ACIDITY FLUCTUATIONS INDUCE STRUCTURAL AND FUNCTIONAL CHANGES IN COLLAGEN HYDROGEL

The extracellular matrix (ECM) is a major part of animal tissues that provides structural support and regulates communication between cells. Due to diseases, injury and tissue abnormalities, the chemical conditions in the ECM may change. For example, in proximity to solid tumors the ECM acidity increases. Increased acidity affects cancer treatment via several phenomena. Low ECM pH decreases the cellular uptake of certain drugs and may affect drug transport towards the tumor. Furthermore, acidity-induced structural and mechanical changes in the ECM can affect cancer cell migration, influencing the potential for metastasis.

The ECM contains various macromolecules, the main one is type I collagen. Here, we use type I collagen hydrogel to model the stromal ECM and study the effect of acidity on ECM structure and function, focusing on conditions relevant to cancer. We control and manipulate the collagen pH and characterize its structure as a function of pH, utilizing methodology ranging from the molecular scale to the nano and micro scales. We use Fourier Transform Infrared spectroscopy (FTIR) to determine the collagen secondary structure and intermolecular crosslinking. We utilize cryo Scanning Electron Microscopy (cryo-SEM) imaging of collagen to characterize its structure as a function of pH while still hydrated. The use of cryo-SEM allows us to observe the collagen fibrils and characterize their thickness, length, and self-arrangement. To best explore the effects of pH on collagen structure, it is essential to study the system as closely as possible to the native form, as hydrogel drying can alter the organization of the fibrils and induce mechanical damage. Furthermore, we link collagen permeability to pH-induced structural changes by instilling fluorescently labeled particles and examine whether acidity-induced changes in collagen structure and permeability are reversible. A better understanding of the connection between the ECM pH, structure, and permeability may improve drug transport and drug uptake by cancer cells and decrease cancer cell migration from solid tumors.