Fibrin gel as an injectable biodegradable scaffold and cell carrier for tissue engineering

Abstract

Due to the increasing needs for organ transplantation and a universal shortage of donated tissues, tissue engineering emerges as a useful approach to engineer functional tissues. Although different synthetic materials have been used to fabricate tissue engineering scaffolds, they have many limitations such as the biocompatibility concerns, the inability to support cell attachment, and undesirable degradation rate. Fibrin gel, a biopolymeric material, provides numerous advantages over synthetic materials in functioning as a tissue engineering scaffold and a cell carrier. Fibrin gel exhibits excellent biocompatibility, promotes cell attachment, and can degrade in a controllable manner. Additionally, fibrin gel mimics the natural blood-clotting process and self-assembles into a polymer network. The ability for fibrin to cure in situ has been exploited to develop injectable scaffolds for the repair of damaged cardiac and cartilage tissues. Additionally, fibrin gel has been utilized as a cell carrier to protect cells from the forces during the application and cell delivery processes while enhancing the cell viability and tissue regeneration. Here, we review the recent advancement in developing fibrin-based biomaterials for the development of injectable tissue engineering scaffold and cell carriers.

Figure 1

Schematic representation of the fibrin aggregation process. Fibrinogen is composed of two sets of Aα-, Bβ-, and γ chains. Each α-chain is connected with E-region through fibrinopeptide A (FPA, orange) and fibrinopeptide B (FPB, green). The D-region is linked with E-region through a coiled segment. Thrombin-mediated cleavage of FPA induces the formation of two-stranded protofibril. Subsequent cleavage of FPB releases α-chain from E-region and contributes to the lateral aggregation of two-stranded protofibrils and fibrin formation [24].

Figure 2

Schematic illustration of two approaches to engineer desired tissue. Cells are isolated from biopsy and mixed with scaffold materials. Subsequently the mixture system is injected into patients' body (left). Alternatively, isolated cells are cultured on a scaffold in vitro and implanted into desired place after the formation of new functional tissue (right). Reprinted (adapted) with permission from [42]. Copyright (2001) American Chemical Society.

Figure 3

Schematic illustration of fabrications of two- and three-dimensional cell culture scaffold. The conventional two-dimensional scaffold is fabricated in advance of cell seeding and the isolated cells are seeded on the surface of scaffold (a). The three-dimensional scaffold cures in the presence of the encapsulated cells. Then, the mixture can be delivered into a mold to gel or directly injected into a defect in the body (b).

Figure 4

H&E staining of histological tissue section. Myocardium wall became thin in the infarction site (arrows in (a)). No vessels and viable cells were observed in infarction site (b). After eight weeks, the treatment of cell transplantation with fibrin gel (c) demonstrated extensive tissue regeneration when compared with cell transplantation without fibrin gel (d). Scale bar indicates 2 mm (a) and 100 μm ((b), (c), and (d)) [47].

Figure 5

Masson's trichrome staining of infarction site after eight weeks for treatment with bone marrow mononuclear cells delivered with ((a), (b), and (c)) and without ((d), (e), and (f)) fibrin gel. The infarction size of treatment with fibrin gel (arrows) is smaller than the treatment without fibrin gel. Treatment with cell-fibrin gel mixture demonstrated a larger amount of viable tissue (red) and a smaller amount of fibrous tissue (blue) when compared to the direct injection of cells without fibrin gel. Scale bar indicates 2 mm in (a), (b), (d), and (e) and 100 μm in (c) and (f) [47].

Figure 6

Isolated cells are suspended in fibrin gel solution. The cell suspension is added into cross-linking agent solution dropwise to form microbeads (a). The microbeads are mixed into injectable scaffold solution and injected into a mold (b). The microbeads degrade gradually and leave micropores in the three-dimensional scaffold for the migration and proliferation of released cells (c).

Figure 7

Fluorescent live/dead staining images. Live cells are stained in green and dead cells are in red. Cells were released from the microbeads after 4 days showing healthy polygonal morphology (arrows in (b)). After 7 days, the number of released cells increased greatly. Cells attached to the tissue culture polystyrene and showed a healthy morphology (c). Cells continued to proliferate (d) and formed confluent monolayer at day 21 (e) [53].

Figure 8

Alizarin staining for the synthesis of bone mineral at 7, 14, and 21 days. The calcium minerals are stained in red. The mineral concentration was measured by osteogenesis assay and the results are shown in (d). The mineral concentration at day 21 is 10-fold higher than day 7, which demonstrated cells released from microbeads synthesized bone mineral successfully [53].