title: Treatment of critically sized femoral defects with recombinant BMP-2 delivered by a modified mPEG-PLGA biodegradable thermosensitive hydrogel.
abstract: Reconstruction of a segmental fracture with massive bone loss is still a challenge for orthopaedic surgeons. The aim of our study was to develop a suitable biodegradable thermosensitive hydrogel system as a carrier for bone morphogenetic protein (BMP)-2 delivery in the treatment of critical-sized femoral defects.
  
  
  
  A block copolymer composed of monomethoxypoly(ethylene glycol) (mPEG), poly(lactic-co-glycolic acid) (PLGA) and 2, 2'-Bis (2-oxazolin) (Box) was synthesized by ring opening polymerization. The synthesized block copolymer was characterized by (1)H-NMR spectroscopy and gel permeation chromatography (GPC). Different biophysical and biochemical properties of the synthesized copolymer, including temperature-induced structure changes, degradation rate, pH changes during hydrolytic degradation, cell toxicity, and the release profile of BMP-2, were also evaluated and/or were compared with those of a well-characterized mPEG-PLGA copolymer. In animal testing, rabbits (n = 36) that received critically sized (10 mm) femoral defects were divided into 6 groups. These experimental groups included an untreated group, autograft, and groups treated with the synthesized copolymer carrying different concentrations of BMP-2 (0, 5, 10, and 20 μg/ml). Bone repair was evaluated using X-ray radiography, histological staining, micro-computed tomography (μCT), biomarker examination and biomechanical testing in a 12-week treatment period.
  
  
  
  A new thermosensitive mPEG-PLGA/Box/mPEG-PLGA block copolymer, or named as BOX copolymer, was successfully prepared. Compared to the reported mPEG-PLGA in vitro, the prepared BOX copolymer at the same weight percent concentrations exhibited wider temperature ranges of gelation, slower degradation rates, higher the pH values, as well as less cytotoxicity. Furthermore, the BMP-2 release from BOX hydrogel exhibited a near-linear release profile in vitro. In animal experiments, treatment of critical-sized bony defects with 25 wt% BOX hydrogel carrying BMP-2 effectively promoted fracture healing during the 12-week trial period and higher concentrations of BMP-2 treatment correlated with better bone quality. Most importantly, clinical outcome and bone healing in the BOX-hydrogel group with 20 μg/ml BMP-2 were nearly equivalent to those in the autograft group in a 12-week treatment course.
  
  
  
  These data support that the use of BOX hydrogel (25 wt%) as a drug delivery system is a promising method in the treatment of large bone defects.
authors.affiliation: Division of Joint Reconstruction, Department of Orthopedic Surgery, Chang-Gung Memorial Hospital, Chiayi, Taiwan.|College of Medicine, Chang-Gung University, Taoyuan, Taiwan.
authors.forename: Kuo-Ti
authors.initials: KT
authors.lastname: Peng
authors.affiliation: Institute of Biomedical Engineering, College of Engineering, College of Medicine, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei, Taiwan.|Biomedical Technology and Device Research Labs, Industrial Technology Research Institute, Hsinchu, Taiwan.
authors.forename: Meng-Yow
authors.initials: MY
authors.lastname: Hsieh
authors.affiliation: Biomedical Technology and Device Research Labs, Industrial Technology Research Institute, Hsinchu, Taiwan.|Department of Chemical Engineering, National Tsing-Hua University, Hsinchu, Taiwan.
authors.forename: Carl T
authors.initials: CT
authors.lastname: Lin
authors.affiliation: Biomedical Technology and Device Research Labs, Industrial Technology Research Institute, Hsinchu, Taiwan.
authors.forename: Chin-Fu
authors.initials: CF
authors.lastname: Chen
authors.affiliation: Division of Joint Reconstruction, Department of Orthopedic Surgery, Chang-Gung Memorial Hospital, Chiayi, Taiwan.|College of Medicine, Chang-Gung University, Taoyuan, Taiwan.
authors.forename: Mel S
authors.initials: MS
authors.lastname: Lee
authors.affiliation: Institute of Biomedical Engineering, College of Engineering, College of Medicine, National Taiwan University, No. 1, Sec. 1, Jen-Ai Road, Taipei, Taiwan. yyhuang@ntu.edu.tw.
authors.forename: Yi-You
authors.initials: YY
authors.lastname: Huang
authors.affiliation: Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang-Gung University, Taoyuan, Taiwan. peyjiumc@mail.cgu.edu.tw.|Department of Nephrology, Chang-Gung Memorial Hospital, Chiayi, Taiwan. peyjiumc@mail.cgu.edu.tw.|Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang-Gung University, 6 West, Chia-Pu Road, Puzi City, Chiayi, 613, Taiwan. peyjiumc@mail.cgu.edu.tw.
authors.forename: Pey-Jium
authors.initials: PJ
authors.lastname: Chang
mesh_terms: D000818:Animals; D064592:Autografts; D063566:Biodegradable Plastics / Q000009:adverse effects / Q000737:chemistry; D015415:Biomarkers / Q000032:analysis; D001696:Biomechanical Phenomena; D055396:Bone Morphogenetic Protein 2 / Q000008:administration & dosage / Q000627:therapeutic use*; D016025:Bone Transplantation / Q000379:methods; D002460:Cell Line; D004195:Disease Models, Animal; D004337:Drug Carriers / Q000009:adverse effects / Q000737:chemistry; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000628:therapy*; D005269:Femur / Q000473:pathology / Q000637:transplantation; D017102:Fracture Healing / Q000187:drug effects*; D005599:Fractures, Ununited / Q000000981:diagnostic imaging / Q000628:therapy*; D006801:Humans; D020100:Hydrogels / Q000009:adverse effects / Q000737:chemistry; D051379:Mice; D011091:Polyesters; D011092:Polyethylene Glycols / Q000009:adverse effects / Q000737:chemistry*; D011098:Polyglactin 910 / Q000009:adverse effects / Q000737:chemistry*; D011817:Rabbits; D011859:Radiography; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000627:therapeutic use; D013696:Temperature; D016212:Transforming Growth Factor beta / Q000008:administration & dosage / Q000627:therapeutic use*; D055114:X-Ray Microtomography
chemical_list: D063566:Biodegradable Plastics; D015415:Biomarkers; D055396:Bone Morphogenetic Protein 2; D004337:Drug Carriers; D020100:Hydrogels; D011091:Polyesters; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C558447:methoxypolyethyleneglycol-poly(lactic-co-glycolic acid); C499469:recombinant human bone morphogenetic protein-2; D011098:Polyglactin 910; D011092:Polyethylene Glycols
keywords: BMP-2; Biodegradable polymer; Fracture healing; Thermosensitive hydrogel; mPEG-PLGA