Construction Of Biomembrane Mimetic Surface/interface Via Phosphorylcholine Technology

Nowadays, the biocompatibility still exists as a main challenge in the field of biomaterials. Getting the inspiration from modern bionics, the work aimed to figure out the difficulties concerning the biocompatibility of biomaterials through the "biomembrane mimicry" technique. Based on the biomimetic design of phosphorylcholine, two kinds of biocompatible surface/interface were constructed on the surface interventional medical devices and on the interface of drug-loaded nanoparticle systems, respectively. Ultimately, this work meant to resolve the restenosis of the intracoronary stent in the field of cardiovascular diseases and to fulfill the demands required in the field drug-loaded nanoparticle systems through modern surface modification techniques.Construction of bio-inspired crosslinkable phosphorylcholine polymer as drug-loaded coating for the coronary artery stent:Novel crosslinkable phosphorylcholine based copolymers were specially designed and synthesized by the radical polymerization from four kinds of monomers including the biomimetic monomer 2-methacryloyloxyethylphosphorylcholine (MPC), the hydrophobic monomer stearyl methacrylate (SMA), the crosslinkable monomers hydroxypropyl methacrylate (HPMA) and trimethoxysilylpropyl methacrylate (TSMA). Crosslinkable coating was prepared through dip coating followed by crosslinking processes. The results from the AFM, Contact Angle and UV indicated that the biomimetic coating existed stably on these substrates within the examined period. At the same time, the results from the contact angle showed that the biomimetic coating experienced a reorganization of the surface amphiphilic molecules when the coating was transferred from the atmosphere environment into the water environment. This reorganization process ultimately provided the biomimetic coating with a phosphorylcholine group riched surface. Platelet adhesion and plasma recalcification time characterizations were carried out on the biomimetic coatings.The results showed that the introduction of the biomimetic coating could increase the plasma recalcification time and that biomimetic coatings could improve the biocompatibility of the biomaterials independently of the hydrophilicity/ hydrophobicity of the substrates. The biomimetic coating could effectively load and release the model drug, Rhodamine S. The primary study on the drug release behavior indicated that the drug releasing behavior could be modulated through the cross-linker in the biomimetic coatings and that the half-life of the drug releasing behavior increased with the increase of the content of the cross-linker in the biomimetic coatings. These results suggested that the biostable, biocompatible and industry-scale applicable drug-loaded biomimetic coating process provided the possibility for the engineering of the coating on the surface of the drug-eluting coronary stent.Uniform, stable and Sirolimus-releasing biomimetic coating was obtained on the coronary artery stent with complex shapes through the combination of the Dip-Coating process and the blowtorch technique. The characterizations by the optical microscopy and confocal laser microscopy (CLSM) indicated that uniform (drug-loaded) biomimetic coating could be realized on the coronary artery stent. The binding force satisfied the requirements brought forward by the medical uses. This stability of the (drug-loaded) biomimetic coating on the coronary artery stent prevented the avulsion or denudation phenomena. The results of the in vitro Sirolimus-releasing test showed that Sirolimus could be long-term, stably and effectively released from the coatings. The results from the in vitro platelet adhesion experiment indicated that the biomimetic coating on the coronary stent surface could effectively reduce the platelet adhesion on the stent surface. The results from the in vivo tests using the carotids of the rabbits and the hearts of the pigs as models showed that Sirolimus-eluting coronary stent could effectively prevented the intimal proliferation.The study on the biomembrane mimetic nanoparticle drug delivery systems based on the phosphorylcholine amphiphiles:Novel biomimetic amphiphiles on the base of cholesterol as hydrophobic segment and poly (2-methacryloyloxyethyl phosphorylcholine) (pMPC) as hydrophilic segment were specially designed and synthesized in the present study via atom transfer radical polymerization (ATRP) of 2-methacryloyloxyethylphosphorylcholine (MPC) using cholesterol-based macroinitiator. Five biomimetic amphiphiles with different molecular weights were obtained by adjusting the macroinitiator to monomer feed ratio.Polymer biomimetic micelles were prepared through dissolving the biomimetic amphiphiles in water. The association behavior of cholesterol-b-poly (2-methacryloyloxyethyl phosphorylcholine) (Chol-pMPCs) in aqueous solution was studied by 'H-NMR, fluorescence probe technique and atomic force microscope (AFM). The 'H-NMR spectrum of the polymer in CD3OD showed both the cholesterol group and the phosphorylcholine group, while the cholesterol group did not appeared in the 'H-NMR spectrum of the polymer in D2O, which implied the formation of the micelle structure. Fluorescence excitation spectra for pyrene probe solubilised in the aggregates of Chol-pMPCs indicated that the critical micelle concentrations of the biomimetic polymers were determined to be about ~10'3 mg/ml, which indicated that the polymer biomimetic micelles had excellent biostability in water. AFM images of the aggregates on mica suggested that the pMPC block formed the biocompatible micelle coronas and the cholesterol block formed the hydrophobic micelle cores. In vitro cell culture method using MC3T3 cells were carried out to evaluate the biocompatibility of the biomimetic micelles. A commercial obtained polymeric amphiphiles, Cholesterol end capped PEO (CPEO), which had a similar structure with CMPC, was used as a control in the cytotoxicity test. MC3T3 cells exposed to CMPC20 and CMPC30 adhered and proliferated at the same rate as cells grown in polymer-free solutions up to 48 h. In both the CPEO20 and CPEO30 solutions (as control), however, cytotoxicity was clearly indicated. These results declared that while CPEO showed obvious cytotoxicity, cytotoxicity of this novel amphiphiles was not observed as indicated by cell culture. These new biomimetic diblock copolymers could be used as "stealthy" nanocapsules for the delivery of hydrophobic drugs.Anti-cancer drug adriamycin (ADR) was chosen as a hydrophobic drug to be incorporated into the inner core of the micelles by oil-in-water method. TEM and AFM of drug loaded micelles showed that the shape of the particles was mostly spherical and the sizes ranged about 30 nm~70 nm in diameter. This dimension compared with the dimension of the viruses and thus they might be able to penetrate the sinusoidal and fenestrated capillaries. Furthermore, Drug loading efficiencies(DLE) researches from UV indicated that the DLE reached about 4% independent of the molecular weights of the copolymers. In the drug delivery study, it was found that while the free ADR exhibited the rapid release behaviour of above 80% within about 30 h, the ADR that was loaded into the inner core of biomimetic nanospheres, showed sustained release characteristics. Moreover, the ADR drug-releasing amount could be regulated through the incorporated amount of ADR. The fluorescence microscopy was used to evaluate the incorporation effect of the biomimetic drug loaded nanospheres by cancer cells K562. Significant intracellular staining was found in the K562 cells, indicating ADR-containing micelles could be internalized by K562 cells. The cell activities of K562 cells after incubation in drug-loaded micelles at the concentration of 10 ug/ml in the CMPC30, CMPC30ADR and the free ADR indicated that the biomimetic copolymers had no influence on the growth of the K562 cells. The results of the cell culture of K562 cell also indicated that the drug-loaded micelles, CMPC30ADR, had the same effect as the free ADR on killing the cancer cells (K562) after 8 days incubation.