Injectable peptide based hydrogels for cardiac regeneration applications

In the last two decades, significant efforts have been made to develop soft materials exploiting the self-assembly of short peptides for biomedical applications. So-called β-sheet forming peptides are very attractive for the design of biomaterials, in particular hydrogels [Saiani et al., Soft Matter, 5, 193, 2009].

Due to the “simplicity” of the structure formed at the molecular level, the relative robustness of the β-sheet assembly and the ease of functionalization, very stable functional hydrogels can be designed with potential applications in a range of fields – from tissue engineering [Mujeeb et al. Acta Biomat 2013, 9, 4609 & C Diaz et al. J Tissue Eng 2014, 5, 1-12] and cell culture [Szkolar et al. J Pept Sci 2014, 20, 578] to drug delivery [Roberts at al. Langmuir 2012, 28, 16196 & Tang et al. Int J Pharm 2014, 465, 427].

One particular aspect which has attracted significant interest is the ability to use these systems to design 3D injectable scaffolds for in-vivo cell delivery.

Figure 1. Schematic representation of the self-assembly and gelation process of β-sheet forming peptides. Hydrogels with tailored properties, in particular mechanical, can be designed to mimic cell niches.

 

FROM IN-VITRO

Figure 2: A “sandwich” approach was used to seed the cells in the hydrogels. A first layer of gel was plated and then washed with cell culture media. Cells were then seeded on top and a second layer of gel deposited on top of the cells. Media was then added on top of the “sandwich” gel/cell/gel construct and changed 5 time during the first hour and subsequently every other day.

Figure 3:
Left: Fluorescent microscopy image of encapsulated DilPos cardiac progenitor cells (rat) showing that their morphology and viability are preserved.
Middle: Superposition of fluorescent and optical microscopy images showing the cardiac progenitor cells in the hydrogel.
Right: Confocal re-constructed images obtained at day 8 showing DilPos cardiac progenitor cells spreading across the gel.

Figure 4: Cardiac progenitor cells (rat) were seeded as described above in the gels and after one week recovered and plated on standard cell culture plastic. Their differentiation was then measured after 2 weeks and compared to cells not conditioned in the hydrogel. The CPC differentiation was dramatically increased after culturing the cells in the gel for one week. The CPC differentiated in cardiomyocytes (left) and smooth muscle (right) cells.

 

TO IN-VIVO

Figure 5:
Left: Hydrogels loaded with rhodamine particles were injected in the left ventricle of a rat heart.
Right: optical image of the rat heart after 7 days showing the injection site and fluorescent microscopy image showing the retention of the rhodamine particles at the injection site.

Figure 7:
Left: Optical and fluorescent images obtained 4 days after injection of hydrogel loaded with cardiac progenitor cells in the rat heart showing their retention at the injection site.
Right: Fluorescent image showing evidence of in-vivo differentiation of the cardiac progenitor cells into cardiomyocytes 10 days after injection.

 

CONCLUSION
Our work clearly shows the potential of these materials as 3D scaffolds for the in-vitro culture of cardiac progenitor cells. In addition, this peptide gel displays proper injectability as well as good properties for the topical delivery of cells, or even drugs, in the host myocardium. These characteristics suggest a possible future application of this biomaterial as a scaffold for cardiac regeneration.

 

Authors: Alberto Saiani (1); Caterina Frati (2); Denise Madeddu (2); Kate Meade (1); Federico Quaini (2)
(1) School of Materials &  Manchester Institute for Biotechnology , University of Manchester, Manchester, UK
(2) Clinical and Experimental Medicine, University-Hospital of Parma, Parma, Italy

Acknowledgments: The authors gratefully acknowledge the European Union FP7 Framework Programme (Grant: BIOSCENT) and UK Engineering and Physical Sciences Research Council for funding this research (Grant no: EP/K016210/1)