In our aging society, the number of patients suffering from poorly healing bone defects increases. Bone morphogenetic proteins (BMPs) are used in the clinic to promote bone regeneration. However, poor control of BMP delivery and thus activity necessitates high doses, resulting in adverse effects and increased costs. It has been demonstrated that messenger RNA (mRNA) provides a superior alternative to protein delivery due to local uptake and prolonged expression restricted to the site of action. Here, we present the development of porous collagen scaffolds incorporating peptide-mRNA nanoparticles (NPs). Nanoparticles were generated by simply mixing aqueous solutions of the cationic cell-penetrating peptide PepFect14 (PF14) and mRNA. Peptide-mRNA complexes were uniformly distributed throughout the scaffolds, and matrices fully preserved cell attachment and viability. There was a clear dependence of protein expression on the incorporated amount of mRNA. Importantly, after lyophilization, the mRNA formulation in the collagen scaffolds retained activity also at 4 °C over two weeks. Overall, our results demonstrate that collagen scaffolds incorporating peptide-mRNA complexes hold promise as off-the-shelf functional biomaterials for applications in regenerative medicine and constitute a viable alternative to lipid-based mRNA formulations.

Messenger RNA (mRNA) is increasingly gaining interest as a modality in vaccination and protein replacement therapy. In regenerative medicine, the mRNA-mediated expression of growth factors has shown promising results. In contrast to protein delivery, successful mRNA delivery requires a vector to induce cellular uptake and subsequent endosomal escape to reach its end destination, the ribosome. Current non-viral vectors such as lipid- or polymer-based nanoparticles have been successfully used to express mRNA-encoded proteins. However, to advance the use of mRNA in regenerative medicine, it is required to assess the compatibility of mRNA with biomaterials that are typically applied in this field. Herein, we investigated the complexation, cellular uptake and maintenance of the integrity of mRNA complexed with gelatin nanoparticles (GNPs). To this end, GNPs with positive, neutral or negative surface charge were synthesized to assess their ability to bind and transport mRNA into cells. Positively charged GNPs exhibited the highest binding affinity and transported substantial amounts of mRNA into pre-osteoblastic cells, as assessed by confocal microscopy using fluorescently labeled mRNA. Furthermore, the GNP-bound mRNA remained stable. However, no expression of mRNA-encoded protein was detected, which is likely related to insufficient endosomal escape and/or mRNA release from the GNPs. Our results indicate that gelatin-based nanomaterials interact with mRNA in a charge-dependent manner and also mediate cellular uptake. These results create the basis for the incorporation of further functionality to yield endosomal release.

To investigate the delivery of next-generation macromolecular drugs, such as engineered proteins and mRNA-containing nanoparticles, there is an increasing push towards the use of physiologically relevant disease models that incorporate human cells and do not face ethical dilemmas associated with animal use. Here, we illustrate the versatility and ease of use of a microfluidic platform for studying drug delivery using high-resolution microscopy in 3D. Using this microfluidic platform, we successfully demonstrate the specific targeting of carbonic anhydrase IX (CAIX) on cells overexpressing the protein in a tumor-mimicking chip system using affibodies, with CAIX-negative cells and non-binding affibodies as controls. Furthermore, we demonstrate this system’s feasibility for testing mRNA-containing biomaterials designed to regenerate bone defects. To this end, peptide- and lipid-based mRNA formulations were successfully mixed with colloidal gelatin in microfluidic devices, while translational activity was studied by the expression of a green fluorescent protein. This microfluidic platform enables the testing of mRNA delivery from colloidal biomaterials of relatively high densities, which represents a first important step towards a bone-on-a-chip platform. Collectively, by illustrating the ease of adaptation of our microfluidic platform towards use in distinct applications, we show that our microfluidic chip represents a powerful and flexible way to investigate drug delivery in 3D disease-mimicking culture systems that recapitulate key parameters associated with in vivo drug application.