The use of clay nanoplatelets to improve hydrogels for tissue engineering applications

Abstract

Event Abstract Back to Event The use of clay nanoplatelets to improve hydrogels for tissue engineering applications Lyndon Charles1, Sara E. Strecker1, Shimon A. Unterman1, Adar Oren1, 2, Michael Philbrook3, Gloria L. Matthews3, Elazer R. Edelman1, 4 and Natalie Artzi1, 5 1 MIT, Institute for Medical Engineering and Science, United States 2 ORT Braude College, Department of Biotechnology Engineering, Israel 3 Genzyme, a Sanofi Company, Orthopaedic Research, United States 4 Brigham and Women's Hospital, Cardiovascular Division, United States 5 Brigham and Women's Hospital, Department of Anesthesiology, United States Introduction: Hydrogels are widely used in tissue regeneration including bone and cartilage, but their tunability is challenged by their hydrophilicity which presents limits in degradation control, mechanical stability, and drug release which strongly influence regenerative outcomes. Hydrogels of polyamidoamine (PAMAM) dendrimer and dextran-aldehyde offer excellent biocompatibility, tunability, and in situ gelation[1]. Here we show the ability of clay nanoplatelets (cNPs) to improve hydrogel degradation and drug release to add further tunability. cNPs also modify the rheological properties[2] of hydrogel precursor solutions and has been optimized by our lab to create easily injectable hydrogels to improve use in minimally invasive procedures. Different sized clays, montmorillonite and laponite, were selected for improved mechanical and rheological properties. The ability to tune these properties using cNPs to create an injectable, biocompatible, drug delivery hydrogel represents a significant improvement over current hydrogels. Tunable clay hydrogels are a suitable candidate for use in tissue regeneration to address common challenges. Materials and Methods: PAMAM dendrimer was purchased from Dedritech, Inc and 10 kDa Dextran (Sigma Aldrich) was oxidized by reacting with sodium periodate. Clays were obtained from Southern Clay Products, Inc. Degradation studies were done in phosphate buffered saline and mass recorded daily. Mouse mesenchymal cells (MSC) were used for in vitro cell studies. Toxicity studies were performed by placing hydrogels in direct contact with C3H10T1/2 cells and imaged using live/dead cell staining kit (Life Technologies). Hydrogels were introduced to cell environment by transwell assay in cell growth and alkaline phosphatase assays (ALP) assays. For ALP, 16 mg simvastatin was loaded into each hydrogel and W20-17 cell line was used. PrestoBlue (Life Technologies) reagent was used to assay cell growth and ALP kit (Sigma Aldrich) was used for ALP expression. Results and Discussion: Degradation behavior of hydrogels was measured by mass loss. Results (Fig1A) show the ability of cNPs to retard hydrogel degradation. While hydrogels show a 20% loss in mass, clay hydrogels lose only 5% of mass over 21 days. Due to their large surface area and charge density, cNPs may add stability by forming networks of clay-clay and clay-polymer interactions, in addition to polymer-polymer interactions. Clay hydrogels also improve biocompatibility and acute toxicity. Early effect on cell growth is reversed with the addition of cNPs (Fig1B) and clay hydrogels mitigate the local, acute toxicity of MSCs (Fig1C) seen adjacent to the hydrogel (Fig1C). Clay addition may enhance polymer interactions and prevent the early release of unbound polymer into the media. Use of hydrogels as drug delivery vehicles is important in tissue regeneration. When added to hydrogels loaded with the osteogenic drug simvastatin, cNPs lead to increased ALP expression in MSCs (Fig1D). This is likely due to increase in simvastatin release from the hydrogel driven by the interruption of the polymer network by cNPs. Conclusion: Here we show that cNPs can modify hydrogel properties to control drug release and improve cell compatibility. This ability to tune hydrogel behavior by addition of cNPs, as well as improving injectability, can enhance their flexibility for use in variable environments and tissue engineering applications.