Star-PCL shape memory polymer (SMP) scaffolds with tunable transition temperatures for enhanced utility

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Tissue Engineering

Background:

• Thermoresponsive shape memory polymers (SMPs) from poly(ε-caprolactone) (PCL) macromers show promise for self-fitting bone scaffolds and self-expanding vaginal stents.
• Current PCL-based scaffolds have a shape actuation temperature (T_m) of ~55 °C, which is too high for certain biomedical applications.
• Increased biodegradation rates are desirable for enhanced bone healing and reduced need for medical device retrieval.

Purpose of the Study:

• To synthesize UV-curable PCL macromers with varying architectures (linear vs. 4-arm star) and molecular weights (M_n) to reduce T_m.
• To fabricate porous scaffolds using these macromers and evaluate their thermal and mechanical properties.
• To assess the impact of macromer architecture and molecular weight on scaffold T_m, degradation, and shape memory behavior for biomedical applications.

Main Methods:

• Preparation of six UV-curable PCL macromers: linear and 4-arm star architectures with M_n of 10, 7.5, and 5 kg mol^-1.
• Fabrication of porous scaffolds via solvent casting particulate leaching (SCPL).
• Characterization of scaffolds for melt transition temperature (T_m), crosslink density, crystallinity, shape memory behavior, radial expansion pressure, modulus, and degradation rate.

Main Results:

• Scaffolds from star-PCL-tetraacrylate (star-PCL-TA) macromers exhibited significant T_m reduction with decreasing M_n compared to linear-PCL-diacrylate (linear-PCL-DA) counterparts.
• Achieved desired T_m profiles: 37 °C < T_m < 55 °C for bone scaffolds and T_m ≤ 37 °C for stents.
• Decreasing M_n increased crosslink density and degradation rate while decreasing crystallinity, especially for star-PCL-TA scaffolds. Shape memory was retained, and radial expansion pressure increased, alongside a modulus reduction.

Conclusions:

• Star-shaped PCL macromers offer a viable strategy to tune T_m for thermoresponsive SMPs.
• The developed scaffolds meet critical temperature requirements for self-fitting bone scaffolds and self-expanding stents.
• Architectural modifications and reduced molecular weight enhance degradation and performance for advanced biomedical applications.