Exploration of electrospinning methods for fabricating synthetic human knee ligaments

Author: Aleksia Pilja

Pilja, Aleksia, 2019 Exploration of electrospinning methods for fabricating synthetic human knee ligaments, Flinders University, College of Science and Engineering

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The ligaments of the knee are crucial in providing particular movement limitations and overall stability to the joint. Cruciate ligaments maintain anteroposterior, rotational and one-plane medial or lateral stability in conjunction with the collateral structures [41]. Rupture to any of the supportive structures disrupts the kinematics of the femoral-tibial joint, causing functional impairment in the initial trauma [39]. In the majority of cases, surgical intervention is required to repair the initial function, however replacement grafts often lack the mechanical properties of the original ligament. Disruption in the stability of the knee eventually causes long-term effects, many associated with early onset osteoarthritis [39]. Investigations into developing a more suitable replacement graft is on the incline, with aims to reduce the occurrence of long-term effects. This study focuses on the development of synthetic ligaments through electrospinning means, with key objectives in replicating the elastic modulus of native knee ligaments. For the anterior cruciate ligament (ACL), the elastic modulus was found to be between 65 and 128 MPa [13,14].

The process of electrospinning involves the development and collection of small-scale fibres, with aims to replicate the fibrous nature of native ligaments. Fibre formation was achieved in the electrospinning device by passing a polymer solution through a high electric field and onto a rotating drum collector. The solutions tested consisted of numerous concentrations of polycaprolactone (PCL) in ratios of chloroform and dimethylformamide (DMF). The fibre stream formed in the process is highly governed by the electrospinning parameters used during experiments. Although influenced by all contributing factors, the fibre morphology was highly dependent on the flow rate of the solution, the applied voltage and the rotational speed of the collecting drum. The solution flow rate was typically set to 1.5 mL/h, while the applied voltage and rotational speed of the collector varied between 20-30 kV and 1000 to 1500 rpm, respectively. After the two-hour test duration, fibre sheets were rolled into a cylindrical bundle structures for mechanical testing. Tensile testing of samples was conducted at a 30% per second strain rate, where resultant data was used to produce stress-strain curves and calculate the elastic modulus of the samples. The unrolled fibres were viewed using a scanning electron microscope (SEM), in order to determine the resulting fibre morphology from the test conditions.

Upon testing, it was found that the 13% w/v PCL concentration solutions produced synthetic ligament samples with desirable mechanical properties. The elastic modulus for these samples was found to be between 69 and 106 MPa (n=8). Although exact fibre alignment was not achieved, an eventual recruitment of fibres under increasing tension was displayed in the stress-strain curves for particular samples. The smallest fibres were seen in the 10% solutions (198 – 366 nm), with diameters within the fibril range of a native ligament. The 13% solutions however, produced larger fibres (0.4 – 2 µm), placing them in the collagen fibre range of native ligaments [23]. Results indicate that a desirable elastic modulus can be achieved in the synthetic electrospun ligaments with the use of 13% w/v PCL solutions and the correct combination of electrospinning parameters

Keywords: Electrosinning, ACL, knee ligaments, synthetic ligament, grafts

Subject: Medical Biotechnology thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Dr Saulo Martelli