Controlled enzymatic degradation of poly(ɛ-caprolactone)-based copolymers in the presence of porcine pancreatic lipase

Fabrication of Vascular Grafts Using Poly(ε-Caprolactone) and Collagen-Encapsuled ADSCs for Interposition Implantation of Abdominal Aorta in Rhesus Monkeys

The production of small-diameter artificial vascular grafts continues to encounter numerous challenges, with concerns regarding the degradation rate and endothelialization being particularly critical. In this study, porous PCL scaffolds were prepared, and PCL vascular grafts were fabricated by 3D bioprinting of collagen materials containing adipose-derived mesenchymal stem cells (ADSCs) on the internal wall of the porous PCL scaffold. The PCL vascular grafts were then implanted in the abdominal aorta of Rhesus monkeys for up to 640 days to analyze the degradation of the scaffolds and regeneration of the aorta. Changes in surface morphology, mechanical properties, crystallization property, and molecular weight of porous PCL revealed a similar degradation process of PCL in PBS at pH 7.4 containing Thermomyces lanuginosus lipase and in situ in the abdominal aorta of rhesus monkeys. The contrast of in vitro and in vivo degradation provided valuable reference data for predicting in vivo degradation based on in vitro enzymatic degradation of PCL for further optimization of PCL vascular graft fabrication. Histological analysis through hematoxylin and eosin (HE) staining and fluorescence immunostaining demonstrated that the PCL vascular grafts successfully induced vascular regeneration in the abdominal aorta over the 640-day period. These findings provided valuable insights into the regeneration processes of the implanted vascular grafts. Overall, this study highlights the significant potential of PCL vascular grafts for the regeneration of small-diameter blood vessels.

Multifunctionality of Iodinated Halogen-Bonded Polymer: Biodegradability, Radiopacity, Elasticity, Ductility, and Self-Healing Ability

A polymer with high contents of ester bonds and iodine atoms was synthesized, exhibiting sufficient biodegradability and radioactivity for biomedical applications. The iodine moieties of the synthesized polyester can generate halogen bonding between molecules, which may develop additional functional properties through the bonding. In this study, poly(glycerol adipate) (PGA) was selected and synthesized as a polyester, which was then adequately conjugated with three different types of iodine compounds via the hydroxy groups of PGA. It was found that the iodine compounds could effectively work as donors of halogen bonding. The thermal analysis by differential scanning calorimetry (DSC) revealed that the glass transition temperature increased with the increase in the strength of interactions caused by π-π stacking and halogen bonding, eventually reaching 49.6 °C for PGA with triiodobenzoic groups. An elastomeric PGA with monoiodobenzoic groups was also obtained, exhibiting a high self-healing ability at room temperature because of the reconstruction of halogen bonding. Such multifaceted performance of the synthesized polyester with controllable thermal/mechanical properties was realized by halogen bonding, leading to a promising biomaterial with multifunctionality.

In situ Hydrogels Prepared by Photo-initiated Crosslinking of Acrylated Polymers for Local Delivery of Antitumor Drugs

A triblock copolymer was synthesized by ring opening polymerization of ε-caprolactone in the presence of poly(ethylene glycol) (PEG). The resulted PCL-PEG-PCL triblock copolymer, PEG and monomethoxy (MPEG) were functionalized by end group acrylation. NMR and FT-IR analyses evidenced the successful synthesis and functionalization of polymers. A series of photo-crosslinked hydrogels composed of acrylated PEG-PCL-Acr and MPEG-Acr or PEG-Acr were prepared by exposure to visible light using lithium phenyl-2,4,6-trimethylbenzoylphosphinate as initiator. The hydrogels present a porous and interconnected structure as shown by SEM. The swelling performance of hydrogels is closely related to the crosslinking density and hydrophilic content. Addition of MPEG or PEG results in increase in water absorption capacity of hydrogels. In vitro degradation of hydrogels was realized in the presence of a lipase from porcine pancreas. Various degradation rates were obtained which mainly depend on the hydrogel composition. MTT assay confirmed the good biocompatibility of hydrogels. Importantly, in situ gelation was achieved by irradiation of a precursor solution injected in the abdomen of mice. Doxorubicin (DOX) was selected as a model antitumor drug to evaluate the potential of hydrogels in cancer therapy. Drug-loaded hydrogels were prepared by in situ encapsulation. In vitro drug release studies showed a sustained release during 28 days with small burst release. DOX-loaded hydrogels exhibit antitumor activity against A529 lung cancer cells comparable to free drug, suggesting that injectable in situ hydrogel with tunable properties could be most promising for local drug delivery in cancer therapy.

Electrospun Polycaprolactone (PCL) Degradation: An In Vitro and In Vivo Study

Polycaprolactone (PCL) is widely used in tissue engineering due to its interesting properties, namely biocompatibility, biodegradability, elastic nature, availability, cost efficacy, and the approval of health authorities such as the American Food and Drug Administration (FDA). The PCL degradation rate is not the most adequate for specific applications such as skin regeneration due to the hydrophobic nature of bulk PCL. However, PCL electrospun fiber meshes, due to their low diameters resulting in high surface area, are expected to exhibit a fast degradation rate. In this work, in vitro and in vivo degradation studies were performed over 90 days to evaluate the potential of electrospun PCL as a wound dressing. Enzymatic and hydrolytic degradation studies in vitro, performed in a static medium, demonstrated the influence of lipase, which promoted a rate of degradation of 97% for PCL meshes. In an in vivo scenario, the degradation was slower, although the samples were not rejected, and were well-integrated in the surrounding tissues inside the subcutaneous pockets specifically created.

Degradation of P(3HB-co-4HB) Films in Simulated Body Fluids

A novel model of biodegradable PHA copolymer films preparation was applied to evaluate the biodegradability of various PHA copolymers and to discuss its biomedical applicability. In this study, we illustrate the potential biomaterial degradation rate affectability by manipulation of monomer composition via controlling the biosynthetic strategies. Within the experimental investigation, we have prepared two different copolymers of 3-hydroxybutyrate and 4-hydroxybutyrate—P(3HB-co-36 mol.% 4HB) and P(3HB-co-66 mol.% 4HB), by cultivating the thermophilic bacterial strain Aneurinibacillus sp. H1 and further investigated its degradability in simulated body fluids (SBFs). Both copolymers revealed faster weight reduction in synthetic gastric juice (SGJ) and artificial colonic fluid (ACF) than simple homopolymer P3HB. In addition, degradation mechanisms differed across tested polymers, according to SEM micrographs. While incubated in SGJ, samples were fragmented due to fast hydrolysis sourcing from substantially low pH, which suggest abiotic degradation as the major degradation mechanism. On the contrary, ACF incubation indicated obvious enzymatic hydrolysis. Further, no cytotoxicity of the waste fluids was observed on CaCO-2 cell line. Based on these results in combination with high production flexibility, we suggest P(3HB-co-4HB) copolymers produced by Aneurinibacillus sp. H1 as being very auspicious polymers for intestinal in vivo treatments.

Antibiotic-Loaded Polymersomes for Clearance of Intracellular Burkholderia thailandensis

Melioidosis caused by the facultative intracellular pathogen Burkholderia pseudomallei is difficult to treat due to poor intracellular bioavailability of antibiotics and antibiotic resistance. In the absence of novel compounds, polymersome (PM) encapsulation may increase the efficacy of existing antibiotics and reduce antibiotic resistance by promoting targeted, infection-specific intracellular uptake. In this study, we developed PMs composed of widely available poly(ethylene oxide)-polycaprolactone block copolymers and demonstrated their delivery to intracellular B. thailandensis infection using multispectral imaging flow cytometry (IFC) and coherent anti-Stokes Raman scattering microscopy. Antibiotics were tightly sequestered in PMs and did not inhibit the growth of free-living B. thailandensis. However, on uptake of antibiotic-loaded PMs by infected macrophages, IFC demonstrated PM colocalization with intracellular B. thailandensis and a significant inhibition of their growth. We conclude that PMs are a viable approach for the targeted antibiotic treatment of persistent intracellular Burkholderia infection.

3D-Printed Enzyme-Embedded Plastics

A simple and environmentally friendly approach toward the thermoplastic processing of rapidly degradable plastic-enzyme composites using three-dimensional (3D) printing techniques is described. Polycaprolactone/Amano lipase (PCL/AL) composite films (10 mm × 10 mm; height [h] = ∼400 μm) with an AL loading of 0.1, 1.0, and 5.0% were prepared via 3D printing techniques that entail direct mixing in the solid state and thermal layer-by-layer extrusion. It was found that AL can tolerate in situ processing temperatures up to 130 °C in the solid-state for 60 min without loss of enzymatic activity. The composites were degraded in phosphate buffer (8 mg/mL, composite to buffer) for 7 days at 37 °C and the resulting average percent total weight loss (WL_avg %) was found to be 5.2, 92.9, and 100%, for the 0.1, 1.0, and 5.0% films, respectively. The degradation rates of PCL/AL composites were found to be faster than AL applied externally in the buffer. Thicker PCL/AL 1.0% films (10 mm × 10 mm; h = ∼500 μm) were also degraded over a 7 day period to examine how the weight loss occurs over time with 3.0, 18.1, 36.4, 46.4, and 70.2% weight loss for days 1, 2, 3, 4, and 7, respectively. Differential scanning calorimetry (DSC) analysis shows that the film's percent crystallinity (D_xtal%) increases over time with D_xtal% = 46.5 for day 0 and 53.1% for day 7. Scanning electron microscopy (SEM) analysis found that film erosion begins at the surface and that water can penetrate the interior via surface pores activating the enzymes embedded in the film. Controlled release experiments utilizing dye-loaded PCL/AL/dye (AL = 1.0%; dye = 0.1%) composites were degraded over a 7 day period with the bulk of the dye released by the fourth day. The PCL/AL multimaterial objects containing AL-resistant polylactic acid (PLA) were also printed and degraded to demonstrate the application of this material on more complex structures.

Enzymatic degradation and biofilm formation during biodegradation of polylactide and polycaprolactone polymers in various environments

The present article presents the results of research on the susceptibility of polylactide, poly(ɛ-caprolactone) and mixtures to biodegradation in conditions imitating natural extracts of compost, activated sludge, sea and river water, determined by the biochemical oxygen consumption by microorganisms and susceptibility to enzymatic degradation with the use of enzyme solutions of fungal microbial origin. Analyzes of both types of degradation were carried out over a period of seven days and in four environments: compost, activated sludge, river and sea water, and four enzymatic solutions containing proteinase K, protease, esterase, and lipase. The amount of oxygen consumed by microorganisms in the presence of the tested films was determined, as well as the weight loss determined after the samples were incubated in enzymatic solutions. Images of the surface of individual samples, taken by fluorescence microscopy and scanning electron microscopy, confirm the formation of bacterial biofilm and the results of biochemical oxygen consumption by microorganisms, or weight loss. It was shown that the compost and activated sludge extract as well as the enzymes proteinase K from Engyodontium album (synonym Tritirachium album) and protease from Bacillus licheniformis had the greatest impact on the biodegradation of the tested materials.

Tissue Engineering and Three-Dimensional Printing in Periodontal Regeneration: A Literature Review

The three-dimensional printing of scaffolds is an interesting alternative to the traditional techniques of periodontal regeneration. This technique uses computer assisted design and manufacturing after CT scan. After 3D modelling, individualized scaffolds are printed by extrusion, selective laser sintering, stereolithography, or powder bed inkjet printing. These scaffolds can be made of one or several materials such as natural polymers, synthetic polymers, or bioceramics. They can be monophasic or multiphasic and tend to recreate the architectural structure of the periodontal tissue. In order to enhance the bioactivity and have a higher regeneration, the scaffolds can be embedded with stem cells and/or growth factors. This new technique could enhance a complete periodontal regeneration. This review summarizes the application of 3D printed scaffolds in periodontal regeneration. The process, the materials and designs, the key advantages and prospects of 3D bioprinting are highlighted, providing new ideas for tissue regeneration.

Biofilm formation during biodegradation of polylactide, poly (3,4 hydroxybutyrate) and poly(ε-caprolactone) in activated sludge

Biodegradable materials, namely pure polylactide (PLA), poly (3,4-hydroxybutyrate) (PHB), poly(ε-caprolactone) (PCL) were investigated to assess their degradability by activated sludge. The study aimed at the isolation of biofilm-forming bacteria and the determination of their hydrolytic activity toward the PLA, PHB, and PCL with embedded PHMG derivatives. The biological oxygen demand and physical properties (tensile strength, water vapor permeability, surface structure) of materials indicated that PCL was the best biodegradable film. Aeromonas and Rhodococcus isolated from the polymers' surface during the process of decomposition showed the ability to form biofilms. The introduction of PHMG derivatives into PLA, PCL, and PHB films did not affect biofilm formation and hydrolase activity for most of the isolates. PHMG derivatives at the concentration of 1% disturbed the degradation process.

Hemodynamic loads distinctively impact the secretory profile of biomaterial-activated macrophages - implications for in situ vascular tissue engineering

Biomaterials are increasingly used for in situ vascular tissue engineering, wherein resorbable fibrous scaffolds are implanted as temporary carriers to locally initiate vascular regeneration. Upon implantation, macrophages infiltrate and start degrading the scaffold, while simultaneously driving a healing cascade via the secretion of paracrine factors that direct the behavior of tissue-producing cells. This balance between neotissue formation and scaffold degradation must be maintained at all times to ensure graft functionality. However, the grafts are continuously exposed to hemodynamic loads, which can influence macrophage response in a hitherto unknown manner and thereby tilt this delicate balance. Here we aimed to unravel the effects of physiological levels of shear stress and cyclic stretch on biomaterial-activated macrophages, in terms of polarization, scaffold degradation and paracrine signaling to tissue-producing cells (i.e. (myo)fibroblasts). Human THP-1-derived macrophages were seeded in electrospun polycaprolactone bis-urea scaffolds and exposed to shear stress (∼1 Pa), cyclic stretch (∼1.04), or a combination thereof for 8 days. The results showed that macrophage polarization distinctly depended on the specific loading regime applied. In particular, hemodynamic loading decreased macrophage degradative activity, especially in conditions of cyclic stretch. Macrophage activation was enhanced upon exposure to shear stress, as evidenced from the upregulation of both pro- and anti-inflammatory cytokines. Exposure to the supernatant of these dynamically cultured macrophages was found to amplify the expression of tissue formation- and remodeling-related genes in (myo)fibroblasts statically cultured in comparable electrospun scaffolds. These results emphasize the importance of macrophage mechano-responsiveness in biomaterial-driven vascular regeneration.

Long-Term Evaluation of Dip-Coated PCL-Blend-PEG Coatings in Simulated Conditions

Our study focused on the long-term degradation under simulated conditions of coatings based on different compositions of polycaprolactone-polyethylene glycol blends (PCL-blend-PEG), fabricated for titanium implants by a dip-coating technique. The degradation behavior of polymeric coatings was evaluated by polymer mass loss measurements of the PCL-blend-PEG during immersion in SBF up to 16 weeks and correlated with those yielded from electrochemical experiments. The results are thoroughly supported by extensive compositional and surface analyses (FTIR, GIXRD, SEM, and wettability investigations). We found that the degradation behavior of PCL-blend-PEG coatings is governed by the properties of the main polymer constituents: the PEG solubilizes fast, immediately after the immersion, while the PCL degrades slowly over the whole period of time. Furthermore, the results evidence that the alteration of blend coatings is strongly enhanced by the increase in PEG content. The biological assessment unveiled the beneficial influence of PCL-blend-PEG coatings for the adhesion and spreading of both human-derived mesenchymal stem cells and endothelial cells.

Dextran-based tube-guides for the regeneration of the rat sciatic nerve after neurotmesis injury

In this work, dextran-based nerve tube-guides were prepared, characterized and used in a standardized animal model of neurotmesis injury. Non-porous and porous transparent tube-guides were obtained by photocrosslinking of two co-macromonomers based on dextran and poly(ε-caprolactone) (PCL). Swelling capacity of the tube-guides ranged from 40-60% with no visible constriction of their inner diameter. In vitro hydrolytic degradation tests showed that the tube-guides maintained their structural integrity up to 6 months. The in vivo performance of the tube-guides was evaluated by entubulation of the rat sciatic nerve after a neurotmesis injury, with a 10 mm-gap between the nerve stumps. The results showed that the tube-guides were able to promote the regeneration of the nerve in a similar manner to what was observed with conventional techniques (nerve graft and end-to-end suture). Stereological analysis proved that nerve regeneration occurred, and both tube-guides presented fibre diameter and g-ratio closer to healthy sciatic nerves. The histomorphometric analysis of Tibialis anterior (TA) skeletal muscle showed decreased neurogenic atrophy in the porous tube-guides treated group, presenting measurements that are similar to the uninjured control.

Chondrogenic phenotype in responses to poly(ɛ-caprolactone) scaffolds catalyzed by bioenzymes: effects of surface topography and chemistry

Biodegradable poly(ε-caprolactone) (PCL) has been increasingly investigated as a promising scaffolding material for articular cartilage tissue repair. However, its use can be limited due to its surface hydrophobicity and topography. In this study, 3D porous PCL scaffolds fabricated by a fused deposition modeling (FDM) machine were enzymatically hydrolyzed using two different biocatalysts, namely Novozyme®435 and Amano lipase PS, at varied treatment conditions in a pH 8.0 phosphate buffer solution. The improved surface topography and chemistry of the PCL scaffolds were anticipated to ultimately boost the growth of porcine articular chondrocytes and promote the chondrogenic phenotype during cell culture. Alterations in surface roughness, wettability, and chemistry of the PCL scaffolds after enzymatic treatment were thoroughly investigated using several techniques, e.g., SEM, AFM, contact angle and surface energy measurement, and XPS. With increasing enzyme content, incubation time, and incubation temperature, the surfaces of the PCL scaffolds became rougher and more hydrophilic. In addition, Novozyme®435 was found to have a higher enzyme activity than Amano lipase PS when both were used in the same enzymatic treatment condition. Interestingly, the enzymatic degradation process rarely induced the deterioration of compressive strength of the bulk porous PCL material and slightly reduced the molecular weight of the material at the filament surface. After 28 days of culture, both porous PCL scaffolds catalyzed by Novozyme®435 and Amano lipase PS could facilitate the chondrocytes to not only proliferate properly, but also function more effectively, compared with the non-modified porous PCL scaffold. Furthermore, the enzymatic treatments with 50 mg of Novozyme®435 at 25 °C from 10 min to 60 min were evidently proven to provide the optimally enhanced surface roughness and hydrophilicity most significantly favorable for induction of chondrogenic phenotype, indicated by the greatest expression level of cartilage-specific gene and the largest production of total glycosaminoglycans.

Effect of organic solvent on enzymatic degradation of cyclic PBS-based polymers by lipase N435

Poly(butylene succinate-co-cyclohexane dimethanol succinate) (P(BS-co-CHDMS)) and poly(butylene succinate-co-butanediol cyclohexanedicarboxylic acid) (P(BS-co-BCHDA)) were catalytically degraded by Candida antarctica lipase Novozyme 435 (N435) in CHCl₃ and THF. The results indicated that the degradation rate was P(BS-co-CHDMS) > P(BS-co-BCHDA) > poly(butylene succinate) (PBS). The degradation rate of copolyesters was higher in CHCl₃ than in THF, the highest degradation rate of 67% being obtained for P(BS-co-CHDMS). Hence, the CHCl₃ solvent is more suitable for the enzyme-catalytic degradation of copolyesters, since the lipase can easier recognize the butylene succinate (BS-), (butanediol cyclohexanedicarboxylic acid) (BCA-), and (cyclohexane dimethanol succinate-type) (CMS-type) ester bonds in this solvent. Moreover, it can recognize the CMS-type ester bonds with a higher specificity than the (butanediol cyclohexanedicarboxylic acid type) (BCA-type) ester bonds. Molecular simulation results indicated that the structure of the lipase was stable in CHCl₃ and THF. However, CHCl₃ proved to be more suitable for a stable activity of the enzyme. The active pocket contains acyl-binding hydrophilic residues which are recognized by the substrate. The increase in the content of saturated cycles can increase the hydrophobicity of the substrate and thus, the amount of substrate bond to enzyme active site is increased, which facilitates the enzymatic degradation of copolyesters.

The degradation and performance of electrospun supramolecular vascular scaffolds examined upon in vitro enzymatic exposure

To maintain functionality during in situ vascular regeneration, the rate of implant degradation should be closely balanced by neo-tissue formation. It is unknown, however, how the implant's functionality is affected by the degradation of the polymers it is composed of. We therefore examined the macro- and microscopic features as well as the mechanical performance of vascular scaffolds upon in vitro enzymatic degradation. Three candidate biomaterials with supramolecularly interacting bis-urea (BU) hard blocks ('slow-degrading' polycarbonate-BU (PC-BU), 'intermediate-degrading' polycarbonate-ester-BU (PC(e)-BU), and 'fast-degrading' polycaprolactone-ester-BU (PCL-BU)) were synthesized and electrospun into microporous scaffolds. These materials possess a sequence-controlled macromolecular structure, so their susceptibility to degradation is tunable by controlling the nature of the polymer backbone. The scaffolds were incubated in lipase and monitored for changes in physical, chemical, and mechanical properties. Remarkably, comparing PC-BU to PC(e)-BU, we observed that small changes in macromolecular structure led to significant differences in degradation kinetics. All three scaffold types degraded via surface erosion, which was accompanied by fiber swelling for PC-BU scaffolds, and some bulk degradation and a collapsing network for PCL-BU scaffolds. For the PC-BU and PC(e)-BU scaffolds this resulted in retention of mechanical properties, whereas for the PCL-BU scaffolds this resulted in stiffening. Our in vitro study demonstrates that vascular scaffolds, electrospun from sequence-controlled supramolecular materials with varying ester contents, not only display different susceptibilities to degradation, but also degrade via different mechanisms. STATEMENT OF SIGNIFICANCE: One of the key elements to successfully engineer vascular tissues in situ, is to balance the rate of implant degradation and neo-tissue formation. Due to their tunable properties, supramolecular polymers can be customized into attractive biomaterials for vascular tissue engineering. Here, we have exploited this tunability and prepared a set of polymers with different susceptibility to degradation. The polymers, which were electrospun into microporous scaffolds, displayed not only different susceptibilities to degradation, but also obeyed different degradation mechanisms. This study illustrates how the class of supramolecular polymers continues to represent a promising group of materials for tissue engineering approaches.

Macrophage-Driven Biomaterial Degradation Depends on Scaffold Microarchitecture

In situ tissue engineering is a technology in which non-cellular biomaterial scaffolds are implanted in order to induce local regeneration of replaced or damaged tissues. Degradable synthetic electrospun scaffolds are a versatile and promising class of biomaterials for various in situ tissue engineering applications, such as cardiovascular replacements. Functional in situ tissue regeneration depends on the balance between endogenous neo-tissue formation and scaffold degradation. Both these processes are driven by macrophages. Upon invasion into a scaffold, macrophages secrete reactive oxygen species (ROS) and hydrolytic enzymes, contributing to oxidative and enzymatic biomaterial degradation, respectively. This study aims to elucidate the effect of scaffold microarchitecture, i.e., μm-range fiber diameter and fiber alignment, on early macrophage-driven scaffold degradation. Electrospun poly-ε-caprolactone-bisurea (PCL-BU) scaffolds with either 2 or 6 μm (Ø) isotropic or anisotropic fibers were seeded with THP-1 derived human macrophages and cultured in vitro for 4 or 8 days. Our results revealed that macroph age-induced oxidative degradation in particular was dependent on scaffold microarchitecture, with the highest level of ROS-induced lipid peroxidation, NADPH oxidase gene expression and degradation in the 6 μm Ø anisotropic group. Whereas, biochemically polarized macrophages demonstrated a phenotype-specific degradative potential, the observed differences in macrophage degradative potential instigated by the scaffold microarchitecture could not be attributed to either distinct M1 or M2 polarization. This suggests that the scaffold microarchitecture uniquely affects macrophage-driven degradation. These findings emphasize the importance of considering the scaffold microarchitecture in the design of scaffolds for in situ tissue engineering applications and the tailoring of degradation kinetics thereof.

Enzyme-catalysed biodegradation of carbon dots follows sequential oxidation in a time dependent manner

Carbon dots (CDs) have recently garnered significant attention owing to their excellent luminescence properties, thereby demonstrating a variety of applications in in vitro and in vivo imaging. Understanding the long-term metabolic fate of these agents in a biological environment is the focus of this work. Here we show that the CDs undergo peroxide catalysed degradation in the presence of lipase. Our results indicate that differently charged CD species exhibit unique degradation kinetics upon being subjected to enzyme oxidation. Furthermore, this decomposition correlates with the relative accessibility of the enzymatic molecule. Using multiple physico-chemical characterization studies and molecular modelling, we confirmed the interaction of passivating surface abundant molecules with the enzyme. Finally, we have identified hydroxymethyl furfural as a metabolic by-product of the CDs used here. Our results indicate the possibility and a likely mechanism for complete CD degradation in living systems that can pave the way for a variety of biomedical applications.

Experimental studies on preparation of the porous and small-diameter poly(ε-caprolactone) external vascular scaffold and its degradability and biocompatibility

Aim: This study was aim to prepare a porous poly(ε-caprolactone) (PCL) biodegradable external vascular scaffold by dipping and leaching method, and to assess its mechanical property, degradability and biocompatibility. Methods: We used the PCL-1, PCL-2 as the raw materials and NaCl particles as the pore-forming agents to construct a porous PCL external vascular scaffold. We tested the mechanical property of the porous PCL external vascular scaffold. The degradability of the scaffold was studied in the presence of thermomyces lanuginosus lipase (TL lipase). After 1, 3, and 5, 7 days, the samples were taken out, and the pH of the media was measured. The form-stability of the scaffold was investigated by macroscopic observation and the microstructure of it was observed by SEM. The cytotoxicity of the scaffold was evaluated by CCK-8 assay. Results: PCL-1 could make a white integrated external vascular scaffold with uniform texture. When the concentration of NaCl was less than or equal to 50%, the tensile strength of the porous PCL-1 external vascular scaffolds were higher than 4.2 Mpa, which meet the demand of clinical vascular transplantation. With the degradation of the scaffold in the lipase media, the form-stability of the scaffold was seriously destroyed, the surface of the scaffold began to degrade with some honeycomb holes, and the pH of the media values were lower than the initial reading of 7.4. Rat adipose-derived stem cells (rADSCs) cultured in the extractions of the porous PCL external vascular scaffold had good proliferation and cell morphology compared to the control group. Conclusion: The porous PCL-1-50 external vascular scaffold, with the 50% concentration of NaCl, had the maximum porosity on the basis of enough mechanical strength which meets the demand of clinical vascular transplantation. Moreover, it had good biocompatibility with rADSCs and the degradation mechanism of the scaffold was surface degradation.

Nanoparticles with high payloads of pipemidic acid, a poorly soluble crystalline drug: drug-initiated polymerization and self-assembly approach

Nowadays, biodegradable polymers such as poly(lactic acid) (PLA), poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(ε-caprolactone) (PCL) remain the most common biomaterials to produce drug-loaded nanoparticles (NPs). Pipemidic acid (PIP) is a poorly soluble antibiotic with a strong tendency to crystallize. PIP incorporation in PLA/PLGA NPs was challenging because of PIP crystals formation and burst release. As PIP had a poor affinity for the NPs, an alternative approach to encapsulation was used, consisting in coupling PIP to PCL. Thus, a PCL-PIP conjugate was successfully synthesized by an original drug-initiated polymerization in a single step without the need of catalyst. PCL-PIP was characterized by NMR, IR, SEC and mass spectrometry. PCL-PIP was used to prepare self-assembled NPs with PIP contents as high as 27% (w/w). The NPs were characterized by microscopy, DLS, NTA and TRPS. This study paves the way towards the production of NPs with high antibiotic payloads by drug-initiated polymerization. Further studies will deal with the synthesis of novel polymer-PIP conjugates with ester bonds between the drug and PCL. PIP can be considered as a model drug and the strategy developed here could be extended to other challenging antibiotics or anticancer drugs and employed to efficiently incorporate them in NPs.

Effect of in vitro enzymatic degradation on 3D printed poly(ε-caprolactone) scaffolds: morphological, chemical and mechanical properties

BACKGROUND

In recent years, the tissue engineering (TE) field has significantly benefited from advanced techniques such as additive manufacturing (AM), for the design of customized 3D scaffolds with the aim of guided tissue repair. Among the wide range of materials available to biomanufacture 3D scaffolds, poly(ε-caprolactone) (PCL) clearly arises as the synthetic polymer with the greatest potential, due to its unique properties - namely, biocompatibility, biodegradability, thermal and chemical stability and processability. This study aimed for the first time to investigate the effect of pore geometry on the in vitro enzymatic chain cleavage mechanism of PCL scaffolds manufactured by the AM extrusion process.

METHODS

Methods: Morphological properties of 3D printed PCL scaffolds before and after degradation were evaluated using Scanning Electron Microscopy (SEM) and micro-computed tomography (μ-CT). Differential Scanning Calorimetry (DSC) was employed to determine possible variations in the crystallinity of the scaffolds during the degradation period. The molecular weight was assessed using Size Exclusion Chromatography (SEC) while the mechanical properties were investigated under static compression conditions.

RESULTS

Morphological results suggested a uniform reduction of filament diameter, while increasing the scaffolds' porosity. DSC analysis revealed and increment in the crystallinity degree while the molecular weight, evaluated through SEC, remained almost constant during the incubation period (25 days). Mechanical analysis highlighted a decrease in the compressive modulus and maximum stress over time, probably related to the significant weight loss of the scaffolds.

CONCLUSIONS

All of these results suggest that PCL scaffolds undergo enzymatic degradation through a surface erosion mechanism, which leads to significant variations in mechanical, physical and chemical properties, but which has little influence on pore geometry.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.

Hyperbranched polyesters as biodegradable and antibacterial additives

Herein, we present novel hyperbranched poly(amino-ester)s functionalized with quaternary ammonium salts.

Synthesis, characterization and enzymatic degradation of copolymers of ε-caprolactone and hydroxy-fatty acids

New copolymers of ε-caprolactone with three hydroxy-fatty acids, 12-hydroxy stearic acid, 16-hydroxyhexadecanoic acid and ricinoleic acid, were synthesized by catalytic polyesterification. The reactions were carried out in solvent-free systems and in organic solvents as well, using tin(II) 2-ethylhexanoate as catalyst, at different temperatures and molar ratios of the comonomers. Cyclic and linear polymeric products with medium molar weight of about 2000 Da have been synthesized and their chemical structures were confirmed by FT-IR, NMR and MALDI-TOF MS analysis. The synthesis parameters were optimized and the ε-caprolactone/hydroxy acid molar ratio was set as 5:1, according to mass spectrometry results. The biodegradability of the newly synthesized polymers was studied in the presence of Candida antarctica B lipase in phosphate buffer solutions (pH=7.4), at 37°C. The weight-loss profile emphasized the degradation of the 16-hydroxyhexadecanoic acid based polymer samples at more than 50% of their initial weight in 18 days of incubation in the presence of the lipase. The composition of the degradation products was assessed using the GC-MS technique and displayed residues of the comonomers moieties.

Hydrolytic and oxidative degradation of electrospun supramolecular biomaterials: In vitro degradation pathways

The emerging field of in situ tissue engineering (TE) of load bearing tissues places high demands on the implanted scaffolds, as these scaffolds should provide mechanical stability immediately upon implantation. The new class of synthetic supramolecular biomaterial polymers, which contain non-covalent interactions between the polymer chains, thereby forming complex 3D structures by self assembly. Here, we have aimed to map the degradation characteristics of promising (supramolecular) materials, by using a combination of in vitro tests. The selected biomaterials were all polycaprolactones (PCLs), either conventional and unmodified PCL, or PCL with supramolecular hydrogen bonding moieties (either 2-ureido-[1H]-pyrimidin-4-one or bis-urea units) incorporated into the backbone. As these materials are elastomeric, they are suitable candidates for cardiovascular TE applications. Electrospun scaffold strips of these materials were incubated with solutions containing enzymes that catalyze hydrolysis, or solutions containing oxidative species. At several time points, chemical, morphological, and mechanical properties were investigated. It was demonstrated that conventional and supramolecular PCL-based polymers respond differently to enzyme-accelerated hydrolytic or oxidative degradation, depending on the morphological and chemical composition of the material. Conventional PCL is more prone to hydrolytic enzymatic degradation as compared to the investigated supramolecular materials, while, in contrast, the latter materials are more susceptible to oxidative degradation. Given the observed degradation pathways of the examined materials, we are able to tailor degradation characteristics by combining selected PCL backbones with additional supramolecular moieties. The presented combination of in vitro test methods can be employed to screen, limit, and select biomaterials for pre-clinical in vivo studies targeted to different clinical applications.

In vitro degradation and cell attachment studies of a new electrospun polymeric tubular graft

Electrospinning technique was utilized to engineer a small-diameter (id = 4 mm) tubular graft. The tubular graft was made from biocompatible and biodegradable polymers polycaprolactone (PCL) and poliglecaprone with 3:1 (PCL:PGC) ratio. Enzymatic degradation effect on the mechanical properties and fiber morphology in the presence of lipase enzyme were observed. Significant changes in tensile strength (1.86-1.49 MPa) and strain (245-205 %) were noticed after 1 month in vitro degradation. The fiber breakage was clearly evident through scanning electron microscopy (SEM) after 4 weeks in vitro degradation. Then, the graft was coated with a collagenous protein matrix to impart bioactivity. Human umbilical vein endothelial cells (HUVECs) and aortic artery smooth muscle cells (AoSMCs) attachment on the coated graft were observed in static condition. Further, HUVECs were seeded on the lumen surface of the grafts and exposed to laminar shear stress for 12 h to understand the cell attachment. The coated graft was aged in PBS solution (pH 7.3) at 37 °C for 1 month to understand the coating stability. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) suggested the erosion of the protein matrix from the coated graft under in vitro condition.