Relationships between surface roughness/stiffness of chitosan coatings and fabrication of corneal keratocyte spheroids: Effect of degree of deacetylation

The choice of ultra-low attachment plates impacts primary human and primary canine hepatocyte spheroid formation, phenotypes, and function

Organotypic three-dimensional liver spheroid cultures in which hepatic cells retain their molecular phenotype and functionality have emerged as powerful tools for preclinical drug development. In recent years a multitude of culture systems have been developed; however, a thorough side-by-side benchmarking of the different methods is lacking. Here, we compared the performance of ten different 96- and 384-well microplate types to support spheroid formation and long-term culture. Specifically, we evaluated differences in spheroid formation kinetics, viability, functionality, expression patterns, and their utility for hepatotoxicity assessments using primary human hepatocytes (PHH) and primary canine hepatocytes (PCH). All 96-well plates enabled formation of PHH liver spheroids, albeit with differences between plates in spheroid size, geometry, and reproducibility. Performance of different 384-wells was less consistent. Only 6/10 microplates supported the formation of PCH aggregates. Interestingly, even if PCH aggregates in these six microplates were more loosely packed than PHH spheroids, they maintained their function and were compatible with long-term pharmacological and toxicological assays. Overall, Corning and Biofloat plates showed the best performance in the formation of both human and canine liver spheroids with highest viability, most physiologically relevant phenotypes, superior CYP activity and lowest coefficient of variation in toxicity assays. The presented data constitutes a valuable resource that demonstrates the impacts of current ultra-low attachment plates on liver spheroid metrics and can guide evidence-based plate selection. Combined, these results have important implications for the cross-comparison of different studies and can facilitate the standardization and reproducibility of three-dimensional liver culture experiments.

Grafted chitosan thin films of various degrees of acetylation as a reusable platform for the investigation of biological interactions

Surface treatment by adhesive polymers is a promising solution to immobilize and study bacteria cells through microscopic assays and, for example, control their growth or determine their susceptibility to antibiotic treatment. The stability of such functional films in wet conditions is crucial, as the film degradation would compromise a persistent use of the coated devices. In this work, low roughness chitosan thin films of degrees of acetylation (DA) ranging from 0.5 % to 49 % were chemically grafted onto silicon and glass substrates and we have demonstrated how the physicochemical properties of the surfaces and the bacterial response were DA-dependent. A fully deacetylated chitosan film presented an anhydrous crystalline structure while the hydrated crystalline allomorph was the preferred structure at higher DA. Moreover, their hydrophilicity increased at higher DA, leading to higher film swelling. Low DA chitosan-grafted substrate favored bacterial growth away from the surface and could be envisioned as bacteriostatic surfaces. Contrarily, an optimum of Escherichia coli adhesion was found for substrates modified with chitosan of DA = 35 %: these surfaces are adapted for the study of bacterial growth and antibiotic testing, with the possibility of reusing the substrates without affecting the grafted film - ideal for limiting single-use devices.

Preparation and Surface Characterization of Chitosan-Based Coatings for PET Materials

Poly(ethylene terephthalate)-PET-is one of the most frequently used polymers in biomedical applications. Due to chemical inertness, PET surface modification is necessary to gain specific properties, making the polymer biocompatible. The aim of this paper is to characterize the multi-component films containing chitosan (Ch), phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), immunosuppressant cyclosporine A (CsA) and/or antioxidant lauryl gallate (LG) which can be utilized as a very attractive material for developing the PET coatings. Chitosan was employed owing to its antibacterial activity and also its ability to promote cell adhesion and proliferation favorable for tissue engineering and regeneration purposes. Moreover, the Ch film can be additionally modified with other substances of biological importance (DOPC, CsA and LG). The layers of varying compositions were prepared using the Langmuir-Blodgett (LB) technique on the air plasma-activated PET support. Then their nanostructure, molecular distribution, surface chemistry and wettability were determined by atomic force microscopy (AFM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), contact angle (CA) measurements and the surface free energy and its components' determination, respectively. The obtained results show clearly the dependence of the surface properties of the films on the molar ratio of components and allow for a better understanding of the coating organization and mechanisms of interactions at the molecular level both inside the films and between the films and the polar/apolar liquids imitating the environment of different properties. The organized layers of this type can be helpful in gaining control over the surface properties of the biomaterial, thus getting rid of the limitations in favor of increased biocompatibility. This is a good basis for further investigations on the correlation of the immune system response to the presence of biomaterial and its physicochemical properties.

Effect of Degree of Deacetylation of Chitosan/Chitin on Human Neural Stem Cell Culture

Stem cell therapy and research for neural diseases depends on reliable reproduction of neural stem cells. Chitosan-based materials have been proposed as a substrate for culturing human neural stem cells (hNSCs) in the pursuit of clinically compatible culture conditions that are chemically defined and compliant with good manufacturing practices. The physical and biochemical properties of chitosan and chitin are strongly regulated by the degree of deacetylation (DD). However, the effect of DD on hNSC behavior has not been systematically investigated. In this study, films with DD ranging from 93% to 14% are fabricated with chitosan and chitin. Under xeno-free conditions, hNSCs proliferate preferentially on films with a higher DD, exhibiting adherent morphology and retaining multipotency. Lowering the DD leads to formation of neural stem cell spheroids due to unsteady adhesion. The neural spheroids present NSC multipotency protein expression reduction and cytoplasmic translocation. This study provides an insight into the influence of the DD on hNSCs behavior and may serve as a guideline for hNSC research using chitosan-based biomaterials. It demonstrates the capability of controlling hNSC fate by simply tailoring the DD of chitosan.

Unraveling the mechanobiology of cornea: From bench side to the clinic

The cornea is a transparent, dome-shaped structure on the front part of the eye that serves as a major optic element and a protector from the external environment. Recent evidence shows aberrant alterations of the corneal mechano-environment in development and progression of various corneal diseases. It is, thus, critical to understand how corneal cells sense and respond to mechanical signals in physiological and pathological conditions. In this review, we summarize the corneal mechano-environment and discuss the impact of these mechanical cues on cellular functions from the bench side (in a laboratory research setting). From a clinical perspective, we comprehensively review the mechanical changes of corneal tissue in several cornea-related diseases, including keratoconus, myopia, and keratectasia, following refractive surgery. The findings from the bench side and clinic underscore the involvement of mechanical cues in corneal disorders, which may open a new avenue for development of novel therapeutic strategies by targeting corneal mechanics.

A facile approach for the determination of degree of deacetylation of chitosan using acid-base titration

Several spectroscopic techniques such as nuclear magnetic resonance (NMR), UV-visible, Fourier transform infrared (FT-IR), etc. have been already used for the determination of degree of deacetylation (DD) of chitosan. These techniques involve the interpretation of spectral data apart from sample preparation for obtaining DD of chitosan. In addition, inaccurate interpretation of data sometimes misleads researchers to get an exact value of DD of chitosan. Among them, NMR is an excellent technique for the estimation of DD of chitosan but expensive and not found easily in every research laboratory. On the other hand, titrimetric methods have been employed by many researchers for determining the DD of chitosan but these existing methods involve many complex calculations, which do not always give accurate results. Moreover, few of the acid-base titration methods are little complicated for execution. Therefore, in this present study, we adopted a very handy and simple acid-base titration method with a new approach and proposed a new equation facilitating the ease of calculation that is not reported elsewhere for the determination of DD value by observing the net volume of NaOH consumed for the complete neutralization of protonated amino groups (-NH₃⁺) of chitosan describing the novelty of the work. All the DD values (77.04 ± 1.36; 81.71 ± 1.73; 91.68 ± 1.42 for CS1, CS2, and CS3 respectively) obtained for various chitosan samples were in good agreement with the reported DD values (>75%, >80%, and >85% for CS1, CS2, and CS3 respectively) mentioned in the specifications of chitosan samples supplied by the manufacturer. Finally, the experimental DD values were further validated with the DD values (77.39%, 81.64%, and 90.5% for CS1, CS2, and CS3 respectively) obtained from the interpretation of ¹³C-NMR spectral data and all the experimental DD values were consistent with the DD values as calculated based on NMR spectra.

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The acid-base titration method with a new approach reported in this article for the determination of degree of deacetylation of chitosan provides an accuracy, reproducibility, and reliability.

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In addition, the reported method with a new approach is very convenient as compared to other existing methods to determine the degree of deacetylation of chitosan.

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The newly introduced equation to estimate degree of deacetylation of chitosan is very simple and convenient.

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The DD values of chitosan obtained by the acid-base titration method are perfectly validated based on ¹³C-NMR data.

Engineering Multi-Cellular Spheroids for Tissue Engineering and Regenerative Medicine

Multi-cellular spheroids are formed as a 3D structure with dense cell-cell/cell-extracellular matrix interactions, and thus, have been widely utilized as implantable therapeutics and various ex vivo tissue models in tissue engineering. In principle, spheroid culture methods maximize cell-cell cohesion and induce spontaneous cellular assembly while minimizing cellular interactions with substrates by using physical forces such as gravitational or centrifugal forces, protein-repellant biomaterials, and micro-structured surfaces. In addition, biofunctional materials including magnetic nanoparticles, polymer microspheres, and nanofiber particles are combined with cells to harvest composite spheroids, to accelerate spheroid formation, to increase the mechanical properties and viability of spheroids, and to direct differentiation of stem cells into desirable cell types. Biocompatible hydrogels are developed to produce microgels for the fabrication of size-controlled spheroids with high efficiency. Recently, spheroids have been further engineered to fabricate structurally and functionally reliable in vitro artificial 3D tissues of the desired shape with enhanced specific biological functions. This paper reviews the overall characteristics of spheroids and general/advanced spheroid culture techniques. Significant roles of functional biomaterials in advanced spheroid engineering with emphasis on the use of spheroids in the reconstruction of artificial 3D tissue for tissue engineering are also thoroughly discussed.

A review of manufacturing capabilities of cell spheroid generation technologies and future development

Spheroid culture provides cells with a three-dimensional environment that can better mimic physiological conditions compared to monolayer culture. Technologies involved in the generation of cell spheroids are continuously being innovated to produce spheroids with enhanced properties. In this paper, we review the manufacturing capabilities of current cell spheroid generation technologies. We propose that spheroid generation technologies should enable tight and robust process controls to produce spheroids of consistent and repeatable quality. Future technology development for the generation of cell spheroids should look into improvement in process control, standardization, scalability and monitoring, in addition to advanced methods of spheroid transfer and characterization.

Poly(gallic acid)-coated polycaprolactone inhibits oxidative stress in epithelial cells

Enzymatic mediated poly (gallic acid) (PGAL), a stable multiradical polyanion with helicoidal secondary structure and high antioxidant capacity, was successfully grafted to poly(ε-caprolactone) (PCL) using UV-photo induction. PCL films were prepared with several levels of roughness and subsequently grafted with PGAL (PCL-g-PGAL). The results on the full characterization of the produced materials by mechanical tests, surface morphology, and topography, thermal and crystallographic analyses, as well as wettability and cell protection activity against oxidative stress, were adequate for tissue regeneration. The in vitro biocompatibility was then assessed with epithelial-like cells showing excellent adhesion and proliferation onto the PCL-g-PGAL films, most importantly, PCL-g-PGAL displayed a good ability to protect cell cultures on their surface against reactive oxygen species. These biomaterials can consequently be considered as novel biocompatible and antioxidant films with high-responsiveness for biomedical or tissue engineering applications.

Regulation of Keratocyte Phenotype and Cell Behavior by Substrate Stiffness

Corneal tissue engineering is an alternative way to solve the problem of lack of corneal donor tissue in corneal transplantation. Keratocytes with a normal phenotype and function in tissue-engineered cornea would be critical for corneal regeneration. Although the role of extracellular/substrate material stiffness is well-known for the regulation of the cell phenotype and cell behavior in many different cell types, its effects in keratocyte culture have not yet been thoroughly studied. This project studied the effect of substrate stiffness on the keratocyte phenotype marker expression and typical cell behavior (cell adhesion, proliferation, and migration), and the possible mechanisms involved. Human primary keratocytes were cultured on tissue culture plastic (TCP, ∼10⁶ kPa) or on plates with the stiffness equivalent of physiological human corneal stroma (25 kPa) or vitreous body (1 kPa). The expression of keratocyte phenotype markers, cell adhesion, proliferation, and migration were compared. The results showed that the stiffness of the substrate material regulates the phenotype marker expression and cell behavior of cultured keratocytes. Physiological corneal stiffness (25 kPa) superiorly preserved the cell phenotype when compared to the TCP and 1 kPa group. Keratocytes had a larger cell area when cultured on 25 kPa plates as compared to on TCP. Treatment of cells with NSC 23766 (Rac1 inhibitor) mimicked the response in the cell phenotype and behavior seen in the transition from soft materials to stiff materials, including the cytoskeletal structure, expression of keratocyte phenotype markers, and cell behavior. In conclusion, this study shows that substrate stiffness regulates the cell phenotype marker expression and cell behavior of keratocytes by Rac1-mediated cytoskeletal reorganization. This knowledge contributes to the development of corneal tissue engineering.

Cell Culture on Low-Fluorescence and High-Resolution Photoresist

2D and 3D topographic cues made of photoresist, a polymer, are used for cell culture and cell analysis. Photoresists used for cell analysis provide the surface conditions necessary for proper cell growth, along with patterning properties of a wide range and high precision, and low auto-fluorescence that does not affect fluorescence imaging. In this study, we developed a thick negative photoresist SJI-001 possessing the aforementioned properties. We evaluated the surface conditions of SJI-001 affecting cell culture. First, we studied the wettability of SJI-001, which was changed by plasma treatment, conducted as a pretreatment on a plastic substrate before cell seeding. SJI-001 was more chemically stable than SU-8 used for fabricating the micro-electromechanical systems (MEMS). Furthermore, the doubling time and adhesion rate of adherent HeLa cells cultured on untreated SJI-001 were 25.2 h and 74%, respectively, thus indicating its suitability for cell culture over SU-8. In addition, we fabricated a cell culture plate with a 3D lattice structure, three micrometers in size, using SJI-001. HeLa cells seeded on this plate remained attached over five days. Therefore, SJI-001 exhibits surface conditions suitable for cell culture and has several bioapplications including microstructures and cell chips for cell culture and cell analysis.

Nanostructure-Enabled and Macromolecule-Grafted Surfaces for Biomedical Applications

Advances in nanotechnology and nanomaterials have enabled the development of functional biomaterials with surface properties that reduce the rate of the device rejection in injectable and implantable biomaterials. In addition, the surface of biomaterials can be functionalized with macromolecules for stimuli-responsive purposes to improve the efficacy and effectiveness in drug release applications. Furthermore, macromolecule-grafted surfaces exhibit a hierarchical nanostructure that mimics nanotextured surfaces for the promotion of cellular responses in tissue engineering. Owing to these unique properties, this review focuses on the grafting of macromolecules on the surfaces of various biomaterials (e.g., films, fibers, hydrogels, and etc.) to create nanostructure-enabled and macromolecule-grafted surfaces for biomedical applications, such as thrombosis prevention and wound healing. The macromolecule-modified surfaces can be treated as a functional device that either passively inhibits adverse effects from injectable and implantable devices or actively delivers biological agents that are locally based on proper stimulation. In this review, several methods are discussed to enable the surface of biomaterials to be used for further grafting of macromolecules. In addition, we review surface-modified films (coatings) and fibers with respect to several biomedical applications. Our review provides a scientific update on the current achievements and future trends of nanostructure-enabled and macromolecule-grafted surfaces in biomedical applications.

From 2D to 3D: The morphology, proliferation and differentiation of MC3T3-E1 on silk fibroin/chitosan matrices

It has been widely accepted that cell culture in two-dimensional (2D) conditions may not be able to represent growth in three-dimensional (3D) conditions. Systematic comparisons between 2D and 3D cell cultures are needed to appropriately use the existing 2D results. In this work, we conducted a comparative study between 2D and 3D cell cultures of MC3T3-E1 using the same type of material (a mixture of silk fibroin (SF) and chitosan (CS)). Our results showed 3D SF/CS scaffold exhibited different effects on cell culture compared with the 2D cases. 1) The cells grown in 3D scaffold showed multiple morphologies. 2) The proliferation of cells in 3D scaffold was long-term and sustainable. 3) Cell differentiation occurred throughout the entire 3D scaffold. The results showed that cell culture in 3D SF/CS scaffold exhibited different features than 2D cases and 3D SF/CS scaffold could be a promising material for 3D cell culture.

Bioengineered keratocyte spheroids fabricated on chitosan coatings enhance tissue repair in a rabbit corneal stromal defect model

Cultivated cell spheroid transplantation is widely studied as a means of facilitating tissue regeneration. Chitosan biomaterial has been shown to promote keratocyte aggregation and multicellular spheroid formation. This study provides further evidence on application of bioengineered keratocyte spheroids for corneal stromal tissue engineering. In an allogeneic rabbit model of stromal destruction caused by bacterial keratitis, the corneas were intrastromally injected with isolated keratocyte suspensions or aggregated spheroid grafts at same cell number. Results of clinical observations and histological examinations on postoperative day 14 showed that when an antibiotic eye drop is only medication for inhibiting bacterial growth, permanent damage to stroma occurs, leading to disorganization of collagen lamellae and tissue structure as well as loss of corneal transparency and visual function. Intrastromal grafting of keratocytes provided additional benefits to overcome drawbacks of limited disease treatment performance associated with topically applied antibiotics. In particular, as compared to their cell suspension counterparts, bioengineered keratocyte spheroids had higher ability to preserve cellular phenotype, secrete collagen matrix, and enhance graft retention, suggesting excellent repair capability for managing stromal tissue defect and alleviating corneal haze/oedema. In summary, the findings emphasize the role of keratocyte configuration (i.e., two-dimensional monolayer or three-dimensional spheroid) in determining therapeutic potency of cellular allografts for stromal tissue reconstruction. Transplantation of keratocyte spheroids cultured on chitosan substrates may represent a promising strategy for corneal stromal repair.

Corneal epithelial cells exposed to shear stress show altered cytoskeleton and migratory behaviour

Cells that form the corneal epithelium, the outermost layer of the cornea, are exposed to shear stress through blinking during waking hours. In this in vitro study, the effect of fluid shear stress on human corneal epithelial cells (HCECs) was investigated. Following exposure to shear stresses of 4 and 8 dyn/cm², HCECs showed cytoskeletal rearrangement with more prominent, organized and elongated filamentous actin. Cytoskeletal changes were time-dependent, and were most significant after 24 hours of shear stress. Higher rates of migration and proliferation, as evaluated by a scratch assay, were also observed following 24 hours of low shear stress exposure (4 dyn/cm²). This result contrasted the poor migration observed in samples scratched before shear exposure, indicating that shear-induced cytoskeletal changes played a key role in improved wound healing and must therefore precede any damage to the cell layer. HCEC cytoskeletal changes were accompanied by an upregulation in integrin β₁ and downregulation of ICAM-1. These results demonstrate that HCECs respond favourably to flow-induced shear stress, impacting their proliferation and migration properties as well as phenotype.

Chitosan-based nanocomposites for the repair of bone defects

Chitosan scaffolds of different deacetylation degrees, average molecular weights and concentrations reinforced with silica nanoparticles were prepared for bone tissue regeneration. The resulting nanocomposites showed similar pore sizes (<300 μm) regardless the deacetylation degree and concentration used in their formulation. Their mechanical compression resistance was increased by a 30% with the addition of silica nanoparticles as nanofillers. The biocompatibility of the three-dimensional chitosan scaffolds was confirmed by the Alamar Blue assay in human primary osteoblasts as well as the formation of cell spheroids indicative of their great potential for bone regeneration. In vivo implantation of the scaffolds in a mice calvaria defect model provided substantial evidences of the suitability of these nanocomposites for bone tissue engineering showing a mature and dense collagenous tissue with small foci of mineralization, vascularized areas and the infiltration of osteoblasts and osteoclasts. Nevertheless, mature bone tissue formation was not observed after eight weeks of implantation.

Assembly of breast cancer heterotypic spheroids on hyaluronic acid coated surfaces

Drug screening is currently demanding for realistic models that are able to reproduce the structural features of solid tumors. 3D cell culture systems, namely spheroids, emerged as a promising approach to provide reliable results during drug development. So far, liquid overlay technique (LOT) is one of the most used methods for spheroids assembly. It comprises cellular aggregation due to their limited adhesion to certain biomaterials, like agarose. However, researchers are currently improving this technique in order to obtain spheroids on surfaces that mimic cancer extracellular matrix (ECM), since cell-ECM interactions modulate cells behavior and their drug resistance profile. Herein, hyaluronic acid (HA) coated surfaces were used, for the first time, for the production of reproducible heterotypic breast cancer spheroids. The obtained results revealed that it is possible to control the size, shape, and number of spheroids gotten per well by changing the HA concentration and the number of cells initially seeded in each well. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1346-1357, 2017.

Chitosan-Based Coating with Antimicrobial Agents: Preparation, Property, Mechanism, and Application Effectiveness on Fruits and Vegetables

Chitosan coating is beneficial to maintaining the storage quality and prolonging the shelf life of postharvest fruits and vegetables, which is always used as the carrier film for the antimicrobial agents. This review focuses on the preparation, property, mechanism, and application effectiveness on the fruits and vegetables of chitosan-based coating with antimicrobial agents. Chitosan, derived by deacetylation of chitin, is a modified and natural biopolymer as the coating material. In this article, the safety and biocompatible and antimicrobial properties of chitosan were introduced because these attributes are very important for its application. The methods to prepare the chitosan-based coating with antimicrobial agents, such as essential oils, acid, and nanoparticles, were developed by other researchers. Meanwhile, the application of chitosan-based coating is mainly due to its antimicrobial activity and other functional properties, which were investigated, introduced, and analyzed in this review. Furthermore, the surface and mechanical properties were also investigated by researchers and concluded in this article. Finally, the effects of chitosan-based coating on the storage quality, microbial safety, and shelf life of fruits and vegetables were introduced. Their results indicated that chitosan-based coating with different antimicrobial agents would probably have wide prospect in the preservation of fruits and vegetables in the future.