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G.T. Timberlake, A.L. Yousef, R.A. Moses, R.S. Givens; Bonding Cornea to Cornea and Cornea to Glass with Light–Activated, Collagen–Crosslinking Dendrimers . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3929.
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© ARVO (1962-2015); The Authors (2016-present)
To synthesize light–activated, poly(amidoamine) (PAMAM) dendrimer reagents to bond cornea to cornea and cornea to transparent solids such as glass and plastic. PAMAM dendrimers are macromolecules that branch outward from a central core, each branch terminating in a primary amine (NH2) group. They exhibit very low toxicity and are non–immunogenic when NH2 groups are replaced with anionic or neutral groups.
A diazopyruvoyl–derivatized Generation 1 PAMAM dendrimer (DiazopyruvoylAmido Polyaminoamine, DAP) was synthesized by replacing the 8 terminal NH2 groups of the dendrimer with light–activatable diazopyruvoyl groups. Upon photolysis, the diazopyruvoyl groups are transformed into ketenes that crosslink primary lysyl and hydroxylysyl amines in Type I collagen and bond to hydroxyl groups on glass surfaces. For bonding, bovine corneal strips (5 X 15 mm) were lyophilized to produce a range of dehydrations. Three µL of 0.2 M DAP in H2O was placed on a corneal strip and a second strip (cornea or 5 X 15 mm glass) was placed on top. The two samples were then sandwiched between quartz slides and exposed to 333 J of 320–500 nm light. Tensile strength of bonded samples was measured with a tensiometer.
Bond tensile strengths were greatest for dehydrated tissue and decreased with increasing tissue hydration. Cornea–to–cornea bonds (n=17) were as high as 92.3 N/cm2, for dehydrated tissue, but only 0.7 – 3.3 N/cm2 with hydrated tissue. Cornea–to glass bonds (n=17) were as high as 36.8 N/cm2 for dehydrated tissue, but 0.0 – 5.1 N/cm2 with hydrated tissue. In control tests, no bonds formed without irradiation or without DAP.
Very strong cornea–to–cornea and cornea–to–glass bonds formed with dehydrated tissue, but much weaker bonds formed with hydrated tissue. This is understandable considering Fratzl & Daxer’s (Biophys J 64;1993) finding that the distance between corneal collagen fibrils decreases with dehydration. Fibrils nearly touch when tissue is fully dehydrated. Consequently, the relatively small (2 nm) DAP molecule spans the distance between fibrils, crosslinking them. We propose that hydrated cornea can be bonded by increasing the crosslinking distance of DAP with larger, longer, higher generation dendrimers and by using co–monomers such as polyethylene glycol diamines. These light–activated dendrimers could replace or augment sutures in corneal wound closure and enable firm attachment of corneal appliances such as keratoprostheses.
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