Horseradish peroxidase-catalysedin situ-forming hydrogels for tissue-engineering applications

Abstract

In situ-forming hydrogels are an attractive class of implantable biomaterials that are used for biomedical applications. These injectable hydrogels are versatile and provide a convenient platform for delivering cells and drugs via minimally invasive surgery. Although several crosslinking methods for preparing in situ forming hydrogels have been developed over the past two decades, most hydrogels are not sufficiently versatile for use in a wide variety of tissue-engineering applications. In recent years, enzyme-catalysed crosslinking approaches have been emerged as a new approach for developing in situ-forming hydrogels. In particular, the horseradish peroxidase (HRP)-catalysed crosslinking approach has received increasing interest, due to its highly improved and tunable capacity to obtain hydrogels with desirable properties. The HRP-catalysed crosslinking reaction immediately occurs upon mixing phenol-rich polymers with HRP and hydrogen peroxide (H2O2) in aqueous media. Based on this unique gel-forming feature, recent studies have shown that various properties of formed hydrogels, such as gelation time, stiffness and degradation rate, can be easily manipulated by varying the concentrations of HRP and H2O2. In this review, we outline the versatile properties of HRP-catalysed in situ-forming hydrogels, with a brief introduction to the crosslinking mechanisms involved. In addition, the recent biomedical applications of HRP-catalysed in situ-forming hydrogels for tissue regeneration are described.

Enhanced tissue adhesiveness of injectable gelatin hydrogels through dual catalytic activity of horseradish peroxidase

“…[10][11][12][13][14] Under the catalysis of HRP, phenol moieties of precursor polymers were oxidized by H 2 O 2 to form CAC crosslinks at ortho positions of benzyl rings or CAO between ortho-C and oxygen atoms of hydroxyl groups to form hydrogels. [15] The chitosan-PEG hydrogels achieved the high adhesive strength and the effective hemostatic property, [10] but their cell-inert behavior limited them in extending to cell delivery applications. To overcome this limitation, the hydroxyphenyl propionic acid-conjugated gelatin (GH) hydrogels containing the inherent RGD peptide being favorable to cells were developed.…”

Photocrosslinked tyramine-substituted hyaluronate hydrogels with tunable mechanical properties improve immediate tissue-hydrogel interfacial strength in articular cartilage

“…The mechanism presumably follows phenolic radical dimerization as in the HRP/H 2 O 2 system, where more stable ring residing phenoxy radicals dimerize to form the C-C bonded dimer and a ring residing radical dimerizes with an oxygen residing radical to form the less common C-O dimer. [36, 37, 42, 53–55] While it has been suggested that other photosensitizers, that operate through a similar mechanism, can be used to photodynamically generate dityramine only riboflavin is considered in this work. [53]…”

“…[41] TA-HA hydrogels are generally formed through reaction with hydrogen peroxide and horseradish peroxidase (HRP). [36, 39, 42] The mechanical properties of TA‐HA hydrogels fabricated through this enzymatic route are tunable by changing the concentrations of HRP and hydrogen peroxide. [35] While use of HRP/H 2 O 2 is the most common method used to crosslink TA in TA-substituted polymers, others have reported TA-hydrogel fabrication using light and tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate, [Ru(bpy) 3 ]Cl 2 .…”

“…[32, 33, 43, 44] Phenols, including TA, have been incorporated into other polymeric materials, such as dextran and chitosan, and gelled using HRP/H 2 O 2 in studies for tissue engineering applications. [42, 45–51]…”

Colloidally stable polypeptide‐based nanogel: Study of enzyme‐mediated nanogelation in inverse miniemulsion

“…HRP catalyzes the decomposition of hydrogen peroxide (H 2 O 2 ) in the presence of a reducing phenol moiety on a polymer precursor backbone, which is converted to a radical product. One equivalent of H 2 O 2 induces the formation of two aromatic radicals, which are readily coupled by a covalent bond to form a crosslinked structure under mild conditions . To ensure effective hydrogel formation, the most suitable molar ratio between H 2 O 2 and tyramine (TYR), as the phenol moiety, was found to be 0.5 …”