pH-Responsive microgel dispersions for repairing damaged load-bearing soft tissue

An important challenge for colloid scientists is to design injectable dispersions that provide structural support for damaged soft tissue and enable regeneration of tissue over the longer term. In this article we highlight a new area of research that aims to produce pH-responsive microgel dispersions that restore the mechanical properties of damaged, load-bearing, soft tissue. Chronic back pain due to degeneration of the intervertebral disc (IVD) is a major health problem and is the primary potential application for the work discussed. pH-Responsive microgel dispersions contain cross-linked polymer particles that swell when the pH approaches the pK_a of the incorporated ionic co-monomer. The work considered here involves microgel particles containing MAA (methacrylic acid). The particles show pronounced pH-triggered swelling. The concentrated microgel dispersions change from a fluid to a gel at pH values greater than ca. 6.2, which is within the physiological pH range. The rheological properties are pH-dependent and can be adjusted using particle composition or concentration. Degenerated IVDs containing injected, gelled, microgel dispersions show improved mechanical properties. The disc height under biomechanically meaningful loads can be restored to values observed in non-degenerated IVDs. We also discuss the steps required to provide a minimally invasive injectable microgel system for restoring both the IVD mechanical properties and regenerating tissue in vivo. The approach discussed should also be suitable for other soft tissue types in the body.