Chemistry-Induced Effects on Cell Behavior upon Plasma Treatment of pNIPAAM

In the field of bioengineering, depending on the required application, the attachment of various biological entities to the biomaterial is either favored or needs to be prevented. Therefore, different surfaces modification strategies were developed in combination with the characteristics of the materials. The present contribution reports on the use of the specific surface property of a thermoresponsive polymer poly(N-isopropylacrylamide) pNIPAAM obtained by spin coating in combination with plasma treatment for tuning cell behavior on treated polymeric surfaces. Topographical information for the plasma-treated pNIPAAM coatings obtained by Atomic Force Microscopy (AFM) measurements evidenced a more compact surface for Ar treatment due to combined etching and redeposition, while for oxygen, a clear increase of pores diameter is noticed. The chemical surface composition as determined by X-ray Photoelectron Spectroscopy showed the specific modifications induced by plasma treatment, namely strong oxidation for oxygen plasma treatment illustrated by eight times increase of O-C=O contribution and respectively an increase of C-N/O=C-N bonds in the case of ammonia plasma treatment. Structural information provided by FTIR spectroscopy reveals a significant increase of the carboxylic group upon argon and mostly oxygen plasma treatment and the increase in width and intensity of the amide-related groups for the ammonia plasma treatment. The biological investigations evidenced that L929 fibroblast cells viability is increased by 25% upon plasma treatment, while the cell attachment is up to 2.8 times higher for the oxygen plasma-treated surface compared to the initial spin-coated pNIPAAM. Moreover, the cell detachment process proved to be up to 2-3 times faster for the oxygen and argon plasma-treated surfaces and up to 1.5 times faster for the ammonia-treated surface. These results show the versatility of plasma treatment for inducing beneficial chemical modifications of pNIPAAM surfaces that allows the tuning of cellular response for improving the attachment-detachment process in view of tissue engineering.

Recent Advances in ROS-Responsive Cell Sheet Techniques for Tissue Engineering

Cell sheet engineering has evolved rapidly in recent years as a new approach for cell-based therapy. Cell sheet harvest technology is important for producing viable, transplantable cell sheets and applying them to tissue engineering. To date, most cell sheet studies use thermo-responsive systems to detach cell sheets. However, other approaches have been reported. This review provides the progress in cell sheet detachment techniques, particularly reactive oxygen species (ROS)-responsive strategies. Therefore, we present a comprehensive introduction to ROS, their application in regenerative medicine, and considerations on how to use ROS in cell detachment. The review also discusses current limitations and challenges for clarifying the mechanism of the ROS-responsive cell sheet detachment.

Construction of novel temperature-responsive hydrogel culture system based on the biomimetic method for stem cell sheet harvest

Temperature-responsive hydrogel culture system is considered as an ideal platform for cell sheet harvest, but its complex preparation methods and harsh reaction conditions limit its application. Inspired by the marine mussels, a biomimetic method presented here is to construct a novel temperature-responsive hydrogel culture system for stem cell sheet harvest. The tissue culture polystyrene is first modified with polydopamine coating, and then amine-terminated poly(N-isopropylacrylamide) is grafted onto the coating via the Schiff base or Michael addition reaction to construct the temperature-sensitive hydrogel culture system. Then, bone marrow stromal cells are cultured on the culture system to construct cell sheets. The prepared culture system shows significant temperature-sensitive property with the grafted concentrations of poly(N-isopropylacrylamide) ranging from 0.5 to 1 g/L. Meanwhile, the constructed culture system has low cytotoxicity and facilitates the stem cell adhesion, proliferation, and cell sheet formation at 37°C. When the culture system is placed in a 20°C environment, the cell sheet can be completely detached from the surface of tissue culture polystyrene without being treated with any enzymes. More importantly, the cell morphology, cell sheet thickness, and the fibril structure of the associated proteins are similar to the cells cultured on the tissue culture polystyrene without modification. The biomimetic, simple, inexpensive, and environmentally friendly preparation of the culture system enables it to be used for the harvest of cell sheet and even applied to tissue engineering for tissue regeneration.

A Robust Method to Generate Mechanically Anisotropic Vascular Smooth Muscle Cell Sheets for Vascular Tissue Engineering

In arterial tissue engineering, mimicking native structure and mechanical properties is essential because compliance mismatch can lead to graft failure and further disease. With bottom-up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve the necessary macroscale properties in the final implant. This study develops a thermoresponsive cell culture platform for growing aligned vascular smooth muscle cell (VSMC) sheets by photografting N-isopropylacrylamide (NIPAAm) onto micropatterned poly(dimethysiloxane) (PDMS). The grafting process is experimentally and computationally optimized to produce PNIPAAm-PDMS substrates optimal for VSMC attachment. To allow long-term VSMC sheet culture and increase the rate of VSMC sheet formation, PNIPAAm-PDMS surfaces were further modified with 3-aminopropyltriethoxysilane yielding a robust, thermoresponsive cell culture platform for culturing VSMC sheets. VSMC cell sheets cultured on patterned thermoresponsive substrates exhibit cellular and collagen alignment in the direction of the micropattern. Mechanical characterization of patterned, single-layer VSMC sheets reveals increased stiffness in the aligned direction compared to the perpendicular direction whereas nonpatterned cell sheets exhibit no directional dependence. Structural and mechanical anisotropy of aligned, single-layer VSMC sheets makes this platform an attractive microstructural building block for engineering a vascular graft to match the in vivo mechanical properties of native arterial tissue.

Dual-Functional Polyethylene Glycol-b-polyhexanide Surface Coating with in Vitro and in Vivo Antimicrobial and Antifouling Activities

In recent years, microbial colonization on the surface of biomedical implants/devices has become a severe threat to human health. Herein, surface-immobilized guanidine derivative block copolymers create an antimicrobial and antifouling dual-functional coating. We report the preparation of an antimicrobial and antifouling block copolymer by the conjugation of polyhexanide (PHMB) with either allyl glycidyl ether or allyloxy polyethylene glycol (APEG; MW 1200 and 2400). The allyl glycidyl ether modified PHMB (A-PHMB) and allyloxy polyethylene glycol_1200/2400 modified PHMB (APEG_1200/2400-PHMB) copolymers were grafted onto a silicone rubber surface as a bottlebrush-like coating, respectively, using a plasma-UV-assisted surface-initiated polymerization. Both A-PHMB and APEG_1200/2400-PHMB coatings exhibited excellent broad-spectrum antimicrobial properties against Gram-negative/positive bacteria and fungi. The APEG₂₄₀₀-PHMB coating displayed an improved antibiofilm as well as antifouling properties and a long reusable cycle, compared with two other coatings, due to its abundant PEG blocks among those copolymers. Also, the APEG₂₄₀₀-PHMB-coated silicone coupons were biocompatible toward mammalian cells, as revealed by in vitro hemocompatibile and cytotoxic assays. An in vivo study showed a significant decline of Escherichia coli colonies with a 5-log reduction, indicating the APEG₂₄₀₀-PHMB coating surface worked effectively in the rodent subcutaneous infection model. This PHMB-based block copolymer coating is believed to be an effective strategy to prevent biomaterial-associated infections.

Autoclaving-Derived Surface Coating with In Vitro and In Vivo Antimicrobial and Antibiofilm Efficacies

Biomedical device-associated infections which engender severe threat to public health require feasible solutions. In this study, block copolymers consisting of antimicrobial, antifouling, and surface-tethering segments in one molecule are synthesized and grafted on polymeric substrates by a facile plasma/autoclave-assisted method. Hetero-bifunctional polyethylene glycol (PEG) with allyl and tosyl groups (APEG-OTs) is first prepared. PEGs with different molecular weights (1200 and 2400 Da) are employed. Polyhexamethylene guanidine (PHMG) which has excellent broad-spectrum antimicrobial activity and thermal/chemical stability, is conjugated with APEG-OTs to generate the block copolymer (APEG-PHMG). Allyl terminated PHMG (A-PHMG) without PEG segments is also synthesized by reacting PHMG with allyl glycidyl ether. The synthesized copolymers are thermal initiated by autoclaving and grafted on plasma pretreated silicone surface, forming permanently bonded bottlebrush-like coatings. Both A-PHMG and APEG_1200/2400 -PHMG coatings exhibit potent antimicrobial activity against gram-positive/negative bacteria and fungus, whereas APEG_1200/2400 -PHMG coatings show superior antifouling activity and long-term reusability to A-PHMG coating. APEG₂₄₀₀ -PHMG coating demonstrates the most effective in vitro antibiofilm and protein/platelet-resistant properties, as well as excellent hemo/biocompatibility. Furthermore, APEG₂₄₀₀ -PHMG greatly reduces the bacteria number with 5-log reduction in a rodent subcutaneous infection model. This rationally designed dual-functional antimicrobial and antifouling coating has great potential in combating biomedical devices/implant-associated infections.

Diffusion-Induced Hydrophilic Conversion of Polydimethylsiloxane/Block-Type Phospholipid Polymer Hybrid Substrate for Temporal Cell-Adhesive Surface

In this study, diffusion-induced hydrophobic-hydrophilic conversion of the surface of the cross-linked polydimethylsiloxane (PDMS) substrate was realized by employing a simple swelling-deswelling process of PDMS substrate in a block-type polymer solution with the aim of development of a temporal cell-adhesive substrate. The ABA block-type polymer composed of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) segment and PDMS segment with over 70% of dimethylsiloxane unit composition could be successfully incorporated in the PDMS substrate during the swelling-deswelling process to prepare the PDMS/phospholipid block copolymer hybrid substrates. During the aging process of the PDMS substrate for 4 days in aqueous medium, its surface property changed gradually from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy and atomic force microscopy data provided strong evidence that the time-dependent hydrophilic conversion of the PDMS/block-type phospholipid polymer hybrid substrate was induced by the diffusion of the hydrophilic PMPC segment in the block-type polymer to be tethered on the substrate. During the hydrophilic conversion process, surface-adsorbed fibronectin was gradually desorbed from the substrate surface, and this resulted in successful detachment of two-dimensional connected cell crowds.

Biomaterials patterned with discontinuous microwalls for vascular smooth muscle cell culture: biodegradable small diameter vascular grafts and stable cell culture substrates

The medial layer of small diameter blood vessels contains circumferentially aligned vascular smooth muscle cells (vSMC) that possess contractile phenotype. In tissue-engineered constructs, these cellular characteristics are usually achieved by seeding planar scaffolds with vSMC, rolling the cell-laden scaffold into a tubular structure, and maturing the construct in a pulsatile bioreactor, a lengthy process that can take up to two months. During the maturation phase, the cells circumferentially orient, their contractile protein expression increases, and they obtain a contractile phenotype. Generating cell culture platforms that enable the rapid production of directionally oriented vSMC with increased contractile protein expression would be a major step forward for blood vessel tissue engineering and would greatly facilitate the in vitro study of vSMC biology. Previously, we developed a micropatterned cell culture surface that promotes orientation and contractile protein expression of vSMC. Herein, we explore two potential applications of this technology. First, we fabricate tubular and biodegradable scaffolds that possess the micropatterning on their exterior surface. When vSMC are seeded on these scaffolds, they initially proliferate in order to fill the microchannels and as confluence is reached the cells align in the direction of the micropatterning resulting in a biodegradable scaffold that is inhabited by circumferentially aligned vSMC within a week. Second, we illustrate that we can generate biostable cell culture surfaces that allow the in vitro study of the cells in a more contractile state. Specifically, we explore contractile protein expression of cells cultured on the micropatterned surfaces with the addition of soluble transforming growth factor beta one (TGFβ1).

Regenerating the cell resistance of micromolded PEG hydrogels

Polydimethylsiloxane stamp materials used during soft lithography undermine the non-fouling behaviour of bio-inert PEG-based hydrogels, resulting in increased protein adsorption and cell adhesion and migration on the gel. This previously unreported phenomenon undermines the function of lab-on-a-chip devices that require the device to be bio-inert, and slows the implementation of promising micromolding and imprinting methods for 3D culture and commercial cell culture systems. We illustrate that the degree of cell adhesion and protein adsorption to the gels correlates with the amount of residual stamp material remaining at the hydrogel interface after fabrication. After identifying this previously unreported phenomenon, we screened multiple polymer cleaning/fabrication techniques in order to maintain/restore the non-fouling properties of the gels including PDMS curing and extraction, use of other common soft lithography stamp materials, post-fabrication cleaning of the hydrogels, and changing the composition of the hydrogel. The optimal solution was determined to be incorporation of reactive sites into the hydrogel during micromolding followed by grafting of PEG macromers to these sites post-fabrication. This treatment resulted in micromolded hydrogels with robust cell resistant properties. Broadly, this work identifies and solves a previously unreported problem in hydrogel micromolding, and specifically reports the development of a cell culture platform that when combined with video microscopy enables high-resolution in situ study of single cell behaviour during in vitro culture.

A thermoresponsive and magnetic colloid for 3D cell expansion and reconfiguration

A dual thermoresponsive and magnetic colloidal gel matrix is described for enhanced stem-cell culture. The combined properties of the material allow enzyme-free passaging and expansion of mesenchymal stem cells, as well as isolation of cells postculture by the simple process of lowering the temperature and applying an external magnetic field. The colloidal gel can be reconfigured with thermal and magnetic stimuli to allow patterning of cells in discrete zones and to control movement of cells within the porous matrix during culture.

Thermoresponsive substrates used for the expansion of human mesenchymal stem cells and the preservation of immunophenotype

The facile regeneration of undifferentiated human mesenchymal stem cells (hMSCs) from thermoresponsive surfaces facilitates the collection of stem cells avoiding the use of animal derived cell detachment agents commonly used in cell culture. This communication proposes a procedure to fabricate coatings from commercially available pNIPAm which is both affordable and a significant simplification on alternative approaches used elsewhere. Solvent casting was used to produce films in the micrometer range and successful cell adhesion and proliferation was highly dependent on the thickness of the coating produced with 1 μm thick coatings supporting cells to confluence. 3T3 cell sheets and hMSCs were successfully detached from the cast coatings upon temperature reduction. Furthermore, results indicate that the hMSCs remained undifferentiated as the surface receptor profile of hMSCs was not altered when cells were detached in this manner.

Responsive systems for cell sheet detachment

Cell sheet engineering has been progressing rapidly during the past few years and has emerged as a novel approach for cell based therapy. Cell sheet harvest technology enables fabrication of viable, transplantable cell sheets for various tissue engineering applications. Currently, the majority of cell sheet studies use thermo-responsive systems for cell sheet detachment. However, other responsive systems began showing their potentials for cell sheet harvest. This review provides an overview of current techniques in creating cell sheets using different types of responsive systems including thermo-responsive, electro-responsive, photo-responsive, pH-responsive and magnetic systems. Their mechanism, approach, as well as applications for cell detachment have been introduced. Further development of these responsive systems will allow efficient cell sheet harvesting and patterning of cells to reconstruct complex tissue for broad clinical applications.