Improved stability and cell response by intrinsic cross-linking of multilayers from collagen I and oxidized glycosaminoglycans

Protein-based layer-by-layer films for biomedical applications

The surface engineering of biomaterials is crucial for their successful (bio)integration by the body, i.e. the colonization by the tissue-specific cell, and the prevention of fibrosis and/or bacterial colonization. Performed at room temperature in an aqueous medium, the layer-by-layer (LbL) coating method is based on the alternating deposition of macromolecules. Versatile and simple, this method allows the functionalization of surfaces with proteins, which play a crucial role in several biological mechanisms. Possessing intrinsic properties (cell adhesion, antibacterial, degradable, etc.), protein-based LbL films represent a powerful tool to control bacterial and mammalian cell fate. In this article, after a general introduction to the LbL technique, we will focus on protein-based LbL films addressing different biomedical issues/domains, such as bacterial infection, blood contacting surfaces, mammalian cell adhesion, drug and gene delivery, and bone and neural tissue engineering. We do not consider biosensing applications or electrochemical aspects using specific proteins such as enzymes.

Lipoplex-Functionalized Thin-Film Surface Coating Based on Extracellular Matrix Components as Local Gene Delivery System to Control Osteogenic Stem Cell Differentiation

A gene-activated surface coating is presented as a strategy to design smart biomaterials for bone tissue engineering. The thin-film coating is based on polyelectrolyte multilayers composed of collagen I and chondroitin sulfate, two main biopolymers of the bone extracellular matrix, which are fabricated by layer-by-layer assembly. For further functionalization, DNA/lipid-nanoparticles (lipoplexes) are incorporated into the multilayers. The polyelectrolyte multilayer fabrication and lipoplex deposition are analyzed by surface sensitive analytical methods that demonstrate successful thin-film formation, fibrillar structuring of collagen, and homogenous embedding of lipoplexes. Culture of mesenchymal stem cells on the lipoplex functionalized multilayer results in excellent attachment and growth of them, and also, their ability to take up cargo like fluorescence-labelled DNA from lipoplexes. The functionalization of the multilayer with lipoplexes encapsulating DNA encoding for transient expression of bone morphogenetic protein 2 induces osteogenic differentiation of mesenchymal stem cells, which is shown by mRNA quantification for osteogenic genes and histochemical staining. In summary, the novel gene-functionalized and extracellular matrix mimicking multilayer composed of collagen I, chondroitin sulfate, and lipoplexes, represents a smart surface functionalization that holds great promise for tissue engineering constructs and implant coatings to promote regeneration of bone and other tissues.

Metal Ion Doping of Alginate-Based Surface Coatings Induces Adipogenesis of Stem Cells

Metal ions are important effectors of protein and cell functions. Here, polyelectrolyte multilayers (PEMs) made of chitosan (Chi) and alginate (Alg) were doped with different metal ions (Ca²⁺, Co²⁺, Cu²⁺, and Fe³⁺), which can form bonds with their functional groups. Ca²⁺ and Fe³⁺ ions can be deposited in PEM at higher quantities resulting in more positive ζ potentials and also higher water contact angles in the case of Fe³⁺. An interesting finding was that the exposure of PEM to metal ions decreases the elastic modulus of PEM. Fourier transformed infrared (FTIR) spectroscopy of multilayers provides evidence of interaction of metal ions with the carboxylic groups of Alg but not for hydroxyl and amino groups. The observed changes in wetting and surface potential are partly related to the increased adhesion and proliferation of multipotent C3H10T1/2 fibroblasts in contrast to plain nonadhesive [Chi/Alg] multilayers. Specifically, PEMs doped with Cu²⁺ and Fe³⁺ ions greatly promote cell attachment and adipogenic differentiation, which indicates that changes in not only surface properties but also the bioactivity of metal ions play an important role. In conclusion, metal ion-doped multilayer coatings made of alginate and chitosan can promote the differentiation of multipotent cells on implants without the use of other morphogens like growth factors.

Chondrogenic differentiation of mesenchymal stem cells through cartilage matrix-inspired surface coatings

The stem cell niche comprises soluble molecules and extracellular matrix components which provide chemical and mechanical cues that determine the differentiation of stem cells. Here, the effect of polyelectrolyte multilayer (PEM) composition and terminal layer fabricated with layer-by-layer technique (LBL) pairing either hyaluronan [in its native (nHA) and oxidized form (oHA)] or chondroitin sulfate (CS) with type I collagen (Col I) is investigated on chondrogenic differentiation of human umbilical mesenchymal stem cells (hUC-MSCs). Physical studies performed to investigate the establishment and structure of the surface coatings show that PEM composed of HA and Col I show a dominance of nHA or oHA with considerably lesser organization of Col I fibrils. In contrast, distinguished fibrilized Col I is found in nCS-containing PEM. Generally, Col I-terminated PEM promote the adhesion, migration, and growth of hUC-MSCs more than GAG-terminated surfaces due to the presence of fibrillar Col I but show a lower degree of differentiation towards the chondrogenic lineage. Notably, the Col I/nHA PEM not only supports adhesion and growth of hUC-MSCs but also significantly promotes cartilage-associated gene and protein expression as found by histochemical and molecular biology studies, which is not seen on the Col I/oHA PEM. This is related to ligation of HA to the cell receptor CD44 followed by activation of ERK/Sox9 and noncanonical TGF-β signaling-p38 pathways that depends on the molecular weight of HA as found by immune histochemical and western blotting. Hence, surface coatings on scaffolds and other implants by PEM composed of nHA and Col I may be useful for programming MSC towards cartilage regeneration.

Extracellular matrix-inspired surface coatings functionalized with dexamethasone-loaded liposomes to induce osteo- and chondrogenic differentiation of multipotent stem cells

Biomimetic surface coatings can be combined with conventional implants to mimic the extracellular matrix (ECM) of the surrounding tissue to make them more biocompatible. Layer-by-layer technique (LbL) can be used for making surface coatings by alternating adsorption of polyanions and polycations from aqueous solutions without need of chemical reactions. Here, polyelectrolyte multilayer (PEM) systems is made of hyaluronic acid (HA) as polyanion and Collagen I (Col) as polycation to mimic the ECM of connective tissue. The PEM are combined with dexamethasone (Dex)-loaded liposomes to achieve a local delivery and protection of this drug for stimulation of osteo- and chondrogenic differentiation of multipotent stem cells. The liposomes possess a positive surface charge that is required for immobilization on the PEM. The surface properties of PEM system show a positive zeta potential after liposome adsorption and a decrease in wettability, both promoting cell adhesion and spreading of C3H10T1/2 multipotent embryonic mouse fibroblasts. Differentiation of C3H10T1/2 was more prominent on the PEM system with embedded Dex-loaded liposomes compared to the basal PEM system and the use of free Dex-loaded liposomes in the supernatant. This was evident by immunohistochemical staining and an upregulation of the expression of genes, which play a key role in osteogenesis (RunX2, ALP, Osteocalcin (OCN)) and chondrogenesis (Sox9, aggrecan (ACAN), collagen type II), determined by quantitative Real-time polymerase chain reaction (qRT-PCR) after 21 days. These findings indicate that the designed liposome-loaded PEM system have high potential for use as drug delivery systems for implant coatings that can induce bone and cartilage differentiation needed for example in osteochondral implants.

Synthesis and Characterization of Oxidized Polysaccharides for In Situ Forming Hydrogels

Polysaccharides are widely used as building blocks of scaffolds and hydrogels in tissue engineering, which may require their chemical modification to permit crosslinking. The goal of this study was to generate a library of oxidized alginate (oALG) and oxidized hyaluronic acid (oHA) that can be used for in situ gelling hydrogels by covalent reaction between aldehyde groups of the oxidized polysaccharides (oPS) and amino groups of carboxymethyl chitosan (CMC) through imine bond formation. Here, we studied the effect of sodium periodate concentration and reaction time on aldehyde content, molecular weight of derivatives and cytotoxicity of oPS towards 3T3-L1 fibroblasts. It was found that the molecular weights of all oPs decreased with oxidation and that the degree of oxidation was generally higher in oHA than in oALG. Studies showed that only oPs with an oxidation degree above 25% were cytotoxic. Initial studies were also done on the crosslinking of oPs with CMC showing with rheometry that rather soft gels were formed from higher oxidized oPs possessing a moderate cytotoxicity. The results of this study indicate the potential of oALG and oHA for use as in situ gelling hydrogels or inks in bioprinting for application in tissue engineering and controlled release.

Engineering osteogenic microenvironments by combination of multilayers from collagen type I and chondroitin sulfate with novel cationic liposomes

Cationic liposomes composed of a novel lipid (N-{6-amino-1-[N-(9Z) -octadec9-enylamino] -1-oxohexan-(2S) -2-yl} -N'- {2- [N, N-bis(2-aminoethyl) amino] ethyl} -2-hexadecylpropandiamide) (OO4) and dioleoylphosphatidylethanolamine (DOPE) possess high amounts of amino groups and are promising systems for lipofection. Moreover, these cationic liposomes can also be used as a polycationic entity in multilayer formation using layer-by-layer technique (LbL), which is a method to fabricate surface coatings by alternating adsorption of polyanions and polycations. Since liposomes are suitable for endocytosis by or fusion with cells, controlled release of their cargo on site is possible. Here, a polyelectrolyte multilayer (PEM) system was designed of chondroitin sulfate (CS) and collagen type I (Col I) by LbL technique with OO4/DOPE liposomes embedded in the terminal layers to create an osteogenic microenvironment. Both, the composition of PEM and cargo of the liposomes were used to promote osteogenic differentiation of C2C12 myoblasts as in vitro model. The internalization of cargo-loaded liposomes from the PEM into C2C12 cells was studied using lipophilic (Rhodamine-DOPE conjugate) and hydrophilic (Texas Red-labeled dextran) model compounds. Besides, the use of Col I and CS should mimic the extracellular matrix of bone for future applications such as bone replacement therapies. Physicochemical studies of PEM were done to characterize the layer growth, thickness, and topography. The adhesion of myoblast cells was also evaluated whereby the benefit of a cover layer of CS and finally Col I above the liposome layer was demonstrated. As proof of concept, OO4/DOPE liposomes were loaded with dexamethasone, a compound that can induce osteogenic differentiation. A successful induction of osteogenic differentiation of C2C12 cells with the novel designed liposome-loaded PEM system was shown. These findings indicate that designed OH4/DOPE loaded PEMs have a high potential to be used as drug delivery or transfection system for implant coating in the field of bone regeneration and other applications.

Contact-Triggered Lipofection from Multilayer Films Designed as Surfaces for in Situ Transfection Strategies in Tissue Engineering

Biomaterials, which release active compounds after implantation, are an essential tool for targeted regenerative medicine. In this study, thin multilayer films loaded with lipid/DNA complexes (lipoplexes) were designed as surface coatings for in situ transfection applicable in tissue engineering and regenerative medicine. The film production and embedding of lipoplexes were based on the layer-by-layer (LbL) deposition technique. Hyaluronic acid (HA) and chitosan (CHI) were used as the polyelectrolyte components. The embedded plasmid DNA was complexed using a new designed cationic lipid formulation, namely, OH4/DOPE 1/1, the advantageous characteristics of which have been proven already. Three different methods were tested regarding its efficiency of lipid and DNA deposition. Therefore, several surface specific analytics were used to characterize the LbL formation, the lipid DNA embedding, and the surface characteristics of the multilayer films, such as fluorescence microscopy, surface plasmon resonance spectroscopy, ellipsometry, zeta potential measurements, atomic force microscopy, and scanning electron microscopy. Interaction studies were conducted for optimized lipoplex-loaded polyelectrolyte multilayers (PEMs) that showed an efficient attachment of C2C12 cells on the surface. Furthermore, no acute toxic effects were found in cell culture studies, demonstrating biocompatibility. Cell culture experiments with C2C12 cells, a cell line which is hard to transfect, demonstrated efficient transfection of the reporter gene encoding for green fluorescent protein. In vivo experiments using the chicken embryo chorion allantois membrane animal replacement model showed efficient gene-transferring rates in living complex tissues, although the DNA-loaded films were stored over 6 days under wet and dried conditions. Based on these findings, it can be concluded that OH4/DOPE 1/1 lipoplex-loaded PEMs composed of HA and CHI can be an efficient tool for in situ transfection in regenerative medicine.

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Effect of microenvironment on adhesion and differentiation of murine C3H10T1/2 cells cultured on multilayers containing collagen I and glycosaminoglycans

Polyelectrolyte multilayer coating is a promising tool to control cellular behavior. Murine C3H10T1/2 embryonic fibroblasts share many features with mesenchymal stem cells, which are good candidates for use in regenerative medicine. However, the interactions of C3H10T1/2 cells with polyelectrolyte multilayers have not been studied yet. Hence, the effect of molecular composition of biomimetic multilayers, by pairing collagen I (Col I) with either hyaluronic acid or chondroitin sulfate, based primarily on ion pairing and on additional intrinsic cross-linking was studied regarding the adhesion and differentiation of C3H10T1/2 cells. It was found that the adhesion and osteogenic differentiation of C3H10T1/2 cells were more pronounced on chondroitin sulfate-based multilayers when cultured in the absence of osteogenic supplements, which corresponded to the significant larger amounts of Col I fibrils in these multilayers. By contrast, the staining of cartilage-specific matrixes was more intensive when cells were cultured on hyaluronic acid-based multilayers. Moreover, it is of note that a limited osteogenic and chondrogenic differentiation were detected when cells were cultured in osteogenic or chondrogenic medium. Specifically, cells were largely differentiated into an adipogenic lineage when cultured in osteogenic medium or 100 ng mL-1 bone morphogenic protein 2, and it was more evident on the oxidized glycosaminoglycans-based multilayers, which corresponded also to the higher stiffness of cross-linked multilayers. Overall, polyelectrolyte multilayer composition and stiffness can be used to direct cell-matrix interactions, and hence the fate of C3H10T1/2 cells. However, these cells have a higher adipogenic potential than osteogenic or chondrogenic potential.

Controlled allylation of polyelectrolytes: a deep insight into chemical aspects and their applicability as building blocks for robust multilayer coatings

Polyelectrolytes (PEs) bearing easily derivatizable functions for possible post-modification under mild conditions can find a broad range of applications in various fields. The present paper describes the successful controlled side-chain allylation of two types of PEs: polyamine-based polycations, i.e. poly(allylamine hydrochloride) (PAH) and branched polyethyleneimine (PEI), and strong polyanions, i.e. poly(sodium vinyl sulfonate) (PVS) and poly(sodium 4-styrene sulfonate) (PSS). PSS has been largely investigated in the literature, while PVS is much less commonly explored. The allylation of each type presents its own drawback, i.e. heterogeneous reaction in the case of strong polyanions and instability of partially protonated allylated polyamine products. Nevertheless, all encountered difficulties could be solved and thoroughly elucidated by different experimental tests. This partial allyl-functionalization does not affect the electrolytic properties of the newly allylated PEs, as evidenced by the effective construction of two series of polyelectrolyte multilayer (PEM) films, namely PEI-ene (PSS-ene/PAH-ene)4 and PEI-ene (PVS-ene/PAH-ene)4, the latter being one of the rare examples developed in the literature. The presence of allyl groups on the PE side-chains allows for the stabilization of the resulting PEM films via thiol-ene photo-crosslinking in the presence of a water-soluble dithiol crosslinker. In order to fix permanently the resulting crosslinked PEM films on substrates, the covalent crosslinking occurs not only between different C=C bonds on PE layers but also with those present on substrates preliminarily functionalized with allyl groups via sulfur–gold chemistry. The robustness of both resulting crosslinked PEM films under strongly basic solution (pH 14) is validated by Quartz Crystal Microbalance (QCM) measurements. The versatility and effectiveness of the present approach is expected to find potential applications in different scientific and technological fields.

Mucin adsorption on vaterite CaCO3 microcrystals for the prediction of mucoadhesive properties

Porous vaterite CaCO₃ crystals are widely used as containers for drug loading and as sacrificial templates to assemble polymer-based nano- and micro-particles at mild conditions. Special attention is paid nowadays to mucosal delivery where the glycoprotein mucin plays a crucial role as a main component of a mucous. In this work mucoadhesive properties of vaterite crystals have been tested by investigation of mucin binding to the crystals as a function of (i) time, (ii) glycoprotein concentration, (iii) adsorption conditions and (iv) degree of mucin desialization. Mucin adsorption follows Bangham equation indicating that diffusion into crystal pores is the rate-limiting step. Mucin strongly binds to the crystals (ΔG = -35 ± 4 kJ mol^-1) via electrostatic and hydrophobic interactions forming a gel and thus giving the tremendous mucin mass content in the crystals of up to 16%. Despite strong intermolecular mucin-mucin interactions, pure mucin spheres formed after crystal dissolution are unstable. However, introduction of protamine, actively used for mucosal delivery, makes the spheres stable via additional electrostatic bonding. The results of this work indicate that the vaterite crystals are extremely promising carriers for mucosal drug delivery and for development of test-systems for the analysis of the mucoadhesion.

Polyelectrolyte multilayers of poly (l-lysine) and hyaluronic acid on nanostructured surfaces affect stem cell response

Laser interference lithography (LIL) and the layer-by-layer (LbL) technique are combined here for the first time to design a system with variable nanotopographies and surface viscoelasticity to regulate cell behavior. LIL is used to generate hexagonally arranged nanostructures of gold with different periodicity. In contrast, LBL is used to assemble a multilayer system of poly-l-lysine and hyaluronic acid on top of the nanostructures. Moreover, the viscoelastic properties of that system are controlled by chemical cross-linking. We show that the topography designed with LIL is still present after multilayer deposition and that the formation of the multilayer system renders the surfaces hydrophilic, which is opposite to the hydrophobic nature of pristine nanostructures. The heterogenic system is applied to study the effect on adhesion and differentiation of human adipose-derived stem cells (hADSC). We show that hADSC spreading is increasing with cross-linking degree on flat multilayers, while it is decreasing on nanostructures modified with multilayers. In addition, early effects on signal transduction processes are seen. Finally, hADSC differentiation into chondrogenic and osteogenic lineages is superior to adipogenic lineages on nanostructures modified with multilayers. Hence, the presented system offers great potential to guide stem cell differentiation on surfaces of implants and tissue engineering scaffolds.

Anti-cancer effect of dung beetle glycosaminoglycans on melanoma

BACKGROUND

Dung beetle glycosaminoglycan is known to possess anti-aging activities. However, its anti-cancer mechanisms are not fully elucidated yet. The objective of this study was to evaluate the anti-cancer effect of insect-derived polymer dung beetle glycosaminoglycan (GAG) after intraperitoneally injecting it to melanoma mice induced by B16F10 cells.

METHODS

To determine molecular mechanism involved in the anti-cancer effect of dung beetle GAG, its origin N-glycan under 3KD Dalton was assayed for melanoma cell cytotoxicity. Quantitative comparisons of adhesive molecule on extracellular matrix and activities of tissue inhibitor of metalloprotease 2 (TIMP-2) were also investigated. In vivo anti-cancer effect of dung beetle GAG on solid tumor size, survival time and gene-expression profiles was also assayed using B10F10 melanoma mice model. Mice with induced melanoma were then treated with Catharsius molossus (dung beetle) GAG (CaG) at 5 mg/kg for 8 weeks to investigate its anti-cancer effects compared to bumblebee (Bombus ignitus) queen glycosaminoglycan (IQG) and Huechys sanguinea glycosaminoglycan (HEG).

RESULTS

These N-glycans derived from these GAG were composed of many linear heparinoid polysaccharides, polymers with hexose and N-acetylhexose. Adminstration with these GAGs increased survival time and decreased melanoma sizes in mice, in accordance with their inhibitory effects on cell growth ratio of melanoma B16F10. In addition, treatment with N-glycans derived from theses glycosaminoglycan increased activities of TIMP-2 in HMVEC cells pretreated with TNF-alpha and in melanoma cells, suggesting that they had anti-inflammatory and anticancer activities. In DNA microarray results, compared to control, CaG treated mouse group showed upregulation of 192 genes including collagen,typeI,alpha1 (Col1a1), consistent with the highly increased in vitro extracellular matrix (ECM) adhesion on collagen 1 and up-regulation of heparanase (Hpse). After treatment with CaG, a total of 152 genes were down-regulated, including nuclear RNA export factor (Nxf3) and hyaluronan proteoglycan link protein1 (Hapln1).

CONCLUSIONS

Glycosaminoglycan, CaG can strengthen ECM by increasing activity of TIMP-2 and adhesion activity on collagen known to inhibit changes of ECM, leading to tumor cell invasion and progression.

Cyclic Redox-Mediated Switching of Surface Properties of Thiolated Polysaccharide Multilayers and Its Effect on Fibroblast Adhesion

Advanced technologies for controlled cell adhesion and detachment in novel biointerface designs profit from stimuli-responsive systems that are able to react to their environment. Here, a multilayer system made of thiolated chitosan and thiolated chondroitin sulfate was constructed, with the potential of switchable inter- and intramolecular thiol/disulfide interactions representing a redox-sensitive nanoplatform. Owing to the formation and cleavage of inherent disulfide bonds by oxidation and reduction, surface properties of the multilayer can be controlled toward protein adsorption/desorption and cell adhesion in a reversible manner. Oxidation of thiols by chloramine-T promotes fibronectin (FN) adsorption and fibroblast cell adhesion, whereas the reduction by tris(2-carboxyethyl)phosphine reverses these effects, leading to low FN adsorption and little cell adhesion and spreading. These effects on the biological systems are related to significant changes of wetting properties, zeta potential, and mechanical properties of these multilayer films. The system presented may be useful for biomedical applications as responsive and obedient surfaces in medical implants and support tissue regeneration.

Biomineralization improves mechanical and osteogenic properties of multilayer-modified PLGA porous scaffolds

Poly-(lactide-co-glycolide acid) (PLGA) has been widely investigated as scaffold material for bone tissue engineering owing to its biosafety, biodegradability, and biocompatibility. However, the bioinert surface of PLGA may fail in regulating cellular behavior and directing osteointegration between the scaffold and the host tissue. In this article, oxidized chondroitin sulfate (oCS) and type I collagen (Col I) were assembled onto PLGA surface via layer by layer technique (LbL) as an adhesive coating for the attachment of inorganic minerals. The multilayer-modified PLGA scaffold was mineralized in vitro to ensure the deposition of nanohydroxyapatite (nHAP). It was found that nHAP crystals were more uniformly and firmly attached on the multilayer-modified PLGA as compared with the pure PLGA scaffold, which remarkably improved PLGA surface and mechanical properties. Additionally, in vitro biocompatibility of PLGA scaffold, in terms of bone mesenchymal stem cells (BMSCs) attachment, spreading and proliferation was greatly enhanced by nHAP coating and multilayer deposition. Furthermore, the fabricated composite scaffold also shows the ability to promote the osteogenic differentiation of BMSCs through the up-regulation of osteogenic marker genes. Thus, this novel biomimetic composite scaffold might achieve a desirable therapeutic result for bone tissue regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2714-2725, 2018.

Stimuli-Responsive Multilayers Based on Thiolated Polysaccharides That Affect Fibroblast Cell Adhesion

Control of the biomaterial properties through stimuli-responsive polymeric platforms has become an essential technique in recent biomedical applications. A multilayer system of thiolated chitosan (t-Chi) and thiolated chondroitin sulfate (t-CS), consisting of five double layers ([t-Chi/t-CS]₅), was fabricated here by applying a layer-by-layer coating strategy. To represent a novel class of chemically tunable nanostructures, the ability to cross-link pendant thiol groups was tested by a rise from pH 4 during layer formation to pH 9.3 and a more powerful chemical stimulus by using chloramine-T (ChT). Following both treatments, the resulting multilayers showed stimuli-dependent behavior, as demonstrated by their content of free thiols, wettability, surface charge, elastic modulus, roughness, topography, thickness, and binding of fibronectin. Studies with human dermal fibroblasts further demonstrated the favorable potential of the ChT-responsive multilayers as a cell-adhesive surface compared to pH-induced cross-linking. Because the [t-Chi/t-CS]₅ multilayer system is responsive to stimuli such as the pH and redox environment, multilayer systems with disulfide bond formation may help to tailor their interaction with cells, film degradation, and controlled release of bioactive substances like growth factors in a stimuli-responsive manner useful in future wound healing and tissue engineering applications.

Cross-linking multilayers of poly-l-lysine and hyaluronic acid: Effect on mesenchymal stem cell behavior

BACKGROUND

Cells possess a specialized machinery through which they can sense physical as well as chemical alterations in their surrounding microenvironment that affect their cellular behavior.

AIM

In this study, we aim to establish a polyelectrolyte multilayer system of 24 layers of poly-l-lysine and hyaluronic acid to control stem cell response after chemical cross-linking.

METHODS AND RESULTS

The multilayer build-up process is monitored using different methods, which show that the studied polyelectrolyte multilayer system grows exponentially following the islands and islets theory. Successful chemical cross-linking is monitored by an increased zeta potential toward negative magnitude and an extraordinary growth in thickness. Human adipose-derived stem cells are used here and a relationship between cross-linking degree and cell spreading is shown as cells seeded on higher cross-linked polyelectrolyte multilayer show enhanced spreading. Furthermore, cells that fail to establish focal adhesions on native and low cross-linked polyelectrolyte multilayer films do not proliferate to a high extent in comparison to cells seeded on highly cross-linked polyelectrolyte multilayer, which also show an increased metabolic activity. Moreover, this study shows the relation between cross-linking degree and human adipose-derived stem cell lineage commitment. Histological staining reveals that highly cross-linked polyelectrolyte multilayers support osteogenic differentiation, whereas less cross-linked and native polyelectrolyte multilayers support adipogenic differentiation in the absence of any specific inducers.

CONCLUSION

Owing to the precise control of polyelectrolyte multilayer properties such as potential, wettability, and viscoelasticity, the system presented here offers great potential for guided stem cell differentiation in regenerative medicine, especially in combination with materials exhibiting a defined surface topography.

Comparative Study of Osteogenic Activity of Multilayers Made of Synthetic and Biogenic Polyelectrolytes

Polyelectrolyte multilayer (PEM) coatings on biomaterials are applied to tailor adhesion, growth, and function of cells on biomedical implants. Here, biogenic and synthetic polyelectrolytes (PEL) are used for layer-by-layer assembly to study the osteogenic activity of PEM with human osteosarcoma MG-63 cells in a comparative manner. Formation of PEM is achieved with biogenic PEL fibrinogen (FBG) and poly-l-lysine (PLL) as well as biotinylated chondroitin sulfate (BCS) and avidin (AVI), while poly(allylamine hydrochloride) (PAH) and polystyrene sulfonate (PSS) represent a fully synthetic PEM used as a reference system here. Surface plasmon resonance measurements show highest layer mass for FBG/PLL and similar for PSS/PAH and BCS/AVI systems, while water contact angle and zeta potential measurements indicate larger differences for PSS/PAH and FBG/PLL but not for BCS/AVI multilayers. All PEM systems support cell adhesion and growth and promote osteogenic differentiation as well. However, FBG/PLL layers are superior regarding MG-63 cell adhesion during short-term culture, while the BCS/AVI system increases alkaline phosphatase activity in long-term culture. Particularly, a multilayer system based on affinity interaction like BCS/AVI may be useful for controlled presentation of biotinylated growth factors to promote growth and differentiation of cells for biomedical applications.

Synthesis of thiolated polysaccharides for formation of polyelectrolyte multilayers with improved cellular adhesion

Intrinsic cross-linking is not only useful for increasing stability, but also for tailoring mechanical properties of polyelectrolyte multilayers (PEM) on implants and tissue engineering scaffolds. Here, a novel route for synthesizing thiolated chitosan (t-Chi) based on the application of 3,3'-dithiodipropionic acid was applied, while thiolated chondroitin sulfate (t-CS) was conjugated by 3,3'-dithiobis (propanoic hydrazide). Both products were subsequently reduced to obtain the free thiols. The thiol content, structural changes and degree of substitution were studied by UV-vis, FTIR, Raman and ¹H NMR spectroscopy, respectively. Chi and CS can be used for PEM formation with the layer-by-layer method, due to the cationic nature of Chi at pH values below 5.0 and the anionic character of CS. Comparative studies on the formation of native Chi/CS versus t-Chi/t-CS PEM with surface plasmon resonance and ellipsometry revealed higher layer mass. We also found that the PEM composed of t-Chi/t-CS had superior cell adhesion properties for human keratinocytes in comparison to the native PEM.

Temperature effect on the build-up of exponentially growing polyelectrolyte multilayers. An exponential-to-linear transition point

In this study, the effect of temperature on the build-up of exponentially growing polyelectrolyte multilayer films was investigated. It aims at understanding the multilayer growth mechanism as crucially important for the fabrication of tailor-made multilayer films. Model poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers were assembled in the temperature range of 25-85 °C by layer-by-layer deposition using a dipping method. The film growth switches from the exponential to the linear regime at the transition point as a result of limited polymer diffusion into the film. With the increase of the build-up temperature the film growth rate is enhanced in both regimes; the position of the transition point shifts to a higher number of deposition steps confirming the diffusion-mediated growth mechanism. Not only the faster polymer diffusion into the film but also more porous/permeable film structure are responsible for faster film growth at higher preparation temperature. The latter mechanism is assumed from analysis of the film growth rate upon switching of the preparation temperature during the film growth. Interestingly, the as-prepared films are equilibrated and remain intact (no swelling or shrinking) during temperature variation in the range of 25-45 °C. The average activation energy for complexation between PLL and HA in the multilayers calculated from the Arrhenius plot has been found to be about 0.3 kJ mol(-1) for monomers of PLL. Finally, the following processes known to be dependent on temperature are discussed with respect to the multilayer growth: (i) polymer diffusion, (ii) polymer conformational changes, and (iii) inter-polymer interactions.

Molecular composition of GAG-collagen I multilayers affects remodeling of terminal layers and osteogenic differentiation of adipose-derived stem cells

The effect of molecular composition of multilayers, by pairing type I collagen (Col I) with either hyaluronic acid (HA) or chondroitin sulfate (CS) was studied regarding the osteogenic differentiation of adhering human adipose-derived stem cells (hADSCs). Polyelectrolyte multilayer (PEM) formation was based primarily on ion pairing and on additional intrinsic cross-linking through imine bond formation with Col I replacing native by oxidized HA (oHA) or CS (oCS). Significant amounts of Col I fibrils were found on both native and oxidized CS-based PEMs, resulting in higher water contact angles and surface potential under physiological condition, while much less organized Col I was detected in either HA-based multilayers, which were more hydrophilic and negatively charged. An important finding was that hADSCs remodeled Col I at the terminal layers of PEMs by mechanical reorganization and pericellular proteolytic degradation, being more pronounced on CS-based PEMs. This was in accordance with the higher quantity of Col I deposition in this system, accompanied by more cell spreading, focal adhesions (FA) formation and significant α2β1 integrin recruitment compared to HA-based PEMs. Both CS-based PEMs caused also an increased fibronectin (FN) secretion and cell growth. Furthermore, significant calcium phosphate deposition, enhanced ALP, Col I and Runx2 expression were observed in hADSCs on CS-based PEMs, particularly on oCS-containing one. Overall, multilayer composition can be used to direct cell-matrix interactions, and hence stem cell fates showing for the first time that PEMs made of biogenic polyelectrolytes undergo significant remodeling of terminal protein layers, which seems to enable cells to form a more adequate extracellular matrix-like environment.

STATEMENT OF SIGNIFICANCE

Natural polymer derived polyelectrolyte multilayers (PEMs) have been recently applied to adjust biomaterials to meet specific tissue demands. However, the effect of molecular composition of multilayers on both surface properties and cellular response, especially the fate of human adipose derived stem cells (hADSCs) upon osteogenic differentiation has not been studied extensively, yet. In addition, no studies exist that investigate a potential cell-dependent remodeling of PEMs made of extracellular matrix (ECM) components like collagens and glycosaminoglycans (GAGs). Furthermore, there is no knowledge whether the ability of cells to remodel PEM components may provide an added value regarding cell growth and differentiation. Finally, it has not been explored yet, how intrinsic cross-linking of ECM derived polyelectrolytes that improve the stability of PEMs will affect the differentiation potential of hADSCs. The current work aims to address these questions and found that the type of GAG has a strong effect on properties of multilayers and osteogenic differentiation of hADSCs. Additionally, we also show for the first time that PEMs made of biogenic polyelectrolytes undergo significant remodeling of terminal layers as completely new finding, which allows cells to form an ECM-like environment supporting differentiation upon osteogenic lineage. The finding of this work may open new avenues of application of PEM systems made by layer by layer (LbL) technique in tissue engineering and regenerative medicine.

Self-assembled Biodegradable Nanoparticles and Polysaccharides as Biomimetic ECM Nanostructures for the Synergistic effect of RGD and BMP-2 on Bone Formation

Producing biomimetic extracellular matrix (ECM) is an effective approach to improve biocompatibility of medical devices. In this study, biomimetic ECM nanostructures are constructed through layer-by-layer self-assembling positively charged chitosan (Chi), negatively charged oxidized sodium alginate (OAlg), and positively charged bovine serum albumin (BSA)-based nanoparticles. The BSA-based nanoparticles in the self-assembled films not only result in porous nanostructures similar to natural ECM, but also preserve the activity and realize the sustained release of Bone morphogenetic protein-2 (BMP-2). The results of bone marrow stem cells (BMSCs) culture demonstrate that the penta-peptide glycine-arginine-glycine-aspartate-serine (GRGDS) grafted Chi/OAlg films favor cell adhesion and proliferation. GRGDS and BMP-2 in biomimetic ECM nanostructures synergistically promote BMSC functions and new bone formation. The RGD and BMP incorporated biomimetic ECM coatings could be applied on a variety of biomedical devices to improve the bioactivity and biocompatibility.

Multilayer Membranes of Glycosaminoglycans and Collagen I Biomaterials Modulate the Function and Microvesicle Release of Endothelial Progenitor Cells

Multilayer composite membrane of biomaterials can increase the function of adipose stem cells or osteoprogenitor cells. Recent evidence indicates endothelial progenitor cells (EPCs) and EPCs released microvesicles (MVs) play important roles in angiogenesis and vascular repair. Here, we investigated the effects of biomaterial multilayer membranes of hyaluronic acid (HA) or chondroitin sulfate (CS) and Collagen I (Col I) on the functions and MVs release of EPCs. Layer-by-layer (LBL) technology was applied to construct the multilayer composite membranes. Four types of the membranes constructed by adsorbing either HA or CS and Col I alternatively with different top layers were studied. The results showed that all four types of multilayer composite membranes could promote EPCs proliferation and migration and inhibit cell senility, apoptosis, and the expression of activated caspase-3. Interestingly, these biomaterials increased the release and the miR-126 level of EPCs-MVs. Moreover, the CS-Col I membrane with CS on the top layer showed the most effects on promoting EPCs proliferation, EPCs-MV release, and miR-126 level in EPCs-MVs. In conclusion, HA/CS and Collagen I composed multilayer composite membranes can promote EPCs functions and release of miR-126 riched EPCs-MVs, which provides a novel strategy for tissue repair treatment.

Hydrogels based on collagen and fibrin – frontiers and applications

Hydrogels are a versatile tool for a multitude of applications in biomedical research and clinical practice. Especially collagen and fibrin hydrogels are distinguished by their excellent biocompatibility, natural capacity for cell adhesion and low immunogenicity. In many ways, collagen and fibrin represent an ideal biomaterial, as they can serve as a scaffold for tissue regeneration and promote the migration of cells, as well as the ingrowth of tissues. On the other hand, pure collagen and fibrin materials are marked by poor mechanical properties and rapid degradation, which limits their use in practice. This paper will review methods of modification of natural collagen and fibrin materials to next-generation materials with enhanced stability. A special focus is placed on biomedical products from fibrin and collagen already on the market. In addition, recent research on the in vivo applications of collagen and fibrin-based materials will be showcased.

Functionality of surface-coupled oxidised glycosaminoglycans towards fibroblast adhesion

Glycosaminoglycans are able to bind many growth factors and adhesive proteins, which affect cell activities such as adhesion, migration, growth and differentiation. Chondroitin sulphate, hyaluronan, sulphated hyaluronan and heparin were oxidised here (aldehyde glycosaminoglycans) to generate aldehydes on vicinal hydroxyl groups of the uronic monomers of glycosaminoglycans for subsequent direct covalent binding to amino-terminated model substrata. The properties of modified surfaces were monitored by water contact angle, zeta potential, ellipsometry measurements and atomic force microscopy showing successful immobilisation of aldehyde glycosaminoglycans. Wetting properties and zeta potentials were related to sulphate content of aldehyde glycosaminoglycans with aldehyde heparin as most wettable and negative surface and aldehyde hyaluronan as the least. The thickness of surface layers measured by ellipsometry indicated a predominant side-on immobilisation of all aldehyde glycosaminoglycans. Atomic force microscopy studies showed that immobilisation of aldehyde hyaluronan lead to a rather smooth surface coating while immobilisation of sulphated aldehyde glycosaminoglycans was characterised by a globular appearance of surfaces with higher roughness. The experiments with human fibroblast studying adhesion under serum-free conditions were carried out to learn about bioactivity of aldehyde glycosaminoglycans. It was observed that the increase in sulphation degree of aldehyde glycosaminoglycans was accompanied by increased adhesion and spreading of cells with stronger expression of focal adhesions and cytoskeletal structures. By contrast, cell adhesion and spreading were lower on aldehyde hyaluronan. Immunofluorescence staining of cells in contact with aldehyde hyaluronan revealed a stronger expression of CD44, which can represent an alternative route of cell adhesion. The results show that oxidised glycosaminoglycans can be successfully applied for the development of bioactive surface coatings. The created biomimetic microenvironment may be useful to engineer surfaces of implants and scaffolds for tissue regeneration.