Thermomechanical Behaviour of Biodegradable Shape-memory Polymer Foams

Suitability of EtO Sterilization for Polydopamine-coated, Self-fitting Bone Scaffolds

Irregularly shaped craniomaxillofacial (CMF) defects may be advantageously treated by "self-fitting" shape memory polymer (SMP) scaffolds, namely those prepared from poly(ε-caprolactone)diacrylate (PCL-DA) networks and PCL-DA/poly(L-lactic acid) (PLLA) (75:25 wt%) semi-interpenetrating polymer networks (semi-IPNs). In addition to achieving good scaffold-tissue contact, a polydopamine (PD) coating can be leveraged to enhance bioactivity for improved osseointegration. Sterilization with ethylene oxide (EtO) represents a logical choice due to its low operating temperature and humidity. Herein, for the first time, the impact of EtO sterilization on the material properties of PD-coated SMP scaffolds was systematically assessed. Morphological features (i.e., pore size and pore interconnectivity), and in vitro bioactivity were preserved as were PCL crystallinity, PLLA crystallinity, and crosslinking. These latter features led to sustained shape memory properties, and compressive modulus. EtO-sterilized, PD-coated scaffolds displayed similar in vitro degradation behaviors versus analogous non-sterilized scaffolds. This included maintenance of compression modulus following 28 days of exposure to non-accelerated degradation conditions.

A bioactive "self-fitting" shape memory polymer scaffold with potential to treat cranio-maxillo facial bone defects

While tissue engineering is a promising alternative for treating critical-sized cranio-maxillofacial bone defects, improvements in scaffold design are needed. In particular, scaffolds that can precisely match the irregular boundaries of bone defects as well as exhibit an interconnected pore morphology and bioactivity would enhance tissue regeneration. In this study, a shape memory polymer (SMP) scaffold was developed exhibiting an open porous structure and the capacity to conformally "self-fit" into irregular defects. The SMP scaffold was prepared via photocrosslinking of poly(ε-caprolactone) (PCL) diacrylate using a SCPL method, which included a fused salt template. A bioactive polydopamine coating was applied to coat the pore walls. Following exposure to warm saline at T>T(trans) (T(trans)=T(m) of PCL), the scaffold became malleable and could be pressed into an irregular model defect. Cooling caused the scaffold to lock in its temporary shape within the defect. The polydopamine coating did not alter the physical properties of the scaffold. However, polydopamine-coated scaffolds exhibited superior bioactivity (i.e. formation of hydroxyapatite in vitro), osteoblast adhesion, proliferation, osteogenic gene expression and extracellular matrix deposition.

Polymeric microstructures with shape-memory properties for biomedical use built by stereolithography

PURPOSE

The aim of this study was to design and build porous microstructures with shape memory behaviour using biodegradable poly(D,L-lactide-co-trimethylene carbonate) dimethacrylate macromers. These microstructures could be advantageous for tissue engineering and other advanced biomedical applications.

METHODS

Porous structures with a gyroid pore network architecture showing average pore sizes of 930 µm and complete pore interconnectivity were prepared by stereolithography. Built structures were characterized by Micro-computed tomography (µ-CT). Shape recovery and shape fixity of microstructures after 40% and 70% compression were evaluated.

RESULTS

At 37 °C the flexible structures showed compression modulus values of 60 KPa and could be fully compressed. Thermal analysis showed that the built networks were amorphous with Tg values of 23 °C. After compression to 40 and 70%, shape fixity and shape recovery of the structures at respectively 0 °C and 37 °C was almost quantitative.

CONCLUSIONS

The well-defined pore network characteristics and the shape-memory properties of these structures allow their use as deployable tissue engineering scaffolds.

Porous Shape Memory Polymers

Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use.

Inorganic-organic shape memory polymer (SMP) foams with highly tunable properties

Thermoresponsive shape memory polymers (SMPs) are a class of smart materials that can return from a temporary to a permanent shape with the application of heat. Porous SMP foams exhibit unique properties versus solid, nonporous SMPs, enabling their utility in different applications, including some in the biomedical field. Reports on SMP foams have focused on those based on organic polymer systems. In this study, we have prepared inorganic-organic SMP foams comprising inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) PCL segments. The PCL segments served as switching segments to induce shape changing behavior whereas the length of the PDMS soft segment was systematically tuned. SMP foams were formed via the photochemical cure of acrylated (AcO) macromers AcO-PCL(40)-block-PDMS(m)-block-PCL(40)-OAc (m = 0, 20, 37, 66 and 130) using a revised solvent casting/particulate leaching (SCPL) method. By varying the PDMS segment length, PDMS-PCL foams having excellent shape memory behavior were obtained that exhibited highly tunable properties, including pore size, % porosity, compressive modulus, and degradation rate.