Theoretical Insights into Chlorhexidine Adsorption on Polycaprolactone and Collagen Based Fibers

The interaction of chlorhexidine (CHX) with polycaprolactone (PCL), carboxylated PCL (PCL-COOH), and collagen-containing composite fibers was investigated using density functional tight-binding calculations (DFTB+) to elucidate the mechanisms regulating the immobilization of drugs in antibacterial polymer biomaterials. This work provides an atomistic comparison of adsorption and absorption mechanisms of chlorhexidine in pristine and functionalized PCL matrices and in collagen-PCL composite fibers. On pristine PCL, CHX exhibits moderate adsorption (-0.54 eV), while carboxylic functionalization significantly enhances binding (-1.10 eV) due to hydrogen bonding and increased electronic polarization. At the same time, the higher cohesive stability of the PCL-COOH matrix makes bulk incorporation of CHX energetically unprofitable, limiting sorption mainly by surface adsorption. In contrast, pristine PCL allows both surface adsorption and limited bulk absorption. Modeling of collagen and collagen-PCL composite fibers shows that collagen provides strong binding sites for CHX (-1.06 eV), comparable to those of PCL-COOH and stronger than those of pristine PCL. Frontier orbital analysis and charge density redistribution indicate donor-acceptor interactions in which CHX acts as an electron donor while the collagen matrix serves as the main electron-accepting component. These results suggest that collagen-rich surfaces in composite fibers may provide an effective strategy for immobilizing antibacterial agents in wound-dressing materials.