In Vitro Grown Micro-Tissues for Cardiac Cell Replacement Therapy in Vivo.

BACKGROUND/AIMS: Different approaches have been considered to improve heart reconstructive medicine and direct delivery of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) appears to be highly promising in this context. However, low cell persistence post-transplantation remains a bottleneck hindering the approach. Here, we present a novel strategy to overcome the low engraftment of PSC-CMs during the early post-transplantation phase into the myocardium of both healthy and cryoinjured syngeneic mice. METHODS: Adult murine bone marrow mesenchymal stem cells (MSCs) and PSC-CMs were co-cultured on thermo-responsive polymers and later detached through temperature reduction, resulting in the protease-free generation of cell clusters (micro-tissues) composed of both cells types. Micro-tissues were transplanted into healthy and cryo-injured murine hearts. Short term cell retention was quantified by real-time-PCR. Longitudinal cell tracking was performed by bioluminescence imaging for four weeks. Transplanted cells were further detected by immunofluorescence staining of tissue sections. RESULTS: We demonstrated that in vitro grown micro-tissues consisting of PSC-CMs and MSCs can increase cardiomyocyte retention by >10fold one day post-transplantation, but could not fully rescue a further cell loss between day 1 and day 2. Neutrophil infiltration into the transplanted area was detected in healthy hearts and could be attributed to the cellular implantation rather than tissue damage exerted by the transplantation cannula. Injected PSC-CMs were tracked and successfully detected for up to four weeks by bioluminescence imaging. CONCLUSION: This approach demonstrated that in vitro grown micro-tissues might contribute to the development of cardiac cell replacement therapies.

Engineering of cardiac microtissues by microfluidic cell encapsulation in thermoshrinking non-crosslinked PNIPAAm gels.

Multicellular agglomerates in form of irregularly shaped or spherical clusters can recapitulate cell-cell interactions and are referred to as microtissues. Microtissues gain increasing attention in several fields including cardiovascular research. Cardiac microtissues are evolving as excellent model systems for drug testingin vitro(organ-on-a-chip), are used as tissue bricks in 3D printing processes and pave the way for improved cell replacement therapiesin vivo. Microtissues are formed for example in hanging drop culture or specialized microwell plates; truly scalable methods are not yet available. In this study, a novel method of encapsulation of cells inpoly-N-isopropylacrylamid(PNIPAAm) spheres is introduced. Murine induced pluripotent stem cell-derived cardiomyocytes and bone marrow-derived mesenchymal stem cells were encapsulated in PNIPAAm by raising the temperature of droplets formed in a microfluidics setup above the lower critical solute temperature (LCST) of 32 °C. PNIPAAM precipitates to a water-insoluble physically linked gel above the LCST and shrinks by the expulsion of water, thereby trapping the cells in a collapsing polymer network and increasing the cell density by one order of magnitude. Within 24 h, stable cardiac microtissues were first formed and later released from their polymer shell by washout of PNIPAAm at temperatures below the LCST. Rhythmically contracting microtissues showed homogenous cell distribution, age-dependent sarcomere organizations and action potential generation. The novel approach is applicable for microtissue formation from various cell types and can be implemented into scalable workflows.

The Potential Application of Biomaterials in Cardiac Stem Cell Therapy.

Biomaterials play a vital role in the field of regenerative medicine and tissue engineering. To date, a large number of biomaterials have been used in cardiovascular research and application. Recently, biomaterials have held a lot of promise in cardiac stem cell therapy. They are used in cardiac tissue engineering to form scaffolds for cellular transplantation, promote angiogenesis, enhance transplanted cell engraftment or influence cell migration. The science of biomaterial designing has evolved to an extent where they can be designed to mimic the microenvironment of a cardiac tissue in vivo and contribute in deciding the fate of transplanted stem cells and induce cardiac lineage oriented stem cell differentiation. In this review, we focus on biomaterials used in cardiovascular stem cell research, tissue engineering and regenerative medicine and conclude with an outlook on future impacts of biomaterial in medical sciences.