Preparation of photodegradable polyacrylamide hydrogels via micellar copolymerization and determination of their phototunable elasticity and swelling behaviors (original) (raw)
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Crosslinked Polyacrylamide Temperature-Sensitive Hydrogel. Synthesis and Characterization
A polyacrylamide hydrogel having a thermoresponsive character was prepared by simultaneous crosslinking solution copolymerization method. Different thermoresponsive properties were obtained by changing the initial ratio of acrylamide and N,N'-methylenebisacrylamide as crosslinker. The swelling behaviour in water until equilibrium was evaluated for all the hydrogel systems.
Photocrosslinked hydrogels based on copolymers of poly(ethylene glycol) and lysine
Journal of Polymer Science Part A-polymer Chemistry, 1994
A group of new, water-soluble poly(ether-urethane)s, derived from poly(ethylene glycol) and the amino acid L-lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. the crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64–88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1M, pH 7.4, 37°C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly(ethylene glycol)-lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful properties. © 1994 John Wiley & Sons, Inc.
Arrays of polyacrylamide hydrogels using a carbodiimide-mediated crosslinking reaction
Journal of Applied Polymer Science, 2014
This study introduces a radical-free approach for generating polyacrylamide (PAM) hydrogels with no toxic residues remaining in the networks. Acrylamide and bisacrylamide, which are neurotoxins, are not used during the hydrogel synthesis and only nontoxic side products are generated. This is achieved using a gentle carbodiimide-mediated crosslinking (CMCL) reaction that does not require complex initiation systems and is effective in the presence of oxygen. This overcomes some of the key limitations related to PAM hydrogel synthesis using free-radical routes and maintains the advantages of synthetic hydrogels over biopolymers. In addition, the CMCL reaction allows for accurate placement of functional groups, which controls hydrogel structure and performance including mechanical strength, swelling capacity, and hydrophobic balance. This flexibility is demonstrated through the synthesis and rheological characterization of a library of structurally diverse hydrogels as well as spherical hydrogels. PAM-based hydrogels are used extensively in a broad number of applications, and this study demonstrates the applicability of this method as a nontoxic and radicalfree complementary alternative route that can generate structures analogous to those prepared using free-radical routes. V
Design of high-toughness polyacrylamide hydrogels by hydrophobic modification
Polymer, 2009
Polyacrylamide (PAAm) hydrogels possessing a very large extensibility at break have been prepared via micellar crosslinking copolymerization of acrylamide monomer and N,N 0 -methylenebis(acrylamide) crosslinker in the presence of hydrophobic comonomers. N-butyl-, N-hexyl-, N-octyl-, and N,N-dihexylacrylamides were used as the hydrophobes in the hydrogel preparation. Incorporation of hydrophobes with an alkyl chain length x > 4 results in an increase in the loss factor tan d of hydrogels due to the formation of temporary junction zones inside the gel network. The number N H of the hydrophobes per hydrophobic block together with the alkyl chain length x of the pendant hydrophobic group were used to tune the loss factor of the hydrogels over two orders of magnitude. Tensile mechanical measurements show that increasing N H or x also increases the degree of toughness of PAAm hydrogels. Keeping constant the hydrophobe level (20 mol%) at an alkyl chain length x ¼ 6, increasing N H from 9 to 30 increased the elongation ratio at break from 125 to 250%. Hydrogels exhibiting a high toughness, i.e., about 300% elongation ratio at break were obtained by modification of PAAm network chains with 10 mol% N-octylacrylamide.
Advanced healthcare materials, 2015
Photodegradable hydrogels have emerged as powerful platforms for studying and directing cellular behavior in a spatiotemporally controlled manner. Photodegradable hydrogels have previously been formed by free radical polymerizations, Michael-type addition reactions, and orthogonal click reactions. Here, an ester-activated photocleavable crosslinker is presented for preparing photodegradable hydrogels by means of a one-step mixing reaction between the crosslinker and a biocompatible polymer containing amino moieties (amino-terminated tetra-arm poly(ethylene glycol) or gelatin). It is demonstrated that photodegradable hydrogels micropatterned by photolithography can be used to culture cells with high viability and proliferation rates. The resulting micropatterned cell-laden structures can potentially be used to create 3D biomaterials for various tissue-engineering applications.
Water-dispersible nanohydrogels of cross-linked polyacrylamide
Colloid and Polymer Science, 2017
Stable water-dispersible nanohydrogels of crosslinked polyacrylamide (PAAm) were obtained by batch (BP) and semicontinuous (SP) processes through inverse m i c r o e m u l s i o n p o l y m e r i z a t i o n u s i n g N , N 'methylenebisacrylamide (NMBAM) as cross-linking agent and bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) as surfactant. The effects of initiator type as 2,2'-Azobis(2amidinopropane) hydrochloride (V-50), potassium persulfate (KPS), ammonium persulfate (APS), and benzoyl peroxide (BPO) on kinetics, particle size, and morphology were studied. It was observed that under the studied conditions, it is possible to form the inverse microemulsions using lower surfactant concentrations than those typically reported for microemulsión polymerization of this monomer. Z-average particle size (Dpz) of final latexes were in the range of 51 to 79 nm for BP, those corresponding to SP were in the interval of 118 to 225 nm, while Dpz of water-dispersed nanohydrogels varied from 530 to 825 nm conserving their spherical morphology. Particle size distributions of both latexes and the water-dispersed nanohydrogels were monomodal. High monomer conversions and fast polymerization rates were observed in all cases, achieving monomer-starved conditions when using low monomer addition rate in SP process.
2002
Hyperbranched poly(ester amide) polymer (Hybrane™ S1200; M n 1200 g/mol) was functionalized with maleic anhydride (MA) and propylene sulfide, to obtain multifunctional crosslinkers with fumaric and thiol-end groups, S1200MA and S1200SH, respectively. The degree of substitution of maleic acid groups (DS) was controlled by varying the molar ratio of MA to S1200 in the reaction mixture. Hydrogels were obtained by UV crosslinking of functionalized S1200 and poly(ethyleneglycol) diacrylate (PEGDA) in aqueous solutions. Compressive modulus increased with decreasing the S1200/PEG ratio and also depended on the DS of the multifunctional crosslinker (S1200). Also, heparin-based macromonomers together with functionalized hyperbranched polymers were used to construct novel functional hydrogels. The multivalent hyperbranched polymers allowed high crosslinking densities in heparin modified gels while introducing biodegradation sites. Both heparin presence and acrylate/thiol ratio have an impact on degradation profiles and morphologies. Hyperbranched crosslinked hydrogels showed no evidence of cell toxicity. Overall, the multifunctional crosslinkers afford hydrogels with promising properties that suggest that these may be suitable for tissue engineering applications.
Designed Monomers and Polymers - DES MONOMERS POLYM, 2004
Copolymerization of N-allyl maleamic acid (AMA) with acrylamide and acrylic acid results in rapid crosslinking in water. Although AMA is slightly soluble in water, it forms clear solutions in 10% of aqueous acrylamide and 20% acrylic acid solutions. By radical initiation with potassium persulfate at 65 ± C or redox initiation at 0 ± C, these solutions undergo gelation in less than 10 min. The crosslinking ef ciency of AMA was estimated based on equilibrium swellings of its acrylamide copolymer gels either by the Flory-Rehner theory or by correlation with swellingcrosslinking density plots of acrylamide-methylene bis-acrylamide (BIS) copolymer gels. These results showed that ef ciency of AMA in crosslinking copolymerization with acrylamide at 0 ± C is less than 10%. On the other hand, its ef ciency rises up to 40-60% and levels off at 65 ± C. Overall results indicate that AMA having maleate and allylic double bonds is an ef cient crosslinker for preparing polyacrylamide and polyacrylic acid gels.
Characterization of hydrogels formed from acrylate modified poly(vinyl alcohol) macromers
Polymer, 2000
Poly(vinyl alcohol) was modified with pendent acrylate groups to form a macromer that was crosslinked via photopolymerization. Polymerization behavior was studied for several initial macromer concentrations using DSC and Near-IR spectroscopy. Under mild photoinitiating conditions (e.g. 0.05 wt% initiator and less than 20 mW/cm 2 of 365 nm light), the hydrogels polymerized to 100% conversion in less than 5 min. To characterize the network structure, the hydrogels formed from the acrylated poly(vinyl alcohol) macromer were compared to gels that were chemically crosslinked with glutaraldehyde and gels that were physically crosslinked by semi-crystalline regions introduced through freeze-thaw cycles. The equilibrium swelling ratio and compressive modulus were characterized for all of the resulting PVA hydrogels, and related to the network structure (i.e. M c through a modified Flory-Rehner equation and rubber elasticity theory. ᭧