Zhigang Suo's research while affiliated with Harvard School of Engineering and Applied Sciences and other places
What is this page?
This page lists the scientific contributions of an author, who either does not have a ResearchGate profile, or has not yet added these contributions to their profile.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
Publications (134)
An aqueous emulsion of conducting polymer is commonly applied on a substrate to form a coating after drying. The coating, however, disintegrates in water. This paper reports a coating prepared using a mixture of two emulsions: an aqueous emulsion of conducting polymer, and an aqueous emulsion of hydrophobic and rubbery chains copolymerized with sil...
Many polymer networks are prepared by crosslinking polymer chains. The polymer chains and crosslinkers are commonly mixed in internal mixers or roll mills. These intense processes break the polymer chains, lower viscosity, and ease mixing. The resulting polymer networks have short chains and a fatigue threshold of ∼100 J m-2. Here, we show that a l...
Hydrogels are being developed to bear loads. Applications include artificial tendons and muscles, which require high strength to bear loads and low hysteresis to reduce energy loss. However, simultaneously achieving high strength and low hysteresis has been challenging. This challenge is met here by synthesizing hydrogels of arrested phase separati...
Corners concentrate elastic fields and often initiate fracture. For small deformations, it is well established that the elastic field around a corner is power-law singular. For large deformations, we show here that the elastic field around a corner is concentrated but bounded. We conduct computation and an experiment on the lap shear of a highly st...
Bovine pericardium (BP) has been used as leaflets of prosthetic heart valves. The leaflets are sutured on metallic stents and can survive 400 million flaps (~10-year life span), unaffected by the suture holes. This flaw-insensitive fatigue resistance is unmatched by synthetic leaflets. We show that the endurance strength of BP under cyclic stretch...
A hydrogel is often fabricated from preexisting polymer chains by covalently crosslinking them into a polymer network. The crosslinks make the hydrogel swell-resistant but brittle. This conflict is resolved here by making a hydrogel from a dough. The dough is formed by mixing long polymer chains with a small amount of water and photoinitiator. The...
Developing methods for chemical sensing is of importance in broad applications, including food safety, healthcare, and ecology. The work herein describes an approach to chemical sensing by interfacial voltage. A test electrode is coated with a dielectric and a receptor. When the test electrode contacts an electrolyte, the receptor adsorbs an analyt...
This paper studies a commonly observed phenomenon: the initiation of fracture from corners in a brittle soft material. A rectangular hydrogel is prepared and glued between two plastic films, such that the hydrogel meets the films at 90-degree corners. When the two plastic films are pulled, the hydrogel undergoes a shear deformation, and the stress-...
Synthesis-property relation is fundamental to materials science, but many aspects of the relation are not well understood for many materials. Impetus for this paper comes from our recent appreciation for the distinct roles of entanglements and crosslinks in a polymer network. Here we study the synthesis-property relation of polyacrylamide hydrogels...
Biological tissues, such as cartilage, tendon, ligament, skin, and plant cell wall, simultaneously achieve high water content and high load-bearing capacity. The high water content enables the transport of nutrients and wastes, and the high load-bearing capacity provides structural support for the organisms. These functions are achieved through nan...
When a polymer network is stretched, some polymer strands do not bear loads. Examples include looped strands, dangling strands, and extremely long strands. When the polymer network is submerged in a solvent, however, all strands mix with solvent molecules. This distinction between strands that bear loads and strands that do not leads us to modify t...
An elastomeric seal needs to be soft to accommodate installation but stiff to block fluid flow. Here we show that the two requirements are better fulfilled by a strain-stiffening elastomer than a neo-Hookean elastomer. We represent the strain-stiffening elastomer using the Gent model, and calculate the deformation in the elastomeric seal using an a...
Many living tissues achieve functions through architected constituents with strong adhesion. An Achilles tendon, for example, transmits force, elastically and repeatedly, from a muscle to a bone through staggered alignment of stiff collagen fibrils in a soft proteoglycan matrix. The collagen fibrils align orderly and adhere to the proteoglycan stro...
A pneumatic soft robot can be made autonomous by carrying a liquid chemical fuel. In the existing design, to transmit the fuel, the pressure of the fuel tank must exceed that of the actuator. Consequently, the fuel tank must be sufficiently stiff, which hardens the robot. Herein, inspired by pit membranes in trees, a chemical pump is developed, whi...
Significance
We develop temperature sensors on the basis of charges accumulated at the electrolyte/dielectric interface and dielectric/electrode interface. The accumulated charges make the temperature sensors self-powered, which simplifies circuit design and enables portable sensing. The sensors are stretchable, but deformation does not affect temp...
The conditions for rupture of a material commonly vary from sample to sample. Of great importance to applications are the conditions for rare-event rupture, but their measurements require many samples and consume much time. Here, the conditions for rare-event rupture are measured by developing a high-throughput experiment. For each run of the exper...
Submerged in an aqueous solution of sodium chloride (NaCl), a poly(N-isopropylacrylamide) (PNIPAM) hydrogel can be in one of two phases: swollen phase and collapsed phase. We measure the equilibrium volume of the hydrogel as a function of temperature T and ionic concentration y. The hydrogel is in the swollen phase when T and y are low, and is in t...
In many applications, glass fabrics are subject to cyclic forces. Here we show that a glass fabric can tear under a much lower cyclic force than monotonic force. For samples of a given width, a threshold force exists below which the fabric does not tear under cyclic load, and a critical force exists at which the fabric tears under monotonic load. F...
Though commonly used, metal electrodes are incompatible with brain tissues, often leading to injury and failure to achieve long-term implantation. Here we report a subdural neural interface of hydrogel functioning as an ionic conductor, and elastomer as a dielectric. We demonstrate that it incurs a far less glial reaction and less cerebrovascular d...
The eye converts an optical signal to an ionic signal. This transduction is mimicked here using a photodiode in contact with ionic conductors, such as hydrogels. Photons generate electron-hole pairs in the photodiode. The photodiode/hydrogel interface forms capacitive coupling so that movements of electrons and holes in the photodiode induce moveme...
The recent development of tough tissue adhesives has stimulated intense interests among material scientists and medical doctors. However, these adhesives have seldom been tested in clinically demanding surgeries. Here we demonstrate adhesive anastomosis in organ transplantation. Anastomosis is commonly conducted by dense sutures and takes a long ti...
A supercapacitor requires two electronic conductors with large surface areas, separated by an ionic conductor. Here we demonstrate a method to print a highly stretchable supercapacitor. We formulate an ink by mixing graphene flakes and carbon nanotubes with an organic solvent, and use the ink to print two interdigitated electronic conductors on the...
Longer and stronger; stiff but not brittle
Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. Two papers now report strategies to create tough but deformable hydrogels (see the Perspective by Bosnjak and Silbe...
Polyurethane (PU) elastomers are among the most used rubberlike materials due to their combined merits, including high abrasion resistance, excellent mechanical properties, biocompatibility, and good processing performance. A PU elastomer exhibits pronounced hysteresis, leading to a high toughness on the order of 10⁴ J/m². However, toughness gained...
A polyacrylamide hydrogel exhibits near-perfect elasticity: its stress-stretch curve is rate-independent and has negligible hysteresis. The near-perfect elasticity results from the large amount of water between the polymer chains. Water has low viscosity and lubricates polymer chains. Here we report that the polyacrylamide hydrogel exhibits rate-de...
Significance
Many surgeries require surgical mesh to be attached firmly at target areas to strengthen tissues, support organs, or repair wounds. Common methods of attachment include sutures, staples, and spiral tacks, but they damage tissues and prolong surgeries. Adhesion has been considered a promising alternative method to attach surgical meshes...
A time-varying magnetic field generates an electric field in an electrolyte, in which ions move. This magnetoionic transduction is studied here in several arrangements. The electrolyte is a hydrogel containing mobile ions, and is in contact with two metallic electrodes. An alternating electric current applied to a metal coil generates a time-varyin...
We peel a highly stretchable silicone (Ecoflex), thickness H and width B, sandwiched between two inextensible films. When the peel front advances steadily in the elastomer, the peel force reaches a plateau Fss, and the ratio 2Fss/B is commonly reported as the toughness of the elastomer. Our data show that this “peel toughness” is not always a mater...
Degradable polymers are under intense development for sustainability and healthcare. Evidence has accumulated that the chemical reaction that decomposes a polymer can also grow a crack. Even under a small load, the crack speed can be orders of magnitude higher than the overall rate of degradation, leading to premature failure. Here, we demonstrate...
Hydrogels are commonly integrated with other materials. In the one-pot synthesis of a hydrogel coating, polymerization, crosslink, and interlink are concurrent. This concurrency, however, is often inapplicable for integrating hydrogels to other materials. For example, a permeable substrate will absorb small molecules in the solution, causing side r...
Rupture of emerging tough hydrogels has received much attention in recent years. It is a fundamental question what length of initial flaws can significantly affect the rupture of a tough hydrogel. Here we study the rupture of a tough hydrogel, using samples with and without initial cuts, under monotonic and cyclic loads. We prepare six samples unde...
Many living tissues achieve functions through architected constituents with strong adhesion. An Achilles tendon, for example, transmits force, elastically and repeatedly, from a muscle to a bone through staggered alignment of stiff collagen fibrils in a soft proteoglycan matrix. The collagen fibrils align orderly and adhere to the proteoglycan stro...
A plastic may degrade in response to a trigger. The kinetics of degradation have long been characterized by the loss of weight and strength over time. These methods of gross characterization, however, are misleading when plastic degrades heterogeneously. Here, we study heterogeneous degradation in an extreme form: the growth of a crack under the co...
It has been common to use brittle constituents to form tough composites. For example, ceramic fibers and a ceramic matrix are brittle, but their composite can be tough, provided the matrix can slide relative to the fibers. Here we study the effect of rate-dependent sliding on toughness. Consider a crack through the matrix, with the fibers being int...
This paper studies the lap shear, in which both the adhesive and adherends are elastic, but the adhesive is much softer than the adherends. The shear lag model identifies a length, called the shear lag length Ls. The energy release rate of a debond crack is affected by the elasticity of both the adhesive and adherends. Their relative importance is...
Biological tissues, such as heart valves and vocal cords, function through complex shapes and high fatigue resistance. Achieving both attributes with synthetic materials is hitherto an unmet challenge. Here we meet this challenge with hydrogels of heterogeneous structures. We fabricate a three-dimensional hydrogel skeleton by stereolithography and...
Hydrogels—natural or synthetic polymer networks that swell in water—can be made mechanically, chemically and electrically compatible with living tissues. There has been intense research and development of hydrogels for medical applications since the invention of hydrogel contact lenses in 1960. More recently, functional hydrogel coatings with contr...
Lap shear and peel are common tests for soft materials. Their results, however, are rarely compared. Here we compare lap shear and peel as tests for measuring toughness. We prepare specimens for both tests by using stiff layers to sandwich a layer of a polyacrylamide hydrogel. We introduce a cut in the hydrogel by scissors, pull one stiff layer at...
Liquid propylene-glycol (PG) has long been used as an anti-icing substance, for example, by spraying on an airplane parked in an airport. In applications, large quantities of PG flow away, which is costly and raises environmental concerns. Here we report propylene-glycol materials, including PG-gels and PG-gel/cotton composites. A PG-gel consists o...
In a previous paper (Zhang et al., 2020), we have demonstrated an adhesive of high fatigue threshold ∼300 J/m² using an as-prepared hydrogel of long-chain polymer network. In most applications, however, hydrogel adhesives are in contact with water. The long-chain hydrogel swells and reduces the fatigue threshold. Here we demonstrate a type of swell...
We describe the materials, designs, experimental measurements, and simulations of a bio-inspired all-solid tunable optical device: ionic eye. A dielectric elastomer functions as an electroactive material. An ionogel functions as an ionic conductor. Both materials are stretchable and transparent. The ionic eye achieves a ∼50% relative change of the...
A family of recently developed devices, hydrogel ionotronics, uses hydrogels as ionic conductors, and uses hydrophobic elastomers as dielectrics. This development has posed a challenge: integrate hydrogels and hydrophobic elastomers—in various manufacturing processes—with strong, stretchable, and transparent adhesion. Here, a multistep dip‐coating...
Degradable polymers are being developed for medical applications and environmental sustainability. The molecular mechanism of degradation is known: a polymer dissociates in response to a trigger, such as light, water, or biomolecules. However, the spatial and temporal processes of degradation are poorly characterized. Here we show that degradation...
When a soft material (gel, elastomer, or biological tissue) is compressed beyond a critical strain, its smooth surface form creases. During this process, a material particle near a crease undergoes a path of load and unload. If the material is elastic, the load and unload do not dissipate energy, and the crease sets in at a critical strain about 0....
Extreme Mechanics Letters, an Elsevier journal, has recently launched a weekly EML Webinar, an online meeting place for mechanicians and their friends, worldwide. The lectures and discussions shed light on the forefront of research and the formative years of researchers, no travel required. Speakers and videos are updated at http://iMechanica.org/n...
When two stretchable materials (e.g., hydrogels, elastomers, and biological tissues) are adhered, the interface should be stretchable, without constraining the deformation and degrading adhesion. Here we develop methods to characterize stretchable adhesion. We do so by topological adhesion, using polyacrylamide hydrogels as adherends, chitosan as s...
Gelation kinetics of polymer chains through covalent bonds depends on many variables and affects many applications. Here we study the gelation kinetics of alginate chains through crosslinkers adipic acid dihydrazide (AAD), with coupling reagents 1-ethyl-3-(3-dimethylaminopropyl) (EDC) and N-hydroxysuccinimide (NHS). We use the rate equation of the...
Functional devices that use hydrogels as ionic conductors and elastomers as dielectrics have the advantage of being soft, stretchable, transparent, and biocompatible, making them ideal for biomedical applications. These devices are typically fabricated by manual assembly. Techniques for the manufacturing of soft materials have generally not looked...
Topological adhesion, or topohesion for brevity, links two polymer networks, to be called adherends, even when the adherend networks carry no functional groups for chemical coupling. Uncrosslinked polymers, called stitch polymers, are spread between the two adherends. In response to a trigger, the stitch polymers form a stitch network in topologica...
Tough adhesion is often achieved by using inelastic dissipaters. However, inelastic dissipaters fail to enhance adhesion under cyclic loads. Here we achieve fatigue-resistant adhesion by using a particularly simple kind of elastic dissipaters: long-chain polymers. Each polymer chain is elastic before rupture. When a single covalent bond of the chai...
Tough adhesion between soft and wet materials is important to many applications in medicine and engineering. Examples include implants, wound dressing, and soft machines. Recent work has highlighted a general principle: tough adhesion can be realized through the synergy of interlink and toughener. Here we develop an adhesive double-network hydrogel...
Adhesion of soft materials is commonly characterized by strength and toughness. Their applicability, however, is often questionable even for widely used test methods. Here we study lap shear using a combination of experiment, theory, and computation. Lap shear has long been used to measure adhesion strength of soft materials, but our experiments sh...
Electroadhesion provides a simple route to rapidly and reversibly control adhesion using applied electric potentials, offering promise for a variety of applications including haptics and robotics. Current electroadhesives, however, suffer from key limitations associated with the use of high operating voltages (>kV) and corresponding failure due to...
Manipulating charges is fundamental to numerous systems, and this ability is achieved through materials of diverse characteristics. This ability is achieved through materials of diverse characteristics. Electrets are dielectrics that trap charges or dipoles. Applications include electrophotography, microphones, air filters and energy harvesters. To...
The integration of polymer networks of dissimilar chemistries, such as hydrogels and hydrophobic elastomers, has enabled numerous existing and emerging applications in engineering and medicine. However, it remains a challenge to adhere polymer networks of dissimilar chemistries when neither network contains functional groups for chemical coupling....
This paper demonstrates that macroporous hydrogels, filled with mobile polymer chains, markedly reduce friction. We fabricate a macroporous hydrogel by freeze and thaw, soak the macroporous hydrogel in an aqueous solution of mobile polymer chains, and slide the polymer-filled macroporous hydrogel against glass. The polymer-filled macroporous hydrog...
Explosion of ping‐pong balls that is caused by the rapid inflation of an elastomer membrane. The illustrated ultrafast actuation is based on a plant‐inspired mechanical instability that occurs in natural rubber and can be remotely triggered, presented in article number 1903391 by Martin Kaltenbrunner and co‐workers. These new types of high‐speed so...
Ionic elastomeric material electronics
Wearable devices often need to be soft or flexible, and ideally, these properties would extend beyond packaging material to also include the electronics. Some soft ionic conductors have been made in the form of flexible, stretchable, and transparent devices, but leaks from these materials is a concern. Kim et...
Rapid energy‐efficient movements are one of nature's greatest developments. Mechanisms like snap‐buckling allow plants like the Venus flytrap to close the terminal lobes of their leaves at barely perceptible speed. Here, a soft balloon actuator is presented, which is inspired by such mechanical instabilities and creates safe, giant, and fast deform...
This paper describes a general method, called topological prime, to stitch functional groups to a substrate of entropic polymer network. The precursor of a topological primer contains polymers, crosslinkers, and coupling agents. When the precursor is applied on the surface of the substrate, the crosslinkers link the primer polymers into a primer ne...
Incorporation of elastomers into bioelectronics that reduces the mechanical mismatch between electronics and biological systems could potentially improve the long-term electronics-tissue interface. However, the chronic stability of elastomers in physiological conditions has not been systematically studied. Here, using electrochemical impedance spec...
The measurement of bite force is important to dental care and research. Current sensors of bite force are made of hard materials, which do not conform to the irregular surfaces of teeth and constrain the movements of muscles. Here we propose a soft sensor made of a hydrogel and a dielectric elastomer. The sensor converts a mechanical force to a cha...
Hydrogels and elastomers are being integrated to make stretchable, transparent, electromechanical devices. In such a device, a dielectric elastomer functions as an electric insulator, and a salt-containing hydrogel functions as an electric conductor. Here we report several experimental observations associated with electric field concentration along...
In article number 1903062, Zhigang Suo and co‐workers report a principle to develop green hydrogel paint based on decoupling of the synthesis and cure processes. As a result, after being manufactured in a factory, the paint product can be used to create hydrogel coatings by anyone. Such a principle re‐opens numerous ways to use hydrogel coatings in...
Stiffness and fatigue threshold are important material parameters in load-carrying applications. However, it is impossible to achieve both high stiffness and high threshold for single-network elastomers and single-network hydrogels. As the polymer chain length increases, the stiffness reduces, but the threshold increases. Here we show that this sti...
Noncovalent adhesion has long been developed for numerous applications, including pressure-sensitive adhesives, wound closure, and drug delivery. Recant advances highlight an urgent need: a general principle to guide the development of instant, tough, noncovalent adhesion. Here we show that noncovalent adhesion can be both instant and tough by sepa...
A hydrogel of covalently crosslinked chains and ionically crosslinked chains has exhibited high toughness. Under deformation, the covalently crosslinked network remains intact, and the ionically crosslinked network dissipates energy by breaking the ionic bonds. Because the broken ionic bonds can reform spontaneously, the damaged hydrogel can recove...
Soft robots require sensors that are soft, stretchable, and conformable to preserve their adaptivity and safety. In this work, hydrogels are successfully applied as large‐strain sensors for elastomeric structures such as soft robots. Following a simple surface preparation step based on silane chemistry, prefabricated sensors are strongly bonded to...
For a hydrogel coating on a substrate to be stable, covalent bonds polymerize monomer units into polymer chains, crosslink the polymer chains into a polymer network, and interlink the polymer network to the substrate. The three processes—polymerization, crosslinking, and interlinking—usually concur. This concurrency hinders widespread applications...
We report an experimental finding that a crack advances in a polydimethylsiloxane (PDMS), under a small stress, in a moist environment. PDMS chains consist of siloxane bonds with methyl side groups. The methyl groups make PDMS hydrophobic, and PDMS hydrolyzes extremely slowly under no stress. Nonetheless, we find that a crack advances under the com...
The next generation of flexible electronics will require highly stretchable and transparent electrodes, many of which consist of a relatively stiff metal network (or carbon materials) and an underlying soft substrate. Typically, such a stiff–soft bilayer suffers from wrinkling or folding when subjected to strains, causing high surface roughness and...
Completely soft, autonomous fluidic robots require valves made of soft materials. Such a soft valve has been demonstrated recently to enable complex movements of soft robots using a single source of air of constant pressure. This paper studies the mechanics of the valve using a combination of experiments and calculations. The valve is made of an el...
Periodic actuation of multiple soft, pneumatic actuators requires coordinated function of multiple, separate components. This work demonstrates a soft, pneumatic ring oscillator that induces temporally coordinated periodic motion in soft actuators using a single, constant-pressure source, without hard valves or electronic controls. The fundamental...
Tough adhesion between wet materials (i.e., synthetic hydrogels and biological tissues) is undergoing intense development, but methods reported so far either require functional groups from the wet materials, involve toxic chemicals, or result in unstable adhesion. Here, we present a method to achieve biocompatible, covalent adhesion, without requir...