Functional star-type polyethylene glycol copolymers for hydrogels and biohybrid gels
Hidrojeller ve biyohibrid hidrojeller için fonksiyonel yıldız şeklinde polietilen glikol kopolimerler
- Tez No: 782597
- Danışmanlar: PROF. DR. MARTIN MOELLER
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2015
- Dil: İngilizce
- Üniversite: Rheinisch-Westfälische Technische Hochschule Aachen
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 219
Özet
Tekrarlanan etilen oksit segmentlerinin polieter molekülü olan poli(etilen oksit) (PEG), hidrofilisite, inert yapı, immünojenik olmayan doğa ve biyouyumluluk gibi birçok avantajı olan en çok kullanılan sentetik polimerdir. Bu benzersiz özellikler, endüstriyel ve biyoloji ile ilgili alanlarda geniş kullanımlarını mümkün kılmıştır. Çok sayıda uygulama alanının varlığına rağmen, PEG'ler LCST, kristalinite, metal iyonu tenlenmesi gibi bazı önemli problemlerle ortaya çıkmıştır.Etilen oksidin farklı komonomerlerle (örneğin, kaprolakton, propilen oksit, laktid asit ve stiren) kopolimerizasyonu ile alternatif moleküllerin sentezi için birçok girişimde bulunulmuştur. Bu çalışmada, çeşitli moleküler ağırlıklara (örneğin, 6, 12 ve 1 kg / mol) ve terminal işlevlerine sahip altı kollu yıldız tipi poli (EO-stat-PO) üzerinde çalıştık. Tez, PEG'lerin kimyasal doğası ve mevcut sınırlamaları ve alternatif PEG kopolimerlerine ilişkin içgörüler üzerine kapsamlı bir derleme ile başladı. Bu bölümde, PEG'lerin sınırlamaları belirtilmiş ve alternatifleri, uygulamalarına özel bir odaklanma ile açıklanmıştır.
Özet (Çeviri)
Poly(ethylene oxide) (PEG), polyether molecule of repeating ethylene oxide segments, is the most used synthetic polymer with many advantages, such as hydrophilicity, inert structure, non-immunogenic nature, and biocompatibility. Those unique features made possible their wide use in industrial and biorelated fields. Although the presence of a vast number of application areas, PEGs have come up with some notable problems, i.e., LCST, crystallinity, metal ion complexation. Many attempts have already been done for the synthesis of alternative molecules with the copolymerization of ethylene oxide with different comonomers (e.g., caprolactone, propylene oxide, lactide acid, and styrene). In this study, we studied six-armed star-type poly(EO-stat-PO) with various molecular weights (e.g., 6, 12 and 1 kg/mol) and terminal functionalities. The thesis started with a comprehensive review on the chemical nature and current limitations of the PEGs and insights into alternative PEG copolymers. In that section, the limitations of the PEGs were stated, and their alternatives were described with a particular focus on their applications. In the following section, rheology and dynamics of the copolymers were studied at entangled and melt states. Those molecules exhibited relatively low viscosity with strong shear thinning behavior. The relaxation of the copolymers showed variations with the polymer content and the molecular weight of the arm. Amorphous configuration was revealed for the copolymers and their interactions with water varied than their solutions in organic solvents with a possible scenario of configurational changes of helical chains. Those molecules did not reveal thermoresponsivity, however, nanoscale aggregates of the stars have been revealed due to hydrophobic interactions and hydrogen bonds with water molecules. Thereafter, we investigated properties of the six-armed sP(EO-stat-PO) and star PEG molecules having comparable molecular weights over viscosity, dynamics in water, phase behavior, and configuration. Both molecules exhibited similar viscous properties with a strong-shear thinning behavior and low elasticity. Amorphous configuration was revealed for the copolymer while the homopolymer was shown to be consisted of the highly crystalline segments. The size range of both molecules were in the range of 7-9 nm and the clusters of ca. 100 nm. In later section, those molecules were functionalized with various reactive groups (e.g., maleimide, vinyl sulfone, allyl, alkyne, succinimide carbonate, ethyl chloride, carboxylic acid, acrylate, aldehyde and silyl). An illustrative example, sP(EO-stat-PO) macromers with terminal acrylate and succinimide carbonate groups used for the layer preparation, and the coatings were evaluated over cell adhesion experiments. Isocyanate (NCO) terminated stars were used for in situ forming macromolecular networks with tunable structural inhomogeneity and elastic stiffness. In that context, water-diglyme solvent mixture at various combinations was used to control the kinetics of the hydrolysis of NCO groups and their subsequent cross-linking reactions. Such control over the cross-linking reactions significantly influenced the mechanical properties of the hydrogels and extends gelation times. Structural inhomogeneity of the gels was decreased due to the occurrence of homogeneous gel matrix. Those molecules were later used for cross-linking of elastin polypeptides over lysine amino acids, which present free nucleophilic amine groups to couple with NCO groups. Those gels were simultaneously functionalized with bicyclononynes (BCN) motives to create functional elastin scaffolds. In the last part of the thesis, star molecules and linear polyvinyl amine molecules were successfully used for the design of ultrathin nanolayers assemblies, which exhibited good stability at humidity conditions over three months.Beyond of the scope of the thesis, three different studies were also described. In the first part, alginate gel formation with well-known non-gelling ion, magnesium (Mg) was shown. Gelation in this system occurs at ca. 5-10 times higher concentration of ions than the reported for calcium-based gels. Alginate network formation with magnesium ions is very slow and is typically accomplished within 2-3 hours. Gelation with magnesium ions is also strongly dependent on alginate chemical composition as the presence of long guluronic units privileges faster gel formation. In the second part, redox-sensitive hydrogels and nanogels were produced by enzymatic cross-linking of thiol-functionalized polymer under mild conditions. Cells can be embedded in the hydrogels and proteins can be entrapped and released from the nanogels. These gels are fully degradable under mild and cytocompatible reductive conditions. In the last part of the appendix section, thermo and pH- responsive microgels from native elastin polypeptides were described, and the cross-linking of polypeptides was carried out by using either hydrophilic or hydrophobic cross-linkers. Both cross-linking approaches yielded elastin microgels, which revealed a volume change transition at 37 and 35.5°C and pH responsivity in the range of 5-7. Preliminary experiments were conducted to evaluate the suitability of these microgels for use as a drug-release system and demonstrated cytocompatibility, enzymatic degradability by elastase, and entrapping and slow release of a water-soluble biopolymerTo conclude, this study describes dynamics and intrinsic properties of the star typed PEG copolymers consisting of randomly distributed ethylene oxide and propylene oxide having various reactivities and their use as for gels and biohybrid hydrogels. These functional star type prepolymers are ideal candidates for a diverse range of applications as described above and have some advantages compared to the PEG homopolymers, which are respected gold stealth polymers for biological applications. We thereby believe that with further control of the structure together with appropriate degradable end groups might create multifunctional platforms at various length scales.
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