Atomic modeling for the initial stage of chromium passivation

The well-known anti-corrosive property of stainless steels is largely attributed to the addition of Cr,which can assist in forming an inert film on the corroding surface.To maximize the corrosion-resistant ability of Cr,a thorough study dealing with the passivation behaviors of this metal,including the structure and composition of the passive film as well as related reaction mechanisms,is required.Here,continuous electrochemical adsorptions of OH-groups of water molecules onto Cr terraces in acid solutions are investigated using DFT methods.Different models with various surface conditions are applied.Passivation is found to begin in the active region,and a fully coated surface mainly with oxide is likely to be the starting point of the passive region.The calculated limiting potentials are in reasonable agreement with passivation potentials observed via experiment.

Physical modification of polyetheretherketone for orthopedic implants

Polyetheretherketone （PEEK） is regarded as one of the most potential candidates for replacing current implant applications. To obtain good bone-implant interfaces, many modification methods have been developed to enable PEEK and PEEK- based composites from bio-inert to bioactive. Among them, physical methods have aroused significant attention and been widely used to modify PEEK for orthopedic implants. This review summarizes current physical modification techniques of PEEK for orthopedic applications, which include composite strategies, surface coating methods and irradiation treatments. The positive consequences of those modification methods will encourage continuing investigations and stimulate the wide range of applications of PEEK-based implants in orthopedics.

In vitro and in vivo evaluation of bone morphogenetic protein- 2 （BMP-2） immobilized collagen-coated polyetheretherketone （PEEK）

Polyetheretherketone （PEEK） is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 （rhBMP-2） was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydroph（bic interaction, collagen was cross-linked with N-（3-dimethylaminopropyl）-N＇-ethyl carbodiimide hydrochloride （EDC） and N-hydro xysuccinimide （NHS）. EDCINHS system also contributed to the immobilization of rhBMP- 2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.

Anti-viral memory T cell responses in the absence of IgG production in a COVID-19 convalescent individual

Cellular and humoral immunity are both important in host defense against severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).Although defects in SARS-CoV-2-specific T cell immunity have been found in patients with severe lung pathology,it is still largely unclear whether virus-specific T cells are sufficient for host protection.Here,we found that in a previously characterized cohort of convalescent subjects,one individual,though lacking detectable anti-viral neutralizing IgG antibodies,showed virus-specific T cell responses,both in CD4^(+)and CD8^(+)T cells.SARS-CoV-2-specific T cells in this and other individuals are maintained for up to 10 months.This study thus further supports a critical role of T cells in host defense against SARS-CoV-2,offering new insights into the design and evaluation of COVID-19 vaccines.