Quantitative Characterization of Collagen in the Fibrotic Capsule Surrounding Implanted Polymeric Microparticles through Second Harmonic Generation Imaging

Abstract

The collagenous capsule formed around an implant will ultimately determine the nature of its in vivo fate. To provide a better understanding of how surface modifications can alter the collagen orientation and composition in the fibrotic capsule, we used second harmonic generation (SHG) microscopy to evaluate collagen organization and structure generated in mice subcutaneously injected with chemically functionalized polystyrene particles. SHG is sensitive to the orientation of a molecule, making it a powerful tool for measuring the alignment of collagen fibers. Additionally, SHG arises from the second order susceptibility of the interrogated molecule in response to the electric field. Variation in these tensor components distinguishes different molecular sources of SHG, providing collagen type specificity. Here, we demonstrated the ability of SHG to differentiate collagen type I and type III quantitatively and used this method to examine fibrous capsules of implanted polystyrene particles. Data presented in this work shows a wide range of collagen fiber orientations and collagen compositions in response to surface functionalized polystyrene particles. Dimethylamino functionalized particles were able to form a thin collagenous matrix resembling healthy skin. These findings have the potential to improve the fundamental understanding of how material properties influence collagen organization and composition quantitatively.

Molecular and tissue alterations of collagens in fibrosis

“…The lack of SHG signal from collagen IV results from the centrosymmetric arrangement of this non-fibrillar collagen [225]. A polarization-resolved SHG microscope has been used to distinct peaks corresponding to collagens I and III in normal human skin [233]. SHG and a phasor approach to fluorescence lifetime imaging allow to separate pixels having different fluorescence lifetimes.…”

Collagen I in the hip capsule plays a role in postoperative clinical function in patients with developmental dysplasia of the hip

“…The major types of collagen in the hip joint capsule are I and III (9,25). Three variations in the COL1A1 gene promoter have been reported in patients with DDH, and a higher rate of total variation in the COL1A1 gene contributes to DDH (26).…”

pH responsive gels that deliver anti-inflammatory drugs

“…Inflammation and formation of the fibrotic capsule were two of the first markers of the host response observed. 99,100 Eventually it became essential to define the fibrotic response as beneficial or inhibitory. Depending on the location of the implants, surface properties, material types, and time-scales over which the studies were conducted, the extent of the host response was found to vary greatly.…”