Preparation of poly(glycolic acid) bonded fiber structures for cell attachment and transplantation

Formation of silk fibroin matrices with different texture and its cellular response to normal human keratinocytes

Three forms of silk fibroin (SF) matrices, woven (microfiber), non-woven (nanofiber), and film form, were used to perform a conformational analysis and cell culture using normal human oral keratinocytes (NHOK). To obtain the SF microfiber (SF-M) matrix, natural grey silk was degummed, while the SF film (SF-F) and nanofiber (SF-N) matrices were prepared by casting and electrospinning the formic acid solutions of the regenerated SF, respectively. For insolubilization, as-prepared SF-F and SF-N matrices were chemically treated with an aqueous methanol solution of 50%. The conformational structures of as-prepared and chemically treated SF matrices were investigated using attenuated total reflectance infrared spectroscopy (ATR-IR) and solid-state 13C CP/MAS nuclear magnetic resonance (NMR) spectroscopy. The as-cast SF-F matrix formed a mainly beta-sheet structure that was similar to the SF-M matrix, whereas the as-spun SF-N matrix had a random coil conformation as the predominant secondary structure. Conformational transitions from random coil to beta-sheet of the as-spun SF-N occurred rapidly within 10 min following aqueous methanol treatment, and were confirmed by solid-state 13C NMR analysis. To assess the cytocompatibility and cells behavior on the different textures of SF, we examined the cell attachment and spreading of NHOK that was seeded onto the SF matrices, as well as the interaction between the cells and SF matrices. Our results indicate that the SF nanofiber matrix may be more preferable than SF film and SF microfiber matrices for biomedical applications, such as wound dressings and scaffolds for tissue engineering.

Micro and nano-fabrication of biodegradable polymers for drug delivery

This paper presents state-of-the-art micro and nano-fabrication techniques for biodegradable polymers. Replication molding, using a rigid or elastic master, can pattern structures on a polymer surface in a submicron resolution at a low cost. Layer-by-layer rapid prototyping methods are promising in producing controlled release units with complicated geometries, release mechanisms and the ability to control microstructure and composition. Special attention is paid to the fast, flexible, and non-invasive laser fabrication techniques that have great potential in the fabrication of biodegradable polymer drug delivery devices in both a laboratory and industry scale.

Effect of PEG-PLLA diblock copolymer on macroporous PLLA scaffolds by thermally induced phase separation

A regular and highly interconnected macroporous poly(L-lactic acid) (PLLA) scaffold was fabricated from a PLLA-dioxane-water ternary system with added polyethylene glycol (PEG)-PLLA diblock using thermally induced phase separation (TIPS). The morphology of the scaffold was investigated in detail by controlling the following TIPS parameters: quenching temperature, aging time, polymer concentration, molecular structure, and diblock concentration. The phase diagram was assessed visually on the basis of the turbidity. The cloud-point curve shifted to higher temperatures with increasing PEG content in the additives (PEG-PLLA diblocks), due to a stronger interaction between PEG and water in solution. The addition of diblock series (0.5 wt% in solution) stabilized interconnections of pores at a later stage without segregation or sedimentation. The pore size of the scaffold could be easily controlled in the range 50-300 microm. A macroporous PLLA scaffold was used to study an MC3T3-E1 cell (an osteoblast-like cell) culture. The cells successfully proliferated in the PLLA scaffold in the presence of added PEG-PLLA diblock for 4 weeks.

The interaction of Schwann cells with chitosan membranes and fibers in vitro

The bridging of nerve gaps is still one of the major problems in peripheral nerve regeneration. A promising alternative for the repair of peripheral nerve injuries is the bioartificial nerve graft, comprised of a biomaterial pre-seeded with Schwann cells (SCs), which is an effective substrate for enhancing nerve regeneration. Interaction between cultured SCs and biomaterials is of importance. For the purposes of this study, culture systems of normal SCs were used. The biocompatibility of chitosan, including chitosan membranes and chitosan fibers, was evaluated in vitro. The growth of SCs was observed by light and scanning electron microscopy at regular intervals. SCs were identified by immunocytochemical staining and the viability of SCs was measured by MTT assay. The experimental results indicated that SCs could grow onto chitosan materials with two different shapes: spherical and long olivary. They contacted with the extensions. The long olivary cells inclined to encircle chitosan fibers up. It was also found that the cells on the chitosan fibers migrated faster than those on the chitosan membranes. There was a good biological compatibility between chitosan and SCs. Compared with the chitosan membranes, SCs migrated more easily onto the stereoframe of chitosan fibers. These studies contribute information necessary to enhancing our understanding of biocompatibility of chitosan.

Paraffin spheres as porogen to fabricate poly(L-lactic acid) scaffolds with improved cytocompatibility for cartilage tissue engineering

Three-dimensional poly(L-lactic acid) (PLLA) scaffolds with high porosity and pore size ranging from 150 to 700 microm were conveniently prepared with paraffin spheres used as porogen. PLLA/1,4-dioxane solution containing a given amount of paraffin spheres was frozen at -25 degrees C to obtain a solidified mixture, followed with freeze drying and subsequent leaching with hexane to remove the 1,4-dioxane and paraffin spheres, respectively. The fabricated PLLA scaffolds were highly porous with evenly distributed and interconnected pores. The microstructures of the PLLA scaffolds as a function of paraffin-sphere size, paraffin-sphere dosage, and PLLA concentration were characterized by confocal laser scanning microscopy (CLSM) and scanning-electronic microscopy (SEM). To improve the cytocompatibility of the bioinert material, a hybrid PLLA scaffold containing Type I collagen was prepared by pressing the collagen solution into the scaffold under reduced pressure. The amounts of the collagen introduced in the scaffolds were detected by ninhydrin method. The distribution of the collagen in the scaffolds was studied with CLSM. Finally, in vitro cell culture was performed by injecting a chondrocyte suspension into the scaffolds. The results showed that the chondrocytes were more evenly distributed and more spread out in the collagen-modified PLLA scaffolds than in the unmodified ones.

A novel electrically conductive and biodegradable composite made of polypyrrole nanoparticles and polylactide

A novel electrically conductive biodegradable composite material made of polypyrrole (PPy) nanoparticles and poly(d,l-lactide) (PDLLA) was prepared by emulsion polymerization of pyrrole in a PDLLA solution, followed by precipitation. The composite was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The electrical stability of the composite containing 5 wt% PPy was investigated in a cell culture environment for 1000 h with 100 mV DC applied voltage. Fibroblasts were cultured on the composite membranes and were stimulated with various DC currents. The PPy particles formed aggregations and constituted microdomains and networks embedded in the PDLLA. With the 1-17% increase in the PPy content, the conductivity of the composite increased by six orders of magnitude. The surface resistivity of the PPy/PDLLA membrane with 3% PPy was as low as 1x10(3) Omega/square. The electrical stability was significantly better in the PPy/PDLLA composite than in the PPy-coated polyester fabrics. For the composite with 5% PPy, the test membrane retained 80% and 42% of the initial conductivity in 100 and 400 h, respectively, following the addition of the MEM solution, compared to 5% and 0.1% for the PPy-coated polyester fabrics. Under 100 mV, a composite membrane 3.0x2.5x0.03cm3 in size and containing 5% PPy sustained a biologically meaningful electrical conductivity in a typical cell culture environment for 1000 h. The growth of fibroblasts was up regulated under the stimulation of medium range intensity of DC current.

Self-hardening calcium phosphate composite scaffold for bone tissue engineering

Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoconductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the cytotoxicity of CPC-fiber composite. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Flexural strength, work-of-fracture (toughness), and elastic modulus were measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 60%. Cell culture was performed with osteoblast-like cells, and cell viability was quantified using an enzymatic assay. Flexural strength (mean+/-SD; n=6) of CPC with 60% fibers was 13.5+/-4.4 MPa, three times higher than 3.9+/-0.5 MPa of CPC Control. Work-of-fracture was increased by 182 times. Long cylindrical macropores 293+/-46 microm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a macroporosity of 55% and a total porosity of 81%. The new CPC-fiber formulation supported cell adhesion, proliferation and viability. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.

Preparation of porous hydrolyzable polyrotaxane hydrogels and their erosion behavior

We have prepared porous polyrotaxane hydrogels by using the salt leaching technique. Porous hydrogels were found to have a uniform and highly porous structure. The size of pores in each hydrogel was directly proportional to the size of the sodium chloride particle used. Structural uniformity of the hydrogels is useful not only for uniform cell distribution, but also for well-controlled material properties. Uniform pore size and distribution may ensure the diffusion of nutrients throughout of the gel and the removal of metabolic wastes from the system. The results of an erosion study in phosphate-buffered saline showed that the erosion time of porous polyrotaxane hydrogels was controlled by the poly(ethylene glycol) (PEG) content in the hydrogels. The erosion time of the porous polyrotaxane hydrogel was observed to be almost the same with the non-porous polyrotaxane hydrogel with the same PEG content. From the erosion study, the erosion time of the polyrotaxane hydrogel may be independent of its morphology. Easy control of the erosion time in the polyrotaxane hydrogels is useful in the preparation of scaffolds for tissue engineering.

Gravity spinning of polycaprolactone fibres for applications in tissue engineering

Poly(epsilon-caprolactone) (PCL) fibres have been produced by wet spinning from solutions in acetone under low shear (gravity flow) conditions. The tensile strength and stiffness of as-spun fibres were highly dependent on the concentration of the spinning solution. Use of a 6% w/v solution resulted in fibres having strength and stiffness of 1.8 MPa and 0.01 GPa, respectively, whereas these values increased to 9.9 MPa and 0.1 GPa when fibres were produced from 20% w/v solutions. Cold drawing to an extension of 500% resulted in further increases in fibre strength (up to 50 MPa) and stiffness (0.3 GPa). The surface morphology of as-spun fibres was modified, to yield a directional grooved pattern by drying in contact with a mandrel having a machined topography characterised by a peak-peak separation of 91 microm and a peak height of 30 microm. Limited in vitro studies of cell behaviour in contact with the fibres were performed using cell culture. The number of attached fibroblasts and myoblasts on as-spun PCL fibres after 5 days in cell culture was lower than on tissue culture plastic by a factor 2 and 1.5, respectively, but higher than on Dacron monofilament by a factor of 4 and 11, respectively. The high fibre compliance and the potential for controlling the fibre surface architecture to promote contact guidance effects together with the maintained proliferation of fibroblasts and myoblasts on as-spun PCL fibres in vitro recommends their use for 3-D scaffold production in soft tissue engineering.

Formation of defined microporous 3D structures starting from cross-linked hydrogels

A new and simple technique was developed to obtain polysaccharide (hyaluronane, alginate and carboxymethylcellulose) -based hydrogels with a defined porous morphology. The technique consists of stratifying a cross-linked hydrogel on a filter with known pore diameter. CO(2) bubbles, produced by the addition of HCl to a porogen salt NaHCO(3), are forced to pass through the filter, and they induce the hydrogel to assume a porous morphology. The presence and distribution of pores was confirmed by scanning-electron microscopy (SEM). A strict correspondence was found between the porosity of the filter and the pore diameter in the hydrogels. Water uptake measurements showed a decreased amount of water taken up by the porous hydrogels compared with the native hydrogels, due to a compacting of the material. An explanation of the porous material properties of Hyal hydrogel was given on the basis of FTIR spectra.

Effect of Chemistry and Morphology on the Biofunctionality of Self-Assembling Diblock Copolypeptide Hydrogels

Amphiphilic, diblock copolypeptides of hydrophilic lysine or glutamic acid and hydrophobic leucine or valine have been observed to self-assemble into rigid hydrogels in aqueous solution at neutral pH and very low volume fraction of polymer, > or =0.5 wt % polypeptide. Laser scanning confocal microscopy and ultra small angle neutron scattering revealed a heterogeneous microstructure with distinct domains of hydrogel matrix and pure water pores. In situ nanoscale characterization, using cryogenic transmission electron microscopy, revealed a porous, interconnected membranous network of assembled polypeptides. At concentrations of polypeptide below gelation, diblocks containing lysine were cytotoxic to cells, whereas those containing glutamic acid were noncytotoxic. At higher polypeptide concentrations, within rigid gel scaffolds, both lysine and glutamic acid based diblocks were noncytotoxic but did not support cell attachment/proliferation. The cationic chemistry observed as cytotoxic in the fluid state was essentially inert in the intact, rigid hydrogel state.

Precursor Tissue Analogs as a Tissue-Engineering Strategy

Natural tissues are composed of functionally diverse cell types that are organized in spatially complex arrangements. Organogenesis of complex tissues requires a coordinated sequential transformation process, with individual stages involving time-dependent expression of cell-cell, cell-matrix, and cell-signal interactions in three dimensions. The common theme of temporal-spatial patterning of these cellular interactions is also observed in other physiological processes, such as growth and development, wound healing, and tumor migration. The "precursor tissue analog" (PTA) applies the temporal-spatial patterning theme to tissue engineering. The goal of PTA in tissue engineering is not to fabricate the final transplantable tissue but rather to guide the dynamic organization, maturation, and remodeling leading to the formation of normal and functional tissues. We describe the critical design principles of PTA. First, structural, mechanical, and physiological requirements of the PTA as a temporary scaffold must be met by a fabrication method with flexibility. The fabrication potential incorporating biological materials such as living cells and plasmid DNA has been addressed. Second, the PTA concept is considered suitable for future tissue engineering in light of the use of undifferentiated stem cells, and may possess a capability to guide stem cells toward diverse differentiation characteristics in situ. To this end, the behavior of the engineered cell and tissue must be monitored in detail. The development of a practical phenotype monitoring system such as a DNA microarray may be integral to the fabrication strategies of PTA. Third, the microtopographical and microenvironmental control on the liquid-solid interaction may lead to a critical design for PTA to provide soluble factors, nutrients, and gases to the cells embedded within the scaffold. We suggest that the level set numerical simulation method may be utilized to engineer the consistent circulation of bioactive liquid throughout the PTA microenvironment.

Preparation of macroporous biodegradable PLGA scaffolds for cell attachment with the use of mixed salts as porogen additives

In the present study, a mixture of ammonium-bicarbonate (NH(4)HCO(3)) and sodium-chloride (NaCl) particles was used as a porogen additive to fabricate highly macroporous biodegradable poly(lactic-co-glycolic acid) (PLGA) scaffolds. A two-step salt-leaching process was performed after the sample had become semisolidified. Compared to the standard solvent-casting/particulate-leaching (SC/PL) technique, the processing time of this approach was significantly shorter: Instead of several days, only half a day was required. In addition, the polymer/salts/solvent mixture can be easily handled and molded into scaffolds of any specific shape-for example, thin sheet, cylindrical, or bone-shaped-for special applications in tissue engineering. Our results demonstrate that these scaffolds have a highly interconnected open-pore structure as well as greater mechanical properties than those made using the standard SC/PL technique. Primary rat osteoblasts seeded into the scaffolds exhibited good seeding efficiency. The method presented here is a promising approach for fabricating scaffolds for tissue engineering applications.

Preparation of macroporous biodegradable poly(L-lactide-co-epsilon-caprolactone) foams and characterization by mercury intrusion porosimetry, image analysis, and impedance spectroscopy

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol % of epsilon-CL, namely P(LA-co-CL(5)) and P(LA-co-CL(40)), respectively, have been made macroporous by freeze-drying solutions in dimethylcarbonate. Most of the freeze-dried foams, prepared by varying polymer concentration and cooling rate, exhibited two main pore populations: (1). longitudinally oriented tube-like macropores with diameters >or=100 microm, and (2). interconnected micropores (10-100 microm). Pore characteristics, including macropore density, mean diameter, and interdistance, as well as micropore density, area, and shape, were determined by image analysis of scanning electron micrographs in order to study the influence of processing and formulation parameters on foam structure and properties. The pore orientation and the 3-D texture also were studied by image analysis and impedance spectroscopy. In the case of the P(LA-co-CL(5)), the macropore diameter increased with the cooling rate while the micropore diameter decreased. The micropores also became more circular when the cooling rate was increased. The pore size and morphology of the P(LA-co-CL(40)) were quite unchanged by varying the cooling rate. All the other conditions being the same, the P(LA-co-CL(5)) foams were better organized than the P(LA-co-CL(40)) foams, and pore orientation was improved at the higher cooling rate. Pore size and morphology also can be controlled by changing the polymer concentration (Cp), as we showed by studying P(LA-co-CL(5)) foams prepared by freeze-drying solutions in the 1-10 w/v % Cp range. Macropore density, average diameter, and interdistance of P(LA-co-CL(5)) foams increased with Cp, but the micropore characteristics remained almost unchanged no matter the Cp. The reliability of the characterization methods has been discussed, with special attention to mercury intrusion porosimetry, which is used primarily for measurement of pore volume and pore size distribution. However, this technique is reported here as a destructive and unreliable method for the characterization of fragile P(LA-co-CL(40)) foams. This study shows that image analysis and impedance spectroscopy can give reliable information relative to the pore morphology and anisotropy of freeze-dried foams.

Scaffold development using selective laser sintering of polyetheretherketone-hydroxyapatite biocomposite blends

In tissue engineering (TE), temporary three-dimensional scaffolds are essential to guide cell proliferation and to maintain native phenotypes in regenerating biologic tissues or organs. To create the scaffolds, rapid prototyping (RP) techniques are emerging as fabrication techniques of choice as they are capable of overcoming many of the limitations encountered with conventional manual-based fabrication processes. In this research, RP fabrication of solvent free porous polymeric and composite scaffolds was investigated. Biomaterials such as polyetheretherketone (PEEK) and hydroxyapatite (HA) were experimentally processed on a commercial selective laser sintering (SLS) RP system. The SLS technique is highly advantageous as it provides good user control over the microstructures of created scaffolds by adjusting the SLS process parameters. Different weight percentage (wt%) compositions of physically mixed PEEK/HA powder blends were sintered to assess their suitability for SLS processing. Microstructural assessments of the scaffolds were conducted using electron microscopy. The results ascertained the potential of SLS-fabricated TE scaffolds.

Thermal and mechanical characteristics of poly(L-lactic acid) nanocomposite scaffold

Inorganic nanosized silicate nanoplatelets were incorporated into biodegradable poly(L-lactic acid) (PLLA) for the purpose of tailoring mechanical stiffness of PLLA porous scaffold systems. Increasing the nucleation density around the foreign body surfaces, the montmorillonite (MMT) nanoplatelets modified with dimethyl dihydrogenated tallow ammonium cations decreased the glass transition temperature and the degree of PLLA crystallinity, which seemingly caused the accelerated biodegradation rate of PLLA nanocomposites due to the enhanced segmental mobility of backbone chains and the expanded amorphous region of PLLA matrix. The tensile modulus was increased from 121.2MPa of pristine polymer scaffold to 170.1MPa of MMT/PLLA nanocomposite scaffold (ca. 40% increment) by the addition of small amount of MMT platelets (5.79 vol%) acting as a mechanical reinforcement of polymer chains in the nanoscale molecular level. Overall, the nanotechnology used in this study may be applied to various scaffold systems of biodegradable polymers and hard/soft scaffold structures requiring critical control and design characteristics of mechanical stiffness and biodegradation rate.

Preliminary biocompatibility experiment of polymer films for laser-assisted tissue welding

BACKGROUND AND OBJECTIVES

The purpose of this study was to examine the impact of a polymer film for liquid solder strength reinforcement on the short term healing of a wound closed by laser-tissue soldering.

MATERIALS AND METHODS

Full thickness incisions created on the dorsum of Sprague-Dawley rats were closed by laser-tissue soldering: albumin solder with Indocyanine Green (ICG) dye was inserted between the incision edges and photothermally coagulated with a diode laser. A poly(DL-lactic-co-glycolic acid) (PLGA) polymer film was implanted subcutaneously in the bottom of the incision (controls had no film). Specimens were harvested at 0, 3, 7, and 14 days for breaking strength testing and histological analysis.

RESULTS

Breaking strengths of the controls at 0 and 14 days were statistically stronger than the specimens with the implanted films (t-test, P < 0.05). A slight difficulty in apposing the wound edges due to the film presence may have contributed to the low acute strengths. Interference with the wound contraction process by the films possibly contributed to the lower breaking strength at 14 days. Wound histology indicated a mild foreign body reaction to the polymer film material.

CONCLUSIONS

The polymer film was well tolerated by the tissue, and the tissue response to the material was consistent with that seen in the literature. The breaking strength differences between control and film-implanted specimens at 0 and 14 days were probably the result of mechanical complications (tissue apposition and wound contraction) due to the presence of the film, and not due to the film material itself. The use of polymer film patches for liquid solder reinforcement and breaking strength enhancement may have certain application specific issues that need to be addressed. Strategies to account for these issues require further research.

Polyhydroxyalkanonate derivatives in current clinical applications and trials

Polyhydroxyalkanonate is a typical biodegradable material, which is permitted for use in the medical and pharmaceutical fields. For its biodegradability, biocompatibility, and toxicological safety, the majority of products practically used are composed of homo-polymers of poly(lactic acid), poly(glycolic acid), and poly(epsilon-caprolactone) and their co-polymers. On the market, suture strings are still the main usage. The needs of biodegradable materials have been being gradually increased by the development of drug delivery systems, tissue engineering, and regenerative medicine. Some types of formulation, that is, mono-fibers, twisted fibers, films, fabrics, sponges, and injectable particles are developed to match each purpose. This article reviews the current clinical applications and trials of polyhydroxyalcanonate products.

Tissue welding with biodegradable polymer films-demonstration of acute strength reinforcement in vivo

BACKGROUND AND OBJECTIVES

To demonstrate, in vivo, acute strength reinforcement benefits of polymer film patches.

STUDY DESIGN/MATERIALS AND METHODS

Full thickness incisions created in a dorsal skin flap of Sprague-Dawley rats were closed by laser-tissue welding: albumin solder was topically applied to the incision on the dermal surface, and a poly(lactic-co-glycolic acid) (PLGA) polymer film placed on the solder as a patch (controls had no film). Breaking strength was tested acutely (15-20 minutes after sacrifice).

RESULTS

The patched incisions were statistically stronger than the controls (ANOVA, P < 0.05).

CONCLUSIONS

Polymer film patches may be a viable method to increase acute breaking strengths of welds using topically applied solder.

A novel method to obtain protein release from porous polymer scaffolds: emulsion coating

To obtain the controlled release of proteins from macro-porous polymeric scaffolds, a novel emulsion-coating method has been developed. In this process, a water-in-oil emulsion, from an aqueous protein solution and a polymer solution, is forced through a prefabricated scaffold by applying a vacuum. After solvent evaporation, a polymer film, containing the protein, is then deposited on the porous scaffold surface. This paper reports the effect of processing parameters on the emulsion coating characteristics, scaffold structure, and protein release and stability. Poly(ether-ester) multiblock copolymers were chosen as the polymer matrix for both scaffolds and coating. Macro-porous scaffolds, with a porosity of 77 vol% and pores of approximately 500 microm were prepared by compression moulding/salt leaching. A micro-porous, homogeneous protein-loaded coating could be obtained on the scaffold surface. Due to the coating, the scaffold porosity was decreased, whereas the pore interconnection was increased. A model protein (lysozyme) could effectively be released in a controlled fashion from the scaffolds. Complete lysozyme release could be achieved within 3 days up to more than 2 months by adjusting the coated emulsion parameters. In addition, the coating process did not reduce the enzymatic activity. This new method appears to be promising for tissue engineering applications.

Enhanced bone marrow stromal cell adhesion and growth on segmented poly(ether ester)s based on poly(ethylene oxide) and poly(butylene terephthalate)

In previous studies in rats and goats, hydrophilic compositions of the PEOT/PBT block copolymer family have shown in vivo calcification and bone bonding. These copolymers are therefore interesting candidates as scaffolding materials in bone tissue engineering applications. Model studies using goat bone marrow stromal cells, however, showed that it was not possible to culture bone marrow stromal cells in vitro on these hydrophilic copolymers. In this paper two ways of surface modifying these materials to improve in vitro bone marrow stromal cell attachment and growth are discussed. Two different approaches are described: (1) blending of hydroxyapatite (HA) followed by CO(2) gas plasma etching; (2) surface modification using CO(2) gas plasma treatments. It was observed that not only HA but also the CO(2) plasma treatment by itself has a positive effect on bone marrow stromal cell attachment and growth. Gas plasma treatment appeared to be the most successful approach, resulting in a large increase in the amount of bone marrow stromal cells present on the surface (determined by a DNA assay). The amount of DNA present on the plasma-treated copolymer 1000/70/30 PEOT/PBT, based on poly(ethylene oxide, M(w) = 1000, 70 m% soft segment), was comparable to the amount present on PDLLA and significantly higher than the amount present on PCL after 7 days of cell culturing. The fact that after gas plasma treatment bone marrow stromal cells do attach to PEOT/PBT copolymers, enables in vitro bone marrow stromal cell culturing, making bone tissue engineering applications of these materials possible.

Evaluation of a galactose-carrying gelatin sponge for hepatocytes culture and transplantation

This study proposes a new three-dimensional culture of mouse hepatocytes in a porous galactose-carrying modified gelatin sponge matrix. The modification of gelatin using galactose residues significantly increased the attachment of hepatocytes on the substrate. A modified gelatin sponge with lactobionic acid (MGLA) was prepared to increase the specific interaction between the hepatocytes and the matrix. Hepatocytes cultured in a three-dimensional MGLA sponge released much less lactate dehydrogenase than those cultured on a collagen Type I-coated monolayer. Moreover, the survival rate of hepatocytes cultured on an MGLA sponge was longer than the survival rate of hepatocytes cultured on a collagen Type I-coated monolayer. Hepatic specific metabolic functions, namely, the secretion of serum albumin and the synthesis of urea, were well maintained and promoted by spheroidal hepatocytes formed in the MGLA sponge.

Interaction of human chondrocytes and NIH/3T3 fibroblasts on chloric acid-treated biodegradable polymer surfaces

It has been recognized that adhesion and proliferation of cells on biodegradable polymers such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and poly(lactide-co-glycolide) (PLGA) depend on the surface properties. The chloric acid (CA) treatment of these films was developed to increase surface wettability and to improve adhesion and proliferation of human chondrocytes and NIH/3T3 fibroblasts. The CA-treated films were characterized by the measurement of water contact angle, electron spectroscopy for chemical analysis (ESCA), and scanning electron microscopy (SEM). The changes of the film surface water contact angle gradually decreased with increase of CA treatment time, owing to the oxygen-based functional groups incorporated on the surface by CA treatment and were in the order PGA > PLGA > PLA due to the number of methyl group on the backbone chain. In ESCA analysis, as CA treatment time increased, the carbon (binding energy, approximately 285 eV) ratio decreased in film surfaces, whereas the oxygen (approximately 532 eV) ratio increased. The human chondrocytes from articular cartilage and mouse NIH/3T3 fibroblasts adhered for 1 day and grown for 2 days on the CA-treated films were counted and observed by SEM. As the surface wettability increased, the number of cells adhered and grown on the surface increased. In conclusion, this study demonstrated that the surface wettability of the biodegradable polymer plays an important role for cell adhesion and proliferation behavior for the application of the tissue engineering.

A novel porous cells scaffold made of polylactide-dextran blend by combining phase-separation and particle-leaching techniques

In this study, a kind of biodegradable material was developed by blending polylactide (PLA) with natural biodegradable dextran, and a novel sponge-like scaffold made of it was fabricated thereof using solvent-casting and particle-leaching technique. To obtain a uniform blend of PLA and dextran by simple solvent-casting method, hydroxyls of dextran should be protected via trimethylsilyl (TMS) groups to make dextran soluble in organic solvents. Benzene was found among the few solvents that could dissolve this TMS-protected dextran (TMSD) well, however, it was not a good solvent for PLA. Therefore, a homogeneous mixed solution of PLA and TMSD could be obtained when a mixture of dichloroform (DCM) and benzene (v/v = 6/4) was used. By this technique, PLA-dextran blend films and even PLA films were observed a microporous structure (pore size around 5-10 microm) formation throughout the films under scanning electron microscope (SEM). Scaffolds that were prepared by dissolving PLA and TMSD in mixed solvent of DCM and benzene and using salt as porogen, were observed the formation of micropores (pore size around 5-10 microm) in the cellular walls of macropores (pore size around 100-200 microm). This microporous structure was closely related to the phase separation occurring during films or foams formation, which was mainly due to the different solubility of PLA and TMSD in benzene, as well as the different evaporation rates of DCM and benzene. In comparison with PLA, the surface and bulk hydrophilicity of PLA-dextran blend films or foams were significantly improved after the TMS groups were removed in methanol, and the results of cell culture on these polymeric substrates exhibited an enhancement on cell attachment and proliferation.

Cell adhesion and morphology in porous scaffold based on enantiomeric poly(lactic acid) graft-type phospholipid polymers

Poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) macromonomers were synthesized for preparation of a novel cytocompatible polymer. The cytocompatible polymer was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA), and the enantiomeric PLLA (or PDLA) macromonomer. The degree of polymerization of the lactic acid in the PLLA and PDLA segments was designed to be ca. 20. The copolymer-coated surface was analyzed with static contact angle by water. From the result, the PLLA (or PDLA) segment and MPC unit were located on the coated surface, and the monomer unit in the copolymer was reconstructed by contacting water. Fibroblast cell culture was performed to evaluate cell adhesion on the coated surface, and the cell morphology was observed. The number of cell adhesion is correlated with the PL(D)LA content, and the cell morphology is correlated with the MPC unit content. The porous scaffold was prepared by the formation of a stereocomplex between the PLLA and PDLA, and the cell adhesion and following cell intrusion was then evaluated. The fibroblast cells adhered on the surface and intruded into the scaffold through the connecting pores after 24 h. The cell morphology became round shape from spreading with the decreasing PLLA (or PDLA) content in the copolymer. It is considered that the change in the cell morphology would be induced by the MPC unit as cytocompatible unit. These findings suggest that the porous scaffold makes it possible to have cytocompatibility and to produce three-dimensional tissue regeneration.

Synthesis, biodegradability, and biocompatibility of lysine diisocyanate-glucose polymers

The success of a tissue-engineering application depends on the use of suitable biomaterials that degrade in a timely manner and induce the least immunogenicity in the host. With this purpose in mind, we have attempted to synthesize a novel nontoxic biodegradable lysine diisocyanate (LDI)- and glucose-based polymer via polymerization of highly purified LDI with glucose and its subsequent hydration to form a spongy matrix. The LDI-glucose polymer was degradable in aqueous solutions at 37, 22, and 4 degrees C, and yielded lysine and glucose as breakdown products. The degradation products of the LDI-glucose polymer did not significantly affect the pH of the solution. The physical properties of the polymer were found to be adequate for supporting cell growth in vitro, as evidenced by the fact that rabbit bone marrow stromal cells (BMSCs) attached to the polymer matrix, remained viable on its surface, and formed multilayered confluent cultures with retention of their phenotype over a period of 2 to 4 weeks. These observations suggest that the LDI-glucose polymer and its degradation products were nontoxic in vitro. Further examination in vivo over 8 weeks revealed that subcutaneous implantation of hydrated matrix degraded in vivo three times faster than in vitro. The implanted polymer was not immunogenic and did not induce antibody responses in the host. Histological analysis of the implanted polymer showed that LDI-glucose polymer induced a minimal foreign body reaction, with formation of a capsule around the degrading polymer. The results suggest that biodegradable peptide-based polymers can be synthesized, and may potentially find their way into biomedical applications because of their biodegradability and biocompatibility.

Tissue engineering of complex tooth structures on biodegradable polymer scaffolds

Tooth loss due to periodontal disease, dental caries, trauma, or a variety of genetic disorders continues to affect most adults adversely at some time in their lives. A biological tooth substitute that could replace lost teeth would provide a vital alternative to currently available clinical treatments. To pursue this goal, we dissociated porcine third molar tooth buds into single-cell suspensions and seeded them onto biodegradable polymers. After growing in rat hosts for 20 to 30 weeks, recognizable tooth structures formed that contained dentin, odontoblasts, a well-defined pulp chamber, putative Hertwig's root sheath epithelia, putative cementoblasts, and a morphologically correct enamel organ containing fully formed enamel. Our results demonstrate the first successful generation of tooth crowns from dissociated tooth tissues that contain both dentin and enamel, and suggest the presence of epithelial and mesenchymal dental stem cells in porcine third molar tissues.

Optimal Biomaterial for Creation of Autologous Cardiac Grafts

Background The optimal cardiac graft for the repair of congenital heart defects will be composed of autologous cells and will grow with the child. The biodegradable material should permit rapid cellular growth and delayed degradation with minimal inflammation. We compared a new material, ε-caprolactone-co- l -lactide sponge reinforced with knitted poly- l -lactide fabric (PCLA), to gelatin (GEL) and polyglycolic acid (PGA), which are previously evaluated materials.

Methods Syngenic rat aortic smooth muscle cells (SMCs, 2×10 6 ) were seeded onto GEL, PGA, and PCLA patches and cultured (n=11 per group). The DNA content in each patch was measured at 1, 2, and 3 weeks after seeding. Histological examination was performed 2 weeks after seeding. Cell-seeded patches were employed to replace a surgically created defect in the right ventricular outflow tract (RVOT) of rats (n=5 per group). Histology was studied at 8 weeks following implantation.

Results In vitro studies showed that the DNA content increased significantly ( P <0.05) in all patches between 1 and 3 weeks after seeding. Histology and staining SMCs for anti-α-smooth muscle actin (αSMA) revealed better growth of cells in the interstices of the grafts with GEL and PCLA than the PGA graft. In vivo studies demonstrated that seeded SMCs survived at least 8 weeks after the patch implantation in all groups. PCLA scaffolds were replaced by more cells with larger αSMA-positive areas and by more extracellular matrix with larger elastin-positive areas than with GEL and PGA. The patch did not thin and expanded significantly. The GEL and PGA patches thinned and expanded. All grafts had complete endothelialization on the endocardial surface.

Conclusions SMC-seeded biodegradable materials can be employed to repair the RVOT. The novel PCLA patches permitted better cellular penetration in vitro and did not thin or dilate in vivo and did not produce an inflammatory response. The cell-seeded PCLA patch may permit the construction of an autologous patch to repair congenital heart defects.

Effect of Well Defined Dodecahedral Porosity on Inflammation and Angiogenesis

Porosity is an important factor in the healing of prosthetic devices. To better understand this phenomenon, porous polyurethane scaffolds were produced by a variation of the phase inversion/porogen extraction technique in which a prepacked column of spherical porogen particles was infiltrated with a polymer solution before polymer precipitation and porogen extraction. Scaffolds contained pores of well defined shape (approaching open faced pentagonal dodecahedra), narrow size distributions (66.1 +/- 1.3 microm, 84.2 +/- 1.7 microm, and 156.9 +/- 1.2 microm) and high interconnectivity (interconnecting windows of 30.1 +/- 0.8 microm, 41.9 +/- 1.5 microm, and 76.4 +/- 2.0 microm, respectively). A high degree of accessible macroporosity (>80%) could be achieved while limiting the mostly inaccessible microporosity to below 2%. The neovascularization and inflammatory responses to the scaffolds were evaluated in the subcutaneous rat model for 4 weeks. The inflammatory response index and foreign body giant cell index could be reduced by 56% (p < 0.05) and 21% (p < 0.02), respectively, when the pore size was increased from 66 microm to 157 microm, whereas the vascularization index and arteriolar index remained unchanged. Thus, a significant decrease in inflammatory response could be achieved without adversely affecting the degree of neovascularization by increasing the size of the pores.

In vivo study of hot compressing molded 50:50 poly (DL-lactide-co-glycolide) antibiotic beads in rabbits

The authors investigated poly (DL-lactide-co-glycolide) beads as an antibiotic delivery system in vivo for the treatment of various surgical infections. In this study, the copolymer 50:50 poly (DL-lactide):co-glycolide was mixed with vancomycin powder and hot compressing molded at 55 degrees C to form 8 mm in diameter biodegradable antibiotic beads. The antibiotic beads were implanted in the distal femoral cavities of rabbits for in vivo investigation. The local concentration of vancomycin was well above the breakpoint sensitivity concentration (the antibiotic concentration at the transition point between bacterial killing and resistance to the antibiotic) for 56 days. The release was most marked during the first day. The diameters of the sample inhibition zone ranged from 8 to 18 mm, and the relative activity of vancomycin ranged from 9.1% to 100%. Only low systemic blood levels of vancomycin were measured after beads implantation. There was no increase in the concentration of blood urea nitrogen and serum creatinine after the implantation. Histological observations showed that the bead materials were biodegradable, resorbed slowly, and did not cause a significant host reaction. This study offers a biodegradable delivery system of antibiotics to treat various surgical infections.

Fabrication of porous biodegradable polymer scaffolds using a solvent merging/particulate leaching method

This study developed a solvent merging/particulate leaching method for preparing three-dimensional porous scaffolds. Poly(L-lactic-co-glycolic acid) (PLGA) and sodium chloride particles were dry-mixed and cast into a special mold, through which a liquid could pass due to a pressure difference. An organic solvent was then poured into the mold to dissolve and merge the PLGA particles under negative pressure. A nonsolvent was conducted into the PLGA/salt composite to solidify and precipitate the merged PLGA matrix. Finally, a large amount of water was passed through the mold to leach out the salt particles so as to create a porous structure. The results revealed that a highly porous three-dimensional scaffold (>85 vol %) with a well interconnected porous structure could be achieved by this process. Porosity and the pore size of the scaffold were controlled using the ratio and the particle size of the added salt particles. A larger-volume scaffold was produced using a larger mold. This work provides a continuous and simple procedure for fabricating a bulk three-dimensional porous scaffold for tissue engineering.

Regeneration of canine peroneal nerve with the use of a polyglycolic acid-collagen tube filled with laminin-soaked collagen sponge: a comparative study of collagen sponge and collagen fibers as filling materials for nerve conduits

A novel artificial nerve conduit was developed and its efficiency was evaluated on the basis of promotion of peripheral nerve regeneration across an 80-mm gap in dogs. The nerve conduit was made of a polyglycolic acid-collagen tube filled with laminin-soaked collagen sponge. Conduits filled with either sponge- or fiber-form collagen were implanted into an 80-mm gap of the peroneal nerve (five dogs for each form). Twelve months postoperatively nerve regeneration was superior in the sponge group both morphometrically (percentage of neural tissue: fiber: 39.7 +/- 5.2, sponge: 43.0 +/- 4.5, n=3) and electrophysiologically (fiber: CMAP 1.06 +/- 0.077, SEP 1.32 +/- 0.127 sponge: CMAP 1.04 +/- 0.106, SEP 1.24 +/- 0.197, n=5), although these differences were not statistically significant. The observed regeneration was complementary to successful results reported previously in the same model, in which collagen fibers exclusively were used. The results indicate a possible superiority of collagen sponge over collagen fibers as filling materials. In addition, the mass-producibility, superior scaffolding potential, and capacity for gradual release of soluble factors of the sponge provide make it an attractive alternative to fine fibers, which are both technologically difficult and costly to produce. This newly developed nerve conduit has the potential to enhance peripheral nerve regeneration across longer gaps commonly encountered in clinical settings.

Alginate as a chondrocyte-delivery substance in combination with a non-woven scaffold for cartilage tissue engineering

For tissue engineering of cartilage, chondrocytes can be seeded in a scaffold and stimulated to produce a cartilage-like matrix. In the present study, we investigated the effect of alginate as a chondrocyte-delivery substance for the construction of cartilage grafts. E210 (a non-woven fleece of polyglactin) was used as a scaffold. When bare' E210 (without alginate and without chondrocytes) was implanted subcutaneously in nude mice for 8 weeks. the explanted tissue consisted of fat and fibrous tissue only. When E210 with alginate but without chondrocytes was implanted in nude mice, small areas of newly formed cartilage were found. Alginate seems to stimulate chondrogenesis of ingrowing cells. When chondrocytes were seeded in E210, large amounts of cartilage were found, independent of the use of alginate. This was expressed by a high concentration of glycosaminoglycans (30 microg/mg w.w.) and the presence of collagen type II (1.5 microg/mg w.w.). Macroscopically the grafts of E210 without alginate were shrunk and warped, whereas the grafts with alginate had kept their original shape during the 8 weeks of implantation. The use of alginate did not lead to inflammatory reactions nor increased capsule formation. In conclusion, the use of alginate to seed chondrocytes in E210 does not influence the amount of cartilage matrix proteins produced per tissue wet weight. However, it provides retention of the graft shape.

Perfusion culture of hepatocytes within galactose-derivatized biodegradable poly(lactide-co-glycolide) scaffolds prepared by gas foaming of effervescent salts

Galactose, a specific ligand for asialoglycoprotein receptor in hepatocytes, was immobilized onto the internal surface of highly porous biodegradable poly(D,L-lactic-co-glycolic acid) scaffolds prepared by gas foaming of effervescent salts. Rat hepatocytes seeded within the scaffolds were cultivated by using a continuous flow and perfusion reactor system. Flow rate of medium circulating through the closed loop bioreactor system was optimized to minimize the extent of cell washout from the scaffold/cell construct while satisfying the oxygen transport rate to the seeded hepatocytes. Using the flow culture system, the scaffolds immobilized with galactose onto its internal surface retained a greater number of hepatocytes than those with unmodified or immobilized with glucose due to specific interactions between seeded hepatocytes and galactose moieties exposed onto the surface of the scaffolds. The perfusion culture system based on galactose-modified macroporous scaffolds, under optimal flow conditions, resulted in much higher albumin secretion rate, approximately 70 pg/cell/day for 7 days, compared to that with glucose modified scaffolds used as a negative control. The enhanced functional activity of hepatocytes seeded within the galactose modified scaffolds was likely caused by the formation of aggregated hepatocytes within the scaffolds.

The design of scaffolds for use in tissue engineering. Part I. Traditional factors

In tissue engineering, a highly porous artificial extracellular matrix or scaffold is required to accommodate mammalian cells and guide their growth and tissue regeneration in three dimensions. However, existing three-dimensional scaffolds for tissue engineering proved less than ideal for actual applications, not only because they lack mechanical strength, but they also do not guarantee interconnected channels. In this paper, the authors analyze the factors necessary to enhance the design and manufacture of scaffolds for use in tissue engineering in terms of materials, structure, and mechanical properties and review the traditional scaffold fabrication methods. Advantages and limitations of these traditional methods are also discussed.

Porous, resorbable, fiber-reinforced scaffolds tailored for articular cartilage repair

Porous 75:25 poly(D,L-lactide-co-glycolide) scaffolds reinforced with polyglycolide fibers were prepared with mechanical properties tailored for use in articular cartilage repair. Compression testing was performed to investigate the influence of physiological testing conditions, manufacturing method, anisotropic properties due to predominant fiber orientation, amounts of fiber reinforcement (0 to 20 wt, %), and viscoelasticity via a range of strain rates. Using the same testing modality, the mechanical properties of the scaffolds were compared with pig and goat articular cartilage. Results showed that mechanical properties of the scaffolds under physiological conditions (aqueous, 37 degrees C) were much lower than when tested under ambient conditions. The manufacturing method and anisotropy of the scaffolds significantly influenced the mechanical properties. The compressive modulus and yield strength proportionally increased with increasing fiber reinforcement up to 20%. From 0.01 to 10 mm/mm/min strain rate, the compressive modulus increased in a logarithmic fashion, and the yield strength increased in a semi-log fashion. The compressive modulus of the non-reinforced scaffolds was most similar to the pig and goat articular cartilage when compared using similar testing conditions and modality, but the improvement in yield strength using the stiffer scaffolds with fiber reinforcement could provide needed structural support for in vivo loads.

Three-dimensional cell-scaffold constructs promote efficient gene transfection: implications for cell-based gene therapy

To date, introduction of gene-modified cells in vivo is still a critical limitation for cell-based gene therapy. In this study, based on tissue engineering techniques, we developed a three-dimensional (3-D) transfection system to be cell-based gene delivery vehicle. Human trophoblast-like ED(27) and fibroblastic NIH3T3 cells were used as model cell lines. Cells were seeded onto PET fibrous matrices and plated on polyethylene terephathalate (PET) films as 2-D transfection control. The cell-matrices and cell-films were transfected with pCMV-betagal and pEGFP (green fluorescent protein) reporter gene vectors using LipofectAmine reagent. Gene expression on 3-D versus 2-D growth surface were investigated. The effects of seeding method, seeding density, porosity of the PET matrix, and culturing time of the cell-matrix complex on cDNA transfection and expression in the 3-D cell-matrix complex were also investigated. The beta-gal assay and GFP detection showed that 3-D transfection promoted a higher gene expression level and longer expression time as compared to 2-D transfection. There existed an optimal initial cell seeding density for gene transfection of 3-D cell-matrix complex. Cells seeded on PET matrices with a lower porosity ( approximately 87%) had higher gene expression activities than cells in the matrices with a higher porosity ( approximately 90%). Also, Higher gene expression levels of beta-gal were obtained for the more uniformly seeded matrices that were seeded with a depth-filtration method. The results from this study demonstrate the potential utility of cells seeded onto 3-D fibrous matrices as cell-based gene delivery vehicle for in vitro study of gene expression or in vivo gene therapy.

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.

Preparation of poly(L-lactic acid) and poly(DL-lactic-co-glycolic acid) foams by use of ice microparticulates

Biodegradable foams of poly(L-lactic acid) (PLLA) and poly(DL-lactic-co-glycolic acid) (PLGA) for tissue engineering were fabricated by a porogen-leaching technique using ice microparticulates as the porogen material. PLLA or PLGA solution in chloroform was mixed with ice microparticulates. The mixtures were frozen by being placed in molds in liquid nitrogen and freeze-dried to form the foams. Scanning electron microscopic observation of the PLLA and PLGA foams showed that evenly distributed and interconnected pore structures were formed in these foams. The porosity and surface area of the foams increased with an increase in the weight fraction of the ice microparticulates, while the median pore size remained unchanged. The pore structures of the foams could be manipulated by controlling processing variables such as the size and weight fraction of the ice microparticulates and polymer concentration.