title: Optimization of an injectable tendon hydrogel: the effects of platelet-rich plasma and adipose-derived stem cells on tendon healing in vivo.
abstract: BACKGROUND
  Acute and chronic tendon injuries would benefit from stronger and more expeditious healing. We hypothesize that supplementation of a biocompatible tendon hydrogel with platelet-rich plasma (PRP) and adipose-derived stem cells (ASCs) would augment the tendon healing process.
  
  
  METHODS
  Using 55 Wistar rats, a full-thickness defect was created within the midsubstance of each Achilles tendon with the addition of one of five experimental conditions: (i) saline control (50-μL), (ii) tendon hydrogel (50-μL), (iii) tendon hydrogel (45-μL)+PRP (5-μL), (iv) tendon hydrogel (45-μL)+2×10(6)-ASCs/mL in phosphate buffered saline (5-μL), and (v) tendon hydrogel (45-μL)+2×10(6)-ASCs/mL in PRP (5-μL). Hydrogel was developed from decellularized, human cadaveric tendons. Fresh rat PRP was obtained per Amable et al.'s technique, and green fluorescent protein/luciferase-positive rat ASCs were utilized. Rats were sacrificed at weeks 1, 2, 4, and 8 after injury. Real-time in vivo bioluminescence imaging of groups with ASCs was performed. Upon sacrifice, Achilles tendons underwent biomechanical and histological evaluation. Comparisons across groups were analyzed using the two-sample Z-test for proportions and the Student's t-test for independent samples. Significance was set at p<0.05.
  
  
  RESULTS
  (i) Bioluminescence imaging demonstrated that total photon flux was significantly increased for hydrogel+PRP+ASCs, versus hydrogel+ASCs for each postoperative day imaged (p<0.03). (ii) Mean ultimate failure load (UFL) was increased for hydrogel augmented with PRP and/or ASCs versus hydrogel alone at week 2 (p<0.03). By week 4, hydrogel alone reached a similar mean UFL to hydrogel augmented with PRP and/or ASCs (p>0.3). However, at week 8, hydrogel with PRP and ASCs demonstrated increased strength over other groups (p<0.05), except for hydrogel with PRP (p=0.25). (iii) Upon histological analysis, Hematoxylin and Eosin staining showed increased extracellular matrix formation in groups containing PRP and increased cellularity in groups containing ASCs. Groups containing both PRP and ASCs demonstrated both of these characteristics.
  
  
  CONCLUSIONS
  PRP and ASCs are easily accessible bioactive products that have potentiating effects on tendon hydrogel. Augmentation with these two factors encourages earlier mechanical strength and functional restoration. Thus, biochemically, tendon hydrogel augmented with PRP and/or ASCs, serves as a promising therapeutic modality for augmenting the tendon healing process after injury.
authors.affiliation: 1 Division of Plastic and Reconstructive Surgery, Stanford University Medical Center , Stanford, California.
authors.forename: Grace Jane
authors.initials: GJ
authors.lastname: Chiou
authors.forename: Christopher
authors.initials: C
authors.lastname: Crowe
authors.forename: Rory
authors.initials: R
authors.lastname: McGoldrick
authors.forename: Kenneth
authors.initials: K
authors.lastname: Hui
authors.forename: Hung
authors.initials: H
authors.lastname: Pham
authors.forename: James
authors.initials: J
authors.lastname: Chang
mesh_terms: D000273:Adipose Tissue / Q000166:cytology*; D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects; D055119:Elastic Modulus / Q000187:drug effects; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000494:pharmacology*; D021621:Imaging, Three-Dimensional; D007267:Injections; D008163:Luminescent Measurements; D053657:Platelet-Rich Plasma / Q000378:metabolism*; D017208:Rats, Wistar; D013194:Staining and Labeling; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D013708:Tendon Injuries / Q000473:pathology / Q000503:physiopathology / Q000628:therapy; D013710:Tendons / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology; D016474:Weight-Bearing; D014945:Wound Healing / Q000187:drug effects*
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate