Colloidal Force Spectroscopy and Cell Biological Investigations on Biomimetic Polyelectrolyte Multilayer Coatings Composed of Chondroitin Sulfate and Heparin

Overcoming the Low-Stability Bottleneck in the Clinical Translation of Liposomal Pressurized Metered-Dose Inhalers: A Shell Stabilization Strategy Inspired by Biomineralization

Currently, several types of inhalable liposomes have been developed. Among them, liposomal pressurized metered-dose inhalers (pMDIs) have gained much attention due to their cost-effectiveness, patient compliance, and accurate dosages. However, the clinical application of liposomal pMDIs has been hindered by the low stability, i.e., the tendency of the aggregation of the liposome lipid bilayer in hydrophobic propellant medium and brittleness under high mechanical forces. Biomineralization is an evolutionary mechanism that organisms use to resist harsh external environments in nature, providing mechanical support and protection effects. Inspired by such a concept, this paper proposes a shell stabilization strategy (SSS) to solve the problem of the low stability of liposomal pMDIs. Depending on the shell material used, the SSS can be classified into biomineralization (biomineralized using calcium, silicon, manganese, titanium, gadolinium, etc.) biomineralization-like (composite with protein), and layer-by-layer (LbL) assembly (multiple shells structured with diverse materials). This work evaluated the potential of this strategy by reviewing studies on the formation of shells deposited on liposomes or similar structures. It also covered useful synthesis strategies and active molecules/functional groups for modification. We aimed to put forward new insights to promote the stability of liposomal pMDIs and shed some light on the clinical translation of relevant products.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Physicochemical Characterization and In Vitro Evaluation

The layer-by-layer (LbL) self-assembly technique is an effective method to immobilize components of the extracellular matrix (ECM) such as collagen and heparin onto, e.g., implant surfaces/medical devices with the aim of forming polyelectrolyte multilayers (PEMs). Increasing evidence even suggests that cross-linking influences the physicochemical character of PEM films since mechanical cues inherent to the substrate may be as important as its chemical nature to influence the cellular behavior. In this study, for the first-time different collagen/heparin films have been prepared and cross-linked with EDC/NHS chemistry. Quartz crystal microbalance, zeta potential analyzer, diffuse reflectance Fourier transform infrared spectroscopy, atomic force microscopy and ellipsometry were used to characterize film growth, stiffness, and topography of different film systems. The analysis of all data proves a nearly linear film growth for all PEM systems, the efficacy of cross-linking and the corresponding changes in the film rigidity after cross-linking and an appropriate surface topography. Furthermore, preliminary cell culture experiments illustrated those cellular processes correlate roughly with the quantity of newly created covalent amide bonds. This allows a precise adjustment of the physicochemical properties of the selected film architecture regarding the desired application and target cells. It could be shown that collagen improves the biocompatibility of heparin containing PEMs and due to their ECM-analogue nature both molecules are ideal candidates intended to be used for any biomedical application with a certain preference to improve the performance of bone implants or bone augmentation strategies.

Protein repellent anti-coagulative mixed-charged cellulose derivative coatings

This study describes the formation of cellulose based polyelectrolyte charge complexes on the surface of biodegradable polycaprolactone (PCL) thin films. Anionic sulphated cellulose (CS) and protonated cationic amino cellulose (AC) were used to form these complexes with a layer-by-layer coating technique. Both polyelectrolytes were analyzed by charge titration methods to elucidate their pH-value dependent protonation behavior. A quartz crystal microbalance with dissipation (QCM-D) in combination with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to follow the growth, stability and water content of up to three AC/CS bi-layers in aqueous environment. This was combined with coagulation studies on one, two and three bilayers of AC/CS, measuring the thrombin formation rate and the total coagulation time of citrated blood plasma with QCM-D. Stable mixed charged bilayers could be prepared on PCL and significantly higher masses of AC than of CS were present in these complexes. Strong hydration due to the presence of ammonium and sulphate substituents on the backbone of cellulose led to a significant BSA repellent character of three bilayers of AC/CS coatings. The total plasma coagulation time was increased in comparison to neat PCL, indicating an anticoagulative nature of the coatings. Surprisingly, a coating solely composed of an AC layer significantly prolonged the total coagulation time on the surfaces although it did not prevent fibrinogen deposition. It is suggested that these cellulose derivative-based coatings can therefore be used to prevent unwanted BSA deposition and fibrin clot formation on PCL to foster its biomedical application.

Biomimetic multilayer coatings deliver gentamicin and reduce implant-related osteomyelitis in rats

Implant-related infections like periprosthetic joint infections (PJI) are still a challenging issue in orthopedic surgery. In this study, we present a prophylactic anti-infective approach based on a local delivery of the antibiotic gentamicin. The local delivery is achieved via a nanoscale polyelectrolyte multilayer (PEM) coating that leaves the bulk material properties of the implant unaffected while tuning the surface properties. The main components of the coating, i.e. polypeptides and sulfated glycosaminoglycans (sGAG) render this coating both biomimetic (matrix mimetic) and biodegradable. We show how adaptions in the conditions of the multilayer assembly process and the antibiotic loading process affect the amount of delivered gentamicin. The highest concentration of gentamicin could be loaded into films composed of polypeptide poly-glutamic acid when the pH of the loading solution was acidic. The concentration of gentamicin on the surface could be tailored with the number of deposited PEM layers. The resulting coatings reveal a bacteriotoxic effect on Staphylococcus cells but show no signs of cytotoxic effects on MC3T3-E1 osteoblasts. Moreover, when multilayer-coated titanium rods were implanted into contaminated medullae of rat tibiae, a reduction in the development of implant-related osteomyelitis was observed. This reduction was more pronounced for the multifunctional, matrix-mimetic heparin-based coatings that only deliver lower amounts of gentamicin.

Biomimetic Designer Scaffolds Made of D,L-Lactide-ɛ-Caprolactone Polymers by 2-Photon Polymerization

IMPACT STATEMENT

In tissue engineering (TE), the establishment of cell targeting materials, which mimic the conditions of the physiological extracellular matrix (ECM), seems to be a mission impossible without advanced materials and fabrication techniques. With this in mind we established a toolbox based on (D,L)-lactide-ɛ-caprolactone methacrylate (LCM) copolymers in combination with a nano-micromaskless lithography technique, the two-photon polymerization (2-PP) to mimic the hierarchical structured and complex milieu of the natural ECM. To demonstrate the versatility of this toolbox, we choose two completely different application scenarios in bone and tumor TE to show the high potential of this concept in therapeutic and diagnostic application.

MSC differentiation on two-photon polymerized, stiffness and BMP2 modified biological copolymers

INTRODUCTION

Bone tissue regeneration requires a three-dimensional biological setting. An ideal scaffold should enable cell proliferation and differentiation by mimicking structure and mechanical properties of the compromised defect as well as carrying growth factors. Two-photon polymerization (2PP) allows the preparation of 3D structures with a micrometric resolution.

METHODS

In this study, 2PP was applied to design scaffolds made from biocompatible methacrylated D,L-lactide-co-ε-caprolactone copolymers (LC) with a controlled porous architecture. Proliferation and differentiation of bone marrow mesenchymal stromal cells on LC was analyzed and compared to a standard inorganic urethane-dimethacrylate (UDMA) matrix. To functionalize LC and UDMA surfaces we analyzed a biomimetic, layer-by-layer coating, which could be modified in stiffness and integration of bone morphogenetic protein 2 (BMP2) and evaluated its effect on osteogenic differentiation.

RESULTS

On LC surfaces, BMSC demonstrated an optimal proliferation within pore sizes of 60-100 μm and showed a continuous expression of Vimentin. On the polyelectrolyte multilayer coating a significant increase in BMSC proliferation and differentiation as marked by Osteonectin expression was achieved using stiffness modification and BMP2 functionalization.

CONCLUSION

Combining 3D-Design with biofunctionalization, LC offers a promising approach for future regenerative applications in osteogenic differentiation of BMSCs.

Molecular weight of surface immobilized hyaluronic acid influences CD44-mediated binding of gastric cancer cells

The physiological importance of the interactions between hyaluronic acid (HA) and its main membrane receptor, CD44, in pathological processes, e.g. cancer, is well recognized. However, these interactions are mainly studied in solution, whereas HA in the extracellular matrix (ECM) is partially immobilized via its interactions with other ECM components. We therefore, developed substrates in which HA is presented in an ECM-relevant manner. We immobilized HA with different molecular weights (Mw) in a Layer-by-Layer (LbL) fashion and studied the interactions of the substrates with CD44 and two human gastric cancer cell lines that overexpress this receptor, namely AGS and MKN45. We demonstrate that MKN45 cells are more sensitive to the LbL substrates as compared with AGS. This difference is due to different CD44 expression: while CD44 is detected mainly in the cytoplasm of AGS, MKN45 express CD44 predominantly at the cell membrane where it is involved in the recognition and binding of HA. The invasiveness of the studied cell lines was also evaluated as a function of HA Mw. Invasive profile characterized by low cell adhesion, high cell motility, high expression of cortactin, formation of invadopodia and cell clusters was observed for MKN45 cells when they are in contact with substrates presenting HA of high Mw.

Concise Review: Fabrication, Customization, and Application of Cell Mimicking Microparticles in Stem Cell Science

Stem and non-stem cell behavior is heavily influenced by the surrounding microenvironment, which includes other cells, matrix, and potentially biomaterials. Researchers have been successful in developing scaffolds and encapsulation techniques to provide stem cells with mechanical, topographical, and chemical cues to selectively direct them toward a desired differentiation pathway. However, most of these systems fail to present truly physiological replications of the in vivo microenvironments that stem cells are typically exposed to in tissues. Thus, cell mimicking microparticles (CMMPs) have been developed to more accurately recapitulate the properties of surrounding cells while still offering ways to tailor what stimuli are presented. This nascent field holds the promise of reducing, or even eliminating, the need for live cells in select, regenerative medicine therapies, and diagnostic applications. Recent, CMMP-based studies show great promise for the technology, yet only reproduce a small subset of cellular characteristics from among those possible: size, morphology, topography, mechanical properties, surface molecules, and tailored chemical release to name the most prominent. This Review summarizes the strengths, weaknesses, and ideal applications of micro/nanoparticle fabrication and customization methods relevant to cell mimicking and provides an outlook on the future of this technology. Moving forward, researchers should seek to combine multiple techniques to yield CMMPs that replicate as many cellular characteristics as possible, with an emphasis on those that most strongly influence the desired therapeutic effects. The level of flexibility in customizing CMMP properties allows them to substitute for cells in a variety of regenerative medicine, drug delivery, and diagnostic systems. Stem Cells Translational Medicine 2018;7:232-240.

Polyelectrolyte multilayer-calcium phosphate composite coatings for metal implants

The preparation of organic-inorganic composite coatings with the purpose to increase the bioactivity of bioinert metal implants was investigated. As substrates, glass plates and rough titanium surfaces (Ti-SLA) were employed. The method comprises the deposition of polyelectrolyte multilayers (PEMLs) followed by immersion of the coated substrate into a calcifying solution of low supersaturation (MCS). Single or mixed PEMLs were constructed from poly-L-lysine (PLL) alternating with poly-L-glutamate, (PGA), poly-L-aspartate (PAA), and/or chondroitin sulfate (CS). ATR-FTIR spectra reveal that (PLL/PGA)10 multilayers and mixed multilayers with a (PLL/PGA)5 base contain intermolecular β-sheet structures, which are absent in pure (PLL/PAA)10 and (PLL/CS)10 assemblies. All PEML coatings had a grainy topography with aggregate sizes and size distributions increasing in the order: (PLL/PGA)n < (PLL/PAA)n < (PLL/CS)n. In mixed multilayers with a (PLL/PGA)n base and a (PLL/PAA)n or (PLL/CS)n top, the aggregate sizes were greatly reduced. The PEMLs promoted calcium phosphate nucleation and early crystal growth, the intensity of the effect depending on the composition of the terminal layer(s) of the polymer. In contrast, crystal morphology and structure depended on the supersaturation, pH, and ionic strength of the MCS, rather than on the composition of the organic matrix. Crystals grown on both uncoated and coated substrates were mostly platelets of calcium deficient carbonate apatite, with the Ca/P ratio depending on the precipitation conditions.

Influence of extracellular matrix proteins and substratum topography on corneal epithelial cell alignment and migration

The basement membrane (BM) of the corneal epithelium presents biophysical cues in the form of topography and compliance that can impact the phenotype and behaviors of cells and their nuclei through modulation of cytoskeletal dynamics. In addition, it is also well known that the intrinsic biochemical attributes of BMs can modulate cell behaviors. In this study, the influence of the combination of exogenous coating of extracellular matrix proteins (ECM) (fibronectin-collagen [FNC]) with substratum topography was investigated on cytoskeletal architecture as well as alignment and migration of immortalized corneal epithelial cells. In the absence of FNC coating, a significantly greater percentage of cells aligned parallel with the long axis of the underlying anisotropically ordered topographic features; however, their ability to migrate was impaired. Additionally, changes in the surface area, elongation, and orientation of cytoskeletal elements were differentially influenced by the presence or absence of FNC. These results suggest that the effects of topographic cues on cells are modulated by the presence of surface-associated ECM proteins. These findings have relevance to experiments using cell cultureware with biomimetic biophysical attributes as well as the integration of biophysical cues in tissue-engineering strategies and the development of improved prosthetics.

Electrochemically controlled stiffness of multilayers for manipulation of cell adhesion

Stimuli-responsive thin films attract considerable attention in different fields. Herein, an electrochemical redox multilayers with tunable stiffness is constructed through the layer-by-layer self-assembly method. The redox ferrocene modified poly(ethylenimine) play an essential role to induce multilayers' swelling/shrinking under an electrochemical stimulus, resulting reversible change of elastic modulus of the multilayers. The adhesion of fibroblast cells can be thus controlled from well spreading to round shape. Such soft multilayers with electrochemically controlled stiffness could have potentials for cell-based applications.

The effect of polyelectrolyte multilayer coated titanium alloy surfaces on implant anchorage in rats

Advances have been achieved in the design and biomechanical performance of orthopedic implants in the last decades. These include anatomically shaped and angle-stable implants for fracture fixation or improved biomaterials (e.g. ultra-high-molecular-weight polyethylene) in total joint arthroplasty. Future modifications need to address the biological function of implant surfaces. Functionalized surfaces can promote or reduce osseointegration, avoid implant-related infections or reduce osteoporotic bone loss. To this end, polyelectrolyte multilayer structures have been developed as functional coatings and intensively tested in vitro previously. Nevertheless, only a few studies address the effect of polyelectrolyte multilayer coatings of biomaterials in vivo. The aim of the present work is to evaluate the effect of polyelectrolyte coatings of titanium alloy implants on implant anchorage in an animal model. We test the hypotheses that (1) polyelectrolyte multilayers have an effect on osseointegration in vivo; (2) multilayers of chitosan/hyaluronic acid decrease osteoblast proliferation compared to native titanium alloy, and hence reduce osseointegration; (3) multilayers of chitosan/gelatine increase osteoblast proliferation compared to native titanium alloy, hence enhance osseointegration. Polyelectrolyte multilayers on titanium alloy implants were fabricated by a layer-by-layer self-assembly process. Titanium alloy (Ti) implants were alternately dipped into gelatine (Gel), hyaluronic acid (HA) and chitosan (Chi) solutions, thus assembling a Chi/Gel and a Chi/HA coating with a terminating layer of Gel or HA, respectively. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bones' response to polyelectrolyte surfaces in vivo. 48 rats were randomly assigned to three groups of implants: (1) native titanium alloy (control), (2) Chi/Gel and (3) Chi/HA coating. Mechanical fixation, peri-implant bone area and bone contact were evaluated by pull-out tests and histology at 3 and 8 weeks. Shear strength at 8 weeks was statistically significantly increased (p<0.05) in both Chi/Gel and Chi/HA groups compared to the titanium alloy control. No statistically significant difference (p>0.05) in bone contact or bone area was found between all groups. No decrease of osseointegration of Chi/HA-coated implants compared to non-coated implants was found. The results of polyelectrolyte coatings in a rat model showed that the Chi/Gel and Chi/HA coatings have a positive effect on mechanical implant anchorage in normal bone.

Polyelectrolyte Multilayer Assemblies on Materials Surfaces: From Cell Adhesion to Tissue Engineering

Controlling the bulk and surface properties of materials is a real challenge for bioengineers working in the fields of biomaterials, tissue engineering and biophysics. The layer-by-layer (LbL) deposition method, introduced 20 years ago, consists in the alternate adsorption of polyelectrolytes that self-organize on the material's surface, leading to the formation of polyelectrolyte multilayer (PEM) films.1 Because of its simplicity and versatility, the procedure has led to considerable developments of biological applications within the past 5 years. In this review, we focus our attention on the design of PEM films as surface coatings for applications in the field of physical properties that have emerged as being key points in relation to biological processes. The numerous possibilities for adjusting the chemical, physical, and mechanical properties of PEM films have fostered studies on the influence of these parameters on cellular behaviors. Importantly, PEM have emerged as a powerful tool for the immobilization of biomolecules with preserved bioactivity.