Tissue-Adaptive Materials with Independently Regulated Modulus and Transition Temperature

Two way workable microchanneled hydrogel suture to diagnose, treat and monitor the infarcted heart

During myocardial infarction, microcirculation disturbance in the ischemic area can cause necrosis and formation of fibrotic tissue, potentially leading to malignant arrhythmia and myocardial remodeling. Here, we report a microchanneled hydrogel suture for two-way signal communication, pumping drugs on demand, and cardiac repair. After myocardial infarction, our hydrogel suture monitors abnormal electrocardiogram through the mobile device and triggers nitric oxide on demand via the hydrogel sutures' microchannels, thereby inhibiting inflammation, promoting microvascular remodeling, and improving the left ventricular ejection fraction in rats and minipigs by more than 60% and 50%, respectively. This work proposes a suture for bidirectional communication that acts as a cardio-patch to repair myocardial infarction, that remotely monitors the heart, and can deliver drugs on demand.

Ambient Environment Adaptive Elastomer Constructed by Microphase Separation and Segment Complexation of Triblock Copolymers

Elastomers with environmental adaption have attracted considerable attention for advanced applications in various areas. Here, we fabricate an ambient environment adaptive elastomer by assembling triblock copolymers polystyrene-b-poly(acrylic acid)-b-polystyrene (SAS) and polystyrene-b-poly(ethylene oxide)-b-polystyrene (SES). Owing to the microphase separation of triblock polymers and hydrogen-bonding complexation of their middle segments, the SAS/SES complex presents dichotomy of vitrified hard PS domains and soft PAA/PEO domains, which presents major relaxation transition in the temperature zone 10-30 °C and relative humidity (RH) 40-60%. The SAS/SES elastomer presents quick adaption to the ambient environment change with temperature and humidity coupling. Moreover, after a loading-unloading cycle training, the SAS/SES elastomer exhibits domain orientation, low energy dissipation, high recovery ratio, and distinct strain stiffening compared with the pristine complex. The SAS/SES elastomer has potential to be used as a sensing and adaption component for complicated intelligent systems.

Microphysiological system recapitulating the pathophysiology of adipose tissue in obesity

A growing body of evidence has indicated that white adipose tissue (AT) remodeling is a major trigger for obesity-associated metabolic complications. However, the scarcity of translational models is an obstacle to the development of medicines that act on adipose restoration. Here, we describe a microphysiological system (MPS) that emulates the unique features of reprogrammed AT as a new in vitro tool for studying AT pathophysiology in obesity. The AT MPS contained mature adipocytes embedded in an extracellular matrix (ECM) hydrogel interfaced with AT microvascular endothelium, which was constantly perfused with fresh media. The unique biochemical signals due to the remodeled ECM in obesity were recapitulated using a decellularized AT ECM (AT dECM) hydrogel, which preserves the features of altered ECM composition in obesity. The mature adipocytes embedded in the AT dECM hydrogel maintained their function and morphology for a week without dedifferentiation. Using the AT MPS, we successfully modeled inflammation-induced AT microvascular dysfunction, the recruitment of immune cells due to the upregulation of cell adhesion molecules, and higher cancer cell adhesion as an indicator of metastasis, which are observed in obese individuals. The AT MPS may therefore represent a promising platform for understanding the dynamic cellular interplay in obesity-induced AT remodeling and validating the efficacy of drugs targeting AT in obesity. STATEMENT OF SIGNIFICANCE: The lack of translational in vitro white adipose tissue (AT) models is one of the main obstacles for understanding the obesity-induced reprogramming and the development of medicines. We report herein the AT microphysiological system (MPS), which recapitulates obesity and normal conditions and yields cell- and AT dECM-derived signals, thereby allowing accurate comparative in vitro analyses. Using the AT MPS, we successfully modeled reprogrammed AT in obesity conditions, including inflammation-induced AT vascular dysfunction, the recruitment of immune cells, and higher cancer cell metastasis, which are observed in obese individuals. Our proposed adipose tissue model providing physiological relevance and complexity may therefore enhance the understanding of obesity-associated disorders and be used to investigate their underlying molecular mechanisms to develop pharmacologic treatment strategies.

Modulus watch: In situ determination of the gel modulus by timing the fluorescence color change

The gel modulus, a key parameter for gel materials, is traditionally determined by cumbersome rheometer. Recently, probe technologies occur to meet the requirements of in situ determination. Till now, in situ and quantitatively testing of gel materials with unabridged structure informations still remains a challenge. Here, we provide a facile, in situ approach to determine the gel modulus, by timing the aggregation of a doped fluorescence probe. The probe shows green emission during aggregation and shifts to blue once it forms aggregates. The higher modulus of the gel, the longer probe's aggregation time. Furthermore, a quantitative correlation of gel modulus with the aggregation time is established. The in situ method not only facilitates the scientific researches in the field of gels, but also provides a new approach for spatiotemporal materials.

Synthetic strain-stiffening hydrogels towards mechanical adaptability

Living organisms are made of wet, soft tissues. However, there is only one candidate to simultaneously replicate the mechanical and composition features of load-bearing tissues, that is, strain-stiffening hydrogels. The conventional mechanical match design principle is mostly limited to stiffness matching. However, this strategy cannot sufficiently and necessarily lead to mechanical matching over the whole physiologic deformation period for tissues and damages the tissues over time. In this review, we aim to provide a comprehensive summary of the reported synthetic strain-stiffening hydrogels and particularly focus on the relationship between their structure and performance. Initially, we present a brief introduction on the significance of strain-stiffening hydrogels in mimicking the mechanics of tissues, and then we discuss the qualitative evaluation of the strain-stiffening behaviors to guide the design of materials towards mimicking soft tissue. After distinguishing the mechanical testing methods, we focus on the methods for the preparation of typical strain-stiffening hydrogels based on categories, such as network without strand entanglement, semiflexible network, and anisotropic networks. Subsequently, we discuss the structural evolution of strain-stiffening hydrogels. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring strain-stiffening hydrogels as tissue-mimics for addressing the societal needs at various frontiers.

Hairy Gels: A Computational Study

We present results of MD and MC simulations of the equilibrium properties of swelling gels with comb-like or bottlebrush subchains and compare them to scaling-theory predictions. In accordance with theory, the simulation results demonstrate that swelling coefficient of the gel increases as a function of the polymerization degree of the main chains and exhibits a very weak maximum (or is virtually constant) as a function of the polymerization degree and grafting density of side chains. The bulk osmotic modulus passes through a shallow minimum as the polymerization degree of the side chains increases. This minimum is attributed to the onset of overlap of side chains belonging to different bottlebrush strands in the swollen gel.

Theoretical advances in molecular bottlebrushes and comblike (co)polymers: solutions, gels, and self-assembly

We present an overview of state-of-the-art theory of (i) conformational properties of molecular bottlebrushes in solution, (ii) self-assembly of di- and triblock copolymers comprising comb-shaped and bottlebrush blocks in solutions and melts, and (iii) cross-linked and self-assembled gels with bottlebrush subchains. We demonstrate how theoretical models enable quantitative prediction and interpretation of experimental results and provide rational guidance for design of new materials with physical properties tunable by architecture of constituent bottlebrush blocks.

Bottlebrush Elastomers with Crystallizable Side Chains: Monitoring Configuration of Polymer Backbones in the Amorphous Regions during Crystallization

Brush-like elastomers with crystallizable side chains hold promise for biomedical applications requiring the presence of two distinct mechanical states below and above body temperature: hard and supersoft. The hard semicrystalline state facilitates piercing of the body whereupon the material softens to match the mechanics of surrounding soft tissue. To understand the transition between the two states, the crystallization process was studied with synchrotron X-ray scattering for a series of brush elastomers with poly(ε-caprolactone) side chains bearing from 7 to 13 repeat units. The so-called bottlebrush correlation peak was used to monitor configuration of bottlebrush backbones in the amorphous regions during the crystallization process. In the course of crystallization, the backbones are expelled into the interlamellar amorphous gaps, which is accompanied by their conformational changes and leads to partitioning to unconfined (melt) and confined (semicrystalline) (conformational) states. The crystallization process starts by consumption of the unconfined macromolecules by the growing crystals followed by reconfiguration of macromolecules within the already grown spherulites.

Superstrong, superstiff, and conductive alginate hydrogels

For the practical use of synthetic hydrogels as artificial biological tissues, flexible electronics, and conductive membranes, achieving requirements for specific mechanical properties is one of the most prominent issues. Here, we demonstrate superstrong, superstiff, and conductive alginate hydrogels with densely interconnecting networks implemented via simple reconstructing processes, consisting of anisotropic densification of pre-gel and a subsequent ionic crosslinking with rehydration. The reconstructed hydrogel exhibits broad ranges of exceptional tensile strengths (8–57 MPa) and elastic moduli (94–1,290 MPa) depending on crosslinking ions. This hydrogel can hold sufficient cations (e.g., Li⁺) within its gel matrix without compromising the mechanical performance and exhibits high ionic conductivity enough to be utilized as a gel electrolyte membrane. Further, this strategy can be applied to prepare mechanically outstanding, ionic-/electrical-conductive hydrogels by incorporating conducting polymer within the hydrogel matrix. Such hydrogels are easily laminated with strong interfacial adhesion by superficial de- and re-crosslinking processes, and the resulting layered hydrogel can act as a stable gel electrolyte membrane for an aqueous supercapacitor.

Specific mechanical properties are one of the most important issues for application of synthetic hydrogels as biological tissue, flexible electronics or in conductive membranes. Here, the authors demonstrate that a reconstruction process consisting of anisotropic densification of pre-gel and subsequent ionic crosslinking and rehydration leads to strong, stiff, and conductive alginate hydrogels with densely interconnecting networks.

Polymer Encapsulation Strategy toward 3D Printable, Sustainable, and Reliable Form-Stable Phase Change Materials for Advanced Thermal Energy Storage

Form-stable phase change materials (PCMs) have garnered tremendous attention in thermal energy storage (TES) owing to their remarkable latent heat. However, the integration of intelligent manufacturing, recycling, and optimized multifunction is considered not feasible for form-stable PCMs due to the restriction of encapsulation technology. Here, an excellent polymer encapsulation strategy is proposed to prepare 3D printable, sustainable, and reliable form-stable PCMs (Si_PCM-x), which are universal for petroleum-based and biobased long alkyl compounds. Si_PCM-x have top-class latent heat, and the phase-change temperatures are tunable from body temperature to high temperature. The in situ formative bottlebrush phase-change polysiloxane networks are used as supporting materials, and the encapsulation mechanism is clarified. Si_rbw-250 can be degraded and re-encapsulated to achieve recycling. Besides, Si_rbw-250 is fabricated as the customer-designed objects with shape-changing behavior via 3D printing. By introducing the metal foams and nano-coatings, the resulting phase-change composites simultaneously exhibit excellent superhydrophobicity, mechanical properties, thermal conductivity, electromagnetic interference shielding behavior, and solar-, electric-, and magnetic-to-thermal energy conversion ability. Besides, S-Ni-Si_PCM-250 can be applied in the wearable functional devices and movable solar-thermal charging. This strategy will lead to huge renovation in the TES field and provide an efficient guideline for designing advanced form-stable PCMs.

High-Performance Smart Hydrogels with Redox-Responsive Properties Inspired by Scallop Byssus

Smart hydrogels with versatile properties, including a tunable gelation time, nonswelling attributes, and biocompatibility, are in great need in the biomedical field. To meet this urgent demand, we explored novel biomaterials with the desired properties from sessile marine organisms. To this end, a novel protein, Sbp9, derived from scallop byssus was extensively investigated, which features typical epidermal growth factor-like (EGFL) multiple repetitive motifs. Our current work demonstrated that the key fragment of Sbp9 (calcium-binding domain (CBD) and 4 EGFL repeats (CE4)) was able to form a smart hydrogel driven by noncovalent interactions and facilitated by disulfide bonds. More importantly, this smart hydrogel demonstrates several desirable and beneficial features, which could offset the drawbacks of typical protein-based hydrogels, including (1) a redox-responsive gelation time (from <1 to 60 min); (2) tunable mechanical properties, nonswelling abilities, and an appropriate microstructure; and (3) good biocompatibility and degradability. Furthermore, proof-of-concept demonstrations showed that the newly discovered hydrogel could be used for anticancer drug delivery and cell encapsulation. Taken together, a smart hydrogel inspired by marine sessile organisms with desirable properties was generated and characterized and demonstrated to have extensive applicability potential in biomedical applications, including tissue engineering and drug release.

An Innovative Solvent-Responsive Coiling-Expanding Stent

Coronary artery disease is the "first killer" in the world, while the classical treatment for this disease is to implant stent. An ideal vascular stent should be nontoxic with self-expanding characteristics, quick expanding speed, and appropriate mechanical supporting property. However, no existing vascular stent covers all properties. Herein, a two-way shape-memory cellulose vascular stent, which can realize shape adjustments by mild solutions such as water and alcohol, is constructed. The shape-memory characteristics, mechanical properties, cell toxicity, and biocompatibility, are systemically investigated by ex vivo experiment as well as molecule simulation and theoretical modeling, revealing that the achieved bilayer two-way shape-memory films (BSMFs) can be used as an artificial vascular stent. In particular, this vascular stent made from BSMFs shows superb biocompatibility according to live/dead cell viability assays. Ex vivo experiments reveal that the novel vascular stent can support arteria coronaria sinistra, or the left main coronary artery, at the opening state while the cross-section of the vessel becomes two times larger than that of the initial state after implantation. Thus, it is believed that effective and scalable BSMFs can make meritorious fundamental contributions to biomaterials science and practical applications such as vascular stents.