Modeling enzymatic kinetic pathways for ring-opening lactone polymerization

Collagen-decorated electrospun scaffolds of unsaturated copolyesters for bone tissue regeneration

Many efforts have been devoted to bone tissue to regenerate damaged tissues, and the development of new biocompatible materials that match the biological, mechanical, and chemical features required for this application is crucial. Herein, a collagen-decorated scaffold was prepared via electrospinning using a synthesized unsaturated copolyester (poly(globalide-co-pentadecalactone)), followed by two coupling reactions: thiol-ene functionalization with cysteine and further conjugation via EDC/NHS chemistry with collagen, aiming to design a bone tissue regeneration device with improved hydrophilicity and cell viability. Comonomer ratios were varied, affecting the copolymer's thermal and chemical properties and highlighting the tunable features of this copolyester. Functionalization with cysteine created new carboxyl and amine groups needed for bioconjugation with collagen, which is responsible for providing biological and structural integrity to the extra-cellular matrix. Bioconjugation with collagen turned the scaffold highly hydrophilic, decreasing its contact angle from 107 ± 2° to 0°, decreasing the copolymer crystallinity by 71%, and improving cell viability by 85% compared with the raw scaffold, thus promoting cell growth and proliferation. The highly efficient and biosafe strategy to conjugate polymers and proteins created a promising device for bone repair in tissue engineering.

Cell Uptake and Biocompatibility of Nanoparticles Prepared from Poly(benzyl malate) (Co)polymers Obtained through Chemical and Enzymatic Polymerization in Human HepaRG Cells and Primary Macrophages

The design of drug-loaded nanoparticles (NPs) appears to be a suitable strategy for the prolonged plasma concentration of therapeutic payloads, higher bioavailability, and the reduction of side effects compared with classical chemotherapies. In most cases, NPs are prepared from (co)polymers obtained through chemical polymerization. However, procedures have been developed to synthesize some polymers via enzymatic polymerization in the absence of chemical initiators. The aim of this work was to compare the acute in vitro cytotoxicities and cell uptake of NPs prepared from poly(benzyl malate) (PMLABe) synthesized by chemical and enzymatic polymerization. Herein, we report the synthesis and characterization of eight PMLABe-based polymers. Corresponding NPs were produced, their cytotoxicity was studied in hepatoma HepaRG cells, and their uptake by primary macrophages and HepaRG cells was measured. In vitro cell viability evidenced a mild toxicity of the NPs only at high concentrations/densities of NPs in culture media. These data did not evidence a higher biocompatibility of the NPs prepared from enzymatic polymerization, and further demonstrated that chemical polymerization and the nanoprecipitation procedure led to biocompatible PMLABe-based NPs. In contrast, NPs produced from enzymatically synthesized polymers were more efficiently internalized than NPs produced from chemically synthesized polymers. The efficient uptake, combined with low cytotoxicity, indicate that PMLABe-based NPs are suitable nanovectors for drug delivery, deserving further evaluation in vivo to target either hepatocytes or resident liver macrophages.

Lipase-mediated direct in situ ring-opening polymerization of ε-caprolactone formed by a chemo-enzymatic method

A novel method to synthesize poly(ε-caprolactone) (PCL) through a three-step, lipase-mediated chemo-enzymatic reaction from cyclohexanone using an immobilized lipase from Trichosporon laibacchii (T. laibacchii) CBS5791 was developed. The immobilized preparation with 1280 U· g^-1 used here was obtained by a method of purification and in situ immobilization where the crude intracellular lipase (cell homogenate) was subjected to partial purification by an aqueous two-phase system (ATPS) consisting of 12% (w/w) polyethylene glycol (PEG) 4000 and 13% (w/w) potassium phosphate (K₂HPO₄) and then in situ immobilization directly on diatomite from the top PEG-rich phase of ATPS. In this multi-step process, the ε-caprolactone (ε-CL) produced by lipase-mediated one-pot two-step chemo-enzymatic oxidation of cyclohexanone was directly subjected to in situ ring-opening polymerization (ROP) started by adding highly hydrophobic solvents. It is necessary to note that ε-CL synthesis and its subsequent ROP were catalyzed by the same lipase. The impact of various reaction parameters, e.g., solvent, cyclohexanone: hydrogen peroxide molar ratio, hydrogen peroxide forms and reaction temperature were investigated. Toluene was selected as a preferred solvent due to supporting the highest molecular weight (M_n = 2168) and moderate ε-CL conversion (65.42%). Through the optimization of reaction conditions, PCL was produced with a M_n of 2283 at 50 °C for 24 h. These results reveal that this lipase-mediated direct ring-opening polymerization of in situ formed ε-CL is an alternative route to the conventional synthesis of PCL.

Polyesters from Macrolactones Using Commercial Lipase NS 88011 and Novozym 435 as Biocatalysts

The demand for environmentally friendly products allied with the depletion of natural resources has increased the search for sustainable materials in chemical and pharmaceutical industries. Polyesters are among the most widely used biodegradable polymers in biomedical applications. In this work, aliphatic polyesters (from globalide and ω-pentadecalactone) were synthesized using a new commercial biocatalyst, the low-cost immobilized NS 88011 lipase (lipase B from Candida antarctica immobilized on a hydrophobic support). Results were compared with those obtained under the same conditions using a traditional, but more expensive, commercial biocatalyst, Novozym 435 (lipase B from C. antarctica immobilized on Lewatit VP OC). When NS 88011 was used in the polymerization of globalide, longer reaction times (240 min)-when compared to Novozym 435-were required to obtain high yields (80-90 wt%). However, higher molecular weights were achieved. When poly(ω-pentadecalactone) was synthesized, high yields and molecular weights (130,000 g mol^-1) were obtained and the enzyme concentration showed strong influence on the polyester properties. This is the first report describing NS 88011 in polymer synthesis. The use of this cheaper enzymatic preparation can provide an alternative for polyester synthesis via enzymatic ring-opening polymerization.

Enzymatic ring-opening polymerization (ROP) of lactides and lactone in ionic liquids and organic solvents: digging the controlling factors

Certain organic solvents and ionic liquids could promote the enzymatic ring-opening polymerization of lactide.

Mixed systems to assist enzymatic ring opening polymerization of lactide stereoisomers

Enzymatic ring opening polymerization of both enantiomers of lactide was performed in toluene. The eROP was kinetically improved by solvent assisted method (by TEA) and gave 6 time faster reaction.

Microstructure Analysis and Model Discrimination of Enzyme-Catalyzed Copolyesters

The comonomer sequence distributions were analyzed for a series of poly(ε-caprolactone-co-δ-valerolactone) (PCV) copolymers using ¹³C nuclear magnetic resonance (NMR) spectroscopy. The four dyad sequences each showed well-resolved peaks in the NMR spectra that allowed easy quantification of the dyad and triad fractions. Although compositional analysis could not discriminate between terminal and penultimate model copolymerization kinetics, the monomer sequence distributions clearly indicated that the lipase-catalyzed copolymerization proceeds via terminal model kinetics. This NMR analytical tool enables rapid characterization of lipase-catalyzed copolymers.

Design and implementation of two-dimensional polymer adsorption models: evaluating the stability of Candida antarctica lipase B/solid-support interfaces by QCM-D

A two-dimensional model of a solid-supported enzyme catalyst bead is fabricated on a quartz crystal microbalance with dissipation monitoring (QCM-D) sensor to measure in situ interfacial stability and mechanical properties of Candida antarctica Lipase B (CAL B) under varied conditions relating to ring-opening polymerization. The model was fabricated using a dual photochemical approach, where poly(methyl methacrylate) (PMMA) thin films were cross-linked by a photoactive benzophenone monolayer and blended cross-linking agent. This process produces two-dimensional, homogeneous, rigid PMMA layers, which mimic commercial acrylic resins in a QCM-D experiment. Adsorption of CAL B to PMMA in QCM-D under varied buffer ionic strengths produces a viscoelastic enzyme surface that becomes more rigid as ionic strength increases. The rigid CAL B/PMMA interface demonstrates up to 20% desorption of enzyme with increasing trace water content. Increased polycaprolactone (PCL) binding at the enzyme surface was also observed, indicating greater PCL affinity for a more hydrated enzyme surface. The enzyme layer destabilized with increasing temperature, yielding near complete reversible catalyst desorption in the model.

Increasing Molecular Mass in Enzymatic Lactone Polymerizations

Using a model developed for the enzyme-catalyzed polymerization and degradation of poly(caprolactone), we illustrate a method and the kinetic mechanisms necessary to improve molecular mass by manipulating equilibrium reactions in the kinetic pathway. For these polymerization/degradation reactions, a water/linear chain equilibrium controls the number of chains in solution. Here, we control the equilibrium by adding water-trapping molecular sieves in the batch polymerization reactions of ε-caprolactone. While ring-opening rates were mostly unaffected, the molecular mass shifted to higher molecular masses after complete conversion was reached, and a good agreement between the experimental and modeling results was found. These results provide a framework to improve the molecular mass for enzyme-catalyzed ring-opening polymerization of lactone.