Enhanced lubrication on tissue and biomaterial surfaces through peptide-mediated binding of hyaluronic acid

Abstract

Lubrication is key for the efficient function of devices and tissues with moving surfaces, such as articulating joints, ocular surfaces and the lungs. Indeed, lubrication dysfunction leads to increased friction and degeneration of these systems. Here, we present a polymer-peptide surface coating platform to non-covalently bind hyaluronic acid (HA), a natural lubricant in the body. Tissue surfaces treated with the HA-binding system exhibited higher lubricity values, and in vivo were able to retain HA in the articular joint and to bind ocular tissue surfaces. Biomaterials-mediated strategies that locally bind and concentrate HA could provide physical and biological benefits when used to treat tissue-lubricating dysfunction and to coat medical devices.

Figure 1. Tissue surface modification with an HABpep-polymer system

a, Schematic of cartilage surface modified with an HABpep designed to interact with and bind HA in surrounding fluid. b, An in vitro covalent strategy for coating the cartilage surface with MAL-PEG-NHS crosslinker, which on reaction with primary amines of the cartilage surface, creates an exposed thiol-reactive surface. Subsequently, a thiolated HABpep is reacted to the maleimide functionality. On exposure to an HA solution, the HA binds to the peptide-polymer coating on the cartilage surface. c, The PEG crosslinker reaction to articular cartilage was confirmed by ATR-FTIR spectroscopy that validated the presence of the ether-rich PEG coating with a large ether peak at ~1066 cm⁻¹. d, PEGylation was further verified by XPS atomic ratios. Compared to unmodified cartilage, coated samples had a carbon to oxygen ratio closer to 2, the ratio in PEG, and significantly lower nitrogen content. e, HA-binding functionality of the peptide-conjugated cartilage was visualized using a biotinylated HA. Biotinylated HA was synthesized and applied to unmodified cartilage and cartilage modified with the HA-binding polymer system. After thorough washing, the biotinylated HA was treated with streptavidin and horseradish peroxidase for visualization. The tissue surfaces treated with the HA-binding polymer coating stained darker than the untreated native cartilage.

Figure 2. Single-step strategy for application of HABpep-polymer system to a tissue surface and functional translation to a joint environment

a, Schematic of synthesis of a PEG bifunctional linker with one end group as an HABpep (GAHWQFNALTVR) and another end that either reacts with the amine groups or binds to a tissue surface via an extracellular matrix (ECM) binding peptide, such as collagen II binding peptide, WYRGRL. First, an HA-binding peptide is linked to a thiol-PEG-SGA linker (i) via amine-SGA conjugation reaction (ii) followed by the Michael-addition reaction of thiol functionality and vinyl dimethyl azlactone (iii). On a tissue surface, this amine-reactive azlactone functionality can be conjugated with either a peptide (iv) that non-covalently binds to ECM components (v), or covalently reacts with the amine functionality present in the tissue (vi). Both (iii) and (iv), with or without HA, can be applied on a tissue surface in a single-step application. b, HA-rhodamine together with HABpep-PEG-Col IIBpep polymer was injected into healthy rat knees in a single step and HA retention was monitored over time using an IVIS spectrum in vivo imager. HA-rhodamine (white arrows) via the HABpep polymer system was retained in rat knees even 72 h post-injection, compared to only 6 h without HABpep coating.

Figure 3. Cartilage surface-bound HA via the HABpep-polymer coating system in the absence of an exogenous lubricant can recapitulate the friction coefficients of high concentration HA lubricants

a, Representative schematic for the preparation and incubation of HABpep coated samples in test solution PBS. Lubrication properties of normal cartilage and severely damaged cartilage coated with the polymer-peptide system were tested in the presence of saline, and compared with uncoated surfaces in either saline or HA. Representative graphs of static friction and kinetic friction vs. pre-sliding time (s) for the normal cartilage sample (b & c) and severely damaged cartilage sample, OA stage 3–4 (d & e). (For statistical analyses: dashed lines represent cartilage samples (no HABpep modification) in PBS vs. HA bath and solid lines represent cartilage samples in PBS vs. cartilage samples coated with bound HA via HABpep in PBS.) Cartilage surface-bound HA via the HABpep-polymer coating system reduced friction values when lubricin is extracted from the tissue. Lubrication properties of normal cartilage and severely damaged cartilage (lubricin removed) coated with the polymer-peptide system was measured in PBS and compared to controls. Representative graphs of static friction and kinetic friction vs. pre-sliding time (s) for the normal cartilage sample (f & g) and severely damaged cartilage sample, OA stage 3–4 (h & i).

Figure 4. Ocular surface application of HABpep-polymer system

a, HABpep polymer system as an eye-drop solution can be used to retain HA on the eye surface. Collagen I-abundant eye tissues without epithelial layers, such as sclera, conjunctiva and cornea, act as anchors for the HABpep polymer system. b, Fluorescence images of HA retention on untreated and treated eye tissues: sclera, conjunctiva and cornea of untreated eye, i) to iii); treated with scrambled collagen I binding peptide (YFDEYSLSQS), iv) to vi); and treated with collagen I binding peptide, vii to ix). c, Contact lens modification with the HABpep polymer system was performed by the covalent reaction methodology. d, Fluorescence images for HA-rhodamine retention on modified contact lens showed relatively darker staining compared to the control.