Enzymatic degradation of dimensionally constrained polyhydroxybutyrate films

Abstract

The effect of dimensional constraint, imparted by a variation in film thickness, on the enzymatic degradation of polyhydroxybutyrate (PHB) is reported. The characterization of the crystalline structure and the surface topography of solvent-cast PHB thin films revealed strong correlations between film thickness and both crystallinity and crystal anisotropy, with the polymer film becoming more amorphous with decreasing thickness. The enzymatic degradation of the PHB films was characterized using a high precision diffraction metrology, which enabled the visualization of small variations in the degradation behavior. The results show that the degradation rate increases with decreasing thickness due to the corresponding decrease in crystallinity. However, in a nanoscopic ultra-thin PHB specimen, produced by μ-transfer molding, enzymatic degradation was impeded. The enzymatic degradation rate of the PHB films therefore was found to exhibit a discontinuous trend with respect to film thickness: initially increasing as film thickness was reduced, and then decreasing dramatically once the thickness was reduced to tens of nanometers. In this regime, enzymatic degradation was hindered by the absence of crystalline regions in the films. These results show that a nano-dimensional constraint on PHB films can result in specimens with a tunable response to extracellular enzymes.

Influence of Depolymerases and Lipases on the Degradation of Polyhydroxyalkanoates Determined in Langmuir Degradation Studies

“…[ 46,47 ] In a more recent study, a crystallizable form of PHB was constrained in two dimensions to obtain amorphous (40–50 nm thickness) and semicrystalline (150 nm thickness) films. The former were resistant to short‐term degradation by a PHB depolymerase from Comamonas testosteroni over a period of 4 h. [ 48 ] Conversely, our study demonstrates that the depolymerase S. exfoliatus K10 does not necessarily bind to crystalline domains in PHAs.…”

Enzymatic Hydrolysis of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) Scaffolds

“…The hydrolysis and enzymatic degradation of PHAs are dependent on their chemical structure and physical properties such as morphology, sample dimensions, molecular weight, and crystallinity [43][44][45]. The degradation process of the PHA scaffolds was monitored by scanning electron microscopy, differential scanning calorimetry, SEC-MALLS, and gravimetrically.…”

Formation of Mesomorphic Polymorph, Thermal-Induced Phase Transition, and Crystalline Structure-Dependent Degradable and Mechanical Properties of Poly(p-dioxanone)

“…In general, the degradation rates of aliphatic polyesters drop with increasing X c and lamellar thickness, − because the amorphous phase can be more readily degraded than the crystalline phase. We proposed that the unique T c -dependent degradation kinetics of PPDO could be attributed to two aspects.…”