Thermosensitive Biodegradable Homopolymer of Trimethylene Carbonate Derivative at Body Temperature

In situ forming macroporous biohybrid hydrogel for nucleus pulposus cell delivery

Degenerative intervertebral disc disease is a common source of chronic pain and reduced quality of life in people over the age of 40. While degeneration occurs throughout the disc, it most often initiates in the nucleus pulposus (NP). Minimally invasive delivery of NP cells within hydrogels that can restore and maintain the disc height while regenerating the damaged NP tissue is a promising treatment strategy for this condition. Towards this goal, a biohybrid ABA dimethacrylate triblock copolymer was synthesized, possessing a lower critical solution temperature below 37 °C and which contained as its central block an MMP-degradable peptide flanked by poly(trimethylene carbonate) blocks bearing pendant oligoethylene glycol groups. This triblock prepolymer was used to form macroporous NP cell-laden hydrogels via redox initiated (ammonium persulfate/sodium bisulfite) crosslinking, with or without the inclusion of thiolated chondroitin sulfate. The resulting macroporous hydrogels had water and mechanical properties similar to those of human NP tissue and were mechanically resilient. The hydrogels supported NP cell attachment and growth over 28 days in hypoxic culture. In hydrogels prepared with the triblock copolymer but without the chondroitin sulfate the NP cells were distributed homogeneously throughout in clusters and deposited collagen type II and sulfated glycosaminoglycans but not collagen type I. This hydrogel formulation warrants further investigation as a cell delivery vehicle to regenerate degenerated NP tissue. STATEMENT OF SIGNIFICANCE: The intervertebral disc between the vertebral bones of the spine consists of three regions: a gel-like central nucleus pulposus (NP) within the annulus fibrosis, and bony endplates. Degeneration of the intervertebral disc is a source of chronic pain in the elderly and most commonly initiates in the NP. Replacement of degenerated NP tissue with a NP cell-laden hydrogel is a promising treatment strategy. Herein we demonstrate that a crosslinkable polymer with a lower critical solution temperature below 37 °C can be used to form macroporous hydrogels for this purpose. The hydrogels are capable of supporting NP cells, which deposit collagen II and sulfated glycosaminoglycans, while also possessing mechanical properties matching those of human NP tissue.

pH Effect on Particle Aggregation of Vanillin End-Capped Polylactides Bearing a Hydrophilic Group Connected by a Cyclic Acetal Moiety

To enhance the pH-responsiveness of poly(lactic acid) (PLA) particles, desired vanillin acetal-based initiators were synthesized and functional PLA was initiated at the chain end. PLLA-V6-OEG₃ particles were prepared using polymers with various M_n values of 2400-4800 g/mol. PLLA-V6-OEG₃ was appropriated to achieve a pH-responsive behavior under physiological conditions within 3 min via the six-membered ring diol-ketone acetal. Moreover, it was found that the polymer chain length (M_n) influenced the aggregation rate. TiO₂ was selected as the blending agent to improve the aggregation rate. The PLLA-V6-OEG₃ blended with TiO₂ was found to accelerate the aggregation rate compared with that without TiO₂, and the best ratio of polymer/TiO₂ was 1:1. To study the effect of the chain end for stereocomplex polylactide (SC-PLA) particles, PLLA-V6-OEG₄ and PDLA-V6-OEG₄ were successfully synthesized. The obtained results of SC-PLA particle aggregation implied that the types of chain end and the molecular weight of polymer could influence the aggregation rate. The SC-V6-OEG₄ blended with TiO₂ could not make our target to aggregate under physiological conditions within 3 min. This study motivated us to control the particle aggregation rate under physiological conditions for applying as a target drug carrier which is significantly influenced by not only the molecular weight but also the hydrophilicity of the chain-end as well as the number of acetal bonds.

Remarkable diastereomeric effect on thermoresponsive behavior of polyurethane based on lysine and tartrate ester derivatives

This study describes the long-distance diastereomeric effect on thermoresponsive properties in water-soluble diastereomeric polyurethanes (PUs) composed of an l-lysine ethyl ester diisocyanate and a trimethylene glycol l-/d-tartrate ester, which have differences in spatial arrangements of the ethyl esters in the mirror image. The PUs based on l-lysine and l-/d-tartrate ester, named l-PU and d-PU, were synthesized with various number average molecular weights from 4700 to 13 100. In turbidimetry, l-PU showed a steep phase transition from 100%T to 0%T within about 10 °C at 4 g L⁻¹, whereas d-PU did not change completely to 0%T transmittance even at 80 °C at 4 g L⁻¹. In addition, the thermoresponsive properties of l-PU were less affected by concentration than those of d-PU. This long-distance diastereomeric effect on thermoresponsive behavior between l-PU and d-PU appeared in common among 6 samples with 4700 to 13 100 number average molecular weight. In the dynamic light scattering experiments at each transmittance, the hydrodynamic diameter (D_h) of l-PU increased up to 1000 nm, while the D_h of d-PU remained almost at 200–300 nm. The C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O stretching vibration of FT-IR spectra showed that d-PU has more hydrogen-bonded ester groups than L-PU. Thus, we speculated that the difference in the retention of polymer chains in the micelle to promote intermicellar bridging generates the long-distance diastereomeric effect.

The long-distance diastereomeric effect on thermoresponsive properties in a polyurethane system consisting of chiral monomers was reported.

In Vivo Degradation Mechanisms of Aliphatic Polycarbonates and Functionalized Aliphatic Polycarbonates

Aliphatic polycarbonates (APCs) have been studied for decades but have not been as utilized as aliphatic polyesters in biomaterial applications such as drug delivery and tissue engineering. With the recognition that functionalized aliphatic polymers can be readily synthesized, increased attention is being paid to these materials. A frequently provided reason for utilizing these polymers is that they degrade to form diols and carbon dioxide. However, depending on the structure and molecular weight of the APC, degradation may not occur. In this review, the mechanisms by which APCs and functionalized APCs have been found to degrade in vivo are examined with the objective of providing guidance in the continued development of these polymers as biomaterials.

Anion-induced thermoresponsiveness in cationic polycysteine and DNA binding

This study describes the synthesis of an l-cysteine-based water-soluble cationic polypeptide, an investigation of its thermoresponsive behaviour in the presence of added anions and its polyplexation with DNA.

Photo-Cross-Linked Polycarbonate Coating with Surface-Erosion Behavior for Corrosion Resistance and Cytocompatibility Enhancement of Magnesium Alloy

Absorbable magnesium (Mg) materials are promising for medical implant applications. However, their corrosion rate and potential toxicity remain a challenge. Herein, a photo-cross-linked coating with suitable durability and unique surface-eroding behavior for enhancement of anticorrosion property and cytocompatibility of AZ31 Mg alloy was developed. The biodegradable allyl-functional polycarbonate, poly[(5-methyl-5-allyloxycarbonyl-1,3-propanediol carbonate)-co-(trimethylene carbonate)] [P(MAC-co-TMC), PMT], was first synthesized by ring-opening copolymerization. The PMT copolymer, pentaerythritol tetrakis(3-mercaptopropionate), and a photoinitiator were then applied on AZ31 Mg alloy by dip coating, and these films were cross-linked via the subsequent photoinitiated thiol-ene click reaction. The poly(l-lactide) (PLLA) and poly(1,3-trimethylene carbonate) (PTMC) coatings without cross-linking were prepared and used as control. Our results show that the cross-linked PMT coatings exhibited superior mechanical properties compared with PLLA and PTMC coatings. Meanwhile, the surface-erosion behavior of the cross-linked PMT coatings remained, as confirmed by scanning electron microscopy analysis. As a result, the cross-linked PMT-coated Mg alloy showed lower corrosion rates, better in vitro corrosion resistance, and much lower cytotoxicity, compared with bare Mg and ones coated with PLLA and PTMC coatings. Results indicate that the cross-linked PMT coatings with unique surface-erosion behavior and good cytocompatibility might be promising to improve the safety and success rate of Mg-based devices and implants.

Assessing Amphiphilic ABAB Zn(II) Phthalocyanines with Enhanced Photosensitization Abilities in In Vitro Photodynamic Therapy Studies Against Cancer

We have previously demonstrated that singlet oxygen photosensitization abilities of Zn(II) phthalocyanines (Zn(II)Pcs) are enhanced through α-functionalization with bulky fluorinated substituents (i.e., bis(trifluoromethyl)phenyl units) at facing positions of ABAB Zn(II)Pcs, where A and B refer to differently functionalized isoindoles. In this work, we have prepared the Zn(II)Pc ABAB 1 endowed with hydrophilic triethylene glycol monomethyl ether (i.e., at the A isoindoles) to provide solubility in aqueous media, together with its A₃B and A₄ counterparts, and compared their ability to behave as photosensitizers for photodynamic therapy. All photophysical data, aggregation studies and preliminary in vitro biological assays in cell cultures of SCC-13 (squamous cell carcinoma) and HeLa (cervical cancer cells), have proved ABAB 1 as the best photosensitizer of the series.

Anionic polycondensation and equilibrium driven monomer formation of cyclic aliphatic carbonates

The current work explores the sodium hydride mediated polycondensation of aliphatic diols with diethyl carbonate to produce both aliphatic polycarbonates and cyclic carbonate monomers. The lengths of the diol dictate the outcome of the reaction; for ethylene glycol and seven other 1,3-diols with a wide array of substitution patterns, the corresponding 5-membered and 6-membered cyclic carbonates were synthesized in excellent yield (70-90%) on a 100 gram scale. Diols with longer alkyl chains, under the same conditions, yielded polycarbonates with an M w ranging from 5000 to 16 000. In all cases, the macromolecular architecture revealed that the formed polymer consisted purely of carbonate linkages, without decarboxylation as a side reaction. The synthetic design is completely solvent-free without any additional post purification steps and without the necessity of reactive ring-closing reagents. The results presented within provide a green and scalable approach to synthesize both cyclic carbonate monomers and polycarbonates with possible applications within the entire field of polymer technology.

Transiently thermoresponsive polymers and their applications in biomedicine

The focus of this review is on the class of transiently thermoresponsive polymers. These polymers are thermoresponsive, but gradually lose this property upon chemical transformation - often a hydrolysis reaction - in the polymer side chain or backbone. An overview of the different approaches used for the design of these polymers along with their physicochemical properties is given. Their amphiphilic properties and degradability into fully soluble compounds make this class of responsive polymers attractive for drug delivery and tissue engineering applications. Examples of these are also provided in this review.

Monoether-Tagged Biodegradable Polycarbonate Preventing Platelet Adhesion and Demonstrating Vascular Cell Adhesion: A Promising Material for Resorbable Vascular Grafts and Stents

We developed a biodegradable polycarbonate that demonstrates antithrombogenicity and vascular cell adhesion via organocatalytic ring-opening polymerization of a trimethylene carbonate (TMC) analogue bearing a methoxy group. The monoether-tagged polycarbonate demonstrates a platelet adhesion property that is 93 and 89% lower than those of poly(ethylene terephthalate) and polyTMC, respectively. In contrast, vascular cell adhesion properties of the polycarbonate are comparable to those controls, indicating a potential for selective cell adhesion properties. This difference in the cell adhesion property is well associated with surface hydration, which affects protein adsorption and denaturation. Fibrinogen is slightly denatured on the monoether-tagged polycarbonate, whereas fibronectin is highly activated to expose the RGD motif for favorable vascular cell adhesion. The surface hydration, mainly induced by the methoxy side chain, also contributes to slowing the enzymatic degradation. Consequently, the polycarbonate exhibits decent blood compatibility, vascular cell adhesion properties, and biodegradability, which is promising for applications in resorbable vascular grafts and stents.

Switching from Controlled Ring-Opening Polymerization (cROP) to Controlled Ring-Closing Depolymerization (cRCDP) by Adjusting the Reaction Parameters That Determine the Ceiling Temperature

Full control over the ceiling temperature (Tc) enables a selective transition between the monomeric and polymeric state. This is exemplified by the conversion of the monomer 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC) to poly(AOMEC) and back to AOMEC within 10 h by controlling the reaction from conditions that favor ring-opening polymerization (Tc > T0) (where T0 is the reaction temperature) to conditions that favor ring-closing depolymerization (Tc < T0). The ring-closing depolymerization (RCDP) mirrors the polymerization behavior with a clear relation between the monomer concentration and the molecular weight of the polymer, indicating that RCDP occurs at the chain end. The Tc of the polymerization system is highly dependent on the nature of the solvent, for example, in toluene, the Tc of AOMEC is 234 °C and in acetonitrile Tc = 142 °C at the same initial monomer concentration of 2 M. The control over the monomer to polymer equilibrium sets new standards for the selective degradation of polymers, the controlled release of active components, monomer synthesis and material recycling. In particular, the knowledge of the monomer to polymer equilibrium of polymers in solution under selected environmental conditions is of paramount importance for in vivo applications, where the polymer chain is subjected to both high dilution and a high polarity medium in the presence of catalysts, that is, very different conditions from which the polymer was formed.

Co-delivery of drugs and plasmid DNA for cancer therapy

Cancer is an extremely complex disease involving multiple signaling pathways that enable tumor cells to evade programmed cell death, thus making cancer treatment extremely challenging. The use of combination therapy involving both gene therapy and chemotherapy has resulted in enhanced anti-cancer effects and has become an increasingly important strategy in medicine. This review will cover important design parameters that are incorporated into delivery systems for the co-administration of drug and plasmid-based nucleic acids (pDNA and shRNA), with particular emphasis on polymers as delivery materials. The unique challenges faced by co-delivery systems and the strategies to overcome such barriers will be discussed. In addition, the advantages and disadvantages of combination therapy using separate carrier systems versus the use of a single carrier will be evaluated. Finally, future perspectives in the design of novel platforms for the combined delivery of drugs and genes will be presented.

Poly(trimethylene carbonate)/Poly(malic acid) Amphiphilic Diblock Copolymers as Biocompatible Nanoparticles

Amphiphilic polycarbonate-poly(hydroxyalkanoate) diblock copolymers, namely, poly(trimethylene carbonate) (PTMC)-b-poly(β-malic acid) (PMLA), are reported for the first time. The synthetic strategy relies on commercially available catalysts and initiator. The controlled ring-opening polymerization (ROP) of trimethylene carbonate (TMC) catalyzed by the organic guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), associated with iPrOH as an initiator, provided iPrO-PTMC-OH, which served as a macroinitiator in the controlled ROP of benzyl β-malolactonate (MLABe) catalyzed by the neodymium triflate salt (Nd(OTf)3). The resulting hydrophobic iPrO-PTMC-b-PMLABe-OH copolymers were then hydrogenolyzed into the parent iPrO-PTMC-b-PMLA-OH copolymers. A range of well-defined copolymers, featuring different sizes of segments (Mn,NMR up to 9300 g mol(-1) ; ÐM =1.28-1.40), were thus isolated in gram quantities, as evidenced by NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, differential scanning calorimetry, and contact angle analyses. Subsequently, PTMC-b-PMLA copolymers with different hydrophilic weight fractions (11-75 %) self-assembled in phosphate-buffered saline upon nanoprecipitation into well-defined nano-objects with Dh =61-176 nm, a polydispersity index <0.25, and a negative surface charge, as characterized by dynamic light scattering and zeta-potential analyses. In addition, these nanoparticles demonstrated no significant effect on cell viability at low concentrations, and a very low cytotoxicity at high concentrations only for PTMC-b-PMLA copolymers exhibiting hydrophilic fractions over 47 %, thus illustrating the potential of these copolymers as promising nanoparticles.

Poly(trimethylene carbonate)-based polymers engineered for biodegradable functional biomaterials

This review presents recent examples of applications and functionalization strategies of poly(trimethylene carbonate), its copolymers, and its derivatives to exploit the unique physicochemical properties of the aliphatic polycarbonate backbone.