Porous Copolymers of ε-Caprolactone as Scaffolds for Tissue Engineering

Stimuli-Responsive Self-Assembly of Poly(2-(Dimethylamino)ethyl Methacrylate-co-(oligo ethylene glycol)methacrylate) Random Copolymers and Their Modified Derivatives

In this work, the synthesis and the stimuli-responsive self-assembly behavior of novel double-hydrophilic poly(2-(dimethylamino)ethyl methacrylate-co-(oligo ethylene glycol)methacrylate) random copolymers and their chemically modified derivatives are presented. The synthesis of P(DMAEMA-co-OEGMA) copolymers of different DMAEMA mass compositions was successfully conducted through RAFT polymerization, further followed by the hydrophilic/hydrophobic quaternization with methyl iodide (CH3I), 1-iodohexane (C6H13I), and 1-iodododecane (C12H25I). The tertiary and quaternary amines are randomly arranged within the DMAEMA segment, responding thus to pH, temperature, and salt alterations in aqueous solutions. Light scattering techniques elucidated the intramolecular self-folding and intermolecular self-assembly of polymer chains of P(DMAEMA-co-OEGMA) copolymers upon exposure to different pHs and temperatures. Q(P(DMAEMA-co-OEGMA)) cationic polyelectrolytes demonstrated moderate response to pH, temperature, and ionic strength as a result of the permanent hydrophilic/hydrophobic profile, closely connected with the attached alkyl chains and the quaternization degree. Moreover, fluorescence spectroscopy measurements confirmed the internal micropolarity and the picture of the aggregate inner structure.

Design and Characterization of Maltose-Conjugated Polycaprolactone Nanofibrous Scaffolds for Uterine Tissue Engineering

Purpose

Uterine anomalies are prevalent in women, and the major treatment assisted to them is hysterectomy as donor availability is extremely low. To overcome this, engineering uterine myometrium smooth muscle tissue has become very important. Several studies have shown that polycaprolactone (PCL) nanofibers are very effective in engineering smooth muscles, as this type of scaffold has structural similarities to the extracellular matrices of the cells. Here, we hypothesize that by electrospinning PCL nanofibers, they form a suitable scaffold for uterine tissue engineering.

Methods

Polycaprolactone nanofibrous scaffolds were fabricated, and surface modification was performed following two step wet chemistry method. First step is aminolysis which introduces the primary amine groups on the PCL scaffolds following which maltose is conjugated on the scaffolds. This was confirmed by the ninhydrin assay for the presence of amine groups. This was followed by ELLA assay where the presence of maltose on the scaffold was quantified. Modified scaffolds were further characterized by scanning electron microscope (SEM), contact angle analysis and Fourier transform infrared spectroscopy (FTIR). MTT assay, live-dead assay and actin staining were performed on the maltose immobilization to study the improvement of the cell attachment and proliferation rates on the modified scaffolds.

Results

Human uterine fibroblast (HUF) cells displayed significant proliferation on the maltose-modified PCL scaffolds, and they also exhibited appropriate morphology indicating that these modified fibers are highly suitable for uterine cell growth.

Conclusion

Our results indicate that the fabricated maltose PCL (MPCL) scaffolds would be a potential biomaterial to treat uterine injuries and promote regeneration.

Lay Summary and Future Work

Uterine anomalies are prevalent in women, and the major treatment is hysterectomy as donor availability is extremely low. Over the past few years, considerable efforts have been directed towards uterine tissue regeneration. This study is to design a tissue engineered scaffold that could act as a human uterine myometrial patch. We propose to create uterine fibroblast-based synthetic scaffolds that act in a condition similar to the intrauterine microenvironment where the embryos are embedded in the uterine wall. For understanding of the efficiency of the myometrial patch, functional characterization will be performed to study the effects of estrogen and prostaglandins on myometrial activity of the designed patch. Results from these experiments will assist a deeper understanding of how to construct a total bioengineered uterus which can substitute the uterus transplantation procedure, which nonetheless is in its initial stages of development.

Graphical Abstract

Recent Developments in Lactone Monomers and Polymer Synthesis and Application

Lactones are a group of compounds that have been known for several decades. The commercial importance of lactones results from the possibility of manufacturing of a broad scope of derivatives and polymers with a wide spectrum of applications. In this work the synthesis and characterization of simple lactones are described, which due to the easy methods of the synthesis are of high importance for the industry. The chemical as well as biochemical methods are included with special attention paid to the methods that avoid metal catalysts, initiators or toxic solvents, allowing the use of the final products for the medical applications, e.g., for controlled drug-release systems, resorbable surgical threads, implants, tissue scaffolds or for the production of drugs. Lactone-based derivatives, such as polymers, copolymers, composites or three-dimensional structures are also presented. The work is focused on the methods for the synthesis of lactones and lactones derivates, as well as on the special properties and application of the studied compounds.

Biomaterials for stem cell engineering and biomanufacturing

Recent years have witnessed the expansion of tissue failures and diseases. The uprising of regenerative medicine converges the sight onto stem cell-biomaterial based therapy. Tissue engineering and regenerative medicine proposes the strategy of constructing spatially, mechanically, chemically and biologically designed biomaterials for stem cells to grow and differentiate. Therefore, this paper summarized the basic properties of embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells. The properties of frequently used biomaterials were also described in terms of natural and synthetic origins. Particularly, the combination of stem cells and biomaterials for tissue repair applications was reviewed in terms of nervous, cardiovascular, pancreatic, hematopoietic and musculoskeletal system. Finally, stem-cell-related biomanufacturing was envisioned and the novel biofabrication technologies were discussed, enlightening a promising route for the future advancement of large-scale stem cell-biomaterial based therapeutic manufacturing.

Highly porous polycaprolactone scaffolds doped with calcium silicate and dicalcium phosphate dihydrate designed for bone regeneration

Polycaprolactone (PCL), dicalcium phosphate dihydrate (DCPD) and/or calcium silicates (CaSi) have been used to prepare highly porous scaffolds by thermally induced phase separation technique (TIPS). Three experimental mineral-doped formulations were prepared (PCL-10CaSi, PCL-5CaSi-5DCPD, PCL-10CaSi-10DCPD); pure PCL scaffolds constituted the control group. Scaffolds were tested for their chemical-physical and biological properties, namely thermal properties by differential scanning calorimetry (DSC), mechanical properties by quasi-static parallel-plates compression testing, porosity by a standard water-absorption method calcium release, alkalinizing activity, surface microchemistry and micromorphology by Environmental Scanning electronic Microscopy (ESEM), apatite-forming ability in Hank Balanced Saline Solution (HBSS) by Energy Dispersive X-ray Spectroscopy (EDX) and micro-Raman, and direct contact cytotoxicity. All mineral-doped scaffolds released calcium and alkalinized the soaking medium, which may favor a good biological (osteogenic) response. ESEM surface micromorphology analyses after soaking in HBSS revealed: pure PCL, PCL-10CaSi and PCL-10CaSi-10DCPD kept similar surface porosity percentages but different pore shape modifications. PCL-5CaSi-5DCPD revealed a significant surface porosity increase despite calcium phosphates nucleation (p < 0.05). Micro-Raman spectroscopy detected the formation of a B-type carbonated apatite (Ap) layer on the surface of PCL-10CaSi-10DCPD aged for 28 days in HBSS; a similar phase (but of lower thickness) formed also on PCL-5CaSi-5DCPD and PCL; the deposit formed on PCL-10CaSi was mainly composed of calcite. All PCL showed bulk open porosity higher than 94%; however, no relevant brittleness was observed in the materials, which retained the possibility to be handled without collapsing. The thermo-mechanical properties showed that the reinforcing and nucleating action of the inorganic fillers CaSi and DCPD improved viscoelastic properties of the scaffolds, as confirmed by the increased value of storage modulus and the slight increase in the crystallization temperature for all the biomaterials. A detrimental effect on the mechanical properties was observed in samples with the highest amount of inorganic particles (PCL-10CaSi-10DCPD). All the scaffolds showed absence of toxicity, in particular PCL-10CaSi-10DCPD. The designed scaffolds are biointeractive (release biologically relevant ions), nucleate apatite, possess high surface and internal open porosity and can be colonized by cells, creating a bone forming osteoblastic microenvironment and appearing interesting materials for bone regeneration purposes.

Towards Sustainable High-Performance Thermoplastics: Synthesis, Characterization, and Enzymatic Hydrolysis of Bisguaiacol-Based Polyesters

The utilization of wood-derived building blocks (xylochemicals) to replace fossil-based precursors is an attractive research subject of modern polymer science. Here, we demonstrate that bisguaiacol (BG), a lignin-derived bisphenol analogue, can be used to prepare biobased polyesters with remarkable thermal properties. BG was treated with different activated diacids to investigate the effect of co-monomer structures on the physical properties of the products. Namely, derivatives of adipic acid, succinic acid, and 2,5-furandicarboxylic acid were used. Moreover, a terephthalic acid derivative was used for comparison purposes. The products were characterized by ¹ H NMR spectroscopy, attenuated total reflectance FTIR spectroscopy, gel-permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry to assess their structural and thermal properties in detail. The polymers showed glass-transition temperatures ranging up to 160 °C and thermal stabilities in excess of 300 °C. Furthermore, the susceptibility of the polyester to enzymatic hydrolysis was investigated to assess the potential for further surface functionalization and/or recycling and biodegradation. Indeed, hydrolysis with two different enzymes from the bacteria Thermobifida cellulosilytica led to the release of monomers, as quantified by HPLC. The results of this study indicate that our new polyesters represent promising renewable and biodegradable alternatives to petroleum-based polyesters currently employed in the plastics industry, specifically for applications in which high-temperature stability is essential to ensure overall system integrity.

* A Paradigm for the Evaluation of Tissue-Engineering Biomaterials and Templates

Procedures for the evaluation of tissue-engineering processes, including those used for the testing of the relevant biomaterials, have not been developed in a logical manner. This perspectives paper discusses the limitations of testing regimes and recommends a very different approach. The main emphasis is on the existing methods for assessing the biological safety of these biomaterials, which, it is suggested, are irrelevant for evaluating materials that are intended to facilitate the generation of new tissue. An algorithm is proposed that sets out the pathway from materials design and characterization through to the production of a file that sets out full biocompatibility, functionality, and tissue incorporation data that are suitable for regulatory consideration for first-in-man experiences. Central to this algorithm is the choice of animal models and the real-time monitoring of the implanted construct performance.

Polymers from sugars: cyclic monomer synthesis, ring-opening polymerisation, material properties and applications

This feature article gives an overview of sugar-based polymers that can be made by ring-opening-polymerisation and their applications.

Pore Structure of Macroporous Polymers Using Polystyrene/Silica Composite Particles as Pickering Stabilizers

A novel approach for the preparation of interconnected macroporous polymers with a controllable pore structure was reported. The method was based on the polymerization of water-in-oil Pickering high internal phase emulsion (HIPE) stabilized by polystyrene (PS)/silica composite particles. The composite Pickering stabilizers were facilely obtained by mixing positively charged PS microspheres and negatively charged silica nanoparticles, and their amphiphilicity could be delicately tailored by varying the ratio of PS and silica. The droplet size of Pickering HIPEs was characterized using an optical microscope. The pore structure of polymer foams was observed using a scanning electron microscope. The interconnectivity of macroporous polymers was evaluated upon their gas permeability, which was greatly improved after etching PS microspheres included in the Pickering stabilizers with tetrahydrofuran. As a result, fine tailoring of the pore structure of polymer foams could be realized by simply tuning the ratio of PS to silica particles in the composite stabilizer.

Inverse high internal phase emulsion polymerization (i-HIPE) of GMMA, HEMA and GDMA for the preparation of superporous hydrogels as a tissue engineering scaffold

A series of novel superporous hydrogels for regenerative medicine were prepared by oil-in-water (o/w) or inverse high internal phase emulsion (i-HIPE) copolymerization of glycerol monomethacrylate (GMMA), 2-hydroxy ethyl methacrylate (HEMA) and glycerol dimethacrylate (GDMA) as a cross-linker using a non toxic solvent and a redox initiator system at the physiological temperature (37 °C). The monomer GMMA was synthesized from glycidyl methacrylate (GMA) by an alternative facile method using Amberlyst-15. The described i-HIPEs showed a significantly wider stability window. The polyHIPE hydrogels were characterized by FTIR, BET method for surface area, mercury porosimetry, SEM, DSC, TGA, XRD, compressive strain and strain recovery. The swelling ratio of the hydrogels and their degradation in 0.007 M NaOH and lipase B (Candida antarctica) solutions were determined gravimetrically and the rate of degradation was explained in terms of the molecular structure of the hydrogels. The morphological studies showed that the pore diameter varied between 20 and 30 μm and the pore throats (interconnecting windows) diameter was in the range of 4-8 μm. The described polyHIPE hydrogels were found to have an open cell morphology and interconnected pore architecture, which are important characteristics for scaffold applications. The initial cytotoxicity study performed according to ISO-10993-5 indicated cytocompatibility (97% cell viability) and the subsequent cell seeding and proliferation study exhibited 55-88% cell viability (increased monotonously from GHG-1 to GHG-5), which could be attributed to modulation of the physical and chemical properties of the hydrogels. The described super porous hydrogels are considered as potential candidates for scaffold materials in tissue engineering applications.

Facile synthesis of biodegradable and clickable polymer

We report a facile approach to synthesize a biodegradable and clickable polymer consisting of ε-caprolactone (CL) and allyl methacrylate (AMA) with phosphazene base as the catalyst via hybrid copolymerization.

Polymeric nanoporous materials fabricated with supercritical CO2 and CO2-expanded liquids

This tutorial review focuses on the recent progress in nanoporous polymeric materials fabricated by newly developed supercritical techniques.