Designing from biobased to closed-loop circularity: Flexible dynamic polyimine-amide networks

In this theoretical review, we begin by discussing brains and minds from a dynamical systems perspective, and then go on to describe methods for characterizing the flexibility of dynamic networks. We discuss how varying degrees and kinds of flexibility may be adaptive (or maladaptive) in different contexts, specifically focusing on measures related to either more disjoint or cohesive dynamics. While disjointed flexibility may be useful for assessing neural entropy, cohesive flexibility may potentially serve as a proxy for self-organized criticality as a fundamental property enabling adaptive behavior in complex systems. Particular attention is given to recent studies in which flexibility methods have been used to investigate neurological and cognitive maturation, as well as the breakdown of conscious processing under varying levels of anesthesia. We further discuss how these findings and methods might be contextualized within the Free Energy Principle with respect to the fundamentals of brain organization and biological functioning more generally, and describe potential methodological advances from this paradigm. Finally, with relevance to computational psychiatry, we propose a research program for obtaining a better understanding of ways that dynamic networks may relate to different forms of psychological flexibility, which may be the single most important factor for ensuring human flourishing.

The ratio of the isochoric and isobaric activation enthalpies at T(g) is used to quantify the relative contributions of the specific volume and temperature to the local segmental dynamics of polyvinylethylene networks. The dynamics of the networks become more dominated by temperature with increasing cross-link density, consistent with an increasing isobaric fragility. We also find a correlation between the isochoric and isobaric fragilities for the polyvinylethylene networks, in accord with a previously reported relationship between these two quantities for polymers and molecular glass-forming liquids [R. Casalini and C. M. Roland, Phys. Rev. E 72, 031503 (2005)].

Poly(acrylic acid-co-N,N'-methylenebisacrylamide) hydrogel films were synthesized by copolymerizing acrylic acid (AAc) with N,N'-methylenebisacrylamide (MBA) as a cross-linker via photo polymerization in the spacing confined between two glass plates. NMR spectroscopy was utilized to determine the cross-linking density. We found that the cross-linking density determined by NMR is higher than that expected from the feed concentrations of cross-linkers, suggesting that MBA is more reactive than AAc and the heterogeneous nature of the cross-linking. In addition to the swelling tests, indentation tests were performed on the hydrogel films under water to investigate effects of the cross-linking density on the adhesion and mechanical properties of the hydrogel films in terms of adhesive pull-off force and Hertz-type elastic modulus. As the cross-linker concentration increased, the effective elastic modulus of the hydrogel films increased dramatically at low cross-linking densities and reached a high steady-state value at higher cross-linking densities. The pull-off force decreased with increasing cross-linker concentration and reached a lower force plateau at high cross-linking densities. An optimal "trade-off" cross-linking density was determined to be 0.02 mol fraction of MBA in the hydrogel, where balanced elastic modulus and adhesive pull-off force can be obtained.

Shape memory polymers (SMPs) have the capacity of memorizing a temporary shape and recovering their initial shape in response to various external stimuli. As one of promising class of intelligent materials, it has attracted great attention because of its potential applications in many areas, such as biomaterials and biotechnology, automotive industry, and aerospace field. Aliphatic polymers play an important role in the molecular design of SMPs owing to its excellent biodegradability and biocompatibility, and suitable thermal transition temperature range. This review focuses on the recent progress of shape memory polymers based on the aliphatic polyesters such as poly(lactic acid) (PLA), poly ( p -dioxanone) (PPDO), poly(butylene succinate) (PBS), poly( ω -pentadecalactone) (PPDL) and poly( ɛ -caprolactone) (PCL) and so on. From the view of architecture design, different systems are classified by block copolymers, crosslinking networks and interpenetrating networks. The influence of architectural features on the shape memory behaviors is also discussed. The block copolymers have been identified a typical mature system in design of dual-shape material, and the crystalline aliphatic polyesters can be served as the netpiont or the molecular switch in a SMP, depending on its transition temperature range among the binary systems. The thermoplastic feature of block copolymers endows an easy processibility. The various architectures of crosslinking network meet the increasing demand of SMPs design. Constructing network with crystallizable polyester segment such as PCL may achieve SMPs in one-way and two-way mode, and the stress-free two-way mode can also be realized by an elaborate architecture with pre-programed treatment. Embedding two segments in one network may achieve a triple-shape memory effect, meanwhile, incorporating two segments in an interpenetrating polymer network may result in a triple-shape material with improved performance. Recently, the SMPs based on dynamic networks become the new trend, which may combine the self-healing with shape memory effect in one system, and both dynamic covalent bond and non-covalent bond have been concerned. In order to fulfill the increasing requirement of application, the SMPs with multi-shape memory effect, multi-responsibility and multi-functionality are highly expected.

The expulsion of hydrocarbons from kerogen is the initial step in the primary migration process, during which the composition of the expelled petroleum is enriched in saturated and aromatic hydrocarbons while the retained bitumen is enriched in polar compounds. The physical and chemical principles responsible for this chemical fractionation are not well understood, and numerous theories have been proposed to explain the expulsion process. A multicomponent equilibrium likely exists between the kerogen matrix and the expelled fluid during petroleum generation and expulsion. To test whether such equilibrium can explain the nature and extent of chemical fractionation, an extended Flory−Rehner Regular Solution Theory model was developed and applied to a series of kerogens of varying structure, generative potential, and maturity. Thermodynamic parameters for immature Type II and IIIC kerogens (solubility parameter, cross-link density, and native swelling) were derived experimentally and extended to higher maturity. Mixtures of model compounds with well-defined properties were created to reflect the composition of primary generated products of kerogen thermal decomposition. Multicomponent equilibrium then was calculated under closed system conditions. The amount and composition of modeled expelled products are most sensitive to the generative potential and cross-link density of the kerogen. In general, lower source richness and cross-link density is associated with bitumen retention and a relative enrichment of the aliphatic components in the expelled fluid. Higher source richness and cross-link density result in earlier expulsion of fluids that are enriched in polar components. The predicted compositions of expelled fluids correspond well with the compositional range observed for produced petroleum. The predicted bitumen (kerogen-retained, soluble organic matter) compositions are uniformly >50% C14+ NSOs at all levels of maturity for all modeled kerogens. A chemically driven equilibrium mechanism based on Regular Solution Theory can explain almost completely the nature and extent of chemical fractionation that takes place during expulsion.

While the incorporation of dynamic covalent bonds (DCBs) in thermosets is widely employed, the materials inevitably downgrade substantially during repetitive physical recycling. Meanwhile, chemical recycling of polymers back to starting monomers often requires significant energy/resource input during the (de/re)polymerization process. To address such a dilemma, we propose a dual-recycling strategy that integrates the advantages of DCBs and chemical recycling by cross-linking chemically recyclable polyesters with DCB-containing cross-linkers. A series of poly(valerolactone) (PVL)-based covalent adaptable networks (CANs) were constructed featuring a functionalized PVL backbone and dynamic boronic-ester-containing cross-linkers to enable simultaneous physical and chemical recyclability. Through fine-tuning the balance between crystallinity and cross-linking density, the CANs exhibited outstanding mechanical properties, including a tensile strength up to 17.7 MPa and an elongation at a break of 1164%. Owing to the dynamic exchange characteristic of boronic esters, the CANs retained nearly identical performance to the original samples after five cycles of physical recycling. Furthermore, the CANs could undergo catalytically assisted chemical recycling with Sn(Oct)2, allowing the recovery of starting monomer. This work provided a valuable approach for the development of dual-recyclable high-performance polymer networks as a potential solution to the current challenges in thermosets recycling.

Schizophrenia is increasingly recognized as a disorder of distributed neural dynamics, but the molecular and genetic contributions are poorly understood. Recent work highlights a role for altered N-methyl-d-aspartate (NMDA) receptor signaling and related impairments in the excitation-inhibitory balance and synchrony of large-scale neural networks. Here, we combined a pharmacological intervention with novel techniques from dynamic network neuroscience applied to functional magnetic resonance imaging (fMRI) to identify alterations in the dynamic reconfiguration of brain networks related to schizophrenia genetic risk and NMDA receptor hypofunction. We quantified "network flexibility," a measure of the dynamic reconfiguration of the community structure of time-variant brain networks during working memory performance. Comparing 28 patients with schizophrenia, 37 unaffected first-degree relatives, and 139 healthy controls, we detected significant differences in network flexibility [F(2,196) = 6.541, P = 0.002] in a pattern consistent with the assumed genetic risk load of the groups (highest for patients, intermediate for relatives, and lowest for controls). In an observer-blinded, placebo-controlled, randomized, cross-over pharmacological challenge study in 37 healthy controls, we further detected a significant increase in network flexibility as a result of NMDA receptor antagonism with 120 mg dextromethorphan [F(1,34) = 5.291, P = 0.028]. Our results identify a potential dynamic network intermediate phenotype related to the genetic liability for schizophrenia that manifests as altered reconfiguration of brain networks during working memory. The phenotype appears to be influenced by NMDA receptor antagonism, consistent with a critical role for glutamate in the temporal coordination of neural networks and the pathophysiology of schizophrenia.

Critical transition of epoxy resin from brittleness to toughness by incorporating CO2-sourced cyclic carbonate

Spherical particles confined to liquid interfaces generally self-assemble into hexagonal patterns. It was theoretically predicted by Jagla two decades ago that such particles interacting via a soft repulsive potential are able to form complex, anisotropic assembly phases. Depending on the shape and range of the potential, the predicted minimum energy configurations include chains, rhomboid and square phases. We recently demonstrated that deformable core-shell particles consisting of a hard silica core and a soft poly(N-isopropylacrylamide) shell adsorbed at an air/water interface can form chain phases if the crosslinker is primarily incorporated around the silica core. Here, we systematically investigate the interfacial self-assembly behavior of such SiO2-PNIPAM core-shell particles as a function of crosslinker content and core size. We observe chain networks predominantly at low crosslinking densities and smaller core sizes, whereas higher crosslinking densities lead to the formation of rhomboid packing. We correlate these results with the interfacial morphologies of the different particle systems, where the ability to expand at the interface and form a thin corona at the periphery depends on the degree of crosslinking close to the core. We perform minimum energy calculations based on Jagla-type pair potentials with different shapes of the soft repulsive shoulder. We compare the theoretical phase diagram with experimental findings to infer to which extent the interfacial interactions of the experimental system may be captured by Jagla pair-wise interaction potentials.

Controlled uptake and release of lysozyme from glycerol diglycidyl ether cross-linked oxidized starch microgel.

The mechanical properties of biomaterials have profound consequences on cellular and host responses, however, the underlying mechanisms remain poorly understood. Presented are findings that confirm a clear relationship between the elastic modulus, the bulk-to-bound water ratio and the adaptive attachment of attachment dependent cells. We show that biomimetic hydrogels possessing no specific integrin binding motifs but that are of lower elastic modulus and lower bulk-to-bound water ratio, preferentially support cell attachment. Anchorage-dependent human muscle fibroblasts (RMS 13) were cultured on tetraethylene glycol (TEGDA) cross-linked poly(2-hydroxyethyl methacrylate) [poly(HEMA)]-based biomimetic hydrogels containing phosphorylcholine (PC) (1 mol%) and dimethylamino amino ethyl methacrylate (DMAEMA), a 3° amine (5 mol%), as well as on silicone and agarose controls. Changes in the cross-link density (1 to 12 mol%) of the hydrogel produced a monotonic reduction in the glass transition temperature, Tg (131.8 °C at 1 mol% TEGDA to 110.4 °C at 12 mol% TEGDA), but an exponential increase in the bulk-to-bound water (4.25 at 1 mol% to 27.04 at 12 mol%) that exactly parallels the increase in elastic modulus as measured by nano-indentation AFM (152 ± 62 kPa at 1 mol% TEGDA to 1777 ± 1152 kPa at 12 mol% TEGDA). Enumeration, MTT assay and fluorescence microscopy following 4, 8 and 12 days of culture confirms that short-term cell viability and long term proliferation were favored on low cross-link density, low modulus hydrogels and that cells were preferentially attached to low cross-link density hydrogels. Bound water is central to the adaptive attachment of attachment dependent cells.

The microstructure of the poly(N-isopropylacrylamide-co-acrylamido-2-methyl-1-propane sulphonic acid) gel, poly(NIPA-co-AMPS), was investigated as a function of temperature and cross-link density using the small angle neutron scattering technique. The sample temperature was varied in the range 30 to 55C. Two different behaviours of poly(NIPA-co-AMPS) gels were observed. At low temperature (30C), the magnitude of the scattered intensity increased with cross-link density suggesting that additional cross-links introduced more inhomogeneities in the gel network. At high temperatures the trend was reversed; that is the lower cross-link density, the higher the scattered intensity. Therefore, the role of cross-links at high temperature was to suppress microphase separation. The fitting of the experimental data with the Rabin and Panyukov theory indicated qualitative agreement.

Polyurethanes (PUs) are indispensable polymeric materials widely employed across diverse industrial sectors due to their excellent thermal stability, chemical resistance, adhesion, and mechanical durability. However, the intrinsic three-dimensional crosslinked network that underpins their performance also presents a fundamental barrier to reprocessing and recycling. Consequently, most end-of-life PU waste is currently managed through landfilling or incineration, resulting in significant resource loss and environmental impact. To address these challenges, this review presents an integrated perspective on sustainable PU systems by unifying green synthesis strategies with closed-loop recovery approaches. First, recent advances in bio-based polyols and phosgene-free isocyanate synthesis derived from renewable resources—such as plant oils, carbohydrates, and lignin—are discussed as viable means to reduce dependence on petrochemical feedstocks and mitigate toxicity concerns. Next, emerging chemical recycling methodologies, including acidolysis and aminolysis, are reviewed with a focus on the selective recovery of high-purity monomers. Finally, PU vitrimers and dynamic covalent polymer networks (DCPNs) based on urethane bond exchange reactions are examined as reprocessable architectures that combine thermoplastic-like processability with the mechanical robustness of thermosets. By integrating synthesis, recovery, and reuse within a unified framework, this review aims to outline a coherent pathway toward establishing a sustainable circular economy for PU materials.

Herein, we describe the preparation of patterned photoresponsive hydrogels by using a facile method. This polymer-network hydrogel coating consists of N-isopropylacrylamide (NIPAAM), cross-linking agent tripropylene glycol diacrylate (TPGDA), and a new photochromic spiropyran monoacrylate. In a pre-study, a linear NIPAAM copolymer (without TPGDA) that contained the spiropyran dye was synthesised, which showed relatively fast photoswitching behaviour. Subsequently, the photopolymerisation of a similar monomer mixture that included TPGDA afforded freestanding hydrogel polymer networks. The light-induced isomerisation of protonated merocyanine into neutral spiropyran under slightly acidic conditions resulted in macroscopic changes in the hydrophilicity of the entire polymer film, that is, shrinkage of the hydrogel. The degree of shrinkage could be controlled by changing the chemical composition of the acrylate mixture. After these pre-studies, a hydrogel film with spatially modulated cross-link density was fabricated through polymerisation-induced diffusion, by using a patterned photomask. The resulting smooth patterned hydrogel coating swelled in slightly acidic media and the swelling was higher in the regions with lower cross-linking densities, thus yielding a corrugated surface. Upon exposure to visible light, the surface topography flattened again, thus showing that a hydrogel coating could be created, the topography of which could be controlled by light irradiation.

Renewable benzoxazine-based thermosets from cashew nut: Investigating the self-healing, shape memory, recyclability and antibacterial activity