The role of microscopic elasticity of nano-carriers in cellular uptake is an important aspect in biomedical research. Herein we have used AFM nano-indentation force spectroscopy and Förster resonance energy transfer (FRET) measurements to probe microelastic properties of three novel cationic liposomes based on di-alkyl dihydroxy ethyl ammonium chloride based lipids having asymmetry in their hydrophobic chains (Lip1818, Lip1814 and Lip1810). AFM data reveals that symmetry in hydrophobic chains of a cationic lipid (Lip1818) imparts higher rigidity to the resulting liposomes than those based on asymmetric lipids (Lip1814 and Lip1810). The stiffness of the cationic liposomes is found to decrease with increasing asymmetry in the hydrophobic lipid chains in the order of Lip1818 > Lip1814 > lip1810. FRET measurements between Coumarin 500 (Donor) and Merocyanine 540 (Acceptor) have revealed that full width at half-maxima (hw) of the probability distribution (P(r)) of donor-acceptor distance (r), increases in an order Lip1818 < Lip1814 < Lip1810 with increasing asymmetry of the hydrophobic lipid chains. This increase in width (hw) of the donor-acceptor distance distributions is reflective of increasing flexibility of the liposomes with increasing asymmetry of their constituent lipids. Thus, the results from AFM and FRET studies are complementary to each other and indicates that an increase in asymmetry of the hydrophobic lipid chains increases elasticity and or flexibility of the corresponding liposomes. Cell biology experiments confirm that liposomal flexibility or rigidity directly influences their cellular transfection efficiency, where Lip1814 is found to be superior than the other two liposomes manifesting that a critical balance between flexibility and rigidity of the cationic liposomes is key to efficient cellular uptake. Taken together, our studies reveal how asymmetry in the molecular architecture of the hydrophobic lipid chains influences the microelastic properties of the liposomes, and hence, their cellular uptake efficiency.

纳米载体的微观弹性在细胞摄取中的作用是生物医学研究的重要方面。在本文中，我们已经使用AFM纳米压痕力光谱和Förster共振能量转移（FRET）测量来探测三种新颖的阳离子脂质体的微弹性性质，这些脂质体是基于二烷基二羟基乙基氯化铵基脂质，它们的疏水链具有不对称性（Lip1818，Lip1814和Lip1810）。AFM数据显示，与基于不对称脂质的脂质体（Lip1814和Lip1810）相比，阳离子脂质（Lip1818）的疏水链中的对称性赋予所得脂质体更高的刚性。发现阳离子脂质体的刚度随着疏水脂质链中不对称性的增加而降低，依次为Lip1818> Lip1814> lip1810。HW）供体-受体距离（r）的概率分布（P（R））的，在增加的顺序Lip1818 <Lip1814 <Lip1810随疏水性脂链的不对称性。这种增加的宽度（HW（1）的供体-受体距离分布反映了脂质体的柔性随其组成脂质的不对称性的增加而增加。因此，来自AFM和FRET研究的结果是相互补充的，并且表明疏水性脂质链的不对称性的增加增加了相应脂质体的弹性和/或柔韧性。细胞生物学实验证实脂质体的柔韧性或刚性直接影响其细胞转染效率，其中发现Lip1814优于其他两种脂质体，这表明阳离子脂质体的柔韧性和刚性之间的关键平衡是有效吸收细胞的关键。在一起