Focus on the interlude between topographic transition and cell response on shape-memory surfaces

Recent advances in shape memory scaffolds and regenerative outcomes

The advent of tissue engineering (TE) technologies has revolutionized human medicine over the last few decades. Despite splendid advances in the fabricating and development of different substrates for regenerative purposes, non-responsive static composites have been used to heal injured tissues. After being transplanted into the target sites, grafts will lose their original features, leading to a reduction in regenerative potential. Along with these statements, the use of shape memory polymers (SMPs), smart substrates with unique physicochemical properties, has been extended in different disciplines of regenerative medicine in recent years. These substrates are intelligent and they can easily change physicogeometry features such as stiffness, strain size, shape, etc. in response to external stimuli. It has been proposed that SMPs can easily acquire their original properties after deformation, even in the presence or absence of certain stimuli. It has been indicated that the application of distinct synthesis protocols is required to fabricate dynamically switchable surfaces with prominent cell-to-substrate interaction, resulting in better regulation of cell function, dynamic growth, and reparative mechanisms. Here, we aimed to scrutinize the prominent regenerative properties of SMPs in the TE and regenerative medicine fields. Whether and how SMPs can orchestrate certain cell behavior, with reconfigurable features and adaptability were discussed in detail.

Nanoimprinting of Crosslinked Polyurethane / Polycaprolactone Blends: Scratch Recovery of Surface Topographies

Scratch recovery of micro-nano-patterned polymer surfaces extends the service life of products that require tunable surface properties and contributes to more sustainable development. Scratch recovery has been widely studied in bulk and 4D-printed polymers via intrinsic self-healing mechanisms. Existing studies on self-healing of micro/nano-scale polymeric surfaces are limited to the recovery of controlled tensile or compressive strain. Scratch recovery requires material transport to close the gap created by a scratch. Here, for the first time, scratch recovery of thermally nanoimprinted polymer surfaces in a heterogeneous polymer is reported. A blend of Polyurethane (TPU) and poly(caprolactone) (PCL) with selectively crosslinked TPU imparts shape-memory properties, and the uncrosslinked PCL retains chain mobility for molecular diffusion during scratch recovery. Scratch recovery of nanoimprinted micro-pillars has been achieved spontaneously and completely by heat and without any pressure input. The healing temperature is determined to be the melting point of PCL at 60 °C. Rapid recovery is also achieved at 60 s with complete closure of scratch width of 5 µm and topography recovery of the nanoimprinted micro-pillars.

4D fabrication of shape-changing systems for tissue engineering: state of the art and perspectives

In recent years, four-dimensional (4D) fabrication has emerged as a powerful technology capable of revolutionizing the field of tissue engineering. This technology represents a shift in perspective from traditional tissue engineering approaches, which generally rely on static-or passive-structures (e.g., scaffolds, constructs) unable of adapting to changes in biological environments. In contrast, 4D fabrication offers the unprecedented possibility of fabricating complex designs with spatiotemporal control over structure and function in response to environment stimuli, thus mimicking biological processes. In this review, an overview of the state of the art of 4D fabrication technology for the obtainment of cellularized constructs is presented, with a focus on shape-changing soft materials. First, the approaches to obtain cellularized constructs are introduced, also describing conventional and non-conventional fabrication techniques with their relative advantages and limitations. Next, the main families of shape-changing soft materials, namely shape-memory polymers and shape-memory hydrogels are discussed and their use in 4D fabrication in the field of tissue engineering is described. Ultimately, current challenges and proposed solutions are outlined, and valuable insights into future research directions of 4D fabrication for tissue engineering are provided to disclose its full potential.

Reconfigurable scaffolds for adaptive tissue regeneration

Tissue engineering and regenerative medicine have offered promising alternatives for clinical treatment of body tissue traumas, losses, dysfunctions, or diseases, where scaffold-based strategies are particularly popular and effective. Over the decades, scaffolds for tissue regeneration have been remarkably evolving. Nevertheless, conventional scaffolds still confront grand challenges in bio-adaptions in terms of both tissue-scaffold and cell-scaffold interplays, for example complying with complicated three-dimensional (3D) shapes of biological tissues and recapitulating the ordered cell regulation effects of native cell microenvironments. Benefiting from the recent advances in "intelligent" biomaterials, reconfigurable scaffolds have been emerging, demonstrating great promise in addressing the bio-adaption challenges through altering their macro-shapes and/or micro-structures. This mini-review article presents a brief overview of the cutting-edge research on reconfigurable scaffolds, summarizing the materials for forming reconfigurable scaffolds and highlighting their applications for adaptive tissue regeneration. Finally, the challenges and prospects of reconfigurable scaffolds are also discussed, shedding light on the bright future of next-generation reconfigurable scaffolds with upgrading adaptability.

Triple and Quadruple Surface Pattern Memories in Nanoimprinted Polymer Blends

Trigger-responsive surfaces with multiple surface properties have wide-ranging application potential from surfaces with trigger-responsive fluid flow to cell culture to optical effects; such surfaces can be achieved through surface morphological changes. Although multiple shape-memory effects are successful in bulk polymers, there is limited programing and recovery of multiple surface memories due to the challenges in fabricating multiple surface topographies with good controllability. Here, we report the synergy between the polymer blend formulation and the thermal nanoimprinting process to achieve multiple microtopography memories. A series of immiscible blends consisting of poly(caprolactone) (PCL) and polyethylene (PE) with distinct thermal transitions governed by distinct crystallization events were augmented with improved elasticity through preferential cross-linking in the polymer blend. The effect of preferential cross-linking by dicumyl peroxide on the elastic property of the PCL/PE has been found to be nonlinearly dependent on the blend composition. This approach enabled triple and quadruple surface pattern fixity and recovery in nanoimprinted PCL/PE blends. Specifically, we demonstrated the recovery of a micropillar structure (diameter: 20 μm and height: 10 μm) from a hierarchical micrograting topography (width: 2 μm and height: 2 μm) when exposed to a thermal stimulus at 60 °C for 180 s. Furthermore, we also demonstrated the recovery of a deformed micrograting followed by a secondary recovery of the micropillar structure.

Cell-Responsive Shape Memory Polymers

Recent decades have seen substantial interest in the development and application of biocompatible shape memory polymers (SMPs), a class of “smart materials” that can respond to external stimuli. Although many studies have used SMP platforms triggered by thermal or photothermal events to study cell mechanobiology, SMPs triggered by cell activity have not yet been demonstrated. In a previous work, we developed an SMP that can respond directly to enzymatic activity. Here, our goal was to build on that work by demonstrating enzymatic triggering of an SMP in response to the presence of enzyme-secreting human cells. To achieve this phenomenon, poly(ε-caprolactone) (PCL) and Pellethane were dual electrospun to form a fiber mat, where PCL acted as a shape-fixing component that is labile to lipase, an enzyme secreted by multiple cell types including HepG2 (human hepatic cancer) cells, and Pellethane acted as a shape memory component that is enzymatically stable. Cell-responsive shape memory performance and cytocompatibility were quantitatively and qualitatively analyzed by thermal analysis (thermal gravimetric analysis and differential scanning calorimetry), surface morphology analysis (scanning electron microscopy), and by incubation with HepG2 cells in the presence or absence of heparin (an anticoagulant drug present in the human liver that increases the secretion of hepatic lipase). The results characterize the shape-memory functionality of the material and demonstrate successful cell-responsive shape recovery with greater than 90% cell viability. Collectively, the results provide the first demonstration of a cytocompatible SMP responding to a trigger that is cellular in origin.

Full-Atomistic Optimized Potentials for Liquid Simulations and Polymer Consistent Force Field Models for Biocompatible Shape-Memory Poly(ε-caprolactone)

Thermally induced shape memory poly(ε-caprolactone) (PCL)-based polymers are one of the most extensively researched families of biocompatible materials. They are degradable under physiological conditions and have high applicability in general biomedical engineering, with cross-linked PCL networks being particularly useful for tissue engineering. In this study, we used the optimized potentials for liquid simulations (OPLS) force field, which is well suited for describing intermolecular interactions in biomolecules, and the class II polymer consistent force field (PCFF) to investigate the properties of telechelic PCL with diacrylates as reactive functionalities on its end groups. PCFF has been specifically parameterized for simulating synthetic polymeric materials. We compare the findings of all-atom molecular dynamics simulations with known experimental data and theoretical assumptions to verify the applicability of both these force fields. We estimated the melt density, volume, transition temperatures, and mechanical characteristics of two-branched PCL diacrylates with a molecular weight of 2481 Da. Our findings point to the utility of the aforementioned force fields in predicting the properties of PCL-based polymers. It also opens avenues for developing PCL cross-linked polymer models and employing OPLS to investigate the interactions of synthetic polymers with biomolecules.

Application and Development of Shape Memory Micro/Nano Patterns

Shape memory polymers (SMPs) are a class of smart materials that change shape when stimulated by environmental stimuli. Different from the shape memory effect at the macro level, the introduction of micro-patterning technology into SMPs strengthens the exploration of the shape memory effect at the micro/nano level. The emergence of shape memory micro/nano patterns provides a new direction for the future development of smart polymers, and their applications in the fields of biomedicine/textile/micro-optics/adhesives show huge potential. In this review, the authors introduce the types of shape memory micro/nano patterns, summarize the preparation methods, then explore the imminent and potential applications in various fields. In the end, their shortcomings and future development direction are also proposed.

Autonomous Nanoscale Chemomechanical Oscillation on the Self-Oscillating Polymer Brush Surface by Precise Control of Graft Density

As a novel functional surface, a self-oscillating polymer brush that undergoes autonomous, periodic swelling/deswelling during the Belousov-Zhabotinsky (BZ) reaction has been developed. Although extensive research has revealed how the fundamental aspects of the BZ reaction can be regulated based on the surface design of the self-oscillating polymer brush, design strategies for the induction of mechanical oscillation remain unexplored. Herein, we investigated the graft density effects on the phase transition behavior, which is an important design parameter for the mechanical oscillation of the modified polymer. The self-oscillating polymer-modified substrates with controlled graft densities were prepared by immobilizing various compositions of an initiator and a noninitiator followed by surface-initiated atom transfer radical polymerization of the self-oscillating polymer chains. In addition to the characterization of each prepared substrate, atomic force microscopy (AFM) and digital holographic microscopy (DHM) were employed to evaluate the density effects on the static and dynamic surface structures. AFM revealed that equilibrium swelling as well as thermoresponsive behavior is profoundly affected by the graft density. Moreover, using DHM, autonomous mechanical oscillation was captured only on the self-oscillating polymer brush with adequate graft density. Notably, the oscillation amplitude (150 nm) and the period (20 s) in this study were superior to those in a previous report on the self-oscillating polymer modified through the grafting-to method by 10- and 3-fold, respectively. This study presents design guidelines for future applications, such as autonomous transport devices.

Dynamic azopolymeric interfaces for photoactive cell instruction

The ability to affect a wide range of biophysical properties through the use of light has led to the development of dynamic cell instructive materials. Using photoresponsive materials such as azopolymers, smart systems that use external, minimally damaging, light irradiation can be used to trigger specific surface morpho-physical properties in the presence of living cells. The interaction of light with an azopolymer film induces a mass migration phenomenon, allowing a variety of topographic patterns to be embossed on the polymeric film. Photoisomerization induces conformational changes at the molecular and macroscopic scale, resulting in light-induced variations of substrate morphological, physical, and mechanical properties. In this review, we discuss the photoactuation of azopolymeric interfaces to provide guidelines for the engineering and design of azopolymer films. Laser micropatterning for the modulation of azopolymer surfaces is examined as a way to diversify the capabilities of these polymers in cellular systems. Mass migration effects induced by azopolymer switching provides a foundation for performing a broad range of cellular manipulation techniques. Applications of azopolymers are explored in the context of dynamic culture systems, gaining insight into the complex processes involved in dynamic cell-material interactions. The review highlights azopolymers as a candidate for various applications in cellular control, including cell alignment, migration, gene expression, and others. Recent advances have underlined the importance of these systems in applications regarding three-dimensional cell culture and stem cell morphology. Azopolymers can be used not only to manipulate cells but also to probe for mechanistic studies of cellular crosstalk in response to chemical and mechanical stimuli.

Photoactive Interfaces for Spatio-Temporal Guidance of Mesenchymal Stem Cell Fate

Patterned surfaces have proved effective in guiding stem cells commitment to a specific lineage by presenting highly ordered biophysical/biochemical cues at the cellmaterial interface. Their potency in controlling cell fate can be significantly empowered by encoding logic of space and time control of signal presentation. Here, azopolymeric photoactive interfaces are proposed to present/withdraw morphophysical signals to living cells using a green light trigger in a non-invasive spatio-temporal controlled way. To assess the potency of these dynamic platforms in controlling cell decision and fate, topography changes are actuated by light at specific times to reverse the fate of otherwise committed human mesenchymal stem cells (hMSC) toward osteoblastic lineage. It is first proved by dynamic change from ordered parallel patterning to flat or grid surfaces, that it is possible to induce cyclic cellular and nuclear stretches. Furthermore, by culturing hMSCs on a specific pattern known to prime them toward osteoblast lineage, the possibility to reroute or reverse stem cell fate decision by dynamic modulation of morphophysical signal is proved. To conclude, dynamic topographies can control the spatial conformation of hMSCs, modulate lineage reversal even after several weeks of culture and redirect lineage specification in response to light-induced changes in the microenvironment.

Dual Thermo- and pH-Responsive Behavior of Double Zwitterionic Graft Copolymers for Suppression of Protein Aggregation and Protein Release

Graft copolymers consisting of two different zwitterionic blocks were synthesized via reversible addition fragmentation chain transfer polymerization. These polymers showed dual properties of thermo- and pH-responsiveness in an aqueous solution. Ultraviolet-visible spectroscopy and dynamic light scattering were employed to study the phase behavior under varying temperatures and pH values. Unlike the phase transition temperatures of other graft copolymers containing nonionic blocks, the phase transition temperature of these polymers was easily tuned by changing the polymer concentration. Owing to the biocompatible and stimuli-responsive nature of the polymers, this system was shown to effectively release proteins (lysozyme) while simultaneously protecting them against denaturation. The positively charged lysozyme was shown to bind with the negatively charged polymer at the physiological pH (pH 7.4). However, it was subsequently released at pH 3, at which the polymer exhibits a positive charge. Protein aggregation studies using a residual enzymatic activity assay, circular dichroism, and a Thioflavin T assay revealed that the secondary structure of the lysozyme was retained even after harsh thermal treatment. The addition of these polymers helped the lysozyme retain its enzymatic activity and suppressed its fibrillation. Both polymers showed excellent protein protection properties, with the negatively charged polymer exhibiting slightly superior protein protection properties to those of the neutral polymer. To the best of the authors' knowledge, this is the first study to develop a graft copolymer system consisting of two different zwitterionic blocks that shows dual thermo- and pH-responsive properties. The presence of the polyampholyte structure enables these polymers to act as protein release agents, while simultaneously protecting the proteins from severe stress.

Shape-Memory Nanofiber Meshes with Programmable Cell Orientation

In this work we report the rational design of temperature-responsive nanofiber meshes with shape-memory properties. Meshes were fabricated by electrospinning poly(ε-caprolactone) (PCL)-based polyurethane with varying ratios of soft (PCL diol) and hard [hexamethylene diisocyanate (HDI)/1,4-butanediol (BD)] segments. By altering the PCL diol:HDI:BD molar ratio both shape-memory properties and mechanical properties could be readily turned and modulated. Though mechanical properties improved by increasing the hard to soft segment ratio, optimal shape-memory properties were obtained using a PCL/HDI/BD molar ratio of 1:4:3. Microscopically, the original nanofibrous structure could be deformed into and maintained in a temporary shape and later recover its original structure upon reheating. Even when deformed by 400%, a recovery rate of >89% was observed. Implementation of these shape memory nanofiber meshes as cell culture platforms revealed the unique ability to alter human mesenchymal stem cell alignment and orientation. Due to their biocompatible nature, temperature-responsivity, and ability to control cell alignment, we believe that these meshes may demonstrate great promise as biomedical applications.

Nuclear position relative to the Golgi body and nuclear orientation are differentially responsive indicators of cell polarized motility

Cell motility is critical to biological processes from wound healing to cancer metastasis to embryonic development. The involvement of organelles in cell motility is well established, but the role of organelle positional reorganization in cell motility remains poorly understood. Here we present an automated image analysis technique for tracking the shape and motion of Golgi bodies and cell nuclei. We quantify the relationship between nuclear orientation and the orientation of the Golgi body relative to the nucleus before, during, and after exposure of mouse fibroblasts to a controlled change in cell substrate topography, from flat to wrinkles, designed to trigger polarized motility. We find that the cells alter their mean nuclei orientation, in terms of the nuclear major axis, to increasingly align with the wrinkle direction once the wrinkles form on the substrate surface. This change in alignment occurs within 8 hours of completion of the topographical transition. In contrast, the position of the Golgi body relative to the nucleus remains aligned with the pre-programmed wrinkle direction, regardless of whether it has been fully established. These findings indicate that intracellular positioning of the Golgi body precedes nuclear reorientation during mouse fibroblast directed migration on patterned substrates. We further show that both processes are Rho-associated kinase (ROCK) mediated as they are abolished by pharmacologic ROCK inhibition whereas mouse fibroblast motility is unaffected. The automated image analysis technique introduced could be broadly employed in the study of polarization and other cellular processes in diverse cell types and micro-environments. In addition, having found that the nuclei Golgi vector may be a more sensitive indicator of substrate features than the nuclei orientation, we anticipate the nuclei Golgi vector to be a useful metric for researchers studying the dynamics of cell polarity in response to different micro-environments.

Shape recovery strain and nanostructures on recovered polyurethane films and their regulation to osteoblasts morphology

Shape memory polyurethanes (SMPUs) have emerged as novel dynamic substrates to regulate cell alignment, in which recovery-induced change in substrates topography has been described as the major contributor. This work, for the first time, confirmed the pivotal roles of recovery strain and phase-separated nanostructures of SMPUs in regulating cell morphology. SMPU films with different stretching ratios (0%, 50%, 100%, and 200%) were found to produce an average recovery strain from 19.41% to 34.04% within 2 h in dulbecco's modified eagle medium (DMEM). Meanwhile, the assembly of hard domains was enhanced during shape recovery, leading to the reorientation of fibrillar apophyses (i.e., nanostructures). Further observation of osteoblast morphology revealed that recovery strain resulted in perpendicular orientation of osteoblasts to strain direction. With the extension of incubation time (24 h), however, the perpendicular orientation was transformed to follow the nanostructures on recovered films, suggesting that the nanostructures might become the determinant of the long-term cell orientation. This study provides a biomechanics-based perspective to understand the dynamic interactions between SMPU and cells, which can help to guide the design of SMPU for specific biomedical applications.

Enzymatically triggered shape memory polymers

Cytocompatible shape memory polymers activated by thermal or photothermal triggers have been developed and established as powerful "smart material" platforms for both basic and translational research. Shape memory polymers (SMPs) that could be triggered directly by biological activity have not, in contrast, been reported. The goal of this study was to develop an SMP that responds directly to enzymatic activity and can do so under isothermal cell culture conditions. To achieve this goal, we designed an SMP with a shape fixing component, poly(ε-caprolactone) (PCL), that is vulnerable to enzymatic degradation and a shape memory component, Pellethane, that is enzymatically stable - as the shape fixing component undergoes enzymatically-catalyzed degradation, the SMP returns to its original, programmed shape. We quantitatively and qualitatively analyzed material properties, shape memory performance, and cytocompatibility of the enzymatically-catalyzed shape memory response. The results demonstrate enzymatic recovery, as contraction of tensile specimens, using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the PCL shape-fixing phase. The results further showed that both the materials and the process of enzymatic shape recovery are cytocompatible. Thus, the SMP design reported here represents both an enzyme responsive material capable of applying a programmed shape change or direct mechanical force and an SMP that could respond directly to biological activity. STATEMENT OF SIGNIFICANCE: Cytocompatible shape memory polymers activated by thermal or photothermal triggers have become powerful "smart material" platforms for basic and translational research. Shape memory polymers that could be triggered directly by biological activity have not, in contrast, been reported. Here we report an enzymatically triggered shape memory polymer that changes its shape isothermally in response to enzymatic activity. We successfully demonstrate enzymatic recovery using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the shape-fixing phase. We further show that both the materials and the process of enzymatic shape recovery are cytocompatible. This new shape memory polymer design can be anticipated to enable new applications in basic and applied materials science as a stimulus responsive material.

Nanoridge patterns on polymeric film by a photodegradation copying method for metallic nanowire networks

A simple photocopying method based on selective polymer photodegradation is proposed for fabricating topographical nanopatterns. Nanoridges are structured on a polyethylene terephthalate film due to ultraviolet shielding of silver nanowire networks.

Thermo-responsive polymers and their application as smart biomaterials

The drastic development of polymeric materials for a wide range of biomedical and biomaterial applications has been explored in the last few decades. Among these materials, a new class of 'smart' or 'intelligent' biomaterial has been developed, and these materials are highly responsive to slight changes in their environments. Due to their dynamically alterable properties, smart materials allow for smart biomaterials to be developed. This review presents smart thermo-responsive polymers and discusses how they may be used as smart biomaterials. We describe typical thermo-responsive polymers that are either lower critical solution temperature-type, upper critical solution temperature-type, or thermo-induced shape-memory polymers. The basic mechanisms of the thermo-response processes will also be described. The applications of smart biomaterials with various forms, such as smart fibres, surfaces and hydrogels, will also be introduced.

A Combinational Effect of "Bulk" and "Surface" Shape-Memory Transitions on the Regulation of Cell Alignment

A novel shape-memory cell culture platform has been designed that is capable of simultaneously tuning surface topography and dimensionality to manipulate cell alignment. By crosslinking poly(ε-caprolactone) (PCL) macromonomers of precisely designed nanoarchitectures, a shape-memory PCL with switching temperature near body temperature is successfully prepared. The temporary strain-fixed PCLs are prepared by processing through heating, stretching, and cooling about the switching temperature. Temporary nanowrinkles are also formed spontaneously during the strain-fixing process with magnitudes that are dependent on the applied strain. The surface features completely transform from wrinkled to smooth upon shape-memory activation over a narrow temperature range. Shape-memory activation also triggers dimensional deformation in an initial fixed strain-dependent manner. A dynamic cell-orienting study demonstrates that surface topographical changes play a dominant role in cell alignment for samples with lower fixed strain, while dimensional changes play a dominant role in cell alignment for samples with higher fixed strain. The proposed shape-memory cell culture platform will become a powerful tool to investigate the effects of spatiotemporally presented mechanostructural stimuli on cell fate.

Dynamically Tunable Cell Culture Platforms for Tissue Engineering and Mechanobiology

Human tissues are sophisticated ensembles of many distinct cell types embedded in the complex, but well-defined, structures of the extracellular matrix (ECM). Dynamic biochemical, physicochemical, and mechano-structural changes in the ECM define and regulate tissue-specific cell behaviors. To recapitulate this complex environment in vitro, dynamic polymer-based biomaterials have emerged as powerful tools to probe and direct active changes in cell function. The rapid evolution of polymerization chemistries, structural modulation, and processing technologies, as well as the incorporation of stimuli-responsiveness, now permit synthetic microenvironments to capture much of the dynamic complexity of native tissue. These platforms are comprised not only of natural polymers chemically and molecularly similar to ECM, but those fully synthetic in origin. Here, we review recent in vitro efforts to mimic the dynamic microenvironment comprising native tissue ECM from the viewpoint of material design. We also discuss how these dynamic polymer-based biomaterials are being used in fundamental cell mechanobiology studies, as well as towards efforts in tissue engineering and regenerative medicine.

Self-Restoration of Superhydrophobicity on Shape Memory Polymer Arrays with Both Crushed Microstructure and Damaged Surface Chemistry

Recently, self-healing superhydrophobic surfaces have become a new research focus due to their recoverable wetting performances and wide applications. However, until now, on almost all reported surfaces, only one factor (surface chemistry or microstructure) can be restored. In this paper, a new superhydrophobic surface with self-healing ability in both crushed microstructure and damaged surface chemistry is prepared by creating lotus-leaves-like microstructure on the epoxy shape memory polymer (SMP). Through a simple heating process, the crushed surface microstructure, the damaged surface chemistry, and the surface superhydrophobicity that are destroyed under the external pressure and/or O₂ plasma action can be recovered, demonstrating that the obtained superhydrophobic surface has a good self-healing ability in both of the two factors that govern the surface wettability. The special self-healing ability is ascribed to the good shape memory effect of the polymer and the reorganization effect of surface molecules. This paper reports the first use of SMP material to demonstrate the self-healing ability of surface superhydrophobicity, which opens up some new perspectives in designing self-healing superhydrophobic surfaces. Given the properties of this surface, it could be used in many applications, such as self-cleaning coatings, microfluidic devices, and biodetection.

Stretching-induced nanostructures on shape memory polyurethane films and their regulation to osteoblasts morphology

Programming such as stretching, compression and bending is indispensible to endow polyurethanes with shape memory effects. Despite extensive investigations on the contributions of programming processes to the shape memory effects of polyurethane, less attention has been paid to the nanostructures of shape memory polyurethanes surface during the programming process. Here we found that stretching could induce the reassembly of hard domains and thereby change the nanostructures on the film surfaces with dependence on the stretching ratios (0%, 50%, 100%, and 200%). In as-cast polyurethane films, hard segments sequentially assembled into nano-scale hard domains, round or fibrillar islands, and fibrillar apophyses. Upon stretching, the islands packed along the stretching axis to form reoriented fibrillar apophyses along the stretching direction. Stretching only changed the chemical patterns on polyurethane films without significantly altering surface roughness, with the primary composition of fibrillar apophyses being hydrophilic hard domains. Further analysis of osteoblasts morphology revealed that the focal adhesion formation and osteoblasts orientation were in accordance with the chemical patterns of the underlying stretched films, which corroborates the vital roles of stretching-induced nanostructures in regulating osteoblasts morphology. These novel findings suggest that programming might hold great potential for patterning polyurethane surfaces so as to direct cellular behavior. In addition, this work lays groundwork for guiding the programming of shape memory polyurethanes to produce appropriate nanostructures for predetermined medical applications.

Combined Chemical Groups and Topographical Nanopattern on the Poly(ε-Caprolactone) Surface for Regulating Human Foreskin Fibroblasts Behavior

Surface chemistry and substrate topography could contribute significantly to providing a biochemical and topographical cues for governing the fate of cells on the cell-material interface. However, the synergies between these two properties have not been exploited extensively for biomaterial design. Herein, we achieved spatial-controlled patterning of chemical groups on the poly(ε-caprolactone) (PCL) surface by elegant UV-nanoimprint lithography (UN-NIL). The introduction of chemical groups on the PCL surface was developed by our newly 6-benzyloxycarbonylmethyl-ε-caprolactone (BCL) monomer, which not only solved the lack of functional groups along the PCL chain but also retained the original favorable properties of PCL materials. The synergetic effect of the chemical groups and nanopatterns on the human foreskin fibroblasts (HFFs) behaviors was evaluated in detail. The results revealed that the patterned functional PCL surfaces could induce enhanced cell adhesion and proliferation, further trigger changes in HFFs morphology, orientation and collagen secretion. Taken together, this study provided a method for straightforward fabrication of reactive PCL surfaces with topographic patterns by one-step process, and they would facilitate PCL as potential candidate for cell cultivation and tissue engineering.

Spatiotemporal control of cardiac anisotropy using dynamic nanotopographic cues

Coordinated extracellular matrix spatiotemporal reorganization helps regulate cellular differentiation, maturation, and function in vivo, and is therefore vital for the correct formation, maintenance, and healing of complex anatomic structures. In order to evaluate the potential for cultured cells to respond to dynamic changes in their in vitro microenvironment, as they do in vivo, the collective behavior of primary cardiac muscle cells cultured on nanofabricated substrates with controllable anisotropic topographies was studied. A thermally induced shape memory polymer (SMP) was employed to assess the effects of a 90° transition in substrate pattern orientation on the contractile direction and structural organization of cardiomyocyte sheets. Cardiomyocyte sheets cultured on SMPs exhibited anisotropic contractions before shape transition. 48 h after heat-induced shape transition, the direction of cardiomyocyte contraction reoriented significantly and exhibited a bimodal distribution, with peaks at ∼45 and -45° (P < 0.001). Immunocytochemical analysis highlighted the significant structural changes that the cells underwent in response to the shift in underlying topography. The presented results demonstrate that initial anisotropic nanotopographic cues do not permanently determine the organizational fate or contractile properties of cardiomyocytes in culture. Given the importance of surface cues in regulating primary and stem cell development, investigation of such tunable nanotopographies may have important implications for advancing cellular maturation and performance in vitro, as well as improving our understanding of cellular development in response to dynamic biophysical cues.

Shape-memory surfaces for cell mechanobiology

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape 'A' to a memorized permanent shape 'B' upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.