Processing Derived Control of Hydrolytic Degradation and Generation of Shape-Memory in Lactide Copolymers

Polylactide and lactide copolymer implants are advantageous in the sense that they are absorbed out of the body, after fulfilling their function as a temporary support for the damaged tissue. For a predictable performance in the physiological environment, the key factors affecting the hydrolytic degradation and their relationship to the manufacturing process should be well known and controlled. Prior to a significant hydrolytic degradation, the physiological environment affects the thermal properties of lactide-based polymers. This phenomenon can be exploited with orientation-based polymer processing methods in order to develop actively moving polymers. The main aims of this thesis was to study the effects of melt-extrusion on the thermal degradation of lactide copolymers, the effects of melt-processing on the hydrolytic degradation at the physiological temperature and the generation of a water-induced shape-memory on lactide copolymer using orientation-based polymer processing. The main focus in the degradation study was the generation of lactide monomer in the extrusion process and the hydrolysis-catalysing effect of the lactide monomer on poly(L/D-lactide) 96L/4D and poly(L-lactide-co-glycolide) 85L/15G. The study of the generated water-induced shape-memory for amorphous poly(D,L-lactide) focused on demonstrating the properties, mechanism and efficacy of the shape-memory. Results showed that during melt-extrusion the polymers degraded due to high shear stress and high melt temperatures. The degradation in the melt generated lactide monomer into the polymer, which significantly affected the hydrolytic degradation in vitro. The degradation rate was directly proportional to the lactide concentration of the polymer and even small quantities of lactide monomer (0.05-0.20 wt-%) were found to affect the retention of mechanical properties in vitro at 37 °C. Mass loss, crystallinity and dimensional stability were also found to be affected. The orientation-programming process generated an oriented temporary structure for poly(D,L-lactide) that was able to transform its shape at 37 °C in an aqueous environment without any external energy and to further adapt to a predefined stress level as a result of stress generation or relaxation. In an aqueous environment at the physiological temperature, the shape-memory is activated by the plasticizing effect of water molecules diffused into the oriented polymer matrix causing a directed relaxation of oriented and preloaded polymer chains. Although the shape-transformation was slow, the efficacy of the shape-memory was demonstrated with shape-memory nails in a pull-out test in which the pull-out force of the nails increased 360 % during a seven day test period in vitro at 37 °C. The results clearly show that functionality in terms of shape-memory can be generated in suitable bioabsorbable polymers without tailoring the polymer chain structure, and thus shortening the time from the development of the technology to its utilization in medical devices

Ascorbic Acid 2-Phosphate-Releasing Supercritical Carbon Dioxide-Foamed Poly(L-Lactide-Co-epsilon-Caprolactone) Scaffolds Support Urothelial Cell Growth and Enhance Human Adipose-Derived Stromal Cell Proliferation and Collagen Production

publishedVersionPeer reviewe

Novel osteoconductive β-tricalcium phosphate/poly(L-lactide-co-e-caprolactone) scaffold for bone regeneration : a study in a rabbit calvarial defect

The advantages of synthetic bone graft substitutes over autogenous bone grafts include abundant graft volume, lack of complications related to the graft harvesting, and shorter operation and recovery times for the patient. We studied a new synthetic supercritical CO2 -processed porous composite scaffold of -tricalcium phosphate and poly(L-lactide-co-caprolactone) copolymer as a bone graft substitute in a rabbit calvarial defect. Bilateral 12mm diameter critical size calvarial defects were successfully created in 18 rabbits. The right defect was filled with a scaffold moistened with bone marrow aspirate, and the other was an empty control. The material was assessed for applicability during surgery. The follow-up times were 4, 12, and 24 weeks. Radiographic and micro-CT studies and histopathological analysis were used to evaluate new bone formation, tissue ingrowth, and biocompatibility. The scaffold was easy to shape and handle during the surgery, and the bone-scaffold contact was tight when visually evaluated after the implantation. The material showed good biocompatibility and its porosity enabled rapid invasion of vasculature and full thickness mesenchymal tissue ingrowth already at four weeks. By 24 weeks, full thickness bone ingrowth within the scaffold and along the dura was generally seen. In contrast, the empty defect had only a thin layer of new bone at 24 weeks. The radiodensity of the material was similar to the density of the intact bone. In conclusion, the new porous scaffold material, composed of microgranular -TCP bound into the polymer matrix, proved to be a promising osteoconductive bone graft substitute with excellent handling properties [GRAPHICS]Peer reviewe

Processing Derived Control of Hydrolytic Degradation and Generation of Shape-Memory in Lactide Copolymers

Polylactide and lactide copolymer implants are advantageous in the sense that they are absorbed out of the body, after fulfilling their function as a temporary support for the damaged tissue. For a predictable performance in the physiological environment, the key factors affecting the hydrolytic degradation and their relationship to the manufacturing process should be well known and controlled. Prior to a significant hydrolytic degradation, the physiological environment affects the thermal properties of lactide-based polymers. This phenomenon can be exploited with orientation-based polymer processing methods in order to develop actively moving polymers. The main aims of this thesis was to study the effects of melt-extrusion on the thermal degradation of lactide copolymers, the effects of melt-processing on the hydrolytic degradation at the physiological temperature and the generation of a water-induced shape-memory on lactide copolymer using orientation-based polymer processing. The main focus in the degradation study was the generation of lactide monomer in the extrusion process and the hydrolysis-catalysing effect of the lactide monomer on poly(L/D-lactide) 96L/4D and poly(L-lactide-co-glycolide) 85L/15G. The study of the generated water-induced shape-memory for amorphous poly(D,L-lactide) focused on demonstrating the properties, mechanism and efficacy of the shape-memory. Results showed that during melt-extrusion the polymers degraded due to high shear stress and high melt temperatures. The degradation in the melt generated lactide monomer into the polymer, which significantly affected the hydrolytic degradation in vitro. The degradation rate was directly proportional to the lactide concentration of the polymer and even small quantities of lactide monomer (0.05-0.20 wt-%) were found to affect the retention of mechanical properties in vitro at 37 °C. Mass loss, crystallinity and dimensional stability were also found to be affected. The orientation-programming process generated an oriented temporary structure for poly(D,L-lactide) that was able to transform its shape at 37 °C in an aqueous environment without any external energy and to further adapt to a predefined stress level as a result of stress generation or relaxation. In an aqueous environment at the physiological temperature, the shape-memory is activated by the plasticizing effect of water molecules diffused into the oriented polymer matrix causing a directed relaxation of oriented and preloaded polymer chains. Although the shape-transformation was slow, the efficacy of the shape-memory was demonstrated with shape-memory nails in a pull-out test in which the pull-out force of the nails increased 360 % during a seven day test period in vitro at 37 °C. The results clearly show that functionality in terms of shape-memory can be generated in suitable bioabsorbable polymers without tailoring the polymer chain structure, and thus shortening the time from the development of the technology to its utilization in medical devices

Ascorbic Acid 2-Phosphate Releasing Supercritically Foamed Porous Poly-L-Lactide-Co-ε-Caprolactone Scaffold Enhances the Collagen Production of Human Vaginal Stromal Cells : A New Approach for Vaginal Tissue Engineering

Background:: The reconstructive surgery of vaginal defects is highly demanding and susceptible to complications, especially in larger defects requiring nonvaginal tissue grafts. Thus, tissue engineering-based solutions could provide a potential approach to the reconstruction of vaginal defects. Methods:: Here, we evaluated a novel porous ascorbic acid 2-phosphate (A2P)-releasing supercritical carbon dioxide foamed poly-L-lactide-co-ε-caprolactone (scPLCLA2P) scaffold for vaginal reconstruction with vaginal epithelial (EC) and stromal (SC) cells. The viability, proliferation, and phenotype of ECs and SCs were evaluated in monocultures and in cocultures on d 1, d 7 and d 14. Furthermore, the collagen production of SCs on scPLCLA2P was compared to that on scPLCL without A2P on d 14. Results:: Both ECs and SCs maintained their viability on the scPLCLA2P scaffold in mono- and coculture conditions, and the cells maintained their typical morphology during the 14-d culture period. Most importantly, the scPLCLA2P scaffolds supported the collagen production of SCs superior to plain scPLCL based on total collagen amount, collagen I and III gene expression results and collagen immunostaining results. Conclusion:: This is the first study evaluating the effect of A2P on vaginal tissue engineering, and the results are highly encouraging, indicating that scPLCLA2P has potential as a scaffold for vaginal tissue engineering. Graphical Abstract: [Figure not available: see fulltext.].Peer reviewe

In vitro degradation of borosilicate bioactive glass and poly(L-lactide-co-ε-caprolactone) composite scaffolds

Composite scaffolds were obtained by mixing various amounts (10, 30 and 50 weight % [wt %]) of borosilicate bioactive glass and poly(l-lactide-co-ε-caprolactone) (PLCL) copolymer. The composites were foamed using supercritical CO₂. An increase in the glass content led to a decrease in the pore size and density. In vitro dissolution/reaction test was performed in simulated body fluid. As a function of immersion time, the solution pH increased due to the glass dissolution. This was further supported by the increasing amount of Ca in the immersing solution with increasing immersion time and glass content. Furthermore, the change in scaffold mass was significantly greater with increasing the glass content in the scaffold. However, only the scaffolds containing 30 and 50 wt % of glasses exhibited significant hydroxyapatite (HA) formation at 72 h of immersion. The compression strength of the samples was also measured. The Young's modulus was similar for the 10 and 30 wt % glass-containing scaffolds whereas it increased to 90 MPa for the 50 wt % glass containing scaffold. Upon immersion up to 72 h, the Young's modulus increased and then remained constant for longer immersion times. The scaffold prepared could have great potential for bone and cartilage regeneration.publishedVersionPeer reviewe

Hydrolysis and drug release from poly(ethylene glycol)-modified lactone polymers with open porosity

The ability to release active agents from a porous scaffold structure in situ enables the simultaneous structural support for the cells proliferating and differentiating towards tissue as well as the stimulation of tissue regeneration. Due to the great potentiality of such approach, drug-releasing scaffolds were fabricated from hydrolytically degradable polymers. Three copolymers of poly(ethylene glycol), ɛ-caprolactone, L- and D,L-lactide were synthesized and blended with bone-growth inducing active agents, dexamethasone (DM) and 2-phospho-L-ascorbic acid trisodium salt (AS). Porous scaffolds were prepared by means of super-critical carbon dioxide foaming. In the final scaffold structures, the particle size, location and the water solubility of the drug affected the release kinetics. As the large and water soluble AS particles were more exposed to the buffer solution compared to small DM particles, the AS release was burst-like whereas DM showed a long-term release. The material structure had a significant effect on the release kinetics as the porous scaffolds released active agents faster compared to the solid cylinders. Furthermore, this study showed the strong effect of polymer degradation and wettability on the release, which were more determinative than the pore architecture.Peer reviewe

Porous poly-L-lactide-co-epsilon-caprolactone scaffold: a novel biomaterial for vaginal tissue engineering

The surgical reconstruction of functional neovagina is challenging and susceptible to complications. Therefore, developing tissue engineering-based treatment methods for vaginal defects is important. Our aim was to develop and test a novel supercritical carbon dioxide foamed poly-L-lactide-co-1-caprolactone (scPLCL) scaffold for vaginal reconstruction. The scaffolds were manufactured and characterized for porosity (65 + 4%), pore size (350 + 150 mm) and elastic modulus (2.8 + 0.4 MPa). Vaginal epithelial (EC) and stromal cells (SC) were isolated, expanded and characterized with flow cytometry. Finally, cells were cultured with scPLCL scaffolds in separate and/or co-cultures. Their attachment, viability, proliferation and phenotype were analysed. Both cell types strongly expressed cell surface markers CD44, CD73 and CD166. Strong expression of CD326 was detected with ECs and CD90 and CD105 with SCs. Both ECs and SCs attached and maintained viability on scPLCL. Further, scPLCL supported the proliferation of especially ECs, which also maintained epithelial phenotype (cytokeratin expression) during 14-day assessment period. Interestingly, ECs expressed uroplakin (UP) Ia, UPIb and UPIII markers: further, UPIa and UPIII expression was significantly higher on ECs cultured on scPLCL than on cell culture plastic.publishedVersionPeer reviewe

Porous poly-L-lactide-co-1-caprolactone scaffold: A novel biomaterial for vaginal tissue engineering

The surgical reconstruction of functional neovagina is challenging and susceptible to complications. Therefore, developing tissue engineering-based treatment methods for vaginal defects is important. Our aim was to develop and test a novel supercritical carbon dioxide foamed poly-L-lactide-co-1-caprolactone (scPLCL) scaffold for vaginal reconstruction. The scaffolds were manufactured and characterized for porosity (65 + 4%), pore size (350 + 150 mm) and elastic modulus (2.8 + 0.4 MPa). Vaginal epithelial (EC) and stromal cells (SC) were isolated, expanded and characterized with flow cytometry. Finally, cells were cultured with scPLCL scaffolds in separate and/or co-cultures. Their attachment, viability, proliferation and phenotype were analysed. Both cell types strongly expressed cell surface markers CD44, CD73 and CD166. Strong expression of CD326 was detected with ECs and CD90 and CD105 with SCs. Both ECs and SCs attached and maintained viability on scPLCL. Further, scPLCL supported the proliferation of especially ECs, which also maintained epithelial phenotype (cytokeratin expression) during 14-day assessment period. Interestingly, ECs expressed uroplakin (UP) Ia, UPIb and UPIII markers: further, UPIa and UPIII expression was significantly higher on ECs cultured on scPLCL than on cell culture plastic.Peer reviewe