One of the important targets in regenerative medicine is to design resorbable materials that can promote formation of new bone in large skeletal defects. One approach to this challenge is to use a bioactive and biodegradable organic matrix that can promote cellular adhesion and direct differentiation. We have here studied matrices composed of peptide amphiphiles (PAs) that self-assemble into nanofibers and create self-supporting gels under cell culture conditions. The bioactivity of PAs was designed by incorporating in their peptide sequences phosphoserine residues, to promote hydroxyapatite formation in the culture medium, and the cell adhesion epitope RGDS. In osteogenic medium supplemented with calcium the PA nanofibers were found to nucleate spheroidal nanoparticles of crystalline carbonated hydroxyapatite approximately 100 nm in diameter. This mineralization mode is not epitaxial relative to the long axis of the nanofibers and occurs in the presence of serine or phosphoserine residues in the peptide sequence of the amphiphiles. Mixing of the phosphoserine- containing PAs with 5 wt.% RGDS-containing PA molecules does not inhibit formation of the mineral nanoparticles. Quantitative real time reverse transcription polymerase chain reaction and immunohistochemistry analysis for alkaline phosphatase (ALP) and osteopontin expression suggest that these mineralized matrices promote osteogenic differentiation of human mesenchymal stem cells. Based on ALP expression, the presence of phosphoserine residues in PA nanofibers seems to favor osteogenic differentiation.
Bibliographical noteFunding Information:
The authors gratefully acknowledge funding support from the National Institutes of Health, National Institute of Dental and Craniofacial Research under award No. 5R01DE015920. Electron microscopy was performed in the Electron Probe Instrumentation Center (EPIC) facility of the NUANCE Center at Northwestern University, which is supported by the NSF-NSEC, NSF-MRSEC, Keck Foundation, the State of Illinois, and Northwestern University. Electron microscopy was also performed in the Biological Imaging Facility (BIF) at Northwestern University, which is supported by Weinberg College of Arts and Sciences, the Department of Neurobiology and Physiology, the Department of Biochemistry, Molecular Biology, and Cell Biology, the Robert H. Lurie Comprehensive Cancer Center and the Rice Foundation. Cell work was performed in the Institute for Bionanotechnology in Medicine (IBNAM) at Northwestern University. We thank Dr. Shuyou Li and Mr. Ben Myers for their technical help with experiments at EPIC, Dr. William Russin and Ms. Ramona Walsh for their technical help with experiments at BIF, and Dr. Ramille Shah, Dr. Shuming Zhang, and Ms. Janet Martinez for their technical help with experiments at IBNAM. Conrado Aparicio would also like to thank the Generalitat de Catalunya for stipend support during his stay at Northwestern University.
- Regenerative medicine
- Tissue engineering