Elsevier

Biomaterials

Volume 182, November 2018, Pages 234-244
Biomaterials

Hyperbaric oxygen-generating hydrogels

https://doi.org/10.1016/j.biomaterials.2018.08.032Get rights and content

Abstract

Oxygen plays a critical role as a substrate for metabolism and as a signaling molecule regulating cellular activities. In particular, hyperbaric oxygen has been demonstrated to facilitate wound healing processes, including cell proliferative activity, tissue growth, and vascular recruitment, via transient oxidative stress in surrounding tissues. In this study, we report hyperbaric oxygen-generating (HOG) hydrogels comprising thiolated gelatin (GtnSH) that can form hydrogel networks in situ via a calcium peroxide-mediated oxidative cross-linking reaction with oxygen generation. We demonstrate that the HOG hydrogels rapidly generate molecular oxygen up to hyperoxic levels and maintain hyperoxic levels for up to 12 days in vitro and 4 h in vivo. The HOG hydrogel enhances cell proliferative activities of human dermal fibroblasts and endothelial cells, which are closely related to wound healing and angiogenesis. Moreover, the HOG hydrogel promotes wound healing with enhanced tissue infiltration and vascular recruitment in vivo. The HOG hydrogels is a new type of oxygen-generating biomaterials that have great potential as advanced hydrogel materials for tissue regenerative medicine applications, including the treatment of wound and vascular disorders.

Introduction

Polymeric hydrogels have been widely utilized as therapeutic vehicles and implants in a broad range of biomedical applications, such as tissue regenerative medicine, wound management, and drug delivery [[1], [2], [3], [4]]. In particular, in situ cross-linkable hydrogels have attracted substantial attention as injectable matrices owing to their tunable properties, minimal invasiveness, and easy encapsulation of therapeutic agents [5]. Recently, many researchers have endeavored to develop dynamic hydrogel matrices that can stimulate the surrounding tissues through various physical, chemical and biological changes when injected into the body. Many studies have demonstrated that the stimuli have been implicated as crucial factors in facilitating wound healing process and tissue repair [[6], [7], [8]].

Oxygen plays a critical role as a metabolic substrate and as a signaling molecule regulating cellular activities, including cell survival, proliferation, migration, and differentiation [9,10]. Growing evidence has demonstrated that oxygen is a crucial factor in wound healing and tissue regeneration, including inflammation, proliferation, collagen synthesis and angiogenesis [[11], [12], [13]]. In particular, an excess supply of oxygen or higher than a normal partial pressure of oxygen (defined as hyperoxia) has been shown to facilitate wound healing process and tissue regeneration. The hyperoxic condition elevates cellular oxygen levels and to temporally increase intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels, which could promote wound healing processes such as proliferation and wound remodeling [[14], [15], [16]]. To date, various therapeutic approaches (e.g., hyperbaric oxygen therapy (HBOT) [17], oxygen carriers [[18], [19], [20]], and peroxide materials [[21], [22], [23]]) have been utilized as oxygen delivery systems for the treatment of wound and vascular disorders as well as tissue regenerative medicine applications. HBOT is currently in clinical use; however, it has limitations such as limited oxygen diffusion and pulmonary damage. Although oxygen carriers and peroxides have been widely used, surmounting some of their limitations, such as toxicity and burst release of oxygen, remains a challenge [24,25]. Although various oxygen-generating biomaterials have been developed, it is still challenging to develop advanced oxygen-delivering carriers that overcome these limitations.

Herein, we report a new type of oxygen-generating biomaterials, hyperbaric oxygen-generating (HOG) hydrogels, that can serve as a bioactive acellular matrix generating hyperbaric oxygen. We demonstrate that the HOG hydrogels rapidly generate oxygen at hyperbaric levels within the matrices and that oxygen was released from the hydrogels in a sustained manner. The HOG hydrogel enhances the proliferative activities of human dermal fibroblasts (HDFs) and endothelial cells (ECs) in vitro and promotes wound healing and repair with enhanced tissue ingrowth and neovascularization from the host tissues in vivo. We suggest that our HOG hydrogel is a promising oxygen-delivering carrier for the treatment of wound and vascular disorders as well as tissue regenerative medicine applications.

Section snippets

Materials

For polymer synthesis and hydrogel fabrication, gelatin (Gtn, type A from porcine skin, less than 300 bloom), 2-iminothiolane hydrochloride (Traut's reagent, TR), calcium peroxide (CaO2), anhydrous dimethyl sulfoxide (DMSO), deuterium oxide (D2O) and catalase (from bovine liver powder, 2000–5000 units/mg) were purchased from Sigma-Aldrich (Saint Louis, MO) and used as obtained without purification. Dulbecco's phosphate-buffered saline (DPBS) was supplied by Gibco (Grand Island, NY). Tris-HCl

Synthesis and characterization of GtnSH polymers

We first synthesized thiolated gelatin (GtnSH) polymers by conjugating Traut's reagent (TR) to a gelatin (Gtn) backbone (Fig. S1a) as previously reported [26]. We selected Gtn as the polymer backbone because of its various desirable properties, including biocompatibility, low cost, and easy modification, as well as its bioactivity [6,32,33]. The chemical structure of the GtnSH conjugates was characterized using proton nuclear magnetic resonance spectrometry (1H NMR). We found that the peak

Conclusion

This study developed a new class of biomaterial that can generate hyperbaric oxygen and act as an injectable and dynamic matrix. We designed gelatin-based HOG hydrogels that can form hydrogel networks in situ through a CaO2-mediated oxidative cross-linking reaction with oxygen generation. The HOG hydrogel has controllable physicochemical properties and oxygen generation by varying the CaO2 content. The HDFs and HUVECs treated with HOG hydrogels showed enhanced cell proliferative activities.

Author contributions

S.P. designed and performed research, analyzed data and wrote the paper; K.M.Park designed research, analyzed data and wrote the paper.

Disclosures

The authors declare that they have no conflict of interest.

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2018M3A9E2023257) and by Incheon National University Research Grant in 2015.

References (55)

  • M. Gholipourmalekabadi et al.

    Oxygen-generating biomaterials: a new, viable paradigm for tissue engineering?

    Trends Biotechnol.

    (2016)
  • Y.W. Kim et al.

    Oxidative stress in angiogenesis and vascular disease

    Blood

    (2014)
  • H. Meng et al.

    Hydrogen peroxide generation and biocompatibility of hydrogel-bound mussel adhesive moiety

    Acta Biomater.

    (2015)
  • C.J. Feeney et al.

    Vulnerability of glial cells to hydrogen peroxide in cultured hippocampal slices

    Brain Res.

    (2008)
  • B. Halliwell et al.

    Hydrogen peroxide in the human body

    FEBS Lett.

    (2000)
  • R. Munday

    Toxicity of thiols and disulphides: involvement of free-radical species

    Free Radic. Biol. Med.

    (1989)
  • Q. Zhang et al.

    Hyperbaric oxygen attenuates apoptosis and decreases inflammation in an ischemic wound model

    J. Invest. Dermatol.

    (2008)
  • M.C. Cushing et al.

    Hydrogel cell cultures

    Science

    (2007)
  • D. Seliktar

    Designing cell-compatible hydrogels for biomedical applications

    Science

    (2012)
  • K.M. Park et al.

    Hypoxia-inducible hydrogels

    Nat. Commun.

    (2014)
  • G.M. Sun et al.

    Dextran hydrogel scaffolds enhance angiogenic responses and promote complete skin regeneration during burn wound healing

    Proc. Natl. Acad. Sci. U. S. A.

    (2011)
  • Y. Lee et al.

    In situ forming and H2O2-Releasing hydrogels for treatment of drug-resistant bacterial infections

    ACS Appl. Mater. Interfaces

    (2017)
  • G.L. Semenza

    Oxygen sensing, homeostasis, and disease

    N. Engl. J. Med.

    (2011)
  • G.L. Semenza

    Life with oxygen

    Science

    (2007)
  • P.G. Rodriguez et al.

    The role of oxygen in wound healing: a review of the literature

    Dermatol. Surg.

    (2008)
  • V.G. Sunkari et al.

    Hyperbaric oxygen therapy activates hypoxia‐inducible factor 1 (HIF‐1), which contributes to improved wound healing in diabetic mice

    Wound Repair Regen.

    (2015)
  • K.L. Gorres et al.

    Prolyl 4-hydroxylase

    Crit. Rev. Biochem. Mol. Biol.

    (2010)
  • Cited by (69)

    • Preparation of lignin-based hydrogels, their properties and applications

      2023, International Journal of Biological Macromolecules
    • Photosynthetic microorganisms for the oxygenation of advanced 3D bioprinted tissues

      2023, Acta Biomaterialia
      Citation Excerpt :

      Hyperbaric oxygen therapy (HBO2) has been extensively explored for direct oxygen delivery. This approach has been used clinically and also in an attempt to increase cellular oxygen concentration within engineered structures for several applications, such as wound healing and bone grafting [16,37,45–47]. Uncontrolled oxygen delivery via HBO2 limits its use for tissue engineering purposes, together with the fact that does not allow for the self-renew of oxygen production and cannot be used to target a specific site [37].

    View all citing articles on Scopus
    View full text