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. 2018 Jul 9;4(7):2308-2313.
doi: 10.1021/acsbiomaterials.8b00343. Epub 2018 Jun 14.

Impact of Pore Size and Surface Chemistry of Porous Silicon Particles and Structure of Phospholipids on Their Interactions

Dongfei Liu  1   1 , Katriina Lipponen  1 , Peng Quan  1   2 , Xiaocao Wan  2 , Hongbo Zhang  1   3 , Ermei Mäkilä  4 , Jarno Salonen  4 , Risto Kostiainen  1 , Jouni Hirvonen  1 , Tapio Kotiaho  1   1 , Hélder A Santos  1   1
Affiliations

Impact of Pore Size and Surface Chemistry of Porous Silicon Particles and Structure of Phospholipids on Their Interactions

Dongfei Liu et al. ACS Biomater Sci Eng. .

Abstract

By exploiting its porous structure and high loading capacity, porous silicon (PSi) is a promising biomaterial to fabricate protocells and biomimetic reactors. Here, we have evaluated the impact of physicochemical properties of PSi particles [thermally oxidized PSi, TOPSi; annealed TOPSi, AnnTOPSi; (3-aminopropyl) triethoxysilane functionalized thermally carbonized PSi, APTES-TCPSi; and thermally hydrocarbonized PSi, THCPSi] on their surface interactions with different phospholipids. All of the four phospholipids were similarly adsorbed by the surface of PSi particles, except for TOPSi. Among four PSi particles, TOPSi with hydrophilic surface and smaller pore size showed the weakest adsorption toward phosphatidylcholines. By increasing the pore size from roughly 12.5 to 18.0 nm (TOPSi vs AnnTOPSi), the quantity of phosphatidylcholines adsorbed by TOPSi was enhanced to the same level of hydrophilic APTES-TCPSi and hydrophobic THCPSi. The 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) exhibited the highest release ratio of phospholipids from all four PSi particles, and phosphatidylserine (DPPS) showed the lowest release ratio of phospholipids from PSi particles, except for TOPSi, which adsorbed less phospholipids due to the small pore size. There is consistency in the release extent of phospholipids from PSi particles and the isosteric heat of adsorption. Overall, our study demonstrates the importance of pore size and surface chemistry of PSi particles as well as the structure of phospholipids on their interactions. The obtained information can be employed to guide the selection of PSi particles and phospholipids to fabricate highly ordered structures, for example, protocells, or biomimetic reactors.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Selected phospholipids and PSi particles. (a) Molecular structure and exact mass of the selected phospholipids, including phosphatidylcholines (DOPC and DSPC), phosphatidylserine (DPPS), and phosphatidylglycerol (DLPG). (b) Surface chemistry and hydrophilicity of the selected PSi particles. HPL, hydrophilic; HPB, hydrophobic. (c–e) Physicochemical properties of PSi particles (n = 2), such as (c) pore size, (d) pore volume, and (e) specific surface area.
Figure 2
Figure 2
Representative SEM images of PSi particles before and after phospholipid adsorption. PSi particles were incubated with the mixture of four phospholipids, DOPC, DSPC, DPPS, and DLPG; the concentration for each phospholipid was 30 nM. The partially enlarged view of the PSi particles shows clearly that the pores are, at least, partially covered by phospholipids.
Figure 3
Figure 3
The absolute amount of phospholipid adsorbed onto the surface of PSi particles. The effect of types of phospholipids, (a) DOPC, (b) DSPC, (c) DPPS and (d) DLPG, were tested at room temperature. On the basis of 1 mg of PSi particles, we calculated the amount of phospholipid adsorbed by AnnTOPSi, TOPSi, APTES-TCPSi, and THCPSi. Data are presented as mean ± s.d. (n = 3).
Figure 4
Figure 4
Absolute amount of phospholipid released from the surface of PSi particles. Four phospholipids, (a) DOPC, (b) DSPC, (c) DPPS, and (d) DLPG, were released from the surface of the PSi particles at room temperature. With regard to the absolute amount of phospholipid released, it was calculated based on 1 mg of PSi particles for each, including AnnTOPSi, TOPSi, APTES-TCPSi, and THCPSi. Data are presented as mean ± s.d. (n = 3).
Figure 5
Figure 5
Isosteric heat of adsorption (Qst) calculated with different phospholipids and PSi particles. (a) DOPC, (b) DSPC, (c) DPPS, and (d) DLPG. DPPS showed the highest isosteric heat of adsorption among the four phospholipids, which indicated the strongest interaction between DPPS and the surface of PSi particles.
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