Immune system’s contribution to the body’s response to material / how do materials interact with the blood

As foreign objects, foreign body reaction (FBR) is undoubtedly cannot be avoided to talk about. Immune system plays an important role to protect the body from foreign objects by recognizing and responding to antigens, which is actually a process of communication as well. And this reaction ranges from mild inflammation to severe reaction, have both the acute (predominantly inflammatory) and chronic(fibrotic) stages. The image given below explains the whole time-table after implantation.

Figure 10. All FBR events after implanted biomaterials. (Carnicer-Lombarte et al., 2021)

Acute inflammation

The acute phase began immediately after implantation. Tissue damage to the body and the release of blood at the time of implantation triggers the immediate accumulation of inflammatory-mediating cells and which called Vroman effect. After a few minutes, neutrophils adhere to proteins and release factors that promote the inflammatory process, such as proteolytic enzymes, which allow monocytes to differentiate into macrophages. Macrophages also release proinflammatory factors such as TNFα (tumor necrosis factor α) and interleukins IL-1b, IL-6 and IL-8. (Carnicer-Lombarte et al., 2021) This acute inflammation will develop into FBR, and the reaction will end if macrophages are successfully degraded, if not, we need to take further action, as explained later. According to Klopfleisch & Jung (2016), magnesium alloy stents we discussed, does not stimulate more adverse inflammation because they are different from ordinary corrosive metals.

Chronic inflammation

The chronic phase of FBR is an inflammatory to fibrotic process in which the implant is encapsulated in a layer of fibrous tissue. During the development of macrophages (switching from a pro-inflammatory activation phenotype (M1 macrophages) to an anti-inflammatory and tissue generating phenotype (M2 macrophages)), which means the elimination of the process of foreign threats to the healing tissue. M2 macrophages reduce the activity of inflammation by releasing anti-inflammatory cytokines such as IL-10, TGF-β attracts local fibroblast populations and promotes differentiation into myofibroblasts after activation to promote wound healing. It is important to note that after the FBR enters the chronic phase, it will remain active indefinitely unless the implant is destroyed or removed. (Carnicer-Lombarte et al., 2021)

Biomaterial with Blood

Materials can interact with blood in various way after be implanted. Blood and biomaterial interact, including protein adsorption, platelet adhesion and activation, thrombosis formation and so on. Firstly, plasma proteins and platelets and materials are quickly adsorbed, resulting in activation, and adsorbed proteins can catalyse and produce biological reactions to materials, and then platelet formation of thrombosis prevents blood contact. (Xu et al., 2014), and it’s called Vroman effect. Plasma proteins can rapidly adsorb onto the surface of biomaterials and form a membrane and which can minimize the direct effect between the surface and cells’ responses.

Basically, more biocompatible materials are less likely to cause adverse immune response.

Figure 11. The interaction between biomaterial and body influenced by proteins and surface property. (Xu et al., 2014)