The magnetoelastic effect, also named as Villari effect and discovered by Italian physicist Emilio Villari in 1865, is the variation of the magnetic field of a material under mechanical stress. This effect has been traditionally observed in rigid metals and metal alloys with an externally applied magnetic field and has been overlooked in the field of soft bioelectronics for three reasons. First, the magnetization variation in the biomechanical stress range is limited. Second, the requirement of the external magnetic field induces structural complexity and bulkiness. Finally, there exists a six orders of magnitude difference in mechanical modulus between magnetoelastic metals/metal alloys and human tissue. In 2021, our lab at the University of California, Los Angeles (UCLA) discovered the giant magnetoelastic effect in a soft system, constructed with micro/nanomagnets dispersed in a silicone matrix. In conjunction with electromagnetic induction, a soft magnetoelastic generator (MEG) is engendered via a two-step conversion system. The first step involves a mechanical-to-magnetic conversion and the second step a magnetic-to-electrical conversion. Together, an MEG-based soft bioelectronics can convert mechanical motions to electricity in a self-powered working manner. The mechanical stress alters the inter-distance and intra-dipole alignment of micromagnets, thereby modifying the magnetic field generated by the soft composite. The soft magnetoelastic composite is used to develop stretchable and water-resistant generators capable of adhering conformably to human skin. These innovative devices have the potential for energy, sensing, and therapeutic applications, opening new avenues for human-body-centered applications. In this dissertation, I will provide the progressive development of MEGs as a new platform technology for assistive technologies. The forthcoming sections outline the breadth of applications that MEGs offer. Then, I will discuss in detail the approaches as the first/co-first author in devising MEG-centered assistive technologies. By combining the unique properties of MEGs with the principles of assistive technology, I have developed intelligent and self-powered solutions, tailored to the requirements of specific user groups. The adaptability, flexibility, and mechanical durability of MEGs make them ideal for creating assistive devices that can enhance mobility, accessibility, and independence for users. Last but not least, I shall explore the challenges, opportunities, and future directions for the development and integration of MEGs in assistive devices. In essence, this dissertation constitutes a substantial stride in the field of soft MEGs, ushering them into the domain of assistive technologies. It showcases the potential of these devices to revolutionize the field, enabling the development of intelligent, self-powered, and user-centric solutions that can significantly improve the quality of life for individuals in need.

Soft bioelectronics have emerged as prominent solutions for diagnostic, energy producing and therapeutic solutions for in vitro, in vivo, and wearable applications, given their self- powered nature, low cost, flexibility, biocompatibility, miniaturized nature, and ability to use at scale. Through their use, electrical stimulation, a renowned modulator of biological activity and tissue regeneration, has re-emerged in a number of growing applicative fields, particularly in the field of neural engineering. In this work, we explore the use of soft bioelectronics for use in neural engineering applications. First we introduce the field of soft bioelectronics, including platform technologies employed, focusing on triboelectric and magnetoelastic generators and their working mechanism. We then debate their use in electrical stimulation for neural engineering. In the core chapters, we first discuss the development of an easy-to-fabricate magnetoelastic platform for in vitro electrical stimulation, including capabilities to scale using 3D printing, adaptation to 6, 12, 24, 48 and 96-well plates, and ability to address issues of wettability, size, third-party powering and biocompability, yielding electric output values of up to 10.52 mA and 9.5 mV. In the following chapter we carry out the first ever application of a magnetoelastic platform in cellular reprogramming and assess its efficacy in helping to promote fibroblast transdifferentiation into neurons using elicited electrical stimulation, increasing transdifferentiation efficiency (up to +104%), and enhancing neuron maturation (up to +251%), providing an easily devisable and scalable electrical stimulation device for research, and paving the way for future permeation of magnetoelastic generator-based implantable devices. Finally, we delve into the design of triboelectric nanogenerators for implantable in vivo use, by discussing a computational study of ultrasound-activated implantable triboelectric generators used in electrical stimulation for neural tissue repair in indications such as spinal cord injury, helping to pave the way for broader use of implanted soft bioelectronics. To conclude this work, some future considerations on electrical stimulation for the above research is provided, and a boarder outlook on the field of soft bioelectronic electrical stimulation for therapeutic applications is given, together with an essay on the permeation of soft bioelectronics in textile form for use in personalized healthcare.

Background

This study is to comprehensively investigate antiretroviral therapy (ART) initiation and retention among domestic migrants living with HIV (DMLH) in Guangdong, China.

Methods

Mixed methods were applied in this dissertation. In-depth interviews were conducted among service providers and DMLH. Two retrospective cohort studies based on secondary data were to investigate ART initiation and retention among DMLH from July 1, 2016, to December 31, 2019.

Results

In the first study, there were four levels of barriers to ART initiation and retention. The policy-level challenges were lack of appropriate medical insurance policy for DMLH and lack of effective reward and punishment mechanism for institutions. Barriers from institutions included a lack of cooperation across different institutions and a lack of flexibility in spending government funds. At the service provider level, shortage of experienced service providers and limited career prospects and low salaries were added to the barriers. Challenges identified at the individual level comprised of lack of HIV related knowledge, side effect, inconvenience to take a leave, lack of family support, and fear of stigma.

In the second study, over half of 22,773 participants were DMLH. Inter-provincial migrants were less likely to initiate ART than that among residents (HR=0.90, 95%CI: 0.86~0.94) and intra-provincial migrants (HR=0.90, 95%CI: 0.86~0.94). Compared to those without migration during the follow-up, those moving to their hometown (HR=0.06, 95%CI: 0.05~0.07) and other cities (HR=0.22, 95%CI: 0.17~0.27) were less likely to take ART. The probability of ART initiation among those returning to their hometown was lower than that among those moving to other cities (HR=0.30, 95%CI: 0.22~0.40).

In the third study, the probability of attrition among inter-provincial migrants (HR=1.15, 95%CI: 1.00~1.33) and intra-provincial migrants (HR=1.20,95%CI: 1.00~1.43) tended to be higher than that among residents in Region A. In Region B, the probability of ART attrition among inter-provincial migrants (HR=0.88, 95%CI: 0.74~1.05) and intra-provincial migrants (HR=0.79, 95%CI: 0.57~1.09) tended to be lower than that among residents.

Conclusion

There were multifaceted barriers for ART initiation and retention among DMLH. Future policies and interventions should properly take domestic migrants’ vulnerability and regional disparity into consideration to improve ART initiation and retention.

Bioelectronics are revolutionizing the future of human life by reshaping fields of medicine and healthcare into a more personalized form. Biomechanical-to-electrical energy conversion is a promising pathway to realize battery-free bioelectronics in the era of the Internet of Things. This conversion is available 24 hours a day and provides up to 100 W output for an average person. Current biomechanical energy conversion mechanisms, including piezoelectric and triboelectric effects, suffer limitations such as low current density and high internal impedance, which arise from their power generation mechanism. Additionally, their output performance is vulnerable to the humidity caused by body fluids, which limits their practical deployment in wearable and implantable bioelectronics. Therefore, there exists a demand to search for an unexploited biomechanical-to-electrical energy conversion mechanism featuring high current output, low internal impedance, waterproofness, and robustness under biomechanical stimulus. Thus, we discovered the giant magnetoelastic effect in a soft polymer system, which was further coupled with magnetic induction to invent a soft magnetoelastic generator (MEG) as a fundamentally new platform technology for building up human-body-powered soft bioelectronics. Soft magnetoelastic bioelectronics are intrinsically waterproof since the magnetic fields can penetrate water with negligible intensity loss. Thus, they demonstrated stable performance in wearable and implantable manners without any encapsulation. This breakthrough has opened alternative avenues for practical human-body-centered energy, sensing, and therapeutic applications. Second, the recent development of soft bioelectronic devices for disease prevention, diagnosis, and treatment presents pressing needs for the creation of an intimate interface between electronic systems and dynamically evolving biological tissues for precise physiological measurement. While ultrathin membrane-based soft bioelectronic devices can conform to biological tissue, mechanical mismatches between the solid materials and the biological tissue still exist. Thus, we developed an intimate liquid bioelectronic interface through the creation of a permanent fluidic magnet (PFM). PFM possesses the reconfigurable functionality to change its shape without losing its permanent magnetism. It will bridge the gap between liquid-state magnets and ferromagnetism, thereby unlocking a wide range of possibilities. Unlike traditional biomedical devices, liquid bioelectronics used for ambulatory monitoring enable the continuous assessment of biomechanical activity over extended periods. Uninterrupted monitoring provides a more comprehensive picture of a patient's health status, capturing any irregularities or abnormalities that may occur intermittently or during daily activities. Since magnetic fields can penetrate biological tissues due to their physical mechanisms, here we described the utilization of PFM for different biomedical applications, including injectable bioelectronics, and liquid acoustic sensors.

Wearable bioelectronics enable the changes in the current reactive and disease-centric healthcare system to a personalized model, focused on disease prevention and health promotion. Harnessing the body’s biomechanical forces is a unique way to develop wearable bioelectronics for personalized healthcare. The research advancements in triboelectric nanogenerators and the���ir ability to produce electrical signals in the presence of deformation, compression, and bending, among other movements have made it very favorable for miniaturized biomechanical motion sensors. In this work, we developed a soft triboelectric nanogenerator (S-TENG) formed with a liquid metal electrode treated with Nickel (Ni-EGaIn) encapsulated between two layers of Polycaprolactone (PCL) electrospun textiles. The Ni-EGaIn liquid demonstrates more tunable characteristics with a viscosity of 2,786 Pa�s at a shear rate of 1 s-1. The PCL cloth effectively wicks moisture keeping the sensor dry and cool with a drying rate of 5.07 % min-1 compared to conventional fabrics such as polyester with a drying rate of 3.93 % min-1. Operating as a single-electrode, the 4x4 cm2 patch demonstrated its ability to produce an open-circuit voltage of 12 V with a short-circuit current of 0.12 mA, ultimately outputting a power density of 7.975 W m-2. The S-TENG exhibited stable performance over many cycles and demonstrated its capability in producing electrical output under varying degrees of deformation in the form of stretching and bending. It has the potential to be integrated into all aspects of wearables such as patches, bracelets, and even clothing. The capabilities of the S-TENG given its power output efficiency, economical practicality, as well as user-friendly structure establishes itself as a promising approach to sustainable, wearable bioelectronic devices.

The conventional magnetoelastic effect describes the variation in magnetic flux density of certain materials under mechanical pressure within the megapascal range. In this study, we introduce porous microstructures into a soft magnetic system, resulting in an enhanced magnetoelasticity, characterized by a counterintuitive increase in magnetic flux density with the application of subtle mechanical pressure. This phenomenon, termed the structure-induced positive magnetoelastic effect, is attributed to the stress-induced redistribution of micromagnets within the porous, soft system, which exhibits a low Young’s modulus and near-zero Poisson’s ratio behavior. The technological impact of this discovery is demonstrated in its application to acoustic sensing and voice recognition, overcoming the low-pressure detection limits of current platform technologies. This breakthrough holds substantial potential for ultrasensitive pressure detection, with wide-ranging applications in extracting subtle physiological information.