Production of Spontaneous Antibacterial Cryogels
Antibiotic resistance is one of the biggest challenges in treating bacterial infections. Apart from
this, frequent nosocomial infections cause many complications, especially in inpatients.
According to the report of Centers for Disease Control and Prevention in 2019, more than 700
thousand people die every year due to bacterial infections worldwide. This situation led to the
development of alternative solutions.
Perhaps the most promising of these solutions is antibacterial materials. Antibacterial hydrogels, which are frequently studied in the literature, are used in many areas such as waste disposal, water treatment, surface coating, especially in the biomedical field.
In this study, it is proposed to produce a hydrogel with inherent antibacterial properties.
It is thought that it will gain high biocompatibility with the N-2-hydroxypropyl methacrylamide
(HPMA) it contains and thus it will be suitable for use in various tissue engineering studies,
especially in wound dressing.
The quaternized 4-vinylpyridine in its structure will provide a positive charge of the polymer. Thus, it is predicted that the material will kill the bacteria by the contact-active mechanism by providing the disintegration of the negatively charged bacterial wall. By choosing the cryogelation method for production, it is aimed that the hydrogel to be obtained has a macro-porous structure.
Thus, it will be able to absorb and kill bacteria cells like a sponge. Unlike hydrogels that release antibacterial agents (biocides) to the environment, it is thought that the toxicity that will occur in the tissue with the antibacterial mechanism will be at a minimum level, thanks to the positive charges in its structure.
The cryogel we recommend in this study is aimed at reducing bacterial infections, preventing
diseases transmitted by contact in public places and treating antibiotic-resistant bacterial
infections more easily.
If it is used as a wound dressing, it will prevent additional infections by
providing antibacterial activity around the wound, so that the tissue heals faster.
It is thought to contribute to water purification or disinfection when it is used in water treatment or disinfection,
and when applied as a surface coating material to various medical devices, it will prevent bacterial biofilm formation and reduce hospital infections.
Literature Review
Hydrogel is a hydrophilic, water-insoluble polymeric macromolecule with high water absorption capacity, can be used in many biomedical fields, porous, flexible, cross-linked polymer chains that can be produced in a wide variety of chemical and physical properties [1-3].
It can be used in the cleaning and purification of water from bacteria, as a tissue scaffold and wound dressing material in tissue engineering, in the removal of chemicals from the environment, in purification processes and in the medical field by gaining antibacterial properties [3, 4].
Antibacterial hydrogels
Antibacterial hydrogels have been an alternative solution developed by researchers especially against antibiotic resistance.
Thanks to the fact that no drugs such as antibiotics are used in the material, resistance does not occur and an effective antibacterial mechanism is formed.
Antibiotic-resistant bacteria, the number of which is increasing, cause the death of more than 13 million people in the world every year with the infections they create [5].
The seriousness of the issue has increased the importance of antibacterial material studies.
Quaternized ammonium groups are frequently used in antibacterial hydrogels because they can break down the negatively charged bacterial wall thanks to their positive charge.
In particular, polymers containing quaternary ammonium groups are used in the production of self-antibacterial hydrogels [6]. 4-vinylpyridine gains antibacterial properties by being positively charged with the quaternization of the tertiary amine group it contains.
N-2-hydroxypropyl methacrylamide (HPMA) is another polymer used in both drug delivery and antibacterial hydrogel applications.
It provides a great advantage due to its biocompatibility [7]. In this study, two polymers will be used by making copolymers with each other.
Thus, the hydrogel to be obtained will both show antibacterial properties and be biocompatible.
The hydrogel, which is aimed to have a contact active mechanism, must be macroporous in order to trap bacteria in its pores. For this reason, the cryogelation method was chosen for the production of the gel.
Cryogelation is the simultaneous cross-linking of polymer in solution at very low temperatures.
It is the ice crystals that freeze in the spaces between the polymers and act as a porogen [8].
With the thawing process after cryogelation, the frozen solution will melt and a macroporous cryogel will emerge. In our study, it was planned to remove the water by drying the frozen gel.
As a result of the study, the above mentioned items
A cryogel with high biocompatibility, non-toxic, macroporous, self-antibacterial and effective mechanism will be obtained by utilizing its properties.
Hypothesis
Antibiotic resistance is one of the biggest problems in the treatment and prevention of bacterial infections.
An average of 13 million people die each year due to bacterial infections.
For this reason, different methods are sought to prevent or treat infection.
Studies on antibacterial materials have revealed promising results in this context.
In this study, macroporous quaternized 4-vinylpyridine (4-VP) and
It has been proposed to produce a positively charged cryogel containing N-2-hydroxypropyl methacrylamide (HPMA) copolymer.
In this context;
- 4-VP can show different chemical and morphological properties as the pH value of the environment it is in changes. The tertiary amine group in the pyridine ring can be made positively charged at acidic pHs and also by quaternization with various agents. In this study, it is predicted that the cryogel will gain antibacterial properties by being quaternized and positively charged.
- N-2-hydroxypropyl methacrylamide (HPMA) is one of the most widely used hydrophilic polymers in biomedical studies.
It was preferred in the thesis study because of its important features such as showing high biocompatibility, non-toxic effect and reducing surface adsorption. Since 4-VP has a toxic effect when used alone, it was thought that a material with low toxicity would be obtained by synthesizing it as a copolymer with biocompatible HPMA. - 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) is a water-soluble crosslinking agent that activates carboxyl and amine groups. It reacts at both room temperature and sub-zero temperatures. Since there is no mediator during crosslinking, the formation of unwanted side groups is prevented. In this study, EDC will perform crosslinking by linking the -COOH groups at the end of the quaternary pyridine ring and the amine groups of ethylene diamine in the medium. In addition, since cryogelation will be used as the production method, the operating temperature of the EDC is also suitable for this reaction temperature.
- Cryogelation was chosen as the production method.
This is because hydrogels produced by cryogelation have macroporous structures.
Since the cryogel we proposed in the study is designed to kill bacteria by trapping, the pore size of the gel should be macro-sized. In this way, it is thought that the desired feature will be achieved.
At the same time, with this process, the liquid absorption capacity of the cryogel will be higher than that of hydrogels.
What is Hydrogel?
Hydrogels have been defined as hydrophilic, water-insoluble polymeric macromolecules.
They are also known as semi-open network systems consisting of entangled or short chains of varying lengths connected by cross-links [1].
In other words, materials obtained by the polymerization of hydrophilic monomers in the presence of crosslinkers or by cross-linking polymer chains with water-loving structure are called hydrogels[2].It was first reported by Wichterle and Lim in 1960. By definition, for a material to be considered a hydrogel, its water content must constitute at least 10% of the total weight (or volume).
Hydrogels also have a similar degree of flexibility to real tissue due to their high water content [3].
Hydrogels are also found in nature.
For example, bacterial biofilms and vegetative structures are motifs that can be found all over nature and contain high amounts of water.
Gelatin and agar are important materials known to be used in ancient times of human history [4].
When exposed to a thermodynamically suitable solvent (water or any biological fluid), these materials, which can hold a large amount of solvent in their pores or in the interstitial spaces in their structure, can reach their maximum dimensions by swelling completely [1].
Hydrogels undergo a pronounced volume phase transition or gel-sol transition in response to certain physical and chemical stimuli.
These physical stimuli; temperature, electric and magnetic field, solvent content, light intensity and intensity, while chemical (or biochemical) benefits can be listed as pH, presence of ions and special chemicals[3].
In most cases, the conformational changes of the hydrogel are reversible.
In other words, after a reaction in which the stimulus is removed, the hydrogel material can return to its original state.
The response to external stimuli depends on the nature of the monomer in the material, the charge density, the presence of chains, and the degree of cross-links [3].
The hydrophilic nature, water absorption capacity and stiffness of hydrogels depend on the presence of hydrophilic side groups in the main chain (backbone) of the molecule.
For example, alcohol, carboxylic acid (-COOH), amide (-CONH2), amino (-NH2) and sulfonic acid (-SO3H) groups can be given [1]
The characteristic properties of hydrogels
The characteristic properties of hydrogels, such as desired functionality, reversibility, sterilizability, and biocompatibility, meet both biological and material requirements for tissue/organ therapy and interaction with biological systems [4].
In addition, thanks to these properties, it is possible to use hydrogels in water purification, ion exchange chromatography, oil recovery, sensor industry, immobilized enzyme industry, agriculture, food packaging, pharmacy and biomedical fields.
Despite the advantageous properties such as hydrophilicity, swelling ability, gelability, mechanical strength, porosity, and biocompatibility, hydrogels also have some disadvantageous properties [1].
Factors such as low solubility, high crystallization, some undesirable mechanical and thermal properties, the presence of unreacted monomers and the use of toxic crosslinkers limit the use of hydrogels.
The biodegradability of the hydrogel depends on the monomer used and the type of bond. For this reason, the biodegradability of hydrogels varies according to the purpose for which they will be used [4].