2.3. Amorphous Minerals 4354 3. Biological Routes to Controlling Morphology 4354 3.1. General Mechanisms 4356 3.1.1. Soluble and Insoluble Organic Molecules 4356 3.1.2. Control over Crystal Polymorph 4357 3.1.3. Control over Crystal Orientation 4359 3.2. Single-Crystal Biominerals 4359 3.2.1. Organic and Inorganic Soluble Additives 4360 3.2.2. Templating of Single-Crystal Morphologies 4361 3.3. Polycrystalline Biominerals 4366 3.3.1. Nacre Formation in Mollusks 4366 3.3.2. ForaminiferasA Biogenic Mesocrystal 4368 3.4. Amorphous Biominerals 4370 3.4.1. Silicification in Diatoms 4370 3.4.2. In Vitro Studies of Silicification in Diatoms 4371 4. Bioinspired Routes to Controlling Crystal Morphologies 4371

Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems

The attachment strategy based on catecholic chemistry has been arousing renewed interest since the work on polymerized catecholic amine (polydopamine) (Messersmith et al., Science, 2007, 318, 426) was published. Catechols and their derived compounds can self-assemble on various inorganic and organic materials, including noble metals, metals, metal oxides, mica, silica, ceramics and even polymers. It opens a new route to the modification of various substrates and the preparation of functional composite materials by simple chemistry. However, there is still not a full review so far about the attachment chemistry despite the dramatically increasing number of publications. This critical review describes the state-of-the-art research in the area: the design and synthesis of catecholic molecules, their adsorption mechanisms and the stability of assemblies in solution, and their applications etc. Some perspectives on future development are raised (195 references).

Bioinspired catecholic chemistry for surface modification.

Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

/pdf/catechol-based-biomimetic-functional-materials-1n5y9a1ut5.pdf

Catechol-Based Biomimetic Functional Materials

Nanoporous anodic aluminium oxide: Advances in surface engineering and emerging applications

Biological membranes play an essential role in living organisms by providing stable and functional compartments, preserving cell architecture, whilst supporting signalling and selective transport that are mediated by a variety of proteins embedded in the membrane. However, mimicking cell membranes – to be applied in artificial systems – is very challenging because of the vast complexity of biological structures. In this respect a highly promising strategy to designing multifunctional hybrid materials/systems is to combine biological molecules with polymer membranes or to design membranes with intrinsic stimuli-responsive properties. Here we present supramolecular polymer assemblies resulting from self-assembly of mostly amphiphilic copolymers either as 3D compartments (polymersomes, PICsomes, peptosomes), or as planar membranes (free-standing films, solid-supported membranes, membrane-mimetic brushes). In a bioinspired strategy, such synthetic assemblies decorated with biomolecules by insertion/encapsulation/attachment, serve for development of multifunctional systems. In addition, when the assemblies are stimuli-responsive, their architecture and properties change in the presence of stimuli, and release a cargo or allow “on demand” a specific in situ reaction. Relevant examples are included for an overview of bioinspired polymer compartments with nanometre sizes and membranes as candidates in applications ranging from drug delivery systems, up to artificial organelles, or active surfaces. Both the advantages of using polymer supramolecular assemblies and their present limitations are included to serve as a basis for future improvements.

/pdf/bioinspired-polymer-vesicles-and-membranes-for-biological-3d546sxrk4.pdf

Bioinspired polymer vesicles and membranes for biological and medical applications

Mechanical phenotyping of cells by atomic force microscopy (AFM) was proposed as a novel tool in cancer cell research as cancer cells undergo massive structural changes, comprising remodelling of the cytoskeleton and changes of their adhesive properties. In this work, we focused on the mechanical properties of human breast cell lines with different metastatic potential by AFM-based microrheology experiments. Using this technique, we are not only able to quantify the mechanical properties of living cells in the context of malignancy, but we also obtain a descriptor, namely the loss tangent, which provides model-independent information about the metastatic potential of the cell line. Including also other cell lines from different organs shows that the loss tangent ( G″ / G′ ) increases generally with the metastatic potential from MCF-10A representing benign cells to highly malignant MDA-MB-231 cells.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsob.140046

Atomic force microscopy-based microrheology reveals significant differences in the viscoelastic response between malign and benign cell lines

The mechanical behavior of lipid bilayers spanning the pores of highly ordered porous silicon substrates was scrutinized by local indentation experiments as a function of surface functionalization, lipid composition, solvent content, indentation velocity, and pore radius. Solvent-containing nano black lipid membranes (nano-BLMs) as well as solvent-free pore-spanning bilayers were imaged by fluorescence and atomic force microscopy prior to force curve acquisition, which allows distinguishing between membrane-covered and uncovered pores. Force indentation curves on pore-spanning bilayers attached to functionalized hydrophobic porous silicon substrates reveal a predominately linear response that is mainly attributed to prestress in the membranes. This is in agreement with the observation that indentation leads to membrane lysis well below 5% area dilatation. However, membrane bending and lateral tension dominate over prestress and stretching if solvent-free supported membranes obtained from spreading giant liposomes on hydrophilic porous silicon are indented. An elastic regime diagram is presented that readily allows determining the dominant contribution to the mechanical response upon indentation as a function of load and pore radius.

Local Membrane Mechanics of Pore-Spanning Bilayers

The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles1,2. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins3. Here, we report a molecular design based on oligo calix[4]arene catenanes—calixarene dimers held together by 16 hydrogen bridges—in which loops within the molecules limit how far the calixarene nanocapsules can be separated. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual nanocapsules. Experimental evidence, supported by molecular dynamics simulations, reveals the presence of an intermediate state involving the concerted rupture of the 16 hydrogen bridges. Stochastic modelling using a three-well potential under external load allows reconstruction of the energy landscape. Stretching experiments on single molecules offer a unique way to study the fundamental theories of statistical mechanics. Researchers have now shown that entangled calix[4]arene dimers can be used in such experiments as a tuneable model system for investigating the strength of hydrogen bonds on a single-molecule level.

Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force

Porous substrates have gained widespread interest for biosensor applications based on molecular recognition. Thus, there is a great demand to systematically investigate the parameters that limit the transport of molecules toward and within the porous matrix as a function of pore geometry. Finite element simulations (FES) and time-resolved optical waveguide spectroscopy (OWS) experiments were used to systematically study the transport of molecules and their binding on the inner surface of a porous material. OWS allowed us to measure the kinetics of protein adsorption within porous anodic aluminum oxide membranes composed of parallel-aligned, cylindrical pores with pore radii of 10–40 nm and pore depths of 0.8–9.6 μm. FES showed that protein adsorption on the inner surface of a porous matrix is almost exclusively governed by the flux into the pores. The pore-interior surface nearly acts as a perfect sink for the macromolecules. Neither diffusion within the pores nor adsorption on the surface are rate limiti...

https://www.goedoc.uni-goettingen.de/goescholar/bitstream/handle/1/9415/Benefits%20and%20Limitations%20of%20Porous%20Substrates%20as%20Biosensors%20for%20Protein%20Adsorption.pdf?sequence=1

Ingo Mey

Papers

Atomic force microscopy-based microrheology reveals significant differences in the viscoelastic response between malign and benign cell lines

Local Membrane Mechanics of Pore-Spanning Bilayers

Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force

Benefits and limitations of porous substrates as biosensors for protein adsorption.

Phase selection of calcium carbonate through the chirality of adsorbed amino acids.