Tissue engineering in cardiovascular surgery: MTT, a rapid and reliable quantitative method to assess the optimal human cell seeding on polymeric meshes

Anatomical 3D Fiber-Deposited Scaffolds for Tissue Engineering: Designing a Neotrachea

The advantage of using anatomically shaped scaffolds as compared to modeled designs was investigated and assessed in terms of cartilage formation in an artificial tracheal construct. Scaffolds were rapid prototyped with a technique named three-dimensional fiber deposition (3DF). Anatomical scaffolds were fabricated from a patient-derived computerized tomography dataset, and compared to cylindrical and toroidal tubular scaffolds. Lewis rat tracheal chondrocytes were seeded on 3DF scaffolds and cultured for 21 days. The 3-(4,5-dimethylthiazol-2yl)-2,5-dyphenyltetrazolium bromide (MTT) and sulfated glycosaminoglycan (GAG) assays were performed to measure the relative number of cells and the extracellular matrix (ECM) formed. After 3 weeks of culture, the anatomical scaffolds revealed a significant increase in ECM synthesis and a higher degree of differentiation as shown by the GAG/MTT ratio and by scanning electron microscopy analysis. Interestingly, a lower scaffold's pore volume and porosity resulted in more tissue formation and a better cell differentiation, as evidenced by GAG and GAG/MTT values. Scaffolds were compliant and did not show any signs of luminal obstruction in vitro. These results may promote anatomical scaffolds as functional matrices for tissue regeneration not only to help regain the original shape, but also for their improved capacity to support larger tissue formation.

Tissue-engineered bone formation using human bone marrow stromal cells and novel beta-tricalcium phosphate

In this study we investigated not only the cellular proliferation and osteogenic differentiation of human bone marrow stromal cells (hBMSCs) on the novel beta-tricalcium phosphate (beta-TCP) scaffolds in vitro but also bone formation by ectopic implantation in athymic mice in vivo. The interconnected porous beta-TCP scaffolds with pores of 300-500 microm in size were prepared by the polymeric sponge method. beta-TCP scaffolds with the dimension of 3 mm x 3 mm x 3 mm were combined with hBMSCs, and incubated with (+) or without (-) osteogenic medium in vitro. Cell proliferation and osteogenic differentiation on the scaffolds were evaluated by scanning electron microscopy (SEM) observation, MTT assay, alkaline phosphatase (ALP) activity and osteocalcin (OCN) content measurement. SEM observation showed that hBMSCs attached well on the scaffolds and proliferated rapidly. No significant difference in the MTT assay could be detected between the two groups, but the ALP activity and OCN content of scaffolds (+) were much higher than those of the scaffolds (-) (p < 0.05). These results indicated that the novel porous beta-TCP scaffolds can support the proliferation and subsequent osteogenic differentiation of hBMSCs in vitro. After being cultured in vitro for 14 days, the scaffolds (+) and (-) were implanted into subcutaneous sites of athymic mice. In beta-TCP scaffolds (+), woven bone formed after 4 weeks of implantation and osteogenesis progressed with time. Furthermore, tissue-engineered bone could be found at 8 weeks, and remodeled lamellar bone was also observed at 12 weeks. However, no bone formation could be found in beta-TCP scaffolds (-) at each time point checked. The above findings illustrate that the novel porous beta-TCP scaffolds developed in this work have prominent osteoconductive activity and the potential for applications in bone tissue engineering.

Mechanical Loading-Dependence of mRNA Expressions of Extracellular Matrices of Chondrocytes Inoculated into Elastomeric Microporous Poly(L-lactide-co-ε-caprolactone) Scaffold

The temporal response of young rabbit chondrocyte metabolism (including biosynthesis of extracellular matrix macromolecules such as collagen and aggrecan, both of which are essential components of normal cartilage tissue, and their messenger ribonucleic acid (mRNA) expression) in microporous elastomeric scaffolds made of poly(L-lactide-co-epsilon-caprolactone) subjected to different compressive regimes (loading frequency, loading duration per cycle, loading period, and continuous or intermittent compression) were studied over a 6-day culture period at 10% of compressive strain. A continuous dynamic compression improved the production of sulfated glycosaminoglycan (S-GAG), most of which was released into the culture medium upon loading. High mRNA expression of type II collagen was exhibited at a frequency of 0.1 Hz. Little frequency dependency was observed for aggrecan. An intermittent loading (24-h cycle of loading and unloading) or short loading and unloading duration per cycle-compression regime maintained high levels of mRNA expression. This strongly suggests that well-controlled mechanical conditioning regimes may control the gene expression of key metabolic substances relevant to functional cartilage tissue while the degree of release of these substances into the culture medium is minimized.

Should human chondrocytes fly? The impact of electromagnetic irradiation on chondrocyte viability and implications for their use in tissue engineering

A significant logistic factor as to the successful clinical application of the autologous tissue engineering concept is efficient transportation: the donor cells need to be delivered to tissue processing facilities which in most cases requires air transportation. This study was designed to evaluate how human chondrocytes react to X-ray exposure. Primary cell cultures were established, cultured, incubated and exposed to different doses and time periods of radiation. Subsequently, quantitative cell proliferation assays were done and qualitative evaluation of cellular protein production were performed. Our results show that after irradiation of chondrocytes with different doses, no significant differences in terms of cellular viability occurred compared with the control group. These results were obtained when chondrocytes were exposed to luggage transillumination doses as well as exposure to clinically used radiation doses. Any damage affecting cell growth or quality was not observed in our study. However, information about damage of cellular DNA remains incomplete.

Mesenchymal Stem Cell Sheets Revitalize Nonviable Dense Grafts: Implications for Repair of Large-Bone and Tendon Defects

BACKGROUND

Large musculoskeletal defects are commonly reconstructed with allogeneic grafts. As cryopreserved allogeneic grafts lack viable cells, this often results in poorer clinical outcome. Current technology can not incorporate large number of cells to the dense grafts. This study aimed to investigate the feasibility of fabricating sheets of mesenchymal stem cells (MSCs) to revitalize cryopreserved grafts.

METHODS

Human MSCs were isolated, characterized, and cultured to form a cell sheet in the presence of ascorbic acid. Once a sheet of MSCs was obtained, it was assembled onto the demineralized bone grafts or frozen tendon grafts by a wrapping technique. Then the assembled structure was cultured for 3 weeks. The macro morphology, histology, and immunohistochemistry of the grafts were evaluated.

RESULTS

It was found that MSCs were able to form coherent cellular sheets within 3 weeks. When assembled with demineralized bone matrix, MSC sheets were similar to in situ periosteum and were able to differentiate into the osteochondral lineage. When assembled with frozen tendon graft, MSCs sheets were well-incorporated within the tissue sheath (peritenon) around the tendon, and adopted the characteristic spindle-shaped morphology of tenocyte-like cells.

CONCLUSIONS

The results therefore demonstrated that MSCs sheets are easily fabricated and can maintain their differentiation potential within particular scaffolds, which would suggest a novel and convenient strategy for revitalizing large tissue grafts to improve clinical outcome.

Behavior of adult human mesenchymal stem cells entrapped in alginate-GRGDY beads

This study demonstrates that adult human mesenchymal cells (MSC) can be encapsulated in alginate beads with a substantially retained viability (>80%) and that a Gly-Arg-Gly-Asp-Tyr (GRGDY) derivative encourages attachment and elongation to form a dense network of cells that is required for a tissue substitute. Because the availability of autologous human material is severely limited, we used and examined the beads in this study as a proxy for larger constructs. These bead constructs were assessed using phase contrast microscopy and standard histological preparations. In addition, we used a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay to examine cell proliferation by dissociating the cell/alginate constructs using trisodium citrate and trypsin/EDTA. MSCs did not proliferate within the alginate-GRGDY matrix during the 2 weeks examined. These results were further substantiated by concurrent cell density measurements using a hemocytometer. In addition, the glucose consumption rate was measured and compared to that of MSCs grown in two-dimensional culture vessels, indicating steady consumption albeit at a lower level in the entrapped MSCs.

Application of Colorimetric Assays to Assess Viability, Growth and Metabolism of Hydrogel-Encapsulated Cells

The applicability of the colorimetric 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays to measure cell growth and viability in hydrogel encapsulation systems was investigated using HepG2 liver cells encapsulated in alginate matrices. The MTT assay was effective in measuring viable cell density in alginate-encapsulated cell systems, demonstrating less variance and higher throughput capability than hemocytometry. The LDH assay was effective in measuring dead cell density in monolayer cultures and in alginate-encapsulated cells simply by measuring the LDH concentration secreted into the medium. Further validation of these assays was shown in two additional cell lines (rat muscle and mouse embryonic fibroblasts). The MTT and LDH assays are particularly significant in the rapid evaluation of in vitro cell encapsulation device design.

Crosslinking of decellularized porcine heart valve matrix by procyanidins

Heart valve diseases have a significant high mortality, and the valve replacement using glutaraldehyde crosslinked porcine heart valves is one of the main curing techniques. But its application is limited due to poor durability, calcification of the valves and immunogenic reactions. The aim of this study was to evaluate the crosslinking effect of procyanidins on porcine heart valve matrix. After crosslinking of the decellularized porcine aortic heart valves by procyanidins, the tensile strength, the in vitro enzymatic degradation resistance, procyanidins release from the crosslinked materials and the cytotoxicity of procyanidins to heart valvular interstitial cells were examined. The results showed that the tensile strength of procyanidins crosslinked valve matrix was higher than that of glutaraldehyde crosslinked valve matrix. Valve matrix crosslinked by 10 mg/ml procyanidins could be stored in D-Hanks solution for at least 45 days without any decline in ultimate tensile strength and maintained the elasticity as the fresh valves. Furthermore, procyanidins was found to release when the crosslinked tissue stored in D-Hanks solution. The release rate was high during the first 4 days and then dramatically decreased thereafter. During releasing phase, the concentration of procyanidins was no toxicity to heart valve interstitial cells. In vitro enzymatic degradation revealed that crosslinked matrix could resist the enzymatic hydrolysis, and the resistant capacity was approximately the same as glutaraldehyde crosslinked valve matrix. This study shows that procyanidins can crosslink porcine heart valves effectively without toxicity. Our results suggested that this method might be a useful approach for preparation of bioprosthetic heart valve.

Serum deprivation improves seeding and repopulation of acellular matrices with valvular interstitial cells

Cell-extracted valvular tissues (acellular scaffolds, or aScaffolds) offer unique advantages over synthetic polymers for cardiac valve engineering applications in that they retain extracellular matrix molecules to support cellular ingrowth. The extracellular matrix is important in directing many cellular pathways, such as adhesion, proliferation, migration, differentiation, and survival. However, repopulating this type of scaffold often requires high seeding densities or recurrent cell delivery. The optimization of valvular interstitial cell (VIC) seeding onto aScaffolds is reported herein. VICs (the most prevalent cell type in valve leaflets) have maximal growth in 15-20% serum concentrations on tissue-culture polystyrene. Interestingly, after VIC seeding onto aScaffolds, a reduction of serum content, from 15% serum to 5% or less, was found to increase significantly the number of adherent cells, as well as induce transfer of VICs from a tissue-culture polystyrene surface to the aScaffold. aScaffolds seeded and cultured with periods of reduced serum levels were shown to support and enhance VIC viability and attachment, as well as accelerate VIC migration into the aScaffold, leading to a uniformly repopulated valve leaflet construct after 4 weeks of static culture.

Biological efficacy of silk fibroin nanofiber membranes for guided bone regeneration

The favorable biological properties of silk fibroin (SF) nanofiber membrane make it a good candidate for clinical applications as a device in bone and periodontal regenerative therapy. The purpose of this study is to evaluate the biocompatibility of the SF nanofiber membrane, and to examine its effect on bone regeneration in a rabbit calvarial model. To examine the biocompatibility of the electrospun SF membrane, we investigated cell proliferation, morphology, and differentiation. The bone regenerative efficacy of the membrane was evaluated in the calvarial defect of rabbits. The cell numbers and osteocalcin production labels were significantly increased in accordance with culture period. Cells had a stellate shape and broad cytoplasmic extensions on the membrane. The cells showed activity of ALPase that was comparable to culture dishes, and were calcified similarly to culture dishes. In in vivo tests, a complete bony union across the defects was observed after 8 weeks. At 12 weeks, the defect had completely healed with new bone. In conclusion, the SF nanofiber membrane was shown to possess good biocompatibility with enhanced bone regeneration and no evidence of any inflammatory reaction. These results strongly suggest that the SF membrane should be useful as a tool for guided bone regeneration.

Fibrin as a cell carrier in cardiovascular tissue engineering applications

In cardiovascular tissue engineering approaches, efficient seeding methods are essential. To achieve this and to save time, cells can be encapsulated in gels. Combining the advantages of a gel as a cell carrier with the advantages of a fiber-based scaffold, providing structural integrity to the developing tissue, might offer several advantages. In this study, seeding by using fibrin as a cell carrier is compared to the conventional static seeding method with regard to tissue development. Seeding with fibrin resulted in less loss of soluble collagen into the medium and a more mature extracellular matrix in a shorter period of time. The use of fibrin degradation inhibitors was shown to inhibit extracellular matrix formation, although it did not hamper cell proliferation. The use of fibrin as a cell carrier to seed cells into a fiber-based scaffold may represent a promising, timesaving approach in cardiovascular tissue engineering applications.

Comparison of three myofibroblast cell sources for the tissue engineering of cardiac valves

The objective of this study was to evaluate the capacity of three clinically useful tissue sources: tricuspid valve leaflet (TVL), carotid artery (CA), and jugular vein (JV), to generate myofibroblasts for potential use in a tissue-engineered cardiac valve replacement. Tissue biopsies of clinically appropriate sizes obtained from juvenile sheep were used for this work. Cells obtained from all three tissue sources exhibited a myofibroblast phenotype in vitro, as demonstrated by their immunoreactivity with antibodies directed against vimentin, alpha-smooth muscle actin, fibronectin, and chondroitin sulfate. Protein synthesis characteristics were defined for the key extracellular matrix components: collagen, glycosaminoglycans, and elastin. Among the three sources, JV generated the highest numbers of cells, and JV cells produced the largest amount of collagen per cell. These data suggest that venous tissue, with its relative ease of accessibility, may generate myofibroblasts potentially useful for the interstitial cellular component of a tissue-engineered cardiac valve.

Protein electrostatic self-assembly on poly(DL-lactide) scaffold to promote osteoblast growth

The development of protein coating on 3D biodegradable scaffold based on electrostatic self-assembly (ESA) to promote osteoblast growth is reported. Poly (ethylenimine) (PEI) was employed to obtain a stable positively charged surface on poly(DL-lactide) (PDL-LA) substrate. An extracellular-matrix (ECM)-like biomacromolecule, gelatin, was chosen as the polyelectrolyte to deposit on the activated PDL-LA substrate via ESA technique. Osteoblast (MC3T3) was then cultured on unmodified and gelatin-modified PDL-LA scaffolds. Osteoblast testing regarding total intracellular protein content, total DNA content, cell activity, and cell morphology on the ECM-like multilayer-modified PDL-LA scaffold showed that osteoblast growth was promoted. It will be easy to replace the gelatin with osteoinductive proteins or other polyelectrolytes to promote specific osteoblast functions. In comparison with conventional coating methods, polyelectrolyte multilayers are easy and stable to prepare. They may be a good choice for the surface modification of complex biomedical devices, especially for the 3D tissue-engineering scaffold. These very flexible systems allow broad medical applications for drug delivery and tissue engineering.

The Challenge to Measure Cell Proliferation in Two and Three Dimensions

Various assays, using different strategies, are available for assessing cultured cell proliferation. These include measurement of metabolic activity (tetrazolium salts and alamarBlue), DNA quantification using fluorophores (Hoechst 33258 and PicoGreen), uptake of radioactively-labeled DNA precursors such as [3H]thymidine, and physical counting (hemocytometer). These assays are well established in characterizing cell proliferation in two-dimensional (2D), monolayer cultures of low cell densities. However, increasing interest in 3D cultures has prompted the need to evaluate the effectiveness of using these assays in high cell density or 3D cultures. We show here that typical cell proliferation assays do not necessarily correlate linearly with increasing cell densities or between 2D and 3D cultures, and are either not suitable or only rough approximations in quantifying actual cell numbers in a culture. Prudent choice of techniques and careful interpretation of data are therefore recommended when measuring cell proliferation in high cell density and 3D cultures.

Assembly of bone marrow stromal cell sheets with knitted poly (L-lactide) scaffold for engineering ligament analogs

The current cell seeding technique has several disadvantages, such as low efficiency of cell attachment to scaffolds and the limited strength of cell-gel composite adhesion to scaffold. These problems warrant further study to improve the assembly of cell to scaffold. Therefore this study aims to fabricate a bone marrow stromal cells (bMSCs) sheet and assemble it on a knitted poly (L-lactide) (PLLA) scaffold for engineering ligament analogs. bMSCs were cultured to form a cell sheet in the presence of ascorbic acid. Once a sheet of bMSCs was obtained, it was assembled onto the knitted scaffold by a wrapping technique. Then the assembled structure was held in place in a spinner flask for 4 weeks. The macromorphology, histology, and biomechanics of the grafts were evaluated. The composite of cell sheet/PLLA scaffold constructs had transformed into tissuelike ligament analogs. Immunohistochemical analysis showed that the components of the analogs were similar to that of ligament tissues, consisting primarily of collagen type I and small amount of collagen type III and tenascin. The failure force of the cell/scaffold assembly under tension (46.68+/-2.29 N) was higher than that of the scaffold group (43.58+/-2.41 N; p<0.05), but tensile stiffness of the cell/scaffold group (20.6+/-1.417 N/mm) was significantly lower than that of the scaffold group (27.6+/-1.449 N/mm; p<0.05). These data showed that the incorporation of bMSCs sheet onto the PLLA scaffold could make the analog stronger and more stretchable. Therefore the approach of assembling bMSCs sheet onto knitted PLLA scaffold is promising for producing tissuelike and functional ligament analogs under dynamic fluid situation for the purpose of anterior cruciate ligament (ACL) reconstruction.

Poly(D,L-lactic acid)-block-(ligand-tethered poly(ethylene glycol)) copolymers as surface additives for promoting chondrocyte attachment and growth

The poly(D,L-lactic acid)-block-(ligand-tethered poly(ethylene glycol)) copolymer was explored to engineer poly(D,L-lactic acid) (PLA) material to promote chondrocyte attachment and growth. The poly(D,L-lactic acid)-block-poly(ethylene glycol) copolymer (PLE) was synthesized by a coupling reaction between PLA and poly(ethylene glycol) (PEG) (M(n) 1000, 2000, and 4000 respectively), with the use of 4,4'-methylenediphenyl diisocyanate (MDI). Then the PLE was activated by methyl sulfonyl chloride and the amino acids or arginine-glycine-aspartic acid tripeptide (RGD) was attached, which was verified by the ninhydrin-UV method. The modified PLA films were simply prepared by blending PLA with PLE derivatives. ATR-FTIR, XPS, contact angle, and AFM results clearly showed that the PEG chain stably enriched on the surface of PLE-modified PLA films. The chondrocyte cytocompatibility test showed the modified PLA films could significantly improve chondrocyte attachment and proliferation.

Surface tailoring of poly(dl-lactic acid) by ligand-tethered amphiphilic polymer for promoting chondrocyte attachment and growth

The ligand-tethered poly(ethylene oxide-propylene oxide-ethylene oxide) (PEO-PPO-PEO) triblock copolymer was explored to engineer poly(DL-lactic acid) (PDL-LA) material to promote cell attachment and growth. The PEO-PPO-PEO was activated by methyl sulfonyl chloride and the amino acid, and peptide were attached. By blending the PDL-LA with the ligand-tethered PEO-PPO-PEO derivatives, the surface of modified PDL-LA film was investigated by ATR-FTIR, XPS and contact angle. The chondrocytes test on different PDL-LA films indicated that the PEO-PPO-PEO amino acid and RGD derivatives modified PDL-LA films could promote chondrocyte attachment and growth. This simple surface treatment method may have potentials for tissue engineering and other biomedical applications.

Osteogenic Differentiation of Human Bone Marrow Stromal Cells on Partially Demineralized Bone Scaffoldsin Vitro

Tissue engineering has been used to enhance the utility of biomaterials for clinical bone repair by the incorporation of an osteogenic cell source into a scaffold followed by the in vitro promotion of osteogenic differentiation before host implantation. In this study, three-dimensional, partially demineralized bone scaffolds were investigated for their ability to support osteogenic differentiation of human bone marrow stromal cells (BMSCs) in vitro. Dynamic cell seeding resulted in homogeneous cell attachment and infiltration within the matrix and produced significantly higher seeding efficiencies when compared with a conventional static seeding method. Dynamically seeded scaffolds were cultured for 7 and 14 days in the presence of dexamethasone and evaluated on biochemical, molecular, and morphological levels for osteogenic differentiation. Significant elevation in alkaline phosphatase activity was observed versus controls over the 14-day culture, with a transient peak indicative of early mineralization on day 7. On the basis of RT-PCR, dexamethasone-treated samples showed elevations in alkaline phosphatase and osteocalcin expression levels at 7 and 14 days over nontreated controls, while bone sialoprotein was produced only in the presence of dexamethasone at 14 days. Scanning electron microscopy evaluation of dexamethasone-treated samples at 14 days revealed primarily cuboidal cells indicative of mature osteoblasts, in contrast to nontreated controls displaying a majority of cells with a fibroblastic cell morphology. These results demonstrate that partially demineralized bone can be successfully used with human BMSCs to support osteogenic differentiation in vitro. This osseous biomaterial may offer new potential benefits as a tool for clinical bone replacement.

Enhanced photodynamic activity of meso-tetra(4-hydroxyphenyl)porphyrin by incorporation into sub-200 nm nanoparticles

A photosensitizer, meso-tetra(hydroxyphenyl)porphyrin (p-THPP) was incorporated into sterile submicronic nanoparticles of poly(D,L-lactide-co-glycolide) (50:50 and 75:25 PLGA) and poly(D,L-lactide) (PLA). With all polymers used, sub-130 nm p-THPP-loaded nanoparticles with similar drug loadings and entrapment efficiencies were produced using the emulsification-diffusion technique. The photodynamic activity (photocytotoxicity) of these nanoparticles was evaluated on EMT-6 mammary tumour cells in comparison with the free drug. The influence of drug concentration (3-10 microg/ml), incubation time (5-60 min) and light dose (6-9 J/cm(2)) on p-THPP photocytotoxic efficiency was investigated. With all p-THPP formulations tested, cell viability decreased with increasing values of these parameters. The beneficial effect of nanoencapsulation compared to free drug was highlighted at drug concentrations up to 6 microg/ml and short incubation times (15-30 min). The most important photocytotoxicity was observed with 50:50 PLGA nanoparticles allowing low drug doses and short drug administration-irradiation intervals for local photodynamic therapy.

Surface engineering of poly(DL-lactide) via electrostatic self-assembly of extracellular matrix-like molecules

We report the development of new biomacromolecule coatings on biodegradable biomaterials based on electrostatic assembly of extracellular matrix-like molecules. Poly(ethylene imine) (PEI) was employed to engineer poly(dl-lactide) (PDL-LA) substrate to obtain a stable positively charged surface. An extracellular matrix- (ECM-) like biomacromolecule, gelatin, was selected as the polyelectrolyte to deposit on the activated PDL-LA substrate via the electrostatic assemble technique. The extracellular matrix-like multilayer on the PDL-LA substrate was investigated by attenuated total reflection (ATR-FTIR), X-ray photoelectron spectrscopy (XPS), contact angle, and atomic force microscopy (AFM). The gradual buildup of the protein layer was investigated by UV-vis spectra, and it was further given a quantitative analysis of the protein layer on the PDL-LA substrate via the radioiodination technique. The stability of the protein layer under aqueous condition was also tested by the radiolabeling method. Chondrocyte was selected as the model system for testing the cell behavior and morphology on modified PDL-LA substrates. The chondrocyte test about cell attachment, proliferation, cell activity and cell morphology by SEM, and confocal laser scanning microscopy (CLSM) investigation on extracellular matrix-like multilayer modified PDL-LA substrate was shown to promote chondrocyte attachment and growth. Comparing conventional coating methods, polyelectrolyte multiplayers are easy and stable to prepare. It may be a good choice for the modification of 3-D scaffolds used in tissue engineering. These very flexible systems allow broad medical applications for drug delivery and tissue engineering.

Surface engineering of poly(D,L-lactic acid) by entrapment of chitosan-based derivatives for the promotion of chondrogenesis

Chitosan and chitosan-amino acid derivatives were explored to engineer poly(D,L-lactic acid) (PDL-LA) as an extracellular matrix-like surface to promote cell adhesion and growth. Four kinds of chitosan-amino acid derivatives were prepared to mimic the carbohydrate moieties of cell matrix glycoprotein. The chitosan-amino acid derivatives were characterized by using Fourier transform infrared and ultraviolet spectra. The amino acid content on chitosan-amino acid derivatives was determined by using a ninhydrin-ultraviolet method. A new strategy, entrapment, was therefore used to modify the PDL-LA membrane with chitosan and chitosan-amino acid derivatives. The results of X-ray photoelectron spectroscopy, attenuated total reflectance-Fourier transform infrared, and contact angle confirmed that a stable thin film of chitosan and its derivatives can be entrapped on the surface of the PDL-LA membrane. From the results of chondrocyte cytocompatibility, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assays, and cell morphology, the chitosan-amino acid derivative modified PDL-LA membranes were shown to promote chondrogenesis. The novel surface treatment method combines the good mechanical property of PDL-LA with the good cytocompatibility of chitosan derivatives, which may have potential for tissue engineering.

Study on the three-dimensional proliferation of rabbit articular cartilage-derived chondrocytes on polyhydroxyalkanoate scaffolds

Polymer scaffold systems consisting of poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx)/polyhydroxybutyrate (PHB) (PHBHHx/PHB) were investigated for possible application as a matrix for the three-dimensional growth of chondrocyte culture. Blend polymers of PHBHHx/PHB were fabricated into three-dimensional porous scaffolds by the salt-leaching method. Chondrocytes isolated from rabbit articular cartilage (RAC) were seeded on the scaffolds and incubated over 28 days, with change of the culture medium every 4 days. PHB scaffold was taken as a control. Methylthiazol tetrazolium (MTT) (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltertra-zolium bromide) assay was used to quantitatively examine the proliferation of chondrocytes. Results showed that chondrocytes proliferated better on the PHBHHx/PHB scaffolds than on PHB one. The maximal cell densities were all observed after 7 days of incubation. As for the blend polymers, cells grew better on scaffolds consisting of PHBHHx/PHB in ratios of 2:1 and 1:2 than they did on PHBHHx/PHB of 1:1. Scanning electron microscopy (SEM) also showed that large quantities of chondrocytes grew initially on the surface of the scaffold. After 7 days, they further grew into the open pores of the blend polymer scaffolds. Morphologically, cells found on the surface of the scaffold exhibited a flat appearance and slowly form confluent cell multilayers starting from 14 to 28 days of the growth. In contrast, cells showed rounded morphology, formed aggregates and islets inside the scaffolds. In addition, chondrocytes proliferated on the scaffold and preserved their phenotype for up to 28 days.

Surface engineering of poly(DL-lactic acid) by entrapment of alginate-amino acid derivatives for promotion of chondrogenesis

Alginate-amino acid derivatives were explored to engineer poly(DL-lactic acid)(PDL-LA) as glycocalyx-like surface to promote cell adhesion and growth. Four different kinds of alginate-amino acid derivatives were synthesized to mimic the glycocalyx of cell membrane to promote chondrogenesis. The alginate-amino acid derivatives were characterized by FT-IR, 1H NMR and UV spectra and the amino acid content on alginate-amino acid derivatives was given by ninhydrin-UV method. A new strategy, entrapment, was then employed to modify PDL-LA membranes with alginate and its amino acid derivatives. The results of XPS, ATR-FTIR and contact angle confirmed that a stable thin film of alginate and its amino acid derivatives can be entrapped on the surface of PDL-LA membrane. The chondrocyte cytocompatibility test and MTT assays indicated that the alginate-amino acid derivatives modified PDL-LA membranes could promote chondrogenesis. The novel surface treatment method may have potentials for tissue engineering and other biomedical applications.

Effect of surface treatment on the biocompatibility of microbial polyhydroxyalkanoates

The biocompatibility of microbial polyesters polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) were evaluated in vitro. The mouse fibroblast cell line L929 was inoculated on films made of PHB, PHBHHx and their blends, polylactic acid (PLA) as control. It was found that the growth of the cells L929 was poor on PHB and PLA films. The viable cell number ranged from 8.8 x 10(2) to 1.8 x 10(4)/cm2 only. Cell growth on the films made by blending PHB and PHBHHx showed a dramatic improvement. The viable cell number observed increased from 9.7 x 10(2) to 1.9 x 10(5) on a series of PHB/PHBHHx blended film in ratios of 0.9/0.1:0/1, respectively, indicating a much better biocompatibility in the blends contributed by PHBHHx. Biocompatibility was also strongly improved when these polymers were treated with lipases and NaOH, respectively. However, the effects of treatment were weakened when PHBHHx content increased in the blends. It was found that lipase treatment had more increased biocompatibility than NaOH. After the treatment biocompatibility of PHB was approximately the same as PLA, while PHBHHx and its dominant blends showed improved biocompatibility compared to PLA.

Tissue engineering: a 21st century solution to surgical reconstruction

Tissue engineering has emerged as a rapidly expanding approach to address the organ shortage problem. It is an "interdisciplinary field that applies the principles and methods of engineering and the life sciences toward the development of biological substitutes that can restore, maintain, or improve tissue function." Much progress has been made in the tissue engineering of structures relevant to cardiothoracic surgery, including heart valves, blood vessels, myocardium, esophagus, and trachea.

Fibrin gel -- advantages of a new scaffold in cardiovascular tissue engineering

OBJECTIVE

The field of tissue engineering deals with the creation of tissue structures based on patient cells. The scaffold plays a central role in the creation of 3-D structures in cardiovascular tissue engineering like small vessels or heart valve prosthesis. An ideal scaffold should have tissue-like mechanical properties and a complete immunologic integrity. As an alternative scaffold the use of fibrin gel was investigated.

METHODS

Preliminary, the degradation of the fibrin gel was controlled by the supplementation of aprotinin to the culture medium. To prevent tissue from shrinking a mechanical fixation of the gel with 3-D microstructure culture plates and a chemical fixation with poly-L-lysine in different fixation techniques were studied. The thickness of the gel layer was changed from 1 to 3 mm. The tissue development was analysed by light, transmission and scanning electron microscopy. Collagen production was detected by the measurement of hydroxyproline. Injection molding techniques were designed for the formation of complex 3-D tissue structures.

RESULTS

The best tissue development was observed at an aprotinin concentration of 20 microg per cc culture medium. The chemical border fixation of the gel by poly-L-lysine showed the best tissue development. Up to a thickness of 3 mm no nutrition problems were observed in the light and transmission electron microscopy. The molding of a simplified valve conduit was possible by the newly developed molding technique.

CONCLUSION

Fibrin gel combines a number of important properties of an ideal scaffold. It can be produced as a complete autologous scaffold. It is moldable and degradation is controllable by the use of aprotinin.

Scaffold precoating with human autologous extracellular matrix for improved cell attachment in cardiovascular tissue engineering

Cell attachment to a scaffold is a precondition for the development of bioengineered valves and vascular substitutes. This attachment is generally facilitated by the use of precoating factors, but some can cause toxic or immunologic side effects. Autologous extracellular matrix (ECM) is used as a precoating factor in our study. Ascending aortic tissue was cultured to obtain human myofibroblasts. Autologous ECM was extracted from the same aortic tissue. Poly(glycolic acid) (PGA) scaffolds were precoated with autologous ECM, human serum, or poly-L-lysine; the control group was pretreated with phosphate buffered saline (PBS). Myofibroblasts were seeded onto each scaffold, and the cell attachment was assayed and compared. Compared with the control group, precoating with human serum, poly-L-lysine, and ECM increased number of attached cells by 24%, 53%, and 48%, respectively. Differences between precoating groups were significant (p < 0.01), except for ECM versus poly-L-lysine. Scanning electron microscopy also demonstrated the high degree of cell attachment to the PGA fibers on scaffolds precoated with ECM and poly-L-lysine. Precoating polymeric scaffold with autologous human extracellular matrix is a very effective method of improving cell attachment in cardiovascular tissue engineering without the potential risk of immunologic reactions.

Fibrin gel as a three dimensional matrix in cardiovascular tissue engineering

OBJECTIVE

In tissue engineering, three-dimensional biodegradable scaffolds are generally used as a basic structure for cell anchorage, cell proliferation and cell differentiation. The currently used biodegradable scaffolds in cardiovascular tissue engineering are potentially immunogenic, they show toxic degradation and inflammatory reactions. The aim of this study is to establish a new three-dimensional cell culture system within cells achieve uniform distribution and quick tissue development and with no toxic degradation or inflammatory reactions.

METHODS

Human aortic tissue is harvested from the ascending aorta in the operation room and worked up to pure human myofibroblasts cultures. These human myofibroblasts cultures are suspended in fibrinogen solution and seeded into 6-well culture plates for cell development for 4 weeks and supplemented with different concentrations of aprotinin. Hydroxyproline assay and histological studies were performed to evaluate the tissue development in these fibrin gel structures.

RESULTS

The light microscopy and the transmission electron microscopy studies for tissue development based on the three-dimensional fibrin gel structures showed homogenous cell growth and confluent collagen production. No toxic degradation or inflammatory reactions could be detected. Furthermore, fibrin gel myofibroblasts structures dissolved within 2 days in medium without aprotinin, but medium supplemented with higher concentration of aprotinin retained the three-dimensional structure and had a higher collagen content (P<0.005) and a better tissue development.

CONCLUSIONS

A three-dimensional fibrin gel structure can serve as a useful scaffold for tissue engineering with controlled degradation, excellent seeding effects and good tissue development.