formulations for controlled , prolonged release of bioactive molecules such as therapeutic proteins , peptides and oligonucleotides have been developed . these formulations are based on solid microparticles or nanoparticles formed of the combination of biodegradable , synthetic polymers such as poly , poly , and copolymers thereof . bioactive molecules are coupled to hydrophilic polymers such as polyethylene glycol or polypropylene glycol and formulated to provide controlled release . the bioactive molecules are more stable , less immunogenic and have improved release rate profiles with lower burst levels and increased drug loading relative to the same bioactive molecules lacking coupled hydrophilic polymers . the controlled release formulations can be administered by injection , by inhalation , nasally , or orally .