Poly-2-methyl-2-oxazoline–modified bioprosthetic heart valve leaflets have enhanced biocompatibility and resist structural degeneration

Synthesis and Polymerization of Thiophene-Bearing 2-Oxazolines and 2-Oxazines

Intrinsically conductive polymers have garnered a great deal of attention for use in medical and bioelectronic applications. Despite this, challenges associated with the mechanical stability, processability, and fabrication of conducting polymers have limited their utility. To circumvent these limitations, thiophene substituted 2-oxazolines (2Ox) and 2-oxazines (2Ozi) are introduced, which can be polymerized to form a thermally stable and potentially melt-processable polymers as precursors for conductive polymers. A series of such monomers are synthesized and yields above 50% are obtained for gram scale reactions. The monomers can subsequently be polymerized using standard cationic ring-opening methods to yield thiophene-bearing poly(2-oxazoline)s (POx) and poly(2-oxazine)s (POzi) with narrow to moderate dispersity. The polymers exhibit glass transition temperatures between 50 °C and 100 °C and thermal stability beyond 250 °C. Moreover, random copolymers can be produced by introducing aliphatic 2-oxazolines during polymer synthesis, which facilitates tailoring of the polymer properties and may enable new applications in melt extrusion printing or electrospinning of precursors for conducting polymer systems. Overall, a facile approach is described for the synthesis of thiophene-functionalized monomers and polymers, providing covalent integration of thiophenes that opens new avenues toward the generation of functional and stimuli-responsive biomaterials.

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn-Mark-Houwink-Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M-0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG.

Bioprosthetic heart valve structural degeneration associated with metabolic syndrome: Mitigation with polyoxazoline modification

Bioprosthetic heart valves (BHV), made from glutaraldehyde-fixed xenografts, are widely used for surgical and transcatheter valve interventions but suffer from limited durability due to structural valve degeneration (SVD). We focused on metabolic syndrome (MetS), a risk factor for SVD and a highly prevalent phenotype in patients affected by valvular heart disease with a well-recognized cluster of comorbidities. Multicenter patient data (N = 251) revealed that patients with MetS were at significantly higher risk of accelerated SVD and required BHV replacement sooner. Using a next-generation proteomics approach, we identified significantly differential proteomes from leaflets of explanted BHV from MetS and non-MetS patients (N = 24). Given the significance of protein infiltration in MetS-induced SVD, we then demonstrated the protective effects of polyoxazoline modification of BHV leaflets to mitigate MetS-induced BHV biomaterial degeneration (calcification, tissue cross-linking, and microstructural changes) in an ex vivo serum model and an in vivo with MetS rat subcutaneous implants.

Inhibition of advanced glycation end product formation and serum protein infiltration in bioprosthetic heart valve leaflets: Investigations of anti-glycation agents and anticalcification interactions with ethanol pretreatment

Bioprosthetic heart valves (BHV) fabricated from heterograft tissue, such as glutaraldehyde pretreated bovine pericardium (BP), are the most frequently used heart valve replacements. BHV durability is limited by structural valve degeneration (SVD), mechanistically associated with calcification, advanced glycation end products (AGE), and serum protein infiltration. We investigated the hypothesis that anti-AGE agents, Aminoguanidine, Pyridoxamine [PYR], and N-Acetylcysteine could mitigate AGE-serum protein SVD mechanisms in vitro and in vivo, and that these agents could mitigate calcification or demonstrate anti-calcification interactions with BP pretreatment with ethanol. In vitro, each of these agents significantly inhibited AGE-serum protein infiltration in BP. However, in 28-day rat subdermal BP implants only orally administered PYR demonstrated significant inhibition of AGE and serum protein uptake. Furthermore, BP PYR preincubation of BP mitigated AGE-serum protein SVD mechanisms in vitro, and demonstrated mitigation of both AGE-serum protein uptake and reduced calcification in vivo in 28-day rat subdermal BP explants. Inhibition of BP calcification as well as inhibition of AGE-serum protein infiltration was observed in 28-day rat subdermal BP explants pretreated with ethanol followed by PYR preincubation. In conclusion, AGE-serum protein and calcification SVD pathophysiology are significantly mitigated by both PYR oral therapy and PYR and ethanol pretreatment of BP.