Cell Culturing
Cells generally exist as three-dimensional aggregates in the body, but in classical plate culturing, cells are cultured in a monolayer fashion with the cells attached to a vessel. Numerous reports have indicated significant differences in cell properties with different culturing environments.
Bone marrow-related cells have a strong tendency to be affected by the scaffold of the culturing environment in which they grow, and many cases have been reported in which cell culturing is promoted using three-dimensional culture supports. PTL 1 discloses a bioreactor that employs a method utilizing a nonwoven fiber matrix that forms a three-dimensional fiber network, to increase and maintain undifferentiated hematopoietic stem cells or hematopoietic precursor cells isolated from a body, when they are outside of the body. Use of a nonwoven fabric is also disclosed in NPL 1 and elsewhere. The stem cell properties of hematopoietic stem cells are known to be easily lost, but NPL 2 teaches that by synthesizing a porous hydrogel and culturing hematopoietic stem cells on it, it is possible to maintain the stem cell properties of the hematopoietic stem cells in a manner specific to the cell source. A more direct case is reported in PTL 2, describing efficient adhesion of bone marrow stem cells by seeding the cells on the surface of a support composed of a calcium phosphate-based compound. In addition, PTL 3 reports that Oshima et al. of the University of Tsukuba seeded and cultured cells recovered from mouse bone marrow on a collagen-treated three-dimensional scaffold formed of polyvinyl formal and transplanted them into mouse dorsal regions, by which they were able to function as artificial bone marrow. However, no sufficiently practical methodology has yet been established.
Moreover, while spatial structure has been shown by previous inventions to be in a strict proportion to function and efficiency, demonstrating the importance of a three-dimensional scaffold structure, this has been approached from the point of view of the general concept of “spatial structure”, or from the viewpoint of bone marrow-like composition or size control of the porous structure, and not from the viewpoint of morphology or anatomy, in terms of similarity of morphological structure. It is desirable to establish a method of culturing bone marrow cells designed from a novel viewpoint that is directed toward establishing a more efficient and highly practical methodology.
Bone Injury and Healing
With a view toward patient QOL, healing of bone injuries, including fractures and bone loss, has traditionally employed techniques using a variety of tools and means, involving methods of anchoring plates or screws in the affected areas. In recent years, bone disease treatment materials and implements with various structural, functional and biocompatible features have been created and utilized in medicine (NPL 3 and PTL 4). In regenerative medicine as well, different methods have been employed in attempts to promote healing of bone injuries including fractures and bone loss, and for example, there have been reports of methods of supplementing affected areas with compound materials obtained by culturing cells such as mesenchymal stem cells in biomaterials such as collagen or apatite, or bioabsorbable materials (PTLs 5 and 6). The therapeutic efficacy of stem cells and the extent to which they contribute has been a matter of dispute (NPL 4).
Such methods are mainly characterized in that materials composed of biological substances, or cell-containing biological substances, or combinations of cells and autolytic substances, are used in the body to supplement wounds or deficient sites, but in some cases these methods are not suitable, for sites with extensive damage or loss or for complex shapes, and in other cases the methods are very time consuming.
In the field of dentistry, certain operations involve leaving a space in the wound area while forming a film on the surface (NPL 5). Such techniques are designed to avoid rapid epithelial formation in the wound area, but are not widely applicable for bone regeneration.
There is demand for a convenient and effective method of treating bone injury that is suitable for a variety of wound surfaces including sites with extensive loss and sites with complex shapes.
Porous Polyimide Film
The term “polyimide” is a general term for polymers including imide bonds in the repeating unit. An “aromatic polyimide” is a polymer in which aromatic compounds are directly linked by imide bonds. An aromatic polyimide has an aromatic-aromatic conjugated structure via an imide bond, and therefore has a strong rigid molecular structure, and since the imide bonds provide powerful intermolecular force, it has very high levels of thermal, mechanical and chemical properties.
Porous polyimide films have been utilized in the prior art for filters and low permittivity films, and especially for battery-related purposes, such as fuel cell electrolyte membranes and the like. PTLs 7 to 9 describe porous polyimide films with numerous macro-voids, having excellent permeability for gases and the like, high porosity, excellent smoothness on both surfaces, relatively high strength and, despite high porosity, also excellent resistance against compression stress in the film thickness direction. All of these are porous polyimide films formed via amic acid.