| Tissue engineering has emerged over the last several decades as a possible therapy for damaged tissues and organs. Within this field, biodegradable scaffolds play an important role by providing physical and biochemical support for both differentiated and progenitor cells during the tissue regeneration process. Herein, we describe growth factory delivery polymer systems for cartilage tissue engineering applications. Insulin-like growth factor I (IGF-I) and transforming growth factor-beta1 (TGF-beta1), in particular, have great significance in cartilage tissue engineering as mitogenic and differentiating factors, respectively. Growth factors were encapsulated in PLGA microspheres using spontaneous emulsion and in vitro release kinetics were characterized by ELISA. Incorporating BSA in the IGF-I formulations decreased the initial burst from 80% to 20%, while using uncapped-PLGA rather than capped, decreased the initial burst of TGFbeta1 from 60% to 0% upon hydration. The bioactivity of released IGF-I and TGF-beta1 was determined using MCF-7 proliferation assay and HT-2 inhibition assay, respectively. Both growth factors were released for up to 70 days in bioactive form. Scaffolds were fabricated via a novel method by fusing bioactive IGF-I and TGF-beta 1 microspheres with dichloromethane vapor. Three scaffolds with tailored release kinetics were fabricated: IGF-I and TGF-beta1 released continuously, TGF-beta1 with IGF-I released sequentially after 10 days, and IGF-I with TGF-beta1 released sequentially after 7 days. Scaffold swelling and degradation were characterized, indicating peak swelling ratio of 4 after 7 days of incubation and showing 50% mass loss after 28 days, both consistent with scaffold release kinetics. In addition, low and high therapeutic TGF-beta1 formulations were fabricated which released TGF-beta1 at 1.1 ng/mL per day and 6.0 ng/mL per day, respectively. Co-culture of the high therapeutic TGF-beta1 formulation with synoviocyte pellets showed equivalence to 10ng/mL bolus addition. Therefore, TGF-beta1 microspheres have the ability to induce synoviocyte chondrogenesis and increase GAG production in vitro. Thus, the ability of these polymer systems to release IGF-I and TGF-beta1 sequentially and at therapeutic rates makes them valuable for cartilage tissue engineering applications. |
