Browsing by Author "Ekenseair, Adam K."

Now showing 1 - 7 of 7
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    In vitroﾠandﾠin vivoﾠevaluation of self-mineralization and biocompatibility of injectable, dual-gelling hydrogels for bone tissue engineering
    (Elsevier, 2015) Vo, Tiffany N.; Ekenseair, Adam K.; Spicer, Patrick P.; Watson, Brendan M.; Tzouanas, Stephanie N.; Roh, Terrence T.; Mikos, Antonios G.
    In this study, we investigated the mineralization capacity and biocompatibility of injectable, dual-gelling hydrogels in a rat cranial defect as a function of hydrogel hydrophobicity from either the copolymerization of a hydrolyzable lactone ring or the hydrogel polymer content. The hydrogel system comprised a poly(N-isopropylacrylamide)-based thermogelling macromer (TGM) and a polyamidoamine crosslinker. The thermogelling macromer was copolymerized with (TGM/DBA) or without (TGM) a dimethyl-γ-butyrolactone acrylate (DBA)-containing lactone ring that modulated the lower critical solution temperature and thus, the hydrogel hydrophobicity, over time. Three hydrogel groups were examined: (1) 15wt.% TGM, (2) 15wt.% TGM/DBA, and (3) 20wt.% TGM/DBA. The hydrogels were implanted within an 8mm critical size rat cranial defect for 4 and 12weeks. Implants were harvested at each timepoint and analyzed for bone formation, hydrogel mineralization and tissue response using microcomputed tomography (microCT). Histology and fibrous capsule scoring showed a light inflammatory response at 4weeks that was mitigated by 12weeks for all groups. MicroCT scoring and bone volume quantification demonstrated a similar bone formation at 4weeks that was significantly increased for the more hydrophobic hydrogel formulations - 15wt.% TGM and 20wt.% TGM/DBA - from 4weeks to 12weeks. A complementary in vitro acellular mineralization study revealed that the hydrogels exhibited calcium binding properties in the presence of serum-containing media, which was modulated by the hydrogel hydrophobicity. The tailored mineralization capacity of these injectable, dual-gelling hydrogels with hydrolysis-dependent hydrophobicity presents an exciting property for their use in bone tissue engineering applications.
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    Injectable hydrogels
    (2016-03-15) Mikos, Antonios G.; Kasper, Kurtis F.; Ekenseair, Adam K.; Vo, Tiffany N.; Boere, Kristel W.M.; Touchet, Tyler J.; Rice University; United States Patent and Trademark Office
    The present disclosure generally relates to injectable compositions. More particularly, the present disclosure relates to injectable, thermogelling hydrogels and associated methods. In one embodiment, the present disclosure provides for a composition comprising a poly(N-isopropylacrylamide)-based macromer and a polyamidoamine-based macromer.
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    Mesenchymal stem cell and gelatin microparticle encapsulation in thermally and chemically gelling injectable hydrogels for tissue engineering
    (Wiley, 2014) Tzouanas, Stephanie N.; Ekenseair, Adam K.; Kasper, F. Kurtis; Mikos, Antonios G.
    In this work, we investigated the viability and osteogenic differentiation of mesenchymal stem cells encapsulated with gelatin microparticles (GMPs) in an injectable, chemically and thermally gelling hydrogel system combining poly(N-isopropylacrylamide)-based thermogelling macromers containing pendant epoxy rings with polyamidoamine-based hydrophilic and degradable diamine crosslinking macromers. Specifically, we studied how the parameters of GMP size and loading ratio affected the viability and differentiation of cells encapsulated within the hydrogel. We also examined the effects of cell and GMP co-encapsulation on hydrogel mineralization. Cells demonstrated long-term viability within the hydrogels, which was shown to depend on GMP size and loading ratio. In particular, increased interaction of cells and GMPs through greater available GMP surface area, use of an epoxy-based chemical gelation mechanism, and the tunable high water content of the thermogelled hydrogels led to favorable long-term cell viability. Compared with cellular hydrogels without GMPs, hydrogels co-encapsulating cells and GMPs demonstrated greater production of alkaline phosphatase by cells at all time-points and a transient early enhancement of hydrogel mineralization for larger GMPs at higher loading ratios. Such injectable, in situ forming hydrogels capable of delivering and maintaining populations of encapsulated mesenchymal stem cells and promoting mineralization in vitro offer promise as novel therapies for applications in tissue engineering and regenerative medicine.
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    Perspectives on the Interface of Drug Delivery and Tissue Engineering
    (Elsevier, 2013) Ekenseair, Adam K.; Kasper, F. Kurtis; Mikos, Antonios G.
    Controlled drug delivery of bioactive molecules continues to be an essential component of engineering strategies for tissue defect repair. This article surveys the current challenges associated with trying to regenerate complex tissues utilizing drug delivery and gives perspectives on the development of translational tissue engineering therapies which promote spatiotemporal cell-signaling cascades to maximize the rate and quality of repair.
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    Structure-Property Evaluation of Thermally and Chemically Gelling Injectable Hydrogels for Tissue Engineering
    (American Chemical Society, 2012) Ekenseair, Adam K.; Boere, Kristel W.M.; Tzouanas, Stephanie N.; Vo, Tiffany N.; Kasper, F. Kurtis; Mikos, Antonios G.
    The impact of synthesis and solution formulation parameters on the swelling and mechanical properties of a novel class of thermally and chemically gelling hydrogels combining poly(N-isopropylacrylamide)-based thermogelling macromers containing pendant epoxy rings with polyamidoamine-based hydrophilic and degradable diamine cross-linking macromers was evaluated. Through variation of network hydrophilicity and capacity for chain rearrangement, the often problematic tendency of thermogelling hydrogels to undergo significant syneresis was addressed. The demonstrated ability to tune postformation dimensional stability easily at both the synthesis and formulation stages represents a significant novel contribution toward efforts to utilize poly(N-isopropylacrylamide)-based polymers as injectable biomaterials. Furthermore, the cytocompatibility of the hydrogel system under relevant conditions was established while demonstrating time- and dose-dependent cytotoxicity at high solution osmolality. Such injectable in situ forming degradable hydrogels with tunable water content are promising candidates for many tissue-engineering applications, particularly for cell delivery to promote rapid tissue regeneration in non-load-bearing defects.
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    Synthesis and Characterization of Thermally and Chemically Gelling Injectable Hydrogels for Tissue Engineering
    (American Chemical Society, 2012) Ekenseair, Adam K.; Boere, Kristel W.M.; Tzouanas, Stephanie N.; Vo, Tiffany N.; Kasper, F. Kurtis; Mikos, Antonios G.
    Novel, injectable hydrogels were developed that solidify through a dual-gelation, physical and chemical, mechanism upon preparation and elevation of temperature to 37°C. A thermogelling, poly(N-isopropylacrylamide)-based macromer with pendant epoxy rings and a hydrolyticallydegradable polyamidoamine-based diamine crosslinker were synthesized, characterized, and combined to produce in situ forming hydrogel constructs. Network formation through the epoxyamine reaction was shown to be rapid and facile, and the progressive incorporation of the hydrophilic polyamidoamine crosslinker into the hydrogel was shown to mitigate the often problematic tendency of thermogelling materials to undergo significant post-formation gel syneresis. The results suggest that this novel class of injectable hydrogels may be attractive substrates for tissue engineering applications due to the synthetic versatility of the component materials and beneficial hydrogel gelation kinetics and stability.
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    Synthesis, Physicochemical Characterization, and Cytocompatibility of Bioresorbable, Dual-Gelling Injectable Hydrogels
    (American Chemical Society, 2014) Vo, Tiffany N.; Ekenseair, Adam K.; Kasper, F. Kurtis; Mikos, Antonios G.
    Injectable, dual-gelling hydrogels were successfully developed through the combination of physical thermogellation at 37 °C and favorable amine:epoxy chemical cross-linking. Poly(N-isopropylacrylamide)-based thermogelling macromers with a hydrolyzable lactone ring and epoxy pendant groups and a biodegradable diamine-functionalized polyamidoamine cross-linker were synthesized, characterized, and combined to produce nonsyneresing and bioresorbable hydrogels. Differential scanning calorimetry and oscillatory rheometry demonstrated the rapid and dual-gelling nature of the hydrogel formation. The postgelation dimensional stability, swelling, and mechanical behavior of the hydrogel system were shown to be easily tuned in the synthesis and formulation stages. The leachable products were found to be cytocompatible under all conditions, while the degradation products demonstrated a dose- and time-dependent response due to solution osmolality. Preliminary encapsulation studies showed mesenchymal stem cell viability could be maintained for 7 days. The results suggest that injectable and thermally and chemically cross-linkable hydrogels are promising alternatives to prefabricated biomaterials for tissue engineering applications, particularly for cell delivery.