Differentiation of physical and chemical cross-linking in gelatin methacryloyl hydrogels

AbstractGelatin methacryloyl (GM) hydrogels have been investigated for almost 20 years, especially for biomedical applications. Recently, strengthening effects of a sequential cross-linking procedure, whereby GM hydrogel precursor solutions are cooled before chemical cross-linking, were reported. It was hypothesized that physical and enhanced chemical cross-linking of the GM hydrogels contribute to the observed strengthening effects. However, a detailed investigation is missing so far. In this contribution, we aimed to reveal the impact of physical and chemical cross-linking on strengthening of sequentially cross-linked GM and gelatin methacryloyl acetyl (GMA) hydrogels. We investigated physical and chemical cross-linking of three different GM(A) derivatives (GM10, GM2A8 and GM2), which provided systematically varied ratios of side-group modifications. GM10 contained the highest methacryloylation degree (DM), reducing its ability to cross-link physically. GM2 had the lowest DM and showed physical cross-linking. The total modification degree, determining the physical cross-linking ability, of GM2A8 was comparable to that of GM10, but the chemical cross-linking ability was comparable to GM2. At first, we measured the double bond conversion (DBC) kinetics during chemical GM(A) cross-linking quantitatively in real-time via near infrared spectroscopy-photorheology and showed that the DBC decreased due to sequential cross-linking. Furthermore, results of circular dichroism spectroscopy and differential scanning calorimetry indicated gelation and conformation changes, which increased storage moduli of all GM(A) hydrogels due to sequential cross-linking. The data suggested that the total cross-link density determines hydrogel stiffness, regardless of the physical or chemical nature of the cross-links.

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PEROXIDE CROSS-LINKING OF EPDM USING MOVING DIE RHEOMETER MEASUREMENTS. I: EFFECTS OF THE THIRD MONOMER CONCENTRATION AND PEROXIDE CONTENT

Rubber Chemistry and Technology ◽

10.5254/rct.14.85968 ◽

2015 ◽

Vol 88 (1) ◽

pp. 40-52 ◽

Cited By ~ 5

Author(s):

He Wang ◽

Ying Ding ◽

Shugao Zhao ◽

Claus Wrana

Keyword(s):

Network Structure ◽

Monomer Concentration ◽

Cross Linking ◽

Cross Link ◽

Peroxide Content ◽

Entanglement Density ◽

The Third ◽

Link Density ◽

Cross Links ◽

Cross Link Density

ABSTRACT The influence of the third monomer 5-ethylene-2-norbornene (ENB) and peroxide content on cure behavior and network structure of peroxide-cured EPDM were investigated by moving die rheometer, NMR relaxation, and dynamic mechanical thermal spectroscopy. According to the rubber elasticity theory, the torque measurement results showed the network structure of peroxide-cured EPDM contained chemical cross-links via combination reaction (Ccom), chemical cross-links via addition reaction (Cadd), and the contribution of entanglement density and network defects to the total cross-link density (CEN). The total cross-link density (Ctot) increased linearly with the peroxide content. The increase of ENB concentration was beneficial for the improvement of cross-linking efficiency of peroxide, but it made the diene conversion of EPDM decrease. CEN was dependent on the third monomer content, which also provided the dominant contribution to the Ctot at low peroxide contents. Furthermore, Ccom and Cadd were dependent on peroxide content linearly, and the latter also was governed by the ENB level.

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Chemistry of collagen cross-links: glucose-mediated covalent cross-linking of type-IV collagen in lens capsules

Biochemical Journal ◽

10.1042/bj2960489 ◽

1993 ◽

Vol 296 (2) ◽

pp. 489-496 ◽

Cited By ~ 73

Author(s):

A J Bailey ◽

T J Sims ◽

N C Avery ◽

C A Miles

Keyword(s):

Type Iv Collagen ◽

Cross Linking ◽

Mechanical And Thermal Properties ◽

Maximum Strain ◽

Scanning Calorimetry ◽

Melting Temperatures ◽

Type Iv ◽

Collagen Molecules ◽

Cross Links

The incubation of lens capsules with glucose in vitro resulted in changes in the mechanical and thermal properties of type-IV collagen consistent with increased cross-linking. Differential scanning calorimetry (d.s.c.) of fresh lens capsules showed two major peaks at melting temperatures Tm 1 and Tm 2 at approx. 54 degrees C and 90 degrees C, which can be attributed to the denaturation of the triple helix and 7S domains respectively. Glycosylation of lens capsules in vitro for 24 weeks caused an increase in Tm 1 from 54 degrees C to 61 degrees C, while non-glycosylated, control incubated capsules increased to a Tm 1 of 57 degrees C. The higher temperature required to denature the type-IV collagen after incubation in vitro suggested increased intermolecular cross-linking. Glycosylated lens capsules were more brittle than fresh samples, breaking at a maximum strain of 36.8 +/- 1.8% compared with 75.6 +/- 6.3% for the fresh samples. The stress at maximum strain (or ‘strength’) was dramatically reduced from 12.0 to 4.7 N.mm.mg-1 after glycosylation in vitro. The increased constraints within the system leading to loss of strength and increased brittleness suggested not only the presence of more cross-links but a difference in the location of these cross-links compared with the natural lysyl-aldehyde-derived cross-links. The chemical nature of the fluorescent glucose-derived cross-link following glycosylation was determined as pentosidine, at a concentration of 1 pentosidine molecule per 600 collagen molecules after 24 weeks incubation. Pentosidine was also determined in the lens capsules obtained from uncontrolled diabetics at a level of about 1 per 100 collagen molecules. The concentration of these pentosidine cross-links is far too small to account for the observed changes in the thermal and mechanical properties following incubation in vitro, clearly indicating that another as yet undefined, but apparently more important cross-linking mechanism mediated by glucose is taking place.

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Cross-linking of the electron-transfer flavoprotein to electron-transfer flavoprotein-ubiquinone oxidoreductase with heterobifunctional reagents

Biochemical Journal ◽

10.1042/bj2550869 ◽

1988 ◽

Vol 255 (3) ◽

pp. 869-876 ◽

Cited By ~ 14

Author(s):

D J Steenkamp

Keyword(s):

Electron Transfer ◽

Small Subunit ◽

Cross Linking ◽

Minor Effect ◽

Electron Transfer Flavoprotein ◽

Ubiquinone Oxidoreductase ◽

Lysine Residues ◽

Cross Links ◽

A Minor ◽

Chemical Cross Linking

The mitochondrial electron-transfer flavoprotein (ETF) is a heterodimer containing only one FAD. In previous work on the structure-function relationships of ETF, its interaction with the general acyl-CoA dehydrogenase (GAD) was studied by chemical cross-linking with heterobifunctional reagents [D. J. Steenkamp (1987) Biochem. J. 243, 519-524]. GAD whose lysine residues were substituted with 3-(2-pyridyldithio)propionyl groups was preferentially cross-linked to the small subunit of ETF, the lysine residues of which had been substituted with 4-mercaptobutyramidine (MBA) groups. This work was extended to the interaction of ETF with ETF-ubiquinone oxidoreductase (ETF-Q ox). ETF-Q ox was partially inactivated by modification with N-succinimidyl 3-(2-pyridyldithio)propionate to introduce pyridyl disulphide structures. A similar modification of ETF caused a large increase in the apparent Michaelis constant of ETF-Q ox for modified ETF owing to the loss of positive charge on some critical lysines of ETF. When ETF-Q ox was modified with 2-iminothiolane to introduce 4-mercaptobutyramidine groups, only a minor effect on the activity of the enzyme was observed. To retain the positive charges on the lysine residues of ETF, pyridyl disulphide structures were introduced by treating ETF with 2-iminothiolane in the presence of 2,2′-dithiodipyridyl. The electron-transfer activity of the resultant ETF preparation containing 4-(2-pyridyldithio)butyramidine (PDBA) groups was only slightly affected. When ETF-Q ox substituted with MBA groups was mixed with ETF bearing PDBA groups, at least 70% of the cross-links formed between the two proteins were between the small subunit of ETF and ETF-Q ox. ETF-Q ox, therefore, interacts predominantly with the same subunit of ETF as GAD. Variables which affect the selectivity of ETF-Q ox cross-linking to the subunits of ETF are considered.

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EXPERIMENTAL VALIDATION OF THE CHARLESBY AND HORIKX MODELS APPLIED TO DE-VULCANIZATION OF SULFUR AND PEROXIDE VULCANIZATES OF NR AND EPDM

Rubber Chemistry and Technology ◽

10.5254/rct.16.83776 ◽

2016 ◽

Vol 89 (4) ◽

pp. 671-688 ◽

Cited By ~ 8

Author(s):

M. A. L. Verbruggen ◽

L. van der Does ◽

W. K. Dierkes ◽

J. W. M. Noordermeer

Keyword(s):

Experimental Validation ◽

Main Chain ◽

Sol Gel ◽

Chain Scission ◽

Cross Linking ◽

Cross Link ◽

Practical Reality ◽

Cross Links ◽

The Cross ◽

Theoretical Considerations

ABSTRACT The theoretical model developed by Charlesby to quantify the balance between cross-links creation of polymers and chain scission during radiation cross-linking and further modifications by Horikx to describe network breakdown from aging were merged to characterize the balance of both types of scission on the development of the sol content during de-vulcanization of rubber networks. There are, however, disturbing factors in these theoretical considerations vis-à-vis practical reality. Sulfur- and peroxide-cured NR and EPDM vulcanizates were de-vulcanized under conditions of selective cross-link and random main-chain scissions. Cross-link scission was obtained using thiol-amine reagents for selective cleavage of sulfur cross-links. Random main-chain scission was achieved by heating peroxide vulcanizates of NR with diphenyldisulfide, a method commonly employed for NR reclaiming. An important factor in the analyses of these experiments is the cross-linking index. Its value must be calculated using the sol fraction of the cross-linked network before de-vulcanization to obtain reliable results. The values for the cross-linking index calculated with sol-gel data before de-vulcanization appear to fit the experimentally determined modes of network scission during de-vulcanization very well. This study confirms that the treatment of de-vulcanization data with the merged Charlesby and Horikx models can be used satisfactorily to characterize the de-vulcanization of NR and EPDM vulcanizates.

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Mechanical and structural consequences of associative dynamic cross-linking in acrylic diblock copolymers

10.26434/chemrxiv.10000232.v5 ◽

2021 ◽

Author(s):

Jacob Ishibashi ◽

Ian Pierce ◽

Alice Chang ◽

Aristotelis Zografos ◽

Bassil El-Zaatari ◽

...

Keyword(s):

Viscoelastic Properties ◽

Diblock Copolymers ◽

Microphase Separation ◽

Network Connectivity ◽

Ethyl Acrylate ◽

Cross Linking ◽

Cross Link ◽

Block Polymers ◽

Link Density ◽

Cross Link Density

The composition of low-Tg n-butylacrylate-block-(acetoxyaceto)ethyl acrylate block polymers is investigated as a strategy to tune the properties of dynamically cross-linked vinylogous urethane vitrimers. As the proportion of the cross-linkable block is increased, the thermorheological properties, structure, and stress relaxation evolve in ways that cannot be explained by increasing cross-link density alone. Evidence is presented that network connectivity defects such as loops and dangling ends are increased by microphase separation. The thermomechanical and viscoelastic properties of block copolymer-derived vitrimers arise from the subtle interplay of microphase separation and network defects.<div> </div>

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FORMULATION AND EVALUATION OF DOXORUBICIN CONTAINING NANOGELS FOR DELIVERY TO CANCER CELLS

Journal of Drug Delivery and Therapeutics ◽

10.22270/jddt.v8i5.1890 ◽

2018 ◽

Vol 8 (5) ◽

pp. 178-183

Author(s):

Manish Kumar ◽

Hemant K. Sharma

Keyword(s):

Average Particle Size ◽

Gellan Gum ◽

Cross Linking ◽

Average Particle ◽

Scanning Calorimetry ◽

Green Method ◽

X Ray ◽

Oppositely Charged ◽

Chemical Cross Linking

The objective of this study is to prepare nanogels were prepared via charged gellan gum. It was prepared by in situ cross linking reaction between two oppositely charged materials by green method without use of chemical cross linking agents. The prepared nanogels were characterized by Dynamic light scattering, scanning electron microscopy, differential scanning calorimetry and X- Ray diffractometry. The prepared formulation had average particle size of 226 nm with polydispersity index of 0.3. The doxorubicin loaded nanogel demonstrated sustained release for 20 h. The prepared nanogels were hemocompatible and cyctocompatible as revealed by hemocompatibility and MTT assay respectively. All results confirmed that these nanogels can be used for cancer treatment. Keywords: Nanogel, Chitosan, Gellan gum, Doxorubicin, Cancer.

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Magnetic composites based on NR and strontium ferrite

Acta Chimica Slovaca ◽

10.2478/acs-2019-0010 ◽

2019 ◽

Vol 12 (1) ◽

pp. 63-69

Author(s):

Ján Kruželák ◽

Andrea Kvasničáková ◽

Rastislav Dosoudil ◽

Ivan Hudec

Keyword(s):

Carbon Black ◽

Strontium Ferrite ◽

Rubber Matrix ◽

Cross Link ◽

Magnetic Composites ◽

Link Density ◽

Cross Links ◽

Cross Link Density ◽

The Cross ◽

Thermo Physical Properties

Abstract Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

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Mapping the Contact Sites of the Escherichia coli Division-Initiating Proteins FtsZ and ZapA by BAMG Cross-Linking and Site-Directed Mutagenesis

International Journal of Molecular Sciences ◽

10.3390/ijms19102928 ◽

2018 ◽

Vol 19 (10) ◽

pp. 2928 ◽

Cited By ~ 7

Author(s):

Winfried Roseboom ◽

Madhvi Nazir ◽

Nils Meiresonne ◽

Tamimount Mohammadi ◽

Jolanda Verheul ◽

...

Keyword(s):

Site Directed Mutagenesis ◽

Cross Linking ◽

Directed Mutagenesis ◽

Amino Acid Residues ◽

Binding Interface ◽

Tetrameric Structure ◽

Z Ring ◽

Cross Links ◽

Chemical Cross Linking

Cell division in bacteria is initiated by the polymerization of FtsZ at midcell in a ring-like structure called the Z-ring. ZapA and other proteins assist Z-ring formation and ZapA binds ZapB, which senses the presence of the nucleoids. The FtsZ–ZapA binding interface was analyzed by chemical cross-linking mass spectrometry (CXMS) under in vitro FtsZ-polymerizing conditions in the presence of GTP. Amino acids residue K42 from ZapA was cross-linked to amino acid residues K51 and K66 from FtsZ, close to the interphase between FtsZ molecules in protofilaments. Five different cross-links confirmed the tetrameric structure of ZapA. A number of FtsZ cross-links suggests that its C-terminal domain of 55 residues, thought to be largely disordered, has a limited freedom to move in space. Site-directed mutagenesis of ZapA reveals an interaction site in the globular head of the protein close to K42. Using the information on the cross-links and the mutants that lost the ability to interact with FtsZ, a model of the FtsZ protofilament–ZapA tetramer complex was obtained by information-driven docking with the HADDOCK2.2 webserver.

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Two DD-Carboxypeptidases fromMycobacterium smegmatisAffect Cell Surface Properties through Regulation of Peptidoglycan Cross-Linking and Glycopeptidolipids

Journal of Bacteriology ◽

10.1128/jb.00760-17 ◽

2018 ◽

Vol 200 (14) ◽

Cited By ~ 7

Author(s):

Satya Deo Pandey ◽

Shilpa Pal ◽

Ganesh Kumar N ◽

Ankita Bansal ◽

Sathi Mallick ◽

...

Keyword(s):

Cell Surface ◽

Mycobacterium Smegmatis ◽

Biofilm Formation ◽

Cross Linking ◽

Surface Lipid ◽

Cross Link ◽

Content Type ◽

Murine Macrophages ◽

Cross Links ◽

Link Formation

ABSTRACTDuring the peptidoglycan (PG) maturation of mycobacteria, the glycan strands are interlinked by both 3-3 (between twomeso-diaminopimelic acids [meso-DAPs]) and 4-3 cross-links (betweend-Ala andmeso-DAP), though there is a predominance (60 to 80%) of 3-3 cross-links. Thedd-carboxypeptidases (dd-CPases) act on pentapeptides to generate tetrapeptides that are used byld-transpeptidases as substrates to form 3-3 cross-links. Therefore,dd-CPases play a crucial role in mycobacterial PG cross-link formation. However, the physiology ofdd-CPases in mycobacteria is relatively unexplored. In this study, we deleted twodd-CPase genes,msmeg_2433andmsmeg_2432, both individually and in combination, fromMycobacterium smegmatismc2155. Though the singledd-CPase gene deletions had no significant impact on the mycobacterial physiology, many interesting functional alterations were observed in the double-deletion mutant,viz., a predominance in PG cross-link formation was shifted from 3-3 cross-links to 4-3, cell surface glycopeptidolipid (GPL) expression was reduced, and susceptibility to β-lactams and antitubercular agents was enhanced. Moreover, the survival rate of the double mutant within murine macrophages was higher than that of the parent. Interestingly, the complementation with any one of thedd-CPase genes could restore the wild-type phenotype. In a nutshell, we infer that the altered ratio of 4-3 to 3-3 PG cross-links might have influenced the expression of surface GPLs, colony morphology, biofilm formation, drug susceptibility, and subsistence of the cells within macrophages.IMPORTANCEThe glycan strands in mycobacterial peptidoglycan (PG) are interlinked by both 3-3 and 4-3 cross-links. Thedd-CPases generate tetrapeptides by acting on the pentapeptides, andld-transpeptidases use tetrapeptides as substrates to form 3-3 cross-links. In this study, we showed that simultaneous deletions of twodd-CPases alter the nature of PG cross-linking from 3-3 cross-links to 4-3 cross-links. The deletions subsequently decrease the expression of glycopeptidolipids (significant surface lipid present in many nontuberculous mycobacteria, includingMycobacterium smegmatis) and affect other physiological parameters, like cell morphology, growth rate, biofilm formation, antibiotic susceptibility, and survival within murine macrophages. Thus, unraveling the physiology ofdd-CPases might help us design antimycobacterial therapeutics in the future.

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PEG Cross-Linked Alginate Hydrogels with Controlled Mechanical Properties

MRS Proceedings ◽

10.1557/proc-530-37 ◽

1998 ◽

Vol 530 ◽

Cited By ~ 2

Author(s):

Petra Eiselt ◽

Jon A. Rowley ◽

David J. Mooney

Keyword(s):

Mechanical Properties ◽

Tissue Engineering ◽

Molecular Weight ◽

Elastic Modulus ◽

Cell Transplantation ◽

Cross Linking ◽

Cross Link ◽

Link Density ◽

A Cell ◽

Cross Link Density

AbstractReconstruction of tissues and organs utilizing cell transplantation offers an attractive approach for the treatment of patients suffering from organ failure or loss. Highly porous synthetic materials are often used to mimic the function of the extracellular matrix (ECM) in tissue engineering, and serve as a cell delivery vehicle for the formation of tissues in vivo. Alginate, a linear copolysaccharide composed of D-mannuronic acid (M) and L-guluronic acid (G) units is widely used as a cell transplantation matrix. Alginate is considered to be biocompatible, and hydrogels are formed in the presence of divalent cations such as Ca2+, Ba2+ and Sr2+. However, ionically cross-linked alginate gels continuously lose their mechanical properties over time with uncontrollable degradation behavior. We have modified alginate via covalent coupling of cross-linking molecules to expand and stabilize the mechanical property ranges of these gels. Several diamino PEG molecules of varying molecular weight (200, 400, 1000, 3400) were synthesized utilizing carbodiimide chemistry. Sodium alginate was covalently cross-linked with these cross-linking molecules, and mechanical properties of the resulting hydrogels were determined. The elastic modulus of the cross-linked alginates depended on the molecular weight of the cross-linking molecules, and ranged from 10-110 kPa. The theoretical cross-link density in the hydrogels was also varied from 3 to 47% (relative to the carboxylic groups in the alginate) and the mechanical properties were measured. The elastic modulus increased gradually and reached a maximum at a cross-link density of 15%. In summary, covalently coupled hydrogels can be synthesized which exhibit a wide range of mechanical properties, and these materials may be useful in a number of tissue engineering applications.

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