Subretinal Implantation of RPE on a Carrier in Minipigs: Guidelines for Preoperative Preparations, Surgical Techniques, and Postoperative Care.

Degenerative disorders of the retina (including age-related macular degeneration), which originate primarily at or within the retinal pigmented epithelial (RPE) layer, lead to a progressive disorganization of the retinal anatomy and the deterioration of visual function. The substitution of damaged RPE cells (RPEs) with in vitro cultured RPE cells using a subretinal cell carrier has shown potential for re-establishing the anatomical structure of the outer retinal layers and is, therefore, being further studied. Here, we present the principles of a surgical technique that allows for the effective subretinal transplantation of a cell carrier with cultivated RPEs into minipigs. The surgeries were performed under general anesthesia and included a standard lens-sparing three-port pars plana vitrectomy (PPV), subretinal application of a balanced salt solution (BSS), a 2.7 mm retinotomy, implantation of a nanofibrous cell carrier into the subretinal space through an additional 3.0 mm sclerotomy, fluid-air exchange (FAX), silicone oil tamponade, and closure of all the sclerotomies. This surgical approach was used in 29 surgeries (18 animals) over the past 8 years with a success rate of 93.1%. Anatomic verification of the surgical placement was carried out using in vivo fundus imaging (fundus photography and optical coherence tomography). The recommended surgical steps for the subretinal implantation of RPEs on a carrier in minipig eyes can be used in future preclinical studies using large-eye animal models.

Subretinal Implantation of Human Primary RPE Cells Cultured on Nanofibrous Membranes in Minipigs.

PURPOSE: The development of primary human retinal pigmented epithelium (hRPE) for clinical transplantation purposes on biodegradable scaffolds is indispensable. We hereby report the results of the subretinal implantation of hRPE cells on nanofibrous membranes in minipigs. METHODS: The hRPEs were collected from human cadaver donor eyes and cultivated on ultrathin nanofibrous carriers prepared via the electrospinning of poly(L-lactide-co-DL-lactide) (PDLLA). "Libechov" minipigs (12-36 months old) were used in the study, supported by preoperative tacrolimus immunosuppressive therapy. The subretinal implantation of the hRPE-nanofibrous carrier was conducted using general anesthesia via a custom-made injector during standard three-port 23-gauge vitrectomy, followed by silicone oil endotamponade. The observational period lasted 1, 2, 6 and 8 weeks, and included in vivo optical coherence tomography (OCT) of the retina, as well as post mortem immunohistochemistry using the following antibodies: HNAA and STEM121 (human cell markers); Bestrophin and CRALBP (hRPE cell markers); peanut agglutining (PNA) (cone photoreceptor marker); PKCα (rod bipolar marker); Vimentin, GFAP (macroglial markers); and Iba1 (microglial marker). RESULTS: The hRPEs assumed cobblestone morphology, persistent pigmentation and measurable trans-epithelial electrical resistance on the nanofibrous PDLLA carrier. The surgical delivery of the implants in the subretinal space of the immunosuppressed minipigs was successfully achieved and monitored by fundus imaging and OCT. The implanted hRPEs were positive for HNAA and STEM121 and were located between the minipig's neuroretina and RPE layers at week 2 post-implantation, which was gradually attenuated until week 8. The neuroretina over the implants showed rosette or hypertrophic reaction at week 6. The implanted cells expressed the typical RPE marker bestrophin throughout the whole observation period, and a gradual diminishing of the CRALBP expression in the area of implantation at week 8 post-implantation was observed. The transplanted hRPEs appeared not to form a confluent layer and were less capable of keeping the inner and outer retinal segments intact. The cone photoreceptors adjacent to the implant scaffold were unchanged initially, but underwent a gradual change in structure after hRPE implantation; the retina above and below the implant appeared relatively healthy. The glial reaction of the transplanted and host retina showed Vimentin and GFAP positivity from week 1 onward. Microglial activation appeared in the retinal area of the transplant early after the surgery, which seemed to move into the transplant area over time. CONCLUSIONS: The differentiated hRPEs can serve as an alternative cell source for RPE replacement in animal studies. These cells can be cultivated on nanofibrous PDLLA and implanted subretinally into minipigs using standard 23-gauge vitrectomy and implantation injector. The hRPE-laden scaffolds demonstrated relatively good incorporation into the host retina over an eight-week observation period, with some indication of a gliotic scar formation, and a likely neuroinflammatory response in the transplanted area despite the use of immunosuppression.

Correction: Inverse heavy-atom effect in near infrared photoluminescent gold nanoclusters.

Correction for 'Inverse heavy-atom effect in near infrared photoluminescent gold nanoclusters' by Goutam Pramanik et al., Nanoscale, 2021, DOI: 10.1039/d1nr02440j.

Inverse heavy-atom effect in near infrared photoluminescent gold nanoclusters.

Fluorophores functionalized with heavy elements show enhanced intersystem crossing due to increased spin-orbit coupling, which in turn shortens the fluorescence decay lifetime (τPL). This phenomenon is known as the heavy-atom effect (HAE). Here, we report the observation of increased τPL upon functionalisation of near-infrared photoluminescent gold nanoclusters with iodine. The heavy atom-mediated increase in τPL is in striking contrast with the HAE and referred to as inverse HAE. Femtosecond and nanosecond transient absorption spectroscopy revealed overcompensation of a slight decrease in lifetime of the transition associated with the Au core (ps) by a large increase in the long-lived triplet state lifetime associated with the Au shell, which contributed to the observed inverse HAE. This unique observation of inverse HAE in gold nanoclusters provides the means to enhance the triplet excited state lifetime.

Kinetics of the Photoexcited States in Thin Films of Metallo-Supramolecular Polymers With Ditopic Thiophene-Bridged Terpyridine Ligands.

Managing the excited-state decay by a supramolecular structure is a crucial issue for organic photovoltaics. We show that in thin films of metallo-supramolecular polymers made of bis(terpyridine-4'-yl)terthiophenes and Z n 2 + coupling ions, the photoexcited states generated by ultrashort laser pulses at the wavelength of 440 nm decay by the bi-molecular annihilation predominantly controlled by the Förster transfer between singlet states. During this bi-molecular annihilation of singlet states, intermediate hot triplet pairs are formed, which subsequently dissociate into long-living diffusing triplet states. It explains a significant shortening of the triplet state rise time with increasing pump fluence. The diffusion coefficient of triplets showed power-law time dependence, with its exponent proportional to the pump fluence, decreasing thus the diffusivity of triplets.

Singlet Fission in Thin Solid Films of Bis(thienyl)diketopyrrolopyrroles.

The singlet fission (SF) process discovered in bis(thienyl)diketopyrrolopyrroles (TDPPs) can boost their potential for photovoltaics (PV). The crystal structures of TDPP analogs carrying n-hexyl, n-butyl, or 2-(adamant-1-yl)ethyl substituents are similar, but contain increasingly slipped stacked neighbor molecules. The observed SF rate constants, kSF , (7±4), (9±3) and (5.6±1.9) ns-1 for thin films of the three compounds, respectively, are roughly equal, but the triplet quantum yields vary strongly: (120±40), (160±40) and (70±16), respectively. The recent molecular pair model reproduces the near equality of all three kSF at the crystal geometries and identifies all possible pair arrangements in which SF is predicted to be faster, by up to two orders of magnitude. However, it is also clear that the presently non-existent ability to predict the rates of processes competing with SF is pivotal for providing a guide for efforts to optimize the materials for PV.

Plasmonic Screening Effect of Gold Nanoparticles Array on Light Absorption in Poly(3-hexyl)Thiophene Thin Film.

The localized surface plasmon (LSP) photophysical phenomenon occurring in metal nanostructures is often presented as a way to effectively couple light into sub-wavelength-scale photovoltaic devices, which would otherwise suffer from a weak light absorption. The simultaneous complementary effect of localized optical field depletion receives far less attention. We studied a system consisting of a planar gold nanoparticles array (AuNP) deposited at the surface of a semiconducting polymer thin film (P3HT). By comparing the UV-vis spectra of P3HT with and without the AuNP array, we have estimated that the AuNPs screen the optical absorption in the interfacial layer of about 3.8 nm effective thickness due the near-field depletion effect. It suggests that the AuNP array may be used to practically "hide" a thin semiconductor layer, e.g., in order to tune the perceived color of the photovoltaic cell embedded in architecture, or in wearable devices.

Phonons spreading from laser-heated gold nanoparticle array accelerate diffusion of excitons in an underlying polythiophene thin film.

Localized surface plasmon (LSP) photophysical phenomena occurring in metal nanostructures are often presented as a method to effectively couple light into photovoltaic devices of sub-wavelength-scale thickness. However, the excitation of LSP is also associated with rapid energy dissipation leading to local heating, which affects the excitation energy pathway. We studied a system consisting of a planar gold nanoparticle (AuNP) array deposited at the surface of a semiconducting polymer thin film (P3HT). We observed heat transfer from laser pulse excited AuNPs into the P3HT, which was evidenced as a long-living thermochromic effect on transient optical absorption. By modeling of the ultrafast kinetics of exciton population evolution, we determined that their decay was caused by their mutual annihilation. The decay rate was controlled by a phonon-assisted one-dimensional diffusion mechanism with a diffusion constant of 2.2 nm2 ps-1. The transferred heat resulted in an increase of the diffusion constant by a factor of almost 2, compared to the control system of P3HT without AuNPs. These results are of practical use for the design of plasmon-enhanced optoelectronic devices.

Time-Resolved Transient Optical Absorption Study of Bis(terpyridyl)oligothiophenes and Their Metallo-Supramolecular Polymers with Zn(II) Ion Couplers.

α,ω-Bis(terpyridyl)oligothiophenes spontaneously assemble with Zn(II) ions giving conjugated constitutional dynamic polymers (dynamers) of the metallo-supramolecular class, which potentially might be utilized in optoelectronics. Their photophysical properties, which are of great importance in this field of application, are strongly influenced by the dynamic morphology. It was assessed in this study by using ultrafast pump-probe optical absorption spectroscopy. We identified and characterized relaxation processes running in photoexcited molecules of these oligomers and dynamers and show impacts of disturbed coplanarity of adjacent rings (twisting the thiophene-thiophene and thiophene-terpyridyl bonds by attached hexyl side groups) and Zn(II) ion couplers on these processes. Major effects are seen in the time constants of rotational relaxation, intersystem crossing, and de-excitation lifetimes. The photoexcited states formed on different repeating units within the same dynamer chain do not interact with each other even at very high excitation density. The method is presented that allows determining the equilibrium fraction of unbound oligothiophene species in a dynamer solution, from which otherwise hardly accessible values of the average degree of polymerization of constitutionally dynamic chains in solution can be estimated.

Roles of octabutoxy substitution and J-aggregation in stabilization of the excited state in nickel phthalocyanine.

Nickel phthalocyanine (NiPc) complexes are known to show a rapid nonradiative deactivation of the photoexcited state through the internal conversion. This could be exploited in practical applications, such as photoprotection and photodynamic therapy. The butoxy substitution of NiPc plays an important role for drug delivery but also greatly influences its photophysics. We prepared novel peripherally substituted 2,3,9,10,16,17,23,24-octabutoxy nickel(II) phthalocyanine and characterized the deactivation pathway of its photoexcited state in solution by femtosecond transient absorption spectroscopy and quantum chemical calculations. We bring experimental evidence for the kinetic model, in which the photoexcitation evolves in two independent branches. In the first branch, assigned to the monomer, it undergoes ultrafast intersystem crossing to a triplet state, which subsequently decays to the ground state through a pathway involving lower-lying triplet states, with a ground-state recovery lifetime of 814 ps. It is about three-times longer than the lifetime published for unsubstituted NiPc. In the second branch, the photoexcitation decayed to a triplet state with an orders of magnitude longer lifetime, with the quantum yield of about 4%. This state showed spectral features of J-aggregates. These findings are important for the applications that rely on singlet oxygen formation or fast nonradiative deactivation of the excited state.