title: Silk based biomaterials to heal critical sized femur defects.
abstract: Bone auto- and allografts have inherent drawbacks, therefore the treatment of non-unions and critical size defects in load bearing long bones would benefit from the use of osteopromotive biodegradable, biocompatible and mechanically durable matrices to enhance migration or delivery of cell populations and/or morphogens/cytokines. Silk fibroin biomaterial scaffolds were evaluated as osteopromotive matrices in critical sized mid-femoral segmental defects in nude rats. Four treatment groups were assessed over 8 weeks in vivo: silk scaffolds (SS) with human mesenchymal stem cells (hMSCs) that had previously been differentiated along an osteoblastic lineage in vitro (group I; pdHMSC/SS); SS with undifferentiated hMSCs (group II; udHMSC/SS); SS alone (group III; SS); and empty defects (group IV). When hMSCs were cultured in vitro in osteogenic medium for 5 weeks, bone formation was characterized with bimodal peak activities for alkaline phosphatase at 2 and 4 weeks. Calcium deposition started after 1 week and progressively increased to peak at 4 weeks, reaching cumulative levels of deposited calcium at 16 mug per mg scaffold wet weight. In vivo osteogenesis was characterized by almost bridged defects with newly formed bone after 8 weeks in group I. Significantly (P < 0.01) greater bone volumes were observed with the pdHMSC/SS (group I) implants than with groups II, III or IV. These three groups failed to induce substantial new bone formation and resulted in the ingrowth of cells with fibroblast-like morphology into the defect zone. The implantation of pdHMSC/SS resulted in significantly (P < 0.05) greater maximal load and torque when compared to the other treatment regimens. The pdHMSC/SS implants demonstrated osteogenic ability in vitro and capacity to thrive towards the healing of critical size femoral segmental defects in vivo. Thus, these new constructs provide an alternative protein-based biomaterial for load bearing applications.
authors.affiliation: Departments of Biomedical Engineering and Chemical and Biological Engineering, Tufts University, Medford, MA 02155, USA. lorenz.meinel@pharma.ethz.ch <lorenz.meinel@pharma.ethz.ch>
authors.forename: L
authors.initials: L
authors.lastname: Meinel
authors.forename: O
authors.initials: O
authors.lastname: Betz
authors.forename: R
authors.initials: R
authors.lastname: Fajardo
authors.forename: S
authors.initials: S
authors.lastname: Hofmann
authors.forename: A
authors.initials: A
authors.lastname: Nazarian
authors.forename: E
authors.initials: E
authors.lastname: Cory
authors.forename: M
authors.initials: M
authors.lastname: Hilbe
authors.forename: J
authors.initials: J
authors.lastname: McCool
authors.forename: R
authors.initials: R
authors.lastname: Langer
authors.forename: G
authors.initials: G
authors.lastname: Vunjak-Novakovic
authors.forename: H P
authors.initials: HP
authors.lastname: Merkle
authors.forename: B
authors.initials: B
authors.lastname: Rechenberg
authors.forename: D L
authors.initials: DL
authors.lastname: Kaplan
authors.forename: C
authors.initials: C
authors.lastname: Kirker-Head
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001672:Biocompatible Materials / Q000378:metabolism / Q000627:therapeutic use*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005269:Femur / Q000187:drug effects* / Q000473:pathology / Q000601:surgery; D005349:Fibroins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation / Q000379:methods; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D011923:Rats, Nude; D047011:Silk / Q000378:metabolism*; D013997:Time Factors; D023822:Tissue Engineering / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods; D014183:Transplantation, Heterologous; D016896:Treatment Outcome
chemical_list: D001672:Biocompatible Materials; D047011:Silk; D005349:Fibroins; D000469:Alkaline Phosphatase; D002118:Calcium