poly-L/D-lactide Research Articles

Human Adipose Stem Cells Differentiated on Braided Polylactide Scaffolds Is a Potential Approach for Tendon Tissue Engineering.

Growing number of musculoskeletal defects increases the demand for engineered tendon. Our aim was to find an efficient strategy to produce tendon-like matrix in vitro. To allow efficient differentiation of human adipose stem cells (hASCs) toward tendon tissue, we tested different medium compositions, biomaterials, and scaffold structures in preliminary tests. This is the first study to report that medium supplementation with 50 ng/mL of growth and differentiation factor-5 (GDF-5) and 280 μM l-ascorbic acid are essential for tenogenic differentiation of hASCs. Tenogenic medium (TM) was shown to significantly enhance tendon-like matrix production of hASCs compared to other tested media groups. Cell adhesion, proliferation, and tenogenic differentiation of hASCs were supported on braided poly(l/d)lactide (PLA) 96l/4d copolymer filament scaffolds in TM condition compared to foamed poly(l-lactide-co-ɛ-caprolactone) (PLCL) 70L/30CL scaffolds. A uniform cell layer formed on braided PLA 96/4 scaffolds when hASCs were cultured in TM compared to maintenance medium (MM) condition after 14 days of culture. Furthermore, total collagen content and gene expression of tenogenic marker genes were significantly higher in TM condition after 2 weeks of culture. The elastic modulus of PLA 96/4 scaffold was more similar to the elastic modulus reported for native Achilles tendon. Our study showed that the optimized TM is needed for efficient and rapid in vitro tenogenic extracellular matrix production of hASCs. PLA 96/4 scaffolds together with TM significantly stimulated hASCs, thus demonstrating the potential clinical relevance of this novel and emerging approach to tendon injury treatments in the future.

Characterization of polylactides with different stereoregularity using electrospray ionization ion mobility mass spectrometry.

We investigated the effect of stereoregularity on the gas-phase conformations of linear and cyclic polylactides (PLA) using electrospray ionization ion mobility mass spectrometry (ESI-IM-MS) combined with molecular dynamics simulations. IM-MS analysis of PLA ions shows intriguing difference between the collision cross section (ΩD) value of poly-L-lactide (PLLA) and poly-LD-lactide (PLDLA) ions with respect to their chain architecture and stereoregularity. In the singly sodiated linear PLA (l-PLA∙Na(+)) case, both l-PLLA and l-PLDLA up to 11mer have very similar ΩD values, but the ΩD values of l-PLLA are greater than that of l-PLDLA ions for larger ions. In the case of cyclic PLA (c-PLA), c-PLLA∙Na(+) is more compact than c-PLDLA∙Na(+) for short PLA ions. However, c-PLLA exhibits larger ΩD value than c-PLDLA for PLA ions longer than 13mer. The origin of difference in the ΩD values was investigated using theoretical investigation of PLAs in the gas phase. The gas-phase conformation of PLA ions is influenced by Na(+)-oxygen coordination and the weak intramolecular hydrogen bond interaction, which are more effectively formed in more flexible chains. Therefore, the less flexible PLLA has a larger ΩD value than PLDLA. However, for short c-PLA, concomitant maximization of both Na(+)-oxygen coordination and hydrogen bond interaction is difficult due to the constricted chain freedom, which makes the ΩD value of PLAs in this range show a different trend compared with other PLA ions. Our study facilitates the understanding of correlation between stereoregularity of PLAs and their structure, providing potential utility of IM-MS to characterize stereoisomers of polymers.

Flexor tendon healing within the tendon sheath using bioabsorbable poly-l/d-lactide 96/4 suture. A histological in vivo study with rabbits

The bioabsorbable poly-L/D-lactide (PLDLA) 96/4 suture has good biomechanical and knot properties, and sufficient tensile strength half-life for flexor tendon repair. In the present study, the biocompatibility of PLDLA suture was compared with that of coated braided polyester suture in the rabbit flexor digitorum profundus tendon repaired within the tendon sheath. Postoperative unrestricted active mobilization was allowed. The tendons were studied histologically after 1-, 3-, 6-, 12-, 26-, and 52-week follow-ups. No differences were found in the biocompatibility between the suture materials, with only scattered multinuclear giant cells near the sutures in both groups from 6 weeks onwards. At 52 weeks, most of the PLDLA material was absorbed and the histological structure of the tendon appeared normal, whereas in the polyester repairs the suture knots filled the repair site, causing bulking of the tendon surface, and the collagen alignment appeared disoriented. The results suggest that the PLDLA 96/4 is a suitable suture material for flexor tendon repair.

Torsion test method for mechanical characterization of PLDLA 70/30 ACL interference screws

This study developed a test method for determining the mechanical properties of poly-L/D-lactide (PLDLA) 70/30 cannulated bioabsorbable anterior cruciate ligament (ACL) interference screws. We proposed a method that defines three characteristic lengths associated with the screw void space, which was designed to receive the screwdriver during insertion of the implant: (1) the clamping length Lc, (2) the screwdriver insertion length Lb, and (3) the gauge length Lg. We tested twenty completely fabricated and finished screws that had been submitted to different levels of hydrolytic degradation. In torsion tests, the variables measured were stiffness, yield torque, yield torque angle, maximum torque and maximum torque angle. These values were correlated with the fracture surface, numerical simulation and molecular weight. The results of the degradation testing, lasting from 0 to 240 days, show a clear transition in the screws' mechanical behavior from ductile to brittle. We concluded that the proposed torsion testing method is appropriate for determining the mechanical properties of cannulated polymeric screws.

Bioabsorbable poly-l/d-lactide (PLDLA) 96/4 triple-stranded bound suture in the modified Kessler repair: an ex vivo static and cyclic tensile testing study in a porcine extensor tendon model

Previously the biomechanical properties of the bioabsorbable poly-L: /D: -lactide (PLDLA) 96/4 suture were found suitable for flexor tendon repair. In this study, three PLDLA suture strands were bound together parallel to each other side-by-side to form a triple-stranded bound suture and the modified Kessler tendon repair was performed. The biomechanical properties of the PLDLA repair in porcine extensor tendons ex vivo were investigated with static and cyclic tensile testing. In both biomechanical tests, the strength of the PLDLA repair achieved the estimated forces needed to withstand active mobilization.

Bioreactor improves the growth and viability of chondrocytes in the knitted poly-L,D-lactide scaffold

In the present study bovine chondrocytes were cultured in two different environments (static flasks and bioreactor) in knitted poly-L,D-lactide (PLDLA) scaffolds up to 4 weeks. Chondrocyte viability was assessed by employing cell viability fluorescence markers. The cells were visualized using confocal laser scanning microscopy and scanning electron microscopy. The mechanical properties and uronic acid contents of the scaffolds were tested. Our results showed that cultivation in a bioreactor improved the growth and viability of the chondrocytes in the PLDLA scaffolds. Cells were observed both on and in between the fibrils of scaffold. Furthermore, chondrocytes cultured in the bioreactor, regained their original round phenotypes, whereas those in the static flask culture were flattened in shape. Confocal microscopy revealed that chondrocytes from the bioreactor were attached on both sides of the scaffold and sustained viability better during the culture period. Uronic acid contents of the scaffolds, cultured in bioreactor, were significantly higher than in those cultured in static flasks for 4 weeks. In summary, our data suggests that the bioreactor is superior over the static flask culture when culturing chondrocytes in knitted PLDLA scaffold.

Poly-L/D-lactide (PLDLA) 96/4 Fibrous Implants

Poly-L/D-lactide (PLDLA) 96/4 fibrous implants have been introduced to engineer functional fibrous constructions in situ. The current study was undertaken to evaluate the guidance of the fibrous tissue formation and the tissue reaction of porous PLDLA 96/4 scaffolds implanted in subcutaneous tissue. Three various PLDLA 96/4 knitted-mesh scaffolds (Loose, Ordinary, and Dense) were implanted subcutaneously in 32 rats, and followed-up from 3 days until 48 weeks postsurgery. Histological examination showed that PLDLA 96/4 scaffolds provided a structurally supporting element for 48 weeks. They were filled with fibrous tissue by 3 weeks. During the follow-up, loose connective tissue was organized into dense connective tissue with thick collagen bundles. At 48 weeks, no statistically significant difference was found in the amount of loose or dense connective tissue between the scaffold groups of various porosities, although the tendency for higher amounts of loose connective tissue was seen in the Loose type scaffolds. PLDLA filament diameters were 121 mum at 2 weeks, 119 mum at 24 weeks and 116 mum at 48 weeks (P = 0.03 between 2 and 48 weeks). Porous PLDLA scaffold induced fibrous tissue formation in situ. This can be exploited in engineering fibrous tissue constructs in vivo for tissue support or replacement purposes.

Histomorphometric Analysis of Poly-L/D-Lactide 96/4 Sutures in the Gastrocnemius Tendon of Rabbits

Common Achilles tendon ruptures are not usually fixed by bioabsorbable sutures due to limitations in their strength retention properties. Modern technology has made it possible to develop bioabsorbable sutures with prolonged strength retention. To evaluate histologically tissue reactions of poly-L/D-lactide (PLDLA) sutures implanted in Achilles tendon of rabbits. Fifteen rabbits were evaluated at 2, 6 and 12 weeks postoperatively, with five rabbits in each follow-up group. PLDLA monofilament sutures were implanted into the medial gastrocnemius tendon. Polyglyconate monofilament sutures with similar diameter (Maxon 4-0, Cyanamid of Great Britain Ltd., Gosport, UK) were implanted in the contralateral gastrocnemius tendon. The histology was studied in hard-resin embedded samples. The thickness of the formed fibrous tissue capsule was determined histomorphometrically. PLDLA led to formation of significantly thinner fibrous tissue capsule than Maxon sutures of the same diameter. Median thickness (PLDLA vs. Maxon) at two weeks was 5.26 vs.13.22 microm, at six weeks 11.66 vs. 80.97 microm, and at 12 weeks 10.63 vs. 17.59 microm (p<0.01). During the 12 week follow-up period, PLDLA sutures implanted intratendineously formed thinner fibrous capsule than Maxon sutures of the same diameter. The suture materials were not totally absorbed by 12 weeks.

Effect of FGF and Polylactide Scaffolds on Calvarial Bone Healing With Growth Factor on Biodegradable Polymer Scaffolds

Repair of bone defects remains a major concern in reconstructive surgery. Synthetic biodegradable polymers have been used as scaffolds for guided bone regeneration. Fibroblast growth factors (FGFs) promote cell growth, differentiation, and tissue maintenance factors. They can stimulate the proliferation of osteogenic cells and chondrocytes, and also promote angiogenesis. Acidic and basic fibroblast growth factors (FGF-1 and FGF-2, respectively) are the best known members of this protein family. To evaluate the healing of experimental bone defects using poly-L/D-lactide (PLDLA) 96/4 scaffolds and FGF-1, 18 adult rats were operated on. A 6-mm diameter critical size defect (CSD) was made in the calvarial bone of each rat. The animals were divided into three treatment groups: 1) Neither scaffold nor FGF was used (control group); 2) scaffold only; and 3) scaffold with FGF-1. Follow-up time was eight weeks. Samples were embedded in methylmethacrylate and 5-microm thick sections from the middle of each specimen were stained with modified Masson-Goldner method. The shape and size of defects were evaluated radiologically. New bone formation was measured histologically and histomorphometrically. Radiologically, in the control group the shape of the defects changed from round to oval and edges were blunt. In the other groups the defects were round with sharp edges. Histomorphometrically, mean surface area of bone trabeculae was 1.05 mm (SD +/- 0.25) in group 1 (no implant), 1.35 mm (SD +/- 0.52) in group 2 (implant) and 0.79 mm (SD +/- 0.34) in group 3 (implant and FGF-1). Histological examinations revealed no or little osteoid in the groups 1 and 2, whereas in the group 3 samples had little or moderate new bone formation. Accordingly, no clear benefit of using knitted PLDLA scaffolds combined with FGF-1 on the healing of calvarial critical size defects in rats could be demonstrated.

Material and knot properties of braided polyester (Ticron®) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures

The purpose of the present study was to investigate in vitro the biomechanical material and knot properties and histomorphometrical knot properties of 3-0 braided polyester suture (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 suture. In Ticron five throws are needed to form a secure knot, and the 1 = 1 = 1 = 1 = 1 and the 2 = 1 = 1 = 1 configurations are recommended. For PLDLA several granny and square knots formed a secure knot, but the 1 = 1 and 1 = 1 = 1 knots were the best. These PLDLA knots had lower yield force and strain at yield point, but higher stiffness than the recommended Ticron knots. The ultimate force values did not differ, but PLDLA knots had significantly higher strain at ultimate point. In the histomorphometrical analysis of the recommended knots, the PLDLA knots had a significantly smaller knot surface area than the Ticron knots. According to these results, PLDLA suture proved to be suitable for flexor tendon repair.

Microscopical Characterization of Poly‐L/D‐Lactide (PLDLA) 96/4 Sutures in the Achilles Tendon of Rabbits

Common Achilles tendon ruptures are usually not fixed by absorbable sutures due to limitations in their strength properties. Modern technology has made it possible to develop bioabsorbable sutures with prolonged strength retention. To evaluate histologically tissue reactions and biodegradation of poly‐L/D‐lactide (PLDLA) sutures implanted in Achilles tendon of rabbits. Fifteen rabbits were operated on and killed within a time schedule of 2, 6 and 12 weeks, with five rabbits in per period. PLDLA monofilament sutures (Tampere University of Technology, Tampere, Finland) were implanted inside the rabbit medial gastrocnemius tendon for biocompatibility testing. Polyglyconate (4.0) monofilament sutures (Maxon®, Cyanamid of Great Britain Ltd., Gosport, UK) with the same diameter were implanted in the contralateral tendon. The histology was studied in hard‐resin embedded samples and the thickness of the encapsule membrane was determined histomorphometrically.PLDLA have significantly smaller capsule formation around each fiber in tendon than Maxon® sutures. The mean capsule thicknesses around PLDLA sutures was 5.26, 11.66, and 10.63 after 2, 6, and 12 weeks respectively. The mean capsule thicknesses around Maxon® sutures was 13.22, 80.97, and 17.59 after 2, 6, and 12 weeks, respectively. In conclusion, by 12 weeks the PLDLA sutures implanted intratendineously formed thinner fibrous capsule than Maxon® sutures of same diameter. The suture materials were not degraded by 12 weeks.Acknowledgments: Research funds from the Technology Development Center in Finland (TEKES, Biowaffle Project 40274/03 and MFM Project 424/31/04), the European Commission (EU Spare Parts Project QLK6‐CT‐2000‐00487), the Academy of Finland (Project 73948) and the Ministry of Education (Graduate School of Biomaterials and Tissue Engineering) are greatly appreciated.

Comparison of strength properties of poly-L/D-lactide (PLDLA) 96/4 and polyglyconate (Maxon�) sutures:In vitro, in the subcutis, and in the achilles tendon of rabbits

Achilles tendon rupture is a common injury. Absorbable sutures are not commonly used because of their limited strength properties. Recently, sutures with prolonged strength retention properties have been developed. The aim of the study is to test the mechanical properties of recently developed poly-L/D-lactide (PLDLA) sutures in comparison with polyglyconate (Maxon) sutures. PLDLA (0.2 mm thick) and Maxon (4.0) sutures were studied in vitro by immersion in a buffered saline solution (pH 7.4). Tensile strength tests were done on sutures retrieved after 1-26 weeks. In vivo, they were implanted in the subcutis of 32 rabbits. Tensile strength tests were done on sutures retrieved after 1-6 weeks. The sutures were also used to repair the Achilles tendon in rabbits. Maximum force before breaking and percentage elongation of tendons were determined. Although PLDLA had a lower initial tensile strength than Maxon, PLDLA showed more prolonged tensile strength retention than Maxon. Tendons repaired with PLDLA, however, had a lower strength than Maxon-repaired tendons at six weeks (insignificant difference). PLDLA has more prolonged tensile strength properties compared with Maxon. Thus, PLDLA offers an alternative to Maxon in repair of the Achilles tendon.

Fibrous wound repair associated with biodegradable poly-L/D-lactide copolymer implants: study of the expression of tenascin and cellular fibronectin.

Extracellular matrix (ECM) proteins are known to play a role in inflammatory and hyperplastic processes. Our aim in the present study was to study the distribution of tenascin (Tn), cellular fibronectins (cFn) and myofibroblasts around biodegradable poly-L/D-lactide (PLA) implants with monoclonal antibodies (MAb). Ethylene-oxide and gamma-irradiation sterilized PLA plate-type implants were inserted into the dorsal subcutaneous tissue of ten adult rabbits. Follow-up times were 4, 12, 16, 36 and 48 wk. Only some inflammatory cells were observed. In electron microscopy, a close coherence between the implant and the stromal tissue was seen. Immunoreactivity for Tn, cFn and alpha-actin was detected as a distinct layer bordering the implant, regardless of the sterilization method for the first 36 wk. From week 36 onwards, Tn immunoreactivity was downregulated while cFn immunoreactivity still persisted. A moderate upregulation for myofibroblasts was seen on the week 48 specimens, when hydrolysation of PLA implant had started. The persistent content of myofibroblasts, Tn and cFn suggests a prolonged wound healing produced by PLA implants. The absence of Tn at the week 48 specimens suggests that cFn, rather than Tn may be needed for alpha-actin-mediated contraction by myofibroblasts.