Browsing by Subject "Swelling"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Publication
    Open Access
    Effect of chemical crosslinking on the swelling and shrinking properties of thermal and pH-responsive Chitosan hydrogels
    (Wiley, 2003-10-07) Heras, Ángeles; Aranaz, Inmaculada; Galed, Gemma; Fernández Valle, María E.; Argüelles Monal, Waldo; Goycoolea Valencia, Francisco Martín; Biología Celular e Histología
    The ability to form a gel through the physical or chemical crosslinking of chitosan has been well documented. In an attempt to mimic biological systems, thermal and pH-sensitive chitosan cylindrical hydrogels were produced by a combination of physical and chemical crosslinking processes. To this end, chitosan hydrogels prepared from alkali chitin were molded in cylinders and, once washed, were further crosslinked with glutaraldehyde at stoichiometric ratios, R (-[–CH=O]/[–NH2]), of 1.61 and 3.22 x10^-2. Variation in swelling as a result of stepwise changes in temperature between 40 and 2 °C at pH values of 7.0, 7.6, and 8.0 revealed that the system responds in markedly different manners dependent upon the pH. At pH 7.0, cooling from 40 to 2 °C results in contraction of the gel network structure. While raising the temperature from 2 to 40 °C leads to a rapid swelling response (i.e., ca. a twofold increase in the amount of solvent uptake). Subsequent cooling to 2 °C is accompanied by a new contraction cycle. At pH 7.6 the temperature dependence of the swelling–contraction behavior is exactly the opposite of that observed at pH 7.0.Very similar trends were observed for the gels at both degrees of crosslinking. The swelling–shrinking behavior observed in gels of pH 7.6, is similar in kind to that of uncrosslinked gels and is interpreted in terms of a lower critical solution temperature (LCST) volume phase transition, driven by hydrophobic association, presumably involving residual acetyl groups in the chitin. The results at pH 7.0 suggest that the slight ionization of the –NH3+ groups leads to the destruction of the hydrophobic hydration thus effectively reversing the negative thermal shrinking.
  • Thumbnail Image
    Publication
    Open Access
    pH and temperature – sensitive chitosan hydrogels: swelling and magnetic resonance imaging (MRI) studies
    (Wiley, 2011-02-25) Goycoolea Valencia, Francisco Martín; Fernández Valle, María E.; Aranaz, Inmaculada; Heras, Ángeles; Biología Celular e Histología; Facultades de la UMU::Facultad de Biología
    MRI and swelling experiments are used to probe the state of water and infer the microstructure of chitosan hydrogels. SEM reveals a porous open scaffold-type structure for hydrogels that were equilibrated at 2 °C before freezing as compared to those equilibrated at 37 °C. ADC MRI measurements reveal an anisotropy in the microstructure of these gels. T1 relaxation MRI values were larger as the pH increased from 7.6 to 12.0, the result of a lower rate of exchange between protons of the hydration sphere of the polymer and bulk water. The thermosensitive and pH-sensitive properties of these hydrogels can be utilized in the development of innovative materials for biotechnological and biomedical applications, including criobiocatalysis and bioremediation as well as in programmed drug delivery.
  • Thumbnail Image
    Publication
    Open Access
    Ultrastructure and 3D transmission electron tomography of collagen fibrils and proteoglycans of swollen human corneal stroma
    (Universidad de Murcia. Departamento de Biología Celular e Histología, 2019) Akhtar, S.; Petrovski, G.; Albert, R.; Alkanaan, A.; Kirat, O.; Khan, A.D.; Almubrad, T.
    Background. The transparency of the cornea is regulated by the unique organization of collagen fibrils (CFs) which is maintained by proteoglycans (PGs). The interlacing of CF lamellae in the anterior stroma provides the biomechanical properties of the cornea. Objective. To investigate the alterations of CFs and PGs in the swollen cornea, with special reference to the anterior stroma by using electron microscopy and 3D ultrastructural tomography. Method. Nine healthy normal scleral corneal rings (age from 40 to 65 years) were hydrated individually in deionised water to induce swelling in the cornea. Three of them were hydrated for 2hr whereas the other three were hydrated for 48hr. The remaining three scleral normal corneal rings were used as a control.The corneas were processed for electron microscopy (E M) to study the CFs and PGs. Ultrathin sections were observed using transmission electron microscopy (JOEL 1400) and digital images of CFs, PGs and lamellae were captured using a bottom mounted Quemesa camera and iTEM Soft Imaging System. The software program ‘Composerx64, version 3.4.2.0’ was used to construct individual 3D images from 120 digital images taken from -60 to +60 degree angles. Results. The 3D tomography showed the degeneration of microfibrils within the CFs of the swollen cornea. The CF diameter was significantly reduced and the interfibrillar spacing significantly increased in both the 2hr and 48hr hydrated corneas compared to the normal cornea. Within the hydrated corneas, the CF diameter was smaller and the interfibrillar spacing was increased in the middle and posterior stroma compared to the anterior stroma. The PG area in both the 2hr and the 48hr hydrated cornea was reduced in the anterior stroma, whereas it was increased in middle and posterior stroma compared to the normal cornea. The density of the PGs in both the 2hr and the 48hr samples, was reduced compared to the density of PGs in the normal cornea. Conclusion. The CFs, PGs and lamellae had degenerated, caused by swelling. 3D imaging demonstrated that the impairment of the microfibrils and PGs within the CF, is caused by the excessive hydration or swelling in the anterior as well as in the middle and posterior stroma. The lamellae of the anterior stroma which provides the biomechanical strength in the normal cornea, had degenerated in the swollen corneas due to the presence of the damaged CFs and PGs.