Takei Y G, Aoki T, Sanui K, Ogata N, Sakurai Y, Okano T
Department of Chemistry, Sophia University, Tokyo, Japan.
Biomaterials. 1995 Jun;16(9):667-73. doi: 10.1016/0142-9612(95)99692-f.
Temperature-responsive semitelechelic poly(N-isopropylacrylamide) (PIPAAm) bearing a carboxyl end group has been chemically immobilized on aminated polystyrene particle surfaces via condensation reaction. PIPAAm-grafted particles were uniformly suspended in aqueous media at lower temperatures. With increasing temperature, PIPAAm-grafted particles aggregated and precipitated. Such reversible changes in particle colloidal behaviour was correlated to temperature-modulated hydrophilic/hydrophobic changes of particle surfaces modified by PIPAAm hydration/dehydration with temperature changes. Interactions between platelets and PIPAAm-grafted surfaces were studied by monitoring cytoplasmic free Ca2+ concentration ([Ca2+]i) changes in platelets using intracellularly-trapped Ca2+ indicator dye, Fura 2, at various temperatures. Although changes in [Ca2+]i in platelets in contact with PIPAAm-grafted particles were not observed below the critical temperature of PIPAAm, significant changes in [Ca2+]i in platelets were induced by contact with particles above this critical temperature. Furthermore, temperature-modulated cell adsorption/desorption control by PIPAAm-grafted particles was investigated using a particle aggregation assay in the presence of lymphocytes. Below the critical temperature of PIPAAm, mixed suspensions were completely homogeneous due to minimal interaction between lymphocytes and hydrated particles. In contrast, aggregated precipitates were observed by increasing the suspension temperature above the critical temperature of PIPAAm resulting from strong hydrophobic interactions between particles with lymphocytes. These precipitates are reversibly resuspended in cold buffer. The feasibility of cell activation/inactivation or cell attachment/detachment control by temperature-modulated surface changes is attractive for suspension cell culture and drug delivery at targeted sites in vivo.
带有羧基端基的温度响应性半遥爪聚（N-异丙基丙烯酰胺）（PIPAAm）已通过缩合反应化学固定在胺化聚苯乙烯颗粒表面。接枝了PIPAAm的颗粒在较低温度下均匀悬浮于水性介质中。随着温度升高，接枝了PIPAAm的颗粒聚集并沉淀。颗粒胶体行为的这种可逆变化与随着温度变化通过PIPAAm水合/脱水修饰的颗粒表面的温度调节亲水性/疏水性变化相关。通过使用细胞内捕获的Ca2+指示剂染料Fura 2在不同温度下监测血小板中细胞质游离Ca2+浓度（[Ca2+]i）的变化，研究了血小板与接枝了PIPAAm的表面之间的相互作用。尽管在PIPAAm的临界温度以下未观察到与接枝了PIPAAm的颗粒接触的血小板中[Ca2+]i的变化，但与高于该临界温度的颗粒接触会诱导血小板中[Ca2+]i的显著变化。此外，在淋巴细胞存在的情况下使用颗粒聚集试验研究了接枝了PIPAAm的颗粒对温度调节的细胞吸附/解吸的控制。在PIPAAm的临界温度以下，由于淋巴细胞与水合颗粒之间的相互作用最小，混合悬浮液完全均匀。相反，由于颗粒与淋巴细胞之间的强疏水相互作用，将悬浮液温度升高到PIPAAm的临界温度以上时会观察到聚集沉淀。这些沉淀可在冷缓冲液中可逆地重新悬浮。通过温度调节表面变化来控制细胞激活/失活或细胞附着/脱离的可行性对于体内悬浮细胞培养和靶向部位的药物递送具有吸引力。
