Cross-linked Triblock Peptide Capsules as Potential Oxygen Carriers

Abstract

Perfluorodecalin (PFD)-filled capsules have been studied for over 15 years as artificial oxygen carriers. However, none of these capsules combines good biocompatibility, good mechanical stability and dispersion stability. Here we propose to use synthetic triblock peptides containing a central block of cysteine units as a cross-linking shell material for capsules with both good biocompatibility and stability. Together with outer aspartate units and inner phenylalanine units, the resulting amphiphilic triblock peptides can encapsulate PFD efficiently to prepare capsules with a suitable diameter, a certain mechanical strength, a large diffusion constant, fast gas exchange rates, and little cytotoxicity. Given the above advantages, these PFD-filled peptide capsules are very promising as potential artificial oxygen carriers.

Figure 1

Structure of cysteine containing triblock peptide and formation of PFD‐filled peptide capsules.

Figure 2

AFM images (left) and height profiles (right) of various PFD‐filled capsules from different triblock peptides. (a) Bu‐Asp₄₀‐Cys₅‐Phe₅, (b) Bu‐Asp₇‐Cys₁₅‐Phe₂.

Figure 3

Size distribution of PFD‐filled Bu‐Asp₇‐Cys₁₅‐Phe₂ capsules as determined by particle tracking.

Figure 4

PFG‐NMR echo decay plots for pure liquid PFD and the PFD in a dispersion of PFD‐filled Bu‐Asp₇‐Cys₁₅‐Phe₂ capsules. The slope obtained for the encapsulated PFD corresponds to a particle diameter of 180 nm. An overall number of 96 measurements in two separate experiments have been averaged for each data point.

Figure 5

Gas exchange process in a dispersion of PFD‐filled Bu‐Asp₆‐Cys₈‐Phe₈ capsules as determined by the chemical shift of the ¹⁹F‐NMR signal. The data were observed under sequential purging with O₂ (blue dots) and with N₂ (green dots) of the capsule dispersion. Three separate measurements have been averaged for each data point.

Figure 6

Cytotoxic effects of PFD‐filled capsules on human HK2 cells. To determine the disruption of cellular membrane integrity, LDH analyses was performed. Control cells were incubated for 4 h with DMEM/F‐12 with GlutaMAX (no supplements), whereas treatment groups were incubated for 4 h with nanocapsules at different concentrations (0.1 %, 0.25 %, 0.5 %, 1 %, 2.5 %, 5 %), respectively. The positive control group corresponded to 10 μl Lysis Buffer treatment for 45 min. Values are expressed as means±SD (n=12) from 4 different experiments. t‐test, two‐way ANOVA with Tukey's multiple comparisons test** P<0.05, *** P<0.0001 as compared to medium.