Coaxial electrospun biomimetic copolymer fibres for application in diffusion magnetic resonance imaging

Abstract

Objective. The use of diffusion magnetic resonance imaging (dMRI) opens the door to characterise brain microstructure because water diffusion is anisotropic in axonal fibres in brain white matter and is sensitive to tissue microstructural changes. As dMRI becomes more sophisticated and microstructurally informative, it has become increasingly important to use a reference object (usually called imaging phantom) for validation of dMRI. This study aims to develop axon-mimicking physical phantoms from biocopolymers and assess their feasibility to validate dMRI measurements. Approach. We employed a simple and one-step method-coaxial electrospinning-to prepare axon-mimicking hollow microfibres from polycaprolactone-b-polyethylene glycol (PCL-b-PEG) and poly(D, L-lactideco-glycolic) acid (PLGA), and used them as building elements to create axon-mimicking phantoms. Electrospinning was firstly conducted using two types of PCL-b-PEG and two types of PLGA with different molecular weights in various solvents with different polymer concentrations for determining their spinnability. The polymer/solvent-concentration combinations with good fibre spinnability were used as the shell material in the following co-electrospinning process in which the polyethylene oxide (PEO) polymer was used as the core material. Following microstructural characterisation of both electrospun and co-electrospun fibres using optical and electron microscopy, two prototype phantoms were constructed from co-electrospun anisotropic hollow microfibres after inserting them into waterfilled test tubes. Main results. Hollow microfibres that mimic the axon microstructure were successfully prepared from the appropriate core and shell material combinations. dMRI measurements of two phantoms on a 7 tesla (T) pre-clinical scanner revealed that diffusivity and anisotropy measurements are in the range of brain white matter. Significance. This feasibility study showed that co-electrospun PCL-b-PEG and PLGA microfibres-based axon-mimicking phantoms could be used in the validation of dMRI methods which seek to characterise white matter microstructure.

Pore size estimation in axon‐mimicking microfibers with diffusion‐relaxation MRI

“…It is important to mention that this is not the first study using phantoms of hollow axon-mimicking fibers. Similar phantoms built with the co-electrospinning technique 45,[56][57][58] have been used previously to validate other dMRI techniques, including diffusion tensor imaging and fiber tracking, 45,59 microscopic fractional anisotropy using q-space trajectory encoding, 60 anomalous diffusion, 61 estimation of pore sizes in tumor tissue phantoms, 62,63 as well as to investigate the stability and reproducibility of various dMRI-derived parameters, 64 the validation of multidimensional dMRI sequences with modulated gradients, 65 and to estimate pore sizes in similar complex microfiber environments using multi-shell dMRI. 47 This study has some limitations.…”

Biomimetic polymer fibers—function by design

“…Another example of the production of a required biological architecture has been presented by Zhou et al They utilized coaxial electrospinning to create hollow poly(ε-caprolactone) (PCL) b-polyethylene glycol (PCL-)b-PEG and PLGA microfibers as reference objects for validating diffusion magnetic resonance brain imaging [96]. This imaging technique is based on the anisotropic diffusion of water in axonal fibers, which typically exhibit diameters ranging from 0.16 to 9 µm [97].…”