Biodegradable Polyglycolic Acid Research Articles

High melt viscosity, low yellowing, strengthened and toughened biodegradable polyglycolic acid via chain extension of aliphatic diisocyanate and epoxy oligomer

Poly(glycolic acid) (PGA) is a biodegradable plastic with excellent degradation rate, barrier properties, and heat resistance. However, its low melt viscosity and narrow processing temperature severely limit its application. To overcome these drawbacks, the aromatic diisocyanates TDI and MDI, aliphatic diisocyanate HDI, and multifunctional epoxy oligomer ADR were used as the chain extender to modify PGA. The PGA/HDI shows a faster chain extension reaction rate and significantly less yellowing than PGA/TDI or PGA/MDI. The combined use of HDI and ADR to modify PGA can produce long chain branched/crosslinked structures, resulting in a significant increase in melt viscosity, with complex viscosity two orders of magnitude higher than that of pure PGA and minimal yellowing. The T-5% of PGA/HDI/ADR is 45 °C higher than that of pure PGA, and its crystallization temperature, crystallization rate and melting temperature are significantly decreased, suggesting that it has a wider processing temperature window. Moreover, the tensile and flexural strength of PGA/HDI/ADR are 113.8 MPa and 216.8 MPa, respectively, an increase of 25% and 26% over pure PGA, while the elongation at break and impact strength increase to 9.5% and 11.6 KJ/m2, respectively, 42% and 176% higher than pure PGA.

Facile synthesis of Cu@Ag/SiO2 catalysts for the selective hydrogenation of dimethyl oxalate to methyl glycolate

A promising route for producing biodegradable polyglycolic acid material from syngas has garnered increasing attentions. In this route, one of the pivotal issues is developing favorable catalysts for semi-hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG). Silver catalysts were reported to be effective but suffered from the high cost. Herein, we prepared small-sized Cu@Ag/SiO2 catalysts with appropriate Ag/Cu ratios by a facile wet impregnation method. This core–shell structure facilitated the intermetallic electronic transference from Cu to Ag. The surface exposure of electron-rich silver species could promote the catalytic activity and MG desorption in the DMO hydrogenation, which achieved high efficiency without compromising the MG selectivity. The optimal catalyst with Ag/Cu mass ratio of 3/2 displayed excellent space time yield towards MG of 47.3 g·gAg−1·h−1. These insights could offer a potential strategy to reduce the silver-based catalyst cost for the semi-hydrogenation of DMO to MG.

Effective preparation of environmentally friendly polyglycolic acid (PGA) nanofibrous membrane with antibacterial property for high-efficiency and low-resistance air filtration

In recent years, the antibacterial air filters have been crucial for protecting human health. However, most commercial filters are made of non-biodegradable petroleum polymers, which poses a great challenge for environment protection of recycling after large-scale use. Hence, the air filtration membrane, biodegradable polyglycolic acid loaded with antibacterial ε-polylysine-dialdehyde microcrystalline celluloses (PGA@EPL-DAMCs), was prepared by electrospinning. The incorporation of EPL-DAMCs varied the morphology of the resultant PGA@EPL-DAMCs and endowed them with good antibacterial activity. In addition, it was found that the PGA/EPL-DAMC-24% exhibited the best filtration efficiency (99.83%) and bacterial rate (up to 99.97% and 99.99% for E.coli and S.aureus, respectively). Finally, the degradation performance of the PGA electrospun membrane was also investigated, indicating that PGA@EPL-DAMCs composite nanofiber membranes had broad prospects in biodegradable filtration material, can be applied to develop biodegradable and environmentally friendly medical protective materials with highly efficient air filtration and significant antimicrobial effects.

Development of Three-Dimensional (3D) Biodegradable Polyglycolic Acid Fiber (PGA) Preforms for Scaffold Applications: Experimental Patterning and Fiber Volume Fraction-Porosity Modeling Study.

Three-dimensional (3D) biodegradable polyglycolic acid fiber (PGA) preforms were developed as temporary scaffolds for three-dimensional tissue regeneration applications. Three-dimensional biodegradable polyglycolic acid fiber (PGA) preforms including various degrees of interlaced structures called 3D plain, semi-interlaced, and orthogonal woven preforms were designed. Analytical relations and finite element model-based software (TexGen) on fiber volume fraction and porosity fraction were proposed to predict scaffolds' stiffness and strength properties considering micromechanics relations. It was revealed that yarn-to-yarn space, density, and angles of all 3D PGA fiber preforms were heterogeneous and demonstrated direction-dependent features (anisotropy). Total fiber volume fractions (Vfp) and porosity fraction (Vtpr) predicted by analytic and numerical modelling of all 3D scaffolds showed some deviations compared to the measured values. This was because yarn cross-sections in the scaffolds were changed from ideal circular yarn (fiber TOW) geometry to high-order ellipse (lenticular) due to inter-fiber pressure generated under a tensile-based macrostress environment during preform formation. Z-yarn modulus (Ez-yarn) and strength (σz-yarn) were probably critical values due to strong stiffness and strength in the through-the-thickness direction where hydrogel modulus and strengths were negligibly small. Morphology of the scaffold showed that PGA fiber sets in the preform were locally distorted, and they appeared as inconsistent and inhomogeneous continuous fiber forms. Additionally, various porosity shapes in the preform based on the virtual model featured complex shapes from nearly trapezoidal beams to partial or concave rectangular beams and ellipsoid rectangular cylinders. It was concluded that 3D polyglycolic acid fiber preforms could be a temporary supportive substrate for 3D tissue regeneration because cells in the scaffold's thickness can grow via through-the-thickness fiber (z-yarn), including various possible mechanobiology mechanisms.

Additive manufacture of PCL/nHA scaffolds reinforced with biodegradable continuous Fibers: Mechanical Properties, in-vitro degradation Profile, and cell study

In this study, an innovative method of “in-situ impregnation” was implemented in the Fused Deposition Modeling (FDM) process to produce poly (∊‐caprolactone) (PCL) scaffolds with enhanced mechanical and biological properties utilizing continuous biodegradable polyglycolic acid (PGA) suture yarns. The study aimed to introduce composite scaffolds, having a nominal porosity of 60% and 0°/60°/120° fibers layout, with tunable mechanical and biological properties for tissue engineering applications. Three different fiber volume contents (15, 25, and 35 vol%) were successfully embedded in the specimens during printing. To enhance the compressive properties, nano‐hydroxyapatite (nHA) was added to the PCL matrix in three levels (0, 10, and 20 wt%). Degradation behaviors of both tensile and compression specimens were also assessed in DMEM and Sörensen buffer. The biological properties of the scaffolds, including surface morphology, biocompatibility, and cell adhesion, were also evaluated. According to the results, incorporating the PGA fibers and nHA particles remarkably enhanced mechanical properties, degradation, and cell adhesion. Also, the composite scaffolds exhibited superior water uptake and hydrophilicity compared to the non-reinforced ones. The results suggest that the introduced 3D printed composite can be produced as a suitable material for bone tissue engineering and resorbable barrier membrane with the desired properties.

Application of self-healing, swellable and biodegradable polymers for wound treatment.

Self-healing, swellable and biodegradable polymers are vital materials that may facilitate the different stages of wound healing. The aim of this research was to prepare wound healing films using self-healing polyvinyl alcohol (PVA), swellable hydroxypropyl methylcellulose (HPMC), biodegradable polyglycolic acid (PGA) sutures and ciprofloxacin antibiotic for improved treatment outcome. Films were formulated through aqueous-based mixing of varying amounts of polyvinyl alcohol (10-20% weight/weight (w/w)) and hydroxypropyl methylcellulose (0.5, 1% w/w) with fixed quantities of ciprofloxacin. PGA sutures were placed as grids within the wet mixtures of the polymers and ciprofloxacin, and thereafter products were air dried. The formulated films were evaluated for swelling ratio, breaking elongation, folding endurance, moisture uptake and loss, compatibility and in vitro antibiotic release. Furthermore, in vivo wound healing was studied using excision model and histopathological examinations. Swelling ratios were above 1.0 and the films were minimally stretchable, with folding endurance greater than 500. Films were stable while moisture uptake and loss were observed to be less than 30%. Among the optimised hydrogel batches, those containing 10% w/w PVA and 1% w/w HPMC with no PGA showed the highest drug release of 73%, whereas the batches with higher PGA content showed higher percentage wound size reduction with minimal scar. The completeness of wound healing with batches containing PVA, HPMC, ciprofloxacin and PGA, along with the standard, is evident considering the massive cornification, regeneration of the epithelial front and stratum spinosum. The findings show that polymer-based multifunctional composite films are suitable for use as dressings for improved wound healing.

Capsid-like biodegradable poly-glycolic acid nanoparticles for a long-time release of nucleic acid molecules

Capsid-like PGA nanoparticles (NPs) allow sustained cell transfection in 2D and 3D configurations.

Xenogeneic-free generation of vascular smooth muscle cells from human induced pluripotent stem cells for vascular tissue engineering

Development of mechanically advanced tissue-engineered vascular grafts (TEVGs) from human induced pluripotent stem cell (hiPSC)-derived vascular smooth muscle cells (hiPSC-VSMCs) offers an innovative approach to replace or bypass diseased blood vessels. To move current hiPSC-TEVGs toward clinical application, it is essential to obtain hiPSC-VSMC-derived tissues under xenogeneic-free conditions, meaning without the use of any animal-derived reagents. Many approaches in VSMC differentiation of hiPSCs have been reported, although a xenogeneic-free method for generating hiPSC-VSMCs suitable for vascular tissue engineering has yet to be established. Based on our previously established standard method of xenogeneic VSMC differentiation, we have replaced all animal-derived reagents with functional counterparts of human origin and successfully derived functional xenogeneic-free hiPSC-VSMCs (XF-hiPSC-VSMCs). Next, our group developed tissue rings via cellular self-assembly from XF-hiPSC-VSMCs, which exhibited comparable mechanical strength to those developed from xenogeneic hiPSC-VSMCs. Moreover, by seeding XF-hiPSC-VSMCs onto biodegradable polyglycolic acid (PGA) scaffolds, we generated engineered vascular tissues presenting effective collagen deposition which were suitable for implantation into an immunodeficient mice model. In conclusion, our xenogeneic-free conditions for generating hiPSC-VSMCs produce cells with the comparable capacity for vascular tissue engineering as standard xenogeneic protocols, thereby moving the hiPSC-TEVG technology one step closer to safe and efficacious clinical translation.

"Smart" Antimicrobial Nanocomplexes with Potential to Decrease Surgical Site Infections (SSI).

The emergence of resistant pathogens is a burden on mankind and threatens the existence of our species. Natural and plant-derived antimicrobial agents need to be developed in the race against antibiotic resistance. Nanotechnology is a promising approach with a variety of products. Biosynthesized silver nanoparticles (AgNP) have good antimicrobial activity. We prepared AgNPs with trans-cinnamic acid (TCA) and povidone–iodine (PI) with increased antimicrobial activity. We synthesized also AgNPs with natural cinnamon bark extract (Cinn) in combination with PI and coated biodegradable Polyglycolic Acid (PGA) sutures with the new materials separately. These compounds (TCA-AgNP, TCA-AgNP-PI, Cinn-AgNP, and Cinn-AgNP-PI) and their dip-coated PGA sutures were tested against 10 reference strains of microorganisms and five antibiotics by zone inhibition with disc- and agar-well-diffusion methods. The new compounds TCA-AgNP-PI and Cinn-AgNP-PI are broad spectrum microbicidal agents and therefore potential coating materials for sutures to prevent Surgical Site Infections (SSI). TCA-AgNP-PI inhibits the studied pathogens stronger than Cinn-AgNP-PI in-vitro and on coated sutures. Dynamic light scattering (DLS), ultraviolet-visible spectroscopy (UV-Vis), Fourier Transform infrared spectroscopy (FT-IR), Raman, X-ray diffraction (XRD), microstructural analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirmed the composition of TCA-AgNP-PI and Cinn-AgNP-PI. Smart solutions involving hybrid materials based on synergistic antimicrobial action have promising future perspectives to combat resistant microorganisms.

Generating strong vascular grafts

Vascular Biology When treating injury or vascular disease, autologous or synthetic grafts are useful, but supplies are limited and often suboptimal. Robust tissue-engineered vascular grafts (TEVGs), particularly ones that can withstand mechanical stress, are highly desirable. Luo et al. generated vascular smooth muscle cells from human induced pluripotent stem cells and cultured them on biodegradable polyglycolic acid scaffolds exposed to pulsatile radial stress. When implanted into rats, these TEVGs showed high mechanical strength with no dilation, elongation, or wall thickening. Moreover, the TEVGs associated with limited thrombosis and showed no teratoma formation. Further optimization and engineering to limit immune rejection should provide cells and tissues suitable for treating injury or dysfunction of the cardiovascular system. Cell Stem Cell 26 , 251 (2020).

3D printed PCL scaffold reinforced with continuous biodegradable fiber yarn: A study on mechanical and cell viability properties

In this study, poly (ε‐caprolactone) (PCL) scaffolds were printed and reinforced, simultaneously, with biodegradable poly glycolic acid (PGA) suture yarn, as a continuous reinforcing fiber, in the Fused Deposition Modeling (FDM) 3D printing process. Albeit PCL is a suitable material for biomedical applications, its low mechanical properties, and low degradation rate have limited its usage. A biocompatible suture yarn was used as the reinforcing material to enhance the mechanical properties and biodegradation characteristics, via an innovative method of continuous fiber embedding in the FDM process. The reinforced PCL samples were 3D printed with the setting porosity value of 60% and 0°/60°/120° lay-down pattern. The mechanical and biological properties of the scaffolds were tested to prove the effectiveness of the produced scaffolds for bone substitute purposes. Mechanical properties assessments showed that with a 22 vol.% suture yarn content in the 3D printed PCL scaffolds, the tensile strength, and elastic modulus remarkably increased up to 374% and 775%, respectively. The degradation of the reinforced PCL was 20 times higher than that of the non-reinforced PCL samples, after ten weeks, dominated by the fiber degradation phenomenon. After three days of cell culture, the proliferation assay of the built scaffovd the non-toxicity of the reinforced PCL.

Polyglycolic acid copolymers from one‐step cationic polymerization of formaldehyde, carbon monoxide, and epoxides derived from PEG

Biodegradable polyglycolic acid (PGA) is conventionally produced via the ring‐opening polymerization of glycolide, the cyclic dimer form of glycolic acid, in the presence of mostly tin‐based catalyst initiators which are rather known to be cytotoxic materials. Our previous studies revealed an alternative method for the synthesis of PGA from the perfectly alternating copolymerization of formaldehyde (from trioxane) and carbon monoxide (CO) under BrØnsted acidic conditions. The poor physical properties of PGA (insolubility in many organic solvents, brown color, etc.) limit its use in other marketing applications in the industry. To improve on the physical properties of PGA, such as solubility and appearance, copolymerization of trioxane, CO, and a minor amount of epoxides derived from polyethylene glycol (PEG) were performed under the same reaction conditions for PGA synthesis (in DCM, at 800 psi CO pressure, with triflic acid catalyst, reaction duration of 72 hours). The results have shown that the addition of minor quantities of epoxide comonomers vastly improves the appearance of the obtained PGA copolymers and allows for the control of the polymeric properties, such as solubility and melting temperature.

Alternative Approach for Synthesizing Polyglycolic Acid Copolymers from C1 Feedstocks and Fatty Ester Epoxides

Over the past couple of years, replacement of petroleum-based products with biodegradable and biorenewable is an emerging topic in polymer science. Biodegradable polyglycolic acid (PGA), the simplest aliphatic linear polyester, can traditionally be synthesized through the ring-opening polymerization of glycolide. Our previous studies revealed that PGA can alternatively be produced via one-step cationic polymerization of formaldehyde from trioxane and carbon monoxide (CO), which are potentially sustainable C1 feedstocks, under Bronsted acidic conditions. In this study, trioxane, CO, and a minor amount of fatty ester epoxides are copolymerized to improve on the physical properties of PGA, such as solubility and appearance, under the same reaction conditions for PGA homopolymer synthesis (in DCM, at 800 psi CO, with triflic acid catalyst, reaction duration of 72 h). The results have shown that the addition of minor quantities of epoxide comonomers vastly improved the solubility and decreased the melting temp...

Safety and durability of the biodegradable felt in aortic surgery: a propensity score-matched study.

Suture line disruption is a serious complication after aortic surgery. We previously reported in a canine model that basic fibroblast growth factor-incorporated biodegradable polyglycolic acid (PGA) felt prevented tissue derangement at the anastomotic site. This study sought to evaluate the safety and durability of this biodegradable felt. Between January 2007 and December 2011, 67 patients who consented to undergo aortic surgery with the basic fibroblast growth factor-incorporated PGA felt were enrolled (Group P). As a control, we retrospectively reviewed the charts of 129 patients who underwent aortic surgery using a polytetrafluoroethylene felt during the same registration period (Group N). On the basis of 18 preoperative covariates, 60 well-matched patient pairs were identified using propensity matching, and their clinical indices were compared. Among the matched pairs, in-hospital mortality and postoperative complication rates did not statistically differ between the groups. During a median follow-up of 4.8 years, the rate of anastomotic aneurysm was 1.7% (1 patient) in both groups. The rates of overall survival and freedom from aortic events did not differ between the groups. In total, 65 anastomoses in Group P and 54 anastomoses in Group N were monitored via computed tomography, and the diameters of the juxta-anastomotic sites in Group N were more likely to be increased than those in Group P {dilatation ratio [(post-discharge diameter - predischarge diameter)/predischarge diameter × 100 (%)]: 4.3% ± 0.6% vs 2.5% ± 0.5%, P = 0.01}. The basic fibroblast growth factor-incorporated PGA felt was as safe and durable as conventional felt for reinforcement in aortic surgery. The attenuation of juxta-anastomotic aortic dilatation by PGA felt reinforcement may provide more beneficial effects on long-term outcomes.

Vascular smooth muscle cells derived from inbred swine induced pluripotent stem cells for vascular tissue engineering.

Development of autologous tissue-engineered vascular constructs using vascular smooth muscle cells (VSMCs) derived from human induced pluripotent stem cells (iPSCs) holds great potential in treating patients with vascular disease. However, preclinical, large animal iPSC-based cellular and tissue models are required to evaluate safety and efficacy prior to clinical application. Herein, swine iPSC (siPSC) lines were established by introducing doxycycline-inducible reprogramming factors into fetal fibroblasts from a line of inbred Massachusetts General Hospital miniature swine that accept tissue and organ transplants without immunosuppression within the line. Highly enriched, functional VSMCs were derived from siPSCs based on addition of ascorbic acid and inactivation of reprogramming factor via doxycycline withdrawal. Moreover, siPSC-VSMCs seeded onto biodegradable polyglycolic acid (PGA) scaffolds readily formed vascular tissues, which were implanted subcutaneously into immunodeficient mice and showed further maturation revealed by expression of the mature VSMC marker, smooth muscle myosin heavy chain. Finally, using a robust cellular self-assembly approach, we developed 3D scaffold-free tissue rings from siPSC-VSMCs that showed comparable mechanical properties and contractile function to those developed from swine primary VSMCs. These engineered vascular constructs, prepared from doxycycline-inducible inbred siPSCs, offer new opportunities for preclinical investigation of autologous human iPSC-based vascular tissues for patient treatment.

Tissue engineering a human phalanx.

A principal purpose of tissue engineering is the augmentation, repair or replacement of diseased or injured human tissue. This study was undertaken to determine whether human biopsies as a cell source could be utilized for successful engineering of human phalanges consisting of both bone and cartilage. This paper reports the use of cadaveric human chondrocytes and periosteum as a model for the development of phalanx constructs. Two factors, osteogenic protein-1 [OP-1/bone morphogenetic protein-7 (BMP7)], alone or combined with insulin-like growth factor (IGF-1), were examined for their potential enhancement of chondrocytes and their secreted extracellular matrices. Design of the study included culture of chondrocytes and periosteum on biodegradable polyglycolic acid (PGA) and poly-l-lactic acid (PLLA)-poly-ε-caprolactone (PCL) scaffolds and subsequent implantation in athymic nu/nu (nude) mice for 5, 20, 40 and 60weeks. Engineered constructs retrieved from mice were characterized with regard to genotype and phenotype as a function of developmental (implantation) time. Assessments included gross observation, X-ray radiography or microcomputed tomography, histology and gene expression. The resulting data showed that human cell-scaffold constructs could be successfully developed over 60weeks, despite variability in donor age. Cartilage formation of the distal phalanx models enhanced with both OP-1 and IGF-1 yielded more cells and extracellular matrix (collagen and proteoglycans) than control chondrocytes without added factors. Summary data demonstrated that human distal phalanx models utilizing cadaveric chondrocytes and periosteum were successfully fabricated and OP-1 and OP-1/IGF-1 accelerated construct development and mineralization. The results suggest that similar engineering and transplantation of human autologous tissues in patients are clinically feasible. Copyright © 2016 John Wiley & Sons, Ltd.

Polyglycolic acid microneedles modified with inkjet-deposited antifungal coatings.

In this study, the authors examined use of piezoelectric inkjet printing to apply an antifungal agent, voriconazole, to the surfaces of biodegradable polyglycolic acid microneedles. Polyglycolic acid microneedles with sharp tips (average tip radius = 25 ± 3 μm) were prepared using a combination of injection molding and drawing lithography. The elastic modulus (9.9 ± 0.3 GPa) and hardness (588.2 ± 33.8 MPa) values of the polyglycolic acid material were determined using nanoindentation and were found to be suitable for use in transdermal drug delivery devices. Voriconazole was deposited onto the polyglycolic acid microneedles by means of piezoelectric inkjet printing. It should be noted that voriconazole has poor solubility in water; however, it is readily soluble in many organic solvents. Optical imaging, scanning electron microscopy, energy dispersive x-ray spectrometry, and Fourier transform infrared spectroscopy were utilized to examine the microneedle geometries and inkjet-deposited surface coatings. Furthermore, an in vitro agar plating study was performed on the unmodified, vehicle-modified, and voriconazole-modified microneedles. Unlike the unmodified and vehicle-modified microneedles, the voriconazole-modified microneedles showed antifungal activity against Candida albicans. The unmodified, vehicle-modified, and voriconazole-modified microneedles did not show activity against Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus. The results indicate that piezoelectric inkjet printing may be useful for loading transdermal drug delivery devices such as polyglycolic acid microneedles with antifungal pharmacologic agents and other pharmacologic agents with poor solubility in aqueous solutions.

Cartilage constructs engineered from chondrocytes overexpressing IGF-I improve the repair of osteochondral defects in a rabbit model

Tissue engineering combined with gene therapy is a promising approach for promoting articular cartilage repair. Here, we tested the hypothesis that engineered cartilage with chondrocytes overexpressing a human insulin-like growth factor I (IGF-I) gene can enhance the repair of osteochondral defects, in a manner dependent on the duration of cultivation. Genetically modified chondrocytes were cultured on biodegradable polyglycolic acid scaffolds in dynamic flow rotating bioreactors for either 10 or 28 d. The resulting cartilaginous constructs were implanted into osteochondral defects in rabbit knee joints. After 28 weeks of in vivo implantation, immunoreactivity to ß-gal was detectable in the repair tissue of defects that received lacZ constructs. Engineered cartilaginous constructs based on IGF-I-overexpressing chondrocytes markedly improved osteochondral repair compared with control (lacZ) constructs. Moreover, IGF-I constructs cultivated for 28d in vitro significantly promoted osteochondral repair vis-à-vis similar constructs cultivated for 10d, leading to significantly decreased osteoarthritic changes in the cartilage adjacent to the defects. Hence, the combination of spatially defined overexpression of human IGF-I within a tissue-engineered construct and prolonged bioreactor cultivation resulted in most enhanced articular cartilage repair and reduction of osteoarthritic changes in the cartilage adjacent to the defect. Such genetically enhanced tissue engineering provides a versatile tool to evaluate potential therapeutic genes in vivo and to improve our comprehension of the development of the repair tissue within articular cartilage defects. Insights gained with additional exploration using this model may lead to more effective treatment options for acute cartilage defects.

Medial Regeneration Using a Biodegradable Felt as a Scaffold Preserves Integrity and Compliance of a Canine Dissected Aorta

Repair of a dissected aorta involves reattaching the media with synthetic glue and/or reinforcement with nonbiodegradable felt. Late complications specific to each aspect of this procedure have been reported. We attempted to regenerate the media by using biodegradable felt. We created a canine model of descending thoracic aortic dissection and compared 4 modes of aortic repair: biodegradable polyglycolic acid (PGA) felt in the media; PGA with basic fibroblast growth factor (bFGF) in the media; PGA with bFGF in the media plus external reinforcement with expanded polytetrafluoroethylene; and primary suture closure of the dissected lumen (control). Repaired aortic stumps were quantitatively tested for suture pull-out strength. Failure force improved 4-fold in all 3 medial reinforcement groups compared with controls. Additionally, animals were kept alive for histological examination and compliance testing 6 months after repair. Compliance of the aortic wall at the anastomotic sites was not essentially affected in the long term except in the group with concomitant external reinforcement (55.9 ± 4.5% reduction; P<0.05). In this group, elastic fiber in the media and collagen fiber in the adventitia tended to diminish relative to the other groups. Regarding vessel density in the repaired false lumen, this external reinforced group had a significantly decreased number. Histological derangement was not observed in control or medial reinforcement groups. Basic FGF, applied with PGA in the dissected lumen, failed to yield additional modifications in this model. Medial reinforcement provides sufficient augmented strength for aortic surgical repair. Medial regeneration using biodegradable felt as a scaffold preserves histological integrity and compliance in the canine dissected aorta.

Modification of the descending thoracic aortic anastomotic site using biodegradable felt: Study in a canine model with or without basic fibroblast growth factor

We investigated the outcomes of reinforcing anastomotic sites using (1) nonbiodegradable polytetrafluoroethylene (PTFE) felt, (2) biodegradable polyglycolic acid (PGA) felt, and (3) PGA felt with basic fibroblast growth factor (bFGF) in a canine descending thoracic aortic replacement model. Thirty-seven beagles underwent descending thoracic aorta replacement using a prosthetic graft with one of the above-mentioned reinforcements or no reinforcement for controls. Histologic evaluations were carried out 1 month and 3 months after surgery. The biomechanical strength of the anastomosis was assessed along the longitudinal axis of the aortic segments using a tensile tester. Local compliance at the anastomotic site was also evaluated in the circumferential direction. The media was significantly thinner in the PTFE group than in the control group (65.8% +/- 5.1% vs 95.0% +/- 9.3% of normal thickness; P < .05). Relative to the control group, the adventitial layer was significantly thinner in the PTFE group (42.3% +/- 8.2% of control; P < .05) but significantly thicker in the PGA and the PGA + bFGF groups (117.2% +/- 11.3% and 134.1% +/- 14.2% of control, respectively; P < .05). There were more vessels in the adventitial layer in the PGA + bFGF group than in the control, PTFE, and PGA groups (29.2 +/- 2.1/mm(2) vs 13.8 +/- 0.8, 5.4 +/- 0.7, 17.0 +/- 1.3/mm(2), respectively; P < .01). There were no significant differences between the four groups in the failure force at anastomotic sites. Local compliance at the anastomotic site was higher in the PGA group than that in the PTFE group (11.6 +/- 1.6 10(-6) m(2)/N vs 5.6 +/- 1.9 10(-6) m(2)/N; P < .05). Reinforcement of the experimental aortic wall with PTFE felt resulted in thinning of the media and adventitia and fewer vessels at the anastomotic site. These histologic changes were not observed when biodegradable felt was used. The bFGF failed to augment the modification of the aortic wall with the exception of increased adventitial vessel number. Biomechanical strength of the anastomosis along the longitudinal axis was comparable in all four groups; however, local vascular compliance was better in the biodegradable PGA felt group.