Page 58 - MSAM-4-2

Materials Science in Additive Manufacturing Fibrous silk in biomedicine

and tissue culture plastic. Specifically, the adhesion of FS biomaterials are urgently required to fully address
strength of tendon cells on FS-RGD increased by 1.3-fold safety concerns regarding their clinical applications.
relative to tissue culture plastic. After 6 weeks, collagen
type I and decorin transcription levels were significantly 3.3. Biodegradation
higher on FS-RGD compared to unmodified FS and tissue The degradation of FS predominantly occurs through
culture plastic. Northern blotting analysis showed that protein hydrolysis and prolonged absorption within
mRNA levels were increased by 2 – 3 times on FS-RGD the body, resulting in a relatively gradual degradation
and FS compared to tissue culture plastic. rate. This gradual degradation allows for sufficient
28
In addition, FS has been explored as a biological mechanical support during cell regeneration and tissue
alternative for ligament reconstruction. Liu et al. repair. Compared with other biological materials, FS
86
constructed FS cables with mechanical properties offers significant advantages in terms of biodegradability.
similar to the human anterior cruciate ligament (ACL), Table 2 presents the biodegradation characteristics of FS,
successfully cultivating human bone marrow stromal stem exhibiting a slow degradation rate (exceeding 12 weeks),
cells (BMSCs) and ligament fibroblasts on these FS cables which ensures long-term mechanical support for tissue
to achieve robust cell adhesion and proliferation. healing. After enzymatic hydrolysis, FS can be absorbed and
utilized by the human body, making it an excellent carrier
85
In another study, Zhou et al. developed an FS/calcium
phosphate cement (FS/CPC) biocomposite, exhibiting material for the controlled release of therapeutic agents.
84
Lee et al. found that when regenerated FS membranes
excellent biocompatibility and osteogenic activity for bone
defect repair. In a rabbit radius defect model, imaging analysis, were implanted subcutaneously in rats, the membrane
thickness gradually decreased, with approximately 65%
histological examination, and scanning electron microscopy of the original thickness remaining after 19 months. In
revealed that the FS/CPC group exhibited early trabecular contrast, widely used synthetic biological materials such
bone formation at 4 weeks, along with significantly higher
maximum bending strength compared to other groups. as polyglycolic acid and polylactic acid produce acidic
by-products upon degradation, which can be harmful
Although the current research is encouraging, concerns after metabolism and absorption by the body. In addition,
remain regarding the long-term safety of FS biomaterials these synthetic materials often experience an early decline
in the human body. First, most biocompatibility studies in mechanical properties during degradation. By contrast,
to date have focused on short- to mid-term periods (3 – the slow degradation rate of FS allows it to maintain good
6 months). Extended studies are necessary to assess the mechanical strength over an extended period.
long-term immune responses to FS biomaterials following
prolonged contact with human tissues. Such studies Research indicates that the degradation rate of FS
should take into account the implantation site and the is primarily determined by its secondary structure,
construct type and utilize appropriate in vivo models for particularly the β-sheet content, which accounts for its
88
comprehensive analysis. Second, the immune reactions slow degradation. In an in vitro experiment, protease
triggered by degradation products of FS biomaterials XIV was used to degrade FS for more than 70 days. It was
– strongly influenced by the size and structure of these found that while the enzyme could degrade FS dissolved
89
products – require further investigation. It is well known in water, it could not degrade FS that had formed a film.
that particulate debris is a major cause of biomaterial This resistance is attributed to the β-sheet structure
implant failure due to the activation of immune responses. shielding enzymatic cleavage sites, thereby extending the
90
Reports by Gellynck et al. suggest that certain FS materials degradation time of FS in the body. Similarly, Lu et al.
87
can induce mild proinflammatory cytokine production demonstrated that FS samples with higher β-sheet content
and enhance phagocytosis. Similarly, digestion of the degraded more slowly, whereas FS with fewer β-sheets
C-terminus of A. pernyi silk by α-trypsin has been shown degraded more rapidly. Furthermore, factors beyond
to reduce cell adhesion and restrict growth, indicating secondary structure – including the FS type, implantation
that degradation can adversely affect FS biocompatibility. site, and in vivo environment – also influence degradation
Furthermore, studies by Lundmark et al. have suggested rates. 91
83
that silk protein degradation products may potentially As a medical biomaterial, the degradation rate of FS
contribute to amyloidosis. Silk fiber solutions have been must align closely with the regeneration and repair rates
found to accelerate the accumulation of amyloid-like of specific tissues, ensuring seamless integration with
substances, leading to tissue degradation. damaged tissues or organs and serving either as a substitute
13
Therefore, comprehensive and long-term investigations or catalyst for regeneration. By adjusting factors such as
into the degradation behavior and immune interactions β-sheet quantity, FS concentration, and implantation site,

Volume 4 Issue 2 (2025) 7 doi: 10.36922/MSAM025130020