Distinct Effects of Heparin and Interleukin‐4 Functionalization on Macrophage Polarization and In Situ Arterial Tissue Regeneration Using Resorbable Supramolecular Vascular Grafts in Rats

Abstract

Two of the greatest challenges for successful application of small‐diameter in situ tissue‐engineered vascular grafts are 1) preventing thrombus formation and 2) harnessing the inflammatory response to the graft to guide functional tissue regeneration. This study evaluates the in vivo performance of electrospun resorbable elastomeric vascular grafts, dual‐functionalized with anti‐thrombogenic heparin (hep) and anti‐inflammatory interleukin 4 (IL‐4) using a supramolecular approach. The regenerative capacity of IL‐4/hep, hep‐only, and bare grafts is investigated as interposition graft in the rat abdominal aorta, with follow‐up at key timepoints in the healing cascade (1, 3, 7 days, and 3 months). Routine analyses are augmented with Raman microspectroscopy, in order to acquire the local molecular fingerprints of the resorbing scaffold and developing tissue. Thrombosis is found not to be a confounding factor in any of the groups. Hep‐only‐functionalized grafts resulted in adverse tissue remodeling, with cases of local intimal hyperplasia. This is negated with the addition of IL‐4, which promoted M2 macrophage polarization and more mature neotissue formation. This study shows that with bioactive functionalization, the early inflammatory response can be modulated and affect the composition of neotissue. Nevertheless, variability between graft outcomes is observed within each group, warranting further evaluation in light of clinical translation.

Marker-Independent Monitoring of in vitro and in vivo Degradation of Supramolecular Polymers Applied in Cardiovascular in situ Tissue Engineering

“…We have previously reported on the use of Raman microspectroscopy as a complementary method to evaluate the local balance between scaffold degradation and neotissue formation in in situ tissue-engineered heart valves ( 15 ) and arteries ( 5 ). In the current study, we specifically investigated whether the modus of degradation (i.e.…”

“…Therefore, in the present study, collagen spectra were extracted from the TCA images of the scaffold regions and compared to collagen signatures of newly formed tissue layers. Conventional methods to assess collagen deposition include histochemical or immunohistochemical staining ( 5 ) or can even be marker-independent when imaging collagen autofluorescence in SHG microscopy ( 4 ). In contrast to quantitative information, these methods are limited in their capability to address qualitative changes in structural composition of collagen fibers.…”

“…Similar to infrared spectroscopy, which has been applied in a few studies to investigate in vitro as well as in vivo polymer degradation ( 18 – 20 ), Raman microspectroscopy allows for the non-destructive detection of molecular changes in both, synthetic as well as biological molecules, and in addition enables the simultaneous visualization of their spatial distribution in Raman imaging setups. In comparison to local polymer degradation, extracellular matrix formation and cellular infiltration in in situ tissue engineering can be studied at a spatial resolution by histological methods ( 21 , 22 ), and were also in the focus in previous publications on in situ tissue-engineered heart valves and carotid implants, where Raman imaging was implemented as complementary method to routine histochemical and immunofluorescence staining ( 5 , 15 ).…”

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

“…PCL is the dominating polymer among the newer scaffolds that are explored for the regeneration of vessels ,,,,− and is preferred because of its mechanical properties (ductility), suturability, and absence of graft dilation. To compensate for its slow degradation rate, it is combined with other polymers.…”

“…When modified with palmitic acid, the biodegradation rate of PGS was decelerated and the performance of the grafts was improved (Figure ). Antithrombogenic polymers or biological molecules have also been tested in vivo with success, namely as an inner layer of POC or functionalization with heparin. , …”