http://www.mtdna.or.kr/neowiz/board/up_files/files_17/Chitin_Chitosan_polymers_chemistrySolubilityFiberFormation.pdf

Chitin and chitosan polymers: Chemistry, solubility and fiber formation

This invention related to a tissue-adhesive sheet comprising a homogeneous, preformed and cross-linked matrix formed from one or more polymers, and having at least one surface that, in use, is exposed, at least one of said one or more polymers being a synthetic polymer and having appendant functional groups of a first form, cross-linking of said matrix being via a proportion of said functional groups of the first form, and the remainder of said functional groups of the first form being free. The sheet is particularly useful as a tissue adhesive and sealant, and is intended for topical application to internal and external surfaces of the body for therapeutic reasons. The invention further relates to sheets comprising a scaffold material, three-dimensional articles formed from similar material to that of the sheet and to implantable medical devices coated with such material.

Tissue-adhesive materials

Adhesion of polymers

Soft materials are materials with a low shear modulus relative to their bulk modulus and where elastic restoring forces are mainly of entropic origin. A sparse population of strong bonds connects molecules together and prevents macroscopic flow. In this review we discuss the current state of the art on how these soft materials break and detach from solid surfaces. We focus on how stresses and strains are localized near the fracture plane and how elastic energy can flow from the bulk of the material to the crack tip. Adhesion of pressure-sensitive-adhesives, fracture of gels and rubbers are specifically addressed and the key concepts are pointed out. We define the important length scales in the problem and in particular the elasto-adhesive length Γ/E where Γ is the fracture energy and E is the elastic modulus, and how the ratio between sample size and Γ/E controls the fracture mechanisms. Theoretical concepts bridging solid mechanics and polymer physics are rationalized and illustrated by micromechanical experiments and mechanisms of fracture are described in detail. Open questions and emerging concepts are discussed at the end of the review.

/pdf/fracture-and-adhesion-of-soft-materials-a-review-4ydkznlufz.pdf

Fracture and adhesion of soft materials: a review.

Melt blending of a variety of conventional isotropic polymers (both crystalline and amorphous) has shown that considerable reinforcement is obtained from the inclusion of thermotropic liquid crystalline polymers (LCP). When the LCP is a minor component it forms highly elongated domains parallel to the flow direction. The intrinsically high strength and stiffness of the LCP improve the mechanical properties of the resulting blend. This approach is distinguished from the common practice of filling polymers with chopped glass and carbon fibers by the fact that the reinforcing component comes into existence during processing (molding or extrusion). Many of the problems associated with fibrous fillers are avoided. For example, viscosity of the “in situ composite” is actually lower than that of the base polymer and wear on the compounding and processing equipment is reduced.

In situ composites: blends of isotropic polymers and thermotropic liquid crystalline polymers

A study has been made of the viscous properties of poly(para-benzamide) (PBA) solutions in dimethyl acetamide, which undergo a transition from an isotopic to an anisotropic (liquid-crystal) state at a definite concentration C*. The polymer solutions behave in many respects (as regards the concentration and temperature dependence of viscosity, etc.) like solutions of low molecular weight compounds forming a liquid crystal phase, although the transitions are less pronounced in the polymer solutions owing to their polydispersity. It is shown that the viscometric method, being extremely sensitive to C*, is convenient for determining phase diagrams of anisotropic polymer solutions. The values of C* as related to the molecular weight of PBA have been determined, and a general criterion for transition from isotropic to anisotropic solutions established; the latter has the form (CM)* ≈ 1.3 × 105 at 20°C. This criterion is in line with the condition for the formation of the liquid-crystal structure in a dispersion of rodlike particles as proposed by Flory.

Generalized concentration dependences of viscosity have been plotted by reducing concentration to C* and viscosity, to the maximum viscosity at the phase transition point. In investigating the flow properties of PBA solutions we revealed the existence of a yield point in the range of low shear stresses, and an intersection of the flow curves of solutions of different concentration at high shear stresses, which excludes a generalized representation of the flow curves in reduced ordinary-type coordinates.

Rheological properties of anisotropic poly(para‐benzamide) solutions

An adhesive composition is provided that contains both a hydrophobic phase and a hydrophilic phase, wherin the hydrophobic phase is composed of a crosslinked hydrophobic polymer composition and the hydrophilic phase is a water-absorbent blend of a hydrophilic polymer and a complementary oligomer capable of crosslinking the hydrophilic polymer through hydrogen bonding, ionic bonding, and/or covalent bonding. The composition is useful as a bioadhesive, for affixing drug delivery systems, wound dressings, bandages, cushions, or the like to a body surface such as skin or mucosal tissue.

Two-phase, water-absorbent bioadhesive composition

We studied the impact of anionic polysaccharide (κ-carrageenan) as a co-gelator of gelatin at different physico-chemical and by varying the κ-carrageenan/gelatin ratio. It has been shown that increasing κ-carrageenan concentration accelerates the gelation and leads to significant increase in the viscoelastic parameters of the modified gels. Non-linearity of viscoelastic properties becomes evident in much lower deformations in comparison with those of native gelatin gels. The strength of gels characterized by the yield stress also increases along with κ-carrageenan concentration. The deformation (but not flow) of gels happens along the rupture surfaces appearing at the apparent yield stress. The melting temperature increases until 45 °C for high κ-carrageenan/gelatin ratio. The suggested explanation of the observed changes in properties of modified gels relates these effects with formation of complexes of gelatin and polysaccharide. FT-IR spectroscopy data show that (bio)polyelectrolyte complex formation is due to electrostatic interaction between positively charged groups in gelatin and negatively charged sulfate groups in κ-carrageenan that leads to conformation changes of gelatin macromolecules. Micrographs (scanning electron microscopy) show that addition of even a small quantity of polysaccharide leads to radical changes in supramolecular structure of modified gels.

The rheology of gelatin hydrogels modified by κ-carrageenan

A water-insoluble, hydrophilic adhesive polymer is provided, wherein the polymer is prepared by polymerization of a composition consisting of a hydrophilic monomer and a dual-function monomer that both (a) undergoes polymerization with the hydrophilic monomer and (b) provides crosslinks in the polymer product. Water-insoluble, hydrophilic adhesive polymer blends are also provided, which are free of covalent crosslinks. The polymers are useful in hydrogel and bioadhesive compositions, which find utility as drug delivery systems (e.g., topical, transdermal, transmucosal, iontophoretic), medical skin coverings, wound dressings and wound healings products, biomedical electrodes, and tooth whitening stripes.

Valery G. Kulichikhin

Papers

Rheological properties of anisotropic poly(para‐benzamide) solutions

Two-phase, water-absorbent bioadhesive composition

The rheology of gelatin hydrogels modified by κ-carrageenan

Covalent and non-covalent crosslinking of hydrophilic polymers and adhesive compositions prepared therewith

Asphaltenes in heavy crude oil: Designation, precipitation, solutions, and effects on viscosity