Using Polymers to Impart Lubricity and Biopassivity to Surfaces: Are These Properties Linked?

Polymer brushes have been widely applied for the reduction of both friction and non‐specific protein adsorption. In many (but not all) applications, such as contact lenses or medical devices, this combination of properties is highly desirable. Indeed, for many polymer‐brush systems, lubricity and resistance to biofouling appear to go hand in hand, with modifications of brush architecture, for example, leading to a similar degree of enhancement (or degradation) in both properties. In the case of poly(ethylene glycol) (PEG) brushes, this has been widely demonstrated. There are, however, examples where this behavior breaks down. In systems where linear brushes are covalently crosslinked during surface‐initiated polymerization (SIP), for example, the presence and the chemical nature of links between grafted chains might or might not influence biopassivity of the films, while it always causes an increment in friction. Furthermore, when the grafted‐chain topology is shifted from linear to cyclic, chemically identical brushes show a substantial improvement in lubrication, whereas their protein resistance remains unaltered. Architectural control of polymer brush films can provide another degree of freedom in the design of lubricious and biopassive coatings, leading to new combinations of surface properties and their independent modulation.     

Effects of Grafting Density and Film Thickness on the Adhesion of Staphylococcus epidermidis to Poly(2‐hydroxy ethyl methacrylate) and Poly(poly(ethylene glycol)methacrylate) Brushes

Thin polymer films that prevent the adhesion of bacteria are of interest as coatings for the development of infection‐resistant biomaterials. This study investigates the influence of grafting density and film thickness on the adhesion of Staphylococcus epidermidis to poly(poly(ethylene glycol)methacrylate) (PPEGMA) and poly(2‐hydroxyethyl methacrylate) (PHEMA) brushes prepared via surface‐initiated atom transfer radical polymerization (SI‐ATRP). These brushes are compared with poly(ethylene glycol) (PEG) brushes, which are obtained by grafting PEG onto an epoxide‐modified substrate. Except for very low grafting densities (ρ = 1%), crystal violet staining experiments show that the PHEMA and PPEGMA brushes are equally effective as the PEG‐modified surfaces in preventing S. epidermis adhesion and do not reveal any significant variations as a function of film thickness or grafting density. These results indicate that brushes generated by SI‐ATRP are an attractive alternative to grafted‐onto PEG films for the preparation of surface coatings that resist bacterial adhesion.

     

Tuning the Surface of Nanoparticles: Impact of Poly(2‐ethyl‐2‐oxazoline) on Protein Adsorption in Serum and Cellular Uptake

Due to the adsorption of biomolecules, the control of the biodistribution of nanoparticles is still one of the major challenges of nanomedicine. Poly(2‐ethyl‐2‐oxazoline) (PEtOx) for surface modification of nanoparticles is applied and both protein adsorption and cellular uptake of PEtOxylated nanoparticles versus nanoparticles coated with poly(ethylene glycol) (PEG) and non‐coated positively and negatively charged nanoparticles are compared. Therefore, fluorescent poly(organosiloxane) nanoparticles of 15 nm radius are synthesized, which are used as a scaffold for surface modification in a grafting onto approach. With multi‐angle dynamic light scattering, asymmetrical flow field‐flow fractionation, gel electrophoresis, and liquid chromatography‐mass spectrometry, it is demonstrated that protein adsorption on PEtOxylated nanoparticles is extremely low, similar as on PEGylated nanoparticles. Moreover, quantitative microscopy reveals that PEtOxylation significantly reduces the non‐specific cellular uptake, particularly by macrophage‐like cells. Collectively, studies demonstrate that PEtOx is a very effective alternative to PEG for stealth modification of the surface of nanoparticles.

     

Facile Fabrication of Bio- and Dual-Functional Poly(2-oxazoline) Bottle-Brush Brush Surfaces

Poly(2-oxazoline)s (POx) bottle-brush brushes have excellent biocompatible and lubricious properties, which are promising for the functionalization of surfaces for biomedical devices. Herein, a facile synthesis of POx is reported which is based bottle-brush brushes (BBBs) on solid substrates. Initially, backbone brushes of poly(2-isopropenyl-2-oxazoline) (PIPOx) were fabricated via surface initiated Cu⁰ plate-mediated controlled radical polymerization (SI-Cu⁰CRP). Poly(2-methyl-2-oxazoline) (PMeOx) side chains were subsequently grafted from the PIPOx backbone via living cationic ring opening polymerization (LCROP), which result in ≈100 % increase in brush thickness (from 58 to 110 nm). The resultant BBBs shows tunable thickness up to 300 nm and high grafting density (σ) with 0.42 chains nm⁻². The synthetic procedure of POx BBBs can be further simplified by using SI-Cu⁰CRP with POx molecular brush as macromonomer (M_n=536 g mol⁻¹, PDI=1.10), which results in BBBs surface up to 60 nm with well-defined molecular structure. Both procedures are significantly superior to the state-of-art approaches for the synthesis of POx BBBs, which are promising to design bio-functional surfaces.     

Selective Uptake of Cylindrical Poly(2‐Oxazoline) Brush‐AntiDEC205 Antibody‐OVA Antigen Conjugates into DEC‐Positive Dendritic Cells and Subsequent T‐Cell Activation

To achieve specific cell targeting by various receptors for oligosaccharides or antibodies, a carrier must not be taken up by any of the very many different cells and needs functional groups prone to clean conjugation chemistry to derive well‐defined structures with a high biological specificity. A polymeric nanocarrier is presented that consists of a cylindrical brush polymer with poly‐2‐oxazoline side chains carrying an azide functional group on each of the many side chain ends. After click conjugation of dye and an anti‐DEC205 antibody to the periphery of the cylindrical brush polymer, antibody‐mediated specific binding and uptake into DEC205⁺‐positive mouse bone marrow‐derived dendritic cells (BMDC) was observed, whereas binding and uptake by DEC205^? negative BMDC and non‐DC was essentially absent. Additional conjugation of an antigen peptide yielded a multifunctional polymer structure with a much stronger antigen‐specific T‐cell stimulatory capacity of pretreated BMDC than application of antigen or polymer–antigen conjugate.     

Poly(ethylene glycol) as a biointeractive electron‐beam resist

Poly(ethylene glycol) (PEG) can serve as an electron‐beam (e‐beam) resist to modulate protein adsorption on and cell adhesion to surfaces. PEG preferentially crosslinks under e‐beam irradiation to create microgels with controllable properties. Here, atomic‐force, scanning electron, and confocal microscopies are used to study discrete microgels formed from solvent‐cast PEG thin films by focused e‐beams with energies between 2 and 30 keV and point doses between 10 and 1000 fC. Consistent with experimental findings, Monte Carlo simulation of electron energy deposition identifies three structures within each microgel: a highly crosslinked core near the point of electron incidence; a lightly crosslinked near corona surrounding the core; and a far corona at the PEG–Si interface. The nature and relative sizes of these three regions and, hence, the microgel–protein interactions depend on the incident electron energy and dose. The far corona creates protein‐repulsive surface hundreds of nanometers or more from the microgel core. The highly crosslinked core is largely shielded by the near corona. These findings can help guide the choice of irradiation conditions to most effectively modulate protein–surface interactions via PEG microgels patterned by e‐beam lithography. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1543–1554     

Poly(N‐vinylpyrrolidone)‐Modified Surfaces for Biomedical Applications

Poly(N‐vinylpyrrolidone) (PVP), an important water soluble synthetic polymer, has many desirable properties including low toxicity, chemical stability, and good biocompatibility. Since PVP is hemocompatible and physiologically inactive, it has been used as a blood plasma substitute. Surface modification with PVP has been investigated extensively over the past few years as a means of preventing nonspecific protein adsorption. PVP may therefore be seen as a promising antifouling surface modifier comparable to poly(ethylene glycol) (PEG). In this review, various approaches for the design and preparation of PVP‐modified surfaces are summarized and potential biomedical applications of these PVP‐modified materials are indicated. Finally, some perspectives on future research on PVP for surface modification are discussed.

     

A pH‐sensitive,strong double‐network hydrogel: Poly(ethylene glycol) methyl ether methacrylates–poly(acrylic acid)

We here describe new double network (DN) hydrogels with excellent mechanical strength and high sensitivity to pH changes. The first polymer network has a bottle brush structure and is formed from oligo‐monomers of poly(ethylene glycol) methyl ether methacrylate (PEGMA). Poly(acrylic acid) (PAA) is used as the second network. This double network features strong intermolecular interactions between the neutral poly(ethylene glycol) (PEG) side chains of PPEGMA and the non‐ionized carboxylic acid groups of the PAA second network. When immersed in solutions with a pH below ～4 the DN hydrogels have a low swelling ratio and are opaque as a result of solvent‐polymer phase separation driven by the formation of dense hydrogen‐bonded clusters. The compression strength (～8 MPa) is at least 14 times higher than the analogous single networks. When immersed in solutions with a pH >4, the hydrogels are transparent and exhibit a high swelling ratio with a compression strength of ～1 MPa. The PEG side chain length can be readily controlled without greatly altering the overall DN topology by choosing PEGMA monomers having different PEG side chain lengths. Longer PEG side branches give higher compression and tensile strengths at pH <4 when hydrogen bonded clusters form. The robust nature of these DN gels over a wide pH range may be useful for applications such as artificial muscles and controlled release devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

An experimental-theoretical analysis of protein adsorption on peptidomimetic polymer brushes

Surface-grafted water-soluble polymer brushes are being intensely investigated for preventing protein adsorption to improve biomedical device function, prevent marine fouling, and enable applications in biosensing and tissue engineering. In this contribution, we present an experimental-theoretical analysis of a peptidomimetic polymer brush system with regard to the critical brush density required for preventing protein adsorption at varying chain lengths. A mussel adhesive-inspired DOPA-Lys (DOPA = 3,4-dihydroxy-phenylalanine; Lys = lysine) pentapeptide surface grafting motif enabled aqueous deposition of our peptidomimetic polypeptoid brushes over a wide range of chain densities. Critical densities of 0.88 nm(-2) for a relatively short polypeptoid 10-mer to 0.42 nm(-2) for a 50-mer were identified from measurements of protein adsorption. The experiments were also compared with the protein adsorption isotherms predicted by a molecular theory. Excellent agreements in terms of both the polymer brush structure and the critical chain density were obtained. Furthermore, atomic force microscopy (AFM) imaging is shown to be useful in verifying the critical brush density for preventing protein adsorption. The present coanalysis of experimental and theoretical results demonstrates the significance of characterizing the critical brush density in evaluating the performance of an antifouling polymer brush system. The high fidelity of the agreement between the experiments and molecular theory also indicate that the theoretical approach presented can aid in the practical design of antifouling polymer brush systems.     

Tailored Poly(2‐oxazoline) Polymer Brushes to Control Protein Adsorption and Cell Adhesion

POx bottle‐brush brushes (BBBs) are synthesized by SIPGP of 2‐isopropenyl‐2‐oxazoline and consecutive LCROP of 2‐oxazolines on 3‐aminopropyltrimethoxysilane‐modified silicon substrates. The side chain hydrophilicity and polarity are varied. The impact of the chemical composition and architecture of the BBB upon protein (fibronectin) adsorption and endothelial cell adhesion are investigated and prove extremely low protein adsorption and cell adhesion on BBBs with hydrophilic side chains such as poly(2‐methyl‐2‐oxazoline) and poly(2‐ethyl‐2‐oxazoline). The influence of the POx side chain terminal function upon adsorption and adhesion is minor but the side chain length has a significant effect on bioadsorption.

     

Single component and selective competitive protein adsorption in a patchy polymer brush: opposition between steric repulsions and electrostatic attractions

This work explores the use of "patchy" polymer brushes to control protein adsorption rates on engineered surfaces and to bind targeted species from protein mixtures with high selectivity but without invoking molecular recognition. The brushes of interest contain embedded cationic "patches" composed of isolated adsorbed poly(l-lysine) coils (PLL) that are about 10 nm in diameter and are randomly arranged on a silica substrate. Around these patches is a protein-resistant poly(ethylene glycol) (PEG) brush that is formed from the adsorption of a PLL-g-PEG graft copolymer on the remaining silica surface. Electrostatic attractions between individual cationic patches and the negative regions of approaching proteins may be energetically insufficient to bind proteins. Furthermore, protein-patch attractions are reduced by steric repulsions between proteins and the PEG brush. We show that protein adsorption, gauged by ultimate short-term coverages and by the initial protein adsorption rate, exhibits an adhesion threshold: pure PEG brushes of the architectures employed here and brushes containing sparse loadings of PLL patches do not adsorb protein. Above a critical PLL patch loading or threshold, protein adsorption proceeds, often dramatically. The PLL patch thresholds are specific to the protein of interest, allowing surfaces to be engineered to adhesively discriminate different proteins within a mixture. The separation achieved is remarkably sharp: one protein adsorbs, but the second is completely rejected from the interface. The surfaces in this study, by virtue of their well-controlled and well-characterized patchy nature, distinguish themselves from multicomponent brushes or brushes used to end-tether peptide sequences and nucleotides.     

Sensitivity of protein adsorption to architectural variations in a protein-resistant polymer brush containing engineered nanoscale adhesive sites

Patchy polymer brushes contain nanoscale (5-15 nm) adhesive elements, such as polymer coils or nanoparticles, embedded at their base at random positions on the surface. The competition between the brush's steric (protein resistant) repulsions and the attractions from the discrete adhesive elements provides a precise means to control bioadhesion. This differs from the classical approach, where functionality is placed on the brush's periphery. The current study demonstrates the impact of poly(etheylene glycol) (PEG) brush architecture and ionic strength on fibrinogen adsorption on brushes containing embedded poly-l-lysine (PLL, 20K MW) coils or "patches". The consistent appearance of a fibrinogen adsorption threshold, a minimum loading of patches on the surface, below which protein adsorption does not occur, suggests multivalent protein capture: Adsorbing proteins simultaneously engage several patches. The surface composition (patch loading) at the threshold is extremely sensitive to the brush height and ionic strength, varying up to a factor of 5 in the surface loading of the PLL patches (~50% of the range of possible surfaces). Variations in ionic strength have a similar effect, with the smallest thresholds seen for the largest Debye lengths. While trends with brush height were the clearest and most dominant, consideration of the PEG loading within the brush or its persistence length did not reveal a critical brush parameter for the onset of adsorption. The lack of straightforward correlation on brush physics was likely a result of multivalent binding, (producing an additional dependence on patch loading), and might be resolved for univalent adsorption onto more strongly binding patches. While studies with similar brushes placed uniformly on a surface revealed that the PEG loading within the brush is the best indicator of protein resistance, the current results suggest that brush height is more important for patchy brushes. Likely the interactions producing brush extension normal to the interface act similarly to drive lateral tether extension to obstruct patches.     

Poly(arylene sulfide)s by nucleophilic aromatic substitution polymerization of 2,7‐difluorothianthrene

Poly(thianthrene phenylene sulfide) and poly(thianthrene sulfide) have been prepared by nucleophilic aromatic substitution polymerization of the activated monomer 2,7‐difluorothianthrene with bis thiophenoxide and sulfide nucleophiles, respectively. The resulting polymers are thermally stable, amorphous materials that have been characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), matrix‐assisted laser desorption/ionization‐time‐of‐flight (MALDI‐TOF) mass spectrometry, UV‐Vis spectroscopy, refractometry, and intrinsic viscosity (IV) measurements. The polymers produced exhibit 5% weight loss values approaching 500 °C in inert and air atmospheres and glass transition temperatures that range from 149 to 210 °C. Poly(thianthrene phenylene sulfide) with a number average molecular weight of 22,100 g/mol has been synthesized with an IV in DMPU of 0.62 dL/g at 30 °C. Creasable films of this polymer have been prepared by solvent casting and melt pressing at 250 °C. Films of poly(thianthrene phenylene sulfide) exhibit transparencies greater than 50% at wavelengths exceeding 400 nm and a high refractive index value of 1.692 at a wavelength of 633 nm, making the polymer interesting for optical applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2453–2461, 2009     

Surface interaction of well‐defined,concentrated poly(2‐hydroxyethyl methacrylate) brushes with proteins

The interaction of concentrated polymer brushes with proteins was chromatographically investigated. By the use of surface‐initiated atom transfer radical polymerization, a low‐polydispersity poly(2‐hydroxyethyl methacrylate) (PHEMA) was densely grafted onto the inner surfaces of silica monoliths with mesopores of about 50 and 80 nm in mean size. The graft density reached 0.4–0.5 chains/nm². The 80‐nm‐mesopore monolithic column with the concentrated PHEMA brush was characterized through the elution of low‐polydispersity pullulans with different molecular weights, clearly showing two modes of size exclusion, that is, one by the mesopores and the other by the brush phase. The latter mode gave a sharp separation with a critical molecular weight (size‐exclusion limit) of about 1000. This molecular size of pullulan was comparable to the distance between the nearest‐neighbor graft points. The elution behaviors of five proteins of different sizes (bovine serum thyroglobulin, bovine serum immunoglobulin G, bovine serum albumin, horse heart myoglobin, and bovine serum aprotinin) were studied with this PHEMA‐grafted column. The smallest protein, aprotinin, with a pullulan‐reduced molecular weight slightly larger than the critical value of 1000, was eluted much behind the corresponding pullulan, and this indicated that it barely got into the brush layer, suffering from a strong affinity interaction within the brush. On the other hand, the other four larger proteins were eluted at the same elution volumes as the equivalent pullulans, and this meant that they were perfectly excluded from the brush layer and separated only in the size‐exclusion mode by the mesopores without an affinity interaction with the brush surface. This excellent inertness of the concentrated brush in the interaction with the large proteins should afford the system long‐term stability against biofouling. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4795–4803, 2007     

Functional Polyolefins: Poly(ethylene)‐graft‐Poly(tert‐butyl acrylate) via Atom Transfer Radical Polymerization From a Polybrominated Alkane

Poly(cis‐cyclooctene) is synthesized via ring‐opening metathesis polymerization in the presence of a chain‐transfer agent and quantitatively hydrobrominated. Subsequent graft polymerization of tert‐butyl acrylate (tBA) via Cu‐catalyzed atom transfer radical polymerization (ATRP) from the non‐activated secondary alkyl bromide moieties finally results in PE‐g‐PtBA copolymer brushes. By varying the reaction conditions, a series of well‐defined graft copolymers with different graft densities and graft lengths are prepared. The maximum extent of grafting in terms of bromoalkyl groups involved is approximately 80 mol%. DSC measurements on the obtained graft copolymers reveal a decrease in T_m with increasing grafting density.     

RAFT‐mediated synthesis and temperature‐induced responsive properties of poly(2‐(2‐methoxyethoxy)ethyl methacrylate) brushes

Well‐defined, high‐density poly(2‐(2‐methoxyethoxy)ethyl methacrylate) [poly(MEO₂MA)] brushes were fabricated through a reliable strategy by the combination of self‐assembly of a monolayer of 3‐aminopropyltrimethoxy silane on silicon surface to immobilize 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid chain transfer agent and reversible addition‐fragmentation chain transfer‐mediated polymerization of MEO₂MA. The whole fabrication process of the poly(MEO₂MA) brushes was followed by water contact angle, grazing angle‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the poly(MEO₂MA) brushes, such as molecular weight and thickness determination, were measured by gel permeation chromatography and ellipsometry, and the grafting density was estimated. The temperature‐responsive property of the poly(MEO₂MA) brushes was further investigated and the result verified the brush‐to‐mushroom phase transition of the poly(MEO₂MA) chains from low to high temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of amphiphilic copolymer brushes: Poly(ethylene oxide)‐graft‐polystyrene

A well‐defined amphiphilic copolymer brush with poly(ethylene oxide) as the main chain and polystyrene as the side chain was successfully prepared by a combination of anionic polymerization and atom transfer radical polymerization (ATRP). The glycidol was first protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether and then copolymerized with ethylene oxide by the initiation of a mixture of diphenylmethylpotassium and triethylene glycol to give the well‐defined polymer poly(ethylene oxide‐co‐2,3‐epoxypropyl‐1‐ethoxyethyl ether); the latter was hydrolyzed under acidic conditions, and then the recovered copolymer of ethylene oxide and glycidol {poly(ethylene oxide‐co‐glycidol) [poly(EO‐co‐Gly)]} with multiple pending hydroxymethyl groups was esterified with 2‐bromoisobutyryl bromide to produce the macro‐ATRP initiator [poly(EO‐co‐Gly)_(ATRP). The latter was used to initiate the polymerization of styrene to form the amphiphilic copolymer brushes. The object products and intermediates were characterized with ¹H NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, Fourier transform infrared, and size exclusion chromatography in detail. In all cases, the molecular weight distribution of the copolymer brushes was rather narrow (weight‐average molecular weight/number‐average molecular weight < 1.2), and the linear dependence of ln[M₀]/[M] (where [M₀] is the initial monomer concentration and [M] is the monomer concentration at a certain time) on time demonstrated that the styrene polymerization was well controlled. This method has universal significance for the preparation of copolymer brushes with hydrophilic poly(ethylene oxide) as the main chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4361–4371, 2006     

Synthesis and characterization of poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s

Poly‐β‐amides (nylons 3) were synthesized via the anionic polymerization of a series of 4‐alkyl‐4‐methyl‐2‐azetidinones where the alkyl group is a methyl, ethyl, propyl, butyl, or pentyl. The “non‐assisted” polymerization was conducted under vacuum, in the bulk, at 160°C, using potassium 2‐pyrrolidonate as catalyst, whereas the “assisted” polymerization was carried in dimethylsulfoxide, at room temperature, using N‐acetylpyrrolidinone‐2 as activator but it gave no polymer with a propyl or bulkier side group. Side reactions occur in all cases. X‐ray spectra showed that poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s are amorphous with propyl, butyl, and pentyl groups, and semi‐crystalline with methyl or ethyl substituents. Both semi‐crystalline polyamides exhibit an extended planar zigzag conformation, with a fiber identity period along the c axis of 4.9 Å. Glass transition temperatures, melting temperatures, and/or decomposition temperatures are also reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 761–769, 1999     

Selective Adsorption of Functionalized Nanoparticles to Patterned Polymer Brush Surfaces and Its Probing with an Optical Trap

The site‐specific attachment of nanoparticles is of interest for biomaterials or biosensor applications. Polymer brushes can be used to regulate this adsorption, so the conditions for selective adsorption of phosphonate‐functionalized nanoparticles onto micropatterned polymer brushes with different functional groups are optimized. By choosing the strong polyelectrolytes poly(3‐sulfopropyl methacrylate), poly(sulfobetaine methacrylate), and poly[2‐(methacryloyloxy)ethyl trimethylammonium chloride], it is possible to direct the adsorption of nanoparticles to specific regions of the patterned substrates. A pH‐dependent adsorption can be achieved by using the polycarboxylate brush poly(methacrylic acid) (PMAA) as substrate coating. On PMAA brushes, the nanoparticles switch from attachment to the brush regions to attachment to the grooves of a patterned substrate on changing the pH from 3 to 7. In this manner, patterned substrates are realized that assemble nanoparticles in pattern grooves, in polymer brush areas, or substrates that resist the deposition of the nanoparticles. The nanoparticle deposition can be directed in a pH‐dependent manner on a weak polyelectrolyte, or is solely charge‐dependent on strong polyelectrolytes. These results are correlated with surface potential measurements and show that an optical trap is a versatile method to directly probe interactions between nanoparticles and polymer brushes. A model for these interactions is proposed based on the optical trap measurements.     

Fabrication of Poly(L‐lactide)‐block‐Poly(ethylene glycol)‐block‐Poly(L‐lactide) Triblock Copolymer Thin Films with Nanochannels: An AFM Study

This paper aims to report the fabrication of biodegradable thin films with micro‐domains of cylindrical nanochannels through the solvent‐induced microphase separation of poly(L ‐lactide)‐block‐poly(ethylene glycol)‐block‐poly(L ‐lactide) (PLA‐b‐PEG‐b‐PLA) triblock copolymers with different block ratios. In our experimental scope, an increase in each of the block lengths of the PLA and PEG blocks led to both a variation in the average number density (146 to 32 per 100 µm²) and the size of the micro‐domains (140 to 427 nm). Analyses by atomic force microscopy (AFM) and fluorescence microscopy indicated that the hydrophilic PEG nanochannels were dispersed in the PLA matrix of the PLA‐b‐PEG‐b‐PLA films. We demonstrated that the micro‐domain morphology could be controlled not only by the block length of PEG, but also by the solvent evaporation conditions.