1.2.1 Hydroxyapatite (HAp)
HAp chemical nature is calcium phosphate and it is retrieved from varied sources which includes mammalian sources such as bone from camel, bovine, horse, marine sources like fish scale, shells, marine plants, algae, and mineral sources. Certain red algal forms such asPhymatolithon calcareum (Kusmanto et al., 2008), Amphiroa ephedra (Oliveira et al., 2007) have calcium carbonate in their structure and are precursors of Hap.
Hydroxyapatite is a biocompatible, porous, renewable and bioactive polymer and has been used as bone filler material. HAp can be mixed with a polycaprolactone to manufacture mechanically strong and porous scaffolds. Hydroxyapatite prepared from aquatic sources is thermostable at higher temperatures of 1200°C (Piccirillo et al., 2013). Hydroxyapatite (HAp) provides efficient absorption surface for functional biomolecules such as protein, DNA and so on and it influences the HAp surface electronic state. Surface electrical properties of HAp such as resistivity and capacitance can be useful as receptors and transducers of biosensors.
1.2.2. Marine Calcium carbonate (CaCO3 or calcite):
Calcite is a precursor molecule for hydroxyapatite and isolated from different marine corals (Lithothamnion glaciale , Coralline officinallis, and Phymatholithon calcareum ), calcifying algae, sponges, echinoderms, foraminifera, mollusks (Ostrea sdulis, Pinctada maxima, Mytilus galloprovincialis ) bryozoans, fish bones, and Crustaceans shells (Andersson & Gledhill, 2013). Calcite has a resemblance to trabecular bones and suitable for orthopedics and dentistry (Srivastava et al., 2015). It has an advantage of porosity and pore interconnectivity as well as a demerit of fast dissolution and poor structural stability (Ben-Nissan, 2003).
1.2.3. Biosilica:
Biosilica is formed by biomineralization of silica known as frustules and formed by sponges, diatoms, radiolarians, and choanoflagellates (Schröder et al., 2008). The silica frustule structure varies in diatom species. There are approximately 3000 species of diatoms with silica exoskeleton. Some of them are Aulacoseria ambigua ,stephanodiscus minutulus , Melosira undulata, andCocconeis placentula . Diatom silica has advantages of high surface area, porous, chemically inert, biocompatible, thermomechanical stability, lightweight, optophotonics features and it acts as ideal biomaterial for tissue designing, drug deliverables, and biosensors. The addition of various metals in silica frustules improves its physiochemical attributes as nanomaterial.
Delasoie and Zobi (2019) revealed the application of biosilica frustule of genera Aulacoseira graulata as drug delivery vehicles to colorectal cancer cells. Other diatom species such asThalassiosira weissflogii, Coscinodiscus concinnus, Thalassiosira pseudomonas and Nitzschia species also can deliver drugs andPhaeodactylum tricornutum, and Odontella are considered suitable for semiconductors (Tramontano et al., 2020). Surface functionalization as well provides a unique opportunity for sustained and controlled drug release capacities and delivery potential.