Bioabsorbable scaffolds for guided bone regeneration and generation

In vitro behaviour of three biocompatible glasses in composite implants

Poly(L,DL-lactide) composites containing filler particles of bioactive glasses 45S5 and S53P4 were compared with a composite containing a slowly dissolving glass S68. The in vitro reactivity of the composites was studied in simulated body fluid, Tris-buffered solution, and phosphate buffered saline. The high processing temperature induced thermal degradation giving cavities in the composites containing 45S5 and S53P4, while good adhesion of S68 to the polymer was observed. The cavities partly affected the in vitro reactivity of the composites. The degradation of the composites containing the bioactive glasses was faster in phosphate buffered saline than in the two other solutions. Hydroxyapatite precipitation suggesting bone tissue bonding capability was observed on these two composites in all three solutions. The slower dissolution of S68 glass particles and the limited hydroxyapatite precipitation suggested that this glass has potential as a reinforcing composition with the capability to guide bone tissue growth in biodegradable polymer composites.

Self-reinforced composites of hydroxyapatite-coated PLLA fibers: fabrication and mechanical characterization

Self-reinforced composites (SRCs) are materials where both the matrix and fiber-reinforcing phase are made up of the same polymer. Improved bonding can be achieved with self-reinforced composites compared to traditional dual-polymer, fiber-reinforced composites owing to the identical chemistry of the components in SRCs. Bonding between the fiber and matrix phase is an important factor in applications where mechanical stability is required, such as in the field of bone repair. In this study, we prepared bioabsorbable poly(L-lactic acid)/hydroxyapatite (PLLA/HA) self-reinforced composites via a three-step process that includes surface etching of the fiber, the deposition of the HA coating onto the PLLA fibers through immersion in simulated body fluid (SBF), and hot compaction molding. Although coated with a layer of HA, self-reinforced composites were successfully generated by hot compaction. The effects of compaction time (15 and 30 min), compaction temperature (140, 150, 155, 160, 165, and 170 °C), and HA wt% (0, 5, 10, and 15 wt%) on flexural mechanical properties were studied. Mechanical test results indicated that in unfilled (no HA) PLLA SRCs, compaction time and temperature increased the flexural modulus of the composites tested. Based on the results obtained for unfilled composites, a single compaction time and temperature condition of 15 min and 170 °C were selected to study the effect of HA loading on the composite mechanical properties. HA was successfully loaded onto the fibers at 0, 5, 10, and 15 wt% before hot compaction and was found to significantly increase flexural modulus (P=0.0001). Modulus values ranged from 8.3 GPa±0.5 (0 wt% HA) to 9.7 GPa±0.6 (15 wt% HA). Microscopy results suggest that the HA in these composites forms a nodular-like structure along the fibers, which allows polymer-polymer contact yet prevents longitudinal shear. The procedure used successfully generated composites with flexural moduli near the lower range of bone that may have a possible clinical use for load-bearing bone-fixation devices.

Asymmetrically porous PLGA/Pluronic F127 membrane for effective guided bone regeneration

Porous guided bone regeneration (GBR) membranes with selective permeability, hydrophilicity and adhesiveness to bone were prepared with PLGA and Pluronic F127 using an immersion precipitation method. The porous PLGA/Pluronic F127 membranes were fabricated by immersing the PLGA/Pluronic F127 mixture solution (in tetraglycol) in a mold into water. The PLGA/Pluronic F127 mixture was precipitated in water by the diffusion of water into PLGA/Pluronic F127 mixture solution. It was observed that the membrane has an asymmetric column-shape porous structure. The top surface of the membrane (water contact side) had nano-size pores (approx. 50 nm) which can effectively prevent from fibrous connective tissue invasion but permeate nutrients, while the bottom surface (mold contact size) had micro-size pores (approx. 40 microm) which can improve adhesiveness with bone. From the investigations of mechanical property, water absorbability, model nutrient permeability and preliminary in vivo bone regeneration, the hydrophilized porous PLGA/F127 (5 wt%) membrane seems to be a good candidate as a GBR membrane for the effective permeation of nutrients and osteoconductivity, as well as good mechanical strength to maintain a secluded space for bone regeneration.

Effect of the Lactide/Glycolide Ratio and Molecular Weight of PLGA on the Bovine BMPs Microspheres Systems

The present investigation was aimed at optimization of BMPs loaded PLGA microspheres formulations resulting in improved encapsulation efficiency and sustained release of BMPs by varying the molecular weight and copolymer composition of PLGA. Double-emulsion solvent evaporation method was used to prepare the microspheres. The effect of polymer molecular weight and copolymer composition on particle properties and release behavior in vitro was reported. The particle size and encapsulation efficiency increased with increase in molecular weight and lactide content of PLGA. While BMPs release in vitro decreased with increase in molecular weight and lactide content of PLGA. SEM pictures revealed that almost all microspheres were spherical but internal morphology was different. The morphology of PLGA microspheres with exorbitant molecular weight(100kD) was anomalistic whereas the morphology of PLGA microspheres with higher glycolide content(50) have porous structures.

In Vivo and In Vitro Study of a Polylactide-Fiber-Reinforced β-Tricalcium Phosphate Composite Cage in an Ovine Anterior Cervical Intercorporal Fusion Model

A poly-70L/30DL-lactide (PLA70)–β-tricalcium phosphate (β-TCP) composite implant reinforced by continuous PLA-96L/4D-lactide (PLA96) fibers was designed for in vivo spinal fusion. The pilot study was performed with four sheep, using titanium cage implants as controls. The composite implants failed to direct bone growth as desired, whereas the bone contact and the proper integration were evident with controls 6 months after implantation. Therefore, the PLA70/β-TCP composite matrix material was further analyzed in the in vitro experiment by human and ovine adipose stem cells (hASCs and oASCs). The composites proved to be biocompatible as confirmed by live/dead assay. The proliferation rate of oASCs was higher than that of hASCs at all times during the 28 d culture period. Furthermore, the composites had only a minor osteogenic effect on oASCs, whereas the hASC osteogenesis on PLA70/β-TCP composites was evident. In conclusion, the composite implant material can be applied with hASCs for tissue engineering but not be evaluated in vivo with sheep.

Poly-lactic acid synthesis for application in biomedical devices - a review

Bioabsorbable polymers are considered a suitable alternative to the improvement and development of numerous applications in medicine. Poly-lactic acid (PLA,) is one of the most promising biopolymers due to the fact that the monomers may produced from non toxic renewable feedstock as well as is naturally occurring organic acid. Lactic acid can be made by fermentation of sugars obtained from renewable resources as such sugarcane. Therefore, PLA is an eco-friendly product with better features for use in the human body (nontoxicity). Lactic acid polymers can be synthesized by different processes so as to obtain products with an ample variety of chemical and mechanical properties. Due to their excellent biocompatibility and mechanical properties, PLA and their copolymers are becoming widely used in tissue engineering for function restoration of impaired tissues. In order to maximize the benefits of its use, it is necessary to understand the relationship between PLA material properties, the manufacturing process and the final product with desired characteristics. In this paper, the lactic acid production by fermentation and the polymer synthesis such biomaterial are reviewed. The paper intends to contribute to the critical knowledge and development of suitable use of PLA for biomedical applications.

Effects of lactide monomer on the hydrolytic degradation of poly(lactide-co-glycolide) 85L/15G

The hydrolytic degradation of oriented poly(L-lactide-co-glycolide) 85 L/15 G (PLGA 85/15) sample materials with various amounts of lactide monomer was monitored in vitro at 37 °C. The materials were manufactured from medical grade PLGA 85/15 by a two-step melt extrusion-die drawing process. Results showed that the hydrolytic degradation rate depended highly on the lactide monomer content, which in turn influenced the retention of mechanical properties, mass loss, crystallinity, and dimensional stability. Even small quantities of lactide monomer (0.05-0.20 wt%) affected especially the retention of mechanical properties, which started to decline rapidly upon the inherent viscosity reaching 0.6-0.8 dl/g due to hydrolytic degradation. Based on our hydrolytic degradation data, we constructed a simplified mathematical model of degradation-related strength retention and recommend it as a functional quality control tool for melt-processed biodegradable medical devices manufactured from poly(L-lactide-co-glycolide) 85 L/15 G.

Fabrication of vascularized bone grafts of predetermined shape with hydroxyapatite-collagen gel beads and autogenous mesenchymal stem cell composites

BACKGROUND

Advances in tissue-engineering techniques have enabled new procedures to be developed for bone regeneration. In this study, for engineering of structural tissues with supporting vascular networks, the authors attempted to produce vascularized tissue-engineered bone grafts using cultured mesenchymal stem cells/hydroxyapatite/collagen gel bead composites and vascular bundle implantation.

METHODS

Twenty-four New Zealand White rabbits underwent implantation of ringed polytetrafluoroethylene vascular grafts (1 x 3 cm) in the medial thigh with the femoral vascular bundle passing through. The polytetrafluoroethylene grafts were left unfilled (group A), filled with hydroxyapatite/collagen gel beads (group B), or filled with mesenchymal stem cells/hydroxyapatite/collagen gel bead composites (group C). At 4, 8, 12, and 16 weeks, the implants were removed and radiographic and histologic examinations were conducted.

RESULTS

Radiographic analysis revealed that the area of radiopacity within the chamber was highest in group C. The average calcified densities of groups B and C were between 0.99 +/- 0.11 and 1.29 +/- 0.14. Histologically, there was fibroadipose tissue within the chamber in group A. New tissue had grown into the matrix of the chambers of groups B and C, and substitution of the biomaterials was seen. Newly formed fibrovascular networks and osteoids were simultaneously seen. Bone marrow was observed in the vascular graft of group C 6 months after implantation.

CONCLUSIONS

Tissue-engineered vascularized bone grafts of predetermined shape were created with mesenchymal stem cell/hydroxyapatite/collagen gel bead composites. The results of this study showed that successful in vivo engineering of vascularized tissue-engineered bone grafts is possible.

Knowledge-based approach towards hydrolytic degradation of polymer-based biomaterials

The concept of hydrolytically degradable biomaterials was developed to enable the design of temporary implants that substitute or fulfill a certain function as long as required to support (wound) healing processes or to control the release of drugs. Examples are surgical implants, e.g., sutures, or implantable drug depots for treatment of cancer. In both cases degradability can help to avoid a second surgical procedure for explanation. Although degradable surgical sutures are established in the clinical practice for more than 30 years, still more than 40% of surgical sutures applied in clinics today are nondegradable.1 A major limitation of the established degradable suture materials is the fact that their degradation behavior cannot reliably be predicted by applying existing experimental methodologies. Similar concerns also apply to other degradable implants. Therefore, a knowledge-based approach is clearly needed to overcome the described problems and to enable the tailored design of biodegradable polymer materials. In this Progress Report we describe two methods (as examples for tools for this fundamental approach): molecular modeling combining atomistic bulk interface models with quantum chemical studies and experimental investigations of macromolecule degradation in monolayers on Langmuir-Blodgett (LB) troughs. Finally, an outlook on related future research strategies is provided.

Computer-aided design and finite-element modelling of biomaterial scaffolds for bone tissue engineering

Scaffold biomaterials for tissue engineering can be produced in many different ways depending on the applications and the materials used. Most research into new biomaterials is based on an experimental trial-and-error approach that limits the possibility of making many variations to a single material and studying its interaction with its surroundings. Instead, computer simulation applied to tissue engineering can offer a more exhaustive approach to test and screen out biomaterials. In this paper, a review of the current approach in biomaterials designed through computer-aided design (CAD) and through finite-element modelling is given. First we review the approach used in tissue engineering in the development of scaffolds and the interactions existing between biomaterials, cells and mechanical stimuli. Then, scaffold fabrication through CAD is presented and characterization of existing scaffolds through computed images is reviewed. Several case studies of finite-element studies in tissue engineering show the usefulness of computer simulations in determining the mechanical environment of cells when seeded into a scaffold and the proper design of the geometry and stiffness of the scaffold. This creates a need for more advanced studies that include aspects of mechanobiology in tissue engineering in order to be able to predict over time the growth and differentiation of tissues within scaffolds. Finally, current perspectives indicate that more efforts need to be put into the development of such advanced studies, with the removal of technical limitations such as computer power and the inclusion of more accurate biological and genetic processes into the developed algorithms.

In vivo and in vitro evaluation of an Acetobacter xylinum synthesized microbial cellulose membrane intended for guided tissue repair

BACKGROUND

Barrier materials as cellulose membranes are used for guided tissue repair. However, it is essential that the surrounding tissues accept the device. The present study histologically evaluated tissue reaction to a microbial cellulose membrane after subcutaneous implantation in mice. Furthermore, the interaction between mesenchymal stem cells and the biomaterial was studied in vitro to evaluate its ability to act as cellular scaffold for tissue engineering.

METHODS

Twenty-five Swiss Albino mice were used. A 10 x 10 mm cellulose membrane obtained through biosynthesis using Acetobacter xylinum bacteria was implanted into the lumbar subcutaneous tissue of each mouse. The mice were euthanatized at seven, 15, 30, 60, and 90 days, and the membrane and surrounding tissues were collected and examined by histology.

RESULTS

A mild inflammatory response without foreign body reaction was observed until 30 days post-surgery around the implanted membrane. Polarized microscopy revealed that the membrane remained intact at all evaluation points. Scanning electron microscopy of the cellulose membrane surface showed absence of pores. The in vitro evaluation of the interaction between cells and biomaterial was performed through viability staining analysis of the cells over the biomaterial, which showed that 95% of the mesenchymal stem cells aggregating to the cellulose membrane were alive and that 5% were necrotic. Scanning electron microscopy showed mesenchymal stem cells with normal morphology and attached to the cellulose membrane surface.

CONCLUSION

The microbial cellulose membrane evaluated was found to be nonresorbable, induced a mild inflammatory response and may prove useful as a scaffold for mesenchymal stem cells.

Fabrication of pre-determined shape of bone segment with collagen-hydroxyapatite scaffold and autogenous platelet-rich plasma

BACKGROUND

Reconstruction of large segment of bony defects is frequently needed in hand surgery. Autogenous bone grafting is considered the standard in management of these bony defects but has limited source of graft material. Collagen and hydroxyapatite have been used as bone-filling materials and are known to serve as the osteoconductive scaffold for bone regeneration. On the other hand, platelet-rich plasma is a kind of natural source of growth factors, and has been used successfully in bone regeneration and improving wound healing. This study was designed to evaluate the effectiveness of using biohybrids of platelet-rich plasma and collagen-hydroxyapatite beads for fabricating of protrusive bone in a rabbit animal model.

METHODS

Biomaterial beads comprised of particulate hydroxyapatite dispersed in fibrous collagen (type I) matrices were prepared and filled in the ringed polytetrafluoroethylene (PTFE) artificial vascular graft (3 cm long, 1 cm in diameter). New Zealand White rabbits were each implanted with two cylindrical PTFE artificial vascular graft over both iliac crests (n = 16). A 2 x 0.5 cm opening was created at the side of each PTFE chamber to allow the content of chamber in contact with the bone marrow of the ileum. The chambers were empty (groups A and D), filled with type I collagen/hydroxyapatite beads (groups B and C). In groups C and D, autologous platelet rich plasma (PRP) was given by transcutaneous injection method into the chambers every week. After 12 weeks, the animals were sacrificed and the chambers were harvested for radiological and histological analysis.

RESULTS

In plain radiographs, the group C chambers had significantly higher bone tissue engineered (average calcified density 0.95, average calcified area 61.83%) compared with other groups (P < 0.001). In histological examination, there was a creeping substitution of the implant by the in-growth of fibrovascular tissue in group C. Abundant fibrovascular networks positioned interstitially between these biomaterial beads in all parts of chamber. Degradation of these beads and newly formed capillaries and osteoids around the degraded matrixes are shown. The continually calcification in the matrixes or degraded matrixes is evidenced by the strong green fluorescence observed under the confocal microscope. In group B, looser architecture without evidence of tissue in-growth was shown. In the scaffold absent groups (A and D), there was only fibrous tissue shown within the chamber.

CONCLUSIONS

In this study, we have demonstrated a feasible approach to fabricate an osseous tissue that meets clinical need. Using the type I collagen/ hydroxyapatite gel beads matrixes and intermittent injection of autologous platelet-rich-plasma, specific 3D osseous tissues with fibrovascular network structure from pre-exist bony margin were successfully created in an in vivo animal model.

Fabrication of porous titanium scaffold materials by a fugitive filler method

A clean powder metallurgy route was developed here to produce Ti foams, using a fugitive polymeric filler, polypropylene carbonate (PPC), to create porosities in a metal-polymer compact at the pre-processing stage. The as-produced foams were studied by scanning electron microscopy (SEM), LECO combustion analyses and X-ray diffraction (XRD). Compression tests were performed to assess their mechanical properties. The results show that titanium foams with open pores can be successfully produced by the method. The compressive strength and modulus of the foams decrease with an increasing level of porosity and can be tailored to those of the human bones. After alkali treatment and soaking in a simulated body fluid (SBF) for 3 days, a thin apatite layer was formed along the Ti foam surfaces, which provides favourable bioactive conditions for bone bonding and growth.

Towards bioinspired superhydrophobic poly(L-lactic acid) surfaces using phase inversion-based methods

The water repellency and self-cleaning ability of many biological surfaces has inspired many fundamental and practical studies related to the development of synthetic superhydrophobic surfaces. However, the investigation of such substrates made of biodegradable polymers has been scarce. Simple approaches based on a single step, performed at room temperature (and pressure), were implemented to obtain superhydrophobic poly(L-lactic acid) (PLLA) surfaces via phase inversion-based methods, without addition of low-surface-energy compounds. Water contact angles above 150 degrees were obtained using some processing conditions. In such cases scanning electronic microscopy micrographs of such surfaces revealed a clear rough texture composed by leafy clusters with micro-nano binary structures. Such materials could be used in specific environmental and biomedical applications, namely in implantable materials or in antibacterial or antithrombogenic surfaces.

Biodegradable gelatin microparticles as delivery systems for the controlled release of bone morphogenetic protein-2

This work evaluated gelatin microparticles and biodegradable composite scaffolds for the controlled release of bone morphogenetic protein-2 (BMP-2) in vitro and in vivo. Gelatin crosslinking (10 and 40mM glutaraldehyde), BMP-2 dose (6 and 60ng BMP-2 per mg dry microparticles), buffer type (phosphate buffered saline (PBS) and collagenase-containing PBS), and gelatin type (acidic and basic) were investigated for their effects on BMP-2 release. Release profiles were also observed using poly(lactic-co-glycolic acid) (PLGA) microparticles with varying molecular weights (8300 and 57,500). In vitro and in vivo studies were conducted using radiolabeled BMP-2; the chloramine-T method was preferred over Bolton-Hunter reagent for radioiodination with this system. BMP-2 release from PLGA microparticles resulted in a moderate burst release followed by minimal cumulative release, while BMP-2 release from gelatin microparticles exhibited minimal burst release followed by linear release kinetics in vitro. Growth factor dose had a small effect on its normalized release kinetics probably because of an equilibrium between gelatin-bound and unbound BMP-2. Differences in release from acidic and basic gelatin microparticles may result from the different pretreatment conditions used for gelatin synthesis. The in vitro release kinetics for both gelatin microparticles alone and within composite scaffolds were dependent largely on the extent of gelatin crosslinking; varying buffer type served to confirm that controlled release relies on enzymatic degradation of the gelatin for controlled release. Finally, in vivo studies with composite scaffolds exhibited minimal burst and linear release up to 28 days. In summary, dose effects on BMP-2 release were found to be minimal while varying gelatin type and release medium can alter release kinetics. These results demonstrate that a systematic control of BMP-2 delivery from gelatin microparticles can be achieved by altering the extent of basic gelatin crosslinking.

Surface characterization and cell response of a PLA/CaP glass biodegradable composite material

Bioabsorbable materials are of great interest for bone regeneration applications, since they are able to degrade gradually as new tissue is formed. In this work, a fully biodegradable composite material containing polylactic acid (PLA) and calcium phosphate (CaP) soluble glass particles has been characterized in terms of surface properties and cell response. Cell cultures were performed in direct contact with the materials and also with their extracts, and were evaluated using the MTT assay, alkaline phosphatase activity, and osteocalcin measurements. The CaP glass and PLA were used as reference materials. No significant differences were observed in cell proliferation with the extracts containing the degradation by-products of the three materials studied. A relation between the materials wettability and the material-cell interactions at the initial stages of contact was observed. The most hydrophilic material (CaP glass) presented the highest cell adhesion values as well as an earlier differentiation, followed by the PLA/glass material. The incorporation of glass particles into the PLA matrix increased surface roughness. SEM images showed that the heterogeneity of the composite material induced morphological changes in the cells cytoskeleton.

Characterization of mineralized collagen-glycosaminoglycan scaffolds for bone regeneration

Mineralized collagen-glycosaminoglycan scaffolds designed for bone regeneration have been synthesized via triple co-precipitation in the absence of a titrant phase. Here, we characterize the microstructural and mechanical properties of these newly developed scaffolds with 50 and 75 wt.% mineral content. The 50 wt.% scaffold had an equiaxed pore structure with isotropic mechanical properties and a Ca-P-rich mineral phase comprised of brushite; the 75 wt.% scaffold had a bilayer structure with a pore size varying in the through-thickness direction and a mineral phase comprised of 67% brushite and 33 wt.% monetite. The compressive stress-strain response of the scaffolds was characteristic of low-density open-cell foams with distinct linear elastic, collapse plateau and densification regimes. The elastic modulus and strength of individual struts within the scaffolds were measured using an atomic force microscopy cantilevered beam-bending technique and compared with the composite response under indentation and unconfined compression. Cellular solids models, using the measured strut properties, overestimated the overall mechanical properties for the scaffolds; the discrepancy arises from defects such as disconnected pore walls within the scaffold. As the scaffold stiffness and strength decreased with increasing overall mineral content and were less than that of natural, mineralized collagen scaffolds, these microstructural/mechanical relations will be used to further improve scaffold design for bone regeneration applications.

Cell-induced response by tetracyclines on human bone marrow colonized hydroxyapatite and Bonelike

Semi-synthetic tetracyclines are commonly used antibiotics that also seem to play an important role in the modulation of the immuno-inflammatory imbalance, verified in several bone diseases. The association of a therapeutic agent (that prevents bacterial infection and induces tissue formation) to a biomaterial aiming to repair/regenerate bone defects could contribute to a more predictable clinical outcome. The present study intends to evaluate the proliferation and functional activity of osteoblast-induced human bone marrow cells, cultured on the surface of hydroxyapatite (HA) and Bonelike, in the presence of therapeutic concentrations of doxycycline and minocycline. First passage bone marrow cells were cultured for 35 days on the surface of HA and Bonelike discs, in the absence or presence of 1 microg ml(-1) doxycycline and minocycline. Cultures performed in standard tissue culture plates were used as control. Doxycycline or minocycline induced cell proliferation and increased the extent of matrix mineralization in osteoblastic cell cultures established in the three substrates. Also, an improved biological behavior was verified in seeded Bonelike compared with HA. The results suggest that the local delivery of tetracyclines might associate the antimicrobial activity in implant-related bone infection with an eventual induction of osteoblastic proliferation and maintenance of the characteristic biological activity of these cells.

Growth and differentiation of osteoblastic cells on 13-93 bioactive glass fibers and scaffolds

This in vitro study was conducted to evaluate the ability of two types of constructs of bioactive, silica-based 13-93 glass fibers to support the growth and differentiation of MC3T3-E1 osteoblastic cells. The two types of constructs tested included single-layer 13-93 glass fiber rafts and three-dimensional porous scaffolds formed from sintered 13-93 fibers. Scanning electron micrographs showed a closely adhering, well-spread morphology of MC3T3-E1 cells seeded on both types of constructs. The scanning electron microscopy images also showed a continuous increase in cell densities during a 6 day incubation on 13-93 glass fiber rafts and scaffolds. Quantitative fluorescence measurements of DNA also revealed a linear increase in cell density during a 6 day incubation on both types of 13-93 constructs. Examination of scaffolds incubated in MTT containing medium showed the presence of metabolically active viable cells within the interior of the scaffold. The addition of ascorbic acid to MC3T3-E1 cells cultured on the 13-93 glass fibers triggered a threefold increase in alkaline phosphatase, a key indicator of osteoblast differentiation. The sintered scaffolds were found to have open, interconnected pores favorable for tissue ingrowth with a compressive strength similar to cancellous bone. Collectively, the results indicate that 13-93 glass fiber scaffolds are a favorable substrate for the growth and differentiation of osteoblasts and a promising material for bone tissue engineering and repair of bone defects.

An optimized β-tricalcium phosphate and agarose scaffold fabrication technique

Biodegradable scaffolds composed of beta-tricalcium phosphate, and a natural hydrogel, agarose, were prepared by a shaping method based on the thermal gelation of the polymeric component. This technique was modified to facilitate the inclusion, during the scaffold preparation stage, of therapeutic agents that could improve the graft performance. Vancomycin was included in materials containing different amounts of agarose and ceramic without affecting the scaffold consolidation process. These materials, easily injectable, behave like a reinforced hydrogel whose swelling behavior and drug release rate depend on their composition.

Biomimetic coating of an apatite layer on poly(L-lactic acid); improvement of adhesive strength of the coating

A biodegradable polymer coated with a bonelike apatite layer on its surface would be useful as a scaffold for bone tissue regeneration. In this study, poly(L-lactic acid) (PLLA) was treated with oxygen plasma to produce oxygen-containing functional groups on its surface. The plasma-treated specimen was then alternately dipped in aqueous CaCl(2) and K(2)HPO(4).3H(2)O solutions three times, to deposit apatite precursors onto the surface. The surface-modified specimen then successfully formed a dense and uniform bonelike surface apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. The adhesive strength between the apatite layer and the specimen surface increased as the power density of the oxygen plasma used increased. The maximum adhesive strength of the apatite layer to the specimen was significantly higher than that to the commercially available artificial bone, HAPEX. The resultant bonelike apatite-PLLA composite would be useful as a scaffold for bone tissue regeneration.

Gelatine/PLLA sponge-like scaffolds: morphological and biological characterization

Biodegradable synthetic polymers such as poly(lactic acid) (PLA) are widely used to prepare scaffolds for cell transplantation and tissue growth, using different techniques set up for the purpose. However the poor hydrophilicity of these polymers represents the main limitation to their use as scaffolds because it causes a low affinity for the cells. An effective way to solve this problem could be represented by the addition of biopolymers that are in general highly hydrophilic. The present work concerns porous biodegradable sponge-like systems based on poly(L-lactic acid) (PLLA) and gelatine. Morphology and porosity characteristics of the sponges were studied by scanning electron microscopy and mercury intrusion porosimetry respectively. Blood compatibility was investigated by bovine plasma fibrinogen (BPF) adsorption test and platelet adhesion test (PAT). The cell culture method was used in order to evaluate the ability of the matrices to work as scaffolds for tissue regeneration. The obtained results indicate that the sponges have interesting porous characteristics, good blood compatibility and above all good ability to support cell adhesion and growth. In fact viable and metabolically active animal cells were found inside the sponges after 8 weeks in culture. On this basis the systems produced seem to be good candidates as scaffolds for tissue regeneration.

Poly-L-D-Lactic Acid Scaffold in the Repair of Porcine Knee Cartilage Lesions

Articular cartilage injuries cause a major clinical problem because of the negligible repair capacity of cartilage. Autologous chondrocyte transplantation is a surgical method developed to repair cartilage lesions. In the operation, cartilage defect is covered with a periosteal patch and the suspension of cultured autologous chondrocytes is injected into the lesion site. The method can form good repair tissue, but new techniques are needed to make the operation easier and to increase the postoperative biomechanical properties of the repair tissue. In this study, we investigated poly-L,D-lactic acid (PLDLA) scaffolds alone or seeded with autologous chondrocytes in the repair of circular 6-mm cartilage lesions in immature porcine knee joints. Spontaneous repair was used as a reference. Histologic evaluation of the repair tissue showed that spontaneous repair exhibited higher scores than either PLDLA scaffold group (with or without seeded chondrocytes). The scaffold material was most often seen embedded in the subchondral bone underneath the defect area, probably because of the hardness of the PLDLA material. However, some of the cell-seeded and nonseeded scaffolds contained cartilaginous tissue, suggesting that invasion of mesenchymal cells inside nonseeded scaffolds had occurred. Hyaluronan deposited in the scaffold had possibly acted as a chemoattractant for the cell recruitment. In conclusion, the PLDLA scaffold material used in this study was obviously mechanically too hard to be used for cartilage repair in immature animals.

In vivo evaluation of a new composite mesh (10% polypropylene/90% poly-L-lactic acid) for hernia repair

The increasing use of mesh insertion for groin hernia repair is dashed by a worrying prevalence of chronic pain frequently related as a reaction to the biomaterial implantation. Thus, new biocompatible prosthesis, designed as a composite material associating polypropylene (PP) and long-term absorbable material, are now under development. In the present study, the typical commercially available Prolene mesh has been compared to two new meshes designed with 3-fold less PP, either alone (light PP) or associated with poly-L-lactic acid (PP-PLA) accounting for 90% of the mesh weight. These PP-mesh variants were implanted in an extraperitoneal position within the abdominal wall of 90 rats. Mesh adhesion and size were determined at autopsy 2, 4 and 8 weeks after implantation (10 animals per group) and morphometric parameters of the host tissues by light microscopy. Prolene and light PP-meshes presented intra-corporeal shrinkage and tissue adhesion, both more pronounced with light-PP, whilst PP-PLA meshes were not affected in spite of a strongest fibrosis. In contrast to Prolene and even more with light PP meshes, inflammation and cell-mediated immune responses were reduced without occurrence of angiogenesis or oedema. All these findings advocate together for a better tolerance of this new composite biomaterial, more likely due to a low macrophage response that appeared statistically correlated to the absence of mesh shrinkage and to a decreased adhesion to the tissue. On the basis of these experimental observations, it could be expected that the better tolerance of this composite biomaterial may avoid both long-term pain and recurrence when used as plug in groin hernia repair.

Investigation on the Biomimetic Scaffold for Bone Tissue Engineering Based on Bioglass-Collagen-Hyaluronic Acid-Phosphatidylserine

The new type of bone tissue engineering scaffold composed of the sol-gel derived bioactive glass particles, type I collagen, hyaluronic acid and phosphatidylserine were prepared through cross-linking and freeze-drying techniques. SEM observation indicated that the scaffold possessed a 3-D interconnected porous structure and a high porosity. The properties of bio-mineralization and cells biocompatibility were investigated using SBF immersion and cells culture methods combined with SEM, XRD and FTIR techniques. The study revealed that this biomimetic scaffold possessed satisfactory functions of cells attachment, bio-mineralization, and cells biocompatibility. The porous structure and the surface of the scaffold which was covered by a bone-like HA crystal layer due to bio-mineralization were profitable for cells attachment and spread.

Gelatine/PLLA sponge-like scaffolds: morphological and biological characterization

Biodegradable synthetic polymers such as poly(lactic acid) are widely used to prepare scaffolds for cell transplantation and tissue growth, using different techniques set up for the purpose. However the poor hydrophilicity of these polymers represents the main limitation to their use as scaffolds because it causes a low affinity for the cells. An effective way to solve this problem could be represented by the addition of biopolymers that are in general highly hydrophilic. The present work concerns porous biodegradable sponge-like systems based on poly(L-lactic acid) and gelatine. Morphology and porosity characteristics of the sponges were studied by scanning electron microscopy and mercury intrusion porosimetry respectively. Blood compatibility was investigated by bovine plasma fibrinogen adsorption test and platelet adhesion test. The cell culture method was used in order to evaluate the ability of the matrices to work as scaffolds for tissue regeneration. The obtained results indicate that the sponges have interesting porous characteristics, good blood compatibility and above all good ability to support cell adhesion and growth. In fact viable and metabolically active animal cells were found inside the sponges after 8 weeks in culture. On this basis the systems produced seem to be good candidates as scaffolds for tissue regeneration.

Use of polylactic acid/polytrimethylene carbonate blends membrane to prevent postoperative adhesions

The objective of the study was to evaluate the effect of a novel biodegradable membrane on the prevention of postoperative adhesion formation. The membrane was prepared by blending 50% PLA (polylactic acid) with 50% PTMC (polytrimethylene carbonate). The prepared blends polymer membrane was more flexible than pure PLA membrane, as measured by glass-transition temperature and tensile study. Cytotoxicity study revealed that PLA/PTMC blends membrane showed good biocompatibility. The membrane elicited slight tissue reaction based on the results of histological study. Thirty adult Japanese rabbits were used for the intestine adhesion model. The treatment group had PLA/PTMC membrane, the control group had chitosan, and the blank control group was not operated. The animals were housed for two weeks and sacrificed to investigate adhesion of intestine. Compared with the blank control group, the treatment group and the control group lowered the extent of adhesions (p < 0.01), but the treatment group was better than the control group (p < 0.05). The in-vivo studies confirmed that PLA/PTMC blends membrane could prevent postoperative adhesions.