Evaluation of substrata effect on cell adhesion properties using freestanding poly(L-lactic acid) nanosheets

Large-Scale Fabrication of Freestanding Polymer Ultrathin Porous Membranes for Transparent Transwell Coculture Systems

Advancements in cell coculture systems with porous membranes have facilitated the simulation of human-like in vitro microenvironments for diverse biomedical applications. However, conventional Transwell membranes face limitations in low porosity (ca. 6%) and optical opacity due to their large thickness (ca. 10 μm). In this study, we demonstrated a one-step, large-scale fabrication of freestanding polymer ultrathin porous (PUP) membranes with thicknesses of hundreds of nanometers. PUP membranes were produced by using a gap-controlled bar-coating process combined with polymer blend phase separation. They are 20 times thinner than Transwell membranes, possessing 3-fold higher porosity and exhibiting high transparency. These membranes demonstrate outstanding molecular permeability and significantly reduce the cell-cell distance, thereby facilitating efficient signal exchange pathways between cells. This research enables the establishment of a cutting-edge in vitro cell coculture system, enhancing optical transparency, and streamlining the large-scale manufacturing of porous membranes.

Porous Polymeric Nanofilms for Recreating the Basement Membrane in an Endothelial Barrier-on-Chip

Organs-on-chips (OoCs) support an organotypic human cell culture in vitro. Precise representation of basement membranes (BMs) is critical for mimicking physiological functions of tissue interfaces. Artificial membranes in polyester (PES) and polycarbonate (PC) commonly used in in vitro models and OoCs do not replicate the characteristics of the natural BMs, such as submicrometric thickness, selective permeability, and elasticity. This study introduces porous poly(d,l-lactic acid) (PDLLA) nanofilms for replicating BMs in in vitro models and demonstrates their integration into microfluidic chips. Using roll-to-roll gravure coating and polymer phase separation, we fabricated transparent ∼200 nm thick PDLLA films. These nanofilms are 60 times thinner and 27 times more elastic than PES membranes and show uniformly distributed pores of controlled diameter (0.4 to 1.6 μm), which favor cell compartmentalization and exchange of large water-soluble molecules. Human umbilical vein endothelial cells (HUVECs) on PDLLA nanofilms stretched across microchannels exhibited 97% viability, enhanced adhesion, and a higher proliferation rate compared to their performance on PES membranes and glass substrates. After 5 days of culture, HUVECs formed a functional barrier on suspended PDLLA nanofilms, confirmed by a more than 10-fold increase in transendothelial electrical resistance and blocked 150 kDa dextran diffusion. When integrated between two microfluidic channels and exposed to physiological shear stress, despite their ultrathin thickness, PDLLA nanofilms upheld their integrity and efficiently maintained separation of the channels. The successful formation of an adherent endothelium and the coculture of HUVECs and human astrocytes on either side of the suspended nanofilm validate it as an artificial BM for OoCs. Its submicrometric thickness guarantees intimate contact, a key feature to mimic the blood-brain barrier and to study paracrine signaling between the two cell types. In summary, porous PDLLA nanofilms hold the potential for improving the accuracy and physiological relevance of the OoC as in vitro models and drug discovery tools.

Biodegradable Polymer Nanosheets Incorporated with Zn-Containing Nanoparticles for Biomedical Applications

So far, poly(L-lactic acid), PLLA nanosheets proved to be promising for wound healing. Such biodegradable materials are easy to prepare, bio-friendly, cost-effective, simple to apply and were shown to protect burn wounds and facilitate their healing. At the same time, certain metal ions are known to be essential for wound healing, which is why this study was motivated by the idea of incorporating PLLA nanosheets with Zn²⁺ ion containing nanoparticles. Upon being applied on wound, such polymer nanosheets should release Zn²⁺ ions, which is expected to improve wound healing. The work thus focused on preparing PLLA nanosheets embedded with several kinds of Zn-containing nanoparticles, their characterization and ion-release behavior. ZnCl₂ and ZnO nanoparticles were chosen because of their different solubility in water, with the intention to see the dynamics of their Zn²⁺ ion release in liquid medium with pH around 7.4. Interestingly, the prepared PLLA nanosheets demonstrated quit similar ion release rates, reaching the maximum concentration after about 10 h. This finding implies that such polymer materials can be promising as they are expected to release ions within several hours after their application on skin.

Comparison of axon extension: PTFE versus PLA formed by a 3D printer

Three-dimensional (3D) printers mainly create 3D objects by stacking thin layers of material. The effect of the tools created using the fused deposition modeling (FDM) 3D printer on nerve cells remains unclear. In this study, the effects of polytetrafluoroethylene (PTFE) models and two different types of polylactic acid (PLA) models (white or natural), were created using the FDM 3D printer on axon extension were compared using the Campenot chamber. Neurons were isolated from the dorsal root ganglia and added to the central compartment of the Campenot chambers after isolation, processing, and culturing. On day 7, after the initiation of the culture, the difference of the axon extensions to the side compartments of each group was confirmed. We also compared the pH and the amount of leakage when each of these chambers was used. The PLA was associated with a shorter axon extension than the PTFE (white p = 0.0078, natural p = 0.00391). No difference in the pH was observed (p = 0.347), but there was a significant difference on multiple group comparison (p = 0.0231) in the amount of leakage of the medium. PTFE was found to be a more suitable material for culturing attachments.

Design of biointerfaces composed of soft materials using controlled radical polymerizations

Soft interface materials have an immense potential for the improvement of biointerfaces, which are the interface of biological and artificially designed materials. Controlling the chemical and physical structures of the interfaces at the nanometer level plays an important role in understanding the mechanism of the functioning and its applications. Controlled radical polymerization (CRP) techniques, including atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization, have been developed in the field of precision polymer chemistry. It allows the formation of well-defined surfaces such as densely packed polymer brushes and self-assembled nanostructures of block copolymers. More recently, a novel technique to prepare polymers containing biomolecules, called biohybrids, has also been developed, which is a consequence of the advancement of CRP so as to proceed in an aqueous media with oxygen. This review article summarizes recent advances in CRP for the design of biointerfaces.

Toughening of Bioceramic Composites for Bone Regeneration

Bioceramics are widely considered as elective materials for the regeneration of bone tissue, due to their compositional mimicry with bone inorganic components. However, they are intrinsically brittle, which limits their capability to sustain multiple biomechanical loads, especially in the case of load-bearing bone districts. In the last decades, intense research has been dedicated to combining processes to enhance both the strength and toughness of bioceramics, leading to bioceramic composite scaffolds. This review summarizes the recent approaches to this purpose, particularly those addressed to limiting the propagation of cracks to prevent the sudden mechanical failure of bioceramic composites.

Spin-coated freestanding films for biomedical applications

Spin-coating is a widely employed technique for the fabrication of thin-film coatings over large areas with smooth and homogeneous surfaces. In recent years, research has extended the scope of spin-coating by developing methods involving the interface of the substrate and the deposited solution to obtain self-supported films, also called freestanding films. Thereby, such structures have been developed for a wide range of areas. Biomedical applications of spin-coated freestanding films include wound dressings, drug delivery, and biosensing. This review will discuss the fundamental physical and chemical processes governing the conventional spin-coating as well as the techniques to obtain freestanding films. Furthermore, developments within this field with a primary focus on tissue engineering applications will be reviewed.

Ultra-thin, transparent, porous substrates as 3D culture scaffolds for engineering ASC spheroids for high-magnification imaging

Three-dimensional (3D) culture is expected to reproduce biological tissues more representatively than monolayer culture, which is important for in vitro research such as drug screening. Recently, various cell culture substrates for spheroid engineering have been developed based on the prevention of cell adhesion. However, despite the expanded usability these substrates provide, they remain limited in terms of optical microscopy imaging of spheroids with high magnification lenses. This is because almost all substrates generated by nanoimprinting hamper the light passing through them owing to their low optical transparency caused by the thickness and surface structure. In this study, we achieved the preparation of spheroids from adipose-tissue derived stem cells (ASCs) on free-standing porous polymeric ultrathin films ("porous nanosheets") consisting of poly(d,l-lactic acid) (PDLLA) with thickness of 120 nm and average pore diameter of 4 μm. ASCs migrated on the porous nanosheet, leading to the spontaneous organization of spheroids anchored via a cell monolayer. The porous nanosheet also provided more than twice the optical transparency in confocal and holographic microscopy observation compared to conventional nanoimprinted substrates for 3D cell culture (NanoCulture Dish). The internal structure of the organized spheroids could be clearly observed with 40× magnification. In addition, the engineered spheroids showed bioactivities indicated by mRNA expression of fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF). Thus, porous nanosheets offer a unique cell culture substrate, not only for engineering 3D cellular organization from stem cells, but also for imaging detailed structure using light microscopy.

Novel Ultrathin Films Based on a Blend of PEG-b-PCL and PLLA and Doped with ZnO Nanoparticles

In this paper, a novel nanofilm type is proposed based on a blend of poly(ethylene glycol)-block-poly(ε-caprolactone) methyl ether (PEG-b-PCL) and poly(l-lactic acid), doped with zinc oxide nanoparticles (ZnO NPs) at different concentrations (0.1, 1, and 10 mg/mL). All nanofilm types were featured by a thickness value of ∼500 nm. Increasing ZnO NP concentrations implied larger roughness values (∼22 nm for the bare nanofilm and ∼67 nm for the films with 10 mg/mL of NPs), larger piezoelectricity (average d₃₃ coefficient for the film up to ∼1.98 pm/V), and elastic modulus: the nanofilms doped with 1 and 10 mg/mL of NPs were much stiffer than the nondoped controls and nanofilms doped with 0.1 mg/mL of NPs. The ZnO NP content was also directly proportional to the material melting point and crystallinity and inversely proportional to the material degradation rate, thus highlighting the stabilization role of ZnO particles. In vitro tests were carried out with cells of the musculoskeletal apparatus (fibroblasts, osteoblasts, chondrocytes, and myoblasts). All cell types showed good adhesion and viability on all substrate formulations. Interestingly, a higher content of ZnO NPs in the matrix demonstrated higher bioactivity, boosting the metabolic activity of fibroblasts, myoblasts, and chondrocytes and enhancing the osteogenic and myogenic differentiation. These findings demonstrated the potential of these nanocomposite matrices for regenerative medicine applications, such as tissue engineering.

Efficient differentiation and polarization of primary cultured neurons on poly(lactic acid) scaffolds with microgrooved structures

Synthetic biodegradable polymers including poly(lactic acid) (PLA) are attractive cell culture substrates because their surfaces can be micropatterned to support cell adhesion. The cell adhesion properties of a scaffold mainly depend on its surface chemical and structural features; however, it remains unclear how these characteristics affect the growth and differentiation of cultured cells or their gene expression. In this study, we fabricated two differently structured PLA nanosheets: flat and microgrooved. We assessed the growth and differentiation of mouse primary cultured cortical neurons on these two types of nanosheets after pre-coating with poly-D-lysine and vitronectin. Interestingly, prominent neurite bundles were formed along the grooves on the microgrooved nanosheets, whereas thin and randomly extended neurites were only observed on the flat nanosheets. Comparative RNA sequencing analyses revealed that the expression of genes related to postsynaptic density, dendritic shafts, and asymmetric synapses was significantly and consistently up-regulated in cells cultured on the microgrooved nanosheets when compared with those cultured on the flat nanosheets. These results indicate that microgrooved PLA nanosheets can provide a powerful means of establishing a culture system for the efficient and reproducible differentiation of neurons, which will facilitate future investigations of the molecular mechanisms underlying the pathogenesis of neurological disorders.

Polysaccharide Coating of Gelatin Gels for Controlled BSA Release

Self-assembly of natural polymers constitute a powerful route for the development of functional materials. In particular, layer-by-layer (LBL) assembly constitutes a versatile technique for the nanostructuration of biobased polymers into multilayer films. Gelatin has gained much attention for its abundance, biodegradability, and excellent gel-forming properties. However, gelatin gels melt at low temperature, thus limiting its practical application. With respect to the above considerations, here, we explored the potential application of gelatin gels as a matrix for protein delivery at physiological temperature. A model protein, bovine serum albumin (BSA), was encapsulated within gelatin gels and then coated with a different number of bilayers of alginate and chitosan (10, 25, 50) in order to modify the diffusion barrier. The coated gel samples were analyzed by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) and confocal Raman spectroscopy, and it was found that the multilayer coatings onto polymer film were interpenetrated to some extent within the gelatin. The obtained results inferred that the coating of gelatin gels with polysaccharide multilayer film increased the thermal stability of gelatin gels and modulated the BSA release. Finally, the influence of a number of bilayers onto the drug release mechanism was determined. The Ritger-Peppas model was found to be the most accurate to describe the diffusion mechanism.

PDMS Sylgard 527-Based Freely Suspended Ultrathin Membranes Exhibiting Mechanistic Characteristics of Vascular Basement Membranes

In the past, significant effort has been made to develop ultrathin membranes exhibiting physiologically relevant mechanical properties, such as thickness and elasticity of native basement membranes. However, most of these fabricated membranes have a relatively high elastic modulus, ∼MPa-GPa, relevant only to retinal and epithelial basement membranes. Vascular basement membranes exhibiting relatively low elastic modulus, ∼kPa, on the contrary, have seldom been mimicked. Membranes demonstrating high compliance, with moduli ranging in ∼kPa along with sub-microscale thicknesses have rarely been reported, and would be ideal to mimic vascular basement membranes in vitro. To address this, we fabricate ultrathin membranes demonstrating the mechanistic features exhibited by their vascular biological counterparts. Salient features of the fabricated ultrathin membranes include free suspension, physiologically relevant thickness ∼sub-micrometers, relatively low modulus ∼kPa, and sufficiently large culture area ∼20 mm². To fabricate such ultrathin membranes, undiluted PDMS Sylgard 527 was utilized as opposed to the conventional diluted polymer-solvent mixture approach. In addition, the necessity to have a sacrificial layer for releasing membranes from the underlying substrates was also eliminated in our approach. The novelty of our work lies in achieving the distinct combination of membranes having thickness in sub-micrometers and the associated elasticity in kilopascal using undiluted polymer, which past approaches with dilution have not been able to accomplish. The ultrathin membranes with average thickness of 972 nm (thick) and 570 nm (thin) were estimated to have an elastic modulus of 45 and 214 kPa, respectively. Contact angle measurements revealed the ultrathin membranes exhibited hybrophobic characteristics in unpeeled state and transformed to hydrophilic behavior when freely suspended. Human umbilical vein endothelial cells were cultured on the polymeric ultrathin membranes, and the temporal cell response to change in local compliance of the membranes was studied by evaluating the cell spread area, density, percentage area coverage, and spread rate. After 24 h, single cells, pairs, and group of three to four cells were noticed on highly compliant thick membranes, having average thickness of 972 nm and modulus of 45 kPa. On the contrary, the cell monolayer was noted on the glass slide acting as a control. For the thin membranes featuring average thickness of 570 nm and modulus of 214 kPa, the cells tend to exhibit response similar to that on control with initiation of monolayer formation. Our results indicate, the local compliance, in turn, the membrane thickness governs the cell behavior and this can have vital implications during disease initiation and progression, wound healing, and cancer cell metastasis.

Applications of Nanosheets in Frontier Cellular Research

Several types of nanosheets, such as graphene oxide (GO) nanosheet, molybdenum disulfide (MoS₂) and poly(l-lactic acid) (PLLA) nanosheets, have been developed and applied in vitro in cellular research over the past decade. Scientists have used nanosheet properties, such as ease of modification and flexibility, to develop new cell/protein sensing/imaging techniques and achieve regulation of specific cell functions. This review is divided into three main parts based on the application being examined: nanosheets as a substrate, nanosheets as a sensitive surface, and nanosheets in regenerative medicine. Furthermore, the applications of nanosheets are discussed, with two subsections in each section, based on their effects on cells and molecules. Finally, the application prospects of nanosheets in cellular research are summarized.

Anticancer activity of drug-loaded calcium phosphate nanocomposites against human osteosarcoma

BACKGROUND

Calcium phosphate (CaP) based nanoparticles are considered to be ideal drug carriers for delivery of anticancer drugs because of their excellent biocompatibility and pH responsiveness. However, CaP nanoparticles have the problems of limited drug load capacity, initial burst release, and short-term release. Thus, we prepared the CaP nanocomposites containing anticancer drug such as caffeic acid (CA-NP), chlorogenic acid (CG-NP), or cisplatin (CP-NP) in the presence of alginate as a polymer template to control the release rate of drugs.

RESULTS

The drug-loaded CaP nanocomposites exhibited spherical shape with a size of under 100 nm and the size of nanocomposites was hardly affected by the addition of drug. UV-visible spectroscopic analysis confirmed the insertion of drug into the CaP nanocomposites. These nanocomposites showed an initial burst release of drug, followed by a prolonged release, in which the release profile of drugs was depended on the solution pH. In addition, the drug-loaded CaP nanocomposites revealed anticancer activity on human osteosarcoma in a manner dependent on concentration of drugs and time.

CONCLUSIONS

The drug-loaded CaP nanocomposites can contribute to the development of a new generation of controlled drug release carriers for chemotherapy of cancers.

Stretchable, adhesive and ultra-conformable elastomer thin films

Thermoplastic elastomers are attractive materials because of the drastic changes in their physical properties above and below the glass transition temperature (T_g). In this paper, we report that free-standing polystyrene (PS, T_g: 100 °C) and polystyrene-polybutadiene-polystyrene triblock copolymer (SBS, T_g: -70 °C) thin films with a thickness of hundreds of nanometers were prepared by a gravure coating method. Among the mechanical properties of these thin films determined by bulge testing and tensile testing, the SBS thin films exhibited a much lower elastic modulus (ca. 0.045 GPa, 212 nm thickness) in comparison with the PS thin films (ca. 1.19 GPa, 217 nm thickness). The lower elastic modulus and lower thickness of the SBS thin films resulted in higher conformability and thus higher strength of adhesion to an uneven surface such as an artificial skin model with roughness (R_a = 10.6 μm), even though they both have similar surface energies. By analyzing the mechanical properties of the SBS thin films, the elastic modulus and thickness of the thin films were strongly correlated with their conformability to a rough surface, which thus led to a high adhesive strength. Therefore, the SBS thin films will be useful as coating layers for a variety of materials.

Confinement of a β-barrel protein in nanoperforated free-standing nanomembranes for ion transport

Bioinspired free-standing nanomembranes (FSNMs) for selective ion transport have been tailored by immobilizing the Omp2a β-barrel membrane protein inside nanoperforations created in flexible poly(lactic acid) (PLA) nanomembranes. Perforated PLA FSNMs have been prepared by spin-coating a 99 : 1 PLA : poly(vinyl alcohol) mixture, and through a phase segregation process nanofeatures with dimensions similar to the entire nanomembrane thickness (∼110 nm) were induced. These nanofeatures have subsequently been transformed into nanoperforations (diameter: ∼51 nm) by selective solvent etching. The protein confined inside the nanopores of PLA FSNMs preserves the β-barrel structure and organizes in ovoid aggregates. The transport properties of Na⁺, K⁺, and Ca²⁺ across non-perforated PLA, nanoperforated PLA, and Omp2a-filled nanoperforated PLA have been monitored by measuring the nanomembrane resistance with electrochemical impedance spectroscopy (EIS). The incorporation of nanoperforations enhances the transport of ions across PLA nanomembranes, whereas the functionality of immobilized Omp2a is essential to exhibit effects similar to those observed in biological nanomembranes. Indeed, Omp2a-filled nanoperforated PLA nanomembranes exhibit stronger affinity towards Na⁺ and Ca²⁺ ions than towards K⁺. In summary, this work provides a novel bioinspired strategy to develop mechanically stable and flexible FSNMs with channels for ion transport, which are precisely located inside artificial nanoperforations, thus holding great potential for applications in biofiltration and biosensing.

Polymeric Microporous Nanofilms as Smart Platforms for in Vitro Assessment of Nanoparticle Translocation and Caco-2 Cell Culture

The study of nanomaterial translocation across epithelial barriers is often hindered by the low permeability of transwell membranes to nanoparticles. To address this issue ultra-thin poly(L-lactic acid) nanofilms with zero tortuosity micropores were developed for use in nanoparticle passage tests. In this study we demonstrate that microporous polymeric nanofilms allow a significantly higher passage of silver nanoparticles in comparison with commercial membranes normally used in transwell inserts. A reliable procedure for collecting free-standing nanofilms which enables their manipulation and use in lab-on-chip systems is described. We also demonstrate the cytocompatibility of porous nanofilms and their ability to sustain the adhesion and proliferation of Caco-2 cells. Ultra-thin microporous membranes show promise as low-cost nanomaterial screening tools and may be used as matrices for the development of bioengineered systems for mimicking the intestinal epithelium.

Cellular Response to Non-contacting Nanoscale Sublayer: Cells Sense Several Nanometer Mechanical Property

Cell adhesion is influenced not only from the surface property of materials but also from the mechanical properties of the nanometer sublayer just below the surface. In this study, we fabricated a well-defined diblock polymer brush composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate (AEMA). The underlying layer of poly(MPC) is a highly viscous polymer, and the surface layer of poly(AEMA) is a cell-adhesive cationic polymer. The adhesion of L929 mouse fibroblasts was examined on the diblock polymer brush to see the effect of a non-contacting underlying polymer layer on the cell-adhesion behavior. Cells could sense the viscoelasticity of the underlying layers at the nanometer level, although the various fabricated diblock polymer brushes had the same surface property and the functional group. Thus, we found a new factor which could control cell spread at the nanometer level, and this insight would be important to design nanoscale biomaterials and interfaces.

Nanostructured ultra-thin patches for ultrasound-modulated delivery of anti-restenotic drug

This work aims to demonstrate the possibility to fabricate ultra-thin polymeric films loaded with an anti-restenotic drug and capable of tunable drug release kinetics for the local treatment of restenosis. Vascular nanopatches are composed of a poly(lactic acid) supporting membrane (thickness: ~250 nm) on which 20 polyelectrolyte bilayers (overall thickness: ~70 nm) are alternatively deposited. The anti-restenotic drug is embedded in the middle of the polyelectrolyte structure, and released by diffusion mechanisms. Nanofilm fabrication procedure and detailed morphological characterization are reported here. Barium titanate nanoparticles (showing piezoelectric properties) are included in the polymeric support and their role is investigated in terms of influence on nanofilm morphology, drug release kinetics, and cell response. Results show an efficient drug release from the polyelectrolyte structure in phosphate-buffered saline, and a clear antiproliferative effect on human smooth muscle cells, which are responsible for restenosis. In addition, preliminary evidences of ultrasound-mediated modulation of drug release kinetics are reported, thus evaluating the influence of barium titanate nanoparticles on the release mechanism. Such data were integrated with quantitative piezoelectric and thermal measurements. These results open new avenues for a fine control of local therapies based on smart responsive materials.

Self-assembly of polydimethylsiloxane structures from 2D to 3D for bio-hybrid actuation

This work aims to demonstrate the feasibility of a novel approach for the development of 3D self-assembled polydimethylsiloxane structures, to be used as engineered flexible matrices for bio-hybrid actuation. We described the fabrication of engineered bilayers, organized in a 3D architecture by means of a stress-induced rolling membrane technique. Such structures were provided with ad hoc surface topographies, for both cell alignment and cell survival after membrane rolling. We reported the results of advanced finite element model simulations, predicting the system behavior in terms of overall contraction, induced by the contractile activity of muscle cells seeded on the membrane. Then, we tested in vitro the structure with primary cardiomyocytes to evaluate the real bio-actuator contraction, thus validating the simulation results. At a later stage, we provided the samples with a stable fibronectin coating, by covalently binding the protein on the polymer surface, thus enabling long-term cultures with C2C12 skeletal muscle cells, a more controllable cell type. These tests revealed cell viability and alignment on the rolled structures, but also the ability of cells to differentiate and to form multinucleated and oriented myotubes on the polymer surface, also supported by a fibroblast feeder layer. Our results highlighted the possibility of developing 3D rolled PDMS structures, characterized by different mechanical properties, as novel bio-hybrid actuators.

Size- and shape-dependent foreign body immune response to materials implanted in rodents and non-human primates

The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

Free-standing nanomembranes, which are emerging as versatile elements in biomedical applications, are evolving from being composed of insulating (bio)polymers to electroactive conducting polymers.

Two dimensional nanosheets as conductive, flexible elements in biomaterials

Two dimensional nanosheets have great potential as conductive and/or flexible elements in biomaterials.

Micropatterned polymeric nanosheets for local delivery of an engineered epithelial monolayer

Like a carpet for cells, micropatterned polymeric nanosheets are developed toward local cell delivery. The nanosheets direct morphogenesis of retinal pigment epithelial (RPE) cells and allow for the injection of an engineered RPE monolayer through syringe needles without the loss of cell viability. Such an ultrathin carrier has the promise of a minimally invasive delivery of cells into narrow tissue spaces.

Influence of nanoparticle-embedded polymeric surfaces on cellular adhesion, proliferation, and differentiation

The development of functional substrates to direct cellular organization is important for biomedical applications such as regenerative medicine and biorobotics. In this study, we prepared freestanding polymeric ultrathin films (nanofilms) consisting of poly(lactic acid) (PLA) and magnetic nanoparticles (MNPs), and evaluated the effects of their surface properties on the organization of cardiac-like rat myoblasts (H9c2). We changed surface properties of the PLA nanofilms (i.e., roughness and wettability) as a function of MNPs concentration. We found that the incorporation of MNPs into the nanofilms enhanced both proliferation and adhesion of H9c2 cells. Through the morphological assessment of the differentiated H9c2 cells, we also found that the presence of MNPs significantly increased the fusion index and the surface area of myotubes. In conclusion, the embedding of MNPs is a simple method to tailor the physicochemical properties of the polymeric nanofilms, yet it is an effective approach to enhance the cellular morphogenesis in the field of cardiac tissue engineering for regenerative medicine and biorobotics applications.

Geometry-driven cell organization determines tissue growths in scaffold pores: consequences for fibronectin organization

To heal tissue defects, cells have to bridge gaps and generate new extracellular matrix (ECM). Macroporous scaffolds are frequently used to support the process of defect filling and thus foster tissue regeneration. Such biomaterials contain micro-voids (pores) that the cells fill with their own ECM over time. There is only limited knowledge on how pore geometry influences cell organization and matrix production, even though it is highly relevant for scaffold design. This study hypothesized that 1) a simple geometric description predicts cellular organization during pore filling at the cell level and that 2) pore closure results in a reorganization of ECM. Scaffolds with a broad distribution of pore sizes (macroporous starPEG-heparin cryogel) were used as a model system and seeded with primary fibroblasts. The strategies of cells to fill pores could be explained by a simple geometrical model considering cells as tensioned chords. The model matched qualitatively as well as quantitatively by means of cell number vs. open cross-sectional area for all pore sizes. The correlation between ECM location and cell position was higher when the pores were not filled with tissue (Pearson's coefficient ρ = 0.45±0.01) and reduced once the pores were closed (ρ = 0.26±0.04) indicating a reorganization of the cell/ECM network. Scaffold pore size directed the time required for pore closure and furthermore impacted the organization of the fibronectin matrix. Understanding how cells fill micro-voids will help to design biomaterial scaffolds that support the endogenous healing process and thus allow a fast filling of tissue defects.

Effect of mechanical instability of polymer scaffolds on cell adhesion

The adhesion of fibroblast on polymer bilayers composed of a glassy polystyrene (PS) prepared on top of a rubbery polyisoprene (PI) was studied. Since the top PS layer is not build on a glassy, or firm, foundation, the system becomes mechanically unstable with decreasing thickness of the PS layer. When the PS film was thinner than 25 nm, the number of cells adhered to the surface decreased and the cells could not spread well. On a parallel experiment, the same cell adhesion behavior was observed on plasma-treated PS/PI bilayer films, where in this case, the surface was more hydrophilic than that of the intact films. In addition, the fluorescence microscopic observations revealed that the formation of F-actin filaments in fibroblasts attached to the thicker PS/PI bilayer films was greater than those using the thinner PS/PI bilayer films. On the other hand, the thickness dependence of the cell adhesion behavior was not observed for the PS monolayer films. Taking into account that the amount of adsorbed protein molecules evaluated by a quartz crystal microbalance method was independent of the PS layer thickness of the bilayer films, our results indicate that cells, unlike protein molecules, could sense a mechanical instability of the scaffold.

Engineered nanomembranes for directing cellular organization toward flexible biodevices

Controlling the cellular microenvironment can be used to direct the cellular organization, thereby improving the function of synthetic tissues in biosensing, biorobotics, and regenerative medicine. In this study, we were inspired by the microstructure and biological properties of the extracellular matrix to develop freestanding ultrathin polymeric films (referred as "nanomembranes") that were flexible, cell adhesive, and had a morphologically tailorable surface. The resulting nanomembranes were exploited as flexible substrates on which cell-adhesive micropatterns were generated to align C2C12 skeletal myoblasts and embedded fibril carbon nanotubes enhanced the cellular elongation and differentiation. Functional nanomembranes with tunable morphology and mechanical properties hold great promise in studying cell-substrate interactions and in fabricating biomimetic constructs toward flexible biodevices.

Inkjet printing of protein microarrays on freestanding polymeric nanofilms for spatio-selective cell culture environment

In the last years, an increasing interest in bio-hybrid systems for what concerns the precise control of cell-material interactions has emerged. This trend leads towards the development of new nano-structured devices such as bioMEMS, tissue-engineering scaffolds, biosensors, etc. In the present study, we focused on the development of a spatio-selective cell culture environment based on the inkjet printing of bio-patterns on polymeric ultra-thin films (nanofilms) composed of poly(methylmethacrylate) (PMMA). Freestanding PMMA nanofilms having hundreds-of-nm thickness were prepared by spin-coating. Different shapes of cell adhesion promoters such as poly (L-lysine) (PLL) were micropatterned by inkjet printing. Moreover, to promote cell adhesion, the surface of PLL microarrays was modified with fibronectin via electorostatic interaction. The selective deposition of C2C12 skeletal muscle cells was confirmed and their viability was qualitatively assessed after 24 h. The combination of muscular cells with protein micropatterned freestanding nanofilm is beneficial for the implementation of new bio-hybrid system in muscular tissue engineering.