[Malithi Weerakkody]

An artificial cell can basically be defined as a particle that replaces or assists cellular functions, and in which biological or non-biological materials are encapsulated within a biological or synthetic polymer membrane. These “cells’” can come in macro, micro, nano and molecular dimensions and are used in various disciplines such as medicine, biotechnology, agriculture, industry, nanorobotics and much more. Depending on their structure or functions they are identified by different terminology such as nanoparticles, nanocapsules, nanosensors, liposomes, lipid vesicles, microcapsules, polymersomes etc.



The Membrane

The membranesorrounding an artificial cell can be either biological or synthetic. This membrane is usually composed of materials such as biodegradable or non-biodegradable simple polymers, lipids, proteins, polymer materials linked with lipids or proteins linked with lipids. Polymeric material used for membrane synthesis determines the porosity of the membrane and the degree of diffusion of the molecules through the membrane. Hydrogel polymers such as alginate or cellulose and thermoplastic polymers such as polyacrylonitrilepolyvinyl chloride are some of the commonly used materials for membrane construction.

The membrane of an artificial cell performs different tasks. Basically, it separates the contents of the cell from the outside and controls the movement of molecules between the cell and the surroundings. Being immunologically inert, these membranes protect the artificial cells from the immune system of a patient when they are used in clinical applications.

Depending on their functions, the complexity of these membranes may vary. For instance, some membranes may have proteins on their surfaces such as enzymes, haemoglobin, antigens or antibody. Some may contain transport carriers or selective channels.



The Interior

Enclosed within the polymer, the artificial cells can contain a variety of bioactive materials such as cells, enzymes, haemoglobin, microorganisms, vaccines, genes, drugs, hormones, proteins, nanoparticles, magnetic materials etc. artificial cells may also contain a combination of these materials.

Few Applications of Artificial Cells

Artificial Cells for Hemoperfusion

Artificial cells are also used for hemoperfusion, i.e. removal of toxic substances from the blood of a patient. These ‘cells’ contain adsorbent materials which retain the contaminants in the blood that diffuse through the membrane. The artificial cells are a cheaper and more effective option compared to the available methods of blood detoxification. Since they restrict the movement of the encased adsorbents into the patient’s blood, they are also considered to be safe. Recent researches have been conducted with artificial cells composed of nanosponges encapsulated within natural red blood cell membranes which can be used for removal of toxins from blood.

Artificial Cells as Oxygen Carriers

Artificial cells containing only haemoglobin (Hb) or red blood cell enzymes along with Hb can be used as oxygen carriers. They can be an effective solution to the various problems associated with blood transfusion one of which is the need of blood typing and matching to avoid immunological reactions in the patient. Since these artificial cells can be sterilised they also eliminate the risk of transmission of diseases such as AIDS through blood transfusion. Furthermore, the artificial oxygen carriers, since they possess stable cellular membranes, are more durable and can be stored for prolonged durations where the natural RBCs can only be stored up to 42 days at 4 Centigrade.

Haemoglobin in purified form cannot be used as an oxygen carrier because it is highly toxic to the kidney. This toxicity arises due to the breakdown of haemoglobin molecule into two toxic dimers which damage liver tissues. In artificial cells, haemoglobin can either be enclosed within the particle or it can be cross-inked to the polymers to form insoluble conjugated haemoglobin. Since these haemoglobin molecules are immobilised, the threat of toxicity is eliminated.

More complex artificial cells, which can be considered as artificial red blood cells have been developed by incorporating Hb as well as RBC enzymes into the cellular element.



Artificial Cells as Drug Delivery Systems

Artificial cells have drawn the attention of the scientists as an alternative method of delivering drugs. These delivery systems have many benefits over the traditional methods such as oral and intravenous administration of drugs. The major advantage is their ability to release the drugs slowly once within the tissues. Modern drug delivering artificial cell systems range from micro to nanodimensions. They are known by different terms such as polymersomes, liposomes, nanoparticles, nanotubules etc.

Apart from these applications, artificial cells are used in various clinical applications such as enzyme therapy, gene therapy and cell therapy. There is also the possibility of enclosing radioactive materials within an artificial cell which could then be used to treat tumours. These cells could be also be designed to target specific tissues by crosslinking proteins that are immunologically compatible to the target tissues.



Artificial Cells in the Future

With the progress in the nanotechnology and molecular biology, novel and more advanced artificial cell types with improved polymer membranes and new contents will be developed. Scientists are also working on with the hope of creating a “living artificial cell” which will be entirely man-made but will mimic biological cells in every other way. There are also predictions that “Programmable Artificial Cell Evolution”, an integrated programme supported by the European Union will eventually succeed in incorporating the artificial cells into computer and robotics technology, thereby making self-repairing computers.

Source:

Artificial cells: biotechnology, nanomedicine, regenerative medicine, blood substitutes, bioencapsulation, cell/stem cell therapy by Chang, Thomas Ming Swi (2007)