In vitro biocompatibility assessment of poly(epsilon-caprolactone) films using L929 mouse fibroblasts

Biodegradable and biocompatible materials are the basis for tissue engineering. As an initial step for developing vascular grafts, the in vitro biocompatibility of poly(epsilon-caprolactone) (PCL), recently suggested for several clinical applications, was evaluated in this study using L929 mouse fibroblasts. Different cellular aspects were analyzed in order to know the cell viability during cell culture on PCL films: adhesion, proliferation, morphology, LDH release and mitochondrial function. Since topography and other surface characteristics of materials play an essential part in cell adhesion, PCL membranes with either smooth or rough surface were prepared, characterized and used to carry out cell cultures. During short culture times, PCL produced a significant stimulation of mitochondrial activity evaluated by reduction of the MTT reagent. The results provide evidences of good adhesion, growth, viability, morphology and mitochondrial activity of cells on PCL films. Therefore, it can be concluded that PCL is a suitable and biocompatible material as a scaffold for vascular graft development.     

Biocompatibility of Poly(epsilon-caprolactone) scaffold modified by chitosan--the fibroblasts proliferation in vitro

In this study, the surface of poly(epsilon-caprolactone) (PCL) scaffold was modified by chitosan (CS) in order to enhance its cell affinity and biocompatibility. It is demonstrated by scanning electronic microscopy (SEM) that when 0.5-2.0 wt% chitosan solutions are used to modify the PCL scaffold, the amount of adhesion of the fibroblasts on the chitosan-modified PCL scaffolds dramatically increase when compared to the control after 7 days cell culture. The results indicate that the chitosan-modified PCL scaffolds are more favorable for cell proliferation by improving the scaffold biocompatibility. The improvement may be helpful for the extensive applications of PCL scaffold in heart valve and blood vessel tissue engineering.     

The effect of PLGA doping of polycaprolactone films on the control of osteoblast adhesion and proliferation in vitro

Poly(epsilon-caprolactone) (PCL) film was modified using specified amounts of poly(d,l-lactide-co-glycolide) (PLGA) to provide a means to control polymer degradation. The aim of the study was to determine the effects of doping PCL with PLGA on the materials degradation, morphology and cell adhesion, to determine the significant variables within the process that could provide further control of cell adhesion. PLGA-doped PCL films were aged in osteogenic medium at 37 degrees C for up to 28 days. The aged samples were analysed in terms of weight loss or weight gain, molecule deposition and surface morphology. Molecule deposition was determined using Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR) and morphology was determined using scanning electron microscopy and interferometric microscopy. The loss of the PLGA doping during degradation enhanced the formation of nano-porous structures in the remaining PCL domains, which attracted the deposition of substances from the osteogenic medium, which favoured the attachment and growth of human osteoblasts. The growth of osteoblasts was influenced by the controlled release of acidic products through polymer blending. Two pairs of FTIR-ATR absorption bands at 1090 and 1110 cm(-1), and at 1180 and 1190 cm(-1) were found to correlate to both PLGA and PCL, respectively. Changing the level of PLGA doping in PCL provided an approach to control the acidic products which can direct the growth of osteoblast cells.     

Biodegradable polymer/hydroxyapatite composites: surface analysis and initial attachment of human osteoblasts

Biodegradable polymer/hydroxyapatite (HA) composites have potential application as bone graft substitutes. Thin films of polymer/HA composites were produced, and the initial attachment of primary human osteoblasts (HOBs) was assessed to investigate the biocompatibility of the materials. Poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLA) were used as matrix materials for two types of HA particles, 50-microm sintered and submicron nonsintered. Using ESEM, cell morphology on the surfaces of samples was investigated after 90 min, 4 h, and 24 h of cell culture. Cell activity and viability were assessed after 24 h of cell culture using Alamar blue and DNA assays. Surface morphology of the polymer/HA composites and HA exposure were investigated using ESEM and EDXA, respectively. ESEM enabled investigation of both cell and material surface morphology in the hydrated condition. Combined with EDXA it permitted chemical and visual examination of the composite. Differences in HA exposure were observed on the different composite surfaces that affected the morphology of attached cells. In the first 4 h of cell culture, the cells were spread to a higher degree on exposed HA regions of the composites and on PLA than they were on PCL. After 24 h the cells were spread equally on all the samples. The cell activity after 24 h was significantly higher on the polymer/HA composites than on the polymer films. There was no significant difference in the activity of the cells on the various composite materials. However, cells on PCL showed higher activity compared to those on PLA. A polymer surface exhibiting "point exposure" of HA appeared to provide a novel and favorable substrate for primary cell attachment. The cell morphology and activity results indicate a favorable cell/material interaction and suggest that PLA and PCL and their composites with HA may be candidate materials for the reconstruction of bony tissue. Further investigations regarding long-term biomaterial/cell interactions and the effects of acidic degradation products from the biodegradable polymers are required to confirm their utility.     

Heparinized PCL/keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation

Abstract

Heparins are capable of improving blood compatibility, enhancing HUVEC viability, while inhibiting HUASMC proliferation. Combination of biodegradable poly(ε-caprolactone) (PCL) with keratin and heparins would provide an anticoagulant and endothelialization supporting environment for vascular tissue engineering. Herein, PCL and keratin were first coelectrospun and then covalently conjugated with heparins. The resulting mats were surface-characterized by ATR-FTIR, SEM, WCA, and XPS. Cell viability data showed that the heparinized PCL/keratin mats could motivate the adhesion and growth of HUVEC, while inhibit HUASMC proliferation. In addition, these mats could prolong blood clotting time and reduce platelet adhesion as well as no erythrolysis. Interestingly, these mats could catalyze the NO donor in blood to release NO, which could enhance endothelial cell growth, while decrease smooth muscle cell proliferation and platelet adhesion. In summary, the heparinized mats would be a good candidate as a scaffold for vascular tissue engineering. This study is novel in that we prepared a type of heparinized tissue scaffold that could catalyze the NO donor to release NO to regulate endothelialization without angiogenesis and thrombus formation.     

Fabrication and characterization of novel nano- and micro-HA/PCL composite scaffolds using a modified rapid prototyping process

Novel three-dimensional scaffolds consisting of nano- and microsized hydroxyapatite (HA)/poly(epsilon-caprolactone) (PCL) composite were fabricated using a modified rapid-prototyping (RP) technique for bone tissue engineering applications. The size of the nano-HA ranged from 20 to 90 nm, whereas that of the micro-HA ranged from 20 to 80 microm. The scaffold macropores were well interconnected, with a porosity of 72-73% and a pore size of 500 microm. The compressive modulus of the nano-HA/PCL and micro-HA/PCL scaffolds was 3.187 +/- 0.06 and 1.345 +/- 0.05 MPa, respectively. The higher modulus of the nano-HA/PCL composite (n-HPC) was to be likely caused by a dispersion strengthening effect. The attachment and proliferation of MG-63 cells on n-HPC were better than that on the micro-HA/PCL composite (m-HPC) scaffold. The n-HPC was more hydrophilic than the m-HPC because of the greater surface area of HA exposed to the scaffold surface. This may give rise to better cell attachment and proliferation. Bioactive n-HA/PCL composite scaffold prepared using a modified RP technique has a potential application in bone tissue engineering.     

Degradation and cell culture studies on block copolymers prepared by ring opening polymerization of epsilon-caprolactone in the presence of poly(ethylene glycol)

Poly(epsilon-caprolactone) (PCL) and its block copolymers with poly(ethylene glycol) (PEG) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of ethylene glycol or PEG, using zinc metal as catalyst. The resulting polymers were characterized by various analytical techniques such as (1)H NMR, SEC, DSC, IR, X-ray, ESEM, and CZE. PCL/PEG copolymers with long PCL chains presented the same crystalline structure as PCL homopolymer, whereas PEG-bearing short PCL blocks retained the crystalline structure of PEG and exhibited an amphiphilic behavior in aqueous solutions. Degradation of PCL and PCL/PEG diblock and triblock copolymers was realized in a 0.13 M, pH 7.4 phosphate buffer at 37 degrees C. The results indicated that the copolymers exhibited higher hydrophilicity and degradability compared with the PCL homopolymer. Large amounts of PEG were released from the bulk after 60 weeks' degradation. In vitro cell culture studies were conducted on scaffolds manufactured via solid free form fabrication by using primary human and rat bone marrow derived stromal cells (hMSC, rMSC). Light, scanning electron, and confocal laser microscopy, as well as immunocytochemistry, showed cell attachment, proliferation, and extracellular matrix production on the surface, as well as inside the scaffold architecture. Copolymers showed better performance in the cell culture studies than the PCL homopolymer.     

Influence of the physical properties of two-dimensional polyester substrates on the growth of normal human urothelial and urinary smooth muscle cells in vitro

Although synthetic biomaterials have a wide range of promising applications in regenerative medicine and tissue engineering, there is limited insight into the basic materials properties that influence cellularisation events. The aim of this study was to investigate the influence of the physical properties of polyester films on the adherence and growth of normal human urothelial and urinary smooth muscle (SM) cells, as part of a programme for the development of potential biomaterials for bladder tissue engineering. Films of different thickness were produced by spin coating from solution. Cell attachment and proliferation were analysed and revealed a reproducible and significant growth advantage over the initial 7 days for both cell types on poly(lactide-co-glycolide) (PLGA) versus poly(epsilon-caprolactone) (PCL), and on thick versus thin films. In order to understand the basis of the variation in cell growth, the surface morphology, degradation behaviour and mechanical properties of the films were investigated. The pattern of cell attachment and growth was found to be unrelated to surface topography and no distinction in film degradation behaviour was found to account for differences in cell growth, except at late time points (14 days), where degradation of thin PLGA films became significant. By contrast, the flexural loss and storage moduli were found to be reduced in films composed of PLGA versus PCL, and also as film thickness increased, indicating that mechanical properties of biomaterials can influence cell growth. We conclude that elastic modulus is relevant to biology at the cellular scale and may also be influential at the tissue/organ level, and is a critical parameter to be considered during development of synthetic biomaterials for tissue engineering.     

Mitochondrial membrane potential and reactive oxygen species content of endothelial and smooth muscle cells cultured on poly(epsilon-caprolactone) films

A transitory but significant stimulation of mitochondrial activity, increase of reactive oxygen species (ROS) and oxidative stress were previously observed in L929 fibroblasts cultured on poly(epsilon-caprolactone) (PCL) films. ROS, mainly formed in mitochondria, play a physiological role but an excessive production can promote endothelial dysfunction, cause oxidative injury to vascular cells, oxidize lipoproteins and accelerate atherothrombogenesis. On the other hand, mitochondria have a crucial position in programmed cell death control and are responsible for ATP synthesis through the coupling of oxidative phosphorylation to respiration. This coupling requires the existence of a mitochondrial membrane potential (Deltapsi(m)). The aim of the present study was to evaluate by flow cytometry the ROS content and Deltapsi(m) of both endothelial (EC) and smooth muscle cells (SMC) cultured on PCL films as a potential substrate for vascular graft development. Cell size, internal complexity and cell cycle were also analyzed to detect the possible appearance of the subG(1) cell fraction, characteristic of apoptotic cells. The effect of treating PCL films with NaOH before culture was also studied. PCL decreases the ROS content of EC during the culture but produces an increase of these levels in SMC after 7 days. PCL also induces variations of Deltapsi(m) which show a significant parallelism with the changes observed in ROS levels proving the importance and sensitivity of these measurements as indicators of the mitochondrial function. The treatment of PCL with NaOH decreases these effects demonstrating the benefits of increasing the surface hydrophilicity before cell culture which improves cell adhesion and proliferation and reduces oxidative stress. Since no important changes have been detected in subG(1) fraction of EC and SMC cultured on either PCL or PCL-NaOH, the changes of Deltapsi(m) observed in the present study cannot be related to apoptosis. These results confirm the potential utility of PCL as a suitable scaffold in Vascular Tissue Engineering.     

PCL-PGLA composite tubular scaffold preparation and biocompatibility investigation

The objective of this paper was to fabricate a biodegradable tubular scaffold for small diameter (d<6 mm) blood vessel tissue engineering. The tube scaffold needed a porous wall for cell attachment, proliferation and tissue regeneration with its degradation. A novel method given in this paper was to coat a porous layer of poly (epsilon-caprolactone) (PCL) on the outside of a poly (glycolic-co-lactic acid) (PGLA with GA:LA=90:10) fiber braided tube to give a PCL-PGLA composite. The PGLA tube was fabricated using a braiding machine by inserting a Teflon tube with the desired diameter in center of the 20 spindles, which are the carriers of PGLA fibers. Changing the diameter of the Teflon tube can vary the inner diameter of a braided PGLA tube. Thermally induced phase separation method was used for PCL solution coating on the surface of the PGLA braided tube. Controlling the polymer concentration, non-solvent addition and quenching temperature generated the pore structures, with pore sizes ranging from 10-30 microm. The fibroblast cells were seeded on the tubular scaffold and cultured in vitro for the biocompatibility investigation. Histology results showed that the fibroblast cells proliferated on the interconnected pore of the PCL porous layer in 1 week.     

Evaluation of ultra-thin poly(epsilon-caprolactone) films for tissue-engineered skin

Various natural and synthetic polymeric materials have been used as scaffold matrices for tissue-engineered skin. However, the commercially available skin replacement products pose problems of poor mechanical properties and immunological rejection. We have thus developed a film of 5 microm thickness, via biaxial stretching of poly(epsilon-caprolactone) (PCL), as a potential matrix for living skin replacements. The aim of this study was to evaluate the feasibility of using biaxially stretched PCL films as matrices for culturing human dermal fibroblasts. For this purpose, we cultured human dermal fibroblasts for 7 days on the films. Glass cover slips and polyurethane (PU) sheets were used as controls. The data from phase contrast light, confocal laser, and scanning electron microscopy suggested that biaxially stretched PCL films support the attachment and proliferation of human dermal fibroblasts. Thymidine-labeling results showed quantitatively that cell proliferation on the PCL films was superior to that on the PU samples. These results indicated that biaxially stretched PCL films supported the growth of human dermal fibroblasts and might have potential to be applied in tissue engineering a dermal equivalent or skin graft.     

Simple surface modification of poly(epsilon-caprolactone) to induce its apatite-forming ability

A biodegradable polymer coated with a bone-like apatite layer on its surface is useful as a scaffold for bone tissue regeneration. In this work, a poly(epsilon-caprolactone) (PCL) surface was modified by an O2 plasma surface treatment to form oxygen-containing functional groups. The plasma-treated samples were subsequently dipped alternately in an alcoholic solution containing calcium ions and one containing phosphate ions to deposit apatite precursors on the surface. The surface-modified PCL samples formed a dense and uniform surface bone-like apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. This surface-modification process is applicable to two-dimensional PCL plates and three-dimensional PCL meshes. In the resulting apatite-PCL composite, the apatite layer strongly adhered to the PCL surface and remained intact after a tape-detachment test. Therefore, this type of composite material will be a useful scaffold for bone tissue engineering.     

Gradient nanofibrous chitosan/poly ɛ-caprolactone scaffolds as extracellular microenvironments for vascular tissue engineering

One of the major challenges of tissue-engineered small-diameter blood vessels is restenosis caused by thrombopoiesis. The goal of this study was to develop a 3D gradient heparinized nanofibrous scaffold, aiding endothelial cells lined on the lumen of blood vessel to prevent thrombosis. The vertical graded chitosan/poly ?-caprolactone (CS/PCL) nanofibrous vessel scaffolds were fabricated with chitosan and PCL by sequential quantity grading co-electrospinning. To mimic the natural blood vessel microenvironment, we used heparinization and immobilization of vascular endothelial growth factor (VEGF) in the gradient CS/PCL. The quantity of heparinized chitosan nanofibers increased gradually from the tunica adventitia to the lumen surfaces in the gradient CS/PCL wall of tissue engineered vessel. More heparin reacted to chitosan nanofiber in gradient CS/PCL than in uniform CS/PCL nanofibrous scaffolds. Antithrombogenic properties of the scaffolds were enhanced by the heparinization of these scaffolds, as shown by activated partial thromboplastin time and platelet adhesion assay. Compared to the uniform CS/PCL scaffold, the release of VEGF from the gradient CS/PCL was more stable and sustained, and the burst release of VEGF was reduced approximately 42.5% within the initial 12 h. The adhesion and proliferation of human umbilical vein endothelial cells (HUVEC) were enhanced on the gradient CS/PCL scaffold. Furthermore, HUVEC grew and formed an entire monolayer on the top side of the gradient CS/PCL scaffold. Therefore, use of vertical gradient heparinized CS/PCL nanofibrous scaffolds could provide an approach to create small-diameter blood vessel grafts with innate properties of mammalian vessels of anticoagulation and rapid induction of re-endothelialization.     

Development of a composite vascular scaffolding system that withstands physiological vascular conditions

Numerous scaffolds that possess ideal characteristics for vascular grafts have been fabricated for clinical use. However, many of these scaffolds may not show consistent properties when they are exposed to physiologic vascular environments that include high pressure and flow, and they may eventually fail due to unexpected rapid degradation and low resistance to shear stress. There is a demand to develop a more durable scaffold that could withstand these conditions until vascular tissue matures in vivo. In this study, vascular scaffolds composed of poly(epsilon-caprolactone) (PCL) and collagen were fabricated by electrospinning. Morphological, biomechanical, and biological properties of these composite scaffolds were examined. The PCL/collagen composite scaffolds, with fiber diameters of approximately 520 nm, possessed appropriate tensile strength (4.0+/-0.4 MPa) and adequate elasticity (2.7+/-1.2 MPa). The burst pressure of the composite scaffolds was 4912+/-155 mmHg, which is much greater than that of the PCL-only scaffolds (914+/-130 mmHg) and native vessels. The composite scaffolds seeded with bovine endothelial cells (bECs) and smooth muscle cells (bSMCs) showed the formation of a confluent layer of bECs on the lumen and bSMCs on the outer surface of the scaffold. The PCL/collagen composite scaffolds are biocompatible, possess biomechanical properties that resist high degrees of pressurized flow over long term, and provide a favorable environment that supports the growth of vascular cells.     

Endothelial cell growth factor (ECGF) enmeshed with fibrin matrix enhances proliferation of EC in vitro.

The vascular biomaterials that are currently used for clinical implants have been considered as poor substrates for human endothelial cell adhesion and spreading. Therefore, thrombotic occlusion is the predominant cause for the failure of small diameter vascular grafts made out of Dacron or Teflon. To reduce surface thrombogenicity of material surfaces used for vascular implants, in vitro seeding of endothelial cells using adhesive protein matrix is under evaluation in various laboratories. Evidences suggest that fibrin matrix is a suitable matrix for endothelial cell (EC) adhesion to the currently available vascular graft materials; however, poor proliferation of attached cells seems to be a major limitation. During this study we have also found that fibrin is a better matrix compared to gelatin to support cell attachment and spreading. However, the poor proliferation of initially attached human umbilical cord vein endothelial cell (HUVEC) necessitated modification of the matrix composition to get a monolayer within a limited period. Since fibrin can form a network of protein bundles, an effort is made to incorporate growth factors within the matrix. Endothelial cell growth factor (ECGF) isolated from bovine hypothalamus is immobilized on the surface with fibrin glue (FG) to promote proliferation of HUVEC. The results demonstrate that proteins with similar molecular weights as growth factors (GF) are retained within the matrix and released into the culture medium for 96 h, in quantities that would be sufficient to promote cell proliferation. When cells were seeded on the matrix composed with components of FG and ECGF, the HUVEC proliferated at a significantly higher rate compared to the cells on surfaces coated with gelatin or fibrin. The EC thus grown on the composite (FG + ECGF) resisted the shear stress as compared to the cells grown on gelatin. The HUVEC monolayer grown on the composite seems thromboresistant as adhesion and activation of platelets are negligible after platelet rich plasma is incubated with the monolayer for about 1 h with agitation. Therefore, the composite of fibrin and ECGF can be a suitable matrix for further evaluation of patients' autologous endothelial cell attachment and proliferation for clinical application.     

Synthesis of novel cholic acid functionalized branched oligo/poly(epsilon-caprolactone)s for biomedical applications

Novel cholic acid functionalized branched oligo/poly(epsilon-caprolactone)s were synthesized through the ring-opening polymerization of epsilon-caprolactone initiated by cholic acid with hydroxyl groups. The molecular weight of the branched polymers can be adjusted by controlling the feed ratio of the initiator cholic acid to the monomer epsilon-caprolactone. Comparing with linear homopolymer poly(epsilon-caprolactone) (PCL), these branched oligo/poly(epsilon-caprolactone)s show much faster hydrolytic degradation rates, implies that our approach provides a convenient and effective strategy to accelerate degradation of the biodegradable polymers with slow degradation rates such as PCL. The cell culture experiment indicates the incorporation of cholic acid moiety to the polymer chain can improve both cell adherence and proliferation obviously.     

Grafting of gelatin on electrospun poly(caprolactone) nanofibers to improve endothelial cell spreading and proliferation and to control cell Orientation

We modified the surface of electrospun poly(caprolactone) (PCL) nanofibers to improve their compatibility with endothelial cells (ECs) and to show the potential application of PCL nanofibers as a blood vessel tissue-engineering scaffold. Nonwoven PCL nanofibers (PCL NF) and aligned PCL nanofibers (APCL NF) were fabricated by electrospinning technology. To graft gelatin on the nanofiber surface, PCL nanofibers were first treated with air plasma to introduce -COOH groups on the surface, followed by covalent grafting of gelatin molecules, using water-soluble carbodiimide as the coupling agent. The chemical change in the material surface during surface modification was confirmed by X-ray photoelectron spectroscopy and quantified by colorimetric methods. ECs were cultured to evaluate the cytocompatibility of surface-modified PCL NF and APCL NF. Gelatin grafting can obviously enhance EC spreading and proliferation compared with the original material. Moreover, gelatin-grafted APCL NF readily orients ECs along the fibers whereas unmodified APCL NF does not. Immunostaining micrographs showed that ECs cultured on gelatin-grafted PCL NF were able to maintain the expression of three characteristic markers: platelet-endothelial cell adhesion molecule 1 (PECAM-1), intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1). The surface-modified PCL nanofibrous material is a potential candidate material in blood vessel tissue engineering.     

Polylactic acid fibre-reinforced polycaprolactone scaffolds for bone tissue engineering

The employment of composite scaffolds with a well-organized architecture and multi-scale porosity certainly represents a valuable approach for achieving a tissue engineered construct to reproduce the middle and long-term behaviour of hierarchically complex tissues such as spongy bone. In this paper, fibre-reinforced composites scaffold for bone tissue engineering applications is described. These are composed of poly-L-lactide acid (PLLA) fibres embedded in a porous poly(epsilon-caprolactone) matrix, and were obtained by synergistic use of phase inversion/particulate leaching technique and filament winding technology. Porosity degree as high as 79.7% was achieved, the bimodal pore size distribution showing peaks at ca 10 and 200 microm diameter, respectively, accounting for 53.7% and 46.3% of the total porosity. In vitro degradation was carried out in PBS and SBF without significant degradation of the scaffold after 35 days, while in NaOH solution, a linear increase of weight lost was observed with preferential degradation of PLLA component. Subsequently, marrow stromal cells (MSC) and human osteoblasts (HOB) reached a plateau at 3 weeks, while at 5 weeks the number of cells was almost the same. Human marrow stromal cell and trabecular osteoblasts rapidly proliferate on the scaffold up to 3 weeks, promoting an oriented migration of bone cells along the fibre arrangement. Moreover, the role of seeded HOB and MSC on composite degradation mechanism was assessed by demonstrating a more relevant contribution to PLLA degradation of MSC when compared to HOB. The novel PCL/PLLA composite scaffolds thus showed promise whenever tuneable porosity, controlled degradability and guided cell-material interaction are simultaneously requested.     

In vivo evaluation of an ultra-thin polycaprolactone film as a wound dressing

The use of ultra-thin films as dressings for cutaneous wounds could prove advantageous in terms of better conformity to wound topography and improved vapour transmission. For this purpose, ultra-thin poly(epsilon-caprolactone) (PCL) films of 5-15 microm thickness were fabricated via a biaxial stretching technique. To evaluate their in vivo biocompatibility and feasibility as an external wound dressing, PCL films were applied over full and partial-thickness wounds in rat and pig models. Different groups of PCL films were used: untreated, NaOH-treated, untreated with fibrin, NaOH-treated with perforations, and NaOH-treated with fibrin and S-nitrosoglutathione. Wounds with no external dressings were used as controls. Wound contraction rate, histology and biomechanical analyses were carried out. Wounds re-epithelialized completely at a comparable rate. Formation of a neo-dermal layer and re-epithelialization were observed in all the wounds. A lower level of fibrosis was observed when PCL films were used, compared to the control wounds. Ultimate tensile strength of the regenerated tissue in rats reached 50-60% of that in native rat skin. Results indicated that biaxially-stretched PCL films did not induce inflammatory reactions when used in vivo as a wound dressing and supported the normal wound healing process in full and partial-thickness wounds.     

Tailoring fiber diameter in electrospun poly(epsilon-caprolactone) scaffolds for optimal cellular infiltration in cardiovascular tissue engineering

Despite the attractive features of nanofibrous scaffolds for cell attachment in tissue-engineering (TE) applications, impeded cell ingrowth has been reported in electrospun scaffolds. Previous findings have shown that the scaffold can function as a sieve, keeping cells on the scaffold surface, and that cell migration into the scaffold does not occur in time. Because fiber diameter is directly related to the pore size of an electrospun scaffold, the objective of this study was to systematically evaluate how cell delivery can be optimized by tailoring the fiber diameter of electrospun poly(epsilon-caprolactone) (PCL) scaffolds. Five groups of electrospun PCL scaffolds with increasing average fiber diameters (3.4-12.1 microm) were seeded with human venous myofibroblasts. Cell distribution was analyzed after 3 days of culture. Cell penetration increased proportionally with increasing fiber diameter. Unobstructed delivery of cells was observed exclusively in the scaffold with the largest fiber diameter (12.1 microm). This scaffold was subsequently evaluated in a 4-week TE experiment and compared with a poly(glycolic acid)-poly(4-hydroxybutyrate) scaffold, a standard scaffold used successfully in cardiovascular tissue engineering applications. The PCL constructs showed homogeneous tissue formation and sufficient matrix deposition. In conclusion, fiber diameter is a crucial parameter to allow for homogeneous cell delivery in electrospun scaffolds. The optimal electrospun scaffold geometry, however, is not generic and should be adjusted to cell size.