ENZYME-MEDIATED PROTEOLYSIS OF FIBROUS BIOPOLYMERS - DISSOLUTION FRONT MOVEMENT IN FIBRIN OR COLLAGEN UNDER CONDITIONS OF DIFFUSIVE OR CONVECTIVE-TRANSPORT

A numerical model based on the convective-diffusive transport of react ing and adsorbing proteolytic enzymes within erodible fibrous biopolym ers was used to predict lysis fronts moving across biogels such as fib rin or collagen. The fiber structure and the transport properties of s olutes in fibrin (or collagen) were related to the local extent of dis solution within the dissolving structure. An accounting for solubiliza tion of adsorbed species into solution from the eroding fiber phase pr ovided for complete conservation of mass in reacting systems containin g over 10 species. At conditions of fibrinolysis typical of clinical s ituations, the model accurately predicted the dynamic rate of lysis fr ont movement for plasmin, urokinase, and tissue plasminogen activator (tPA)-mediated lysis of fibrin gels measured in vitro. However, under conditions of extremely fast fibrinolysis using high enzyme concentrat ions, fibrinolytic fronts moved very rapidly (>0.1 mm/mm)-faster than predicted for diffusion-limited reactions-at nearly constant velocity for over 2 h, indicating non-Fickian behavior. This was due to proteol ysis-mediated retraction of dissolving fibrin fibers that resulted in fiber convection and front-sharpening within 3 mu m of the reaction fr ont, as observed by digitally enhanced microscopy. In comparing the mo del to fibrinolysis measurements using human lys(77)-plasmin, the aver age first order rate constant for non-crosslinked fibrin bond cleavage by fibrin-bound plasmin was calculated to be 5 s(-1), assuming that 1 0 cleavages per fibrin monomer were required to solubilize each monome r. The model accurately predicted lysis front movement using pressure- driven permeation of plasmin or urokinase into fibrin as well as liter ature data obtained under well-mixed conditions for tPA-mediated fibri nolysis. This numerical formulation provides predictive capability for optimization of proteolytic systems which include thrombolytic therap y, wound healing, controlled drug release, and tissue engineering appl ications. (C) 1995 John Wiley & Sons, Inc.