Many compounds used as active substances are decomposed or deactivated before they reach their targets. Delivery of oligopeptides and proteins is particularly difficult. Oral delivery is often ineffective due to protein or oligopeptide disintegration in digestive tract. Delivery by intravenous or subcutaneous injection is inconvenient whereas delivery by inhalation often leads to allergic response. Transdermal delivery is quite ineffective due to inefficiency of protein transport through skin.

There are hopes that some of the mentioned above problems could be solved by packing proteins into small particles with degradable cores and shells protecting nanoparticle content from premature contact with an organism. Proper chemical structure of the shell should eliminate or at least reduce induction of immunoresponse of the organism.

Recently, we developed methods suitable for synthesis of block copolymers composed of biodegradable polylactide and polyether (poly(ethylene oxide) and polyglycidol) biocompatible blocks [1]. In this work we will report on formation of nanoparticles from these copolymers and on their loading with drug models.

Nanoparticles were made by two methods. The first one did consist on self-assembly of copolymer molecules above critical aggregation concentration (CAC). For investigated copolymers CAC ranged from 8 mg/l to 0.15 g/L. According to the second method the particles were formed by dialysis. Namely, polymer solution in organic water miscible solvent (e.g. acetonitrile) was dialyzed against water. Slow exchange of organic solvent for water resulted in gradually decreased solvent quality and led to formation of nanoparticles. Diameters of obtained particles ranged from 20 to 300 nm, depending on copolymer structure and method of particle formation.

Self-assembly of block copolymers carried on in presence of hydrophobic compounds (e.g. pyrene used as a model) leads to formation of loaded particles. The effective loading with proteins was achieved by dialysis of protein and copolymer solutions. In this way particles with 30 wt% protein content were obtained.

It was found that not loaded and protein loaded particles are stable in pH range from 2 to 10. Only in a 1 M NaOH (i.e. at conditions not encountered in the organism) the polylactide-b- polyether nanoparticles are quickly decomposed.

Hydroxyl groups in colpolymers containing polyglycidol segments could be used for further functioonalization (e.g. in reaction with cyclic anhydride). CAC for nanoparticles formed from copolymers containing carboxyl groups was dependent on presence of Ca⁺² cations that did act as particle stabilizers. Modification of copolymers by introduction of azobenzene moieties allowed obtaining light sensitive nanoparticles. Proper tailoring of chemical structure of chromophores may allow formation of nanoparticles releasing bioactive compounds under irradiation with near-visible infrared light that is able to penetrate few centimeters through the soft tissue.

[1]. M.Gadzinowski, S.Sosnowski, J. Polym. Sci.: Part A: Polym. Chem., 2003, 41, 3750.

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