Influence of chain microstructure on the hydrolytic degradation of copolymers from 1,3-trimethylene carbonate and L-lactide

4D printing of biodegradable elastomers with tailorable thermal response at physiological temperature

4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.

Hydrolytic Degradation of Comb-Like Graft Poly (Lactide-co-Trimethylene Carbonate): The Role of Comonomer Compositions and Sequences

The effect of sequence on copolymer properties is rarely studied, especially the degradation behavior of the biomaterials. A series of linear-comb block, gradient, random copolymers were successfully achieved using hydroxylated polybutadiene as the macroinitiator by simple ring-opening polymerization of l-lactide (l-LA) and 1,3-trimethylene carbonate (TMC). The hydrolytic degradation behaviors of the copolymers were systemically evaluated by using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscopy (SEM) to illustrate the influences of comonomer compositions and sequence structures. The linear-comb block copolymers (lcP(TMC-b-LLA)) with different compositions had different degradation rates, which increased with l-LA content. Thermal property changes were observed with decreased T_m and increased ΔH_m in all block copolymers during the degradation. To combine different sequence structures, unique degradation behaviors were observed for the linear-comb block, gradient and random copolymers even with similar comonomer composition. The degradation rates of linear-comb PLLA-gradient-PTMC (lcP(LLA-grad-TMC)) and linear-comb PLLA-random-PTMC (lcP(LLA-ran-TMC)) were accelerated due to the loss of regularity and crystallinity, resulting in a remarkable decrease on weight retention and molar mass. The hydrolysis degradation rate increased in the order lcP(TMC-b-LLA), lcP(LLA-ran-TMC), lcP(LLA-grad-TMC). Therefore, the hydrolytic degradation behavior of comb-like graft copolymers depends on both the compositions and the sequences dramatically.

Poly (propylene fumarate)/β-calcium phosphate composites for enhanced bone repair

A composite based on poly (propylene fumarate) (PPF) was investigated as a potential bone repair material for clinical use and it showed low heat release, suitable mechanical property and good biocompatibility. The in situ curing process would finish in less than 10 min. Compared with PMMA, PPF/TCP showed great decrease in heat release as the maximum temperature during curing process was 54.7 °C ± 1.69 °C. The compressive strength was between 109 ± 2 and 133 ± 6 MPa and the compressive modulus was 146 ± 11 to 161 ± 27 MPa, which were believed to be compatible and further supportive to surrounding bone. Besides, the surface morphology and hydrophilicity could be tailored by adjusting the content of β-calcium phosphate (β-TCP). Relatively stable pH value during degradation in PBS solution implied that it would not bring about acidification when implanted in vivo. In addition, PPF/TCP would boost mineralization and the apatite-like deposits on surface may advance the integrity of bone and materials. Moreover, the PPF/TCP obviously degraded and new bone formed especially when loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) in vivo. In summary, PPF/TCP composites showed suitable physical and chemical properties as well as good bioactivity and may therefore be a promising material for bone repair.

Poly(l-lactide) and Poly(l-lactide- co-trimethylene carbonate) Melt-Spun Fibers: Structure-Processing-Properties Relationship

l-Lactide/trimethylene carbonate copolymers have been produced as multifilament fibers by high-speed melt-spinning. The relationship existing between the composition, processing parameters and physical properties of the fibers has been disclosed by analyzing how the industrial process induced changes at the macromolecular level, i.e., the chain microstructure and crystallinity development. A poly(l-lactide) and three copolymers having trimethylene carbonate contents of 5, 10 and 18 mol % were synthesized with high molecular weight ( M_n) up to 377 kDa and narrow dispersity. Their microstructure, crystallinity and thermal properties were dictated by the composition. The spinnability was then assessed for all the as-polymerized materials: four melt-spun multifilament fibers with increasing linear density were collected for each (co)polymer at a fixed take-up speed of 1800 m min^-1 varying the mass throughput during the extrusion. A linear correlation resulted between the as-spun fiber properties and the linear density. The as-spun fibers could be further oriented, developing more crystallinity and improving their tensile properties by a second stage of hot-drawing. This ability was dependent on the composition and crystallinity achieved during the melt-spinning and the parameters selected for the hot-drawing, such as temperature, draw ratio and input speed. The crystalline structure evolved to a more stable form, and the degree of crystallinity increased from 0-52% to 25-66%. Values of tensile strength and Young's modulus up to 0.32-0.61 GPa and 4.9-8.4 GPa were respectively achieved.

The impact of shape memory test on degradation profile of a bioresorbable polymer

The semicrystalline poly(L-lactide) (PLLA) belongs to the materials with shape memory effect (SME) and as a bioresorbable and biocompatible polymer it have found many applications in medical and pharmaceutical field. Assessment of the SME impact on the polymer degradation profile plays crucial role in applications such as drug release systems or in regenerative medicine. Herein, the results of in vitro degradation studies of PLLA samples after SME full test cycle are presented. The samples were loaded and deformed in two manners: progressive and non-progressive. The performed experiments illustrate also influence of the material mechanical damages, caused e.g. during incorrect implantation of PLLA product, on hydrolytic degradation profile. Apparently, degradation profiles are significantly different for the material which was not subjected to the deformation and the deformed ones. The materials after deformation of 50% (in SME cycle) was characterized by non-reversible morphology changes. The effect was observed in deformed samples during the SME test which were carried out ten times.

In vitro and in vivo degradation behavior of poly(trimethylene carbonate-co-d,l-lactic acid) copolymer

We present P(TMC-co-DLLA) copolymer with the molar ratio of TMC: DLLA = 15: 85 was used to systematic study of in vivo and in vitro degradation behaviors. Dense homogeneous copolymer specimens were prepared by compression molding method. The in vitro and in vivo degradation were, respectively, performed at simulative body condition and implanted into rat’s subcutaneous condition. Investigations were followed via physicochemical and histological analysis such as SEM, GPC, DSC, FTIR and H&E stain. The results demonstrate that copolymeric material can degrade in phosphate buffer solution (PBS) and in rat’s body, and the in vivo degradation rate is faster. Obvious decline of molecule weight and mass loss has been observed, which led to the attenuation of mechanical strength. Furthermore, apart from the hydrolysis, macrophagocytes took part in the phagocytosis in vivo, indicating that degradation rate could be regulated by the combinational mechanism. It is concluded that P(TMC-co-DLLA) copolymer is a promising candidate for tissue repair.

Electrospinning and mechanical properties of P(TMC-co-LLA) elastomers

P(TMC-co-LLA) elastomers have shown great potential for various biomaterial and tissue engineering applications.

Effects of aliphatic polyesters on activation of the immune system: studies on macrophages

There is a constant search for biodegradable polymers with biocompatible characteristics. However, the reported materials are rarely tested for their immunostimulatory properties, which is an important issue as immune cells activated by the polymers might cause their rejection and lead to further injury to the host tissues. Therefore, the aim of the present study was to determine if biodegradable polymers are able to activate RAW 264.7 macrophages. Aliphatic polyesters, poly(L-lactide) (PLLA), poly(L-lactide-co-trimethylene carbonate) (PLTMC), poly(glycolide-co-L-lactide) (PGLA), poly(glycolide-co-L-lactide-co-ε-caprolactone) (PGLCap) and poly(glycolide-co-ε-caprolactone) (PGCap), processed into foils by slip-casting, were characterized in terms of their structure ((1)H-NMR, GPC, DSC) and surface properties (chemical composition, water contact angle, surface free energy, topography and roughness). RAW 264.7 cells were cultured on the materials for 3 or 5 days and their adherence, numbers of apoptotic/necrotic cells, as well as production of several cytokines/chemokines and other inflammation-related molecules (matrix metalloproteinases, nitric oxide) was evaluated. The study demonstrated that PLLA and PGLA did not influence macrophage activation and survival. In contrast, PLTMC, PGLCap and PGCap significantly decreased macrophage adherence, increased ratio of apoptosis and up-regulated synthesis/release of numerous inflammatory mediators. Thus, the latter materials might initiate an undesired inflammatory reaction. The above effects of the polymers were attributed to their high hydrophobicity and low polarity due to the presence of ε-caproyl blocks (PGLCap and PGCap), and/or high flexibility and susceptibility to mechanical deformation due to low glasstransition temperature (PLTMC, PGLCap and PGCap). In conclusion, while PLLA and PGLA do not affect macrophage functioning, the other materials (PLTMC, PGLCap, PGCap) up-regulate macrophage activity.

Copolymerization of l-lactide/trimethylene carbonate by organocatalysis: controlled synthesis of comb-like graft copolymers with side chains with different topologies

Synthesis of comb-like graft copolymers of lcP(LLA-co-TMC) from an organocatalyst/PB–OH system: including lcP(TMC-b-LLA), lcP(LLA-grad-TMC) and lcP(LLA-ran-TMC).

Tensile properties and in vitro degradation of P(TMC-co-LLA) elastomers

P(TMC-co-LLA) elastomers have shown great potential for various biomaterials applications. This study investigated properties key to such applications. Six statistical copolymers with 16 to 49 mol% TMC were synthesized and it was found that the LLA sequence length changed from 14 to 3 for the copolymer series while the M[combining macron]_n decreased from 63 to 31 kg mol^-1 with increasing TMC content. The thermal properties showed lower T_g values with increasing TMC content which agreed with the Fox equation. Solvent cast films exhibited Young's modulus values between 2.8 and 271 MPa, ultimate tensile strength of 0.6-15.5 MPa and elongation at failure from 356 to 1287%. In vitro degradation in PBS at 37 °C over 34 weeks demonstrated an induction period of 9 weeks during which the water content was minimal for all copolymers. Copolymer films with 21 or greater mol% TMC were found to undergo homogeneous bulk degradation, while films with 16 mol% TMC underwent heterogeneous bulk degradation.

In vivo degradation of copolymers prepared from L-lactide, 1,3-trimethylene carbonate and glycolide as coronary stent materials

A series of high molecular weight polymers were prepared by ring opening polymerization of L-lactide (L-LA), 1,3-trimethylene carbonate (TMC) and glycolide using stannous octoate as catalyst. The resulting polymers were characterized by gel permeation chromatography, (1)H nuclear magnetic resonance, differential scanning calorimeter and tensile tests. All the polymers present high molecular weights. Compared with PLLA and PTLA copolymers, the terpolymers exhibit interesting properties such as improved toughness and lowered crystallinity with only slightly reduced mechanical strength. In vivo degradation was performed by subcutaneous implantation in rats to evaluate the potential of the copolymers as bioresorbable coronary stent material. The results show that all the polymers conserved to a large extent their mechanical properties during the first 90 days, except the strain at break which exhibited a strong decrease. Meanwhile, significant molecular weight decrease and weight loss are detected in the case of terpolymers. Therefore, the PTLGA terpolymers present a good potential for the development of totally bioresorbable coronary stents.

Selective degradation in aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase

Controlling the course of the degradation of aliphatic polyesters is a key question when designing new degradable materials.

Effect of biodegradation and de novo matrix synthesis on the mechanical properties of valvular interstitial cell-seeded polyglycerol sebacate-polycaprolactone scaffolds

The development of living heart valves that grow with the patient is a promising strategy for heart valve replacements in pediatric patients. Despite active research in the field of tissue engineered heart valves there have been limited efforts to optimize the balance between biodegradation of the scaffolds and de novo extracellular matrix (ECM) synthesis by cells and study their consequences on the mechanical properties of the cell-seeded construct. This study investigates the effect of in vitro degradation and ECM secretion on the mechanical properties of hybrid polyester scaffolds. The scaffolds were synthesized from blends of fast degrading polyglycerol sebacate (PGS) and slowly degrading polycaprolactone (PCL). PGS-PCL scaffolds were electrospun using a 2:1 ratio of PGS to PCL. Accelerated hydrolytic degradation in 0.1 mM sodium hydroxide revealed 2-fold faster degradation of PGS-PCL scaffolds compared with PCL scaffolds. Thermal analysis and scanning electron microscopy demonstrated marginal change in PCL scaffold properties, while PGS-PCL scaffolds showed preferential mass loss of PGS and thinning of the individual fibers during degradation. Consequently, the mechanical properties of PGS-PCL scaffolds decreased gradually with no significant change for PCL scaffolds during accelerated degradation. Valvular interstitial cells (VICs) seeded on PGS-PCL scaffolds showed higher ECM protein secretion compared with PCL. Thus the mechanical properties of the cell-seeded PCL scaffolds did not change significantly compared with acellular scaffolds, probably due to slower degradation and ECM deposition by VICs. In contrast, the PGS-PCL scaffolds exhibited a gradual decrease in the mechanical properties of the acellular scaffolds due to degradation, which was compensated for by new matrix secreted by VICs seeded on the scaffolds. Our study demonstrated that the faster degrading PGS component of PGS-PCL accelerated the degradation rate of the scaffolds. VICs, on the other hand, were able to remodel the synthetic scaffold, depositing new matrix proteins and maintaining the mechanical properties of the scaffolds.

In vivo study on the histocompatibility and degradation behavior of biodegradable poly(trimethylene carbonate-co-D,L-lactide)

The aim of this study was to explore the in vivo behavior and histocompatibility of poly(trimethylene carbonate-co-D,L-lactide) (PDLLA/TMC) and its feasibility of manufacturing cardiovascular stents. Copolymers with 50/50 molar ratio were synthesized by ring-opening polymerization with TMC and D, L-LA, or TMC and L-LA. Poly(L-lactide) (PLLA) was synthesized as a control. The films of the three polymers were implanted into 144 Wistar rats. At different time points of implantation, polymer films were explanted for the evaluation of degradation characteristics and histocompatibility using size exclusion chromatography , nuclear magnetic resonance , environmental scanning electron microscope , and optical microscope. Results showed that there were differences in the percentage of mass loss, molecular weight, shape and appearance changes, and inflammation cell counts between different polymers. With the time extended, the film's superficial structure transformed variously, which was rather obvious in the polymer of PDLLA/TMC. In addition, there were relatively lower inflammation cell counts in the PDLLA/TMC and poly(trimethylene carbonate-co-L-lactide) (PLLA/TMC) groups at different time points in comparison with those in the PLLA group. The differences were of statistical significance (P< 0.05) in the group of PDLLA/TMC vs. PLLA, and the group of PLLA/TMC vs. PLLA, but not within the PDLLA/TMC and PLLA/TMC groups (P> 0.05). These results suggested that the polymer of PDLLA/TMC (50/50) with favorable degradation performance and histocompatibility is fully biodegradable and suitable for manufacturing implanted cardiovascular stents.