Lilija G. Damshkaln

Vascularization of wide pore agarose–gelatin cryogel scaffolds implanted subcutaneously in diabetic and non-diabetic mice

Polymeric scaffolds have been reported to promote angiogenesis, facilitating oxygen delivery; however, little is known about the effect of diabetes on the neo-vascularization of implanted polymeric scaffolds at subcutaneous (SC) sites. In this study we compare the effect of diabetes on scaffold vascularization following SC implantation into diabetic and non-diabetic mice. Wide pore agarose cryogel scaffolds with grafted gelatin were prepared by a two-step freezing procedure and subsequent thawing. The scaffolds were implanted subcutaneously into streptozoticin-induced diabetic mice and control, non-diabetic mice. The vascularization process was estimated using histological sections, in which endothelial cells were identified by Von Willebrand factor (vWF) and CD31 antigen staining and the pericyte layer was confirmed by alpha-smooth muscle actin (alpha-SMA) visualization. Comparative analysis showed a similar thickness of fibrous capsules around the vascularized scaffolds in both diabetic and non-diabetic animals. Intensive staining for alpha-SMA indicated the formation of mature blood vessels in the surrounding fibrous capsule and tissue invading the scaffold area. No statistically significant differences in capillary density and area occupied by blood vessels were found between diabetic and non-diabetic mice. In conclusion, the present study shows no adverse effects of diabetes on new blood vessel formation in SC implanted agarose cryogel scaffolds with grafted gelatin.

Study of cryostructuration of polymer systems. XVI. Freeze–thaw‐induced effects in the low concentration systems amylopectin–water

Studies of the freeze–thaw behavior of low-concentrated (0.01–0.25 g/dL) water solutions and dilute pastes (0.5–1.0 g/dL) of maize starch amylopectin showed that cryogenic treatment of these systems resulted in the formation of precipitated matter, whose yield and thermal characteristics (melting temperature and enthalpy) depended on the initial polymer concentration and conditions of freezing, frozen storage, and thawing. Research of the kinetic features of these cryoprecipitation events revealed at least two stages for this process: (i) a rapid stage, when the precipitation of virtually all of the dissolved polysaccharide occurred while the system was freezing, and (ii) a slower stage, the rate of which was mainly dependent on the thawing regimes or duration of the sample storage frozen at subzero temperatures. Cryoprecipitation phenomena were observed to be most extensive at temperatures 1–2° below the melting point of the frozen system.

Study of cryostructuration of polymer systems. XV. Freeze–Thaw‐induced formation of cryoprecipitate matter from low‐concentrated aqueous solutions of poly(vinyl alcohol)

Freeze-thaw treatment of low-concentrated (<C * ) aqueous solutions of poly(vinyl alcohol) (PVA) results in the formation of a cryoprecipitate fraction. It is shown that the efficiency of such a process (the yield of PVA cryoprecipitation) depends on the initial polymer concentration in the solution to be frozen and the conditions of a cryogenic influence. The key factor is defrostation dynamics: The slower the thawing rate, the higher the cryoprecipitation yield. The iodine-staining method is employed for the quantitative analysis of PVA concentrations in the solutions under study and the necessity of the use of reduced (0-2oC) temperatures throughout such a PVA quantification is demonstrated. Observation of the kinetics of the freeze-thaw-induced formation of cryoprecipitate matter reveals the extreme character of the temperature dependence of the efficacy of PVA macromolecule aggregation, the extreme point being situated in the vicinity of -2°C.

Study of cryostructuration of polymer systems. XVIII. Freeze–thaw influence on water‐solubilized artificial mixtures of amylopectin and amylose

The effects caused by cryogenic treatment (freezing-frozen storage-thawing) of 0.5-2.0 g/dL solutions of individual starch polysaccharides, namely, amylopectin (solvents: water or 0.35M NaCl aqueous solution) and amylose (solvent: 0.35M NaCl aqueous solution), and also of 0.5 g/dL solutions of their artificial mixtures with various amylopectin/amylose ratios were studied. Freezing of these systems at temperatures from -6 to -24°C for 18 h and subsequent thawing resulted in the formation of cryogelled or cryoprecipitated matter whose morphology and yield depended on the type of polysaccharide, initial polymer concentration, portion of each macromolecular component in the mixed systems, and conditions of cryogenic treatment. Comparison of the process efficiency in the mixed systems during the formation of precipitates (from storage at room temperature) and cryoprecipitates (as a result of cryogenic treatment) revealed the promoting effects of the freezing-thawing influence on polymer-polymer association and showed the presence of some synergism in the mutual interaction of these polysaccharides.

Cryostructuring of polymer systems. Wide pore poly(vinyl alcohol) cryogels prepared using a combination of liquid–liquid phase separation and cryotropic gel-formation processes

Novel, previously unknown, wide pore poly(vinyl alcohol) cryogels (PVACGs) have been prepared through a cryotropic gelation approach when water–PVA–gum arabic (GuAr) ternary liquid systems were used as feeds. The following set of conditions necessary for obtaining wide-porous, permeable for a water flow, and, simultaneously, mechanically strong enough PVACGs was established: the total concentration of gelling component—PVA (MW of 86 kDa) and non-gelling polymer—GuAr (MW of ∼650 kDa) should exceed ∼14 wt%, the GuAr : PVA ratio should be near 1 : 1 (w/w), and the feed pH should be within the range of ∼5 to 11. The phase diagrams for the water–PVA–GuAr ternary liquid systems at pH 5.3 and 10.0 have demonstrated that such “optimum” compositions are in the vicinity of the rectilinear diameters of the respective diagrams, and that the limit of GuAr solubility in the PVA-rich phase is small. In such cases this GuAr fraction strongly binds with PVA, especially under alkaline conditions, within the gel forming phase of heterophase PVACG. Light microscopy studies revealed the presence of at least three distinct kinds of pores in these cryogels. First, there are interconnected channel-like gross pores with a cross-section of 100–200 μm and larger which are the replicas of continuous GuAr-rich phase in the two-phase polymeric systems appearing due to the liquid–liquid phase separation in the ternary water–PVA–GuAr system. The second type are isolated roundish large pores ca. 10–70 μm in diameter being the replicas of the GuAr-rich phase dispersed as liquid droplets in the PVA-rich phase. In the third, there are smaller rounded pores ∼1 to 5 μm in diameter being the replicas of ice polycrystals. Such a sophisticated “poly-porous” morphology of the studied PVA cryogels is their unique feature distinguishing them from other known PVA cryogels.