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Tensile test of PEG-DA hydrogels: elastic modulus vs. strain at break for different PEG-DA contents (see online version for colours)
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In this work, a systematic study of the viscoelastic properties of hydrogels based on polyethylene glycol diacrylate (PEG-DA) is presented. In addition to artificial PEG-DA-based hydrogels, natural hydrogels in the form of human articular cartilage were examined. Specimens were (unconfined) compression tested under static and dynamic load. Besides...
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... Hydrogels can be produced from natural biomaterials, such as collagen and hyaluronic acid-naturally present in AC-or from synthetic materials, such as polyglycolic acid (PGA), polylactic acid (PLA) and polyethylene glycol (PEG), which can be tailored to attain specific mechanical properties [5]. Among synthetic hydrogels, polyethylene glycol diacrylate (PEGDA), synthesized via PEG acrylation and photopolymerizable with UV light, is particularly attractive for cartilage regeneration: PEGDA hydrogels exhibit high hydrophilicity, resembling the aqueous AC environment, and can achieve a compressive modulus comparable to native cartilage (790 ± 360 kPa) [21,22]. Furthermore, PEGDA scaffolds have been shown to sustain TGF-β-mediated chondrogenesis of undifferentiated cells, such as MSCs [23]. ...
Functional articular cartilage regeneration remains an unmet medical challenge, increasing the interest for innovative biomaterial-based tissue engineering (TE) strategies. Hydrogels, 3D macromolecular networks with hydrophilic groups, present articular cartilage-like features such as high water content and load-bearing capacity. In this study, 3D porous polyethylene glycol diacry-late (PEGDA) hydrogels were fabricated combining the gas foaming technique and a UV-based crosslinking strategy. The 3D porous PEGDA hydrogels were characterized in terms of their physical , structural and mechanical properties. Our results showed that the size of the hydrogel pores can be modulated by varying the initiator concentration. In vitro cytotoxicity tests showed that 3D porous PEGDA hydrogels presented high biocompatibility both with human chondrocytes and os-teoblast-like cells. Importantly, the 3D porous PEGDA hydrogels supported the viability and chon-drogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cell (hBM-MSC)-based spheroids as demonstrated by the positive staining of typical cartilage extracellular matrix (ECM) (glycosaminoglycans (GAGs)) and upregulation of chondrogenesis marker genes. Overall, the produced 3D porous PEGDA hydrogels presented cartilage-like mechanical properties and supported MSC spheroid chondrogenesis, highlighting their potential as suitable scaffolds for cartilage TE or disease modelling strategies.
... Hydrogels can be produced from natural biomaterials, such as collagen and hyaluronic acid -naturally present in AC -, or from synthetic materials, such as polyglycolic acid (PGA), polylactic acid (PLA), and polyethylene glycol (PEG)which can be tailored to attain specific mechanical properties [5]. Among synthetic hydrogels, polyethylene glycol diacrylate (PEGDA), synthesized via PEG acrylation and photopolymerizable with UV light, is particularly attractive for cartilage regeneration: PEGDA hydrogels exhibit high hydrophilicity, resembling the aqueous AC environment, and can achieve a compressive modulus comparable to native cartilage (790 ± 360 kPa) [21,22]. Furthermore, PEGDA scaffolds have been shown to sustain TGF-β-mediated chondrogenesis of undifferentiated cells, such as MSCs [23]. ...
Functional articular cartilage regeneration remains an unmet medical challenge, increasing the interest for innovative biomaterial-based tissue engineering (TE) strategies. Hydrogels, 3D macromolecular networks with hydrophilic groups, present articular cartilage-like features such as high water content and load-bearing capacity. In this study, 3D porous polyethylene glycol diacrylate (PEGDA) hydrogels were fabricated combining the gas foaming technique and an UV-based crosslinking strategy. The 3D porous PEGDA hydrogels were characterized in terms of their physical, structural and mechanical properties. Our results showed that the size of the hydrogels pores can be modulated by varying the initiator concentration. In vitro cytotoxicity tests showed that 3D porous PEGDA hydrogels presented high biocompatibility both with human chondrocytes and osteoblast-like cells. Importantly, the 3D porous PEGDA hydrogels supported the viability and chondrogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells (hBM-MSCs)-based spheroids as demonstrated by the positive staining of typical cartilage extracellular matrix (ECM) (glycosaminoglycans (GAGs)) and upregulation of chondrogenesis marker genes. Overall, the produced 3D porous PEGDA hydrogels presented cartilage-like mechanical properties and supported MSC-spheroid chondrogenesis, highlighting their potential as suitable scaffolds for cartilage TE or disease modelling strategies.
... Notably, the use of F I G U R E 1 Crosslinking reaction of PEGDA under radiation (ultraviolet or visible light) and the presence of photoinitiator. this hydrogel in biomedical applications has been approved by FDA. 25 Drug delivery, cell encapsulation, and fabrication of scaffolds in tissue regeneration are among the common biomedical applications of PEGDA hydrogel 26 notably bone, 27 cartilage, 28 and cornea tissue engineering . 29,30 The ability to manipulation of mechanical properties has caused PEGDA hydrogel used in a wide range of applications such as vocal fold and bone applications. ...
Three‐dimensional (3D) bioprinting is a promising method for the fabrication of tissue engineering constructs. The bioprintable materials with cells or other biological parts, which are called bioinks, are arranged layer by layer and make multicellular structures. Not all materials can be printed, and a set of requirements should be met to formulate the appropriate bioink. Poly (ethylene glycol) (PEGDA), as a synthetic polymer, is a promising choice for regenerative medicine applications due to its biocompatibility, ease of crosslinking, and adjustability of its mechanical and chemical properties depending on the application. This review aims to guide and familiarize the reader with the PEGDA‐based bioink as a raw material of the 3D‐bioprinting method, its properties, and applications in soft and hard tissue engineering.
... Therefore, it becomes imperative to explore alternative testing approaches that can provide more accurate representations of the mechanical properties at the desired scale, ensuring that the performance of PEGDA hydrogels aligns appropriately with their biomedical applications [145,163]. To obtain accurate surface mechanical properties at the micro and nanoscale, advanced techniques such as AFM and nanoindentation are commonly employed in various studies [182]. Although indentation testing may produce comparable results to compression testing in terms of the elastic modulus, it differs significantly due to differences in loading geometry and boundary conditions [183][184][185]. ...
In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices.
... high aspect ratio and multi-layered, 20 is nontrivial to ensure precision alignment of the applied force vector to the principal axes of the layers. 30 Such misalignment can lead to imprecise measurements due to buckling or inhomogeneous surface loading and is more pronounced in multi-layered structures with layer thickness in sub-tens of microns. 30 Contrarily, methods such as nanoindentation and atomic force microscopy (AFM) are more suitable for assessing the surface properties of multilayered 3D printed structures, 27,31,32 particularly when the alignment between applied force and layer orientation is critical. ...
... 30 Such misalignment can lead to imprecise measurements due to buckling or inhomogeneous surface loading and is more pronounced in multi-layered structures with layer thickness in sub-tens of microns. 30 Contrarily, methods such as nanoindentation and atomic force microscopy (AFM) are more suitable for assessing the surface properties of multilayered 3D printed structures, 27,31,32 particularly when the alignment between applied force and layer orientation is critical. [33][34][35][36][37] In this study, the effect of number of layers and layers thickness on the surface nanomechanical and creep behaviour of multi-layered PEGDA hydrogel printed by LbL projection lithography was investigated. ...
Hydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigatedthe nanomechanical properties of monolithic and multi-layered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerisation and layer-by-layer projection lithography processes, respectively. An increase in number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. We also found that the decreasing number of layers induces a lower Creep Index (CIT) in 3D printed PEGDA hydrogels. This reduction was attributed to the mesoscale imperfections that appears as pockets of voids at the interfaces of the multi-layered hydrogels due to localised regions of unreacted prepolymer resulting in variations in defect density in the samples examined. An increase in the degree of crosslinking introduced by higher dosage of UV exposure leads to higher elastic modulus. This implies that the elastic modulus and creep behaviour of hydrogels are governed and influenced by the degree of crosslinking and defect density of the layers and interfaces. These finding can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels which are critical for the performance of living cells and tissues can be engineered through control of the fabrication parameters.
... The poisson ratio (v) for PEGDA is assumed as 0.5 due to its elastomeric character [28]. ...
Understanding multi-component transport through polymer membranes is critical for separation applications such as water purification, energy devices, etc. Specifically for CO2 reduction cells, where the CO2 reduction products (alcohols and carboxylate salts), crossover of these species is undesirable and improving the design of ion exchange membranes to prevent this behavior is needed. Previously, it was observed that acetate transport increased in copermeation with alcohols for cation exchange membranes consisting of poly(ethylene glycol) diacrylate (PEGDA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and that the inclusion of poly(ethylene glycol) methacrylate (PEGMA) (n = 5, n represents the number of ethylene oxide repeat units) could suppress this behavior. Here, we further investigate the role of PEGMA in modulating fractional free volume and transport behavior of alcohols and carboxylates. PEGDA-PEGMA membranes of varied membranes are fabricated with both varied pre −polymerization water content at constant PEGMA (n = 9) content and varied PEGMA content at two pre −polymerization water contents (20 and 60 wt.% water). Permeability to sodium acetate also decreases in these charge-neutral PEGDA-PEGMA membranes compared to PEGMA-free films. Therefore, incorporation of comonomers such as PEGMA with long side chains may provide a useful membrane chemistry structural motif for preventing undesirable carboxylate crossover in polymer membranes.
... The presence of a fluid phase can affect to a great extent the mechanical behavior of the hydrogel in compressive mode [18] and the typical timedependent mechanical response shown in this condition [8,19]. Experimental studies in the literature adopted different drained and undrained experimental conditions, and therefore the estimated values of Young's modulus were found to differ by more than 50% depending on the adopted experimental method [8,9,20]. Moreover, the mechanical properties of PVA hydrogels are known to be extremely sensitive to the preparation conditions, including PVA molecular weight, percentage weight of PVA in water, and cross-linking method. ...
Polyvinyl alcohol (PVA) hydrogels are extensively used as scaffolds for tissue engineering, although their biodegradation properties have not been optimized yet. To overcome this limitation, partially oxidized PVA has been developed by means of different oxidizing agents, obtaining scaffolds with improved biodegradability. The oxidation reaction also allows tuning the mechanical properties, which are essential for effective use in vivo. In this work, the compressive mechanical behavior of native and partially oxidized PVA hydrogels is investigated, to evaluate the effect of different oxidizing agents, i.e., potassium permanganate, bromine, and iodine. For this purpose, PVA hydrogels are tested by means of indentation tests, also considering the time-dependent mechanical response. Indentation results show that the oxidation reduces the compressive stiffness from about 2.3 N/mm for native PVA to 1.1 ÷ 1.4 N/mm for oxidized PVA. During the consolidation, PVA hydrogels exhibit a force reduction of about 40% and this behavior is unaffected by the oxidizing treatment. A poroviscoelastic constitutive model is developed to describe the time-dependent mechanical response, accounting for the viscoelastic polymer matrix properties and the flow of water molecules within the matrix during long-term compression. This model allows to estimate the long-term Young’s modulus of PVA hydrogels in drained conditions (66 kPa for native PVA and 34–42 kPa for oxidized PVA) and can be exploited to evaluate their performances under compressive stress in vivo, as in the case of cartilage tissue engineering.
... This latter trend is in agreement with our data as the values of the modulus determined by tensile tests are, respectively, 3.8 (for 1) and 4-fold (for 2) higher than those obtained by DMA in shear stress mode (Table 1). Markedly, the storage modulus for the hydrogels obtained using Irgacure 2959 was lower, indicating that better mechanical properties were reached with both 1 and 2. Finally, the moduli measured for the materials obtained from 1 and 2 were similar to the value reported for materials obtained using a thermal initiator (Young Modulus 12 MPa) [32]. This means that we are able to reach the same materials properties after only 2 min of mild irradiation, clearly showing the interest of our system for the rapid preparation of hydrogels. ...
In this work, two new water-soluble photoinitiators based on the α-alkoxy-arylketone scaffold have been synthesized and investigated for their ability to initiate photopolymerization for the preparation of hydrogels. The efficiency of these new Type I photoinitiators was compared to that of benchmark ones (2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone—Irgacure 2959 and 2-hydroxy-2-methyl propiophenone—Irgacure 1173). In combination with additive (carbene-borane), a good initiating ability was found under air. Mechanical properties of the prepared hydrogels were investigated by tensile tests and dynamic mechanical analysis (DMA). Markedly, hydrogels could be prepared with the newly proposed initiating systems in mild conditions (i.e., under air, using low light intensity @405 or 395 nm and without specialized glassware) and exhibited similar properties to those prepared by harsher approaches (thermal treatment or UV light).
... Compression modulus of elasticity can be determined using the spherical indentation technique [18,19], however, the understanding of the numerical values of the modulus of elasticity determined by indentation is underpinned by a complex combination of theoretical and experimental work [20]. Furthermore, indentation measurements consistently result in lower moduli values compared with uniaxial measurements [21], which makes indentation measurements incomparable with the moduli values that material manufacturers use to characterise their hydrogels for the contact lens industry. ...
Purpose
To investigate the stress-strain behaviour of 9 soft contact lens materials, that are commonly used in the market, under uniaxial compression loading.
Methods
Seven types of hydrogel and two types of silicone-hydrogel soft contact lens materials were hydrated in phosphate-buffered saline (PBS) solution then subjected to uniaxial compression loads. The load rate was set to 16.0 N/min starting with two consecutive initial 5.0 N loading cycles followed by three relaxation periods of 4.0 min within which there were two more 5.0 N loading cycles and eventually, a full loading cycle that stopped at a load of 49.0 N. The load and contraction data obtained experimentally were analysed to derive the stress-strain behaviour. Finite Element (FE) analysis was then utilised to evaluate the performance of soft contact lenses on the human eye and handling lenses off the eye.
Results
Unlike tensile tests, all tested materials showed nonlinear behaviour when tested under compression. When fitted to first-order Ogden hyperelastic model, parameter μ was found to be varying in the range 0.12 to 0.74 MPa and material parameter α was found to be varying in the range 8.2 to 20.326 among the nine tested materials. Compression modulus of elasticity was 2.2 times higher than the tensile modulus of elasticity on average. FE simulation with nonlinear Ogden constitutive model showed a limited change (8%~12%) in the optical performance when compared to other material models, however, it predicted higher stress when the lens was simulated under bending during off-eye handling.
Conclusions
Compression tests revealed slightly nonlinear behaviour when materials were strained under compression stress down to 15% ~ 30% of their nominal heights. Considering the physiological compression loading range of 8 mmHg, secant moduli of elasticity were 1.5% to 6.9% higher than the tension moduli of elasticity depending on the material. Tensile-based moduli of elasticity could be used in FE analysis as a step towards simulating the optical performance of soft contact lenses on-eye. However, nonlinear compression-based material models are recommended for FE analysis of soft contact lenses when lens-handling is investigated off-eye.
... En effet, les hydrogels grâce à leur capacité à réticuler dans des conditions douces -indispensables dans le cas d'utilisations médicales -ont une excellente biocompatibilité et ils possèdent des propriétés biophysiques et biochimiques [62][63][64][65][66] ajustables qui en font des composés d'intérêts pour ces applications. Il existe différents modes de synthèse des hydrogels [67][68][69] : par polymérisation en masse, par des réactions de polymérisation réalisée en suspension -cette méthode ayant l'avantage d'obtenir des produits sous forme de poudre ou de microsphères -par greffage sur un support ou bien même par irradiation. La synthèse d'hydrogels par irradiation peut être réalisée via des radiations ionisantes de fortes énergies (tels que les rayons gammas) ou par radiation lumineuse. ...
... Les valeurs du module de Young sont similaires à celles obtenues au cours du chapitre précédent (Chap II, §E.2.c, p 148). La valeur du module de Young déterminée par traction est du même ordre de grandeur (environ 10 MPa) que celle déterminée par le groupe de Gäbler[69] sur des hydrogels de PEGDA synthétisés thermiquement. Par ailleurs, les valeurs du module de Young mesurées par cisaillement sont supérieures à celles obtenues par le groupe de Turturro[70] (de l'ordre de 1 MPa) lors de la préparation d'hydrogels de PEGDA contenant différents taux d'agents de transferts (via la triéthanolamine) et de co-monomère (1-vinyl-2-pyrrolidinone) amorcée par l'Eosine-Y sous irradiation visible (514 nm).Ces dérivés de naphtalimide ont donc permis d'aboutir au développement d'un nouveau système amorceur tri-composants. ...
La polymérisation par voie photochimique prend de plus en plus d’ampleur dans les domaines académiques et industriels de par ses avantages par rapport à la polymérisation thermique. En effet, contrairement à son homologue thermique, la polymérisation photochimique permet un contrôle spatial mais également temporel, la polymérisation n’ayant lieu qu’au court de l'irradiation et dans les zones choisies. De plus, cette voie de synthèse est, la plupart du temps, plus rapide que pour la polymérisation thermique. La polymérisation par voie photochimique nécessite moins d’énergie que celle par voie thermique. Ainsi, le choix de la voie photochimique plutôt que thermique prend tout son sens dans un contexte mondial où l’empreinte carbone devient l’une des préoccupations industrielles majeures lors de la mise en place de nouveaux procédés. La photopolymérisation est donc déjà présente dans de nombreux secteurs tels que le bâtiment, l’automobile, la dentisterie, l’impression 3D… Mais les recherches doivent encore être poursuivies afin que cette méthode réponde aussi bien aux critères industriels qu'environnementaux actuels. De multiples recherches ont déjà été menées sur la polymérisation par voie photochimique. Cependant la plupart des systèmes photoamorceurs (PA) développés sont efficaces sous radiation ultraviolette qui demeurent nocives pour l’utilisateur ce qui empêchent ainsi leur utilisation dans certains domaines dont notamment les applications médicales (dentisterie ou pansements chirurgicaux par exemple). De plus, les sources de radiations UV sont la plupart du temps énergivores ce qui va à l’encontre de la tendance actuelle de réduction drastique des coûts énergétiques. Ainsi, le développement depuis plusieurs années de nouvelles sources d’irradiation - telles que les diodes électroluminescentes – moins énergétiques (et de moins en moins chères) et avec une plus grande durée de vie a permis de relancer et réveiller l’intérêt des industriels pour la photopolymérisation. Il est donc nécessaire de développer de nouveaux systèmes photoamorceurs pour le domaine du visible.En se décalant vers les longueurs d’ondes visible, l’énergie fournie au système photoamorceur pour créer des espèces réactives (telles que des radicaux dans le cas de la polymérisation radicalaire) est moins importantes. En conséquent pour que le système photoamorceur mis en place soit efficace et puisse rivaliser avec les systèmes PA conventionnels, deux stratégies peuvent être envisagées. La première consiste à former plus d’espèces réactives notamment par l’emploi de système catalytique – c’est le cas des approches par catalyse photo-redox par exemple. Tant dis que la seconde stratégie est de jouer sur la nature des espèces réactives formées. En effet, une meilleure réactivité de ces dernières peut compenser la perte d’énergie perçue par le système PA. Les travaux de cette thèse visent notamment à développer de nouveaux systèmes PA en s’appuyant sur cette dernière stratégie. [...]
