The effect of scaffold degradation rate on three-dimensional cell growth and angiogenesis

Growth and electrophysiological properties of rat embryonic cardiomyocytes on hydroxyl- and carboxyl-modified surfaces

Biodegradable scaffolds such as poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) or poly(glycolic acid) (PGA) are commonly used materials in tissue engineering. The chemical composition of these scaffolds changes during degradation which provides a differential environment for the seeded cells. In this study we have developed a simple and relatively high-throughput method in order to test the physiological effects of this varying chemical environment on rat embryonic cardiac myocytes. In order to model the different degradation stages of the scaffold, glass coverslips were functionalized with 11-mercaptoundecanoic acid (MUA) and 11-mercapto-1-undecanol (MUL) as carboxyl- and hydroxyl-groups presenting surfaces, and with trimethoxysilylpropyldiethylenetriamine (DETA) and (3-aminopropyl)triethoxysilane (APTES) as controls. Embryonic cardiac myocytes formed beating islands on all tested surfaces, but the number of attached cells and beating patches was significantly lower on MUL compared to any of the other functionalized surfaces. Moreover, whole-cell patch-clamp experiments showed that the average length of action potentials generated by the beating-cardiac myocytes were significantly longer on MUL compared to the other surfaces. Our results, using our simple test system, are in basic agreement with earlier observations that utilized a complex 3D biodegradable scaffold. Thus, surface functionalization with self-assembled monolayers combined with histological/physiological testing could be a relatively high throughput method for biocompatibility studies and for the optimization of the material/tissue interface in tissue engineering.

In vitro precultivation alleviates post-implantation inflammation and enhances development of tissue-engineered tubular cartilage

Tissue-engineered tubular cartilage is a promising graft for tracheal reconstruction. But polylactic acid/polyglycolic acid (PLA/PGA) fibers, the frequently used scaffolds for cartilage engineering, often elicit an obvious inflammation response following implantation into immunocompetent animals. We propose that the inflammation could be alleviated by in vitro precultivation. In this study, after in vitro culture for either 2 days (direct implantation group (DI)) or for 2 weeks (precultivation implantation group (PI)), autologous tubular chondrocyte-PLA/PGA constructs were subcutaneously implanted into rabbits. In the PI group, after 2 weeks of precultivation, most of the fibers were found to be completely embedded in an extracellular matrix (ECM) produced by the chondrocytes. Importantly, no obvious inflammatory reaction was observed after in vivo implantation and homogeneous cartilage-like tissue was formed with biomechanical properties close to native tracheal cartilage at 4 weeks post-implantation. In the DI group, however, an obvious inflammatory reaction was observed within and around the cell-scaffold constructs at 1 week implantation and only sporadic cartilage islands separated by fibrous tissue were observed at 4 weeks. These results demonstrated that the post-implantation inflammatory reaction could be alleviated by in vitro precultivation, which contributes to the formation of satisfactory tubular cartilage for tracheal reconstruction.

The relationship between the mechanical properties and cell behaviour on PLGA and PCL scaffolds for bladder tissue engineering

Previous work on 2D synthetic films showed growth of human bladder stromal cells was enhanced on materials with lower moduli that mimic the elastic properties of native tissue. This study developed 3D synthetic foam scaffolds for soft tissue engineering by emulsion freeze-drying. Foams of poly(lactide-co-glycolide) (PLGA) and poly(epsilon-caprolactone) (PCL) were extensively characterised using scanning electron microscopy, mercury porosimetry, dynamic mechanical analysis, degradation analysis, size exclusion chromatography and differential scanning calorimetry. Foams of 85-88% porosity and 35 microm pore diameter were selected for further study; the storage modulus of PCL foams was around half that of PLGA (2 MPa vs 4 MPa) and closer to the reported value for native bladder tissue. Urinary tract stromal cells showed a 4.4 and 2.4-fold higher attachment and rate of growth, respectively, on PCL scaffolds, as assessed by a modified 3-[4,5-dimethyl(thiazol-2yl)-3,5-diphery] tetrazolium bromide assay. A greater contractile force was exerted by cells seeded in PLGA than on PCL scaffolds, raising the possibility that the reduced rate of proliferation of cells on PLGA scaffolds may reflect differentiation into a contractile phenotype. This study has generated PCL foam scaffolds with properties that may be pertinent to the tissue engineering of the bladder and other soft tissues.

Preparation and properties of a chitosan-based carrier of corneal endothelial cells

A novel chitosan-based membrane that was made of hydroxypropyl chitosan, gelatin and chondroitin sulfate was used as a carrier of corneal endothelial cells. The characteristics of the blend membrane, such as transparency, equilibrium water content, permeability, mechanical properties, protein absorption ability, hydrophilicity and surface morphology, were determined. To study the effects of the membrane on cell attachment and growth, rabbit corneal endothelial cells were cultured on this artificial membrane. The biodegradability and biocompatibility of the blend membrane were in vivo evaluated by its implantation into the muscle of the rats. Glucose permeation results demonstrated that the blend membrane had higher glucose permeability than natural human cornea. Scanning electron microscopy (SEM) analysis of the membranes demonstrated that no fibrils were observed. As a result, the optical transparency of the membrane was as good as the natural human cornea. The average value of tensile strength of the membrane was 13.71 MPa for dry membrane and 1.48 MPa for wet membrane. The value of elongation at break of the wet was 45.64%. The cultured rabbit corneal endothelial cells formed a monolayer on the blend membrane which demonstrated that the membrane was suitable for corneal endothelial cells to attach and grow. In addition, the membranes in vivo showed a good bioabsorption property. The mild symptoms of inflammation at sites of treatment could be resolved as the implant was absorbed by the host. The results of this study demonstrated that the hydroxypropyl chitosan-chondroitin sulfate-gelatin blend membrane can potentially be used as a carrier for corneal endothelial cell transplantation.

Degradation and healing characteristics of small-diameter poly(epsilon-caprolactone) vascular grafts in the rat systemic arterial circulation

BACKGROUND

Long-term patency of conventional synthetic grafts is unsatisfactory below a 6-mm internal diameter. Poly(epsilon-caprolactone) (PCL) is a promising biodegradable polymer with a longer degradation time. We aimed to evaluate in vivo healing and degradation characteristics of small-diameter vascular grafts made of PCL nanofibers compared with expanded polytetrafluoroethylene (ePTFE) grafts.

METHODS AND RESULTS

We prepared 2-mm-internal diameter grafts by electrospinning using PCL (M(n)=80, 000 g/mol). Either PCL (n=15) or ePTFE (n=15) grafts were implanted into 30 rats. Rats were followed up for 24 weeks. At the conclusion of the follow-up period, patency and structural integrity were evaluated by digital subtraction angiography. The abdominal aorta, including the graft, was harvested and investigated under light microscopy. Endothelial coverage, neointima formation, and transmural cellular ingrowth were measured by computed histomorphometry. All animals survived until the end of follow-up, and all grafts were patent in both groups. Digital subtraction angiography revealed no stenosis in the PCL group but stenotic lesions in 1 graft at 18 weeks (40%) and in another graft at 24 weeks (50%) in the ePTFE group. None of the grafts showed aneurysmal dilatation. Endothelial coverage was significantly better in the PCL group. Neointimal formation was comparable between the 2 groups. Macrophage and fibroblast ingrowth with extracellular matrix formation and neoangiogenesis were better in the PCL group. After 12 weeks, foci of chondroid metaplasia located in the neointima of PCL grafts were observed in all samples.

CONCLUSIONS

Small-diameter PCL grafts represent a promising alternative for the future because of their better healing characteristics compared with ePTFE grafts. Faster endothelialization and extracellular matrix formation, accompanied by degradation of graft fibers, seem to be the major advantages. Further evaluation of degradation and graft healing characteristics may potentially lead to the clinical use of such grafts for revascularization procedures.

In vitro study of hydroxyapatite-based photocurable polymer composites prepared by laser stereolithography and supercritical fluid extraction

The fabrication of three-dimensional (3-D) structures using computer-controlled ultraviolet (UV) photopolymerization of acrylates (laser stereolithography) often results in the trapping of residual unreacted monomer and initiator. These residuals can leach from the finished structure and affect the biological response of cells and tissues. Thus the potential applications of these structures for tissue engineering have not been fully realized. In this paper we demonstrate that conventional post-lithography treatments followed by processing in the environmentally benign solvent, supercritical carbon dioxide (scCO(2)), dramatically increased biocompatibility. The scCO(2) processing of pure polyacrylate and polyacrylate/hydroxyapatite composite structures extracts residuals from all structures including those that had received full conventional post-lithography treatment (acetone washing/UV drying). Human osteoblast cells seeded on the extracted surfaces of these structures demonstrated increased cell attachment and proliferation on the scCO(2)-treated materials.

The synergic effect of polylactide fiber and calcium phosphate particle reinforcement in poly epsilon-caprolactone-based composite scaffolds

In this work, three-dimensional porous composite scaffolds, based on poly(epsilon-caprolactone) (PCL), were fabricated through the combination of a filament winding technique and a phase inversion/salt leaching process. Sodium chloride crystals were used as the porogen agent, and poly(lactic acid) (PLA) fibers and calcium phosphates as reinforcement. The aim of the current work is to assess the effective synergistic role of bioactive particles (i.e. alpha-tricalcium phosphates (alpha-TCP)) and PLA fibers on the morphology and mechanical response of the final scaffold. Morphological investigations performed on fiber-reinforced composite scaffolds with different PCL/alpha-TCP volume ratios (0%, 13%, 20% and 26%) show a high porosity degree (ca. 80%), pore interconnection and a homogeneous distribution of pores within the scaffold. More specifically, a bimodal pore size distribution was observed. This comprised microporosity (pores with radii ranging from 0.1 to 10 microm, which were strictly related to solvent extraction) and macroporosity (pores with radii from 10 to 300 microm, which were ascribable to the leaching of porogen elements). Static compressive tests showed that the effect of alpha-TCP on the mechanical response was to increase the elastic modulus up to a maximum value of 2.21+/-0.24 MPa, depending on the concentration of alpha-TCP added. This effect may be explained through the interaction of calcium-deficient hydroxyapatite crystals, formed as a consequence of a hydrolysis reaction of alpha-TCP, and the fiber-reinforced polymer matrix. The correct balance between chemical composition and spatial organization of reinforcement systems allows the attainment of an ideal compromise between mechanical response and bioactive potential, facilitating the development of composite scaffolds for bone tissue engineering applications.

Spatial and temporal patterns of bone formation in ectopically pre-fabricated, autologous cell-based engineered bone flaps in rabbits

Biological substitutes for autologous bone flaps could be generated by combining flap pre-fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre-fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10-20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell-scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro-computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1+/-0.7 mm and 1.0+/-0.4 mm at 8 weeks to 3.7+/-0.6 mm and 1.4+/-0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre-fabrication of large cell-based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts.

Impact of pore size on the vascularization and osseointegration of ceramic bone substitutes in vivo

The repair of bone defects with biomaterials depends on a sufficient vascularization of the implantation site. We analyzed the effect of pore size on the vascularization and osseointegration of biphasic calcium phosphate particles, which were implanted into critical-sized cranial defects in Balb/c mice. Dense particles and particles with pore sizes in the ranges 40-70, 70-140, 140-210, and 210-280 microm were tested (n = 6 animals per group). Angiogenesis, vascularization, and leukocyte-endothelium interactions were monitored for 28 days by intravital microscopy. The formation of new bone and the bone-interface contact (BIC) were determined histomorphometrically. Twenty-eight days after implantation, the functional capillary density was significantly higher with ceramic particles whose pore sizes exceeded 140 microm [140-210 microm: 6.6 (+/-0.8) mm/mm(2); 210-280 microm: 7.3 (+/-0.6) mm/mm(2)] than with those whose pore sizes were lesser than 140 microm [40-70 microm: 5.3 (+/-0.4) mm/mm(2); 70-140 microm: 5.6 (+/-0.3) mm/mm(2)] or with dense particles [5.7 (+/-0.8) mm/mm(2)]. The volume of newly-formed bone deposited within the implants increased as the pore size increased [40-70 microm: 0.07 (+/-0.02) mm(3); 70-140 microm: 0.10 (+/-0.06) mm(3); 140-210 microm: 0.13 (+/-0.05) mm(3); 210-280 microm: 0.15 (+/-0.06) mm(3)]. Similar results were observed for the BIC. The data demonstrates pore size to be a critical parameter governing the dynamic processes of vascularization and osseointegration of bone substitutes.

Porous poly(lactic-co-glycolic acid) microsphere as cell culture substrate and cell transplantation vehicle for adipose tissue engineering

Tissue engineering often requires ex vivo cell expansion to obtain a large number of transplantable cells. However, the trypsinization process used to harvest ex vivo expanded cells for transplantation interrupts interactions between cultured cells and their extracellular matrices, facilitating apoptosis and consequently limiting the therapeutic efficacy of the transplanted cells. In the present study, open macroporous poly(lactic-co-glycolic acid) (PLGA) microspheres were used as a cell culture substrate to expand human adipose-derived stromal cells (ASCs) ex vivo and as a cell transplantation vehicle for adipose tissue engineering, thus avoiding the trypsinization necessary for transplantation of ex vivo expanded cells. Human ASCs cultured on macroporous PLGA microspheres in stirred suspension bioreactors expanded 3.8-fold over 7 days and differentiated into an adipogenic lineage. The apoptotic activity of ASCs cultured on microspheres was significantly lower than that of trypsinized ASCs. ASCs cultured on microspheres survived much better than trypsinized ASCs upon transplantation. The implantation of ASCs cultured on microspheres resulted in much more extensive adipose tissue formation than the implantation of ASCs cultured on plates, trypsinized, and subsequently mixed with microspheres. Ex vivo cell expansion and transplantation using this system would improve the therapeutic efficacy of cells over the current methods used for tissue engineering.

A Parametric Study on the Processing and Physical Characterization of PLGA 50/50 Bioscaffolds

The ability to control the characteristics of scaffolds is important such that scaffolds can be fine tuned for specific applications. In this study, the effects of processing parameters on cell morphology and mechanical properties of PLGA 50/50 bioscaffolds for tissue engineering applications were investigated. Specifically, the effects of salt particle sizes and salt-to-polymer mass ratios on the scaffold relative density, average pore size and density, open-cell porosity, and mechanical properties were examined. The PLGA samples were processed using a salt leaching technique in a batch-foaming setup. Experiments showed that pore size and density were dependent on the salt particle size used, and that as the salt-to-polymer mass ratio increased, the porosity increased while the relative density decreased. The results showed that by varying the salt parameters during fabrication, the scaffold characteristics and morphology can be controlled.

Electrospun bioresorbable heart valve scaffold for tissue engineering

Currently marketed mechanical or biological prosthetic heart valves are regarded as valid substitutes for native heart valves suffering from degenerative pathologies. These devices require strict follow-up due to dysfunctions or post-surgical complications. Potential drawbacks of these medical devices are calcification, tearing of the cusps, thromboembolism and hemolysis. In this context, a tissue engineering approach offers a promising alternative scenario. In this paper, a trileaflet poly(epsilon-caprolactone) (PCL) heart valve scaffold prototype has been manufactured by electrospinning technique using a custom-made rotating target. Process parameters were selected in order to achieve suitable microstructure and mechanical performance. The electrospun heart valve prototype was functionally characterized by means of a pulse duplicator in order to evaluate the mechanical/hydraulic response to the imposed testing conditions. Leaflets synchronously opened in the ejection phase and the proper apposition of the leaflets prevented high leakage volumes in the diastolic phase. This preliminary study suggests a successful perspective for the proposed approach in designing a novel tissue engineered bioresorbable heart valve.

Comparison of morphology and mechanical properties of PLGA bioscaffolds

In this study, bioscaffolds using poly(DL-lactide-co-glycolide) acid (PLGA) were fabricated and studied. The gas foaming/salt leaching technique in a batch foaming setup was employed, and the effects of material composition of PLGA on the morphology and mechanical properties using this process were investigated. Two material compositions of PLGA 50/50 and 85/15 were used, and characterization of scaffolds fabricated with these materials showed that a lower relative density can be achieved with an increasing poly(DL-lactide) acid (PDLLA) content; however, higher open-cell porosity was obtained with lower PDLLA content. Furthermore, the effect of PLGA composition on modulus of the scaffolds was minor.

Porous bioactive nanostructured scaffolds for bone regeneration: a sol-gel solution

Considerable advances have been seen in materials with tailored nanostructures in recent years, owing, in part, to increased demands placed on material properties in fields, such as tissue regeneration and wound healing. This review focuses on the developments made in nanoporous bioactive glasses, their novel nanocomposites and their application to bone regeneration. Bioactive glasses have the ability to stimulate new bone growth as they dissolve in the body. Sol-gel bioactive glasses have a nanoporosity that provides sites for cell attachment and tailorable degradation rates. Importantly, the glasses can be made into interconnected porous structures that can be used as 3D templates for bone growth, although, because they are glasses, they cannot be implanted directly into sites that are under cyclic loading. Composites provide a partial solution to this problem, although their bioactive and degradation properties are not ideal, therefore novel nanocomposites are needed. The route to these potentially ideal materials is described.

The degradation profile of novel, bioresorbable PCL-TCP scaffolds: an in vitro and in vivo study

Degradation studies of scaffolds are important in bone tissue engineering. Previously, novel poly(epsilon-caprolactone)-20% tricalcium phosphate (PCL-TCP) based scaffolds were developed and proven useful for bone regeneration. In this study in vitro degradation analyses were carried out with the PCL-TCP scaffolds immersed in standard culture medium for 24 weeks. In vivo degradation was performed with the scaffolds implanted in the abdomen of rats for the same period of time. Results demonstrated greater degradation of PCL-TCP scaffolds in vivo than in vitro. At 24 weeks, the increase of average porosity of the scaffolds in vivo was 29.2% compared to 2.65% in vitro. Gel permeation chromatography (GPC) analysis revealed a decrease of 29% and 20% respectively in the Mn and Mw values after 24 weeks in vitro. However, a significant decrease in Mn and Mw values (79.6% and 88.7% respectively) were recorded in vivo. The mechanical properties however, were relatively similar and closely match those of cancellous bone even at 24 weeks. The results showed that the scaffold can be used for dentoalveolar reconstruction and PCL-TCP scaffolds have shown to possess the potential to degrade within the desired time period of 5-6 months and favorable mechanical properties.

Closure of the pleural dead space after pneumonectomy in a rabbit model: use of bioabsorbable lactic acid and caprolactone copolymer cubes

The remaining pleural dead space after pulmonary resection sometimes causes serious complications, such as empyema. The objective of this study was induction of granulation tissue in uninfected pleural space after pneumonectomy in a rabbit model using implantation of bioabsorbable and porous poly-l-lactic acid and epsilon-caprolactone copolymer (PLAC) cubes. Twelve Japanese white rabbits were randomly split into two groups: the control group (n = 6) underwent simple left pneumonectomy, whereas the experimental group (n = 6) underwent left pneumonectomy followed by filling of the left hemithorax with PLAC cubes. One rabbit in each group was killed at 1, 2, 3, and 6 months after surgery, and pleural tissue was evaluated. In the experimental group, granulation tissue inside the PLAC cubes had begun to form at 1 month after implantation. From 3 months to 6 months, proliferated granulation tissue occupied the left postpneumonectomy pleural space with no residual space. The implanted PLAC material was being gradually degraded. We were able to induce self-assembled granulation tissue in the pleural space after pneumonectomy in a rabbit model using bioabsorbable PLAC cubes. The use of this technique allowed the residual pleural space to be closed after pulmonary resection.

Macromolecular biomaterials for scaffold-based vascular tissue engineering

Cardiovascular diseases are increasingly becoming the main cause of death all over the world, which has led to an increase in the economic and social burden of such diseases. Vascular tissue engineering (VTE) is providing a route towards interesting applications, mainly focussing on the in vitro, in vivo, or combined in vitro/in vivo regeneration of small-diameter blood vessels (<6 mm) for coronary or peripheral vascular substitutions. Although different approaches have been investigated in the past two decades to achieve this aim, the most common method uses a macromolecular-based structure to scaffold cells during the regeneration process. Therefore, the aim of this work is to comprehensively review macromolecular biomaterials that were designed, developed, fabricated, and tested for scaffolding VTE. In an effort to provide a comprehensive overview, this review will mainly focus on the mechanical properties of the construct and its biological performance that results from the scaffold colonization during cell growth.

Preparation of Bioactive Poly(Lactic-Co-Glycolic)Acid and Silica Gel Fibers Mixed Non-Woven Fabric

Poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. Poly(lactic-co-glycolic)acid solution was prepared by dissolving it in the hexafluoroisopropanol. Then, they were transferred to two separate syringes which were connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica gel containing calcium and poly(lactic-co-glycolic)acid solution were spun together under the electric field of 2 ㎸/㎝. The FE-SEM observations showed that the silica gel and poly(lactic-co-glycolic)acid fibers were mixed together completely and its handling property was much improved compared to that of the non-woven silica gel fabric. After soaking in the SBF for 1 week, low crystalline apatite crystals were also observed to occur on the silica fiber surfaces first and then they were also observed to occur on the poly(lactic-co-glycolic)acid fiber surfaces. From the results, it can be concluded that the poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric made by electro-spinning method has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Poly(ɛ-Caprolactone) and Poly (L-Lactic-Co-Glycolic Acid) Degradable Polymer Sponges Attenuate Astrocyte Response and Lesion Growth in Acute Traumatic Brain Injury

This study evaluated the response of rat brain to 2 degradable polymers (poly (L-lactic-co-glycolic acid) (PLGA), and poly(epsilon-caprolactone) (PCL)), two common materials in tissue engineering. PLGA has been extensively studied in the brain for controlled drug release as injectable microspheres and is generally accepted as biocompatible in that capacity. Biocompatibility in other forms and for different functions in the brain has not been widely studied. PCL was chosen as an alternative to PLGA for its slower degradation and less-acidic pH upon degradation. Porous scaffolds were made from both polymers and implanted into rat cerebral cortex for 1 and 4 weeks. Morphology, defect size, activation of microglia (OX-42) and astrocytes (glial fibrillary acidic protein (GFAP)), infiltration of activated macrophages (major histocompatibility complex (MHC)-II), and ingrowth of neurons (beta-tubulin type III (Tuj-1)) and progenitor cells (nestin) were analyzed using hematoxylin and eosin staining and immunofluorescence. PCL induced a lower inflammatory response than PLGA, as demonstrated by lower MHC-II and GFAP expression and greater ingrowth. Both polymers alleviated astrocytic activation and prevented enlargement of the defect. Tuj-1-, nestin-, and GFAP-positive cells were observed growing on both polymers at the peripheries of the sponge implants, demonstrating their permissiveness to neural ingrowth. These findings suggest that both polymers attenuate secondary death and scarring and that PCL might have advantages over PLGA.

A biodegradable vascularizing membrane: a feasibility study

Regenerative medicine and in vivo biosensor applications require the formation of mature vascular networks for long-term success. This study investigated whether biodegradable porous membranes could induce the formation of a vascularized fibrous capsule and, if so, the effect of degradation kinetics on neovascularization. Poly(l-lactic acid) (PLLA) and poly(dl-lactic-co-glycolic) acid (PLGA) membranes were created by a solvent casting/salt leaching method. Specifically, PLLA, PLGA 75:25 and PLGA 50:50 polymers were used to vary degradation kinetics. The membranes were designed to have an average 60mum pore diameter, as this pore size has been shown to be optimal for inducing blood vessel formation around nondegradable polymer materials. Membrane samples were imaged by scanning electron microscopy at several time points during in vitro degradation to assess any changes in pore structure. The in vivo performance of the membranes was assessed in Sprague-Dawley rats by measuring vascularization within the fibrous capsule that forms adjacent to implants. The vascular density within 100microm of the membranes was compared with that seen in normal tissue, and to that surrounding the commercially available vascularizing membrane TheraCyte. The hemoglobin content of tissue containing the membranes was measured by four-dimensional elastic light scattering as a novel method to assess tissue perfusion. Results from this study show that slow-degrading membranes induce greater amounts of neovascularization and a thinner fibrous capsule relative to fast degrading membranes. These results may be due both to an initially increased number of macrophages surrounding the slower degrading membranes and to the maintenance of their initial pore structure.

The in vivo assessment of a novel scaffold containing heparan sulfate for tissue engineering with human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are an attractive tissue engineering avenue for the repair and regeneration of bone. In this study we detail the in vivo performance of a novel electrospun polycaprolactone scaffold incorporating the glycosaminoglycan heparan sulfate (HS) as a carrier for hMSC. HS is a multifunctional regulator of many key growth factors expressed endogenously during bone wound repair, and we have found it to be a potent stimulator of proliferation in hMSCs. To assess the potential of the scaffolds to support hMSC function in vivo, hMSCs pre-committed to the osteogenic lineage (human osteoprogenitor cells) were seeded onto the scaffolds and implanted subcutaneously into the dorsum of nude rats. After 6 weeks the scaffolds were retrieved and examined by histological methods. Implanted human cells were identified using a human nuclei-specific antibody. The host response to the implants was characterized by ED1 and ED2 antibody staining for monocytes/macrophages and mature tissue macrophages, respectively. It was found that the survival of the implanted human cells was affected by the host response to the implant regardless of the presence of HS, highlighting the importance of controlling the host response to tissue engineering devices.

Biodegradable magnesium scaffolds: Part 1: appropriate inflammatory response

Current tissue engineering strategies focus on the replacement of pathologically altered tissues by the transplantation of cells in combination with supportive biocompatible scaffolds. Scaffolds for tissue engineering strategies in musculoskeletal research require an appropriate mechanical stability. In recent studies, considerable attention has thus been given to magnesium alloys as biodegradable implants. The aim of this study was to characterize the biocompatibility of magnesium scaffolds by the inflammatory host response. Open porous scaffolds made of the magnesium alloy AZ91D were implanted into the distal femur condyle of rabbits and were compared to autologous bone, which was transplanted into the contralateral condyle in a 3 and 6 months follow-up group. After 3 months, magnesium scaffolds were already largely degraded and most of the original magnesium alloy has disappeared. Concomitantly, a fibrous capsule enclosed the operation site. Histological analysis revealed that the magnesium scaffolds caused no significant harm to their neighboring tissues. This study shows that even fast degrading magnesium scaffolds show a good biocompatibility and react in vivo with an appropriate inflammatory host response. Magnesium alloy based implants are therefore a very promising approach in the development of mechanically suitable and open porous scaffolds for the replacement of subchondral bone in cartilage tissue engineering.

Enhanced bone regeneration with BMP-2 loaded functional nanoparticle-hydrogel complex

As an efficient sustained release system of BMP-2, a functional nanoparticle-hydrogel complex, composed of heparin-functionalized nanoparticles and fibrin gel, was developed and used as a bone graft. In vivo bone formation was evaluated by soft X-ray, histology, alkaline phosphatase (ALP) activity, immunostaining, and mineral content analysis, based on the rat calvarial critical size defect model. Significantly improved and effective bone regeneration was achieved with the recombinant BMP-2 (4 mug) loaded nanoparticle-fibrin gel complex, as compared to bare fibrin gel, the nanoparticle-fibrin gel complex without BMP-2, or even the BMP-2 loaded fibrin gel. These improvements included areas such as radiodensity, the bone-specific ALP activity, the osteocalcin immunoreactivity, and the ratios of calcium and phosphate contents with respect to normal bone in the regenerated bone area. The remodeling process of new bone developed with BMP-2 was significantly enhanced, and more mature and highly-mineralized bone was obtained by utilizing the functional nanoparticle-hydrogel complex. These results indicate that the nanoparticle-fibrin gel complex can be a promising candidate for a new bone defect replacement matrix, and an enhanced BMP-2 carrier.

Treatment of diabetic wounds with fetal murine mesenchymal stromal cells enhances wound closure

Diabetes impairs multiple aspects of the wound-healing response. Delayed wound healing continues to be a significant healthcare problem for which effective therapies are lacking. We have hypothesized that local delivery of mesenchymal stromal cells (MSC) at a wound might correct many of the wound-healing impairments seen in diabetic lesions. We treated excisional wounds of genetically diabetic (Db-/Db-) mice and heterozygous controls with either MSC, CD45(+) cells, or vehicle. At 7 days, treatment with MSC resulted in a decrease in the epithelial gap from 3.2 +/- 0.5 mm in vehicle-treated wounds to 1.3 +/- 0.4 mm in MSC-treated wounds and an increase in granulation tissue from 0.8 +/- 0.3 mm(2) to 2.4 +/- 0.6 mm(2), respectively (mean +/- SD, P < 0.04). MSC-treated wounds also displayed a higher density of CD31(+) vessels and exhibited increases in the production of mRNA for epidermal growth factor, transforming growth factor beta 1, vascular endothelial growth factor, and stromal-derived growth factor 1-alpha. MSC also demonstrated greater contractile ability than fibroblast controls in a collagen gel contraction assay. The effects of locally applied MSC are thus sufficient to improve healing in diabetic mice. Possible mechanisms of this effect include augmented local growth-factor production, improved neovascularization, enhanced cellular recruitment to wounds, and improved wound contraction.

Apatite Forming Ability of a Non-Woven Silica Fabric Containing Calcium

Non-woven silica fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. It was transferred to a syringe, which was connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica fibers containing calcium were spun under the electric field of 2 KV/cm. Their diameters were in the range from about 0.3 μm to 8 μm. It was heat-treated at 300 oC for 3 hours. After soaking in the SBF for 1 week, low crystalline apatite crystals were observed to occur on their surfaces. From the results, it can be concluded that the non-woven silica fabric containing calcium made by electro-spinning method and then heat-treated has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Preparation and in vitro and in vivo characterization of composite microcapsules for cell encapsulation

Cell encapsulation technology raises great hopes in medicine and biotechnology. Transplantation of encapsulated pancreatic islets represents a promising approach to the final cure of type 1 diabetes mellitus. Unfortunately, long-term graft survival and functional competence remain only partially fulfilled. Failure was often ascribed to the lack of biocompatibility generating inflammatory response, limited immunobarrier competence, hypoxia, and low beta-cell replication. In the present work, ketoprofen loaded biodegradable microspheres, embedded into alginate/poly-L-ornithine/alginate microcapsules, were prepared in order to release ketoprofen at early stages after implantation. Morphology, size, in vitro release behaviour, and in vivo biocompatibility were assessed. The effect of some preparation parameters was also evaluated. Polymeric microspheres were spherical and smooth, two populations of about 5 and 20 microm of mean diameter characterized the particle size distribution. A high burst effect was observed for all preparations during in vitro release studies. Ketoprofen, plasticizing the polymeric matrix, could be responsible of this release behaviour. Alginate/poly-L-ornithine/alginate microcapsules were not modified upon ketoprofen loaded microspheres encapsulation and an optimal dispersion was obtained. Composite system showed good biocompatibility when a high molecular weight polymer was employed. Therefore a potentially suitable composite system for cell encapsulation was obtained. This system may be successfully used to release NSAIDs and other active molecules capable to improve cell system functional performance and life-span.

A tissue engineering approach to meniscus regeneration in a sheep model

OBJECTIVE

Regeneration of the meniscal tissue occurs to a limited extent, and the loss of meniscal tissue leads to osteoarthritis. A new biomaterial consisting of hyaluronic acid and polycaprolactone was used as a meniscus substitute in sheep to evaluate the properties of the implant material with regard to size, biomechanical stability, tissue ingrowth, and integration.

METHODS

Eight sheep (right stifle joints) were treated with three total and three partial meniscus replacements while two meniscectomies served as empty controls. The animals were euthanized after 6 weeks. The specimens were assessed by gross inspection and histology, and compared with the nonoperated left joints.

RESULTS

The surgical technique was found to be feasible. The implants remained in position, did not tear, and showed excellent tissue ingrowth to the capsule. Tissue integration was also observed between the original meniscus and the implant. However, graft compression and extrusion occurred. The histological investigation revealed tissue formation, cellular infiltration and vascularization. Cartilage degeneration was more severe in the operated joints.

CONCLUSION

The present study shows promising results concerning the qualities of this biomaterial with regard to implantation technique, stability and tissue ingrowth.

Angiogenic and inflammatory response to biodegradable scaffolds in dorsal skinfold chambers of mice

For tissue engineering, scaffolds should be biocompatible and promote neovascularization. Because little is known on those specific properties, we herein studied in vivo the host angiogenic and inflammatory response after implantation of commonly used scaffold materials. Porous poly(L-lactide-co-glycolide) (PLGA) and collagen-chitosan-hydroxyapatite hydrogel scaffolds were implanted into dorsal skinfold chambers of balb/c mice. Additional animals received cortical bone as an isogeneic, biological implant, while chambers of animals without implants served as controls. Angiogenesis and neovascularization as well as leukocyte-endothelial cell interaction and microvascular permeability were analyzed over 14 day using intravital fluorescence microscopy. PLGA scaffolds showed a slight increase in leukocyte recruitment compared to controls. This was associated with an elevation of microvascular permeability, which was comparable to that observed in isogeneic bone tissue. Of interest, PLGA induced a marked angiogenic response, revealing a density of newly formed capillaries almost similar to that observed in bone implants. Histology showed infiltration of macrophages, probably indicating resorption of the biomaterial. In contrast, hydrogel scaffolds induced a severe inflammation, as indicated by an approximately 15-fold increase of leukocyte-endothelial cell interaction and a marked elevation of microvascular permeability. This was associated by induction of apoptotic cell death within the surrounding tissue and a complete lack of ingrowth of newly formed microvessels. Histology confirmed adequate engraftment of PLGA and isogeneic bone but not hydrogel within the host tissue. PLGA scaffolds show a better biocompatibility than hydrogel scaffolds and promote vascular ingrowth, guaranteeing adequate engraftment within the host tissue.

Small molecule inducers of angiogenesis for tissue engineering

Engineering of implantable tissues requires rapid induction of angiogenesis to meet the significant oxygen and nutrient demands of cells during tissue repair. To this end, our laboratories have utilized medicinal chemistry to synthesize non-peptide-based inducers of angiogenesis to aid tissue engineering. In this study, we describe the evaluation of SC-3-149, a small molecule compound with proliferative effects on vascular endothelial cells. Specifically, exogenous exposure of SC-3-149 induced an 18-fold increase in proliferation of human microvascular endothelial cells in vitro at low micromolar potency by day 14 in culture. Moreover, SC-3-149 significantly increased the formation of endothelial cord and tubelike structures in vitro, and improved endothelial scratch wound healing within 24 h. SC-3-149 also significantly inhibited vascular endothelial cell death owing to serum deprivation and high acidity (pH 6). Concurrent incubation of SC-3-149 with vascular endothelial growth factor increased cell survivability under serum-deprived conditions by an additional 7%. In addition, in vivo injection of SC-3-149 into the rat mesentery produced qualitative increases in microvessel length density. Taken together, our studies suggest that SC-3-149 and its analogs may serve as promising new angiogenic agents for targeted drug delivery and therapeutic angiogenesis in tissue engineering.

Chemical and biological properties of supramolecular polymer systems based on oligocaprolactones

We show that materials with a diverse range of mechanical and biological properties can be obtained using a modular approach by simply mixing different ratios of oligocaprolactones that are either end-functionalized or chain-extended with quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties. The use of two UPy-synthons allows for easy synthesis of UPy-modified polymers resulting in high yields. Comparison of end-functionalized UPy-polymers with chain-extended UPy-polymers shows that these polymers behave distinctively different regarding their material and biological properties. The end-modified UPy-polymer is rather stiff and brittle due to its high crystallinity. Disks made of this material fractures after subcutaneous implantation. The material shows a low inflammatory response which is accompanied by the formation of a fibrous capsule, reflecting the inertness of the material. The chain-extended UPy-material on the contrary is practically free of crystalline domains and shows clear flexible properties. This material deforms after in-vivo implantation, accompanied with cellular infiltration. By mixing both polymers, materials with intermediate properties concerning their mechanical and biological behaviour can be obtained. Surprisingly, a 20:80 mixture of both polymers with the chain-extended UPy-polymer in excess shows flexible properties without visible deformation upon implantation for 42 days. This mixture, a blend formed by intimate mixing through UPy-UPy interaction, also shows a mild tissue response accompanied with the formation of a thin capsule. The material does not become more crystalline upon implantation. Hence, this mixture might be an ideal scaffold material for soft tissue engineering due to its flexibility and diminished fibrous tissue formation, and illustrates the strength of the modular approach.

Bioactive Non-Woven Silica Fabric Made Through Electro-Spinning Method

Non-woven silica fabric was made by electro-spinning method for the application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of water, hydrochloric acid and ethanol. It was transferred to a syringe (spinneret), which was connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica fibers were spun under the electric field of 2 KV/cm. Their diameters were in the range from about 100 nm to 5 µm. After soaking in the SBF for 4 week, low crystalline apatite crystals were observed to occur partly on their surfaces. From the results, it can be concluded that the non-woven silica fabric made by electro-spinning method has the apatite forming ability in the SBF and it means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

In vitro response of MC3T3-E1 pre-osteoblasts within three-dimensional apatite-coated PLGA scaffolds

Biomimetic apatites have been reported to promote osteogenic activities in numerous in vivo and in vitro models, but the precise mechanism by which the apatite microenvironment promotes such activities is not well understood. Such mechanistic studies require reproducible model systems that are relevant to tissue engineering practices. Although two-dimensional (2D) apatite-coated polystyrene culture dishes provide practicality and reproducibility, they do not simulate the effects of the three-dimensional (3D) microenvironment and degrading polymeric substrates. A simple 3D model system to address these relevant effects, and its utilization in the investigation of apatite-promoted osteoblastic differentiation in vitro is reported in this paper. Apatite coating was achieved by sequentially immersing poly(lactide-co-glycolide) (PLGA) scaffolds into different simulated body fluids (SBF). SEM, EDX, FTIR, TEM electron diffraction confirmed the apatite coating to comprise of calcium-deficient carbonated hydroxyapatite crystals. While both apatite-coated and non-coated PLGA scaffolds supported MC3T3-E1 attachment, spreading, and proliferation, significant differences in osteoblastic differentiation were observed. Relative to non-coated controls, quantitative real-time PCR revealed significant apatite-associated suppression of alkaline phosphatase (ALP), early upregulation of osteopontin (OPN) at 3 days, and upregulation of osteocalcin (OCN) and bone sialoprotein (BSP) at 4 weeks. In summary, apatite-promoted osteoblastic differentiation can be observed in a 3D model system that is relevant to tissue engineering.

The effect of microsphere degradation rate on the efficacy of polymeric microspheres as bulking agents: An 18-month follow-up study

The injection of bulking substances has been proposed as a new therapy to treat urinary incontinence and vesicoureteral reflux. Our previous study demonstrated that poly(lactic-co-glycolic acid) (PLGA) microspheres have the potential to serve as a bulking agent for urological injection therapies. Hybrid tissues exhibiting a bulking effect were formed in vivo by PLGA microsphere injection, but long-term volume stability was not proven. In this study, we hypothesized that the biodegradation rate of the bulking substance (polymer microspheres) would affect the duration of volume conservation of the induced hybrid tissue. To test this hypothesis, rapidly degrading 75:25 PLGA microspheres and slowly degrading poly(L-lactic acid) (PLLA) microspheres were used as injectable bulking agents for the injection therapy. In vitro degradation tests showed that the mass losses of PLLA and PLGA were 16 and 96% of the initial masses, respectively, at 30 weeks. PLLA and PLGA microspheres were injected into the subcutaneous dorsum of mice. Both types of microspheres were easily injectable through 24-gauge needles. Histological examinations at various time points indicated that host cells from the surrounding tissues migrated to the spaces between both types of injected microspheres and formed new hybrid tissue structures. Lymphocyte migration was noted around the implanted PLGA and PLLA microspheres, but the inflammatory reaction diminished with time. Importantly, the volume of the PLLA hybrid tissues slowly decreased to 52% of the initial volume at 12 months and maintained that volume until 18 months, whereas the volume of the PLGA hybrid tissues rapidly decreased to 22% at 6 months, and the PLGA hybrid tissues disappeared at 11 months. These results show that the biodegradation rate of the bulking substance may be useful for controlling the duration of volume conservation of the induced hybrid tissue.

Synthesis and evaluation of poly(diol citrate) biodegradable elastomers

Herein, we report the synthesis and evaluation of a novel family of biodegradable and elastomeric polyesters, poly(diol citrates). Poly(diol citrates) were synthesized by reacting citric acid with various diols to form a covalent cross-linked network via a polycondensation reaction without using exogenous catalysts. The tensile strength of poly(diol citrates) were as high as 11.15+/-2.62 MPa and Young's modulus ranged from 1.60+/-0.05 to 13.98+/-3.05 MPa under the synthesis conditions that were investigated. Elongation was as high as 502+/-16%. No permanent deformation was found during mechanical tests. The equilibrium water-in-air contact angles of measured poly(diol citrates) films ranged from 15 degrees to 53 degrees . The mechanical properties, degradation and surface characteristics of poly(diol citrates) could be controlled by choosing different diols as well as by controlling the cross-link density of the polyester network. Various types of poly(diol citrate) scaffolds were fabricated to demonstrate their processing potential. These scaffolds were soft and could recover from deformation. In vitro and in vivo evaluation using cell culture and subcutaneous implantation, respectively, confirmed cell and tissue compatibility. The introduction of poly(diol citrates) will expand the repertoire of currently available biodegradable polymeric elastomers and should help meet the requirements of tissue engineering applications.

Cell sheet engineering: recreating tissues without biodegradable scaffolds

While tissue engineering has long been thought to possess enormous potential, conventional applications using biodegradable scaffolds have limited the field's progress, demonstrating a need for new methods. We have previously developed cell sheet engineering using temperature-responsive culture dishes in order to avoid traditional tissue engineering approaches, and their related shortcomings. Using temperature-responsive dishes, cultured cells can be harvested as intact sheets by simple temperature changes, thereby avoiding the use of proteolytic enzymes. Cell sheet engineering therefore allows for tissue regeneration by either direct transplantation of cell sheets to host tissues or the creation of three-dimensional structures via the layering of individual cell sheets. By avoiding the use of any additional materials such as carrier substrates or scaffolds, the complications associated with traditional tissue engineering approaches such as host inflammatory responses to implanted polymer materials, can be avoided. Cell sheet engineering thus presents several significant advantages and can overcome many of the problems that have previously restricted tissue engineering with biodegradable scaffolds.

Ketoprofen controlled release from composite microcapsules for cell encapsulation: Effect on post-transplant acute inflammation

Cell encapsulation technology raises hopes in medicine and biotechnology. Encapsulated pancreatic islets is a promising approach for the final solution of Type 1 diabetes. Unfortunately, evidence of long-term encapsulated islet graft survival and functional competence lies behind expectancy. Failure was often ascribed to the lack of biocompatibility generating inflammatory response, or limited immunobarrier competence or hypoxia or finally, low beta-cell replication. In order to prevent severe inflammation at early stages after implantation, composite microcapsules were designed. Biodegradable microspheres containing ketoprofen were enveloped into the well established alginate/poly-L-ornithine/alginate capsules. Polyester microspheres were prepared, by solvent evaporation, and characterized for encapsulation efficiency, particle size and in vitro release. Biocompatibility and efficacy to prevent the inflammatory response were studied in vivo. Good encapsulation efficiency and the desired particle size were achieved. In vitro release studies evidenced a high burst effect probably due to a plasticizing effect of both water and ketoprofen. The composite systems showed good biocompatibility and capacity to completely avoid the inflammatory response and the pericapsular cell overgrowth. In conclusion, the inflammatory response in the immediate post-transplant period can be circumvented using multicompartment microcapsules releasing non-steroidal anti inflammatory drugs.

Matrix metalloproteinase 9 facilitates collagen remodeling and angiogenesis for vascular constructs

Degradation of the extracellular matrix, facilitated by matrix metalloproteinases (MMPs), can lead to mechanical failure of vascular constructs, suggesting that MMP inhibition could improve survival of constructs. Therefore, we investigated the role of MMP-9 in collagen remodeling in vitro, focusing on the three major steps of production, degradation, and organization. Because an adequate blood supply is essential for survival of tissue-engineered constructs, we also evaluated the influence of MMP-9 deficiency on angiogenesis in vivo by implantation of thin biodegradable polymer scaffolds. Using aortic smooth muscle cells (SMCs) from wild-type and genetically deficient (9KO) mice, we examined the role of MMP-9 in collagen mRNA expression and protein accumulation, both with and without ascorbic acid treatment. We measured collagen assembly in a fibrillogenesis assay. We investigated in vivo angiogenesis and cell invasion, using fluorescence microangiography and histology. MMP-9 deficiency did not affect collagen mRNA production or polymer scaffold degradation, but collagen accumulation was greater in cultures of 9KO SMCs than in wild-type SMCs. Both MMP-9 deficiency and chemical inhibition impaired collagen degradation. Ascorbic acid treatment enhanced collagen production by 9KO SMCs compared with wild-type SMCs at 3 days, but by 7 days this effect was reversed. MMP-9 improved fibrillogenesis of collagen, significantly more on ascorbic acid treatment. MMP-9 deficiency dramatically decreased inflammatory cell invasion, but also capillary formation within biodegradable polymer scaffolds in vivo. Our data suggest that MMP inhibition, by impairing collagen organization and angiogenesis, might have detrimental effects on the survival of vascular constructs.

Rapid prototyping in tissue engineering: challenges and potential

Tissue engineering aims to produce patient-specific biological substitutes in an attempt to circumvent the limitations of existing clinical treatments for damaged tissue or organs. The main regenerative tissue engineering approach involves transplantation of cells onto scaffolds. The scaffold attempts to mimic the function of the natural extracellular matrix, providing a temporary template for the growth of target tissues. Scaffolds should have suitable architecture and strength to serve their intended function. This paper presents a comprehensive review of the fabrication methods, including conventional, mainly manual, techniques and advanced processing methods such as rapid prototyping (RP) techniques. The potential and challenges of scaffold-based technology are discussed from the perspective of RP technology.

Polímeros bioreabsorvíveis na engenharia de tecidos

A Engenharia de Tecidos consiste em um conjunto de conhecimentos e técnicas para a reconstrução de novos órgãos e tecidos. Baseada em conhecimentos das áreas de ciência e engenharia de materiais, biológica e médica, a técnica envolve a expansão in vitro de células viáveis do paciente doador sobre suportes de polímeros bioreabsorvíveis. O suporte degrada enquanto um novo órgão ou tecido é formado. Os poli(alfa-hidróxi ácidos) representam a principal classe de polímeros sintéticos bioreabsorvíveis e biodegradáveis utilizados na engenharia de tecidos. No desenvolvimento e na seleção desses materiais, o tempo de degradação é fundamental para o sucesso do implante. Os estudos e os desafios atuais são normalmente direcionados ao entendimento das relações entre composição química, cristalinidade, morfologia do suporte, e o processamento desses materiais. Este artigo faz uma revisão dos trabalhos recentes sobre a utilização dos polímeros sintéticos bioreabsorvíveis como suportes na engenharia de tecidos.