Poly(vinyl alcohol) (PVA) is a water‐soluble synthetic polymer with excellent film‐forming, emulsifying, and adhesive properties. The aim of this study is to design a simple process for PVA cross‐linking with sodium trimetaphosphate to form membrane devices suitable for biomedical applications. This procedure requires no organic solvent, nor melting process to obtain films with high mechanical strength. Fabrication of a small diameter tube from a PVA film is easy with a single wrapping step around a Teflon rod. Dynamic mechanical analysis demonstrated that, upon removal of the applied stress, the PVA film with a Young's modulus of 2 × 105 kPa returns to its original size and shape. The wall thickness of PVA tubes is 344 ± 13 µm (n = 12), which is close to the wall thickness of a human artery (350–710 µm). Suture retention of a PVA tube is excellent (140 ± 11 g), close to that of human vessels. The burst pressure of PVA tubes is found to be 507 ± 25 mm Hg, more than three times higher than the human healthy systolic arterial pressure. Under arterial pressure, there was no leakage even after needle puncture, contrary to clinical vascular expanded polytetrafluoroethylene prostheses. Finally, PVA tubes of 2 mm in diameter are used to replace a segment of an infrarenal aorta in rats. For at least one week, no mechanical nor thrombotic complications are noticed even in the absence of anticoagulant or antiplatelet treatment. Graft patency is also evidenced with non‐invasive imaging techniques. As a conclusion, this novel cross‐linking method confers to poly(vinyl alcohol) particular mechanical properties such as compliance, elasticity and resistance to mechanical stress, compatible with the circulatory blood flow.
To test the effect of the matrix polymer on diffusion, we have measured the self-diffusion
coefficients of water and poly(ethylene glycol) of a molecular weight of 600 (PEG-600) in aqueous systems
of selected polymers using the pulsed-gradient spin-echo NMR technique. The polymers used in this study
include poly(vinyl alcohol) (PVA), hydroxypropyl methyl cellulose (HPMC), poly(N,N-diethylacrylamide)
(PNNDEA), and poly(N-isopropylacrylamide) (PNIPA). The polymer concentrations varied from 0 to 0.38
g/mL. The effect of the polymer network on the self-diffusion coefficients of the solvent (water) and a
solute (PEG-600) was investigated by analyzing the diffusion data with the use of the free volume model
of Yasuda et al. [Yasuda, H.; Lamaze, C. E.; Ikenberry, L. D. Makromol. Chem.
1968, 118, 19], the diffusion
model proposed by Phillies [Phillies, G. D. J. Macromolecules
1986, 19, 2367], and the model of Petit et
al. [Petit, J.-M.; Roux, B.; Zhu, X. X.; Macdonald, P. M. Macromolecules
1996, 29, 6031]. The results
obtained with PVA, HPMC, PNNDEA, and PNIPA are used to evaluate the applicability of these models
in polymer−water−solute ternary systems. The physical significance of the parameters used in the models
is discussed.
Pulsed-field gradient NMR spectroscopy was used to study the diffusion of three different
poly(propyleneimine) dendrimers with hydrophilic triethylenoxy methyl ether terminal groups (generations
2, 4, and 5) in poly(vinyl alcohol) aqueous solutions and gels. The effects of the diffusant size, polymer
concentration (from 0 to 0.26 g/mL), and temperature on the self-diffusion coefficients have been studied,
and the model of Petit et al. [Macromolecules
1996, 29, 6031] was used to fit the experimental data. The
Stokes−Einstein hard-sphere radii were also calculated in the zero concentration limit and were compared
with those of the linear poly(ethylene glycol)s under the same conditions. The proton NMR relaxation
times (T
1 and T
2) were measured to study the mobility of the dendrimer core part and terminal group as
a function of the dendrimer size.
Alginate is widely used for cell microencapsulation and transplantation. There is a lack of standardization of alginate purity and composition. In a previous study, we compared different alginate purification methods and concluded that polyphenol and endotoxin contaminants were eliminated efficiently but residual protein contaminants persisted with all of the methods under evaluation. The objective of this study was to test the hypothesis that residual proteins play a role in the immunogenicity of certain alginate preparations. Using preparative size exclusion chromatography (SEC) and a large scale purification protocol that was derived from the findings obtained with SEC, we substantially decreased the protein content of alginate preparations. When implanted into mouse peritoneum, barium alginate beads made of alginates that were purified using SEC or the derived large scale protocol induced significantly less pericapsular cell adhesion than those made with control alginates. In conclusions, these results suggest that removing residual protein contamination may decrease the immunogenicity of certain alginate preparations. The measurement of proteins could be used as a screening method for evaluating alginate preparations.
The penetration of water into cross-linked high amylose starch tablets was studied at different temperatures by nuclear magnetic resonance (NMR) imaging, which follows the changes occurring at the surface and inside the starch tablets during swelling. It was found that the swelling was anisotropic, whereas water diffusion was almost isotropic. The water proton image profiles at the initial stage of water penetration were used to calculate the initial diffusion coefficient. The swelling and water concentration gradients in this controlled release system show significant temperature dependence. Diffusion behavior changed from Fickian to Case II diffusion with increasing temperature. The observed phenomena are attributed to the gelatinization of starch and the pseudo-cross-linking effect of double helix formation.
Pharmaceutical tablets made of modified high-amylose starch have a hydrophilic polymer matrix into which water can penetrate with time to form a hydrogel. Nuclear magnetic resonance imaging was used to study the water penetration and the swelling of the matrix of these tablets. The tablets immersed in water were imaged at different time intervals on a 300 MHz NMR spectrometer. Radial images show clearly the swelling of the tablets and the water concentration profile. The rate constants for water diffusion and the tablet swelling were extracted from the experimental data. The water diffusion process was found to follow case II kinetics at 25 degrees C. NMR imaging also provided spin density profiles of the water penetrating inside the tablets.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.