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Mechanical and swelling properties of hydrogels
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrogels have been used as one of the novel soft materials in many biomedical applications such as drug delivery and tissue engineering for recent decades.

In the main part of this work, bi-functional poly(ethylene glycol) (PEG) precursors with either thiols (PEG-SH) or allyls (PEG-Al) , covering molecular weights from 3 kDa to 8 kDa were synthesized and thoroughly characterized by 1H NMR, 13C NMR, FT-Raman and MALDI-TOF techniques. By combining PEG precursors with complementary trifunctional crosslinkers, a library of well-defined single-network hydrogels was efficiently constructed via the robust UV-initiated thiol-ene coupling (TEC) chemistry. Novel sequential interpenetrating network (seqIPN) hydrogels based on PEG were fabricated by diffusing and afterwards crosslinking secondary-network precursors within dense (2 kDa) to loose (8 kDa) primary networks. The impacts of polymer chain length and diffusion time on the swelling and mechanical properties were assessed for the seqIPN hydrogels. Additionally, disperse red 13 decorated PEG 2 kDa and 8 kDa were synthesized and used as probes to monitor the secondary-network precursor diffusion rate by UV/Vis spectroscopy. 

FT-Raman and leaching tests were conducted to evaluate the efficiency of the TEC reaction for the development of PEG networks and their gel fractions. All gels were fully crosslinked within 5 minutes and with the gel fraction above 84%. The chain length of PEG, location of functional groups of PEGs, solvents, solid content were found to have directly influence on the mechanical and swelling properties of PEG single-network hydrogels. The utilization of the diffusion time dependent seqIPN strategy enabled further freedom to control the swelling and mechanical properties of PEG hydrogels, with the degree of water swelling ranged from 280 – 870% and the tensile modulus ranging from 1135 kPa to 175 kPa.

Furthermore, the seqIPN strategy was utilized for fiber reinforced free radical polymerized hydrogels. N, N-dimethylacrylamide (DMA) with crosslinker poly(ethylene glycol) diacrylate were diffused in bacterial cellulose (BC) aerogel thereafter UV crosslinked to form BC-DMA hydrogels. FT-Raman and leaching tests were conducted to evaluate the efficiency of the free radical polymerization and the BC-DMA gel fractions. After UV cure for 10 minutes, robust DMA networks were formed within BC aerogels with over 94% gel fraction. The high porosity and robust interpenetrating DMA network within BC fibers were further analysed with FE-SEM. Compression tests showed that fiber reinforced DMA hydrogels have higher compression modulus than DMA hydrogels, ranging from 4.4 to 8.3 MPa with water content from 78 to 70%.

Place, publisher, year, edition, pages
KTH: KTH Royal Institute of Technology, 2012. , 67 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:63
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-105539ISBN: 978-91-7501-471-5 (print)OAI: oai:DiVA.org:kth-105539DiVA: diva2:571374
Public defence
2012-12-06, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 2012

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2012-11-22Bibliographically approved
List of papers
1. Characterization of Well-Defined Poly(ethylene glycol) Hydrogels Prepared by Thiol-ene Chemistry
Open this publication in new window or tab >>Characterization of Well-Defined Poly(ethylene glycol) Hydrogels Prepared by Thiol-ene Chemistry
Show others...
2011 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 49, no 18, 4044-4054 p.Article in journal (Refereed) Published
Abstract [en]

Considering the large number of applications for hydrogels, a better understanding of the relation between molecular structure and mechanical properties for well-defined hydrogel is essential. A new library has been compiled of poly(ethylene glycol) polymers (PEG) of different length end functionalized with diallyl, dithiol, and dimethacrylate, and crosslinked with complementary trifunctional crosslinkers. In this study, the hydrogels were initially analyzed by FT-Raman and NMR to study the conversion ratio of the functional groups. The effects of solvent type, solid content concentration, curing time and length of the PEG chains on the final leaching, swelling and tensile properties of the hydrogels were studied.

Keyword
crosslinking, elastic modulus, hydrogels, properties, synthesis, thiol-ene chemistry
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-41788 (URN)10.1002/pola.24847 (DOI)000294818600018 ()2-s2.0-80051709540 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20111003Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2017-12-08Bibliographically approved
2. Sequential interpenetrating poly(ethylene glycol) hydrogels prepared by UV-initiated thiol–ene coupling chemistry
Open this publication in new window or tab >>Sequential interpenetrating poly(ethylene glycol) hydrogels prepared by UV-initiated thiol–ene coupling chemistry
2013 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 51, no 2, 363-371 p.Article in journal (Refereed) Published
Abstract [en]

Poly(ethylene glycol) (PEG)-diallyls, ranging from 2 to 8 kDa, were successfully reacted with a trifunctional thiol crosslinker via thiol–ene coupling reaction to construct four different primary PEG hydrogels. These systems were used as scaffolds for the preparation of a library of sequential interpenetrating networks (SeqIPNs). The solid content of the secondary networks varied between 21 and 34% and was dependent on the length of the absorbing PEGs. The gel fractions for the IPNs were above 85%. Additionally, the lowest degree of swelling was found for the IPN based on 2-kDa PEG (315%), whereas the 8-kDa PEG IPN exhibited a value of 810%. The SeqIPN strategy facilitated hydrogel systems that cover a larger domain of tensile modulus (192–889 kPa) when compared with single hydrogel networks (175–555 kPa).

Keyword
hydrogels, modulus, networks, polyethers, poly(ethylene glycol), swelling degree, thiol–ene click chemistry, UV curing
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-105557 (URN)10.1002/pola.26393 (DOI)000312448800016 ()2-s2.0-84870981886 (Scopus ID)
Funder
Swedish Research Council, 2010-453
Note

QC 20121122

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
3. The influence of diffusion time on the properties of sequential interpenetrating PEG hydrogels
Open this publication in new window or tab >>The influence of diffusion time on the properties of sequential interpenetrating PEG hydrogels
2013 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 51, no 6, 1378-1386 p.Article in journal (Refereed) Published
Abstract [en]

Four sets comprising a total of 16 sequential interpenetrating network (SeqIPN) hydrogels were efficiently fabricated via UV initiated thiol-ene coupling chemistry and from 2 kDa or 8 kDa primary poly(ethylene glycol) (PEG) networks (S2 and S8). Each primary system delivered four different SeqIPNs constructed after 2, 4, 20, and 44 h diffusion of secondary network PEG precursors, 2 kDa and 8 kDa. This allowed the assessment of both mechanical and swelling properties for a wide range of novel hydrogels ranging from loosely crosslinked SeqIPN 8-8 to densely crosslinked SeqIPN 2-2 systems. All gel fractions of secondary networks were above 83% and 44 h of diffusion was found sufficient to fully saturate the primary networks. Disperse red functionalized PEGs (2 kDa and 8 kDa) were further used as probes to investigate the diffusion mechanisms. The impact of diffusion time on loosely crosslinked S8 network with a swelling degree of 970% and tensile modulus of 175 kPa displayed a significant change in the final properties. For instance, a 2 h diffusion of 2 kDa PEG precursors generated a SeqIPN 8-2:2 comprising a secondary network solid content of 34% with a water swelling degree 580% and a tensile modulus of 365 kPa. On saturation, that is, 44 h of diffusion, SeqIPN 2-8:44 exhibited 64% of secondary network solid content, a swelling capacity of 380% and over fourfold of tensile modulus (758 kPa) when compared with the primary network S8. SeqIPN hydrogel with the highest tensile modulus and lowest degree of water swelling was obtained after 44 h diffusion of 2 kDa PEG precursors within the densely crosslinked S2 primary network. In this case, SeqIPN 2-2:44 noted a water swelling capability of 280% and a tensile modulus over 1 MPa. The latter was twofold when compared with S2 with a tensile modulus of 555 kPa. Consequently, the diffusion time of secondary network is a promising parameter to control and that enables the fabrication of PEG hydrogels with a wider window of mechanical and swelling properties.

Keyword
crosslinking, diffusion, hydrogels, mechanical properties, poly(ethylene glycol), polyethers, sequential interpenetrating network (IPN), swelling degree, thiol-ene chemistry, UV curing, UVvis spectroscopy
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-105564 (URN)10.1002/pola.26506 (DOI)000314975700013 ()2-s2.0-84873683102 (Scopus ID)
Funder
Swedish Research Council, 2010-453
Note

QC 20130325. Updated from submitted to published.

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
4. Mechanical properties of N, N-dimethylacrylamide hydrogels reinforced with bacterial cellulose aerogel
Open this publication in new window or tab >>Mechanical properties of N, N-dimethylacrylamide hydrogels reinforced with bacterial cellulose aerogel
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-105566 (URN)
Note

QS 2012

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2012-11-22Bibliographically approved

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