Plastic Surgery Research Council
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Presenter: Xing Zhao, MD
Co-Authors: Omobono MA; Jang S; Randolph MA; Redmond RW; Gill TJ; Yaremchuk MJ
Massachusetts General Hospital and Harvard Medical School

INTRODUCTION: Photochemical crosslinking of biological scaffolds using visible light and riboflavin-5-phosphate adds mechanical strength as well as, more importantly, a much greater resistance to enzymatic degradation, allowing the shape and size of the hydrogel/chondrocytes implants to be retained both in vitro and vivo, which is a very promising manoeuvre for cartilage regeneration.

MATERIALS AND METHODS: Type-I bovine collagen, fibrin glue, and a 50:50 mixture of collagen and fibrin were combined with 250?M RF5P to create 4.5mm diameter cylindrical hydrogels. Constructs were either non-photocrosslinked (control) or exposed to 20J/cm2 of visible blue light. Articular chondrocytes were isolated from Yorkshire swine and seeded in hydrogel suspension at a density of 40x106 cells/mL. Cell-free gels were subjected to enzymatic degradation using 0.025%w/v type-II collagenase or 0.001%w/v papain enzyme and measured for the time of degradation, tdeg, on an incubated rocker. Cell-free and cell-seeded gels were also measured for bulk modulus, G , on a TA Instruments AR-G2 rheometer using a frequency sweep from 1-10 radians/second with constant 2% strain rate and an 1000 ?m gap under continuous, room-temperature oscillation. Cell-seeded hydrogels were loaded into devitalized swine hyaline cartilage rings for subcutaneous implantation in nude mice for 3 weeks before histological analyse.

RESULTS: Photocrosslinked protein hydrogels showed a trend towards higher tdeg values, and composite collagen/fibrin constructs showed a 4-fold increase resistance to collagenase degradation when photocrosslinked (Fig 1). There was no significant difference in G between photocrosslinked and control groups for single-material constructs, but a 18-fold increase in G was shown after photocrosslinking in cell-less composite constructs, as well as a 9-fold increase in cell-seeded constructs (Fig 2). The in vivo results showed various neocartilage matrix formation and integration status(Fig 3).

DISCUSSION: Photocrosslinking of hydrogels increases mechanical properties and its resistance to biodegradation, and permits neocartilage formation.

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