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Nanotechnology has not only attracted attention in the field of drug delivery, but also achieved many successes in the field of tissue engineering. Nano dressing can be defined as a dressing of nanomaterials as a matrix. The birth of nano dressings brings new treatments for wound repair and burn care, such as nano hydrogels, nanofibers, nanofilms, dendrimers, and polymer conjugates (acting as the drug release during wound treatment, growth factor supplementation and artificial skin). The role of nano dressings includes antibacterial and anti-inflammatory, acting on tissue functional cells, optimizing matrix improvement, and promoting stem cell proliferation and differentiation.
Characteristics of nano dressings
The important function of the dressing is to replace the damaged skin or tissue. The dressing is a medical material that promotes wound healing and tissue repair, such as gauze, bandages and sponges. Ideal dressings should have the following functions in application: resist mechanical factors (such as dirt, collisions), resist pollution and chemical stimuli, prevent double infections (such as inflammation); prevent dryness and loss of body fluids (electrolyte loss); prevent heat loss, actively affecting the wound healing process through debridement; and create a microenvironment that promotes wound healing. The special physicochemical properties of nano dressings make it superior to traditional dressings in tissue repair and wound treatment, specifically:
- It is equivalent to the diameter of natural tissue fibers;
- With diverse forms and a wide range of choices, including nanoparticles, nanocrystals, nanotubes, nanofibers, nanofilms;
- The specific surface area is very large and the adsorption performance is good;
- It has high mechanical strength, light weight, and can reduce the squeeze of the wound;
- Itself can be antibacterial;
- It can embed or load drugs, growth factors, proteins, etc., and play a role of slow release.
The large specific surface area and the porous structure can greatly improve the contact area or probability of the nano dressing with the cells or tissues, so that the nano dressing can easily enter the wound tissue cells or stay in the cells to regulate the biological signals, and promote the cell growth, proliferation and differentiation before tissue repair process. Nano dressings also improve the local microenvironment of tissue cell growth, regulate and optimize the formation of extracellular matrix, promote tissue cell regeneration and migration to the wound, and create conditions for post-repair tissue remodeling. For more serious tissue defects or injuries that cannot be repaired quickly under natural conditions, the application of nano dressings to the wound provides a “platform” for the migration and colonization of surrounding normal cells to the defect area, accelerating the growth of regenerating cells and secretion of the matrix to promote the repair of defects. In the treatment of burns, it is necessary to cover a large area of wounds with as little therapeutic material as possible to protect the skin and promote wound healing. Nano dressings meet this requirement.
Nano dressings also provide a support for tissue engineered skin implants. Wounded skin often loses the epidermal layer that constitutes a mechanical barrier. Nanofibers provide good mechanical support while achieving therapeutic effects.
The chemical drug or bioactive molecule can be embedded in the nano dressing and released into the wound tissue by dissolution of pores or materials in the dressing. By adjusting the porosity of the nano dressing and the composition and structure of the nanofibers, the release rate of the active molecules can be controlled. The sustained-release property not only avoids the toxicity of local high-concentration drugs, but also ensures the persistence of the drug in the damaged area and the stability of the drug, further promoting the regeneration and repair of damaged cells. Nano dressings can also carry adult stem cells and progenitor cells, and continue to release “seed cells” to the defect and differentiate them into adult cells, accelerating the regeneration and tissue repair of defective cells.
The molecular structure of the polymer is diverse (such as linear, star, tree and hyperbranched), and there are many surface binding sites, which are easily combined with active molecules. The surface of the polymer is modified by functional groups and can be coupled with antibacterial drugs to kill or inhibit various chronic wound-infecting microorganisms such as Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. Polymer drug conjugates, polymer protein conjugates, polymer micelles and the like have been used as drug carriers for tissue repair and wound care. The composition of polymer protein growth factor can produce good interfacial interaction with the wound microenvironment, and has important application value in the field of tissue repair. According to the actual needs of wound care and tissue repair, the best results can be obtained by controlling the physical properties (rheological, hydrophilic), mechanical properties (plasticity) of nano-dressings, and introducing active ingredients.
Nano silver dressing
The ions of various metals have antibacterial action, and the order of antibacterial action is: Ag>Hg>Cu>Cd>Cr> Ni> Pd>Co>Zn>Fe. However, Hg, Cd, Pd and Cr have residual toxicity to human body, and ions of Ni, Co and Cu have dyeing effect on objects. In fact, the commonly used metal antibacterial agent is silver antibacterial agent. Metallic silver-based external preparations have long been used in a wide range of aerobic and anaerobic microbial broad-spectrum antibacterial agents. At low concentrations, silver cations (Ag+) have inhibitory effects on many pathogens (bacteria, viruses, eukaryotes, etc.) and are often used in ulcer care and public health.
Nano-inorganic antibacterial agents, due to quantum effects, small size effects and extremely large specific surface area, have antibacterial effects unmatched by conventional antibacterial agents, while having high safety and long-lasting efficacy. The antibacterial properties of nano-silver are far greater than traditional silver antibacterial agents. Nano-silver is widely used as an antibacterial material in medical catheters, surgical instruments, dental antibacterial materials, reproductive health and family planning appliances, and wound dressings. Evaluation of the safety of nano-silver dressings is a key step in its clinical entry. After local or systemic absorption of silver, it may cause cytotoxicity. Increasing the interaction between the medical dressing carrier and the nano-silver and properly controlling the slow release rate of the nano-silver can help to effectively reduce the toxicity of silver. Through the cooperation of the polymer carrier and the nano-silver, the stability of the nano-silver can be controlled, and the scale and morphology of the nano-particle can also be controlled. By using the environmentally sensitive response of the polymer matrix, controlling the change of the dressing structure, realizing the controlled release of nano-silver, reducing the dose of nano-silver acting on the wound surface, and improving the durability of the action and the efficiency of the nano-silver, it can effectively improve the safety of silver-containing materials.
References
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Mohan Y M, Vimala K; Thomas V. et al. Controlling of silver nanoparticles structure by hydrogel networks. J Colloid Interface Sci, 2010, 342: 73-82.