Blood-Compatible Polymer for Hepatocyte Culture with High Hepatocyte-Specific Functions toward Bioartificial Liver Development

Altering the bio-inert properties of surfaces by fluorinated copolymers of mPEGMA

Hydrophilic materials display "bio-inert properties", meaning that they are less recognized as foreign substances by proteins and cells. Such materials are often water soluble; therefore, one general approach to enable the use of these materials in various applications deals with copolymerizing hydrophilic monomers with hydrophobic ones to facilitate such resulting copolymers water insoluble. However, reducing the hydrophilic monomer amount may reduce the bio-inert properties of the material. The decrease in bio-inert properties can be avoided when small amounts of fluorine are used in copolymers with hydrophilic monomers, as presented in this article. Even in small quantities (7.9 wt%), the fluorinated monomer, 1,1,1,3,3,3-hexafluoropropan-2-yl 2-fluoroacrylate (FAHFiP), contributed to the improved hydrophobicity of the polymers of the long side-chain poly(ethylene glycol) methyl ether methacrylate (mPEGMA) bearing nine ethylene glycol units turning them water insoluble. As evidenced by the AFM deformation image, a phase separation between the FAHFiP and mPEGMA domains was observed. The copolymer with the highest amount of the fluorinated monomer (66.2 wt%) displayed also high (82 %) FAHFiP amount at the polymer-water interface. In contrast, the hydrated sample with the lowest FAHFiP/highest mPEGMA amount was enriched of three times more hydrophilic domains at the polymer-water interface compared to that of the sample with the highest FAHFiP content. Thus, by adding a small FAHFiP amount to mPEGMA copolymers, water insoluble in the bulk too, could be turned highly hydrophilic at the water interface. The high content of intermediate water contributed to their excellent bio-inert properties. Platelet adhesion and fibrinogen adsorption on their surfaces were even more decreased as compared to those on poly(2-methoxyethyl acrylate), which is typically used in medical devices.

Enrichment of Cancer Cells Based on Antibody-Free Selective Cell Adhesion

Blood-compatible and cell-adhering polymer materials are extremely useful for regenerative medicine and disease diagnosis. (Meth)acryl polymers with high hydrophilicity have been widely used in industries, and attempts to apply these polymers in the medical field are frequently reported. We focused on crosslinked polymer films prepared using bifunctional monomers, which are widely used as coating materials, and attempted to alter the cell adhesion behavior while maintaining blood compatibility by changing the chemical structure of the crosslinker. Four bifunctional monomers were studied, three of which were found to be blood-compatible polymers and to suppress platelet adhesion. The adhesion behavior of cancer cells to polymer films varied; moreover, the cancer model cells MCF-7 [EpCAM(+)] and MDA-MB-231 [EpCAM (-)], with different expression levels of epithelial cell adhesion molecule (EpCAM), showed distinct adhesion behavior for each material. We suggest that a combination of these materials has the potential to selectively capture and enrich highly metastatic cancer cells.

Roles of interfacial water states on advanced biomedical material design

When biomedical materials come into contact with body fluids, the first reaction that occurs on the material surface is hydration; proteins are then adsorbed and denatured on the hydrated material surface. The amount and degree of denaturation of adsorbed proteins affect subsequent cell behavior, including cell adhesion, migration, proliferation, and differentiation. Biomolecules are important for understanding the interactions and biological reactions of biomedical materials to elucidate the role of hydration in biomedical materials and their interaction partners. Analysis of the water states of hydrated materials is complicated and remains controversial; however, knowledge about interfacial water is useful for the design and development of advanced biomaterials. Herein, we summarize recent findings on the hydration of synthetic polymers, supramolecular materials, inorganic materials, proteins, and lipid membranes. Furthermore, we present recent advances in our understanding of the classification of interfacial water and advanced polymer biomaterials, based on the intermediate water concept.

Modulation of Biological Responses of Tumor Cells Adhered to Poly(2-methoxyethyl acrylate) with Increasing Cell Viability under Serum-Free Conditions

Circulating tumor cells in body fluids are important biomarkers in cancer diagnosis. The culture of tumor cells isolated from body fluids can provide intrinsic information about tumors and can be used to screen for the best anticancer drugs. However, the culture of primary tumor cells has been hindered by their low viability and difficulties in recapitulating the phenotype of primary tumors in in vitro culture. The culture of tumor cells under serum-free conditions is one of the methodologies to maintain the phenotype and genotype of primary tumors. Poly(2-methoxyethyl acrylate) (PMEA)-coated substrates have been investigated to prolong the proliferation of tumor cells under serum-free conditions. In this study, we investigated the detailed behavior and the mechanism of the increase in tumor cell viability after adherence to PMEA substrates. The blebbing formation of tumor cells on PMEA was attributed not to apoptosis but to the low adhesion strength of cells on PMEA. Moreover, blebbing tumor cells showed amoeboid movement and formed clusters with other cells via N-cadherin, leading to an increase in tumor cell viability. Furthermore, the behaviors of tumor cells adhered to PMEA under serum-free conditions were involved in the activation of the PI3K and Rho-associated protein kinase pathways. Thus, we propose that PMEA would be suitable for the development of devices to cultivate primary tumor cells under serum-free conditions for the label-free diagnosis of cancer.

Mimicking Physiologically Relevant Hepatocyte Zonation Using Immunomodulatory Silk Liver Extracellular Matrix Scaffolds toward a Bioartificial Liver Platform

Mimicking nativelike metabolic zonation is indispensable to develop an efficient bioartificial liver model, as it facilitates physiological cues, hepatocyte polarity, and phenotypic functions. The present study shows the first evidence of hepatocyte metabolic heterogeneity in an in vitro liver model encompassing liver extracellular matrix (ECM)-functionalized silk scaffolds (LECM-SF) by altering ECM proportion. Upon static culture, individual LECM-SF scaffold supports differential synthetic and metabolic functions of cultured primary neonatal rat hepatocytes (PNRHs), owing to discrete biophysical attributes. A single in vitro liver system comprising PNRHs seeded LECM-SF scaffolds assisting periportal to pericentral gradient functions is stacked and matured in a perfusion bioreactor to simulate oxygen gradient. The scaffold with high ECM supports periportal-specific albumin synthesis, urea secretion, and bile duct formation, albeit scaffold with low ECM supports pericentral-specific cytochrome P450 activity. Extensive physicochemical characterizations confirmed the stability and interconnected porous network of scaffolds, signifying cellular infiltration and bidirectional nutrient diffusion. Furthermore, scaffolds demonstrate minimal thrombogenicity, reduced foreign-body response, and enhanced pro-remodeling macrophage activation, supporting constructive tissue remodeling. The developed liver model with zone-specific functions would be a promising avenue in bioartificial liver and drug screening.

Role of interfacial water in determining the interactions of proteins and cells with hydrated materials

Water molecules play a crucial role in biointerfacial interactions, including protein adsorption and desorption. To understand the role of water in the interaction of proteins and cells at biological interfaces, it is important to compare particular states of hydration water with various physicochemical properties of hydrated biomaterials. In this review, we discuss the fundamental concepts for determining the interactions of proteins and cells with hydrated materials along with selected examples corresponding to our recent studies, including poly(2-methoxyethyl acrylate) (PMEA), PMEA derivatives, and other biomaterials. The states of water were analyzed by differential scanning calorimetry, in situ attenuated total reflection infrared spectroscopy, and surface force measurements. We found that intermediate water which is loosely bound to a biomaterial, is a useful indicator of the bioinertness of material surfaces. This finding on intermediate water provides novel insights and helps develop novel experimental models for understanding protein adsorption in a wide range of materials, such as those used in biomedical applications.

Synthesis of Amphiphilic Statistical Copolymers Bearing Methoxyethyl and Phosphorylcholine Groups and Their Self-Association Behavior in Water

Biocompatible amphiphilic statistical copolymers P(MEA/MPCm) composed of 2-methoxyethyl acrylate (MEA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) were prepared with three different mol% of the hydrophilic unit MPC (m = 6, 12 and 46 mol%). The monomer reactivity ratios of MEA (rMEA) and MPC (rMPC) were 0.53 and 2.21, respectively. The rMEA × rMPC value of 1.17 demonstrated that statistical copolymerization was successful. P(MEA/MPC12) and P(MEA/MPC46) copolymers did not undergo aggregation in water, whereas the P(MEA/MPC6) copolymer formed micelles in water with a hydrodynamic radius (Rh) of 96.9 nm and a critical aggregation concentration, which was determined using pyrene fluorescence, at 0.0082 g/L. The restricted motion of the protons in the hydrophobic MEA units in the micelles' cores provided additional evidence of self-association in P(MEA/MPC6).

Electrodeposition of Zwitterionic PEDOT Films for Conducting and Antifouling Surfaces

Conferring antifouling properties can extend the use of conducting polymers in biosensors and bioelectronics under complex biological conditions. On the basis of the antifouling properties of a series of zwitterionic polymers, we synthesized new thiophene-based compounds bearing a phosphorylcholine, carboxybetaine, or sulfobetaine pendant group. The monomers were synthesized by a facile reaction of thiol-functionalized 3,4-ethylenedioxythiophene with zwitterionic methacrylates. Electrochemical copolymerization was performed to deposit zwitterionic poly(3,4-ethylenedioxythiophene) (PEDOT) films with tunable conducting and antifouling properties on a conducting substrate. Electrochemical impedance spectroscopy showed that the conductivity and capacitance decreased with increasing zwitterionic content in the films. Protein adsorption and cell adhesion studies showed the effects of the type and content of zwitterions on the antifouling characteristics. Optimization of the electrodeposition conditions enabled development of both conducting and antifouling polymer films. These antifouling conjugated functional polymers have promising applications in biological environments.

A Computational Method for Classifying Different Human Tissues with Quantitatively Tissue-Specific Expressed Genes

Tissue-specific gene expression has long been recognized as a crucial key for understanding tissue development and function. Efforts have been made in the past decade to identify tissue-specific expression profiles, such as the Human Proteome Atlas and FANTOM5. However, these studies mainly focused on "qualitatively tissue-specific expressed genes" which are highly enriched in one or a group of tissues but paid less attention to "quantitatively tissue-specific expressed genes", which are expressed in all or most tissues but with differential expression levels. In this study, we applied machine learning algorithms to build a computational method for identifying "quantitatively tissue-specific expressed genes" capable of distinguishing 25 human tissues from their expression patterns. Our results uncovered the expression of 432 genes as optimal features for tissue classification, which were obtained with a Matthews Correlation Coefficient (MCC) of more than 0.99 yielded by a support vector machine (SVM). This constructed model was superior to the SVM model using tissue enriched genes and yielded MCC of 0.985 on an independent test dataset, indicating its good generalization ability. These 432 genes were proven to be widely expressed in multiple tissues and a literature review of the top 23 genes found that most of them support their discriminating powers. As a complement to previous studies, our discovery of these quantitatively tissue-specific genes provides insights into the detailed understanding of tissue development and function.

A simple strategy for robust preparation and characterisation of hydrogels derived from chitosan and amino functional monomers for biomedical applications

Molecular interactions of amino functional (AF) monomers with chitosan (CS) lead to the formation of external stimuli responsive hydrogels (HGs). These have the potential to produce biomaterials with novel properties by a simple blending approach. Six independent AF monomers such as diethylenetriamine (DETA), bis(3-aminopropyl)amine (BAPA), 3,3'-diamino-N-methyldipropyleamine (DAMPA), hexamethylenediamine (HMDA), N,N-dimethylethylamine (DMEA) and diethylamine (DEA) with distinct functional groups and chain lengths were designed to form stable HGs at physiological pH. Such AF monomers are able to form HGs within a short time (in the range from 10 to 19 seconds) by physically interacting with CS. This is an alternative to the covalently crosslinking reaction process, providing cost effective HG biomaterials. HG complexes were characterized by rheometry, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The interaction between AF monomers and the CS polymer has been discussed and the results have been confirmed by FTIR analysis. The storage modulus (G'), loss modulus (G'') and complex viscosity (η*) were evaluated for all HGs using a rheometer, and the ratios of CS and the particular AF monomer were optimized for stable HG formation. The swelling ratio was evaluated using a simple method and was found to be directly related to the structure of the AF monomer, pH and temperature. These HGs were utilised for encapsulation, and the release of active molecules (e.g., reactive red 120 (RR120) as a model compound) was measured at low pH 5.5, physiological pH 7.4 and high pH 9.5. The cell viability and cellular compatibility of the HGs were evaluated in vitro cell culture, demonstrating that all the five different types of HGs support cellular compatibility, attachment and growth. The physical mixing of AF monomers with CS is expedited for the development of new bespoke economically viable biomaterials.

Functional hepatocyte clusters on bioactive blend silk matrices towards generating bioartificial liver constructs

The creation of in vitro functional hepatic tissue simulating micro-environmental niche of native liver is a keen area of research due to its demand in bioartificial liver (BAL) and cell-based tissue engineering. Here, we investigated the potential of novel blend (BA) silk scaffold fabricated by blending mulberry (Bombyx mori, BM) silk fibroin with cell adhesion motif (RGD) rich non-mulberry (Antheraea assamensis, AA) silk fibroin, in generating a functional liver construct. Three-dimensional (3D) porous silk scaffolds (BM, AA and BA) were physico-chemically characterized and functionally evaluated using human hepatocarcinoma cells (HepG2) and primary neonatal rat hepatocytes. The growth and distribution of hepatocytes within the scaffolds were tracked by FESEM, alamar blue proliferation assay and live/dead staining. Hemocompatible BA scaffolds supported the formation of high density hepatocyte clusters, facilitating cell-matrix and cell-cell interactions. Blend scaffolds evinced enhanced liver-specific functions of cultured hepatocytes in terms of albumin synthesis, urea synthesis and cytochrome P450 enzyme activity over 21 days. Subcutaneous implantation of scaffolds demonstrated minimal macrophage infiltration in blend scaffolds. These findings substantiate that the integral property of blend (BA) scaffold offers a befitting environment by influencing spheroidal growth of hepatocytes with enhanced biological activity. Collectively, the present study provides a new 3D bio-matrix niche for growing functional liver cells that would have future prospects in BAL as well as regenerative medicine.

STATEMENT OF SIGNIFICANCE

An end stage liver disease called cirrhosis perturbs the self-healing ability and physiological functions of liver. Due to the scarcity of healthy donors, a functional in vitro hepatic construct retaining the liver-specific functions is in great demand for its prospects in bioartificial liver (BAL) and cell-based tissue engineering. Physicochemical attributes of a matrix influence the behavior of cultured hepatocytes in terms of attachment, morphology and functionality. Mulberry and non-mulberry silk fibroin presents unique amino acid sequence with difference in hydrophobicity and crystallinity. Considering this, the present study focuses on the development of a suitable three-dimensional (3D) bioactive matrix incorporating both mulberry silk fibroin and cell adhesion motif (RGD) rich non-mulberry silk fibroin. Porous silk blend scaffolds facilitated the formation of hepatocyte clusters with enhanced liver-specific functions emphasizing both cell-cell and cell-matrix interactions. Hemocompatibility and integral property of blend scaffolds offers a biological niche for seeding functional liver cells that would have future prospects in biohybrid devices.

Promotion of Adipogenesis of 3T3-L1 Cells on Protein Adsorption-Suppressing Poly(2-methoxyethyl acrylate) Analogs

Stem cell differentiation is an important issue in regenerative medicine and tissue engineering. It has been reported that cell shape is one of the factors that determine the lineage commitment of mesenchymal stem cells (MSCs). Therefore, the substrates have been developed to control their shapes. Recently, we found that poly(2-methoxyethyl acrylate) (PMEA) analogs can control tumor cell shape through the alteration of protein adsorption. Here, the adipogenesis of an adipocyte-progenitor cell, 3T3-L1 cells, was attempted; adipogenesis was to be regulated by surfaces coated with PMEA analogs through the control of their shape. The adipogenesis of 3T3-L1 cells was promoted on the surfaces coated with PMEA and its analogs, PMe3A and PMe2A. Evident focal adhesions were hardly observed on these surfaces, suggesting that integrin signal activation was suppressed. Additionally, actin assembly and cell spreading were suppressed on these surfaces. Therefore, the surfaces coated with PMEA analogs are expected to be suitable surfaces to regulate adipogenesis through the suppression of cell spreading. Additionally, we found that protein adsorption correlated with actin assembly and adipogenesis.

Blood-compatible poly (2-methoxyethyl acrylate) for the adhesion and proliferation of lung cancer cells toward the isolation and analysis of circulating tumor cells

Circulating tumor cells have received attention for their role in cancer diagnosis and the decision on which chemotherapeutic course to take. For these purposes, the isolation of circulating tumor cells has been important. Previously, we reported that non-blood cells can adhere on blood-compatible polymer substrates, such as poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate). In this study, we examined whether blood-compatible poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) allow the adhesion and growth of A549 lung cancer cells for isolating circulating tumor cells by adhesion-mediated manner to diagnose metastatic cancer and to decide on the chemotherapeutic course. A549 cells can adhere on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates via an integrin-dependent mechanism after 1 h of incubation, suggesting that blood-compatible poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates possess the ability to capture circulating tumor cells selectively from peripheral blood. After 1 day of culture, A549 cells started to spread on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates. A549 can also grow on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates. Additionally, the chemoresistance of A549 cells against 5-fluorouracil on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates was similar to that on the conventional cell culture substrate, tissue culture polystyrene. These results indicate that circulating tumor cells can be cultured on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates after they are isolated from peripheral blood, and poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates can be used as circulating tumor cell culture substrates for screening anti-cancer drugs. Therefore, poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates might be able to be applied to the development of a new device for a circulating tumor cell–based diagnosis of metastatic cancer and a personalized medicine approach regarding the decision of which chemotherapeutic course should be taken.

Adhesion-based simple capture and recovery of circulating tumor cells using a blood-compatible and thermo-responsive polymer-coated substrate

Circulating tumor cells (CTCs) have been a focus of study for metastatic cancer diagnostics, in in vitro anti-cancer drug screening to decide the chemotherapeutic course, and cancer biology research.