Effect of some factors on fabrication of poly(L-lactic acid) microporous foams by thermally induced phase separation using N,N-dimethylacetamide as solvent

Biocompatible, highly interconnected microporous poly(L-lactic acid) (PLLA) foams or scaffolds with nano-fibrous structure, containing pores with diameters of 0.1-3.5 μm and fibers with diameters of 300-700 nm scale, were prepared through the thermally induced liquid-liquid phase separation (TIPS) method using N,N'-dimethyl acetamide (DMAc) as solvent. Various foam morphologies were obtained by changing parameters involved in the TIPS process, such as polymer concentration, solvent composition, and quenching temperatures. The morphology of different foams was examined by scanning electron microscopy, whereas the pore size and the pore size distribution were calculated. The results showed that most porous foams presented nano-fibrous structure with interconnected open pores. In the case of using DMAc as solvent, with increasing polymer concentration, either the average pore diameter or the pore size distribution exhibited a maximum value at 0.05 g/mL polymer concentration and quenching temperature of -30°C. It was found that all the pore size distribution fit the F-distribution equation. With increasing the quenching temperature from -30°C to -10°C, the maximum average pore diameter of the foams decreased and the pore size distribution became narrower, whereas the polymer concentration exhibiting the maximum pore size and widest pore size distribution increased from 0.05 g/mL to 0.07 g/mL. In the case of using the mixed solvent of DMAc/DOX (1,4-dioxane) from 9/1 to 7/3 (v/v) there appeared a maximum value of average pore diameter and a widest pore size distribution all at 0.05 g/mL PLLA concentration and quenching temperature of -30°C. The maximum pore size tends to increase with increasing DOX content.     

Multi-Scale Modification of Metallic Implants With Pore Gradients,Polyelectrolytes and Their Indirect Monitoring In vivo

Metallic implants, especially titanium implants, are widely used in clinical applications. Tissue in-growth and integration to these implants in the tissues are important parameters for successful clinical outcomes. In order to improve tissue integration, porous metallic implants have being developed. Open porosity of metallic foams is very advantageous, since the pore areas can be functionalized without compromising the mechanical properties of the whole structure. Here we describe such modifications using porous titanium implants based on titanium microbeads. By using inherent physical properties such as hydrophobicity of titanium, it is possible to obtain hydrophobic pore gradients within microbead based metallic implants and at the same time to have a basement membrane mimic based on hydrophilic, natural polymers. 3D pore gradients are formed by synthetic polymers such as Poly-L-lactic acid (PLLA) by freeze-extraction method. 2D nanofibrillar surfaces are formed by using collagen/alginate followed by a crosslinking step with a natural crosslinker (genipin). This nanofibrillar film was built up by layer by layer (LbL) deposition method of the two oppositely charged molecules, collagen and alginate. Finally, an implant where different areas can accommodate different cell types, as this is necessary for many multicellular tissues, can be obtained. By, this way cellular movement in different directions by different cell types can be controlled. Such a system is described for the specific case of trachea regeneration, but it can be modified for other target organs. Analysis of cell migration and the possible methods for creating different pore gradients are elaborated. The next step in the analysis of such implants is their characterization after implantation. However, histological analysis of metallic implants is a long and cumbersome process, thus for monitoring host reaction to metallic implants in vivo an alternative method based on monitoring CGA and different blood proteins is also described. These methods can be used for developing in vitro custom-made migration and colonization tests and also be used for analysis of functionalized metallic implants in vivo without histology.     

Fabrication of a Bioactive,PCL-based "Self-fitting" Shape Memory Polymer Scaffold

Tissue engineering has been explored as an alternative strategy for the treatment of critical-sized cranio-maxillofacial (CMF) bone defects. Essential to the success of this approach is a scaffold that is able to conformally fit within an irregular defect while also having the requisite biodegradability, pore interconnectivity and bioactivity. By nature of their shape recovery and fixity properties, shape memory polymer (SMP) scaffolds could achieve defect “self-fitting.” In this way, following exposure to warm saline (~60 ºC), the SMP scaffold would become malleable, permitting it to be hand-pressed into an irregular defect. Subsequent cooling (~37 ºC) would return the scaffold to its relatively rigid state within the defect. To meet these requirements, this protocol describes the preparation of SMP scaffolds prepared via the photochemical cure of biodegradable polycaprolactone diacrylate (PCL-DA) using a solvent-casting particulate-leaching (SCPL) method. A fused salt template is utilized to achieve pore interconnectivity. To realize bioactivity, a polydopamine coating is applied to the surface of the scaffold pore walls. Characterization of self-fitting and shape memory behaviors, pore interconnectivity and in vitro bioactivity are also described.     

Porous devices derived from co-continuous polymer blends as a route for controlled drug release

In this study we examine the release profile of bovine serum albumin (BSA) from a porous polymer matrix derived from a co-continuous polymer blend. The porosity is generated through the selective extraction of one of the continuous phases. This is the first study to examine the approach of using morphologically tailored co-continuous polymer blends as a template for generating porous polymer materials for use in controlled release. A method for the preparation of polymeric capsules is introduced, and the effect of matrix pore size and surface area on the BSA release profile is investigated. Furthermore, the effect of surface charge on release is examined by surface modification of the porous substrate using layer-by-layer deposition techniques. Synthetic, nonerodible polymer, high-density polyethylene (HDPE), was used as a model substrate prepared by melt blending with two different styrene-ethylene-butylene copolymers. Blends with HDPE allow for the preparation of porous substrates with small pore sizes (300 and 600 nm). A blend of polylactide (PLA) and polystyrene was also used to prepare porous PLA with a larger pore size (1.5 microm). The extents of interconnectivity, surface area, and pore dimension of the prepared porous substrates were examined via gravimetric solvent extraction, BET nitrogen adsorption, mercury porosimetry, and image analysis of scanning electron microscopy micrographs. With a loading protocol into the porous HDPE and PLA involving the alternate application of pressure and vacuum, it is shown that virtually the entire porous network was accessible to BSA loading, and loading efficiencies of between 80% and 96% were obtained depending on the pore size of the carrier and the applied pressure. The release profile of BSA from the microporous structure was monitored by UV spectrophotometry. The influence of pore size, surface area, surface charge, and number of deposited layers is demonstrated. It is shown that an effective closed-cell structure in porous PLA can be prepared, effectively eliminating all short-term BSA release.     

Monitoring of cAMP-imprinted polymer by fluorescence spectroscopy

Conventional functional monomers together with fluorescent monomer, trans-4-[p-(N,N-dimethylamino)styryl]-N-vinylbenzylpyridinium chloride (vb-DMASP), were copolymerised in the presence of a target molecule, nucleotide-cAMP that acted as a molecular template. The polymer was copolymerised in thin-layer films. After removal of the template the functionalised cavities that exist in the fluorescent material are able to specifically bind the template. Subsequent adsorption of the template-cAMP causes quenching of fluorescence of the polymer. The specific photochemical processes accompanying the template adsorption are discussed further. The imprinted polymers monitored by both steady-state and time-resolved fluorescence techniques show specificity and selectivity of binding of the template on the imprinted functionalised cavities.     

Supercritical CO2 Foaming of Thermoplastic Materials Derived from Maize: Proof-of-Concept Use in Mammalian Cell Culture Applications

Background

Foams are high porosity and low density materials. In nature, they are a common architecture. Some of their relevant technological applications include heat and sound insulation, lightweight materials, and tissue engineering scaffolds. Foams derived from natural polymers are particularly attractive for tissue culture due to their biodegradability and bio-compatibility. Here, the foaming potential of an extensive list of materials was assayed, including slabs elaborated from whole flour, the starch component only, or the protein fraction only of maize seeds.

Methodology/Principal Findings

We used supercritical CO₂ to produce foams from thermoplasticized maize derived materials. Polyethylene-glycol, sorbitol/glycerol, or urea/formamide were used as plasticizers. We report expansion ratios, porosities, average pore sizes, pore morphologies, and pore size distributions for these materials. High porosity foams were obtained from zein thermoplasticized with polyethylene glycol, and from starch thermoplasticized with urea/formamide. Zein foams had a higher porosity than starch foams (88% and 85%, respectively) and a narrower and more evenly distributed pore size. Starch foams exhibited a wider span of pore sizes and a larger average pore size than zein (208.84 vs. 55.43 μm², respectively). Proof-of-concept cell culture experiments confirmed that mouse fibroblasts (NIH 3T3) and two different prostate cancer cell lines (22RV1, DU145) attached to and proliferated on zein foams.

Conclusions/Significance

We conducted screening and proof-of-concept experiments on the fabrication of foams from cereal-based bioplastics. We propose that a key indicator of foamability is the strain at break of the materials to be foamed (as calculated from stress vs. strain rate curves). Zein foams exhibit attractive properties (average pore size, pore size distribution, and porosity) for cell culture applications; we were able to establish and sustain mammalian cell cultures on zein foams for extended time periods.     

Honeycomb-structured porous films from polypyrrole-containing block copolymers prepared via RAFT polymerization as a scaffold for cell growth

Honeycomb-structured porous films were prepared using customized amphiphilic block copolymers, synthesized by RAFT polymerization. Pyrrole was templated along an amphiphilic block copolymer, composed of polystyrene and poly(acrylic acid). Subsequent oxidation of pyrrol to polypyrrole, resulted in the formation of a soluble polypyrrole-containing polymer. Gel permeation chromatography and dynamic light scattering studies confirmed the solubility of the resulting customized amphiphilic block copolymer, in both water and organic solvent, forming either micelles or inverse aggregates. Porous films with a hexagonal array of micron-sized pores were generated with the polymer, using the breath figures templating technique. The resulting films were found to be non-cytotoxic and hence suitable as scaffolds for tissue engineering. Initial fibroblast cell culture studies on these scaffolds demonstrated a dependency of cell attachment on the pore size of scaffolds.     

One‐Step Template‐Free Synthesis of Highly Porous Boron Nitride Microsponges for Hydrogen Storage

Highly porous, sponge‐like boron nitride materials, namely microsponges (BNMSs), with ultrahigh surface areas up to 1900 m² g^‐1, are prepared by a facile, one‐step, template‐free reaction of boric acid and dicyanamide. Detailed analysis confirms the increase of the interlayer (0002) distances compared to standard graphitic BN and reveals special dislocation structures in the BNMSs. The resulting textural parameters such as the Brunauer‐Emmett‐Teller (BET) specific surface areas and pore volumes are easily tunable over a wide range by adjusting the synthesis temperature or composition of the precursors. It is demonstrated that these microporous materials (with pore widths of 1.0 nm) display comparatively high and reversible H₂ sorption capacities from 1.65 to 2.57 wt% at 1 MPa and –196 °C on a material basis.     

A Stretchable Polymer–Carbon Nanotube Composite Electrode for Flexible Lithium‐Ion Batteries: Porosity Engineering by Controlled Phase Separation

Flexible energy‐storage devices have attracted growing attention with the fast development of bendable electronic systems. However, it still remains a challenge to find reliable electrode materials with both high mechanical flexibility/toughness and excellent electron and lithium‐ion conductivity. This paper reports the fabrication and characterization of highly porous, stretchable, and conductive polymer nanocomposites embedded with carbon nanotubes (CNTs) for application in flexible lithium‐ion batteries. The systematic optimization of the porous morphology is performed by controllably inducing the phase separation of polymethylmethacrylate (PMMA) in polydimethylsiloxane (PDMS) and removing PMMA, in order to generate well‐controlled pore networks. It is demonstrated that the porous CNT‐embedded PDMS nanocomposites are capable of good electrochemical performance with mechanical flexibility, suggesting these nanocomposites could be outstanding anode candidates for use in flexible lithium‐ion batteries. The optimization of the pore size and the volume fraction provides higher capacity by nearly seven‐fold compared to a nonporous nanocomposite.     

Supramolecular Polymerization Promoted In Situ Fabrication of Nitrogen‐Doped Porous Graphene Sheets as Anode Materials for Li‐Ion Batteries

A novel strategy of utilizing supramolecular polymerization for fabricating nitrogen doped porous graphene (NPG) with high doping level of 12 atom% as the anode material for lithium ion batteries is reported for the first time. The introduction of supramolecular polymer (melamine cyanurate) functions not only as a spacer to prevent the restacking of graphene sheets but also as a sacrificial template to generate porous structures, as well as a nitrogen source to induce in situ N doping. Therefore, pores and loose‐packed graphene thin layers with high N doping level are very effectively formed in NPG after the annealing process. Such highly desired structures immediately offer remarkably improved Li storage performance including high reversible capacity (900 mAh g^?1 after 150 cycles) with good cycling and rate performances. The effects of annealing temperature and heating rates on the final electrochemical performance of NPG are also investigated. Furthermore, the low cost, facile, and scalable features of this novel strategy may be helpful for the rational design of functionalized graphene‐based materials for diverse applications.     

Molecular imprinted polymer with cloned bacterial protein template enriches authentic target in cell extract

Here we describe a new method for preparing a protein-imprinted polymer with a cloned bacterial protein template, which recognizes/adsorbs authentic target protein present at a relatively low level in cell extract. In this work, cloned pig cyclophilin 18 (pCyP18) was used as a template. The template protein was selectively assembled with memory molecules from their library, which consists of numerous limited length polymer chains with randomly distributed recognition sites and immobilizing sites. These assemblies of protein and memory molecules were adsorbed by porous polymeric beads and immobilized by cross-linking polymerization. After removing the template, binding sites that were complementary to the target protein in size, shape and the position of recognition groups were exposed, and their confirmation was preserved by the cross-linked structure. The synthesized imprinted polymer was used to adsorb authentic pCyP18 from cell extract, and its proportional content was enriched 300 times.     

制备大孔径静电纺丝组织工程支架的研究进展

研究表明静电纺丝可以制备出模拟细胞外基质的三维结构,其中限制静电纺丝纤维支架应用的问题之一就是纤维排列紧密导致支架的孔径较小,从而阻碍了细胞的浸入,组织中血管化的形成以及支架与宿主细胞的融合。为了增大支架的孔径,提高孔隙率,许多研究者提出了相应的策略。本文综述了多种制备大孔径静电纺丝纤维支架的方法,主要包括不同接收装置控制电场分布、盐粒子/聚合物析出法、水浴接收、低温静电纺丝以及激光/紫外烧蚀法等,以上的方法都能够有效的增大静电纺丝三维支架的孔径,进而提高了细胞的浸润性、营养物质的传输以及废物的排出,为静电纺丝纤维支架在组织工程中的应用奠定了基础。     

Separation/enrichment of active natural low content protein using protein imprinted polymer

We describe a new type of protein-imprinted polymer for separation/enrichment of active natural protein present at a relatively low level in cell extracts, with a cloned bacterial protein as template. In this work, cloned pig cyclophilin 18 (pCyP18) was used as template. The template protein was selectively assembled with assistant recognition polymer chains (ARPCs) from their library, which consists of numerous limited length polymer chains with randomly distributed recognition and immobilizing sites. These assemblies of protein and ARPCs were adsorbed by porous polymeric beads and immobilized by cross-linking polymerization. After removing the template, the synthesized imprinted polymer was used to adsorb authentic pCyP18 from cell extract, and its proportional content was enriched 200 times. The assay of peptidyl-prolyl cis-trans-isomerase (PPIase) activity showed that natural pCyP18 is more active than cloned pCyP18 and, in particular, it is much more sensitive to the suppressant cyclosporine A (CsA).     

Chitosan scaffolds containing silicon dioxide and zirconia nano particles for bone tissue engineering

A scaffold harboring the desired features such as biodegradation, biocompatibility, porous structure could serve as template for bone tissue engineering. In the present study, chitosan (CS), nano-scaled silicon dioxide (Si) and zirconia (Zr) were combined by freeze drying technique to fabricate a bio-composite scaffold. The bio-composite scaffold (CS/Si/Zr) was characterized by SEM, XRD and FT-IR studies. The scaffold possessed a porous nature with pore dimensions suitable for cell infiltration and colonization. The presence of zirconia in the CS/Si/Zr scaffold decreased swelling and increased biodegradation, protein adsorption and bio-mineralization properties. The CS/Si/Zr scaffold was also found to be non-toxic to rat osteoprogenitor cells. Thus, we suggest that CS/Si/Zr bio-composite scaffold is a potential candidate to be used for bone tissue engineering.     

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template''s channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.     

Growth of endothelial cells on microfabricated silicon nitride membranes for an<Emphasis Type="Italic">in vitro</Emphasis> model of the blood-brain barrier

The blood-brain barrier (BBB) is composed of the brain capillaries, which are lined by endothelial cells displaying extremely tight intercellular junctions. Several attempts at creating anin vitro model of the BBB have been met with moderate success as brain capillary endothelial cells lose their barrier properties when isolated in cell culture. This may be due to a lack of recreation of thein vivo endothelial cellular environment in these models, including nearly constant contact with astrocyte foot processes. This work is motivated by the hypothesis that growing endothelial cells on one side of an ultra-thin, highly porous membrane and differentiating astrocyte or astrogliomal cells on the opposite side will lead to a higher degree of interaction between the two cell types and therefore to an improved model. Here we describe our initial efforts towards testing this hypothesis including a procedure for membrane fabrication and methods for culturing endothelial cells on these membranes. We have fabricated a 1 μm thick, 2.0 μm pore size, and ∼55% porous membrane with a very narrow pore size distribution from low-stress silicon nitride (SiN) utilizing techniques from the microelectronics industry. We have developed a base, acid, autoclave routine that prepares the membranes for cell culture both by cleaning residual fabrication chemicals from the surface and by increasing the hydrophilicity of the membranes (confirmed by contact angle measurements). Gelatin, fibronectin, and a 50/50 mixture of the two proteins were evaluated as potential basement membrane protein treatments prior to membrane cell seeding. All three treatments support adequate attachment and growth on the membranes compared to the control.     

3D Amorphous Carbon with Controlled Porous and Disordered Structures as a High‐Rate Anode Material for Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have a promising application prospect for energy storage systems due to the abundant resource. Amorphous carbon with high electronic conductivity and high surface area is likely to be the most promising anode material for SIBs. However, the rate capability of amorphous carbon in SIBs is still a big challenge because of the sluggish kinetics of Na⁺ ions. Herein, a three‐dimensional amorphous carbon (3DAC) with controlled porous and disordered structures is synthesized via a facile NaCl template‐assisted method. Combination of open porous structures of 3DAC, the increased disordered structures can not only facilitate the diffusion of Na⁺ ions but also enhance the reversible capacity of Na storage. When applied as anode materials for SIBs, 3DAC exhibits excellent rate capability (66 mA h g^?1 at 9.6 A g^?1) and high reversible capacity (280 mA h g^?1 at a low current density of 0.03 A g^?1). Moreover, the controlled porous structures by the NaCl template method provide an appropriate specific surface area, which contributes to a relatively high initial Coulombic efficiency of 75%. Additionally, the high‐rate 3DAC material is prepared via a green approach originating from low‐cost pitch and NaCl template, demonstrating an appealing development of carbon anode materials for SIBs.     

Copper-containing mesoporous bioactive glass coatings on orbital implants for improving drug delivery capacity and antibacterial activity

Anophthalmic orbit restoration with artificial implants is usually accompanied with the risks of bacterial penetration and implant exposure. Here, we develop a facile evaporation-inducing self-assembly approach to modify the porous hydroxyapatite (pHA) orbital implants by using sol–gel derived CuO-containing mesoporous bioactive glass (Cu-MBG). The Cu-MBG coatings with 0–5 mol% CuO were prepared in the pore wall of pHA by immersion-evaporation-ageing route in the sol precursor of Cu-MBG. Brunauer–Emmett–Teller and Barrette-Joyner-Halenda analyses showed that the specific surface area and pore volume were slightly decreased with increasing CuO content, while the Cu-MBG-modified pHA maintained a sustained release of ofloxacin and significantly inhibited the bacterial viability (Staphylococcus aureus and Escherichia coli). These studies demonstrate that the Cu-MBG modification provides an effective and facile strategy to endow combined biological performances of pHA orbital implants and potentially reduce implant-related side effects.     

Synthesis of highly water-soluble fluorescent conjugated glycopoly(p-phenylene)s for lectin and Escherichia coli

Two facile, convenient, and versatile synthetic approaches are used to covalently attach carbohydrate residues to conjugated poly(p-phenylene)s (PPPs) for highly water-soluble PPPs bearing alpha-mannopyranosyl and beta-glucopyranosyl pendants (polymers A and B), which highly fluoresce in phosphate buffer (pH 7.0). The post-polymerization functionalization approach is to treat bromo-bearing PPP (polymer 1) with 1-thiolethyl-alpha-D-mannose tetraacetate or 1-thiol-beta-D-glucose tetraacetate in THF solution in the presence of K(2)CO(3) at room temperature through formation of thioether bridges, affording polymer 2a or 2b. The prepolymerization functionalization approach is to polymerize a well-defined sugar-carrying monomer, affording polymer 2a. Polymers 2a and 2b were deacetylated under Zemplén conditions in methanol and methylene chloride containing sodium methoxide, affording polymers A and B, respectively. The multivalent display of carbohydrates on the fluorescent conjugated glycopolymer overcomes the characteristic low binding affinity of the individual carbohydrates to their receptor proteins. Titration of concanavalin A (Con A) to alpha-mannose-bearing polymer A resulted in significant fluorescent quenching of the polymer with Stern-Volmer quenching constant of 4.5 x 10(7). Incubation of polymer A with Escherichia coli (E. coli) lead to formation of fluorescently stained bacterial clusters. Beta-glucose-bearing polymer B displayed no response to Con A and E. coli.