scholarly journals Design and control of a visual servomechanism for automating corneal cross-linking treatment in keratoconus patients

2015 ◽  
Vol 23 ◽  
pp. 602-614
Author(s):  
Onurcan ŞAHİN ◽  
Erdinç ALTUĞ
Keyword(s):  
Cross Linking ◽  
And Control

scholarly journals Characterization of the stilbenedisulphonate binding site on band 3 Memphis variant II (Pro-854→Leu)

1996 ◽  
Vol 317 (2) ◽  
pp. 509-514 ◽  
Author(s):  
James M. SALHANY ◽  
Renee L. SLOAN ◽  
Lawrence M. SCHOPFER
Keyword(s):  
Binding Site ◽  
Conformational Changes ◽  
Covalent Binding ◽  
Band 3 ◽  
Blood Group Antigen ◽  
Cross Linking ◽  
Anion Exchange Protein ◽  
Membrane Bound ◽  
And Control

Band 3 Memphis variant II is a mutant anion-exchange protein associated with the Diego a+ blood group antigen. There are two mutations in this transporter: Lys-56 → Glu within the cytoplasmic domain, and Pro-854 → Leu within the membrane-bound domain. The Pro-854 mutation, which is thought to give rise to the antigenicity, is located within the C-terminal subdomain of the membrane-bound domain. Yet, there is an apparent enhancement in the rate of covalent binding of H2DIDS (4,4´-di-isothiocyanatodihydro-2,2´-stilbenedisulphonate) to ‘lysine A’ (Lys-539) in the N-terminal subdomain, suggesting widespread conformational changes. In this report, we have used various kinetic assays which differentiate between conformational changes in the two subdomains, to characterize the stilbenedisulphonate site on band 3 Memphis variant II. We have found a significantly higher H2DIDS (a C-terminal-sensitive inhibitor) affinity for band 3 Memphis variant II, due to a lower H2DIDS ‘off’ rate constant, but no difference was found between mutant and control when DBDS (4,4´-dibenzamido-2,2´-stilbenedisulphonate) (a C-terminal-insensitive inhibitor) ‘off’ rates were measured. Furthermore, there were no differences in the rates of covalent binding to lysine A, for either DIDS (4,4´-di-isothiocyanato-2,2´-stilbenedisulphonate) or H2DIDS. However, the rate of covalent intrasubunit cross-linking of Lys-539 and Lys-851 by H2DIDS was abnormally low for band 3 Memphis variant II. These results suggest that the Pro-854 → Leu mutation causes a localized conformational change in the C-terminal subdomain of band 3.

Tensile strength of handsheets prepared with macerated fibres from solid wood modified with cross-linking agents

Holzforschung ◽  
2015 ◽  
Vol 69 (8) ◽  
pp. 959-966 ◽  
Author(s):  
Stergios Adamopoulos ◽  
Reza Hosseinpourpia ◽  
Carsten Mai
Keyword(s):  
Tensile Strength ◽  
Strength Loss ◽  
Solid Wood ◽  
Cross Linking ◽  
Microscopic Appearance ◽  
Finite Span ◽  
The Stability ◽  
And Control ◽  
Additional Role ◽  
Modified Wood

Abstract This study was conducted to explain the tensile strength loss of wood due to the modification with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and glutaraldehyde (GA). Modified and control wood blocks were macerated to deliberate fibres, and handsheets were produced thereof. The nitrogen content of the fibres indicated that maceration removed the major proportions of DMDHEU. The stability of GA in wood during maceration was not assessed. Tensile strength determined at zero span (z-strength) and finite span (f-strength) was equal for the handsheets from DMDHEU-modified fibres and the control handsheets. The microscopic appearance of the tested finite-span paper strips from DMDHEU-modified fibres mainly indicated interfibre failure and did not differ from the fibre fracture mode of the control handsheets. In contrast, the z-strength of the handsheets from GA-modified fibres was lower than that of controls and decreased with increasing content of GA in the initial modified wood. The f-strength behaviour of the handsheets from GA-modified fibres was the opposite: it was higher than that of controls and increased with increasing GA content. The microscopic appearance of the rapture zones of the finite-span testing mainly indicated intrafibre failure for the GA-modified fibres. It was concluded that cross-linking is likely to be the major reason for tensile strength loss of GA- and DMDHEU-modified wood. In terms of DMDHEU-modified wood, the incrustation of the cell wall by the resin and the reduction in pliability could play an additional role.

Development and control of a blend morphology by In situ cross-linking of the dispersed phase

1994 ◽  
Vol 53 (12) ◽  
pp. 1675-1686 ◽  
Author(s):  
A. De Loor ◽  
P. Cassagnau ◽  
A. Michel ◽  
B. Vergnes
Keyword(s):  
Cross Linking ◽  
Dispersed Phase ◽  
Blend Morphology ◽  
And Control

scholarly journals Alpha-Chain cross-linking in fibrin(ogen) Marburg

Blood ◽  
1995 ◽  
Vol 86 (3) ◽  
pp. 989-1000 ◽  
Author(s):  
JH Sobel ◽  
I Trakht ◽  
HQ Wu ◽  
S Rudchenko ◽  
R Egbring
Keyword(s):  
Polymer Network ◽  
Factor Xiiia ◽  
Cross Linking ◽  
Clotting System ◽  
Covalent Interaction ◽  
Alpha Chain ◽  
Parent Protein ◽  
Lysine Residues ◽  
And Control

Abstract The fibrinogen structural variant, Marburg (A alpha 1–460B beta gamma)2, is comprised of normal B beta and gamma chains but contains severely truncated A alpha chains that are missing approximately one half of their factor XIIIa cross-linking domain. Immunochemical studies of fibrin(ogen) Marburg were conducted to characterize the degree to which deletion of a defined A alpha-chain segment, A alpha 461–610, can affect the process of fibrin stabilization, ie, the factor XIIIa- mediated covalent interaction that occurs between alpha chains of neighboring fibrin molecules and between alpha chains and alpha 2 antiplasmin (alpha 2PI). The ability of Marburg (and control) alpha chains to serve as a substrate for factor XIIIa and undergo cross- linking was examined in an in vitro plasma clotting system. The capacity for alpha-chain cross-linking was evaluated both as the covalent incorporation of the small synthetic peptide, NQEQVSPLTLLK (which represents the first 12 amino acids of alpha 2PI and includes the factor XIIIa-sensitive glutamine residue responsible for the cross- linking of alpha 2PI to fibrin), and as the appearance of native (ie, natural), high-molecular-weight, cross-linked alpha-chain species. Antibodies specific for the (A)alpha and gamma/gamma-gamma chains of fibrin(ogen) and for the peptide and its parent protein, alpha 2PI (68 kD), were used as immunoblotting probes to visualize the various cross- linked products formed during in vitro clotting. Recalcification of Marburg plasma in the presence of increasing concentrations of peptide resulted in the formation of peptide-decorated Marburg alpha-chain monomers. Their size at the highest peptide concentration examined indicated the incorporation of a maximum of 3 to 4 mol of peptide per mole of alpha-chain. In the absence of alpha 2PI 1–12 peptide, the alpha chains of Marburg fibrin cross-linked to form oligomers and polymers, as well as heterodimers that included alpha 2PI. Both the peptide-decorated monomers and the native cross-linked alpha-chain species of Marburg fibrin were smaller than their control plasma counterparts, consistent with the truncated structure of the parent Marburg A alpha chain. Collectively, the findings indicate that, although deletion of the A alpha chain region no. 461–610 in fibrinogen Marburg prevents formation of an extensive alpha polymer network (presumably due to the absence of critical COOH-terminal lysine residues), it does not interfere with initial events in the fibrin stabilization process, namely, factor XIII binding and the ability of alpha chains to undergo limited cross-linking to one another and to alpha 2PI.

scholarly journals Alpha-Chain cross-linking in fibrin(ogen) Marburg

Blood ◽  
1995 ◽  
Vol 86 (3) ◽  
pp. 989-1000 ◽  
Author(s):  
JH Sobel ◽  
I Trakht ◽  
HQ Wu ◽  
S Rudchenko ◽  
R Egbring
Keyword(s):  
Polymer Network ◽  
Factor Xiiia ◽  
Cross Linking ◽  
Clotting System ◽  
Covalent Interaction ◽  
Alpha Chain ◽  
Parent Protein ◽  
Lysine Residues ◽  
And Control

The fibrinogen structural variant, Marburg (A alpha 1–460B beta gamma)2, is comprised of normal B beta and gamma chains but contains severely truncated A alpha chains that are missing approximately one half of their factor XIIIa cross-linking domain. Immunochemical studies of fibrin(ogen) Marburg were conducted to characterize the degree to which deletion of a defined A alpha-chain segment, A alpha 461–610, can affect the process of fibrin stabilization, ie, the factor XIIIa- mediated covalent interaction that occurs between alpha chains of neighboring fibrin molecules and between alpha chains and alpha 2 antiplasmin (alpha 2PI). The ability of Marburg (and control) alpha chains to serve as a substrate for factor XIIIa and undergo cross- linking was examined in an in vitro plasma clotting system. The capacity for alpha-chain cross-linking was evaluated both as the covalent incorporation of the small synthetic peptide, NQEQVSPLTLLK (which represents the first 12 amino acids of alpha 2PI and includes the factor XIIIa-sensitive glutamine residue responsible for the cross- linking of alpha 2PI to fibrin), and as the appearance of native (ie, natural), high-molecular-weight, cross-linked alpha-chain species. Antibodies specific for the (A)alpha and gamma/gamma-gamma chains of fibrin(ogen) and for the peptide and its parent protein, alpha 2PI (68 kD), were used as immunoblotting probes to visualize the various cross- linked products formed during in vitro clotting. Recalcification of Marburg plasma in the presence of increasing concentrations of peptide resulted in the formation of peptide-decorated Marburg alpha-chain monomers. Their size at the highest peptide concentration examined indicated the incorporation of a maximum of 3 to 4 mol of peptide per mole of alpha-chain. In the absence of alpha 2PI 1–12 peptide, the alpha chains of Marburg fibrin cross-linked to form oligomers and polymers, as well as heterodimers that included alpha 2PI. Both the peptide-decorated monomers and the native cross-linked alpha-chain species of Marburg fibrin were smaller than their control plasma counterparts, consistent with the truncated structure of the parent Marburg A alpha chain. Collectively, the findings indicate that, although deletion of the A alpha chain region no. 461–610 in fibrinogen Marburg prevents formation of an extensive alpha polymer network (presumably due to the absence of critical COOH-terminal lysine residues), it does not interfere with initial events in the fibrin stabilization process, namely, factor XIII binding and the ability of alpha chains to undergo limited cross-linking to one another and to alpha 2PI.

scholarly journals The αC domains of fibrinogen affect the structure of the fibrin clot, its physical properties, and its susceptibility to fibrinolysis

Blood ◽  
2005 ◽  
Vol 106 (12) ◽  
pp. 3824-3830 ◽  
Author(s):  
Jean-Philippe Collet ◽  
Jennifer L. Moen ◽  
Yuri I. Veklich ◽  
Oleg V. Gorkun ◽  
Susan T. Lord ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Viscoelastic Properties ◽  
Fibrin Clot ◽  
Factor Xiiia ◽  
Cross Linking ◽  
Branch Points ◽  
Biophysical Properties ◽  
Definitive Evidence ◽  
And Control ◽  
Scanning Electron

The functions of the αC domains of fibrinogen in clotting and fibrinolysis, which have long been enigmatic, were determined using recombinant fibrinogen truncated at Aα chain residue 251. Scanning electron microscopy and confocal microscopy revealed that the fibers of α251 clots were thinner and denser, with more branch points than fibers of control clots. Consistent with these results, the permeability of α251 clots was nearly half that of control clots. Together, these results suggest that in normal clot formation, the αC domains enhance lateral aggregation to produce thicker fibers. The viscoelastic properties of α251 fibrin clots differed markedly from control clots; α251 clots were much less stiff and showed more plastic deformation, indicating that interactions between the αC domains in normal clots play a major role in determining the clot's mechanical properties. Comparing factor XIIIa cross-linked α251 and control clots showed that γ chain cross-linking had a significant effect on clot stiffness. Plasmin-catalyzed lysis of α251 clots, monitored with both macroscopic and microscopic methods, was faster than lysis of control clots. In conclusion, these studies provide the first definitive evidence that the αC domains play an important role in determining the structure and biophysical properties of clots and their susceptibility to fibrinolysis.

scholarly journals Physical Interactions Strengthen Chemical Gelatin Methacryloyl Gels

Gels ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 4 ◽  
Author(s):  
Lisa Rebers ◽  
Tobias Granse ◽  
Günter Tovar ◽  
Alexander Southan ◽  
Kirsten Borchers
Keyword(s):  
Network Formation ◽  
Sol Gel ◽  
Solution Viscosity ◽  
Cross Linking ◽  
Physical Network ◽  
Helix Formation ◽  
Triple Helix Formation ◽  
Sol Gel Transition ◽  
And Control ◽  
Chemical Cross Linking

Chemically cross-linkable gelatin methacryloyl (GM) derivatives are getting increasing attention regarding biomedical applications. Thus, thorough investigations are needed to achieve full understanding and control of the physico-chemical behavior of these promising biomaterials. We previously introduced gelatin methacryloyl acetyl (GMA) derivatives, which can be used to control physical network formation (solution viscosity, sol-gel transition) independently from chemical cross-linking by variation of the methacryloyl-to-acetyl ratio. It is known that temperature dependent physical network formation significantly influences the mechanical properties of chemically cross-linked GM hydrogels. We investigated the temperature sensitivity of GM derivatives with different degrees of modification (GM2, GM10), or similar degrees of modification but different methacryloyl contents (GM10, GM2A8). Rheological analysis showed that the low modified GM2 forms strong physical gels upon cooling while GM10 and GM2A8 form soft or no gels. Yet, compression testing revealed that all photo cross-linked GM(A) hydrogels were stronger if cooling was applied during hydrogel preparation. We suggest that the hydrophobic methacryloyl and acetyl residues disturb triple helix formation with increasing degree of modification, but additionally form hydrophobic structures, which facilitate chemical cross-linking.

Two-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography

2018 ◽  
Vol 103 (1) ◽  
pp. 137-142
Author(s):  
João Baptista N S Malta ◽  
H Kaz Soong ◽  
Bernardo Kaplan Moscovici ◽  
Mauro Campos
Keyword(s):  
Repeated Measures ◽  
Spherical Aberration ◽  
Randomised Clinical Trial ◽  
Cross Linking ◽  
Control Group ◽  
First Year ◽  
Control Groups ◽  
Mixed Regression ◽  
And Control

AimsTo evaluate the safety and efficacy of corneal cross-linking (CXL) followed by photorefractive keratectomy (PRK) for refractive correction in patients with bilateral asymmetric topography.MethodsForty-four patients (88 eyes) were enrolled in this prospective randomised clinical trial. CXL with subsequent PRK after 6 months was performed in one eye (study group), and PRK alone was performed in contralateral eyes (control group). Patients were followed for 24 months after PRK. Outcome measures investigated included visual acuity (VA), refraction, aberrometry, topography, pachymetry and endothelial cell count. Groups were compared with linear mixed regression and repeated measures logistic regression. Multiple comparison adjustment with the Holm procedure was performed.ResultsAt baseline, the logMAR VA (best spectacle corrected) in study and control groups was 0.12±0.13 (mean±SD) and 0.08D±0.14, respectively, and axial inferior–superior index (IS) (topographic IS) in study and control groups were 0.59D±0.31D and 0.58D±0.32D, respectively. After 24 months, a mean under correction of −0.50D was observed in both groups. Change from baseline in logMAR VA in study and control groups was 0.00D±0.08D and −0.02D±0.10D, respectively. Frequency of haze at 30 months in study and control group eyes was, respectively, 18.2% and 4.6% (p=0.05). There was no statistical difference between groups in spherical aberration and coma after adjustment for multiple comparisons.ConclusionsNon-simultaneous CXL followed by PRK may be performed safely, and refractive results over a 2-year follow-up are highly similar in virgin and previously cross-linked corneas. Despite using mitomycin C, corneal haze can be significantly higher in the first year after PRK in eyes pretreated with CXL.

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