The effects of pulsed electromagnetic field on bone regeneration

• Main Author: Suryani, Luvita
• Other Authors: Swee Hin Teoh
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Bioengineering
• Online Access: https://hdl.handle.net/10356/152756
• Institution: Nanyang Technological University

Pulsed electromagnetic field (PEMF) is known for its bone healing ability in non-union fractures and spinal fusions. PEMF therapy is reported to be relatively pain-free and non-invasive. However, there is lack of consistency in investigating the effects of PEMF on test subjects. Various types of PEMF-emitting devices were used to test different subjects (cells and animals). The optimal set of PEMF parameters for bone healing application is still an ongoing research topic. In addition, currently there is also a lack of research done on the effects of PEMF flux direction and movement since most of the studies conducted used PEMF that is in stationary condition. The objective of this thesis is to study the effect of PEMF on osteogenesis. Due to the inconsistencies of existing commercially available PEMF devices, we specially designed our own PEMF-emitting device. PEMF parameters such as duration of exposure, intensity, and dynamic movement were tested. The studies were carried out on: (a) cellular (MC3T3-E1 and mesenchymal stem cells), (b) 3D tissue scaffolds (3D-printed from Osteopore International Pte Ltd.), and (c) animal (chicken embryo) models. Three different PEMF configurations were designed and built. They were classified into: (a) Stationary PEMF emitted by solenoid coils for MC3T3-E1, mesenchymal stem cells (MSCs, from monkey and rabbit), and chicken embryos, (b) PEMF emitted by two Helmholtz coils which moved in two directions using a specially designed biaxial bioreactor (manufactured by Quintech) for MC3T3-E1 cells, (c) PEMF emitted by two Helmholtz coils with perfusion flow and biaxial rotation using bioreactor for the 3D-printed scaffolds. The results showed that the PEMF emitted from these devices was constantly uniform throughout the duration of exposure on the test subjects. They were modelled with COMSOL Multiphysics software and were consistent with the on-site measurement. Different lengths of exposure and intensities of PEMF were tested on both immortalized pre-osteoblastic cell line, MC3T3-E1, and primary rabbit MSCs. The results showed that 0.6mT, 50 Hz, 30 minutes daily PEMF exposure improved the proliferation of both types of cells regardless of the culture media types. MSCs displayed higher metabolic activity as compared to MC3T3-E1. However, as the intensity of PEMF increased, the effects of PEMF on MSCs were lessened. The oscillating movement of PEMF improved both cell proliferation and calcium deposition of MC3T3-E1, especially those cultured in differentiating media. It was hypothesized that PEMF could affect the opening of calcium ion channel and enhance the release of intracellular calcium ions which might trigger downstream pathways that led to increasing cell proliferation. The dynamic motion of oscillating PEMF might intensify this occurrence since PEMF flux would cut through the cells, producing eddy currents. There were also indications that window of efficacy of PEMF treatment existed. The first week of PEMF treatment elicited the highest cell proliferation. In addition, the longer exposure to PEMF and the higher the intensity did not result in better cell response, proving that the efficacy of PEMF treatment could be maximized within this window. This optimized set of parameters (0.6mT, 50 Hz, 30 minutes) were then applied to both chicken embryo and 3D-tissue models. Chicken embryo was chosen because PEMF could penetrate inside without going through muscles, bones, and other tissues before reaching to the embryo, which may dampen the effects of exposure. The results showed that PEMF improved the bone volume fraction (BV/TV) of chicken embryo. This was measured on day 14 of the embryonic age which corresponded to the increase of calcium ions content in amniotic fluid. However, prolonged PEMF exposure resulted in lesser value on day 18. It was hypothesized that the increase in calcium ions on day 18 was directed towards the development of internal organ since PEMF-exposed chicken embryo had larger value of stomach and heart dried weight as compared to the non-exposed group. This was also an indication of the existence of window of efficacy of PEMF to affect a specific stage in chicken embryo development. The optimized set of PEMF was paired with multimodal bioreactor to culture primary MSC-laden 3D scaffold. The bioreactor moved in two directions and the culture media was perfused into the scaffolds-containing chamber. Results showed that PEMF-exposed 3D scaffolds had more than twice the cell numbers as compared to those that were not exposed to PEMF on both day 7 and 14. Compared with those cultured in stationary condition with only perfusion, the combination of PEMF and biaxial rotation stimulations improved both cell proliferation and calcium deposition in differentiating media on both day 7 and 14. This thesis provided specially designed devices that emitted uniform PEMF exposure to test different subjects. The configuration parameters were also tunable, which allowed versatile usage of PEMF depending on the focus of the study. The chicken embryo model for osteogenesis study of PEMF also laid a foundation for further developmental biology studies involving the effects of man-made EMFs. The optimized set of parameters for osteogenesis could enhance cell proliferation and mineralization on 3D scaffolds. These scaffolds could be potentially used as bone grafts and benefit patients who have less MSCs count as PEMF could help in improving the cell numbers.