The effect of surface microtopography of poly(dimethylsiloxane) on protein adsorption, platelet and cell adhesion

Chemical homogeneous poly(dimethylsiloxane) (PDMS) surface with dot-like protrusion pattern was used to investigate the individual effect of surface microtopography on protein adsorption and subsequent biological responses. Fibrinogen (Fg) and fibronectin (Fn) were chosen as model proteins due to their effect on platelet and cell adhesion, respectively. Fg labeled with ¹²⁵I and fluorescein isothiocyanate (FITC) was used to study its adsorption on flat and patterned surfaces. Patterned surface has a 46% increase in the adsorption of Fg when compared with flat surface. However, the surface area of the patterned surface was only 8% larger than that of the flat surface. Therefore, the increase in the surface area was not the only factor responsible for the increase in protein adsorption. Clear fluorescent pattern was visualized on patterned surface, indicating that adsorbed Fg regularly distributed and adsorbed most on the flanks and valleys of the protrusions. Such distribution and local enrichment of Fg presumably caused the specific location of platelets adhered from platelet-rich plasma (PRP) and flowing whole blood (FWB) on patterned surface. Furthermore, the different combination of surface topography and pre-adsorbed Fn could influence the adhesion of L929 cells. The flat surface with pre-adsorbed Fn was the optimum substrate while the virgin patterned surface was the poor substrate in terms of L929 cells spread.     

Photopolymerized injectable RGD-modified fumarated poly(ethylene glycol) diglycidyl ether hydrogels for cell growth

In this study, photopolymerized hydrogels of fumarated poly(ethylene glycol) diglycidyl-co- poly(ethylene glycol) diacrylate have been synthesized and modified with cell adhesion peptide, Arg-Gly-Asp (RGD). The structural and mechanical properties of the hydrogels are found to be poly(ethylene glycol) diacrylate (PEGDA) dependent. The percentage of gelation is increased from 72 to 89 wt.-% when the amount of the crosslinker co-monomer (PEGDA) in the hydrogel formulation is increased from 20 to 40 wt.-%. In the present case, the equilibrium mass swelling is decreased from 216 to 93%. The viscosities of the uncured formulations have also been measured and likewise, the results were influenced by the increasing amount of PEGDA that reduced the value from 83 to 36 cP. The compressive modulus of the prepared hydrogels was improved with the addition of the PEGDA. Cell growth experiments have been performed by comparing the properties of the hydrogels with and without RGD units. The results show that RGD units enhance the adhesion of cells to the surface of the hydrogels. SEM-EDS studies reveal that nitrogen and calcium are produced on the osteoblast-seeded surface of the scaffold within the culture time period. [Figure: see text].     

Simple poly(dimethylsiloxane) surface modification to control cell adhesion

Poly(dimethylsiloxane) (PDMS) has a long history of exploitation in a variety of biological and medical applications. Particularly in the past decade, PDMS has attracted interest as a material for the fabrication of microfluidic biochip. The control of cell adhesion on a PDMS surface is important in many microfluidic applications such as cell culture or cell‐based chemicals/drug testing. Unlike many complicated approaches, this study reports simple methods of PDMS surface modification to effectively inhibit or conversely enhance cell adhesion on a PDMS surface using Pluronic surfactant solution and poly‐L ‐lysine, respectively. This research basically succeeded our prior work to further confirm the long‐term capability of 3% Pluronic F68 surfactant to suppress cell adhesion on a PDMS surface over a 6‐day cell culture. Microscopic observation showed that the treated PDMS surface created an unfavorable interface, where chondrocytes seemed to clump together on day 2 and 6 after chondrocyte seeding, and there was no sign of chondrocyte spreading. On the opposite side, results demonstrated that the poly‐L ‐lysine‐treated surface significantly increased fibroblast adhesion by 32% in contrast to the untreated PDMS, which is comparable to the commercial cell‐culture‐grade microplate. However, fibronectin treatment did not have such an effect. All these fundamental information is found useful for any PDMS‐related application. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of stable micropatterns of gold on cell-adhesion-resistant hydrogels assisted by a hetero-bifunctional macromonomer linker

Surface patterning is very useful in biomaterial studies, yet it is not easy to prepare a micropattern with cell-adhesion contrast that is stable in a wet environment. Recently, a platform technique of transfer photolithography was invented to fabricate stable metal microarrays on the surface of a cell-adhesion resistant and mechanically biomimetic poly(ethylene glycol) hydrogel; the linker is the key chemical in such a transfer strategy. This article reports the design and synthesis of a hetero-bifunctional macromonomer linker with a thiol group at one end and an acryloyl group at the other end. The bifunctional linker was characterized by GPC and ¹H NMR, and the average number of thiol groups in the bifunctional linker was detected by Ellman’s reagent. The regent stability under wet conditions was also confirmed by the model reactants. The resultant micropatterned surfaces are meaningful for future studies of cell behaviors on mechanically biomimetic matrixes.     

Interaction of hepatocytes with polyelectrolyte complex(I): the effect of nonspecific interaction on adhesion of the cell

The adhesion of hepatocytes to polyelectrolyte complex (PEC), prepared by mixing of aqueous solutions of polycation and polyanion, is discussed. Four PECs, poly((dimethyliminio)ethylene(dimethyliminio)methylene‐1,4‐phenylenemethylene dichloride)–poly(acrylic acid)2X–(PAA), 2X‐poly(acrylic acid–co‐2‐ethylhexylacrylate(COA), 2X‐poly(acrylicacid–co‐butylacrylate) (CBA) and 2X‐poly(acrylic acid–co‐laurylacrylate)(CLA) were prepared. Hydrophobic properties of these PECs increased in the order of 2X–PAA < 2X–COA < 2X–CLA ≤ 2X–CBA. About all the hepatocytes adhered rapidly to various PECs even in the absence of serum, while fewer cells adhered to polystrene (tissue culture grade) dishes. At 37 °C (biological condition) about 70–80% of cells adhered to a collagen‐coated dish, but at 4 °C (nonbiological condition), no cell adhered to it. Nonactive cells (prepared by a single cycle of freezing and thawing) did not adhere to collagen, either. On the contrary about 40% of cells adhered to PEC‐coated dishes even at 4 °C, and nonactive cells also adhered to them. Cytocharosine B and colchicine, which are known as inhibitors of the polymerization of intracellular matrix, did not prevent cell adhesion to PECs. From these results it was suggested that hepatocytes adhered to PEC‐coated dishes mainly through a nonbiological interaction. Copyright © 1999 John Wiley & Sons, Ltd.     

Control of endothelial cell adhesion to polymer surface by ion implantation

The bio‐compatibility of ion implanted polymers has been studied by means of in vitro attachment measurements of bovine aorta endothelial cells. The specimens used were polystyrene (PS), polyethylene (PE), polypropylene (PP) and expanded polytetrafluoroethylene (ePTFE). He⁺ and Ne⁺ ion implantation were performed at an energy of 150 keV with fluences between 1 × 10 ¹³ to 1 × 10 ¹⁷ ions/cm ² at room temperature. Wettability was estimated by means of a sessile drop method. The chemical and physical structures of ion implanted polymers were investigated by contact angle measurements, atomic force microscopy and X‐ray photoelectron spectroscopic analysis in relation to cell attachment behavior. The strength of cell attachment on ion implanted specimens at static and under flow conditions was also measured. Ion implanted PP and ePTFE were found to exhibit remarkably higher adhesion and spreading of endothelial cells than non‐implanted specimens. In contrast to these findings, ion implanted PS and PE only demonstrated a little improvement of cell adhesion in this assay. Copyright © 2001 John Wiley & Sons, Ltd.     

Stainless steel modified with poly(ethylene glycol) can prevent protein adsorption but not bacterial adhesion

The surface of AISI 316 grade stainless steel (SS) was modified with a layer of poly(ethylene glycol) (PEG) (molecular weight 5000) with the aim of preventing protein adsorption and bacterial adhesion. Model SS substrates were first modified to introduce a very high density of reactive amine groups by the adsorption of branched poly(ethylenimine) (PEI) from water. Methoxy-terminated aldehyde-poly(ethylene glycol) (M-PEG-CHO) was then grafted onto the PEI layers using reductive amination at the lower critical solution temperature (LCST) of the PEG in order to optimize the graft density of the linear PEG chains. The chemical composition and uniformity of the surfaces were determined using X-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-SSIMS) in the imaging mode. The effects of PEI concentration and different substrate pre-cleaning methods on the structure and stability of the final PEG layer was examined. Piranha solution proved to be the most effective method for removing adventitious hydrocarbon contamination, compared to cleaning with ultrasonication in organic solvents, and was the SS substrate that produced the most stable and thickest PEI layer. The surface density of PEI was shown to increase with increasing PEI concentration (up to 30 mg/ml), as determined from XPS measurements, and subsequently produced the PEG layer with the highest density of attached chains. In model experiments using β-lactoglobulin no protein adsorption was detected on the optimized PEG surface as determined by XPS and ToF-SSIMS analysis. However, neither the adhesion of a Gram-negative (Pseudomonas sp.) nor a Gram-positive (Listeria monocytogenes) bacterium was affected by the coating as equal numbers adhered to all surfaces tested. Our results show that preventing protein adsorption is not a prerequisite stopping bacterial adhesion, and that other mechanisms most likely play a role.     

Poly(N-isopropylacrylamide)-based thermo-responsive surfaces with controllable cell adhesion

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermo-responsive surfaces can switch their wettability (from wettable to non-wettable) and adhesion (from sticky to non-sticky) according to external temperature changes. These smart surfaces with switchable interfacial properties are playing increasingly important roles in a diverse range of biomedical applications; these controlling cell-adhesion behavior has shown great potential for tissue engineering and disease diagnostics. Herein we reviewed the recent progress of research on PNIPAAm-based thermo-responsive surfaces that can dynamically control cell adhesion behavior. The underlying response mechanisms and influencing factors for PNIPAAm-based surfaces to control cell adhesion are described first. Then, PNIPAAm-modified two-dimensional flat surfaces for cell-sheet engineering and PNIPAAm-modified three-dimensional nanostructured surfaces for diagnostics are summarized. We also provide a future perspective for the development of stimuli-responsive surfaces.     

Synthesis of a difunctional orthogonal coupler for the preparation of carbohydrate-functionalized sP(EO-stat-PO) hydrogels

The synthesis and characterization of a new difunctional coupler (4) based on trimethylolpropane (TMP) are described. The coupler is used to connect biologically active N-acetylglucosamine (GlcNAc) on amino-reactive microtiter plates and on star-shaped poly[(ethylene oxide)-stat-(propylene oxide)] hydrogel layers in microtiter plates. The biological activity of immobilized carbohydrates is determined using an enzyme-linked lectin assay.     

Synthesis and characterization of thermoresponsive poly(ethylene glycol)‐based hydrogels and their magnetic nanocomposites

Temperature‐responsive hydrogels are one of the most widely studied types of stimuli‐responsive hydrogel systems. Their ability to transition between their swollen and collapsed states makes them attractive for controlled drug delivery, microfluidic devices, and biosensor applications. Recent work has shown that poly(ethylene glycol) (PEG) methacrylate polymers are temperature‐responsive and exhibit a wide range of lower critical solution temperatures based on the length of ethylene glycol units in the macromer chain. The addition of iron oxide nanoparticles into the hydrogel matrix can provide the ability to remotely heat the gels upon exposure to an alternating magnetic field (AMF). In this work, diethylene glycol (n = 2) methyl ether methacrylate and PEG (n = 4.5) methyl ether methacrylate copolymers were polymerized into hydrogels with 5 mol % PEG 600 (n = 13.6) dimethacrylate as the crosslinker along with 5 wt % iron oxide nanoparticles. Volumetric swelling studies were completed from 22 to 80 °C and confirmed the temperature‐responsive nature of the hydrogel systems. The ability of the gels to collapse in response to rapid temperature changes when exposed to an AMF was demonstrated showing their potential use in biomedical applications such as controlled drug delivery and hyperthermia therapy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3229–3235, 2010     

Poly(vinylpyrrolidone-b-styrene) block copolymers tethered surfaces for protein adsorption and cell adhesion regulation

Poly(vinylpyrrolidone-b-styrene) (PVP-b-PS) diblock copolymers tethered to glass surfaces were prepared, and the effects on protein adsorption and cellular behavior to the glass and the modified glass surfaces investigated. The PVP-b-PS grafting process was confirmed by water contact angle and XPS measurements. The results obtained for the water contact angles suggest that there are two phases that coexist on the PVP-b-PS block copolymer tethered surface, under aqueous conditions. Although the PVP-b-PS surface possessed, to some extent, a protein resistant property, following introduction of the PS segment to the end of tethered PVP, both fibrinogen and lysozyme adsorption were increased significantly. The PVP-b-PS modified surface, based on Western-blot analysis, appeared to have the greatest amount of surface bound vitronectin, however the conformation of the adsorbed vitronectin may have subsequently been affected by the surface tethered copolymer as was suggested by cell culture results. From these results, we proposed that protein adsorption and cell adhesion can be regulated by tuning the chemical compositions of diblock copolymers tethered to surfaces.     

Homophilic interaction of the L1 family of cell adhesion molecules

Homophilic interaction of the L1 family of cell adhesion molecules plays a pivotal role in regulating neurite outgrowth and neural cell networking in vivo. Functional defects in L1 family members are associated with neurological disorders such as X-linked mental retardation, multiple sclerosis, low-IQ syndrome, developmental delay, and schizophrenia. Various human tumors with poor prognosis also implicate the role of L1, a representative member of the L1 family of cell adhesion molecules, and ectopic expression of L1 in fibroblastic cells induces metastasis-associated gene expression. Previous studies on L1 homologs indicated that four N-terminal immunoglobulin-like domains form a horseshoe-like structure that mediates homophilic interactions. Various models including the zipper, domain-swap, and symmetry-related models are proposed to be involved in structural mechanism of homophilic interaction of the L1 family members. Recently, cryo-electron tomography of L1 and crystal structure studies of neurofascin, an L1 family protein, have been performed. This review focuses on recent discoveries of different models and describes the possible structural mechanisms of homophilic interactions of L1 family members. Understanding structural mechanisms of homophilic interactions in various cell adhesion proteins should aid the development of therapeutic strategies for L1 family cell adhesion molecule-associated diseases.     

Morphological and mechanical properties of tannic acid/PAAm semi-IPN hydrogels for cell adhesion

A series of hydrogels were fabricated from tannic acid (TA), a typical plant polyphenol widely present in wood, and polyacrylamide (PAAm) by semi-IPN and cryogelation techniques. The introduction of TA into the PAAm network endows the system with enhanced cell adhesion properties. The cryogels with open interconnected macropores had a superfast swelling rate and a high swelling ratio, as well as high elasticity in response to compression. The degradation of the hydrogels can be tuned by modulating the content of cross-linker poly(ethylene glycol) diacrylate (PEGDA). Cytotoxicity results revealed that the hydrogels were non-toxic to COS-7 cells. All these results suggested that TA/PAAm semi-IPN hydrogels have great potential for applications in tissue engineering.     

On the swelling behavior of poly(N-Isopropylacrylamide) hydrogels exposed to perfluoroalkyl acids

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.     

Interaction of catalase with cationic hydrogels: Influence of pH,kinetics of process and isotherms of adsorption

The adsorption interaction of catalase Penicillium vitale with cationic polymer hydrogels prepared from the vinyl ether of monoethanolamine was studied at various pHs of phosphate buffer solution, interaction times and enzyme concentrations. The hydrogels behaved as anion exchange swellable gel adsorbents. The formation of stable polymer–protein complexes with high enzymatic activity has been shown. The dependence of the interaction degree of protein macromolecules on swelling coefficients of gel has been found. The isotherms of protein adsorption indicate the thermodynamical irreversibility of the process. Copyright © 1999 John Wiley & Sons, Ltd.     

Suppression of cell and platelet adhesion to star-shaped 8-armed poly(ethylene glycol)-poly(L-lactide) block copolymer films

To explore the potential of a star-shaped 8-armed poly(ethylene glycol)35K-block-poly(L-lactide)37K (8-armed PEG35K-b-PLLA37K: M(n) of PEG = 35 000, M(n) of PLLA = 37 000) film as a novel bioabsorbable adhesion-prevention membrane, the water structure, surface contact angle, protein adsorption, and cell and platelet anti-adhesion properties of such a hydrated film are investigated. Based on the results, it is found that the 8-armed PEG35K-b-PLLA37K film exhibits a biologically inert surface, which is the result of a large number of PEG chains and a free water layer on the film surface. This leads to a reduction in protein absorption and cell and platelet adhesion onto the film surface. This implies that the star-shaped 8-armed PEG35K-b-PLLA37K film can be utilized as a novel bioabsorbable adhesion-prevention membrane.     

Fabrication of substrates with defined mechanical properties and topographical features for the study of cell migration

Both substrate topography and substrate mechanical properties are known to influence cell behavior, but little is known about how they act in concert. Here, a method is presented to introduce topographical features into PA hydrogel substrates that span a wide range of physiological E values. Gel swelling plays a significant role in the fidelity of protruding micromolded features, with the most efficient pattern transfer occurring at a crosslinking concentration equal to or greater than ≈5%. In contrast, swelling does not influence the spacing fidelity of microcontact printed islands of collagen on 2D PA substrates. BAECs cultured on micromolded PA substrates exhibit contact guidance along ridges patterned for all E tested.     

Poly(2‐oxazoline) hydrogels crosslinked with aliphatic bis(2‐oxazoline)s: Properties,cytotoxicity, and cell cultivation

A series of hydrogels from 2‐ethyl‐2‐oxazoline and three bis(2‐oxazoline) crosslinkers—1,4‐butylene‐2,2′‐bis(2‐oxazoline), 1,6‐hexamethylene‐2,2′‐bis(2‐oxazoline), and 1,8‐octamethylene‐2,2′‐bis(2‐oxazoline)—are prepared. The hydrogels differ by the length of aliphatic chain of crosslinker and by the percentage of crosslinker (2–10%). The influence of the type and the percentage of the crosslinker on swelling properties, mechanical properties, and state of water is studied. The equilibrium swelling degree in water ranges from 2 to 20. With a proper selection of the crosslinker, Young's modulus can be varied from 10 kPa to almost 100 kPa. To evaluate the potential for medical applications, the cytotoxicity of extracts and the contact toxicity toward murine fibroblasts are measured. The hydrogels with the crosslinker containing a shorter aliphatic exhibit low toxicity toward fibroblast cells. Moreover, the viability and the proliferation of pancreatic β‐cells incubated inside hydrogels for 12 days are analyzed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1548–1559     

NMR study of the structure and properties of poly(MMA-co-VP) crosslinked hydrogels

¹H- and ¹³C-NMR techniques were used to study the microscopic structure of NMA/VP copolymer hydrogels. Evidence was obtained for a plasticization effect of MMA chains by VP. An original ¹H-NMR approach revealed the existence of several types of water with various degree of bounding to the polymer network, a conclusion that is corroborated by a complementary ¹³C-NMR study. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3619–3625, 1997     

Using an electrical potential to reversibly switch surfaces between two states for dynamically controlling cell adhesion

Smart surfaces presenting both antifouling molecules with a charged functional group at their distal end, and molecules that are terminated by RGD peptides for cell adhesion, were fabricated and characterized (see picture). By applying potentials of +300 or -300?mV, the surfaces could be dynamically switched to make the peptide accessible or inaccessible to cells.