Hydrogel Devices Research Articles

Hollow Hydrogels for Excellent Aerial Water Collection and Autonomous Release

AbstractAir moisture is a valuable and omnipresent resource of fresh water. However, traditional water collectors come with an enduring problem of the water‐release step, which requires special devices and additional energy to remove the water from the adsorbent, such as heat, sunlight, or both. Herein, we report the first composite conical hollow hydrogel architecture fabricated through a film‐to‐tube transforming protocol, designed to harvest water from aerial humidity. This hollow hydrogel device can rapidly collect water from humid air to a saturation point, whereupon it automatically and continually releases fresh water at room temperature. The entire water collection and release process does not require any external assistance. Therefore, this device is highly suitable for emergency water collection in arid areas. As an exemplary demonstration, positioning the hollow hydrogel device next to a plant turns into an individualized system for irrigation. Since the device is biodegradable, it eventually decomposes and becomes an organic fertilizer after the water supply is not required. For long‐term application, the water‐release process can be monitored in real time by an electronic device to indicate the amount of collected water. The hollow hydrogel combines the humidity‐adsorbing capacity with autonomous water release that carries the potential for harvesting water from humidity to address the shortage of fresh water, especially in arid locations where other sources of water are scarce or inaccessible.

Ionic Potential Relaxation Effect in a Hydrogel Enabling Synapse-Like Information Processing.

The next-generation brain-like intelligence based on neuromorphic architectures emphasizes learning the ionic language of the brain, aiming for efficient brain-like computation and seamless human-computer interaction. Ionic neuromorphic devices, with ions serving as information carriers, provide possibilities to achieve this goal. Soft and biocompatible ionic conductive hydrogels are an ideal substrate for constructing ionic neuromorphic devices, but it remains a challenge to modulate the ion transport behavior in hydrogels to mimic neuroelectric signals. Here, we describe an ionic potential relaxation effect in a hydrogel device prepared by sandwiching a layer of polycationic hydrogel (CH) between two layers of neutral hydrogel (NH), allowing this device to simulate various electrical signal patterns observed in biological synapses, including short- and long-term plasticity patterns. Theoretical and experimental results show that the selective permeation and hysteretic diffusion of ions caused by the anion selectivity of the CH layer are responsible for potential relaxation. Such an effect allows us with hydrogels to enable synapse-like information processing functions, including tactile perception, learning, memory, and neuromorphic computing. Additionally, the hydrogel device can operate stably even under 180° bending and 50% tensile strain, expanding the pathway for implementing advanced brain-like intelligent systems.

Closed-loop photo- and electrocatalysis using floatable hierarchical hydrogel device for efficient waste-derived fuel production

Closed-loop photo- and electrocatalysis using floatable hierarchical hydrogel device for efficient waste-derived fuel production

Multi-deformable interpenetrating network thermosensitive hydrogel fluorescent device for real-time and visual detection of nitrite

Functionalized thermosensitive hydrogel materials exhibit excellent properties for the fabrication of sensing devices that enable real-time visual detection of food safety duo to their good plasticity and powerful loading capacity. Here, a ratiometric fluorescent device based on an interpenetrating network (IPN) thermosensitive hydrogel was designed to embed functionalized Au nanoclusters (Au NCs) and Blue Carbon dots (BCDs) composites in a multi-network structure to build a sensitive hazardous material nitrite (NO2-) chemsensor. The hydrogel was utilized poloxamer 407 (P407), lignin and cellulose to form stable IPN structure, which resulted in complementation and synergy, thereby strengthening its porous network structure. The combination of fluorescent nanoprobes with the porous network structure has the potential to enhance stable fluorescence signals and improve sensing sensitivity. Moreover, the thermosensitive liquid-solid transition characteristics of the hydrogel facilitate its preparation into diverse sensing devices following curing at room temperature. The hydrogel device, when combined with a smartphone system, converted image information into data information, thereby enabling the accurate quantification of NO2- with a detection limit of 9.38 nM in 2 s. The designed multi-functional hydrogel device is capable of real-time differentiation of NO2- dosage with the naked eye, offering a high-contrast, rapid-response sensing methodology for visual assessment of food freshness. This research contributes to the expansion of hydrogel materials applications and the detection of hazardous materials in food safety.

3D-printed multifunctional biomass hydrogel device for controlled photothermal distribution and molecular release

Photothermal therapy based on photothermal conversion has received increasing attention due to its non-invasiveness and low side effects. In this study, a 3D-printed biomass photothermal therapy device was prepared for accurate control of photothermal conversion and molecular release. The prepared black phosphorus nanosheets (BPNSs) showed excellent photothermal performance and antibacterial activity. A temperature-regulated sol-gel reversible system was prepared with konjac glucomannan (KGM), tara gum (TG), BPNSs, and manganese dioxide (MnO2) nanoparticles. The sol-gel transition was attributed to the change of interactions of hydrogen bond, and molecular entanglement. Photothermal conversion films with accurate multi-layer and array structures were prepared by 3D printing using the biomass sol-gel conversion system. The photothermal conversion efficiency was regulated by the concentration of BPNSs and MnO2. Under infrared radiation (808 nm, 1 W/cm2) for 5 min, the temperatures of hydrogel films with a MnO2 concentration of 0, 0.5, and 1 % were raised from 25 to 29.3, 61.8, and 90.8 °C, respectively. The accurate temperature distribution induced the controlled release of small active molecules such as epigallocatechin gallate (EGCG) loaded in hydrogels, which was resulted from the changes in the hydrogel structure and the decrease in adsorption energy between polysaccharide and EGCG at high temperatures. This study provides a biomass 3D-printed multifunctional photothermal therapy device and more understanding of the molecular release during photothermal conversion.

WSe2/chitosan-based wearable multi-functional platform for monitoring electrophysiological signals, pulse rate, respiratory rate, and body movements.

Acleanroom free optimized fabrication of a low-cost facile tungsten diselenide (WSe2) combined with chitosan-based hydrogel device is reportedfor multifunctional applications including tactile sensing, pulse rate monitoring, respiratory rate monitoring, human body movements detection, and human electrophysiological signal detection. Chitosan being a natural biodegradable, non-toxic compound serves as a substrate to the semiconducting WSe2 electrode which is synthesized using a single step hydrothermal technique. Elaborate characterization studies are performed to confirm the morphological, structural, and electrical properties of the fabricated chitosan/WSe2 device. Chitosan/WSe2 sensor with copper contacts on each side is put directly on skin to capture human body motions. The resistivity of the sample was calculated as 26 kΩ m-1. The device behaves as an ultrasensitive pressure sensor for tactile and arterial pulse sensing with response time of 0.9s and sensitivity of around 0.02kPa-1. It is also capable for strain sensing with a gauge factor of 54 which is significantly higher than similar other reported electrodes. The human body movements sensing can be attributed to the piezoresistive character of WSe2 that originates from its non-centrosymmetric structure. Further, the sensor is employed for monitoring respiratory rate which measures to 13 counts/min for healthy individual and electrophysiological signals like ECG and EOG which can be used later for detecting numerous pathological conditions in humans. Electrophysiological signal sensing is carried out using a bio-signal amplifier (Bio-Amp EXG Pill) connected to Arduino. The skin-friendly, low toxic WSe2/chitosan dry electrodes pave the way for replacing wet electrodes and find numerous applications in personalized healthcare.

Self-powered smart pressure sensors by stimuli-responsive ion transport within layered hydrogels

Self-powered ionic sensors represent an emerging class of device capable of detecting and converting external stimuli, such as pressure and temperature, into electrical outputs without the need for an external power source. However, they often suffer from relatively low sensitivity, and their detection capability is typically limited to the magnitude of external stimulus. In this study, we present a smart pressure sensor consisting of nanowire electrodes and three-component ionic hydrogels with distinct stiffnesses and ion selectivities. Our hydrogel device effectively converts external pressure into a convective flow of cations, which are efficiently captured by the nanowire electrodes, yielding remarkable electrical outputs. In addition, upon local compression, the hydrogel device induces a convective flow that guides cations to the nearest electrode with minimal frictional force. This creates local inhomogeneous ionic distributions around the electrodes, enabling the detection of the local position and directional movements of the applied pressure without the need for additional electrical circuits. By enabling the simultaneous detection of pressure magnitude, local position, and movement, our device is capable of encoding intricate movements into distinct electrical outputs, thereby presenting a novel avenue for the development of advanced self-powered sensors with enhanced capabilities.

3D printed micro-structured hydrogel device with transmittance-changeable soft ‘armor’ camouflage for dual-encryption

Hydrogel-based physical dual-encryption typically relies on the reversible shape-deformation of polymer chains for the decryption. However, the stored information is confronted by indecipherability at the microscale because the intrinsic relaxation of polymer chains would disrupt the fidelity of encoded information. Inspired by female Doryteuthis opalescens squid’s camouflage strategy (i.e., switching a stripe on its mantle from nearly transparent to opaque white), we devised a reversible transmittance-changeable hydrogel layer to fully cover the mono-encrypted information layer for dual-encryption. The micro-structured hydrogel was manufactured via 3D printing to encode the information, which can be decoded by UV-induced fluorescent emission. Then, the white camouflage hydrogel was constructed to conceal the mono-encrypted layer, which will not affect the information encoding layer during the reversible polymer chain mobility. The information can be decoded with alkaline solution and UV irradiation in a rapid speed, i.e., in 4 min, with good reusability. Moreover, the information was accurately unveiled even at microscale resolution, holding great promise for high-level encryption at the device level.

A novel intralamellar semi‐bioresorbable keratoprosthesis—Part A: Design conception, material perspective, and device manufacturing

AbstractCorneal diseases are a significant cause of visual impairment and blindness. The first‐line treatment for corneal opacity is penetrating keratoplasty (human donor cornea transplantation). At present, keratoprosthesis (KPro), an artificial cornea, is the last resort for correcting end‐stage corneal blindness and is usually supported by donor tissue. This article describes a new intralamellar tissue‐free KPro design concept and its preparation method. Wherein, an injection‐molding route is adopted to create a mechanically and structurally stable near‐KPro geometry using a photo‐polymerized poly(2‐hydroxyethyl methacrylate) (pHEMA) with 4% Bisphenol A dimethacrylate (BisMA) crosslinked (PC4) hydrogel composition. Prior to this, the physico‐mechanical properties of crosslinked hydrogels matching corneal tissue are identified, and the surface morphological characteristics of silk cocoon membranes are ascertained in choosing suitable KPro materials. Cytocompatibility tests on PC4 and silk‐incorporated PC4 hydrogels using rabbit corneal fibroblast cell‐line evidenced enhancement in cell growth on silk‐PC4 surfaces. Furthermore, near KPro geometry is surface‐profiled to create a one‐of‐a‐kind design with clear optics and a silk‐bioactivated composite‐based haptic‐flange hydrogel network containing site‐specific submillimeter‐scale perforations to improve tissue integration. Considering this unique KPro geometry, the optic‐haptic‐flange construct is a tissue‐free semi‐bioresorbable hydrogel device presumed to provide stability under the influence of intraocular pressure (IOP) and eyelid shear. Through this study, it is identified new KPro materials facilitate significant cytocompatibility while complimented with site‐specific novel design would offer tissue ingrowth with gradual resorption of silk, leaving behind a stable intralamellar tissue integrated with hydrogel when implanted in the corneal niche.

Femtosecond‐Laser Direct‐Writing Hydrogel‐Based Microlens Arrays Customized with Multi‐Dimensional Optical Configurations for Information Encryption

AbstractFemtosecond‐laser direct‐writing lithography prints tunable 3D micro/nano‐scale optical devices based on hydrogel materials have garnered significant attention owing to their use in optical applications. Although the refractive index (RI) is an important parameter of optical devices, a quantitative measurement to determine that of femtosecond‐laser‐induced microstructures is lacking. This study proposes a novel method to measure the RI change of a tunable hydrogel device in different environments using a femtosecond‐laser‐customized multidimensional grating. As hydrogels can be tuned by changing the pH values, the specific RI changes of a hydrogel are first quantitatively investigated with different pH values such that the proposed method can be employed to precisely control the dynamic and tunable optical performance of hydrogel optical devices. To this end, a 3D hydrogel microlens array (HMA) with variable focal lengths is designed and manufactured to verify its dynamic and tunable optical performances. The HMA displays reversible and tunable imaging capabilities, confirming its application in information encryption. As a proof of concept, a customized sequence of letters “CFAE” is successfully obtained as the “output” by assigning the pre‐set pH values as the “code” and the original letter sequence as the “input.”

PO2 reporter composite hydrogel macroencapsulation devices for magnetic resonance imaging oxygen quantification.

Hydrogel cell encapsulation devices are a common approach to reduce the need for chronic systemic immunosuppression in allogeneic cell product transplantation. Macroencapsulation approaches are an appealing strategy, as they maximize graft retrievability and cell dosage within a single device; however, macroencapsulation devices face oxygen transport challenges as geometries increase from preclinical to clinical scales. Device design guided by computational approaches can facilitate graft oxygen availability to encapsulated cells in vivo but is limited without accurate measurement of oxygen levels within the transplant site and graft. In this study, we engineer pO2 reporter composite hydrogels (PORCH) to enable spatiotemporal measurement of oxygen tension within macroencapsulation devices using the proton Imaging of siloxanes to map tissue oxygenation levels (PISTOL) magnetic resonance imaging approach. We engineer two methods of incorporating siloxane oximetry reporters within hydrogel devices, an emulsion and microbead-based approach, and evaluate PORCH cytotoxicity on co-encapsulated cells and accuracy in quantifying oxygen tension in vitro. We find that both emulsion and microbead PORCH approaches enable accurate in situ oxygen quantification using PISTOL magnetic resonance oximetry, and that the emulsion-based PORCH approach results in higher spatial resolution.

Efficient Generation of Skin Organoids from Pluripotent Cells via Defined Extracellular Matrix Cues and Morphogen Gradients in a Spindle-Shaped Microfluidic Device.

Pluripotent stem cell-derived skin organoids (PSOs) emerge as a developmental skin model that is self-organized into multiple components, such as hair follicles. Despite their impressive complexity, PSOs are currently generated in the absence of 3D extracellular matrix (ECM) signals and have several major limitations, including an inverted anatomy (e.g., epidermis inside/dermis outside). In this work, a method is established to generate PSOs effectively in a chemically-defined 3D ECM environment. After examining various dermal ECM molecules, it is found that PSOs generated in collagen-type I (COLI) supplemented with laminin 511 (LAM511) exhibit increased growth compared to conventional free-floating conditions, but fail to induce complete skin differentiation due in part to necrosis. This problem is addressed by generating the PSOs in a 3D bioprinted spindle-shaped hydrogel device, which constrains organoid growth longitudinally. This culture system significantly reduces organoid necrosis and leads to a twofold increase in keratinocyte differentiation and an eightfold increase in hair follicle formation. Finally, the system is adapted as a microfluidic device to create asymmetrical gradients of differentiation factors and improves the spatial organization of dermal and epidermal cells. This study highlights the pivotal role of ECM and morphogen gradients in promoting and spatially-controlling skin differentiation in the PSO framework.

Structuring and Shaping of Mechanically Robust and Functional Hydrogels toward Wearable and Implantable Applications.

Hydrogels possess unique features such as softness, wetness, responsiveness, and biocompatibility, making them highly suitable for biointegrated applications that have close interactions with living organisms. However, conventional man-made hydrogels are usually soft and brittle, making them inferior to the mechanically robust biological hydrogels. To ensure reliable and durable operation of biointegrated wearable and implantable devices, mechanical matching and shape adaptivity of hydrogels to tissues and organs are essential. Recent advances in polymer science and processing technologies have enabled mechanical engineering and shaping of hydrogels for various biointegrated applications. In this review, polymer network structuring strategies at micro/nanoscales for toughening hydrogels are summarized, and representative mechanical functionalities that exist in biological materials but are not easily achieved in synthetic hydrogels are further discussed. Three categories of processing technologies, namely, 3D printing, spinning, and coating for fabrication of tough hydrogel constructs with complex shapes are reviewed, and the corresponding hydrogel toughening strategies are also highlighted. These developments enable adaptive fabrication of mechanically robust and functional hydrogel devices, and promote application of hydrogels in the fields of biomedical engineering, bioelectronics, and soft robotics.

Digital Light Processing 4D Printing of Poloxamer Micelles for Facile Fabrication of Multifunctional Biocompatible Hydrogels as Tailored Wearable Sensors.

The lack of both digital light processing (DLP) compatible and biocompatible photopolymers, along with inappropriate material properties required for wearable sensor applications, substantially hinders the employment of DLP 3D printing in the fabrication of multifunctional hydrogels. Herein, we discovered and implemented a photoreactive poloxamer derivative, Pluronic F-127 diacrylate, which overcomes these limitations and is optimized to achieve DLP 3D printed micelle-based hydrogels with high structural complexity, resolution, and precision. In addition, the dehydrated hydrogels exhibit a shape-memory effect and are conformally attached to the geometry of the detection point after rehydration, which implies the 4D printing characteristic of the fabrication process and is beneficial for the storage and application of the device. The excellent cytocompatibility and in vivo biocompatibility further strengthen the potential application of the poloxamer micelle-based hydrogels as a platform for multifunctional wearable systems. After processing them with a lithium chloride (LiCl) solution, multifunctional conductive ionic hydrogels with antifreezing and antiswelling properties along with good transparency and water retention are easily prepared. As capacitive flexible sensors, the DLP 3D printed micelle-based hydrogel devices exhibit excellent sensitivity, cycling stability, and durability in detecting multimodal deformations. Moreover, the DLP 3D printed conductive hydrogels are successfully applied as real-time human motion and tactile sensors with satisfactory sensing performances even in a -20 °C low-temperature environment.

Serum albumin hydrogels designed by protein Re-association for self-powered intelligent interactive systems

Advancements in protein structural engineering have made it possible to design protein materials that can mediate between humans and intelligent systems, manifesting a combination of characteristics such as elastic recovery, electrical conductivity, and stability. This work describes the design of a hydrogel using bovine serum albumin (BSA), based on protein-protein interactions and sulfhydryl-alkene click reactions. The multiple α-helices of BSA were intertwined together by the multi-armed olefin derivatives, acting like Lego blocks to form a gel network and locking in bound water and ions, thus imparting mechanical recovery characteristics (demonstrating 80 % recovery after the compressive strain and 638 % after tensile strain), electrical conductivity, resistance to freezing (maintaining mechanical properties after being frozen at -20 °C for 48 h), biocompatibility (the cell viability of mouse pre-osteoblast-like cells in the hydrogels was 97.5 %), antimicrobial properties, and biodegradability to the BSA hydrogels. A multi-channel wireless signal acquisition system based on BSA hydrogel devices designed for bioenergy conversion and harvesting was developed for the real-time detection of human motion along with a human-mechanics interaction system for manipulating robotic gestures with simple human finger movements. This restructuring of the BSA structure represents a significant advancement in the systematic exploration of protein structures and the development of protein materials. These applications serve as a secure bridge between humans and energy storage devices.

Stable Flexible Electronic Devices under Harsh Conditions Enabled by Double-Network Hydrogels Containing Binary Cations.

Hydrogels are increasingly used in flexible electronic devices, but the mechanical and electrochemical stabilities of hydrogel devices are often limited under specific harsh conditions. Herein, chemically/physically cross-linked double-network (DN) hydrogels containing binary cations Zn2+ and Li+ are constructed in order to address the above challenges. Double networks of chemically cross-linked polyacrylamide (PAM) and physically cross-linked κ-Carrageenan (κ-CG) are designed to account for the mechanical robustness while binary cations endow the hydrogels with excellent ionic conductivity and outstanding environmental adaptability. Excellent mechanical robustness and ionic conductivity (25 °C, 2.26 S·m-1; -25 °C, 1.54 S·m-1) have been achieved. Utilizing the DN hydrogels containing binary cations as signal-converting materials, we fabricated flexible mechanosensors. High gauge factors (resistive strain sensors, 2.4; capacitive pressure sensors, 0.82 kPa-1) and highly stable sensing ability have been achieved. Interestingly, zinc-ion hybrid supercapacitors containing the DN hydrogels containing binary cations as electrolytes have achieved an initial capacity of 52.5 mAh·g-1 at a current density of 3 A·g-1 and a capacity retention rate of 82.9% after 19,000 cycles. Proper working of the zinc-ion hybrid supercapacitors at subzero conditions and stable charge-discharge for more than 19,000 cycles at -25 °C have been demonstrated. Overall, DN hydrogels containing binary cations have provided promising materials for high-performance flexible electronic devices under harsh conditions.

A separation-free paper-based hydrogel device for one-step reactive oxygen species determination by a smartphone.

Paper-based analytical devices (PADs) are very convenient for determining biomarkers in point-of-care (POC) diagnosis while requiring sample pre-treatment or impurity separation. This study reports a novel hydrogel-coupled, paper-based analytical device (PAD) for separation-free H2O2 colorimetric detection in both aqueous solution and cell lysis with sample-to-answer analysis by directly loading into the sample test zone. By encapsulating an inorganic mimic enzyme and chromogenic substrate into the sodium alginate (SA) hydrogel, amplification of the color signal after catalyzing the substrate could be achieved. Taking advantage of the nanoscale porous structure of the hydrogel and the lateral flow channel of the PAD, large interference fragments or bio-macromolecules are prevented from diffusing into the chromogenic reaction, whereas the small target molecules enter the sensing region to trigger the catalytic reaction. This method demonstrated a rapid and accurate analysis with a limit of detection as low as 0.06 mM and detection selectivity. Our proposed device requires no enzyme and is separation-free, portable, easy-to-fabricate, and low-cost, and may offer a platform for quantitative or qualitative analysis of other analytes in body fluids for POC applications.

Tunable Hydrogel Electronics for Diagnosis of Peripheral Neuropathy.

Peripheral neuropathy characterized by rapidly increasing numbers of patients is commonly diagnosed via analyzing electromyography signals obtained from stimulation-recording devices. However, existing commercial electrodes have difficulty in implementing conformal contact with skin and gentle detachment, dramatically impairing stimulation/recording performances. Here, we develop on-skin patches with polyaspartic acid-modified dopamine/ethyl-based ionic liquid hydrogel (PDEH) as stimulation/recording devices to capture electromyography signals for the diagnosis of peripheral neuropathy. Triggered by a one-step electric field treatment, the hydrogel achieves rapid and wide-range regulation of adhesion and substantially strengthened mechanical performances. Moreover, hydrogel patches assembled with a silver-liquid metal (SLM) layer exhibit superior charge injection and low contact impedance, capable of capturing high-fidelity electromyography. We further verify the feasibility of hydrogel devices for accurate diagnoses of peripheral neuropathy in sensory, motor, and mixed nerves. For various body parts, such as fingers, the elderly's loose skin, hairy skin, and children's fragile skin, we regulate the adhesion of PDEH-SLM devices to establish intimate device/skin interfaces or ensure benign removal. Noticeably, hydrogel patches achieve precise diagnoses of nerve injuries in these clinical cases while providing extra advantages of more effective stimulation/recording performances. These patches offer a promising alternative for the diagnosis and rehabilitation of neuropathy in future. This article is protected by copyright. All rights reserved.

Lignosulfonate sodium assisted PEDOT-based all-gel supercapacitors with enhanced supercapacitance and wide temperature tolerance

Conducting polymer hydrogels are typically employed in all-gel supercapacitors; however, Poly[3,4-ethylene-dioxythiophene] (PEDOT)-based hydrogel supercapacitors still suffer from low capacitance because of the low packing density of PEDOT in the electrodes. Here, we demonstrate lignosulfonate sodium (LS) as an excellent template to synthesize various LS-PEDOT conductive nanofillers for high mass-loading LS-PEDOT/PAAM hydrogel electrodes. Then, the optimum LS-PEDOT/PAAM electrode was assembled with a redox-active LS/PAAM/Fe3+ hydrogel electrolyte to form sandwich-structured all-gel supercapacitors, which could deliver a high specific capacitance of 672.5 mF/cm2 and an energy efficiency of 60 μWh/cm2, which are three times higher than the 220 mF/cm2 and 19.5 μWh/cm2 of the device without Fe3+ at the same condition. Such a device shows excellent temperature tolerance from −30 to 100 °C. Besides, the LS-PEDOT/PAAM electrode has excellent photothermal conversion effects under simulated solar illumination. The sluggish electrochemical performance of the SC under low temperatures could be significantly boosted by ~50 % under simulated solar light. All of these findings demonstrate that the capacitance performance of the PEDOT-based hydrogel device is successfully improved not only at room temperature but also under subzero conditions.

A user's guide to degradation testing of polyethylene glycol-based hydrogels: From in vitro to in vivo studies.

Poly(ethylene glycol) (PEG)-based hydrogels have gained significant attention in the field of biomedical applications due to their versatility and antifouling properties. Acrylate-derivatized PEG hydrogels (PEGDA) are some of the most widely studied hydrogels; however, there has been debate around the degradation mechanism and predicting resorption rates. Several factors influence the degradation rate of PEG hydrogels, including backbone and endgroup chemistry, macromer molecular weight, and polymer concentration. In addition to hydrogel parameters, it is necessary to understand the influence of biological and environmental conditions (e.g., pH and temperature) on hydrogel degradation. Rigorous methods for monitoring degradation in both in vitro and in vivo settings are also critical to hydrogel design and development. Herein, we provide guidance on tailoring PEG hydrogel chemistry to achieve target hydrolytic degradation kinetics for both resorbable and biostable applications. A detailed overview of accelerated testing methods and hydrogel degradation characterization is provided to aid researchers in experimental design and interpreting in vitro-in vivo correlations necessary for predicting hydrogel device performance.