Complementary biomolecular coassemblies direct energy transport for cardiac photostimulators

Abstract

Charge and energy transport within living systems are fundamental processes that enable the autonomous function of excitable cells and tissues. To date, localized control of these transport processes has been enabled by genetic modification approaches to render light sensitivity to cells. Here, we present peptidic nanoassemblies as constituents of a cardiac biomaterial platform that leverages complementary sequence interactions to direct photoinduced energy transport at the cellular interface. Photophysical characterizations and conductivity measurements confirm the occurrence of energy/charge transfer and photocurrent generation upon optical excitation in both dry and electrolytic environments. Comparing an electrostatic sequence pair against a sequence-matched donor-acceptor coassembly, we demonstrate that the sequence design with charge complementarity shows more prominent photocurrent behavior. With the flanking bioadhesive units, the primary and stem cell-derived cardiomyocytes interfaced with covalently stabilized films of the optoelectronic nanostructures exhibited material-stimulated genotypic, structural, or functional cardiac features. Collectively, our findings introduce an optoelectronic cardiac biomaterial where coassembled peptide nanostructures are molecularly designed to induce light sensitivity in excitable cells without gene modification, influencing in vitro cardiac contractile behavior and expression of cardiac markers.

Keywords: biomaterials; cardiac tissue engineering; peptide nanostructures; photostimulation; self-assembly.

Fig. 1.

Photocurrent-generating coassembly of π-conjugated peptides as a cellular photostimulation platform. (A) Chemical structures of designed peptides of KFKF-PDI, KFKF-4T, and DGREFEF-4T. (B) Absorption and photoluminescence (PL) spectra of coassembly system (λ_exc = 400 nm). (C) Schematic for donor–acceptor coassembly with charge-complementary peptide sequence. (D) Optimized geometry of the coassembly between DGREFEF-4T (ten molecules on the left) and KFKF-PDI (ten molecules on the right) and mixed charge transport with light stimulation; schematic of the cellular photostimulation platform based on photocurrent-generating peptide assemblies.

Fig. 2.

Self-assembly of π-conjugated peptides from molecules, solution state, to solid state. (A) Optimized dimer geometry of coassembly system. (B) Circular dichroism (CD) spectra of both individual and coassembly systems. (C) Transmission electron microscope (TEM) images of both individual and coassembly systems. (Scale bar, 300 nm.) (D) ¹³C solid-state NMR spectrum (natural abundance) of the coassembly. (E) Grazing-incidence small-angle X-ray scattering (GISAXS) of solid-state films of both individual and coassembly systems.

Fig. 3.

Photocurrent generation measurements for peptide-based interfaces. (A) Schematic diagram for the film structure of peptide assemblies on a conductive polymer layer. (B) Energy level diagram of donor and acceptor molecules showing charge generation process and the optical gaps calculated from the onset of absorption spectra. Photocurrent of peptide assemblies in (C) solid-state film and (D) Tyrode’s solution under illumination of 415 nm. Photocurrent of peptide assemblies in (E) solid-state film and (F) Tyrode’s solution under illumination of 530 nm. Photocurrent of KFKF-4T/KFKF-PDI in (G) solid-state film and (H) Tyrode’s solution under illumination of 415 and 530 nm.

Fig. 4.

Dynamics of photoinduced excited states of peptide assemblies. Transient absorption (TA) spectra patterns of peptide assemblies in solution: (A) Coassembly; (B) DGREFEF-4T; (C) KFKF-PDI. TA spectra profiles of peptide assemblies in solution: (D) Coassembly; (E) DGREFEF-4T; (F) KFKF-PDI TA intensity decay of peptide assemblies in (G) solution or (H) film state with Tyrode’s solution. Excitation wavelength = 400 nm.

Fig. 5.

Interfacing optoelectronic peptides with cardiomyocytes. (A) Images of immunostained NRVMs on isotropic peptide-based films and anisotropic gelatin-peptides. (Scale bar, 10 µm.) (B) Images of immunostained hiPSC-CMs on peptide assemblies. (Scale bar, 10 µm.) (C) Gene expression profiling of hiPSC-CMs on peptide coassembly films vs. fibronectin/Geltrex-coated substrate (control) on day 22 with and without light exposure. P-value: *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; Statistical analysis was done using one-way ANOVA followed by Tukey’s honestly significant difference (HSD) test. n=12 to 13.

Fig. 6.

Calcium handling behavior of NRVMs on optoelectronic peptides. (A) Calcium flux frequency of NRVMs on glass and peptide coassembly films; P-value: *P < 0.05; Statistical analysis was done using the Mann–Whitney test; n=12 for control; n=10 for peptide coassembly. Sp.: Spontaneous beating. (B) Representative calcium transient beating curves of NRVMs measured before exposure to 415 nm pulsed LED source (spontaneous/ sp., which is no longer than 1 to 2 min before light was turned on), at the start of 415 nm light stimulation (stimulation time=0), and after 5 min of 415 nm light stimulation.