AbstractsBiology & Animal Science

Significant efforts have been focused on preparing degradable polymeric biomaterials with controllable properties, which have the potential to stimulate specific cellular responses at the molecular level. Click reactions provide a universal tool box to achieve that goal through molecular level design and modification. This dissertation demonstrates multiple methodologies and techniques to develop advanced biomaterials through combining degradable polymers and click chemistry.In my initial work, a novel class of amino acid-based poly(ester urea)s (PEU) materials was designed and prepared for potential applications in bone defect treatment. PEUs were synthesized via interfacial polycondensation, and showed degradability in vivo and possessed mechanical strength superior to conventionally used polyesters. Further mechanical enhancement was achieved after covalent crosslinking with a short peptide crosslinker derived from osteogenic growth peptide (OGP). The in vitro and in an in vivo subcutaneous rat model demonstrated that the OGP-based crosslinkers promoted proliferative activity of cells and accelerated degradation properties of PEUs. As a continuous study, extra efforts were focused on the development of PEUs with functional pendant groups, including alkyne, azide, alkene, tyrosine phenol, and ketone groups. PEUs with Mw exceeding to 100K Da were obtained via interfacial polycondensation, and the concentration of pendent groups was varied using a copolymerization strategy. Electrospinning was used to fabricate PEU nanofiber matrices with mechanical strengths suitable for tissue engineering. A series of biomolecules were conjugated to nanofiber surface following electrospinning using click reactions in aqueous media. The ability to derivatize PEUs with biological motifs using high efficient chemical reactions will significantly expand their use in vitro and in vivo. Based on similar principles, a series of mono- and multifunctionalized polycaprolactone (PCL) bearing various clickable groups, including ketone, alkyne, azide, and methyl acrylate (MA), were synthesized via ring opening polymerization. A quartz crystal microbalance (QCM) was used to quantify the rate and extent of surface conjugation between RGD peptides and polymer thin films. The successful conjugation was further confirmed by static contact angle and NMR measurements. QCM results also verified and quantified the sequential immobilization of peptides onto polymer films.Besides polymer functionalization click reactions were also utilized for hydrogel fabrication and post-gelation modification. Polyethylene glycol-based hydrogels were formed via oxime ligation. The gelation process and final mechanical strength of the hydrogels can be tuned using pH and the catalyst concentration. The time scale to reach the gel point and complete gelation, and the storage modulus of hydrogels can be tuned in two orders of magnitude. Azide- and alkene-functionalized hydrogels were also fabricated, and further post-gelation functionalization was achieved via alkyne-azide…