilon\ (\varepsilon>0)$. For small $\varepsilon$, we show that the supremum is $\varepsilon + 2\varepsilon^{1.5} + O(\varepsilon^2)$. This quantifies the approximate symmetry of small KL divergence between Gaussians. We also find the infimum of $KL(\mathcal{N}_1||\mathcal{N}_2)$ when $KL(\mathcal{N}_2||\mathcal{N}_1)\geq M\ (M>0)$. We give the conditions when the supremum and infimum can be attained. Second, for any three $n$-dimensional Gaussians $\mathcal{N}_1$, $\mathcal{N}_2$, and $\mathcal{N}_3$, we find an upper bound of $KL(\mathcal{N}_1||\mathcal{N}_3)$ if $KL(\mathcal{N}_1||\mathcal{N}_2)\leq \varepsilon_1$ and $KL(\mathcal{N}_2||\mathcal{N}_3)\leq \varepsilon_2$ for $\varepsilon_1,\varepsilon_2\ge 0$. For small $\varepsilon_1$ and $\varepsilon_2$, we show the upper bound is $3\varepsilon_1+3\varepsilon_2+2\sqrt{\varepsilon_1\varepsilon_2}+o(\varepsilon_1)+o(\varepsilon_2)$. This reveals that KL divergence between Gaussians follows a relaxed triangle inequality. Importantly, all the bounds in the theorems presented in this paper are independent of the dimension $n$. Finally, We discuss the applications of our theorems in explaining counterintuitive phenomenon of flow-based model, deriving deep anomaly detection algorithm, and extending one-step robustness guarantee to multiple steps in safe reinforcement learning.Comment: arXiv admin note: text overlap with arXiv:2002.0332

Electrospinning of polylactic acid fibres containing tea tree and manuka oil

Here the effect of tea tree and manuka essential oils (EOs) on the mechanical properties and antibacterial activity of electrospun polylactic acid (PLA) fibres is investigated. It is found that the essential oils work as plasticisers for PLA, lowering the glass transition temperature of the resulting composite fibres up to 60% and increasing elongation-at-break and tensile strength up to 12 times. Manuka EO is particularly successful in blocking the formation of biofilms of Staphylococcus epidermidis that is typically involved in nosocomial infections associated with implanted devices. The results demonstrate that natural extracts can be used to control the mechanical behaviour of PLA fibres and to confer antibacterial activity

Electrospun Nanofibres Containing Antimicrobial Plant Extracts

Over the last 10 years great research interest has been directed toward nanofibrous architectures produced by electrospinning bioactive plant extracts. The resulting structures possess antimicrobial, anti-inflammatory, and anti-oxidant activity, which are attractive for biomedical applications and food industry. This review describes the diverse approaches that have been developed to produce electrospun nanofibres that are able to deliver naturally-derived chemical compounds in a controlled way and to prevent their degradation. The efficacy of those composite nanofibres as wound dressings, scaffolds for tissue engineering, and active food packaging systems will be discussed