Control of cell adhesion by mechanical reinforcement of soft polyelectrolyte films with nanoparticles

Surface Modification with Particles Coated or Made of Polymer Multilayers

The coating of particles or decomposable cores with polyelectrolytes via Layer-by-Layer (LbL) assembly creates free-standing LbL-coated functional particles. Due to the numerous functions that their polymers can bestow, the particles are preferentially selected for a plethora of applications, including, but not limited to coatings, cargo-carriers, drug delivery vehicles and fabric enhancements. The number of publications discussing the fabrication and usage of LbL-assembled particles has consistently increased over the last vicennial. However, past literature fails to either mention or expand upon how these LbL-assembled particles immobilize on to a solid surface. This review evaluates examples of LbL-assembled particles that have been immobilized on to solid surfaces. To aid in the formulation of a mechanism for immobilization, this review examines which forces and factors influence immobilization, and how the latter can be confirmed. The predominant forces in the immobilization of the particles studied here are the Coulombic, capillary, and adhesive forces; hydrogen bonding as well as van der Waal's and hydrophobic interactions are also considered. These are heavily dependent on the factors that influenced immobilization, such as the particle morphology and surface charge. The shape of the LbL particle is related to the particle core, whereas the charge was dependant on the outermost polyelectrolyte in the multilayer coating. The polyelectrolytes also determine the type of bonding that a particle can form with a solid surface. These can be via either physical (non-covalent) or chemical (covalent) bonds; the latter enforcing a stronger immobilization. This review proposes a fundamental theory for immobilization pathways and can be used to support future research in the field of surface patterning and for the general modification of solid surfaces with polymer-based nano- and micro-sized polymer structures.

Biopolymer-Based Multilayer Capsules and Beads Made via Templating: Advantages, Hurdles and Perspectives

One of the undeniable trends in modern bioengineering and nanotechnology is the use of various biomolecules, primarily of a polymeric nature, for the design and formulation of novel functional materials for controlled and targeted drug delivery, bioimaging and theranostics, tissue engineering, and other bioapplications. Biocompatibility, biodegradability, the possibility of replicating natural cellular microenvironments, and the minimal toxicity typical of biogenic polymers are features that have secured a growing interest in them as the building blocks for biomaterials of the fourth generation. Many recent studies showed the promise of the hard-templating approach for the fabrication of nano- and microparticles utilizing biopolymers. This review covers these studies, bringing together up-to-date knowledge on biopolymer-based multilayer capsules and beads, critically assessing the progress made in this field of research, and outlining the current challenges and perspectives of these architectures. According to the classification of the templates, the review sequentially considers biopolymer structures templated on non-porous particles, porous particles, and crystal drugs. Opportunities for the functionalization of biopolymer-based capsules to tailor them toward specific bioapplications is highlighted in a separate section.

Hyaluronic-Acid-Based Organic-Inorganic Composites for Biomedical Applications

Applications of natural hyaluronic acid (HYH) for the fabrication of organic-inorganic composites for biomedical applications are described. Such composites combine unique functional properties of HYH with functional properties of hydroxyapatite, various bioceramics, bioglass, biocements, metal nanoparticles, and quantum dots. Functional properties of advanced composite gels, scaffold materials, cements, particles, films, and coatings are described. Benefiting from the synergy of properties of HYH and inorganic components, advanced composites provide a platform for the development of new drug delivery materials. Many advanced properties of composites are attributed to the ability of HYH to promote biomineralization. Properties of HYH are a key factor for the development of colloidal and electrochemical methods for the fabrication of films and protective coatings for surface modification of biomedical implants and the development of advanced biosensors. Overcoming limitations of traditional materials, HYH is used as a biocompatible capping, dispersing, and structure-directing agent for the synthesis of functional inorganic materials and composites. Gel-forming properties of HYH enable a facile and straightforward approach to the fabrication of antimicrobial materials in different forms. Of particular interest are applications of HYH for the fabrication of biosensors. This review summarizes manufacturing strategies and mechanisms and outlines future trends in the development of functional biocomposites.

An in situ mechanical adjustable double crosslinking hyaluronic acid/poly-lysine hydrogel matrix: Fabrication, characterization and cell morphology

Cell fate and morphologies are influenced by the mechanical property of matrix. However, the relevant works about the dynamic adjustable of matrix mechanical property is rare and most of them need extra stimulation, such as the controllable of the degradation. In this study, double crosslinking (DC) hydrogels are fabricated by sequential covalent crosslinking and electrostatic interactions between hyaluronic acid and poly-lysine. Without any extra stimulation or treatment, the compressive stress of DC-hydrogels increases from 22.4 ± 9.4 kPa to 320.1 ± 6.6 kPa with the elongation of incubation time in DMEM solution. The change of compressive stress of matrix induced the morphology of L929 fibroblast cells adjusted from the distributed round shape to spheroid cell clusters and finally to spread shape. RNA sequence analysis also demonstrated that the differentially gene expression and GO enrichment between the cells seeded on the DC-hydrogel with different incubation time. In addition, by increasing the electrostatic interactions ratio of the hydrogel, the biodegradation, compressive stress and energy dissipation of the DC-hydrogels were also significantly improved. Therefore, our study provides new and critical insights into the design strategy to achieve DC-hydrogels which can in situ alter cells morphology and open up a new avenue for the application of disease therapy.

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.

Layer-By-Layer Assemblies of Biopolymers: Build-Up, Mechanical Stability and Molecular Dynamics

Rapid development of versatile layer-by-layer technology has resulted in important breakthroughs in the understanding of the nature of molecular interactions in multilayer assemblies made of polyelectrolytes. Nowadays, polyelectrolyte multilayers (PEM) are considered to be non-equilibrium and highly dynamic structures. High interest in biomedical applications of PEMs has attracted attention to PEMs made of biopolymers. Recent studies suggest that biopolymer dynamics determines the fate and the properties of such PEMs; however, deciphering, predicting and controlling the dynamics of polymers remains a challenge. This review brings together the up-to-date knowledge of the role of molecular dynamics in multilayers assembled from biopolymers. We discuss how molecular dynamics determines the properties of these PEMs from the nano to the macro scale, focusing on its role in PEM formation and non-enzymatic degradation. We summarize the factors allowing the control of molecular dynamics within PEMs, and therefore to tailor polymer multilayers on demand.

Polyelectrolyte Multilayer Capsule (PEMC)-Based Scaffolds for Tissue Engineering

Tissue engineering (TE) is a highly multidisciplinary field that focuses on novel regenerative treatments and seeks to tackle problems relating to tissue growth both in vitro and in vivo. These issues currently involve the replacement and regeneration of defective tissues, as well as drug testing and other related bioapplications. The key approach in TE is to employ artificial structures (scaffolds) to support tissue development; these constructs should be capable of hosting, protecting and releasing bioactives that guide cellular behaviour. A straightforward approach to integrating bioactives into the scaffolds is discussed utilising polyelectrolyte multilayer capsules (PEMCs). Herein, this review illustrates the recent progress in the use of CaCO3 vaterite-templated PEMCs for the fabrication of functional scaffolds for TE applications, including bone TE as one of the main targets of PEMCs. Approaches for PEMC integration into scaffolds is addressed, taking into account the formulation, advantages, and disadvantages of such PEMCs, together with future perspectives of such architectures.

Lithography-Based 3D Bioprinting and Bioinks for Bone Repair and Regeneration

The fabrication of scaffolds that precisely mimic the natural structure and physiochemical properties of bone is still one of the most challenging tasks in bone tissue engineering. 3D printing techniques have drawn increasing attention due to their ability to fabricate scaffolds with complex structures and multiple bioinks. For bone tissue engineering, lithography-based 3D bioprinting is frequently utilized due to its printing speed, mild printing process, and cost-effective benefits. In this review, lithography-based 3D bioprinting technologies including SLA and DLP are introduced; their typical applications in biological system and bioinks are also explored and summarized. Furthermore, we discussed possible evolution of the hardware/software systems and bioinks of lithography-based 3D bioprinting, as well as their future applications.

Hydrogel-Colloid Composite Bioinks for Targeted Tissue-Printing

The development of extrusion-based bioprinting for tissue engineering is conditioned by the design of bioinks displaying adequate printability, shape stability, and postprinting bioactivity. In this context, simple bioink formulations, made of cells supported by a polymer matrix, often lack the necessary versatility. To address this issue, intense research work has been focused on introducing colloidal particles into the ink formulation. By creating weak cross-links between polymer chains, added particles modify the rheology and mechanical behavior of bioinks to improve their printability and structural integrity. Additionally, nano- and microscopic particles display composition- and structure-specific properties that can affect the cellular behavior and enhance the formation of tissue within the printed material. This Review offers a comprehensive picture of the role of colloids in bioprinting from a physicochemical and biological perspective. As such, it provides guidance on devising adaptable bioinks for the fabrication of biomimetic tissues.

Hyaluronic Acid/Polylysine Composites for Local Drug Delivery: A Review

Site specific drug delivery systems (DDS) are usually developed to overcome the side effects of conventional ones (e.g. injections or oral ingestions), creating smart drug delivery vehicles characterized with greater efficiency, safety, predictable therapeutic response as well as controlled and prolonged drug release periods. DDS made of hyaluronic acid (HA) and poly-L-lysine (PLL) are promising candidates in the field of local drug delivery due to their high biocompatibility. Moreover, electrostatic attractions between negatively charged HA and positively charged PLL can be used to fabricate multilayer films, bilayer films and hydrogels, avoiding the application of toxic crosslinking agents. In this review, we report the preparation of HA/PLL composites exploiting their intrinsic properties, as well as developed composite application possibilities as controlled drug delivery systems in bone tissue, central nervous system and gene engineering.

Polymer- and Hybrid-Based Biomaterials for Interstitial, Connective, Vascular, Nerve, Visceral and Musculoskeletal Tissue Engineering

In this review, materials based on polymers and hybrids possessing both organic and inorganic contents for repairing or facilitating cell growth in tissue engineering are discussed. Pure polymer based biomaterials are predominantly used to target soft tissues. Stipulated by possibilities of tuning the composition and concentration of their inorganic content, hybrid materials allow to mimic properties of various types of harder tissues. That leads to the concept of "one-matches-all" referring to materials possessing the same polymeric base, but different inorganic content to enable tissue growth and repair, proliferation of cells, and the formation of the ECM (extra cellular matrix). Furthermore, adding drug delivery carriers to coatings and scaffolds designed with such materials brings additional functionality by encapsulating active molecules, antibacterial agents, and growth factors. We discuss here materials and methods of their assembly from a general perspective together with their applications in various tissue engineering sub-areas: interstitial, connective, vascular, nervous, visceral and musculoskeletal tissues. The overall aims of this review are two-fold: (a) to describe the needs and opportunities in the field of bio-medicine, which should be useful for material scientists, and (b) to present capabilities and resources available in the area of materials, which should be of interest for biologists and medical doctors.

Hierarchy of Hybrid Materials-The Place of Inorganics-in-Organics in it, Their Composition and Applications

Hybrid materials, or hybrids incorporating both organic and inorganic constituents, are emerging as a very potent and promising class of materials due to the diverse, but complementary nature of the properties inherent of these different classes of materials. The complementarity leads to a perfect synergy of properties of desired material and eventually an end-product. The diversity of resultant properties and materials used in the construction of hybrids, leads to a very broad range of application areas generated by engaging very different research communities. We provide here a general classification of hybrid materials, wherein organics-in-inorganics (inorganic materials modified by organic moieties) are distinguished from inorganics-in-organics (organic materials or matrices modified by inorganic constituents). In the former area, the surface functionalization of colloids is distinguished as a stand-alone sub-area. The latter area-functionalization of organic materials by inorganic additives-is the focus of the current review. Inorganic constituents, often in the form of small particles or structures, are made of minerals, clays, semiconductors, metals, carbons, and ceramics. They are shown to be incorporated into organic matrices, which can be distinguished as two classes: chemical and biological. Chemical organic matrices include coatings, vehicles and capsules assembled into: hydrogels, layer-by-layer assembly, polymer brushes, block co-polymers and other assemblies. Biological organic matrices encompass bio-molecules (lipids, polysaccharides, proteins and enzymes, and nucleic acids) as well as higher level organisms: cells, bacteria, and microorganisms. In addition to providing details of the above classification and analysis of the composition of hybrids, we also highlight some antagonistic yin-&-yang properties of organic and inorganic materials, review applications and provide an outlook to emerging trends.

Spreading of Cell Aggregates on Zwitterion-Modified Chitosan Films

The sulfobetaine (SB) moiety, which comprises a quaternary ammonium group linked to a negatively charged sulfonate ester, is known to impart nonfouling properties to interfaces coated with polysulfobetaines or grafted with SB-polymeric brushes. Increasingly, evidence emerges that the SB group is, overall, a better antifouling group than the phosphorylcholine (PC) moiety extensively used in the past. We report here the synthesis of a series of SB-modified chitosans (CH-SB) carrying between 20 and 40 mol % SB per monosaccharide unit. Chitosan (CH) itself is a naturally derived copolymer of glucosamine and N-acetyl-glucosamine linked with a β-1,4 bond. Analysis by quartz crystal microbalance with dissipation (QCM-D) indicates that CH-SB films (thickness ∼ 20 nm) resist adsorption of bovine serum albumin (BSA) with increasing efficiency as the SB content of the polymer augments (surface coverage ∼ 15 μg cm^-2 for films of CH with 40 mol % SB). The cell adhesivity of CH-SB films coated on glass was assessed by determining the spreading dynamics of CT26 cell aggregates. When placed on chitosan films, known to be cell-adhesive, the CT26 cell aggregates spread by forming a cell monolayer around them. The spreading of CT26 cell aggregates on zwitterion-modified chitosans films is thwarted remarkably. In the cases of CH-SB30 and CH-SB40 films, only a few isolated cells escape from the aggregates. The extent of aggregate spreading, quantified based on the theory of liquid wetting, provides a simple in vitro assay of the nonfouling properties of substrates toward specific cell lines. This assay can be adopted to test and compare the fouling characteristics of substrates very different from the chemical viewpoint.

Fabrication of sulphonated poly(ethylene glycol)-diacrylate hydrogel as a bone grafting scaffold

To improve the biological performance of poly(ethylene glycol)-diacrylate (PEGDA) hydrogel as an injectable bone grafting scaffold, sodium methallyl sulphonate (SMAS) was incorporated into PEGDA hydrogel. The physiochemical properties of the resultant polymers were assessed via Fourier transform infrared spectroscopy (FTIR), swelling ratio, zeta potential, surface morphology, and protein adsorption analysis. MC3T3-E1 cells were seeded on the hydrogel to evaluate the effect of the sulphonated modification on their attachment, proliferation, and differentiation. The results of FTIR and zeta potential evaluations revealed that SMAS was successfully incorporated into PEGDA. With increasing concentrations of SMAS, the swelling ratio of the hydrogels increased in deionized water but stayed constant in phosphate buffered saline. The protein adsorption also increased with increasing concentration of SMAS. Moreover, the sulphonated modification of PEGDA hydrogel not only enhanced the attachment and proliferation of osteoblast-like MC3T3-E1 cells but also up-regulated alkaline phosphatase activity as well as gene expression of osteogenic markers and related growth factors, including collagen type I, osteocalcin, runt related transcription factor 2, bone morphogenetic protein 2, and transforming growth factor beta 1. These findings indicate that the sulphonated modification could significantly improve the biological performance of PEGDA hydrogel. Thus, the sulphonated PEGDA is a promising scaffold candidate for bone grafting.

Colloidal Lignin Particles as Adhesives for Soft Materials

Lignin has interesting functionalities to be exploited in adhesives for medicine, foods and textiles. Nanoparticles (NPs) < 100 nm coated with poly (_L-lysine), PL and poly(_L-glutamic acid) PGA were prepared from the laccase treated lignin to coat nanocellulose fibrils (CNF) with heat. NPs ca. 300 nm were prepared, β-casein coated and cross-linked with transglutaminase (Tgase) to agglutinate chamois. Size exclusion chromatography (SEC) and Fourier-transform infrared (FTIR) spectroscopy were used to characterize polymerized lignin, while zeta potential and dynamic light scattering (DLS) to ensure coating of colloidal lignin particles (CLPs). Protein adsorption on lignin was studied by quartz crystal microbalance (QCM). Atomic force microscopy (AFM) was exploited to examine interactions between different polymers and to image NPs with transmission electron microscopy (TEM). Tensile testing showed, when using CLPs for the adhesion, the stress improved ca. 10 and strain ca. 6 times compared to unmodified Kraft. For the β-casein NPs, the values were 20 and 8, respectively, and for the β-casein coated CLPs between these two cases. When NPs were dispersed in adhesive formulation, the increased Young’s moduli confirmed significant improvement in the stiffness of the joints over the adhesive alone. Exploitation of lignin in nanoparticulate morphology is a potential method to prepare bionanomaterials for advanced applications.

Atomic force microscopy for imaging and nanomechanical characterisation of live nematode epicuticle: A comparative Caenorhabditis elegans and Turbatrix aceti study

Atomic force microscopy (AFM), a powerful tool in interdisciplinary biomedical research, has been applied here to investigate the surface of live nematodes epicuticle. We have used AFM in PeakForce Tapping non-resonant imaging and nanomechanical characterisation mode to investigate and compare the surface features of epicuticle of two free-living microscopic nematodes, Caenorhabditis elegans and Turbatrix aceti. We have successfully immobilised live anesthetized adult nematodes on glass supports using either layer-by-layer-deposited polyelectrolyte films or bioadhesive coatings, which allowed for imaging the living nematodes in native environment. We have obtained AFM images and corresponding nanomechanical maps of annular rings and furrows, demonstrating the differences in topography and structure between the species. Our results demonstrate that AFM in PeakForce Tapping mode can be used to image and characterise surfaces of relatively-large live immobilised multicellular organisms, which can be further applied to a number of invertebrates.

Polyelectrolyte multilayers for bio-applications: recent advancements

The synergistic relationship between structure and the bulk properties of polyelectrolyte multilayer (PEM) films has generated tremendous interest in their application for loading and release of bioactive species. Layer-by-layer assembly is the simplest, cost effective process for fabrication of such PEMs films, leading to one of the most widely accepted platforms for incorporating biological molecules with nanometre precision. The bulk reservoir properties of PEM films render them a potential candidate for applications such as biosensing, drug delivery and tissue engineering. Various biomolecules such as proteins, DNA, RNA or other desired molecules can be incorporated into the PEM stack via electrostatic interactions and various other secondary interactions such as hydrophobic interactions. The location and availability of the biological molecules within the PEM stack mediates its applicability in various fields of biomedical engineering such as programmed drug delivery. The development of advanced technologies for biomedical applications using PEM films has seen rapid progress recently. This review briefly summarises the recent successes of PEM being utilised for diverse bio-applications.

Binding Mechanism of the Model Charged Dye Carboxyfluorescein to Hyaluronan/Polylysine Multilayers

Biopolymer-based multilayers become more and more attractive due to the vast span of biological application they can be used for, e.g., implant coatings, cell culture supports, scaffolds. Multilayers have demonstrated superior capability to store enormous amounts of small charged molecules, such as drugs, and release them in a controlled manner; however, the binding mechanism for drug loading into the multilayers is still poorly understood. Here we focus on this mechanism using model hyaluronan/polylysine (HA/PLL) multilayers and a model charged dye, carboxyfluorescein (CF). We found that CF reaches a concentration of 13 mM in the multilayers that by far exceeds its solubility in water. The high loading is not related to the aggregation of CF in the multilayers. In the multilayers, CF molecules bind to free amino groups of PLL; however, intermolecular CF-CF interactions also play a role and (i) endow the binding with a cooperative nature and (ii) result in polyadsorption of CF molecules, as proven by fitting of the adsorption isotherm using the BET model. Analysis of CF mobility in the multilayers by fluorescence recovery after photobleaching has revealed that CF diffusion in the multilayers is likely a result of both jumping of CF molecules from one amino group to another and movement, together with a PLL chain being bound to it. We believe that this study may help in the design of tailor-made multilayers that act as advanced drug delivery platforms for a variety of bioapplications where high loading and controlled release are strongly desired.

Facile modulation of cell adhesion to a poly(ethylene glycol) diacrylate film with incorporation of polystyrene nano-spheres

Poly(ethylene glycol) diacrylate (PEGDA) is a common hydrogel that has been actively investigated for various tissue engineering applications owing to its biocompatibility and excellent mechanical properties. However, the native PEGDA films are known for their bio-inertness which can hinder cell adhesion, thereby limiting their applications in tissue engineering and biomedicine. Recently, nano composite technology has become a particularly hot topic, and has led to the development of new methods for delivering desired properties to nanomaterials. In this study, we added polystyrene nano-spheres (PS) into a PEGDA solution to synthesize a nano-composite film and evaluated its characteristics. The experimental results showed that addition of the nanospheres to the PEGDA film not only resulted in modification of the mechanical properties and surface morphology but further improved the adhesion of cells on the film. The tensile modulus showed clear dependence on the addition of PS, which enhanced the mechanical properties of the PEGDA-PS film. We attribute the high stiffness of the hybrid hydrogel to the formation of additional cross-links between polymeric chains and the nano-sphere surface in the network. The effect of PS on cell adhesion and proliferation was evaluated in L929 mouse fibroblast cells that were seeded on the surface of various PEGDA-PS films. Cells density increased with a larger PS concentration, and the cells displayed a spreading morphology on the hybrid films, which promoted cell proliferation. Impressively, cellular stiffness could also be modulated simply by tuning the concentration of nano-spheres. Our results indicate that the addition of PS can effectively tailor the physical and biological properties of PEGDA as well as the mechanical properties of cells, with benefits for biomedical and biotechnological applications.

Surface Patterning of Gold Nanoparticles on PEG-Based Hydrogels to Control Cell Adhesion

We report on a versatile and easy approach to micro-pattern gold nanoparticles (Au NPs) on 8-arm poly(ethylene glycol)-vinyl sulfone thiol (8PEG-VS-SH) hydrogels, and the application of these patterned Au NPs stripes in controlling cell adhesion. Firstly, the Au NPs were patterned on silicon wafers, and then they were transferred onto reactive, multifunctional 8PEG-VS-SH hydrogels. The patterned, micrometer-sized Au NPs stripes with variable spacings ranging from 20 μm to 50 μm were created by our recently developed micro-contact deprinting method. For this micro-contact deprinting approach, four different PEG-based stamp materials have been tested and it was found that the triblock copolymer PEG-PPG-PEG-(3BC) stamp established the best transfer efficiency and has been used in the ongoing work. After the successful creation of micro-patterns of Au NPs stripes on silicon, the patterns can be transferred conveniently and accurately to 8PEG-VS-SH hydrogel films. Subsequently these Au NPs patterns on 8PEG-VS-SH hydrogels have been investigated in cell culture with murine fibroblasts (L-929). The cells have been observed to adhere to and spread on those nano-patterned micro-lines in a remarkably selective and ordered manner.

Cell Guidance on Nanostructured Metal Based Surfaces

Metal surface nanostructuring to guide cell behavior is an attractive strategy to improve parts of medical implants, lab-on-a-chip, soft robotics, self-assembled microdevices, and bionic devices. Here, we discus important parameters, relevant trends, and specific examples of metal surface nanostructuring to guide cell behavior on metal-based hybrid surfaces. Surface nanostructuring allows precise control of cell morphology, adhesion, internal organization, and function. Pre-organized metal nanostructuring and dynamic stimuli-responsive surfaces are used to study various cell behaviors. For cells dynamics control, the oscillating stimuli-responsive layer-by-layer (LbL) polyelectrolyte assemblies are discussed to control drug delivery, coating thickness, and stiffness. LbL films can be switched "on demand" to change their thickness, stiffness, and permeability in the dynamic real-time processes. Potential applications of metal-based hybrids in biotechnology and selected examples are discussed.

Biodegradation-Resistant Multilayers Coated with Gold Nanoparticles. Toward a Tailor-made Artificial Extracellular Matrix

Polymer multicomponent coatings such as multilayers mimic an extracellular matrix (ECM) that attracts significant attention for the use of the multilayers as functional supports for advanced cell culture and tissue engineering. Herein, biodegradation and molecular transport in hyaluronan/polylysine multilayers coated with gold nanoparticles were described. Nanoparticle coating acts as a semipermeable barrier that governs molecular transport into/from the multilayers and makes them biodegradation-resistant. Model protein lysozyme (mimics of ECM-soluble signals) diffuses into the multilayers as fast- and slow-diffusing populations existing in an equilibrium. Such a composite system may have high potential to be exploited as degradation-resistant drug-delivery platforms suitable for cell-based applications.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Investigating cell-substrate and cell-cell interactions by means of single-cell-probe force spectroscopy

Cell adhesion forces are typically a mixture of specific and nonspecific cell-substrate and cell-cell interactions. In order to resolve these phenomena, Atomic Force Microscopy appears as a powerful device which can measure cell parameters by means of manipulation of single cells. This method, commonly known as cell-probe force spectroscopy, allows us to control the force applied, the area of interest, the approach/retracting speed, the force rate, and the time of interaction. Here, we developed a novel approach for in situ cantilever cell capturing and measurement of specific cell interactions. In particular, we present a new setup consisting of two different half-surfaces coated either with recrystallized SbpA bacterial cell surface layer proteins (S-layers) or integrin binding Fibronectin, on which MCF-7 breast cancer cells are incubated. The presence of a clear physical boundary between both surfaces benefits for a quick detection of the region under analysis. Thus, quantitative results about SbpA-cell and Fibronectin-cell adhesion forces as a function of the contact time are described. Additionally, the importance of the cell spreading in cell-cell interactions has been studied for surfaces coated with two different Fibronectin concentrations: 20 μg/mL (FN20) and 100 μg/mL (FN100), which impact the number of substrate receptors. Microsc. Res. Tech. 80:124-130, 2017. © 2016 Wiley Periodicals, Inc.

Magnetic nanoparticle film reconstruction modulated by immersion within DMSA aqueous solution

The process of reconstruction of pre-fabricated films comprising maghemite nanoparticles deposited onto flat glass substrates triggered by immersion into aqueous solutions of meso-2,3-dimercaptosuccinic acid (DMSA) at increasing concentration (0.025, 0.050, and 0.100 mol/L) is herein reported. The evolution of this process was assessed by measuring the time (t) dependence of the particle analysis histogram width (W) extracted from atomic force microscopy images. Furthermore, a physical picture to model the film reconstruction which provides reconstruction time constants associated to single particles (τ1) and small agglomerates (τn), the key units associated to the process, ranging from τ1 = 2.9 and τn = 3.4 hour (0.025 mol/L) to τ1 = 5.1 and τn = 4.6 hour (0.100 mol/L) is proposed. The nanoparticle-based film reconstruction triggered by an exogenous stimulus, the use of the W versus t data to describe the process and the model picture accounting for the recorded data have not been previously reported.

Hyaluronic Acid/Poly-l-Lysine Multilayers as Reservoirs for Storage and Release of Small Charged Molecules

Polyelectrolyte multilayer films are nowadays very attractive for bioapplications due to their tunable properties and ability to control cellular response. Here we demonstrate that multilayers made of hyaluronic acid and poly-l-lysine act as high-capacity reservoirs for small charged molecules. Strong accumulation within the film is explained by electrostatically driven binding to free charges of polyelectrolytes. Binding and release mechanisms are discussed based on charge balance and polymer dynamics in the film. Our results show that transport of molecules through the film-solution interface limits the release rate. The multilayers might serve as an effective platform for drug delivery and tissue engineering due to high potential for drug loading and controlled release.

Micro-contact printing of PEM thin films: effect of line tension and surface energies

A theory and method for calculating printing resolution limits for microcontact printing of a condensed polyelectrolyte multilayer thin film, based on surface energies and line tension is presented.

Temperature-induced molecular transport through polymer multilayers coated with PNIPAM microgels

Composite polymer films with temperature controlled permeability are designed by coating soft polyelectrolyte multilayers with PNIPAM microgels.

Pharmacological aspects of release from microcapsules - from polymeric multilayers to lipid membranes

This review is devoted to pharmacological applications of principles of release from capsules to overcome the membrane barrier. Many of these principles were developed in the context of polymeric multilayer capsule membrane modulation, but they are also pertinent to liposomes, polymersomes, capsosomes, particles, emulsion-based carriers and other carriers. We look at these methods from the physical, chemical or biological driving mechanisms point of view. In addition to applicability for carriers in drug delivery, these release methods are significant for another area directly related to pharmacology - modulation of the permeability of the membranes and thus promoting the action of drugs. Emerging technologies, including ionic current monitoring through a lipid membrane on a nanopore, are also highlighted.

Mimicking bubble use in nature: propulsion of Janus particles due to hydrophobic-hydrophilic interactions

Bubbles are widely used by animals in nature in order to fulfill important functions. They are used by animals in order to walk underwater or to stabilize themselves at the water/air interface. The main aim of this work is to imitate such phenomena, which is the essence of biomimetics. Here, bubbles are used to propel and to control the location of Janus particles in an aqueous medium. The synthesis of Janus SiO2-Ag and polystyrene-Ag (PS-Ag) particles through embedment in Parafilm is presented. The Janus particles, partially covered with catalytically active Ag nanoparticles, are redispersed in water and placed on a glass substrate. The active Ag sites are used for the splitting of H2O2 into water and oxygen. As a result, an oxygen bubble is formed on one side of the particle and promotes its propulsion. Once formed, the bubble-particle complex is stable and therefore, can be manipulated by tuning hydrophilic-hydrophobic interactions with the surface. In this way a transition between two- and three- dimensional motion is possible by changing the hydrophobicity of the substrate. Similar principles are used in nature.

Adhesion behaviors on superhydrophobic surfaces

The adhesion behaviors of superhydrophobic surfaces have become an emerging topic to researchers in various fields as a vital step in the interactions between materials and organisms/materials. Controlling the chemical compositions and topological structures via various methods or technologies is essential to fabricate and modulate different adhesion properties, such as low-adhesion, high-adhesion and anisotropic adhesion on superhydrophobic surfaces. We summarize the recent developments in both natural superhydrophobic surfaces and artificial superhydrophobic surfaces with various adhesions and also pay attention to superhydrophobic surfaces switching between low- and high-adhesion. The methods to regulate or translate the adhesion of superhydrophobic surfaces can be considered from two perspectives. One is to control the chemical composition and change the surface geometric structure on the surfaces, respectively or simultaneously. The other is to provide external stimulations to induce transitions, which is the most common method for obtaining switchable adhesions. Additionally, adhesion behaviors on solid-solid interfaces, such as the behaviors of cells, bacteria, biomolecules and icing on superhydrophobic surfaces are also noticeable and controversial. This review is aimed at giving a brief and crucial overview of adhesion behaviors on superhydrophobic surfaces.

Facile preparation of raspberry-like superhydrophobic polystyrene particles via seeded dispersion polymerization

A simple and facile approach was developed to fabricate raspberry-like or snowman-like particles via seeded dispersion polymerization by just changing the ratio of second monomer styrene (St) to seeds in which poly(styrene-co-hydrolyzed-methacryloxypropyltrimethoxysilane) [P(St-co-MPS)] latex was used as seeds with hydrolyzed-MPS as a cross-linking agent. The morphologies of final products were confirmed by field-emission scanning electron microscopy and transmission electron microscopy. Interestingly, the seed part of snowman-like particles showed raspberry-like with adsorbing quantities of PS particles while the other part smooth. The formation mechanism of the raspberry-like particles was also discussed. The superhydrophobic surface with both the static contact angle of 158° and high adhesion to water could be achieved by the hydrophobization of the particulate film with octadecyltrimethoxysilane that was formed from the raspberry-like particles decorated by a thin layer of silica nanoparticles. Further, through encapsulating Ag nanoparticles within the surface, the obtained raspberry-like PS/Ag/SiO2 nanocomposite particles exhibited excellent antibacterial property simultaneously.

Robust and flexible free-standing films for unidirectional drug delivery

Robust and flexible free-standing polymer films for unidirectional drug delivery are fabricated by sandwiching drug-containing polyelectrolyte multilayer films between poly(lactic-co-glycolic acid) (PLGA) barrier and capping layers. The drug-containing films are fabricated by layer-by-layer (LbL) assembly of chemically cross-linked poly(allylamine hydrochloride)-dextran (PAH-D) microgel and hyaluronic acid (HA), which can load negatively charged cancer-inhibiting drug, methotrexate (MTX). Because the PLGA barrier layer effectively blocks MTX release, MTX can be predominantly released from the PLGA capping layer of the free-standing film. This increases the efficacy of released MTX to cancer cells while minimizing its side effects on the normal tissues. We believe that the unidirectional drug delivery free-standing films can open a new avenue to design of highly efficient drug delivery systems for biomedical application.

New surface-enhanced Raman scattering platforms: composite calcium carbonate microspheres coated with astralen and silver nanoparticles

Surface-enhanced Raman scattering (SERS) microspectroscopy is a very promising label-free, noncontact, and nondestructive method for real-time monitoring of extracellular matrix (ECM) development and cell integration in scaffolds for tissue engineering. Here, we prepare a new type of micrometer-sized SERS substrate, core-shell microparticles composed of solid carbonate core coated with silver nanoparticles and polyhedral multishell fullerene-like structure, astralen. Astralen has been assembled with polyallylamine hydrochloride (PAH) by the layer-by-layer manner followed by Ag nanoparticle formation by means of a silver mirror reaction, giving the final structure of composite particles CaCO3(PAH/astralen)x/Ag, where x = 1-3. The components of the microparticle carry multiple functionalities: (i) an easy identification by Raman imaging (photostable astralen) and (ii) SERS due to a rough surface of Ag nanoparticles. A combination of Ag and astralen nanoparticles provides an enhancement of astralen Raman signal by more than 1 order of magnitude. Raman signals of commonly used scaffold components such as polylactide and polyvinyl alcohol as well as ECM component (hyaluronic acid) are significantly enhanced. Thus, we demonstrate that new mechanically robust and easily detectable (by astralen signal or optically) core-shell microspheres based on biocompatible CaCO3 can be used as SERS platform. Particle design opens many future perspectives for fabrication of SERS platforms with multiple functions for biomedical applications, for example, for theranostic.