title: Injectable gelatin derivative hydrogels with sustained vascular endothelial growth factor release for induced angiogenesis.
abstract: Injectable biomaterials are attractive for soft tissue regeneration because they are handled in a minimally invasive manner and can easily adapt to complex defects. However, inadequate vascularization of the injectable constructs has long been a barrier, leading to necrosis or volume reduction after implantation. In this work, we developed a three-step process to synthesize injectable gelatin-derived hydrogels that are capable of controlling growth factor delivery to induce angiogenesis. In our approach, tyramine was first introduced into gelatin chains to provide enzymatic crosslinking points for gel formation after injection. Next, heparin, a polysaccharide with binding domains to many growth factors, was covalently linked to the tyramine-modified gelatin. Finally, vascular endothelial growth factor (VEGF) was incorporated into the gelatin derivative by binding with the heparin in the gelatin derivative, and an injectable gel with controlled VEGF release was formed by an enzymatic catalytic reaction with hydrogen peroxide (H2O2) and horseradish peroxidase (HRP). The gelation time, mechanical properties and degradation of the gel was readily tailored by the gelatin concentration and the ratio of H2O2/HRP. Binding VEGF to heparin stabilizes this growth factor, protects it from denaturation and proteolytic degradation and subsequently prolongs the sustained release. An in vitro release study and bioactivity assay indicated that the VEGF was released in a sustained manner with high bioactivity for over 3 weeks. Furthermore, a chicken chorioallantoic membrane (CAM) assay and animal experiments were performed to evaluate in vivo bioactivity of the VEGF released from the hydrogels. After 5 days of incubation on CAM, the number of blood vessels surrounding the heparin-modified hydrogels was increased by 2.4-fold compared with that of the control group. Deeper and denser cell infiltration and angiogenesis in the heparin-modified gelatin/VEGF gels were observed compared to the controls after being subcutaneously injected in the dorsal side of the mice for 2 weeks. Interestingly, even without the incorporation of VEGF, the heparin-modified gelatin derivative still had the capability to induce angiogenesis to a certain degree. Our results suggest that the gelatin derivative/VEGF is an excellent injectable delivery system for induced angiogenesis of soft tissue regeneration.
authors.affiliation: Department of Plastic and Aesthetic Surgery, Southwest Hospital, Third Military Medical University, Chongqing 400038, People's Republic of China; Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, TX 75246, USA.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, TX 75246, USA; Department of Operative Dentistry & Endodontics, State Key Laboratory of Military Stomatology, School of Stomatology, Fourth Military Medical University, Xi'an 710032, People's Republic of China.
authors.forename: Tiejun
authors.initials: T
authors.lastname: Qu
authors.affiliation: Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, TX 75246, USA; West China Hospital, West China School of Medicine, Sichuan University, Chengdu 610041, People's Republic of China.
authors.forename: Chen
authors.initials: C
authors.lastname: Ding
authors.affiliation: Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, TX 75246, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Ma
authors.affiliation: Department of Pathology, School of Stomatology, Jilin University, Changchun 130021, People's Republic of China.
authors.forename: Hongchen
authors.initials: H
authors.lastname: Sun
authors.affiliation: Department of Plastic and Aesthetic Surgery, Southwest Hospital, Third Military Medical University, Chongqing 400038, People's Republic of China. Electronic address: sli1953@yahoo.com.
authors.forename: Shirong
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, Dallas, TX 75246, USA. Electronic address: xliu@bcd.tamhsc.edu.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Liu
mesh_terms: D000818:Animals; D000925:Anticoagulants / Q000737:chemistry / Q000494:pharmacology; D002642:Chick Embryo; D003692:Delayed-Action Preparations / Q000737:chemistry / Q000494:pharmacology; D005780:Gelatin / Q000737:chemistry / Q000494:pharmacology; D006493:Heparin / Q000737:chemistry / Q000494:pharmacology; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D020100:Hydrogels / Q000737:chemistry / Q000494:pharmacology; D056965:Injections, Intraocular; D051379:Mice; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D042461:Vascular Endothelial Growth Factor A / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000925:Anticoagulants; D003692:Delayed-Action Preparations; D020100:Hydrogels; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D005780:Gelatin; D006493:Heparin
keywords: Angiogenesis; Gelatin; Heparin; Injectable hydrogel; VEGF