The degradation of poly(trimethylene carbonate) implants: The role of molecular weight and enzymes

Comprehensive review of materials, applications, and future innovations in biodegradable esophageal stents

Esophageal stricture (ES) results from benign and malignant conditions, such as uncontrolled gastroesophageal reflux disease (GERD) and esophageal neoplasms. Upper gastrointestinal endoscopy is the preferred diagnostic approach for ES and its underlying causes. Stent insertion using an endoscope is a prevalent method for alleviating or treating ES. Nevertheless, the widely used self-expandable metal stents (SEMS) and self-expandable plastic stents (SEPS) can result in complications such as migration and restenosis. Furthermore, they necessitate secondary extraction in cases of benign esophageal stricture (BES), rendering them unsatisfactory for clinical requirements. Over the past 3 decades, significant attention has been devoted to biodegradable materials, including synthetic polyester polymers and magnesium-based alloys, owing to their exceptional biocompatibility and biodegradability while addressing the challenges associated with recurring procedures after BES resolves. Novel esophageal stents have been developed and are undergoing experimental and clinical trials. Drug-eluting stents (DES) with drug-loading and drug-releasing capabilities are currently a research focal point, offering more efficient and precise ES treatments. Functional innovations have been investigated to optimize stent performance, including unidirectional drug-release and anti-migration features. Emerging manufacturing technologies such as three-dimensional (3D) printing and new biodegradable materials such as hydrogels have also contributed to the innovation of esophageal stents. The ultimate objective of the research and development of these materials is their clinical application in the treatment of ES and other benign conditions and the palliative treatment of malignant esophageal stricture (MES). This review aimed to offer a comprehensive overview of current biodegradable esophageal stent materials and their applications, highlight current research limitations and innovations, and offer insights into future development priorities and directions.

Engineered Hierarchical Microdevices Enable Pre-Programmed Controlled Release for Postsurgical and Unresectable Cancer Treatment

Drug treatment is required for both resectable and unresectable cancers to strive for any meaningful improvement in patient outcomes. However, the clinical benefit of receiving conventional systemic administrations is often less than satisfactory. Drug delivery systems are preferable substitutes but still fail to meet diverse clinical demands due to the difficulty in programming drug release profiles. Herein, a microfabrication concept, termed "Hierarchical Multiple Polymers Immobilization" (HMPI), is introduced and biodegradable-polymer-based hierarchical microdevices (HMDs) that can pre-program any desired controlled release profiles are engineered. Based on the first-line medication of pancreatic and breast cancer, controlled release of single gemcitabine and the doxorubicin/paclitaxel combination in situ for multiple courses is implemented, respectively. Preclinical models of postsurgical pancreatic, postsurgical breast, and unresectable breast cancer are established, and the designed HMDs are demonstrated as well-tolerable and effective treatments for inhibiting tumor growth, recurrence, and metastasis. The proposed HMPI strategy allows the creation of tailorable and high-resolution hierarchical microstructures for pre-programming controlled release according to clinical medication schedules, which may provide promising alternative treatments for postsurgical and unresectable tumor control.

In vitro enzymatic degradation of the PTMC/cross-linked PEGDA blends

Introduction: Poly(1,3-trimethylene carbonate) (PTMC) is a flexible amorphous polymer with good degradability and biocompatibility. The degradation of PTMC is critical for its application as a degradable polymer, more convenient and easy-to-control cross-linking strategies for preparing PTMC are required. Methods: The blends of poly(trimethylene carbonate) (PTMC) and cross-linked poly(ethylene glycol) diacrylate (PEGDA) were prepared by mixing photoactive PEGDA and PTMC and subsequently photopolymerizing the mixture with uv light. The physical properties and in vitro enzymatic degradation of the resultant PTMC/cross-linked PEGDA blends were investigated. Results: The results showed that the gel fraction of PTMC/cross-linked PEGDA blends increased while the swelling degree decreased with the content of PEGDA dosage. The results of in vitro enzymatic degradation confirmed that the degradation of PTMC/cross-linked PEGDA blends in the lipase solution occurred under the surface erosion mechanism, and the introduction of the uv cross-linked PEGDA significantly improved the resistance to lipase erosion of PTMC; the higher the cross-linking degree, the lower the mass loss. Discussion: The results indicated that the blends/cross-linking via PEGDA is a simple and effective strategy to tailor the degradation rate of PTMC.

Dual responsive self-healing hydrogels with wide stability and excellent mechanical strength based on aliphatic polycarbonate

The wide development of hydrogels had been used in many filed due to the high water-containing and tough three-dimensional structure, however, the poor mechanical and multi-functional properties of hydrogel can be limited in its applications deeply. Herein, the dual responsive self-healing hydrogels with tough mechanical properties were manufactured by dual-physical cross-linking based on biodegradable aliphatic polycarbonate. Choosing the soft and hard segments to design the polymeric hydrogel not only can facilitate the dual-dynamic bonding interactions but also the resilient hydrogels possess robust and controllable mechanical strength (6.51 MPa). Furthermore, the results of swelling and stability tests of the materials indicated that the swelling ability of the biodegradable hydrogels can be regulated by the hydrophilic group, and the maximal swelling ratio in water and the equilibrium water content is 66% and 40%, respectively. It is worth mentioning that the tough hydrogels embrace dual-responsive high efficiency of self-healing ability, and the self-healing time is 2 h at 50 °C or 10 h under pH = 5, suggesting that the obtained hydrogels can respond to temperature and pH value to drive the fracture interface for fast self-healing, which will offer new opportunities for stimuli-responsive materials and wound healing.

Investigating the Biodegradation Mechanism of Poly(trimethylene carbonate): Macrophage-Mediated Erosion by Secreting Lipase

Poly(trimethylene carbonate) (PTMC), as one of the representatives of biodegradable aliphatic polycarbonates, has been found to degrade in vivo via surface erosion. This unique degradation behavior and the resulting nonacidic products make it more competitive with aliphatic polyesters (e.g., polylactide) in clinical practice. However, this surface degradation mechanism is complicated and not fully understood to date despite the findings that several reactive oxygen species and enzymes can specifically degrade PTMC in vitro. Herein, the biodegradation mechanism of PTMC was investigated by using possible degradation factors, distinct cell lines, and the inhibitors of these factors. The results demonstrate that PTMC undergoes a specific macrophage-mediated erosion. Macrophages tend to fuse into giant cells and elicit a typical inflammatory response by releasing proinflammatory cytokines. In addition, macrophages are suggested to primarily secrete enzymes (lipase specifically) to erode the PTMC bulk extracellularly as inhibiting their activity effectively prevented this eroding process. The clarification of the biodegradation mechanism in this work suggests that the degradation of PTMC highly depends on the foreign body response. Thus, it reminds the researchers to consider the effect of the microenvironment on the degradation and drug release of PTMC-based implantation devices and localized drug delivery systems.

Poly (trimethylene carbonate)/doxycycline hydrochloride films in the treatment of Achilles tendon defect in rats

Introduction: In this study, Poly (trimethylene carbonate)/Doxycycline hydrochloride (PTMC/DH) films were introduced to repair the Achilles tendon defects for the first time. Methods: (PTMC/DH) films with different DH content of 10, 20, and 30% (w/w) were prepared by solvent casting. The in vitro and in vivo drug release of the prepared PTMC/DH films was investigated. Results: The results of drug release experiments showed that the PTMC/DH films released effective concentrations of doxycycline for more than 7 and 28 days in vitro and in vivo, respectively. The results of antibacterial activity experiments showed diameters of 25.00 ± 1.00 mm, 29.33 ± 1.15 mm, and 34.67 ± 1.53 mm, respectively, for the inhibition zones produced by the release solutions of PTMC/DH films with 10, 20 and 30% (w/w) DH at 2 h, indicating that the drug-loaded films could inhibit Staphylococcus aureus well. After treatment, the Achilles tendon defects have recovered well, as indicated by the more robust biomechanical properties and the lower fibroblast density of the repaired Achilles tendons. Pathology revealed that the pro-inflammatory cytokine, IL-1β, and the anti-inflammatory factor, TGF-β1, peaked in the first three days and gradually decreased as the drug was released more slowly. Discussion: These results demonstrated that the PTMC/DH films have great potential for regenerating Achilles tendon defects.

Current research progress of local drug delivery systems based on biodegradable polymers in treating chronic osteomyelitis

Chronic osteomyelitis is one of the most challenging diseases in orthopedic treatment. It is usually treated with intravenous antibiotics and debridement in clinical practice, which also brings systemic drug side effects and bone defects. The local drug delivery system of antibiotics has the characteristics of targeted slow release to the lesion site, replacing systemic antibiotics and reducing the toxic and side effects of drugs. It can also increase the local drug concentration, achieve sound bacteriostatic effects, and promote bone healing and formation. Currently, PMMA beads are used in treating chronic osteomyelitis at home and abroad, but the chain beads need to be removed after a second operation, inconveniences patients. Biodegradable materials have been extensively studied as optimal options for antibiotic encapsulation and delivery, bringing new hope for treating chronic osteomyelitis. This article reviews the research progress of local drug delivery systems based on biodegradable polymers, including natural and synthetic ones, in treating chronic osteomyelitis.

Efficacy Evaluation of Ciprofloxacin-Loaded Poly (Trimethylene Carbonate) Implants in the Treatment of Chronic Osteomyelitis

In this study, poly (trimethylene carbonate) (PTMC) with excellent biocompatibility was synthesized via ring-opening of TMC to prepare the Ciprofloxacin-loaded PTMC implants, and antibacterial effects in vitro or in vivo of the resulting implants were investigated to evaluate the potential for treating chronic osteomyelitis. The in vitro results showed the Ciprofloxacin-loaded PTMC implants could sustain release ciprofloxacin at a release amount of about 90 μg/d for 28 days and possessed excellent antibacterial effect, as evidenced by the smaller size of the antibacterial ring of 32.6 ± 0.64 mm and the biofilm inhibition of 60% after 28 days of release. The in vivo results showed that after 28 days of treatment, the body weight and the white blood cell counts of chronic-osteomyelitis-model rats in the treatment group reached 381.6 ± 16.8 g and (7.86 ± 0.91) ×10⁹/L, respectively, returning to normal rapidly compared with the control and blank group, indicating the remarkable antibacterial effect of the Ciprofloxacin-loaded PTMC implants. X-ray images and HE staining results also confirmed that most of the proximal and middle parts of the tibia returned to typical structures and new and trabecular bone had been formed for the rats in the treatment group, and no inflammatory cells were found as compared to the control and blank groups, after 28 days of treatment. The significant lower number of colonies of (9.92 ± 1.56) × 10 CFU/g in the treatment group also suggests that the Ciprofloxacin-loaded PTMC implants achieve a practical antibacterial effect through a local application.

A surface-eroding poly(1,3-trimethylene carbonate) coating for magnesium based cardiovascular stents with stable drug release and improved corrosion resistance

Magnesium alloys with integration of degradability and good mechanical performance are desired for vascular stent application. Drug-eluting coatings may optimize the corrosion profiles of magnesium substrate and reduce the incidence of restenosis simultaneously. In this paper, poly (trimethylene carbonate) (PTMC) with different molecular weight (50,000 g/mol named as PTMC5 and 350,000 g/mol named as PTMC35) was applied as drug-eluting coatings on magnesium alloys. A conventional antiproliferative drug, paclitaxel (PTX), was incorporated in the PTMC coating. The adhesive strength, corrosion behavior, drug release and biocompatibility were investigated. Compared with the PLGA control group, PTMC coating was uniform and gradually degraded from surface to inside, which could provide long-term protection for the magnesium substrate. PTMC35 coated samples exhibited much slower corrosion rate 0.05 μA/cm2 in comparison with 0.11 μA/cm2 and 0.13 μA/cm2 for PLGA and PTMC5 coated counterparts. In addition, PTMC35 coating showed more stable and sustained drug release ability and effectively inhibited the proliferation of human umbilical vein vascular smooth muscle cells. Hemocompatibility test indicated that few platelets were adhered on PTMC5 and PTMC35 coatings. PTMC35 coating, exhibiting surface erosion behavior, stable drug release and good biocompatibility, could be a good candidate as a drug-eluting coating for magnesium-based stent.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Poly(trimethylene carbonate) flexible intestinal anastomosis scaffolds to reduce the probability of intestinal fistula and obstruction

Biodegradable anastomat play an important role in the reconstruction process of the digestive tract. However, the biocompatibility and organizational compliance of anastomotic tubes still need to be improved. Electrospun tissue engineering scaffolds have excellent biomimetic extracellular matrix properties, biocompatibility and biodegradability. In the present study, electrospun poly(trimethylene carbonate) (PTMC) intestinal anastomosis scaffolds loaded with triclosan (TCS) were reported to reduce the probability of intestinal fistula and obstruction. When the viscosity average molecular weight of PTMC was 157 × 103, the elastic modulus and tensile strength of the anastomosis scaffolds could reach 20.11 MPa and 16.08 MPa, respectively, which indicated that the anastomosis scaffolds exhibited excellent tensile flexibility. The degradation of PTMC was accelerated with the increase of Mw. After 28 days, the weight and length of the anastomosis scaffolds reduced 40% and 50%, respectively. Furthermore, the application of PTMC anastomosis scaffolds could promote intestinal healing and reduce the probability of intestinal fistula and obstruction.

Progress in the Preparation of Functional and (Bio)Degradable Polymers via Living Polymerizations

This review presents the latest developments in (bio)degradable approaches and functional aliphatic polyesters and polycarbonates prepared by typical ring-opening polymerization (ROP) of lactones and trimethylene carbonates. It also considers several recent innovative synthetic methods including radical ring-opening polymerization (RROP), atom transfer radical polyaddition (ATRPA), and simultaneous chain- and step-growth radical polymerization (SCSRP) that produce aliphatic polyesters. With regard to (bio)degradable approaches, we have summarized several representative cleavable linkages that make it possible to obtain cleavable polymers. In the section on functional aliphatic polyesters, we explore the syntheses of specific functional lactones, which can be performed by ring-opening copolymerization of typical lactone/lactide monomers. Last but not the least, in the recent innovative methods section, three interesting synthetic methodologies, RROP, ATRPA, and SCSRP are discussed in detail with regard to their reaction mechanisms and polymer functionalities.

Surface-Degradable Drug-Eluting Stent with Anticoagulation, Antiproliferation, and Endothelialization Functions

Drug-eluting stents (DES) have been widely applied for saving the life of patients with coronary artery diseases (CADs). However, conventional polymers such as polylactic acid (PLA) and poly (lactic-co-glycolic acid) (PLGA), which are widely applied for drug-eluting stents studies, have serious bulk erosion problems, like high local acidity and poor mechanical properties. Instead, we chose surface erosion polymer poly (1, 3-trimethylene carbonate) (PTMC) as a drug carrier in this study. Here, we fabricated and characterized a novel durable-polymer drug-eluting 316 L stainless steel (SS) stent, in which the inner surface was coated with a Ti–O film using the magnetron sputtering method to promote the growth of endothelial cells (ECs). On the outer layer of the stent, first, a Ti–O film was deposited and, then, on top of it a rapamycin-loaded PTMC coat was deposited using the ultrasonic atomization spray method. This dual coating inhibited the migration and expansion of smooth muscle cells (SMCs). The drug coating also inhibited the adhesion/activation of platelets. In tests on dogs, it was found the novel stent promoted re-endothelialization and reduced restenosis, in contrast to the plain SS stent. Thus, the novel stent may have promise for use in treating patients with CAD.

The In Vitro Enzymatic Degradation of Cross-Linked Poly(trimethylene carbonate) Networks

The in vitro enzymatic degradation of cross-linked poly(trimethylene carbonate) networks (PTMC-Ns) was performed in lipase solutions at 37 °C, and the effect of the initial molecular weight and cross-linker amount as well as the cross-linker type on the degradation rate of PTMC-Ns was investigated. Due to their denser structure and more hydrophobic surface as well as the higher glass transition temperature, a slower degradation rate was seen for PTMC-Ns with high initial molecular weight at a given cross-linker amount. Similar results could be observed as the cross-linker amount increased, and cross-linker type also influenced the degradation rate of PTMC-Ns. Furthermore, the enzymatic degradation of PTMC-Ns was accelerated by the surfactants role of lipase via surface erosion mechanism, the enzymatic degradation rate was higher than that of hydrolysis case. The results indicated that PTMC-Ns were promising candidates for clinical subcutaneous implants, especially due to their tunable degradation rate and enhanced form-stability as well as no acidic degradation products.

A novel one-pot process for the preparation of linear and hyperbranched polycarbonates of various diols and triols using dimethyl carbonate

A novel one-pot method for preparation of high molecular-weight linear and hyperbranched polycarbonates from diols and triols with dimethyl carbonate.