Use of photosynthetic scaffolds in tissue engineering

Abstract

The present invention is concerned with a photosynthetic scaffold that delivers oxygen and its uses for tissue engineering and the treatment of ischemia.

Claims

1. A method for treating injured tissue, comprising applying a structure or carrier matrix seeded with photosynthetically active cells to the injured tissue such that the photosynthetically active cells directly contact the injured tissue, wherein the photosynthetically active cells deliver oxygen to the injured tissue.

2. The method of claim 1, wherein the photosynthetically active cells are from the genus Chlamydomonas.

3. The method of claim 2, wherein the Chlamydomonas is Chlamydomonas reinhardtii.

4. The method of claim 1, wherein the photosynthetically active cells are encapsulated with a permeable immunologically inert material.

5. The method of claim 4, wherein the permeable immunologically inert material is a natural or synthetic polymer.

6. The method of claim 5, wherein the natural or synthetic polymer is a hydrogel or alginate.

7. The method of claim 1, wherein at least some of the photosynthetically active cells have been genetically engineered to contain nucleic acids encoding for at least one bioactive molecule.

8. The method of claim 1, wherein the injured tissue comprises damage of at least one of skin, nerve, bone, cartilage and blood tissue.

9. The method of claim 1, wherein at least some of the photosynthetically active cells are genetically engineered cells containing nucleic acids encoding for at least one pro-angiogenic factor.

10. The method of claim 1, wherein the structure or carrier matrix comprises a biofilm.

11. The method of claim 1, wherein applying the structure or carrier matrix seeded with photosynthetic cells hinders hypoxia and increases tissue regeneration.

12. The method of claim 1, wherein the structure or carrier matrix comprises nutrients for growth of the photosynthetically active cells.

13. The method of claim 1, wherein the structure or carrier matrix comprises a wound dressing.

14. The method of claim 1, wherein the structure or carrier matrix comprises a surgical suture.

15. The method of claim 1, wherein the structure or carrier matrix is biocompatible and biodegradable.

16. The method of claim 1, wherein at least some of the photosynthetically active cells are genetically modified cells.

Description

(1) The present invention is explained in more detail in the following example and the figures. The example and the figures describe preferred embodiments and are not intended to restrict the scope of the invention.

(2) FIG. 1 shows schematically how scaffolds of the present invention work. A standard scaffold is seeded with photosynthetically active cells (1) that when exposed to light release oxygen (2).

(3) FIG. 2 shows micrographs of Chlamydomonas cells seeded on a scaffold of the present invention. A; SEM shows the presence of photosynthetic cells in the inner cavities of the scaffold. Lower picture represents a magnified area and white arrows shows some algae. B; the proliferation of Chlamydomonas in dermal scaffolds was determined by quantifying increase in the pixel intensity along the time. C. Shows a microscopic view of algae 7 days after seeding. Results show high biocompatibility and proliferation of Chlamydomonas in dermal scaffolds.

(4) FIG. 3 shows micrographs of cell co-culture. Chlamydomonas cells and fibroblasts were co-cultured in dishes and on a scaffold for dermal regeneration. The micrographs on the left show the distribution of Chlamydomonas and fibroblasts in a culture dish. Both types of cells can be distinguished by their color and morphology-Chlamydomonas (white and round) are indicated with arrows. The micrographs on the right show that in the presence of Chlamydomonas the fibroblasts in a collagen scaffold remain metabolically active after 1 week in co-culture. Metabolic activity can be observed as dark dots in the cells (MTT assay). Scale bar represent 100 .mu.m.

(5) FIG. 4 shows a block diagram wherein hypoxia and metabolic activity have been plotted for fibroblasts growing on photosynthetic scaffolds (comprising photosynthetic cells, according to the present invention) and on standard scaffolds (without photosynthetic cells, for control). The mouse fibroblasts were incubated under hypoxic conditions (1% O.sub.2). As can be seen in the diagram, after 24 hours fibroblasts seeded in control scaffolds express higher levels of the hypoxic marker HIF-1.alpha. (A), metabolic activity was substantially increased in photosynthetic scaffolds (B) and cell death was reduced (C). Moreover, massive cell death induced by hypoxia was inhibited under co-culture conditions (D). In this assay live and dead cells in control (left) and photosynthetic conditions (right) are represented in green and red respectively, which can not be observed in gray scale.

(6) FIG. 5 shows the behavior of Chlamydomonas in a bio film. Algae were mixed with fibrin and sprayed over a plastic surface. A: High proliferation of algae (black arrows) was observed 1 week after seeding. B: After hypoxic incubation (1% O.sub.2), the presence of light induce increase of oxygen from 1% up to 50% after 48 hours.

(7) FIG. 6 shows images of a full skin defect model. Animals are anesthetized and areas of skin—1.5 cm diameter—are surgically removed and replaced by scaffolds of the present invention containing photosynthetic cells. Scale bar represent 1 cm.

(8) FIG. 7 shows an image of an in vivo transplantation. After 1 week of transplantation animals were sacrificed and the skin graft was removed. It was found that the dermis of the animal presents a light-green color due to the presence of chlorophyll in the tissue in regeneration (panels A-B). Moreover, PCR analysis showed that algae can survive after transplantation (panel C). A specific band for algae was found to be expressed in photosynthetic scaffold (labeled “P” in panel C) but not in controls (labeled “C” in panel C). Here Chlamydomonas were used as positive control (labeled “CR” in panel C).

EXAMPLE 1

(9) Experiments in vitro and in vivo have been performed to show the favorable properties of the photosynthetic scaffolds of the present invention.

(10) In a first test it was evaluated if algae of the species Chlamydomonas reinhardtii (CR) are able to grow in a collagen scaffold. CR were cultured in vitro in a scaffold that is known for tissue engineering. As shown in FIG. 2, biocompatibility of the CR in the scaffold results in a high proliferation capacity of the algae. After showing that CR can be cultivated in the scaffold, they were grown with mouse fibroblast (NIH 3T3 cells). FIG. 3 shows the interaction and distribution of both cells in normal culture dishes (FIG. 3 left) and in the collagen scaffold (FIG. 3 right). Viability of fibroblast was evaluated by metabolic assay (MTT) and viability of CR was confirmed by direct visualization of the cells by light microscopy (mobility).

(11) In order to determine whether the “photosynthetic scaffold” can support the metabolic requirements of fibroblasts, CR and NIH 3T3 were co-cultured under hypoxic condition (1% O.sub.2) in the presence of a light source. Oxygen was constantly monitored by a commercially available system (PreSens, Regensburg, Germany). Results show that the photosynthetic scaffold allows to significantly reduce the hypoxic marker HIF-1.alpha. (FIG. 4A). Moreover, under such conditions metabolic activity was drastically increased (FIG. 4B) and cell death was decreased (FIG. 4C). Finally, live/dead studies, performed in cell culture dishes, show that when cells are incubated during 4 days under hypoxic conditions almost all cells are dead (FIG. 4D; left). In contrast to that the presence of the algae fully avoids such effect (FIG. 4D; right).

(12) Next, similar experiments were performed in a bio-film containing CR. As shown in FIG. 5, CR are able to proliferate in fibrin (FIG. 5A), releasing significant amounts of oxygen (FIG. 5B).

(13) The feasibility of this approach was evaluated in vivo. For that, a bilateral full skin defect was created in the back of 6 nude mice and the skin was replaced by a scaffold containing 5.times.10.sup.6 CR (FIG. 6). 1 week after of transplantation, the scaffolds were removed and integration and viability of the algae in the new tissue was analyzed. Results showed that animals can survive after transplantation, presenting a light-green color of the dermis in regeneration (FIG. 7A). Moreover, presence of RNA derived from the algae showed that algae were metabolically active 1 week after implantation (FIG. 7B).

(14) Moreover, long term in vivo experiments have been carried out. The results show that animals can survive for at least 2 months in the presence of “photosynthetic scaffolds” containing algae.