Cell transplantation can become much more effective, when cells are placed on a carrier –this is the reason why Russian scientists are searching for an ideal material to build such carriers. Scientists from Tomsk and Moscow consider porous titanium to be a promising material for cell therapy.

Today scientists are very close to final creation of artificial analogues for tissues and organs; however, solution for this problem requires development of carriers for cells. Lifetime of cells, which are arranged on a carrier, is much longer than that of cells, which are simply introduced into a tissue, thus making transplantation much more effective. Various materials are used as carriers – graphite, polymers, ceramic material, metals and alloys, such as porous titanium nickelide, stainless steel and cobalt-and-chrome alloys. Despite all merits, mentioned materials cause bad inflammations and cell death. Moreover, nickel ions are carcinogens, and chrome ions penetrate cell membranes and damage DNA.

Biologically inert titanium lacks all indicated drawbacks. When titanium concentration in an organism grows several-fold, still no cancer, allergy or intoxication is detected. No wonder that porous titanium is now widely used for medical purposes, and when medics were confronted with a question of finding a carrier for implants, they harked back to this material.

Porous titanium is made of sintered titanium powder. After sintering powder particles form a skeleton, having open pores with 50-200 μm in diameter. Porous titanium is an elastic and durable material with mechanical properties being similar to spongy substance of human thigh bone. Annealing in alcohol lamp flame and further saturation with liquid makes porous titanium suitable for carrying cells. Experiments have shown that bone marrow cells are able to grow on plates made of porous titanium. Titanium plates were kept in growth medium with cell suspension for 24 hours and then were transferred to fresh-made growth medium. Bone marrow cells, which inhabited carrier pores, felt first-class even after six weeks have passed, during which the culture has taken on the properties of a real tissue. Young bone marrow cells, for instance, which characteristics are close to stem cells, stayed inside carrier pores and almost never left them – this is the way natural stem cells behave, not leaving bone marrow. However, mature cells actively traveled into environment.

Porous titanium served as a base for human “artificial fetal liver” – research fellows have planted liver cells of 11-week-old fetus to described carrier. Artificial organ was transplanted to mice, and wasn’t rejected, and even started functioning in three or four weeks – this observation was proved by high amount of red blood cells with fetal (embryonic) hemoglobin, because the only place for forming fetal hemoglobin, which was almost never found in adult mice, was “artificial liver”.

Recipient mice suffered from malignant tumor, however, a transplant, containing fetal cells, has lowered neoplastic process activity by 26% – possible explanation is “transplant versus tumor” reaction. Unfortunately, 30 per cent of mice showed different reaction – “transplant versus host”. When transplanted embryonic cells have matured and formed an immunogenic tissue, immune conflict took place. Scientists detected immune response, which was classified as “moderate” because of immense amount of transplanted cells. Researchers consider porous titanium to possess “immuno-blocking” or “barrier” characteristics, suppressing “transplant versus host” reaction, which would have been much stronger, because mice received no immunosuppressive agents.

Thus, porous titanium is now acknowledged as a material, safe for transplantation, and implants, developed on the base of said material, are considered to be hybrid artificial organs, designed for temporary or permanent replacement of natural organs, which lost their functions.

Source:
    Russian Science News
    Zimmer.com
    Tecomet.com

Kizilova Anna