טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKelmansky Regina
SubjectDevelopment of Neat Bioadhesives
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Assistant Professor Mizrahi Boaz
Full Thesis textFull thesis text - English Version


Abstract

Adhesive biomaterials are increasingly used to restore surface lacerations and abrasions, serving as a proper replacement for surgical sutures, and/or fill void spaces within tissues. Many commercially available bioadhesive materials (i.e. Fibrin sealant? and BioGlue?) adhere weakly to tissues due to their high water content and weak structural integrity. Others, like cyanoacrylates (e.g. Dermabond? and Vetbond?), provide desirable mechanical properties but suffer from poor biocompatibility attributable to their high water content.

The main goals of this work are: 1) to develop neat (without solvent) bioadhesives to achieve a system with improved mechanical properties in comparison to hydrogels, without compromising toxicity; 2) to substitute the polymer poly(ethylene glycol) (PEG) with complementary end groups which would react with each other; 3) to obtain adhesives by mixing the two substituted polymers which would lead to crosslinking of the matrix and to the formation of a sticky solid; 4) to characterize different compositions comprising of different volumetric ration of the two substituted polymers, chemically and mechanically; 5) to assess in-vitro and in-vivo toxicity of the adhesives.

We have developed two water-free, liquid four-armed low molecular weight (Mw = 2000 Da) PEG polymers modified with N-hydroxysuccinimide (NHS) or with amine (NH2) end groups. The modifications resulted in two complementary polymers PEG4-NHS in a substitution degree of 83%, and PEG4-NH2 in a substitution degree of 65%, respectively. Upon mixing, the mixture changes from liquids in room temperature to an elastic solid. A series of adhesives were prepared by mixing different volumes of the two substituted polymers. We showed that adhesion properties increased with the increase of the PEG4-NHS content, where the composition consists of 90% PEG4-NHS displayed the highest mechanical properties and adhesion strength. 

For cytoxicity, composition of 90% PEG4-NHS presented the lowest cytotoxicity (~50% survivors) on CCL1 cells. Toxicity increased with the decrease in PEG4-NHS content.  

Based on the mechanical strength, adhesion strength and cytotoxicity assay results, the composition of 90% PEG4-NHS was chosen for in-vivo test. This combination was injected to the subcutaneous space in the back of rats. After 4 and 14 days post injection, the tissues which were in closeness to the injected adhesive (skin and muscle) were harvested and sent for slide preparation and H&E staining, following histological analysis to estimate the level of inflammation caused by the injected substance.  Skin tissues which were in closeness to the injected adhesive did not show any inflammation factors, in contrast to the commercially available adhesive Dermabond? which caused moderate inflammation to skin. 

Muscle tissues in closeness to which the chosen adhesive composition was injected, exhibited mild sub-chronic inflammation 4 days post injection. On day 14 the observed inflammation was chronic remained mild, presenting more fibroblasts and collagen which are typical for healing process, similar to the obtained inflammation after 14 days from the injection of Dermabond?.

This material’s combination of desirable mechanical properties and high biocompatibility has potential in numerous biomedical applications such as wound sealing and bleeding control, controlled drug delivery tool and tissue reconstruction.