Developing advanced technologies for healthcare and human-machine interfaces requires multifunctional tools that can naturally integrate with the human body. The existing systems, as exemplified by a variety of medical electronics and interventional tools, provide critical capabilities for physiological investigation and therapies. However, their rigid, static and bulky forms limit their possibility of naturally interfacing with the biological tissues that are soft, dynamic and three-dimensional.
Our research focuses on bio-mimetic approaches to the engineering of soft materials and devices that can naturally integrate with the human body. We emulate the structures and physical functions of soft tissues with biocompatible nanocomposites. Multiscale fabrication techniques generate reconfigurable 3D structures, allowing for integration of advanced electronic components and biomaterials into organ-compliant forms. As exemplified by artificial cartilage, kirigami optics, and cardiac electronic membranes, our efforts span across a continuous spectrum of materials science and device engineering. The integrative approaches seek to enable fully functional systems for implantable biomedical tools, tissue engineering platforms, wearable electronics, energy and environmental technologies, and in many other applications.
Recent Works:
1. Aramid Nanofiber Composites as Soft Tissue Mimics
Biological tissues often exhibit amazing behaviors that are difficult to replicate with synthetic materials. For instance, load-bearing soft tissues, such as cartilage, artery walls, ligaments and other connective tissues, are water-rich yet display high stiffness, strength, deformability and fracture toughness, partly due to their sophisticated network of stiff collagen nanofibers and soft biomacromolecules.
In this research, we looked into the possibility of emulating the structures and physical properties of these natural materials with synthetic nanocomposites. Aramid nanofibers (ANFs) derived from Kevlar® and poly(vinyl alcohol) (PVA) are exploited to construct composite hydrogels, which exhibit unusually high mechanical properties matching or exceeding those of their prototype tissue, e.g., articular cartilage. Engineering of the reconfigurable hydrogen bonding between stiff ANFs and soft PVA leads to synergistic stiffening and toughening, similar to the key behaviors of many biological structural materials. Although their water content is 70%-92%, the composites possess tensile moduli of ~9.1 MPa, ultimate tensile strains of ~325%, compressive strengths of ~26 MPa, and fracture toughness as high as ~9,200 J/m^2. Furthermore, the composite nanofiber network can self-organize under stress, allowing for effective load bearing and viscoelastic energy dissipation. Their mechanical behavior, chemical composition and biocompatibility permit further utilization in soft tissue engineering and biomedical implants.
Representative publications:
Advanced Materials 30, 1703343 (2018)
Angewandte Chemie International Edition 56, 11744 (2017)
Advanced Functional Materials 26, 8435 (2016)
2. Organ-Conformal 3D Electronics
Tools for high-density multiparametric physiological mapping and stimulation are crucial for both basic and clinical medicine. Recently emerged flexible electronic systems have enabled important abilities, but their embodiments as 2D sheets limit their possibility for integration over the full 3D organ surface and their reliable contact for long-term use.
In this research, we created 3D conformal electronic membranes that can integrate across the entire surface of the heart and potentially other organs, and are capable of spatiotemporal measurement and stimulation. During this work, a collection of semiconductor devices, electronic sensors and stimulators were constructed in compliant and stretchable formats. Using 3D imaging and printing techniques, these components form patient-specific membranes that intimately envelope the organ of interest. In an example of cardiac application, the elastic membranes maintain stable contact with the epicardial surface without impairing the mechanical functions of the beating heart, acting as an “instrumented pericardium”. These devices allowed for high-fidelity mapping of electrical activation, pH, temperature and strain, as well as for application of electrical, optical and thermal stimulation. The system establishes a high-performance bio-electronic interface for investigating cardiac physiological processes and for delivering precision therapies.
Representative publications:
Advanced Materials 27, 1731 (2015)
Nature Communications 5, 3329 (2014)
3. Design and Fabrication of Soft Devices
While the conventional electronic technologies rely on rigid semiconductor chips and circuit boards, developing bio-integrated systems requires new classes of materials and device architecture that exhibit mechanical behaviors similar to soft and deformable biological tissues. We explored a variety of material fabrication techniques that enable preparation of soft and reconfigurable devices suitable for bio-integration. Motifs from fractal patterns or kirigami paper arts provide great inspiration for generating large-area structures with extreme strain tolerance. When combined with micro-patterning methods adapted from semiconductor manufacturing, as well as recently emerged techniques for layer-by-layer assembled nanocomposites, these concepts enable a number of device capabilities that are not achievable with conventional technologies. Examples include strain-tunable gratings for optical beam steering, electrodes for pain-free cardiac electrotherapy, strain sensors for interventional surgical tools, and many others. Active materials components, ranging from semiconductor nanomembranes and conductive polymers to nanotextured platinum alloys and carbon nanomaterial composites, can be micro-fabricated into fully functional soft devices. The results obtained from these works build up a general toolbox for addressing the challenges in creating soft and reconfigurable devices with practical utilities.
Representative publications:
ACS Nano 11, 7587 (2017)
ACS Nano 10, 6156 (2016)
Nature Materials 14, 785 (2015)
Advanced Materials 27, 1731 (2015)
Science 333, 838 (2011)
