Scaffold for tissue engineering fabricated by non-isothermal supercritical carbon dioxide foaming of a highly crystalline polyester

Porous scaffolds of a random co-polymer of ω-pentadecalactone (PDL) and ε-caprolactone (CL) (poly(PDL–CL)), synthesized by biocatalysis, were fabricated by supercritical carbon dioxide (scCO₂) foaming. The co-polymer, containing 31 mol.% CL units, is highly crystalline (T_m = 82 °C, ΔH_m = 105 J g^?1) thanks to the ability of the two monomer units to co-crystallize. The co-polymer can be successfully foamed upon homogeneous absorption of scCO₂ at T > T_m. The effect of soaking time, depressurization rate and cooling rate on scaffold porosity, pore size distribution and pore interconnectivity was investigated by micro X-ray computed tomography. Scaffolds with a porosity in the range 42–76% and an average pore size of 100–375 μm were successfully obtained by adjusting the main foaming parameters. Process conditions in the range investigated did not affect the degree of crystallinity of poly(PDL–CL) scaffolds. A preliminary study of the mechanical properties of the scaffolds revealed that poly(PDL–CL) foams may find application in the regeneration of cartilage tissue.     

Solvent-dependent properties of electrospun fibrous composites for bone tissue regeneration

Biodegradable polymer–ceramic composite scaffolds have gained importance in recent years in the field of orthopedic biomaterials and tissue engineering scaffolds for improving the rate of degradation and limited mechanical properties of bioactive ceramics. This study sought to create composites using the electrospinning process to achieve fibrous scaffolds with uniform fiber morphologies and uniform ceramic dispersions. Composites consisting of 20% hydroxyapatite/80% β-tricalcium phosphate (20/80 HA/TCP) and poly (ε-caprolactone) (PCL) were fabricated. The 20/80 HA/TCP composition was chosen as the ceramic component because of previous reports of greater bone tissue formation in comparison with HA or TCP alone. For electrospinning, PCL was dissolved in either methylene chloride (Composite–MC) or a combination of methylene chloride (80%) and dimethylformamide (20%) (Composite–MC + DMF). Composite–MC mats contained a bimodal distribution of fiber diameters with nanofibers between larger, micron-sized fibers with an average pore size of 79.6 ± 67 μm, whereas Composite–MC + DMF fibers had uniform fiber diameters with an average pore size of 7.0 ± 4.2 μm. Elemental mapping determined that the ceramic was distributed throughout the mat and inside the fiber for both composites. However, physical characterization using differential scanning calorimetry (DSC) and mechanical testing revealed that the ceramic in the mats produced with MC + DMF were more uniformly dispersed than the ceramic in the mats produced with MC alone. Maximum tensile stress and strain were significantly higher for Composite–MC + DMF mats compared with Composite–MC mats and were comparable with the mechanical properties of mats of PCL alone. For both composites, there was molecular interaction between the PCL and the ceramic, as demonstrated by a maximum increase of ～10 °C in the glass transition values with the addition of the ceramic, as confirmed by Fourier transform infrared analysis. In addition, the crystallization behavior of the composites suggested that the ceramic was acting as a nucleating agent. Cell viability studies using human mesenchymal stem cells (MSC) showed that both composite scaffolds supported cell growth. However, cell numbers at early time points in culture were significantly higher on mats produced from MC + DMF compared with mats prepared with MC alone. Further examination revealed that cells were able to infiltrate the pores of the Composite–MC mats, but remained on the outer surface of the Composite–MC + DMF and unfilled PCL mats during the culture period. The results of this study demonstrate that the solvent or solvent combination used in preparing the electrospun composite mats plays a critical role in determining its properties, which may, in turn, affect cell behavior.     

Effect of hydroxyapatite on the biodegradation and biomechanical stability of polyester nanocomposites for orthopaedic applications

The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyester, i.e., hydroxy-terminated high molecular weight poly(proplyene fumarate) (HT-PPFhm), was investigated. A thermoset nanocomposite was prepared with nanoparticles of calcined HAP (<100 nm, rod-like shape, filler content 30 wt.%), HT-PPFhm and N-vinyl pyrrolidone, dibenzoyl peroxide and N,N-dimethyl aniline. Two more nanocomposites were prepared with precipitated HAP nanoparticles (<100 nm rod-like shape) and commercially available HAP nanoparticles (<200 nm spherical shape), respectively. Calcined HAP nanoparticles resulted in very good crosslinking in the resin matrix with high crosslinking density and interfacial bonding with the polymer, owing to the rod-like shape of the nanoparticles; this gave improved biomechanical strength and modulus and also controlled degradation of the nanocomposite for scaffold formation. The tissue compatibility and osteocompatibility of the nanocomposite containing calcined HAP nanoparticles was evaluated. The tissue compatibility was studied by intramuscular implantation in a rabbit animal model for 3 months as per ISO standard 10993/6. The in vivo femoral bone repair was also carried out in the rabbit animal model as per ISO standard 10993/6. The nanocomposite containing calcined HAP nanoparticles is both biocompatible and osteocompatible.     

Premature degradation of poly(α-hydroxyesters) during thermal processing of Bioglass®-containing composites

Bioactive, biodegradable composites are increasingly being explored as bone replacement materials and as scaffolds for tissue engineering. Their properties are not only dependent on the properties of the filler and matrix, but are also determined by their interaction. This study investigated the effect on poly(d,l-lactide) (PDLLA) matrix when processed at high-temperatures in the presence of Bioglass^® particulate filler. Composites with different filler contents were compounded at elevated temperatures by co-extrusion followed by compression moulding and compared with composites of similar composition prepared by thermally induced phase separation (TIPS), a low-temperature processing route. It was found that the inclusion of Bioglass^® in PDLLA under elevated temperatures resulted in the degradation of the matrix, leading to a reduction in the mechanical properties of the composites and in the molecular weight of the matrix. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy showed the presence of a peak at 1600 cm^?1 in the composite material, particularly when processed at elevated temperatures, whereas no peak at this wavelength was discernible for the pure PDLLA. Furthermore, time-based ATR-FTIR spectra taken at elevated temperatures on the TIPS-processed composites showed an increase in the intensity of the peak at 1600 cm^?1 and a concomitant reduction of the CO stretch peak at 1745 cm^?1 with time. This suggested the formation of a carboxylate salt by-products as a consequence of a reaction at the interface between the Bioglass^® filler and the PDLLA matrix. Therefore, the results confirmed that this degradation was not solely due to shear effects during the extrusion process. This work thereby supports the assertion that, in the presence of Bioglass^® filler particles, poly(α-hydroxyester)-based composites should not be processed at elevated temperatures.     

Influence of the bonding substrate in dental composite polymerization stress testing

Our objective was to compare the polymerization stress (σ_pol) of a series of composites obtained using poly(methyl methacrylate) (PMMA) or glass as bonding substrates, and to compare the results with those from in vitro microleakage of composite restorations. The tested hypothesis was that stress values obtained in a less rigid testing system (i.e. using PMMA) would show a better relationship with microleakage data. Five dental composites were tested: Filtek Z250 (FZ), Z100 (Z1), Concept (CO), Durafill (DU) and Heliomolar (HM). σ_pol was determined in 1 mm high specimens inserted between two rods (? = 5 mm) of either PMMA or glass. The composite elastic modulus (E) was obtained by three-point bending. σ_pol and E data were submitted to a one-way analysis of variance/Tukey test (α = 0.05). For the microleakage test (MI), bovine incisors received cylindrical cavities (? = 5 mm, h = 2 mm), which were restored in bulk. After storage for 24 h in water, specimens were subjected to dye penetration using AgNO₃ as tracer. Specimens were sectioned twice, perpendicularly, and microleakage was measured (in millimeters) under 20× magnification. Data from MI were submitted to the Kruskal–Wallis test. Means (SD) of σ_pol (MPa) using glass/PMMA were FZ: 7.5(1.8)^A/2.5(0.2)^bc; Z1: 7.3(0.5)^A/2.8(0.3)^ab; CO: 6.8(1.1)^A/3.2(0.5)^a; DU: 4.5(0.7)^B/2.0(0.2)^bc; HM: 3.5(0.2)^B/2.3(0.3)^c. σ_pol obtained using PMMA rods were 34–67% lower than with glass. Means (SD) for tooth average/tooth maximum microleakage were FZ: 0.92(0.19)^B/1.53(0.30)^a; Z1: 1.19(0.21)^A/1.75(0.20)^a; CO: 1.26(0.25)^A/1.78(0.24)^a; DU: 0.83(0.30)^B/1.68(0.46)^a; HM: 0.81(0.27)^B/1.64(0.54)^a. The tested hypothesis was confirmed, as the composites showed the same ordering both in the polymerization stress test using PMMA rods and in the microleakage test.     

Synergistic effects of electrospun PLLA fiber dimension and pattern on neonatal mouse cerebellum C17.2 stem cells

Topographical features, including fiber dimensions and pattern, are important aspects in developing fibrous scaffolds for tissue engineering. In this study aligned poly(l-lactide) (PLLA) fibers with diameters of 307 ± 47, 500 ± 53, 679 ± 72 and 917 ± 84 nm and random fibers with diameters of 327 ± 40, 545 ± 54, 746 ± 82 and 1150 ± 109 nm were obtained by optimizing the electrospinning parameters. We cultured neonatal mouse cerebellum C17.2 cells on the PLLA fibers. These neural stem cells (NSCs) exhibited significantly different growth and differentiation depending upon fiber dimension and pattern. On aligned fibers cell viability and proliferation was best on 500 nm fibers, and reduced on smaller or larger fibers. However, on random fibers cell viability and proliferation was best with the smallest (350 nm) and largest (1150 nm) diameter fibers. Polarized and elongated cells were orientated along the fiber direction on the aligned fibers, with focal contacts bridging the cell body and aligned fibers. Cells of spindle and polygonal morphologies were randomly distributed on the random fibers, with no focal contacts observed. Moreover, longer neurites were obtained on the aligned fibers than random fibers within the same diameter range. Thus, the surface topographic morphologies of fibrous scaffolds, including fiber pattern, dimensions and mesh size, play roles in regulating the viability, proliferation and neurite outgrowth of NSCs. Nevertheless, our results indicated that aligned 500 nm fiber are most promising for fine tuning the design of a nerve scaffold.     

Incorporation of biodegradable electrospun fibers into calcium phosphate cement for bone regeneration

Inherent brittleness and slow degradation are the major drawbacks for the use of calcium phosphate cements (CPCs). To address these issues, biodegradable ultrafine fibers were incorporated into the CPC in this study. Four types of fibers made of poly(ε-caprolactone) (PCL) (PCL12: 1.1 μm, PCL15: 1.4 μm, PCL18: 1.9 μm) and poly(l-lactic acid) (PLLA4: 1.4 μm) were prepared by electrospinning using a special water pool technique, then mixed with the CPC at fiber weight fractions of 1%, 3%, 5% and 7%. After incubation of the composites in simulated body fluid for 7 days, they were characterized by a gravimetric measurement for porosity evaluation, a three-point bending test for mechanical properties, microcomputer topography and scanning electron microscopy for morphological observation. The results indicated that the incorporation of ultrafine fibers increases the fracture resistance and porosity of CPCs. The toughness of the composites increased with the fiber fraction but was not affected by the fiber diameter. It was found that the incorporated fibers formed a channel-like porous structure in the CPCs. After degradation of the fibers, the created space and high porosity of the composite cement provides inter-connective channels for bone tissue in growth and facilitates cement resorption. Therefore, we concluded that this electrospun fiber-CPC composite may be beneficial to be used as bone fillers.     

Nanofiber size-dependent sensitivity of fibroblast directionality to the methodology for scaffold alignment

The sensitivity of fibroblast guidance on directional cues provided by aligned nanofibers is studied for scaffolds of successively smaller fiber sizes (740 ± 280, 245 ± 85, 140 ± 40, and 80 ± 10 nm) fabricated using mandrel and electrical alignment methodologies for electrospun nanofibers (～10° angular deviation (AD)), as well as nanoimprint methodologies for perfectly aligned fibers (0° AD). On aligned scaffolds of large fibers (～740 nm) cell directionality closely follows the underlying fibers, irrespective of the alignment method. However, on mandrel aligned scaffolds of successively smaller fibers the cell directionality exhibits greater deviations from the underlying fiber alignment due to the higher likelihood of interaction of cell lamellipodia with multiple, rather than single, nanofibers. Using electrically aligned scaffolds, fibroblast directionality deviations can be maintained in the range of nanofiber alignment deviation for fiber sizes down to ～100 nm. This improvement in cell guidance is attributed to molecular scale directional adhesion cues for cell receptors, which occur within electrically aligned scaffolds due to fiber polarization parallel to the geometric alignment axis of the nanofiber under the modified electric field during electrospinning. While fibroblast directionality is similar on electrically aligned vs. nanoimprinted scaffolds for fiber sizes >100 nm, cell directionality is influenced more strongly by the perfect alignment cues of the latter on ～100 nm fiber scaffolds. The scaffold alignment methodology is hence highly significant, especially for tissue engineering applications requiring sub-100 nm aligned fibers.     

Dexamethasone-loaded scaffolds prepared by supercritical-assisted phase inversion

The aim of this study was to evaluate the possibility of preparing dexamethasone-loaded starch-based porous matrices in a one-step process. Supercritical phase inversion technique was used to prepare composite scaffolds of dexamethasone and a polymeric blend of starch and poly(l-lactic acid) (SPLA) for tissue engineering purposes. Dexamethasone is used in osteogenic media to direct the differentiation of stem cells towards the osteogenic lineage. Samples with different drug concentrations (5–15 wt.% polymer) were prepared at 200 bar and 55 °C. The presence of dexamethasone did not affect the porosity or interconnectivity of the polymeric matrices. Water uptake and degradation studies were also performed on SPLA scaffolds. We conclude that SPLA matrices prepared by supercritical phase inversion have a swelling degree of nearly 90% and the material presents a weight loss of ～25% after 21 days in solution. Furthermore, in vitro drug release studies were carried out and the results show that a sustained release of dexamethasone was achieved over 21 days. The fitting of the power law to the experimental data demonstrated that drug release is governed by an anomalous transport, i.e., both the drug diffusion and the swelling of the matrix influence the release of dexamethasone out of the scaffold. The kinetic constant was also determined. This study reports the feasibility of using supercritical fluid technology to process in one step a porous matrix loaded with a pharmaceutical agent for tissue engineering purposes.     

Synergistic effect of surface modification and scaffold design of bioplotted 3-D poly-ε-caprolactone scaffolds in osteogenic tissue engineering

The hydrophobic nature and the regular scaffold architecture of bioplotted poly(ε-caprolactone) (PCL) scaffolds present some hurdles for homogeneous tissue formation and differentiation. The current hypothesis is that a synergistic effect of applied surface modification and scaffold design enhances colonization and osteogenic differentiation. First, PCL scaffolds with a 0/90° lay-down pattern (0/90) were plotted and subjected to an oxygen plasma (O₂) or multistep surface modification, including post-argon 2-amino-ethylmethacrylate grafting (AEMA), followed by immobilization of gelatin type B (gelB) and physisorption of fibronectin (gelB Fn). Secondly, scaffolds of different designs were plotted (0/90° shift (0/90 S), 0/45° and 0/90° with narrow pores (0/90 NP)) and subjected to the double protein coating. Preosteoblasts were cultured on the scaffolds and the seeding efficiency, colonization and differentiation were studied. The data revealed that a biomimetic surface modification improved colonization (gelB Fn > gelB > AEMA > O₂). Compact scaffold architectures (0/90 NP, 0/45, 0/90 S > 0/90) positively influenced the seeding efficiency and differentiation. Interestingly, the applied surface modification had a greater impact on colonization than the scaffold design. In conclusion, the combination of a double protein coating with a compact design enhances tissue formation in the plotted PCL scaffolds.     

Varying the diameter of aligned electrospun fibers alters neurite outgrowth and Schwann cell migration

Aligned, electrospun fibers have shown great promise in facilitating directed neurite outgrowth within cell and animal models. While electrospun fiber diameter does influence cellular behavior, it is not known how aligned, electrospun fiber scaffolds of differing diameter influence neurite outgrowth and Schwann cell (SC) migration. Thus, the goal of this study was to first create highly aligned, electrospun fiber scaffolds of varying diameter and then assess neurite and SC behavior from dorsal root ganglia (DRG) explants. Three groups of highly aligned, electrospun poly-l-lactic acid (PLLA) fibers were created (1325 + 383 nm, large diameter fibers; 759 + 179 nm, intermediate diameter fibers; and 293 + 65 nm, small diameter fibers). Embryonic stage nine (E9) chick DRG were cultured on fiber substrates for 5 days and then the explants were stained against neurofilament and S100. DAPI stain was used to assess SC migration. Neurite length and SC migration distance were determined. In general, the direction of neurite extension and SC migration were guided along the aligned fibers. On the small diameter fiber substrate, the neurite length was 42% and 36% shorter than those on the intermediate and large fiber substrates, respectively. Interestingly, SC migration did not correlate with that of neurite extension in all situations. SCs migrated equivalently with extending neurites in both the small and large diameter scaffolds, but lagged behind neurites on the intermediate diameter scaffolds. Thus, in some situations, topography alone is sufficient to guide neurites without the leading support of SCs. Scanning electron microscopy images show that neurites cover the fibers and do not reside exclusively between fibers. Further, at the interface between fibers and neurites, filopodial extensions grab and attach to nearby fibers as they extend down the fiber substrate. Overall, the results and observations suggest that fiber diameter is an important parameter to consider when constructing aligned, electrospun fibers for nerve regeneration applications.     

Electrically conductive nanofibers with highly oriented structures and their potential application in skeletal muscle tissue engineering

Recent trends in scaffold design have focused on materials that can provide appropriate guidance cues for particular cell types to modulate cell behavior. In this study highly aligned and electrically conductive nanofibers that can simultaneously provide topographical and electrical cues for cells were developed. Thereafter their potential to serve as functional scaffolds for skeletal muscle tissue engineering was investigated. Well-ordered nanofibers, composed of polyaniline (PANi) and poly(ε-caprolactone) (PCL), were electrospun by introducing an external magnetic field in the collector region. Incorporation of PANi into PCL fibers significantly increased the electrical conductivity from a non-detectable level for the pure PCL fibers to 63.6 ± 6.6 mS cm^?1 for the fibers containing 3 wt.% PANi (PCL/PANi-3). To investigate the synergistic effects of topographical and electrical cues using the electrospun scaffolds on skeletal myoblast differentiation, mouse C2C12 myoblasts were cultured on random PCL (R-PCL), aligned PCL (A-PCL), random PCL/PANi-3 (R-PCL/PANi) and aligned PCL/PANi-3 (A-PCL/PANi) nanofibers. Our results showed that the aligned nanofibers (A-PCL and A-PCL/PANi) could guide myoblast orientation and promote myotube formation (i.e. approximately 40% and 80% increases in myotube numbers) compared with R-PCL scaffolds. In addition, electrically conductive A-PCL/PANi nanofibers further enhanced myotube maturation (i.e. approximately 30% and 23% or 15% and 18% increases in the fusion and maturation indices) compared with non-conductive A-PCL scaffolds or R-PCL/PANi. These results demonstrated that a combined effect of both guidance cues was more effective than an individual cue, suggesting a potential use of A-PCL/PANi nanofibers for skeletal muscle regeneration.     

Biodegradable fibrous scaffolds with diverse properties by electrospinning candidates from a combinatorial macromer library

The properties of electrospun fibrous scaffolds, including degradation, mechanics and cellular interactions, are important for their use in tissue engineering applications. Although some diversity has been obtained previously in fibrous scaffolds, optimization of scaffold properties relies on iterative techniques in both polymer synthesis and processing. Here, we electrospun candidates from a combinatorial library of biodegradable and photopolymerizable poly(β-amino ester)s (PBAEs) to show that the diversity in properties found in this library is retained when processed into fibrous scaffolds. Specifically, three PBAE macromers were electrospun into scaffolds and possessed similar initial mechanical properties, but exhibited mass loss ranging from rapid (complete degradation within ～2 weeks) to moderate (complete degradation within ～3 months) to slow (only partial degradation after 3 months). These trends in mechanics and degradation mimicked what was previously observed in the bulk polymers. Although cellular adhesion was dependent on the polymer composition in films, adhesion to scaffolds that were electrospun with gelatin was similar on all formulations and controls. To further illustrate the diverse properties that are attainable in these systems, the fastest and slowest degrading polymers were electrospun together into one scaffold, but as distinct fiber populations. This dual-polymer scaffold exhibited behavior in mass loss and mechanics with time that fell between the single-polymer scaffolds. In general, this work indicates that combinatorial libraries may be an important source of information and specific polymer compositions for the fabrication of electrospun fibrous scaffolds with tunable properties.     

Bone regeneration in rat calvarial defects implanted with fibrous scaffolds composed of a mixture of silicate and borate bioactive glasses

Previous studies have evaluated the capacity of porous scaffolds composed of a single bioactive glass to regenerate bone. In the present study, scaffolds composed of a mixture of two different bioactive glasses (silicate 13-93 and borate 13-93B3) were created and evaluated for their response to osteogenic MLO-A5 cells in vitro and their capacity to regenerate bone in rat calvarial defects in vivo. The scaffolds, which have similar microstructures (porosity = 58?67%) and contain 0, 25, 50 and 100 wt.% 13-93B3 glass, were fabricated by thermally bonding randomly oriented short fibers. The silicate 13-93 scaffolds showed a better capacity to support cell proliferation and alkaline phosphatase activity than the scaffolds containing borate 13-93B3 fibers. The amount of new bone formed in the defects implanted with the 13-93 scaffolds at 12 weeks was 31%, compared to values of 25, 17 and 20%, respectively, for the scaffolds containing 25, 50 and 100% 13-93B3 glass. The amount of new bone formed in the 13-93 scaffolds was significantly higher than in the scaffolds containing 50 and 100% 13-93B3 glass. While the 13-93 fibers were only partially converted to hydroxyapatite at 12 weeks, the 13-93B3 fibers were fully converted and formed a tubular morphology. Scaffolds composed of an optimized mixture of silicate and borate bioactive glasses could provide the requisite architecture to guide bone regeneration combined with a controllable degradation rate that could be beneficial for bone and tissue healing.     

Repairing a critical-sized bone defect with highly porous modified and unmodified baghdadite scaffolds

This is the first reported study to prepare highly porous baghdadite (Ca₃ZrSi₂O₉) scaffolds with and without surface modification and investigate their ability to repair critical-sized bone defects in a rabbit radius under normal load. The modification was carried out to improve the mechanical properties of the baghdadite scaffolds (particularly to address their brittleness) by coating their surfaces with a thin layer (～400 nm) of polycaprolactone (PCL)/bioactive glass nanoparticles (nBGs). The β-tricalcium phosphate/hydroxyapatite (TCP/HA) scaffolds with and without modification were used as the control groups. All of the tested scaffolds had an open and interconnected porous structure with a porosity of ～85% and average pore size of 500 μm. The scaffolds (six per scaffold type and size of 4 mm × 4 mm × 15 mm) were implanted (press-fit) into the rabbit radial segmental defects for 12 weeks. Micro-computed tomography and histological evaluations were used to determine bone ingrowth, bone quality, and implant integration after 12 weeks of healing. Extensive new bone formation with complete bridging of the radial defect was evident with the baghdadite scaffolds (modified/unmodified) at the periphery and in close proximity to the ceramics within the pores, in contrast to TCP/HA scaffolds (modified/unmodified), where bone tended to grow between the ulna adjacent to the implant edge. Although the modification of the baghdadite scaffolds significantly improved their mechanical properties, it did not show any significant effect on in vivo bone formation. Our findings suggest that baghdadite scaffolds with and without modification can serve as a potential material to repair critical sized bone defects.     

Biofilm formation on bone grafts and bone graft substitutes: Comparison of different materials by a standard in vitro test and microcalorimetry

We analyzed the initial adhesion and biofilm formation of Staphylococcus aureus (ATCC 29213) and S. epidermidis RP62A (ATCC 35984) on various bone grafts and bone graft substitutes under standardized in vitro conditions. In parallel, microcalorimetry was evaluated as a real-time microbiological assay in the investigation of biofilm formation and material science research. The materials β-tricalcium phosphate (β-TCP), processed human spongiosa (Tutoplast?) and poly(methyl methacrylate) (PMMA) were investigated and compared with polyethylene (PE). Bacterial counts (log₁₀ cfu per sample) were highest on β-TCP (S. aureus 7.67 ± 0.17; S. epidermidis 8.14 ± 0.05) while bacterial density (log₁₀ cfu per surface) was highest on PMMA (S. aureus 6.12 ± 0.2, S. epidermidis 7.65 ± 0.13). Detection time for S. aureus biofilms was shorter for the porous materials (β-TCP and processed human spongiosa, p < 0.001) compared to the smooth materials (PMMA and PE), with no differences between β-TCP and processed human spongiosa (p > 0.05) or PMMA and PE (p > 0.05). In contrast, for S. epidermidis biofilms the detection time was different (p < 0.001) between all materials except between processed human spongiosa and PE (p > 0.05). The quantitative analysis by quantitative culture after washing and sonication of the material demonstrated the importance of monitoring factors like specific surface or porosity of the test materials. Isothermal microcalorimetry proved to be a suitable tool for an accurate, non-invasive and real-time microbiological assay, allowing the detection of bacterial biomass without removing the biofilm from the surface.     

PEGylated PEI-based biodegradable polymers as non-viral gene vectors

Novel functional biodegradable gene vectors, poly(l-succinimide)-g-polyethylenimines-g-poly(ethylene glycol) (PSI-g-PEI-g-PEGs) were synthesized by conjugating methoxy poly(ethylene glycol) (mPEG, M_w = 750 Da) to PEI segments (M_w = 800 Da) of PSI-g-PEI. The physicochemical properties of PSI-g-PEI-g-PEGs, including buffering capability, pDNA binding ability, cytotoxicity, zeta potential and the particle size of polymer/pDNA complexes, were explored. The influence of PEGylation was discussed based on a comparative study of PSI-g-PEI-g-PEGs, PSI-g-PEI and PEI25k (M_w = 25 kDa). SEM images revealed that PSI-g-PEI-g-PEG/pDNA particles have a regular shape with the diameter ranging from 70 to 170 nm. PEGylation could suppress the aggregation occurrence between complexes, resulting in a reduction of the polymer/pDNA complex size. PSI-g-PEI-g-PEGs exhibited remarkably lower cytotoxicity compared to PSI-g-PEI and PEI25k. In 293T and HeLa cells, the obtained PSI-g-PEI-g-PEGs showed very high transfection efficiency compared to PEI25k. Fluorescent confocal microscopy demonstrated that PSI-g-PEI-g-PEGs could effectively transport pGL-3 plasmids into the nuclei of HeLa cells. Taking into account the continued high transfection efficacy and decreased toxicity after PEG modification, PSI-g-PEI-g-PEGs show great potential as the non-viral vectors for gene transfection.     

Influence of the fiber diameter and surface roughness of electrospun vascular grafts on blood activation

Electrospun grafts have been widely investigated for vascular graft replacement due to their ease and compatibility with many natural and synthetic polymers. Here, the effect of the processing parameters on the scaffold’s architecture and subsequent reactions of partially heparinized blood triggered by contacting these topographies were studied. Degrapol® (DP) and poly(lactic-co-glycolic acid) (PLGA) electrospun fibrous scaffolds were characterized with regard to fiber diameter, pore area and scaffold roughness. The study showed that electrospinning parameters greatly affect fiber diameter together with pore dimension and overall scaffold roughness. Coagulation cascade activation, early platelet adhesion and activation were analyzed after 2 h of exposure of blood to the biomaterials. While no differences were found between DP and PLGA with similar topographies, the blood reactions were observed to be dependent on the fiber diameter and scaffold roughness. Scaffolds composed of thin fibers (diameter <1 μm) triggered very low coagulation and almost no platelets adhered. On the other hand, scaffolds with a bigger fiber diameter (2–3 μm) triggered higher thrombin formation and more platelets adhered. The highest platelet adhesion and activations rates as well as coagulation cascade activation were found in blood incubated in contact with the scaffolds produced with the biggest fiber diameter (5 μm). These findings indicate that electrospun grafts with small fiber diameter (<1 μm) could perform better with reduced early thrombogenicity due to lower platelet adhesion and lower activation of platelets and coagulation cascade.     

Flexible and elastic porous poly(trimethylene carbonate) structures for use in vascular tissue engineering

Biocompatible and elastic porous tubular structures based on poly(1,3-trimethylene carbonate), PTMC, were developed as scaffolds for tissue engineering of small-diameter blood vessels. High-molecular-weight PTMC (M_n = 4.37 × 10⁵) was cross-linked by gamma-irradiation in an inert nitrogen atmosphere. The resulting networks (50–70% gel content) were elastic and creep resistant. The PTMC materials were highly biocompatible as determined by cell adhesion and proliferation studies using various relevant cell types (human umbilical vein endothelial cells (HUVECs), smooth muscle cells (SMCs) and mesenchymal stem cells (MSCs)). Dimensionally stable tubular scaffolds with an interconnected pore network were prepared by particulate leaching. Different cross-linked porous PTMC specimens with average pore sizes ranging between 55 and 116 μm, and porosities ranging from 59% to 83% were prepared. These scaffolds were highly compliant and flexible, with high elongations at break. Furthermore, their resistance to creep was excellent and under cyclic loading conditions (20 deformation cycles to 30% elongation) no permanent deformation occurred. Seeding of SMCs into the wall of the tubular structures was done by carefully perfusing cell suspensions with syringes from the lumen through the wall. The cells were then cultured for 7 days. Upon proliferation of the SMCs, the formed blood vessel constructs had excellent mechanical properties. Their radial tensile strengths had increased from 0.23 to 0.78 MPa, which is close to those of natural blood vessels.