(639e) Pulsatile Growth Factor Release From Novel Aptamer-Functionalized Composites

Pulsatile release of molecules from cells is a critical mechanism evolved in nature. This mechanism has been mimicked for controlled protein release that holds great potential for the treatment of various human diseases. One of the promising protein delivery systems is hydrogels. However, hydrogels are high permeable materials that make them difficult to retain and release target proteins at predetermined time points for a long time period. We recently developed a novel composite with affinity particles and hydrogel. The affinity particles were tethered with nucleic acid aptamers. The aptamers are screened from DNA/RNA libraries so that they have high binding affinity and specificity to target proteins. In this work, the pulsatile release was demonstrated by using platelet-derived growth factor-BB (PDGF-BB), its aptamer, and agarose hydrogel as a model. The microscopy imaging revealed that the affinity particles were well distributed in the composite. Because therapeutic efficacy and safety of the delivery systems are also dependent on their mechanical properties, we also examined the storage and loss moduli of the composites. The rheology data showed that the incorporation of affinity particles into the hydrogel did not cause significance difference in the storage and loss moduli. After the characterization of the composite, two sets of controlled release experiments were performed. The first experiment was used to illustrate the effectiveness of the aptamers in retaining PDGF-BB in the composite. It was found that, approximately 70% of the loaded PDGF-BB molecules were released from the control composite within the first day. In contrast, this initial release from the affinity composite was dramatically decreased to less than 10 %. After the first-day release, the PDGF-BB release from the affinity composite was released less than 1% for each day. Thus, the first experiment gave us the conclusion that the aptamers could prevent rapid PDGF-BB release from a permeable hydrogel. The expected novelty of affinity particles included not only the retaining of proteins in a highly permeable hydrogel, but also the triggered release of proteins. The second controlled-release experiment was performed to illustrate whether the molecular triggers could induce pulsatile protein release. Experimentally, the functionality of FAM-labeled triggers was studied by examining their capability of interacting with the affinity particles incorporated in the hydrogel. The microscopy imaging demonstrated that the triggers could easily penetrate the composite and bind the affinity particles in the composite environment. Importantly, the pulsatile protein release from the composites was achieved after the molecular triggers were added into the system. After the composite was triggered for one hour, approximately 20% of proteins were released in one day. These data show that the novel aptamer-functionalized composite holds great potential for controlling protein release in a pulsatile manner. ---The support from the NSF (DMR-0955358) is gratefully acknowledged---