The hydrogels are polymeric structures, high content in water , soft and elastic, with a high absorption capacity and do not dissolve in any liquid . Its applications are diverse; from gardening to medical indications such as wound treatment or drug release. In fact, these polymers , considered for years to be one of the best drug release pathways in the body, have been shown to have very good biocompatibility characteristics and physical properties that make them similar to living tissue .
Summary
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- 1 Definition
- 2 Features
- 3 Classification of hydrogels
- 1 Other behavior
- 4 Applications of hydrogels
- 1 Contact lenses
- 2 Prosthesis in tissues
- 3 Human duct prosthetics
- 4 Suture lining
- 5 Surgery
- 6 Hemodialysis
- 7 Hemoperfusion
- 8 In the treatment of cancer
- 5 Sources
Definition
There is no precise definition of the term hydrogel, the most usual description refers to them as cross-linked polymeric materials in the form of a three-dimensional network of natural or synthetic origin, which swell in contact with water forming soft and elastic materials, and which retain a significant fraction of it in its structure without dissolving.
Polymeric solids are especially suitable for forming gels thanks to their long chain structure. The flexibility of these chains makes it possible for them to deform to allow solvent molecules to enter their three-dimensional structure.
characteristics
Hydrogels have a series of particular characteristics such as:
- Hydrophilic character: due to the presence in the structure of water soluble groups (-OH,
-COOH, -CONH2, -CONH, SO3H).
- Insoluble in water: due to the existence of a three-dimensional polymer network in its structure.
- They have a soft and elastic consistency which is determined by the starting hydrophilic monomer and the low crosslinking density of the polymer.
- They swell in water, increasing their volume considerably until reaching a chemical- physical balance , but without losing their shape. The non-hydrated form is called xerogel.
Crosslinking in hydrogels is due not only to covalent bonds (σ bonds), typical of any crosslinked material, but also to Van der Waals intermolecular forces and to hydrogen bonds .
In hydrogels, there are also other types of interactions such as electrostatic forces, both attractive and repulsive, intermolecular bonds of hydrophobic components and ionic interactions.
Hydrogels classification
Hydrogels can be classified in various ways depending on which particular characteristics and properties are taken as a reference.
Based on the nature of the lateral groups: -Neutrals -Ionic (anionic, cationic, ampholytic).
According to its mechanical and structural characteristics: -In related networks -Ghost networks.
Depending on the preparation method: -Homopolymeric, copolymeric, multipolymeric network, -Interpenetrated polymeric network.
Based on the physical structure of the network -Amorphs -Semicrystallines -Structures by hydrogen bonds -Hydrocolloidal aggregates.
Other behavior
Hydrogels may also exhibit swelling behavior dependent on the external environment, they are then said to be physiologically sensitive hydrogels. Some of the factors that affect the swelling of this type of hydrogels include pH , temperature , ionic strength and electromagnetic radiation .
Hydrogel Applications
Above all, those applications that we can frame in the field of biomedicine stand out.
Contact lenses
For this application it is required that:
The lens must allow oxygen to enter the cornea
- The tear fluid should form a film between the cornea and the lens
- Said lens must resist the force of the eyelid to avoid possible visual instabilities.
The classification of hydrogels for this application is normally done according to their water content, since this characteristic determines the amount of oxygen that they can diffuse.
Tissue prosthetics
The physical properties of hydrogels allow their use in soft tissue prostheses. In brain implants, different hydrogels have been used that act as a substrate for tissue healing and growth, as well as in the encapsulation, transplantation and release of cells and in the regeneration of axons. Collagen and alginate hydrogels have been used in the reproduction of cartilage tissue, in reconstructive surgery of the atrium., obtaining cartilage very similar to the natural ones. Poly (HEMA) has been used in breast prostheses, offering advantages over fatty tissues that tend to be reabsorbed, and other synthetic materials such as silicones, since hydrogels are permeable to body fluids. Poly (vinyl alcohol) hydrogels and interpenetrated hydrogens (IPN), reinforced or not, have better mechanical properties and have been studied as possible substitutes for intervertebral discs, ligaments and tendons .
Human duct prosthesis
Hydrogels have also been used in prostheses of the ureter, bile ducts, and esophagus.
Suture lining
Hydrogels do not have the proper mechanical properties for use in surgical sutures, however, their biocompatibility has allowed their use as a suture coating. The benefits of this coating are manifested in increased cell growth and in the elimination of some harmful effects produced by traditional sutures.
Surgery
Hydrogels have been used when retinal detachment , corneal surgery, and glaucoma correction occur .
Sodium hyaluronate hydrogels have also been used in pelvic and abdominal surgery.
Finally, we can highlight the use of gelatin and polyglutamic acid hydrogels as air hole sealants that commonly appear in chest and lung operations .
Hemodialysis
The hemodialysis is a therapeutic technique which allows the removal of toxins from the blood in patients kidney . Although regenerated cellulose membranes are used in this technique , membranes exhibiting selective permeability have been tested, based on polymers and copolymers of PHEMA, N-vinylpyrrolidone, acrylic acid, and acrylonitrile.
Hemoperfusion
Hemoperfusion is a therapeutic technique used in the treatment of uremic patients. The main problem with this technique is the need for biocompatible absorbents that have some degree of specificity against certain toxins in the blood. Various types of activated carbonthey have a high surface area and have a high adsorption capacity for certain toxins, but they have low compatibility with blood. Hydrogels have been used as a coating material for activated carbon grains, improving their biocompatibility. The hydrogels that cover the activated carbon particles act as membranes, and two types of coating are usually carried out: by impregnation (coating of the surface of the pores) or by encapsulation (total coating of the external surface).
In cancer treatment
Hydrogels can be used to treat diseases such as cancer . The procedure is, in theory, simple. The polymer, in the case of the hydrogel, is loaded with a drug that can be released after detecting external changes (changes in light, temperature or pH). The objective is similar to that used for plants : to achieve more effective time in therapies by controlling the dose (overdoses and “subdoses”) when the body requires it.
Two other properties are also needed. The first is to release the drug only in the areas affected by the disease, that is, “customize the release.” The second is to control the size of the hydrogel so as not to obstruct the blood lines. These two conditions for the use of hydrogels in biomedicine are precisely the two difficulties detected by specialists to achieve their full effectiveness.
Current treatments still fail to differentiate between healthy and diseased cells, so that all are affected by the therapeutic method. And although this first problem can be overcome, there is also another problem that current hydrogels present: their molecular size. The most effective way to administer drugs is through the blood, since the blood reaches the affected areas in a very short time, but you cannot inject very large molecules because they can obstruct the pathways or cause problems in the body, such as angina pectoris and even myocardial acute infarction .