| Ocular neovascularization diseases including age-related macular degeneration are the leading causes of blindness in developing countries. Because of the chronic nature of the disease and the fast elimination of drug in the eye, monthly repeated intravitreal injection are required to achieve best therapeutic outcome. However, repeated intravitreal injection increases the risk of developing ocular complications and decreases the patient compliance. In this thesis, an injectable chemically crosslinked hydrogel formulation of an anti-VEGF antibody therapeutic for eye diseases was developed and evaluated in vitro and in vivo. We demonstrated for the first time that the prolonged release of protein therapeutics can be achieved in the eye for at least 6 months.;Different from previous attempts of using physical hydrogel, chemically crosslinking between polymer precursors was designed as the gelation method. Vinylsulfone-thiol reaction pair was chosen for its fast reaction kinetics in physiological condition and biocompatibility. To modify polymers to contain vinyl sulfone groups or thiol groups, we introduced simple "click" chemistry based reactions which was applicable to a majority of hydroxyl-containing water soluble polymers including hyaluronic acid, dextran, PVA and alginate with controllable degree of modification. The development of these simple reactions provided us with wide varieties of starting materials for formulation optimization. To enable rational design of formulations for our application, we developed a simple model based on De Gennes' Blob Theory to understand hydrogel formation from crosslinking polymer solution. By estimating hydrogel as a semidilute solution fixed at entanglement points, the relation between polymer properties and hydrogel properties was evaluated from theoretical perspectives and validated using experiments. From this model, we can calculate minimum gelation concentration and estimate hydrogel mesh size based solely on polymer parameters such as molecular weight and radius of gyration. The model also sheds new insights on the effect of crosslinker density or degree of modification on hydrogel's mechanical properties and mesh size. Based on this model, we controlled the mesh size of hydrogel and minimize the undesirable protein binding between protein and with hydrogel material, and successfully developed an in situ hyaluronic acid/dextran based hydrogel capable of releasing the model therapeutic protein, AvastinRTM, for at least 3 months in vitro with tunable release rate. The biocompatibility and in vivo release of one formulation was evaluated in rabbit eye. The intraocular pressure (IOP) measurement, fundus morphology observation using binocular indirect ophthalmoscope (BIO), electroretinogram (ERG) and histology showed that the gel was well tolerated. AvastinRTM was released continuously from the gel formulation and maintained above therapeutically relevant concentration in the vitreous for least 6 months. |
