Influences of surface chemistry and swelling of salt-treated polyelectrolyte multilayers on migration of smooth muscle cells

Damage-induced basal epithelial cell migration modulates the spatial organization of redox signaling and sensory neuron regeneration

Epithelial damage leads to early reactive oxygen species (ROS) signaling, which regulates sensory neuron regeneration and tissue repair. How the initial type of tissue injury influences early damage signaling and regenerative growth of sensory axons remains unclear. Previously we reported that thermal injury triggers distinct early tissue responses in larval zebrafish. Here, we found that thermal but not mechanical injury impairs sensory axon regeneration and function. Real-time imaging revealed an immediate tissue response to thermal injury characterized by the rapid Arp2/3-dependent migration of keratinocytes, which was associated with tissue scale ROS production and sustained sensory axon damage. Isotonic treatment was sufficient to limit keratinocyte movement, spatially restrict ROS production, and rescue sensory neuron function. These results suggest that early keratinocyte dynamics regulate the spatial and temporal pattern of long-term signaling in the wound microenvironment during tissue repair.

Damage-induced basal epithelial cell migration modulates the spatial organization of redox signaling and sensory neuron regeneration

Epithelial damage leads to early reactive oxygen species (ROS) signaling, which regulates sensory neuron regeneration and tissue repair. How the initial type of tissue injury influences early damage signaling and regenerative growth of sensory axons remains unclear. Previously we reported that thermal injury triggers distinct early tissue responses in larval zebrafish. Here, we found that thermal but not mechanical injury impairs sensory axon regeneration and function. Real-time imaging revealed an immediate tissue response to thermal injury characterized by the rapid Arp2/3-dependent migration of keratinocytes, which was associated with tissue-scale ROS production and sustained sensory axon damage. Isotonic treatment was sufficient to limit keratinocyte movement, spatially restrict ROS production and rescue sensory neuron function. These results suggest that early keratinocyte dynamics regulate the spatial and temporal pattern of long-term signaling in the wound microenvironment during tissue repair.

BDNF-loaded PDADMAC-heparin multilayers: a novel approach for neuroblastoma cell study

Biomaterial science has contributed tremendously to developing nanoscale materials for delivering biologically active compounds, enhancing protein stability, and enabling its therapeutic use. This paper presents a process of formation of polyelectrolyte multilayer (PEM) prepared by sequential adsorption of positively charged polydiallyldimethylammonium chloride (PDADMAC) and negatively charged heparin sodium salt (HP), from low polyelectrolyte concentration, on a solid substrate. PEM was further applied as a platform for the adsorption of a brain-derived growth factor (BDNF), which is a protein capable of regulating neuronal cell development. The multilayers containing BDNF were thoroughly characterized by electrokinetic (streaming potential measurements, SPM) and optical (optical waveguide lightmode spectroscopy, OWLS) techniques. It was found that BDNF was significantly adsorbed onto polyelectrolyte multilayers terminated by HP under physiological conditions. We further explore the effect of established PEMs in vitro on the neuroblastoma SH-SY5Y cell line. An enzyme-linked immunosorbent assay (ELISA) confirmed that BDNF was released from multilayers, and the use of the PEMs intensified its cellular uptake. Compared to the control, PEMs with adsorbed BDNF significantly reduced cell viability and mitochondrial membrane polarization to as low as 72% and 58%, respectively. HPLC analysis showed that both PDADMAC-terminated and HP-terminated multilayers have antioxidative properties as they almost by half decreased lipid peroxidation in SH-SY5Y cells. Finally, enhanced formation of spheroid-like, 3D structures was observed by light microscopy. We offer a well-characterized PEM with antioxidant properties acting as a BDNF carrier, stabilizing BDNF and making it more accessible to cells in an inhomogeneous, dynamic, and transient in vitro environment. Described multilayers can be utilized in future biomedical applications, such as boosting the effect of treatment by selective anticancer as adjuvant therapy, and in biomedical research for future development of more precise neurodegenerative disease models, as they enhance cellular 3D structure formation.

Facile calcium ion-regulated grafting of dense and highly stretched hyaluronan for selective mediation of cancer cells rolling under high-speed flow

The development of materials that selectively mediate the rolling of cancer cells is important for the high-throughput enrichment of high-speed cancer cells. Here we constructed a dense and stretched low molecular weight hyaluronic acid (HA_9.6k)-modified surface to selectively promote the rolling of CD44-high cancer cells. The HA surface (calcium ion-regulated HA_9.6k surface, Ca-rHA) was fabricated via a calcium ion-regulated method, where calcium ion incorporation induced the shrink of HA_9.6k chains to achieve the highest reported grafting density of about 2.73 ± 0.20 × 10⁴ HA chains μm^-2. Upon the removal of calcium ions, the dense HA_9.6k chains switched to a highly stretched conformation. The high density and flexibility of Ca-rHA bearing abundant binding sites enhanced the rolling of CD44-high cancer cells and reduced the velocity of cells from 1389 µm s^-1 to 99 µm s^-1 (7%), comparable to that of the physiological rolling event and outperforming traditional grafting-to HA and E-selectin, without causing phenotypic changes. When processing complex samples under high-speed flow, Ca-rHA selectively mediated the rolling of cancer cells and enriched their ratio to peripheral blood mononuclear cells from 1:1 to 15:1. As the only reported artificial biomaterial capable of selectively mediating the rolling of cancer cells under a physiological high-speed flow, Ca-rHA holds promise in enriching intact cells for downstream analysis in the clinics by encouraging the surface-cell contacts. STATEMENT OF SIGNIFICANCE: The development of materials that selectively mediate the rolling of cancer cells is important for the high-throughput enrichment of cancer cells rolling under high-speed flow, yet is less reported. To selectively promote the rolling of cancer stem cell marker CD44-high cancer cells, a surface with dense and stretched low molecular weight hyaluronic acid (HA_9.6k) was constructed. With Ca²⁺ regulation, HA_9.6k chains shrank to achieve the highest reported grafting density of 2.73 ± 0.20 × 10⁴ chains μm^-2 and further switched to a highly stretched conformation after the removal of Ca²⁺ ions. As the only reported artificial biomaterial capable of selectively mediating the rolling of cancer cells under a physiological high-speed flow, this Ca²⁺-regulated HA_9.6k surface holds promise in enriching intact cells for downstream analysis in the clinics.

Tubular TPU/SF nanofibers covered with chitosan-based hydrogels as small-diameter vascular grafts with enhanced mechanical properties

Native grafts such as internal mammary artery and saphenous vein are the main choice for coronary artery bypass graft. However, due to the limitations associated with their availability and rapid failure caused by hyperplasia, small diameter tissue-engineered vascular grafts (TEVGs) with sufficient post-implantation patency are urgently demanded as artificial alternatives. In our previous work, we innovatively fabricated a bilayer vascular graft providing appropriate structural and biological properties using electrospinning and freeze-drying methods. It was proved that the mechanical properties of the proposed graft enhanced in comparison with using either of methods individually. Here, we adopted the same methods and incorporated an anticoagulant internal layer (inner diameter 4 mm), comprised of co-electrospun fibers of silk fibroin (SF) and heparinized thermoplastic polyurethane (TPU), and an external highly porous hydrogel fabricated by freeze-drying method. The electrospun layer exhibited strong mechanical properties including superior elastic modulus (4.92 ± 0.11 MPa), suture retention force (6.73 ± 0.83 N), elongation at break (196 ± 4%), and comparable burst pressure (1140 ± 12 mmHg) while the external hydrogel provided SMCs viability. The heparin was released in a sustain manner over 40 days, and the cytocompatibility and blood compatibility of scaffold were approved using MTT assay and platelet adhesion test. Thus, the proposed graft has a potential to be used as an artificial blood vessel scaffold for later in-vivo transplantation.

Self-Patterning Polyelectrolyte Multilayer Films: Influence of Deposition Steps and Drying in a Vacuum

Typically, laterally patterned films are fabricated by lithographic techniques, external fields, or di-block copolymer self-assembly. We investigate the self-patterning of polyelectrolyte multilayers, poly(diallyldimethylammonium) (PDADMA)/poly(styrenesulfonate) (PSS)_short. The low PSS molecular weight (M_w(PSS_short) = 10.7 kDa) is necessary because PSS_short is somewhat mobile within a PDADMA/PSS_short film, as demonstrated by the exponential growth regime at the beginning of the PDADMA/PSS_short multilayer build-up. No self-patterning was observed when the PDADMA/PSS film consisted of only immobile polyelectrolytes. Atomic force microscopy images show that self-patterning begins when the film consists of seven deposited PDADMA/PSS_short bilayers. When more bilayers are added, the surface ribbing evolved into bands, and circular domains were finally observed. The mean distance between the surface structures increased monotonously with the film thickness, from 70 to 250 nm. Scanning electron microscopy images showed that exposure to vacuum resulted in thinning of the film and an increase in the mean distance between domains. The effect is weaker for PSS_short-terminated films than for PDADMA-terminated films. The mechanism leading to domain formation during film build-up and the effect of post-preparation treatment are discussed.

Titanium-Based Alloy Surface Modification with TiO2 and Poly(sodium 4-styrenesulfonate) Multilayers for Dental Implants

Implant placement is an important repair method in dentistry and orthopedics. Increasing efforts have focused on optimizing the biocompatibility and osseointegration properties of titanium (Ti) and Ti-based alloys. In this work, Ti-based alloys were modified by the layer-by-layer (LbL) technique, which is a simple and versatile method for surface modification. The morphology and chemical structure of LbL films of poly(sodium 4-styrenesulfonate) (PSS) and Ti dioxide (TiO₂) nanoparticles were first characterized employing ultraviolet-visible and Fourier-transform infrared spectroscopies as well as atomic force microscopy for further application in Ti-based alloy implants. The changes provoked by the LbL PSS/TiO₂ film on the Ti-based alloy surfaces were then investigated by scanning electron microscopy and micro-Raman techniques. Finally, in vivo tests (immunolabeling and biomechanical analysis) performed with screw implants in rats suggested that PSS/TiO₂ multilayers promote changes in both topography and chemical surface properties of the screw, providing beneficial effects for osteoblast activity. This simple and relatively low-cost growth process can open up possibilities to improve dental implants and, probably, bone implants in general.

Development and characterization of a suturable biomimetic patch for cardiac applications

3D scaffolds used to repair damaged tissues should be able to mimic both composition and functions of natural extracellular matrix, which is mainly composed of polysaccharides and proteins. In our previous research new biomimetic sponges, based on blends of alginate with gelatin, were produced and characterized for myocardial tissue engineering applications. It was observed that these scaffolds can potentially function as a promising cardiac extracellular matrix substitute, but a reinforcement is required to improve their suturing properties. Aim of the present work was the development of a suturable biomimetic patch by the inclusion of a synthetic mesh within an alginate/gelatin scaffold. The mesh, produced by dry spinning, was made of eight superimposed layers of polycaprolactone microfibers, each one rotated of 45° with respect to the adjacent one. Reinforced scaffolds were obtained through the use of a mold, specially designed to place the fibrous mesh exactly in the center of the sponge. Both the reinforcement mesh and the reinforced scaffold were characterized. A perfect integration between the mesh and the sponge was observed. The fibrous mesh reduced the capacity of the sponge to absorb water, but the degree of hydrophilicity of the material was still comparable with that of natural cardiac tissue. The reinforced system showed a suitable stability in aqueous environment and it resulted much more resistant to suturing than not reinforced scaffold and even than human arteries. Polycaprolactone mesh was not cytotoxic and the reinforced scaffold was able to support cardiomyocytes adhesion and proliferation. Overall, the obtained results confirmed that the choice to modify the alginate/gelatin sponges through the insertion of an appropriate reinforcement system turned out to be correct in view of their potential use in myocardial tissue engineering.

Organic-to-water dispersible Mn:ZnS–ZnS doped core–shell quantum dots: synthesis, characterization and their application towards optical bioimaging and a turn-off fluorosensor

Dot-in-dot core/shell Mn:ZnS/ZnS QDs as a good fluorescent agent for bioimaging and a turn-off fluorescent probe for detection of heavy metal ions.

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.

Induction of cell self-organization on weakly positively charged surfaces prepared by the deposition of polyion complex nanoparticles of thermoresponsive, zwitterionic copolymers

We have developed inducible cell self-organization through weakly positively charged culture surfaces. In this study, a thermoresponsive and zwitterionic copolymer comprised of N,N-dimethylaminoethyl methacrylate (DMAEMA) and methacrylic acid (MA) (PDMAEMA-co-PMA; Mn: ∼9.7 × 10⁴ g/mol; PDMAEMA/PMA ratio: 10) was designed for inducing cell self-organization. The copolymer formed single polymer-derived polyion complex (sPIC) nanoparticles following dissolution in an aqueous solution. The sPIC nanoparticles had a positive charge (ca. 25 mV). Self-organization occurred in adipose-derived vascular stromal cell monolayers cultivated on sPIC-deposited surfaces. There were dramatic morphological changes of these cells with the formation of capillary-like networks and single-cell aggregates with little cytotoxicity. This was a significant improvement compared with cells grown on previously developed surfaces deposited with PIC, a mixture of PDMAEMA and plasmid DNA. Thus, sPICs of PDMAEMA-co-PMA may allow for the accurate evaluation of a variety of cell behaviors with less cytotoxicity, and may facilitate additional potential medical applications such as cell-based therapy and drug discovery. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1009-1015, 2017.

Growth and motility of human skin fibroblasts on multilayer strong polyelectrolyte films

Polyelectrolyte multilayers (PEMs) have found application in modifying material surfaces to make them adhesive or non-adhesive for animal cells. However, PEMs made of strong polyelectrolytes are not fully recognized in the literature. This study focuses on the interplay between the properties of PEM assembled from strong polyelectrolytes and cell adhesion and motility. Strong polycations (with quaternary ammonium groups) and a polyanion (with sulfonate groups) were obtained by modification of poly(allylamine hydrochloride) (PAH). Two types of multilayer films were assembled from these PAH derivatives and used to investigate the behavior of human skin fibroblasts (HSFs). The effect of surface charge, hydrophobicity, and film thickness on adhesion of HSFs in a serum-containing medium was studied with immunofluorescence microscopy. The results showed that adhesion of HSFs was strongly depended on the chemical functions of the terminal layer, whereas the wettability was not important. The surface of PEM can be strongly cytophobic (the quaternary ammonium terminal groups) or strongly cytophilic (the sulfonate terminal groups). Finally, the motile activity of HSFs seeded on glass coated with a varying number of polymer layers was investigated. It was demonstrated using an in vitro model that coating the substrate with only two polymer layers can considerably increase the average speed of HSFs movement and stimulate cell migration into the wound.

Gelatin modified ultrathin silk fibroin films for enhanced proliferation of cells

Silk fibroin (SF) films were modified with gelatin (G) to explore if such SF/G films could enhance the surface biocompatibility of silk as cell growth biomaterials. Ultrathin films were coated from aqueous SF solutions pre-mixed with different amounts of G. It was found that the SF/G blended films after methanol treatment were highly stable in physiological conditions. The incorporation of G smoothed the surface morphology of the SF/G films formed. Surface-exposed RGD sequences were successfully identified on the SF/G films through specific recognition of an integrin-mimicking peptide (bearing the sequence of CWDDGWLC). Cell culture experiments with 3T3 fibroblasts demonstrated that SF/G films with 1.2-20% (w/w) G gave clear improvement in promoting cell attachment and proliferation over pure SF films. Films containing 10-20% (w/w) of G showed cell attachment and growth even superior to the pure G films. The differences as observed from this study suggest that due to the lack of mechanical strength associated with its high solubility, G could not work alone as a cell growth scaffold. The enhanced cellular responses from the blended SF/G films must result from improvement in film stability arising from SF and in cytocompatibility arising from G. The results thus indicate the potential of the SF/G blends in tissue engineering and biomedical engineering where physical and biological properties could be manipulated via mixing either as bulk biomaterials or for coating purposes.

Endothelial responses of magnesium and other alloying elements in magnesium-based stent materials

Biodegradable tailored magnesium (Mg) alloys are some of the most promising scaffolds for cardiovascular stents. During the course of degradation after implantation, all the alloying elements in the scaffold will be released to the surrounding vascular tissues. However, fundamental questions regarding the toxicity of alloying elements towards vascular cells, the maximum amount of each element that could be used in alloy design, or how each of the alloying elements affects vascular cellular activity and gene expression, are still not fully answered. This work systematically addressed these questions by revealing how application of different alloying elements commonly used in Mg stent materials influences several indices of human endothelial cell health, i.e., viability, proliferations, cytoskeletal reorganizations, migration, and the gene expression profile. The overall cell viability and proliferation showed a decreasing trend with increasing concentrations of the ions, and the half maximal effective concentrations (EC50) for each element were determined. When applied at a low concentration of around 10 mM, Mg had no adverse effects but improved cell proliferation and migration instead. Mg ions also altered endothelial gene expression significantly in a dose dependent manner. Most of the changed genes are related to angiogenesis and the cell adhesion signaling pathways. Findings from this work provide useful information on maximum safe doses of these ions for endothelial cells, endothelial responses towards these metal ions, and some guidance for future Mg stent design.

Adsorption of plasma proteins and fibronectin on poly(hydroxylethyl methacrylate) brushes of different thickness and their relationship with adhesion and migration of vascular smooth muscle cells

The surface-grafted poly(hydroxylethyl methacrylate) (PHEMA) molecules were demonstrated to show a brush state regardless of their molecular length (molecular weight). Adsorption of proteins from 10% fetal bovine serum (FBS), fibronectin (Fn) and bovine serum albumin (BSA) was quantified by ellipsometry, revealing that the amounts of FBS and Fn decreased monotonously along with the increase of PHEMA thickness, whereas not detectable for BSA when the PHEMA thickness was larger than 6 nm. Radio immunoassay found that the adsorption of Fn from 10% FBS had no significant difference regardless of the PHEMA thickness. However, ELISA results showed that the Arg-Gly-Asp (RGD) activity of adsorbed Fn decreased with the increase of PHEMA thickness. By comparison of cellular behaviors of vascular smooth muscle cells (VSMCs) being cultured in vitro in the normal serum-containing medium and the Fn-depleted serum-containing medium, the significant role of Fn on modulating the adhesion and migration of VSMCs was verified. Taking account all the results, the Fn adsorption model and its role on linking the biomaterials surface to the VSMCs behaviors are proposed.

Development of biocompatible and proton-resistant quantum dots assembled on gelatin nanospheres

In this study, biocompatible and proton-resistant CdSe quantum dots (QDs) assembled on gelatin nanospheres (GNs) have been synthesized by combining the two-step desolvation method with the layer-by-layer assembly technique. The core-shell fluorescent gelatin nanosphere consists of a gelatin core and a four-layer shell of hydrophilic CdSe QDs assembled through polyelectrolytes (PE). The morphology, microstructures, and photostability of the hybrid spheres were further investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorospectrometery, and confocal fluorescent microscopy (CFM), respectively. The average diameter of the hybrid QDs-gelatin nanospheres (QDs-GNs) is estimated at 484 ± 40 nm. Our results indicate that the 20 ± 5 nm of the shell is attributed to the four-layer of CdSe QDs assembled through the PE. QD-GNs show a strong photoluminescence with the maximum emission (λ(em)) at 613 nm at the excitation wavelength of 470 nm. The core-shell QDs-GNs are able to resist quenching in acidic solution (pH < 4). Furthermore, core-shell QDs-GNs show a longer lifetime in a broad range of pH values, from 9 to 1. The calculated average lifetime (τ(ave)) of QDs-GNs is about 889 ± 23 ps, which is 3-fold longer than that of MUA-QDs (263 ± 10 ps) at pH 7.0. The enhanced lifetime of QDs-GNs is almost 9 times of that of CdSe QDs when pH value is 1. Meanwhile, the cell viability study shows that no significant toxic effect is imposed on the NIH/3T3 mouse fibroblast cell line when the concentration of QD-GNs is below 5 mg/mL. It is expected that this new biocompatible fluorescent nanospheres could be an excellent alternative fluorescent imaging agent for cell labeling, especially in acidic conditions.

The effect of electrically charged polyion complex nanoparticle-coated surfaces on adipose-derived stromal progenitor cell behaviour

Surface characteristics of biomaterials such as wettability, rigidity, roughness, and electrical charge affect the fate of transplanted cells such as progenitor cells or stem cells for use in regenerative medicine. Of these, the effects of surface electrical charges on cellular behaviour such as adhesion, proliferation, and differentiation are not well understood. We prepared precisely charged culture surfaces ranging from -28 mV to +21 mV, simply by surface deposition of polyion complex nanoparticles prepared by mixing a positively charged thermoresponsive homopolymer, poly(N,N-dimethylaminoethyl methacrylate), with negatively charged plasmid DNA at various charge ratios. Drastic morphological changes of adipose-derived vascular progenitor cells were generated on the positively charged surface of organized forms at +19 mV. Capillary-like networks or single aggregates of these cells were selectively created depending on cell seeding density. Our findings offer new insights that may aid develop stem cell-processing techniques for use in regenerative medicine.

Directional migration of vascular smooth muscle cells guided by a molecule weight gradient of poly(2-hydroxyethyl methacrylate) brushes

Directional migration of cells mediated by gradient cues in vitro can mimic the corresponding biological events in vivo and thereby provides a way to disclose the cascade responses in tissue regeneration processes and to develop novel criteria for design of tissue-inductive biomaterials. In this work, a molecular weight gradient of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes with a thickness ranging from 3 to 30 nm and slopes of 0.8-3.2 nm/mm were fabricated by using surface-initiated atom transfer radical polymerization (ATRP) and a dynamically controlled reaction process. The PHEMA gradients were characterized by X-ray photoelectron spectrometry (XPS) and ellipsometry. The adhesion number, spreading area, adhesion force, and expression of focal adhesion and actin fibers of vascular smooth muscle cells (VSMCs) decreased along with the increase of the PHEMA brushes length. The VSMCs exhibited preferential orientation and enhanced directional migration toward the direction of reduced PHEMA thickness, whose extent was dependent on the gradient slope and polymer thickness. Most of the cells were oriented, and 87% of the cells moved directionally at the optimal conditions.