In the current study, we introduced a new water‐soluble polyphosphazene containing hydroxyl groups, poly(propyleneglycol)phosphazene (PPGP). The PPGP is converted to PPGP‐TiO2 cross‐linked polymer via hydrothermal reaction with Ti(OBu)4. The properties of the obtained polymers were assessed by 1H‐NMR, 31P‐NMR, Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) spectroscopic methods, thermal techniques (DSC‐TGA), FESEM–EDX investigations, cyclic voltammetry (CV) and Zeta potential measurements. In order to predict PPGP‐TiO2 cross‐linked polymer structure and obtain HOMO–LUMO maps and COMSO sigma profile, quantum calculations were used by DMol3 module based on Dispersion‐corrected density functional theory (DFT‐D) in Materials Studio Software2017. As a common bone substitute material, hydroxyapatite (HAp) was prepared using a modified method and closely characterized by appropriate analysis. The PPGP cytotoxicity was examined using C2C12 and L929 cell lines and Escherichia coli. The C2C12 differentiation using PPGP (as media supplement) was quantified by alkaline phosphatase activity assay. The biocompatibility of PPGP‐TiO2 was compared with HAp using mentioned cell lines and acute inflammatory testing. The results demonstrated that cell proliferation and osteoblastic differentiation increased in presence of PPGP. Both in vitro and in vivo evidence indicated that the novel scaffold had significant viability, exhibiting notable adaptability with its surrounding living tissue.

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With more than two years in COVID-19 pandemic, the underlying virus is mutating which indicates it is not over yet hence SARS-CoV-2 Spike RBD is a potent candidate for immunological development purposes. Here, we produced a recombinant-RBD protein from micro- to macro-scale production by Pichia pastoris with high purity that was assessed by immunological tests. A recombinant-RBD compromising 283 residues (31kDa) was constructed after epitope analyses. The target gene was initially cloned into Escherichia coli Top10 genotype and transformed into Pichia pastoris CBS7435 muts for protein production. The production was scaled-up in a 10L fermenter after 1L shake-flask cultivation. The product was ultrafiltered and purified using ION-Exchange chromatography. IgG-positive human sera for SARS-CoV-2 were employed by ELISA test to evaluate the antigenicity and specific binding of the produced protein. Bioreactor cultivation yielded 4g/L of target protein after 160 hours fermentation, and ion-exchange chromatography indicated a purity of > 95%. Human serum ELISA test performed in four parts (1–4) and ROC curve area under curve (AUC) was > 0.96 for each part. The mean specificity and sensitivity of each part was (100, 91.5) respectively. In conclusion, the recombinant-RBD can be used for IgG-based serologic kit and preventive purposes for patients with COVID-19 infection.