Frequently, the human body is susceptible to injuries such as the fracture of one or more of its bones, so it is necessary to use implants or some fixation element to keep the fragments of the fracture together, allowing an orderly repair that facilitates healing or compensates the lack or loss of bone tissue. Temporary orthopedic implants have been used clinically to repair broken or fractured bones during the healing process. The most used are plates, screws, nails, wires, and intramedullary nails. It is usually necessary to perform operations to open the injury site, join the bony pieces with these elements, wait long enough to allow the bones to heal, and then remove them in a second surgery.
In recent years, research has focused on developing biodegradable materials, thanks to the fact that they reduce the need for a second surgical intervention to remove the implant when the tissue is regenerated. Therefore, magnesium alloys have emerged as promising degradable implants due to their characteristic of being easily corroded in aqueous solutions. In addition, magnesium within metallic materials possesses the most similar mechanical properties to those of human bone, such as Young's modulus, compressive strength, and density, significantly reducing the risks of stress shielding and other failures associated with bone implants.
However, the rapid uncontrolled corrosion of magnesium, being associated with the release of hydrogen (H2) that occurs in biological media, is a disadvantage that can lead to some problems such as osteolysis or the formation of spaces between implants and tissues. Therefore, it is still a challenge to define strategies that allow controlling the high rate of degradation of Mg for its applications as biodegradable implants. Strategies have been investigated to control the rate of degradation of these alloys, including microstructural and surface modification techniques.
The first approach involves the alloying of magnesium with relatively noble elements such as Aluminum, Zinc, Manganese, Calcium, Lithium, among others, or physical modifications such as mechanical treatments, manufacture of metallic glasses, or plastic deformations associated with lamination, stretching, or extrusion processes. On the other hand, the second approach involves modifying the surface by performing coatings to control the corrosion rate of metals and their alloys.
One of the surface modification strategies used in this approach is biofunctionalization, a procedure that consists of immobilizing short peptide sequences, oligopeptides, to long peptide chains such as proteins, on the surface of the material, to improve the rate of degradation of metals and cell adhesion. In this technique, the proteins or molecules used have generally been of synthetic origin is common. However, the use of biological materials has begun to increase due to the multiple benefits from the economic point of view, the manufacturing technique, toxicity, and cell biocompatibility.
Due to the above, sources of natural proteins have been sought that can be executed for this process and that, in addition, can provide properties that help in the biocompatibility and corrosion of the implant. Considering these requirements, it was found that the biomass of microalgae is characterized by being a great source of protein, which has been shown to contribute to improving bone regeneration because they stimulate cell growth, adhesion, and proliferation. They have anti-inflammatory, antibacterial, antimicrobial, antioxidant, and healing properties. And they do not trigger immune responses due to their high compatibility.
On the other hand, microalgae extracts, and biomass are being implemented as corrosion inhibitors, as they have excellent bioactive compounds that protect metal surfaces by forming a stable inhibition layer. Where the percentage of protein contained in the biomass is directly proportional to the efficiency of the inhibitor, suggesting that protein macromolecules are probably responsible for the inhibitory action observed by the biomass of microalgae. The foregoing is supported by the fact that the protein has functional groups with different degrees of polarity such as amino, carboxyl, and hydroxyl groups, which have been determined to inhibit corrosion.
Another advantage of using microalgae is that they are found in varied ecological environments, freshwater, or marine habitat, and can adapt to any condition of temperature, pH, and amount of nutrients, in the same way, they are characterized by their high growth rate in contrast to terrestrial plant.
According to the literature review carried out, no studies have yet been reported on the use of microalgae as biomolecules for functionalization on metallic substrates and there are few studies on microalgae focused on the bone system and as corrosion inhibitors for metals (magnesium). Therefore, it is proposed to biofunctionalized a magnesium surface with the biomass of Chlorella sp., to improve resistance to Mg corrosion and promote osseointegration. This experimentation has been divided into three stages: activation, silanization, and immobilization of the microalgae; These will be characterized using electrochemical tests (EIS-TAFEL), atomic absorption, SEM, XRD, and cytotoxicity study. As a result, the biofunctionalized material is expected to exhibit a better degradation rate and higher cell adhesion than the base material.
