The current contribution serves as a critical update to a previous feature article from us (Macromol. Rapid Commun. 2012, 33, 958−971), and highlights the latest advances in the preparation of single ...chain polymeric nanoparticles and initial—yet promising—attempts towards mimicking the structure of natural biomacromolecules via single‐chain folding of well‐defined linear polymers via so‐called single chain selective point folding and repeat unit folding. The contribution covers selected examples from the literature published up to ca. September 2015. Our aim is not to provide an exhaustive review but rather highlight a selection of new and exciting examples for single‐chain folding based on advanced macromolecular precision chemistry. Initially, the discussion focuses on the synthesis and characterization of single‐chain folded structures via selective point folding. The second part of the feature article addresses the folding of well‐defined single‐chain polymers by means of repeat unit folding. The current state of the art in the field of single‐chain folding indicates that repeat unit folding‐driven nanoparticle preparation is well‐advanced, while initial encouraging steps towards building selective point folding systems have been taken. In addition, a summary of the—in our view—open key questions is provided that may guide future biomimetic design efforts.
The synthesis and characterization of single‐chain nanoparticles based on well‐defined functional linear synthetic macromolecules via selective point folding as well as repeat unit folding are critically discussed via selected recent examples.
Herein, various 3D additive manufacturing approaches are reviewed in terms of two important figures of merit: maximum voxel printing rate and minimum voxel size. Voxel sizes from several 100 µm down ...to the 100 nm scale are covered. Original results on multifocus two‐photon printing at around voxel printing rates of 107 voxels s−1 are presented in this context, which significantly surpass previous best values. These advances are illustrated by and applied to the making of microstructured 3D (chiral) mechanical metamaterials that are composed of more than one‐hundred‐thousand unit cells in three dimensions. Previous best values for unit cells of similar complexity are smaller by two orders of magnitude.
A 3D manufacturing machine tool is presented that allows for printing rates of nearly ten million voxels per second and sub‐micrometer voxel sizes. This result is set into a broad context. As an example, it is applied to the manufacturing of 3D mechanical metamaterials with more than one‐hundred‐thousand complex unit cells and about three‐hundred‐billion voxels.
Emerging applications of a new class of materials, sequence‐defined macromolecules, are explored. Such molecularly highly defined macromolecules require stringent synthesis and purification ...procedures, yet offer unprecedented application possibilities. The first examples of molecular data storage and related technologies are already starting to emerge today. From a more fundamental point of view, such macromolecules offer a unique opportunity to determine quantitative structure–property relationships (QSPR), which critically aids in designing materials with applications ranging from catalysis to artificial enzymes.
Emerging applications of a new class of materials, sequence‐defined macromolecules, are explored. The first examples of molecular data storage and related technologies are starting to emerge. From a more fundamental point of view, such macromolecules offer a unique opportunity to determine quantitative structure–property relationships (QSPR), which will critically aid in designing materials with applications ranging from catalysis to artificial enzymes.
Well‐defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative ...grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and—importantly—examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single‐chain methodologies.
The performance of functional polymer interfaces is not only determined by the type of tethered macromolecule, but critically rests on the density of the grafted chains. The key characteristics of the current methods for grafting‐density determination are quantitatively assed, while, concomitantly, a perspective is provided for the development of advanced and direct methods to assess this critical parameter.
Polymeric networks have been intensely investigated and a large number of applications have been found in areas ranging from biomedicine to materials science. Network fabrication via light‐induced ...reactions is a particularly powerful tool, since light provides ready access to temporal and spatial control, opening an array of synthetic access routes for structuring the network geometry as well as functionality. Herein, the most recent light‐induced modular reactions and their use in the formation of precision polymeric networks are collated. The synthetic strategies including photoinduced thiol‐based reactions, Diels–Alder systems, and photogenerated reactive dipoles, as well as photodimerizations, are discussed in detail. Importantly, applications of the fabricated networks via the aforementioned reactions are highlighted with selected examples. Concomitantly, we provide future directions for the field, emphasizing the most critically required advances.
Photoinduced polymeric network formation is one of the most employed processes for network fabrication, since light provides ready access to temporal and spatial control. Recent light‐induced modular reactions, such as photoinduced thiol‐based reactions, Diels–Alder systems, 1,3‐dipolar additions, or photodimerizations are successfully employed for the formation of precision polymeric networks with applications in a wide array of fields, entailing enticing prospects for future developments.
The present feature article highlights the preparation of polymeric nanoparticles and initial attempts towards mimicking the structure of natural biomacromolecules by single chain folding of ...well‐defined linear polymers through covalent and non‐covalent interactions. Initially, the discussion focuses on the synthesis and characterization of single chain self‐folded structures by non‐covalent interactions. The second part of the article summarizes the folding of single chain polymers by means of covalent interactions into nanoparticle systems. The current state of the art in the field of single chain folding indicates that covalent‐bond‐driven nanoparticle preparation is well advanced, while the first encouraging steps towards building reversible single chain folding systems by the use of mutually orthogonal hydrogen‐bonding motifs have been made.
The synthesis and characterization of polymeric nanoparticles and initial attempts towards mimicking the structure of natural biomacromolecules by single chain folding of well‐defined functional linear synthetic macromolecules are critically reviewed.
4D Printing at the Microscale Spiegel, Christoph A.; Hippler, Marc; Münchinger, Alexander ...
Advanced functional materials,
06/2020, Volume:
30, Issue:
26
Journal Article
Peer reviewed
Open access
3D printing of adaptive and dynamic structures, also known as 4D printing, is one of the key challenges in contemporary materials science. The additional dimension refers to the ability of 3D printed ...structures to change their properties—for example, shape—over time in a controlled fashion as the result of external stimulation. Within the last years, significant efforts have been undertaken in the development of new responsive materials for printing at the macroscale. However, 4D printing at the microscale is still in its early stages. Thus, this progress report will focus on emerging materials for 4D printing at the microscale as well as their challenges and potential applications. Hydrogels and liquid crystalline and composite materials have been identified as the main classes of materials representing the state of the art of the growing field. For each type of material, the challenges and critical barriers in the material design and their performance in 4D microprinting are discussed. Importantly, further necessary strategies are proposed to overcome the limitations of the current approaches and move toward their application in fields such as biomedicine, microrobotics, or optics.
Toward dynamic microstructures: This progress report focuses on emerging materials for 4D printing at the microscale, with special emphasis on hydrogels and liquid crystalline and composite materials, as well as their challenges and potential applications.
Dynamic and adaptive materials are powerful constructs in macromolecular and polymer chemistry with a wide array of applications in drug delivery, bioactive systems, and self‐healing materials. Very ...often, dynamic materials are based on carefully tailored cyclodextrin host–guest interactions. The precise incorporation of these host and guest moieties into macromolecular building blocks allows the formation of complex macromolecular structures with predefined functions. Thus, dynamic materials with extraordinary adaptive property profiles—responsive to thermal, chemical, and photonic fields—become accessible. This Review explores the hierarchical formation of dynamic materials and complex macromolecular structures from the molecular via the macromolecular to the colloidal and macroscopic level, with a specific emphasis on the functionality and responsiveness of the assemblies, specifically in biological contexts.
A host of opportunities: Dynamic and adaptive materials play an important role in the chemistry of contemporary soft materials with applications in stimuli‐responsive, bioactive, delivery, and self‐healing systems. This Review highlights dynamic materials based on cyclodextrin host–guest chemistry and macromolecular building blocks.
Stimuli-responsive microstructures are critical to create adaptable systems in soft robotics and biosciences. For such applications, the materials must be compatible with aqueous environments and ...enable the manufacturing of three-dimensional structures. Poly(N-isopropylacrylamide) (pNIPAM) is a well-established polymer, exhibiting a substantial response to changes in temperature close to its lower critical solution temperature. To create complex actuation patterns, materials that react differently with respect to a stimulus are required. Here, we introduce functional three-dimensional hetero-microstructures based on pNIPAM. By variation of the local exposure dose in three-dimensional laser lithography, we demonstrate that the material parameters can be altered on demand in a single resist formulation. We explore this concept for sophisticated three-dimensional architectures with large-amplitude and complex responses. The experimental results are consistent with numerical calculations, able to predict the actuation response. Furthermore, a spatially controlled response is achieved by inducing a local temperature increase by two-photon absorption of focused light.
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