Kazuro L. Fujimoto

Synthesis, characterization and therapeutic efficacy of a biodegradable, thermoresponsive hydrogel designed for application in chronic infarcted myocardium.

Injection of a bulking material into the ventricular wall has been proposed as a therapy to prevent progressive adverse remodeling due to high wall stresses that develop after myocardial infarction. Our objective was to design, synthesize and characterize a biodegradable, thermoresponsive hydrogel for this application based on copolymerization of N-isopropylacrylamide (NIPAAm), acrylic acid (AAc) and hydroxyethyl methacrylate-poly(trimethylene carbonate) (HEMAPTMC). By evaluating a range of monomer ratios, poly(NIPAAm-co-AAc-co-HEMAPTMC) at a feed ratio of 86/4/10 was shown to be ideal since it formed a hydrogel at 37 degrees C, and gradually became soluble over a 5 month period in vitro through hydrolytic cleavage of the PTMC residues. HEMAPTMC, copolymer and degradation product chemical structures were verified by NMR. No degradation product cytotoxicity was observed in vitro. In a rat chronic infarction model, the infarcted left ventricular (LV) wall was injected with the hydrogel or phosphate buffered saline (PBS). In the PBS group, LV cavity area increased and contractility decreased at 8 wk (p<0.05 versus pre-injection), while in the hydrogel group both parameters were preserved during this period. Tissue ingrowth was observed in the hydrogel injected area and a thicker LV wall and higher capillary density were found for the hydrogel versus PBS group. Smooth muscle cells with contractile phenotype were also identified in the hydrogel injected LV wall. The designed poly(NIPAAm-co-AAc-co-HEMAPTMC) hydrogel of this report may thus offer an attractive biomaterial-centered treatment option for ischemic cardiomyopathy.

Intra-myocardial biomaterial injection therapy in the treatment of heart failure: Materials, outcomes and challenges.

Heart failure initiated by coronary artery disease and myocardial infarction (MI) is a widespread, debilitating condition for which there are a limited number of options to prevent disease progression. Intra-myocardial biomaterial injection following MI theoretically provides a means to reduce the stresses experienced by the infarcted ventricular wall, which may alter the pathological remodeling process in a positive manner. Furthermore, biomaterial injection provides an opportunity to concurrently introduce cellular components and depots of bioactive agents. Biologically derived, synthetic and hybrid materials have been applied, as well as materials designed expressly for this purpose, although optimal design parameters, including degradation rate and profile, injectability, elastic modulus and various possible bioactivities, largely remain to be elucidated. This review seeks to summarize the current body of growing literature where biomaterial injection, with and without concurrent pharmaceutical or cellular delivery, has been pursued to improve functional outcomes following MI. The literature to date generally demonstrates acute functional benefits associated with biomaterial injection therapy across a broad variety of animal models and material compositions. Further functional improvements have been reported when cellular or pharmaceutical agents have been incorporated into the delivery system. Despite these encouraging early results, the specific mechanisms behind the observed functional improvements remain to be fully explored and future studies employing hypothesis-driven material design and selection may increase the potential of this approach to alleviate the morbidity and mortality of heart failure.

Tailoring the degradation kinetics of poly(ester carbonate urethane)urea thermoplastic elastomers for tissue engineering scaffolds

Biodegradable elastomeric scaffolds are of increasing interest for applications in soft tissue repair and regeneration, particularly in mechanically active settings. The rate at which such a scaffold should degrade for optimal outcomes, however, is not generally known and the ability to select from similar scaffolds that vary in degradation behavior to allow such optimization is limited. Our objective was to synthesize a family of biodegradable polyurethane elastomers where partial substitution of polyester segments with polycarbonate segments in the polymer backbone would lead to slower degradation behavior. Specifically, we synthesized poly(ester carbonate)urethane ureas (PECUUs) using a blended soft segment of poly(caprolactone) (PCL) and poly(1,6-hexamethylene carbonate) (PHC), a 1,4-diisocyanatobutane hard segment and chain extension with putrescine. Soft segment PCL/PHC molar ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 were investigated. Polymer tensile strengths varied from 14 to 34 MPa with breaking strains of 660-875%, initial moduli of 8-24 MPa and 100% recovery after 10% strain. Increased PHC content was associated with softer, more distensible films. Scaffolds produced by salt leaching supported smooth muscle cell adhesion and growth in vitro. PECUU in aqueous buffer in vitro and subcutaneous implants in rats of PECUU scaffolds showed degradation slower than comparable poly(ester urethane)urea and faster than poly(carbonate urethane)urea. These slower degrading thermoplastic polyurethanes provide opportunities to investigate the role of relative degradation rates for mechanically supportive scaffolds in a variety of soft tissue repair and reconstructive procedures.

Generating Elastic, Biodegradable Polyurethane/Poly(lactide-co-glycolide) Fibrous Sheets with Controlled Antibiotic Release via Two-Stream Electrospinning

Damage control laparotomy is commonly applied to prevent compartment syndrome following trauma but is associated with new risks to the tissue, including infection. To address the need for biomaterials to improve abdominal laparotomy management, we fabricated an elastic, fibrous composite sheet with two distinct submicrometer fiber populations: biodegradable poly(ester urethane) urea (PEUU) and poly(lactide-co-glycolide) (PLGA), where the PLGA was loaded with the antibiotic tetracycline hydrochloride (PLGA-tet). A two-stream electrospinning setup was developed to create a uniform blend of PEUU and PLGA-tet fibers. Composite sheets were flexible with breaking strains exceeding 200%, tensile strengths of 5-7 MPa, and high suture retention capacity. The blending of PEUU fibers markedly reduced the shrinkage ratio observed for PLGA-tet sheets in buffer from 50% to 15%, while imparting elastomeric properties to the composites. Antibacterial activity was maintained for composite sheets following incubation in buffer for 7 days at 37 degrees C. In vivo studies demonstrated prevention of abscess formation in a contaminated rat abdominal wall model with the implanted material. These results demonstrate the benefits derivable from a two-stream electrospinning approach wherein mechanical and controlled-release properties are contributed by independent fiber populations and the applicability of this composite material to abdominal wall closure.

Cerebrospinal Dysfunction After Endovascular Stent-Grafting via a Median Sternotomy: The Frozen Elephant Trunk Procedure

BACKGROUND Endovascular stent grafting through a median sternotomy for a distal arch aneurysm (the frozen elephant trunk procedure) is an alternative to synthetic graft replacement. But spinal cord dysfunction can easily occur as a complication after surgery. Although its cause is uncertain, some attempts at prevention have been instituted. We address the mechanism of spinal cord dysfunction and evaluate the efficacy of our preventive measures. METHODS There were 22 men and 2 women with an average age of 71 (59 to 83) years. There were 22 true aneurysms (13 fusiform, nine saccular), one chronic dissection, and one penetrating aortic ulcer. The following strategies for prevention of spinal cord dysfunction were utilized: low flow perfusion through both axillary arteries (n = 10); pigtail catheter guidance (n = 19); use of a shorter graft with anchoring sutures (n = 12); flooding of the operative field with carbon dioxide (n = 7); aortic unclamping (n = 7), and use of ultra-thin woven Dacron grafts (n = 15). RESULTS There was no operative mortality, but cerebrospinal dysfunction complicated four cases (17%): one paraplegia, one stroke along the basilar artery, and two cases of temporary spinal cord dysfunction (paresthesia of the right leg and urinary disturbance). Cerebrospinal dysfunction tended to occur in fusiform aneurysms (31%, p = 0.044). Except when low flow antegrade perfusion through both the axillary arteries was utilized, which resulted in no cases of paraplegia or paraparesis (p = 0.064), the methods used for prevention of cerebrospinal dysfunction appeared to have little efficacy. CONCLUSIONS Cerebrospinal dysfunction is a serious complication of the frozen elephant trunk procedure. Its cause has not been clarified, but it tends to occur in fusiform-type aneurysms. Antegrade perfusion through both axillary arteries while the aorta is open may be helpful in its prevention.

Morphological and mechanical characteristics of the reconstructed rat abdominal wall following use of a wet electrospun biodegradable polyurethane elastomer scaffold

Although a variety of materials are currently used for abdominal wall repair, general complications encountered include herniation, infection, and mechanical mismatch with native tissue. An approach wherein a degradable synthetic material is ultimately replaced by tissue mechanically approximating the native state could obviate these complications. We report here on the generation of biodegradable scaffolds for abdominal wall replacement using a wet electrospinning technique in which fibers of a biodegradable elastomer, poly(ester urethane)urea (PEUU), were concurrently deposited with electrosprayed serum-based culture medium. Wet electrospun PEUU (wet ePEUU) was found to exhibit markedly different mechanical behavior and to possess an altered microstructure relative to dry processed ePEUU. In a rat model for abdominal wall replacement, wet ePEUU scaffolds (1x2.5 cm) provided a healing result that developed toward approximating physiologic mechanical behavior at 8 weeks. An extensive cellular infiltrate possessing contractile smooth muscle markers was observed together with extensive extracellular matrix (collagens, elastin) elaboration. Control implants of dry ePEUU and expanded polytetrafluoroethylene did not experience substantial cellular infiltration and did not take on the native mechanical anisotropy of the rat abdominal wall. These results illustrate the markedly different in vivo behavior observed with this newly reported wet electrospinning process, offering a potentially useful refinement of an increasingly common biomaterial processing technique.

Right ventricular outflow tract repair with a cardiac biologic scaffold.

Background: Surgical reconstruction of congenital heart defects is often limited by the nonresorbable material used to approximate normal anatomy. In contrast, biologic scaffold materials composed of resorbable non-cross-linked extracellular matrix (ECM) have been used for tissue reconstruction of multiple organs and are replaced by host tissue. Preparation of whole organ ECM by decellularization through vascular perfusion can maintain much of the native three-dimensional (3D) structure, strength, and tissue-specific composition. A 3D cardiac ECM (C-ECM) biologic scaffold material would logically have structural and functional advantages over materials such as Dacron™ for myocardial repair, but the in vivo remodeling characteristics of C-ECM have not been investigated to date. Methods and Results: A porcine C-ECM patch or Dacron patch was used to reconstruct a full-thickness right ventricular outflow tract (RVOT) defect in a rat model with end points of structural remodeling function at 16 weeks. The Dacron patch was encapsulated by dense fibrous tissue and showed little cellular infiltration. Echocardiographic analysis showed that the right ventricle of the hearts patched with Dacron were dilated at 16 weeks compared to presurgery baseline values. The C-ECM patch remodeled into dense, cellular connective tissue with scattered small islands of cardiomyocytes. The hearts patched with C-ECM showed no difference in the size or function of the ventricles as compared to baseline values at both 4 and 16 weeks. Conclusions: The C-ECM patch was associated with better functional and histomorphological outcomes compared to the Dacron patch in this rat model of RVOT reconstruction.

Naive rat amnion-derived cell transplantation improved left ventricular function and reduced myocardial scar of postinfarcted heart.

Stem cells contained in the amniotic membrane may be useful for cellular repair of the damaged heart. Previously, we showed that amnion-derived cells (ADCs) express embryonic stem cell surface markers and pluripotent stem cell-specific transcription factor genes. These ADCs also possess the potential for mesoderm (cardiac) lineage differentiation. In the present study we investigated whether untreated naive ADC transplantation into the injured left ventricular (LV) myocardium is beneficial as a cell-based cardiac repair strategy in a rat model. ADCs were isolated from Lewis rat embryonic day 14 amniotic membranes. FACS analysis revealed that freshly isolated ADCs contained stage-specific embryonic antigen-1 (SSEA-1), Oct-4-positive cells, and mesenchymal stromal cells, while hematopoietic stem cell marker positive cells were absent. Reverse transcription-PCR revealed that naive ADCs expressed cardiac and vascular specific genes. We injected freshly isolated ADCs (2 × 106 cells suspended in PBS, ADC group) into acutely infarcted LV myocardium produced by proximal left coronary ligation. PBS was injected in postinfarction controls (PBS group). Cardiac function was assessed at 2 and 6 weeks after injection. ADC treatment attenuated LV dilatation and sustained LV contractile function at 2 and 6 weeks in comparison to PBS controls (p < 0.05, ANOVA). LV peak systolic pressure and maximum dP/dt of ADC-treated heart were higher and LV end-diastolic pressure and negative dP/dt were lower than in PBS controls (p < 0.05). Histological assessment revealed that infarcted myocardium of the ADC-treated group had less fibrosis, thicker ventricular walls, and increased capillary density (p < 0.05). The fate of injected ADCs was confirmed using ADCs derived from EGFP(+) transgenic rats. Immunohistochemistry at 6 weeks revealed that EGFP(+) cells colocalized with von Willebrand factor, α-smooth muscle actin, or cardiac troponin-I. Our results suggest that naive ADCs are a potential cell source for cellular cardiomyoplasty.

The effect of polymer degradation time on functional outcomes of temporary elastic patch support in ischemic cardiomyopathy

Biodegradable polyurethane patches have been applied as temporary mechanical supports to positively alter the remodeling and functional loss following myocardial infarction. How long such materials need to remain in place is unclear. Our objective was to compare the efficacy of porous onlay support patches made from one of three types of biodegradable polyurethane with relatively fast (poly(ester urethane)urea; PEUU), moderate (poly(ester carbonate urethane)urea; PECUU), and slow (poly(carbonate urethane)urea; PCUU) degradation rates in a rat model of ischemic cardiomyopathy. Microporous PEUU, PECUU or PCUU (n = 10 each) patches were implanted over left ventricular lesions 2 wk following myocardial infarction in rat hearts. Infarcted rats without patching and age-matched healthy rats (n = 10 each) were controls. Echocardiography was performed every 4 wk up to 16 wk, at which time hemodynamic and histological assessments were performed. The end-diastolic area for the PEUU group at 12 and 16 wk was significantly larger than for the PECUU or PCUU groups. Histological analysis demonstrated greater vascular density in the infarct region for the PECUU or PCUU versus PEUU group at 16 wk. Improved left ventricular contractility and diastolic performance in the PECUU group was observed at 16 wk compared to infarction controls. The results indicate that the degradation rate of an applied elastic patch influences the functional benefits associated patch placement, with a moderately slow degrading PECUU patch providing improved outcomes.

Biodegradable elastic patch plasty ameliorates left ventricular adverse remodeling after ischemia–reperfusion injury: A preclinical study of a porous polyurethane material in a porcine model

OBJECTIVE Myocardial infarction (MI) can lead to irreversible adverse left ventricular remodeling resulting in subsequent severe dysfunction. The objective of this study was to investigate the potential for biodegradable, elastomeric patch implantation to positively alter the remodeling process after MI in a porcine model. METHODS Yorkshire pigs underwent a 60-minute catheter balloon occlusion of the left circumflex artery. Two weeks after MI animals underwent epicardial placement of a biodegradable, porous polyurethane (poly(ester urethane)urea; PEUU) patch (MI+PEUU, n = 7) or sham surgery (MI+sham, n = 8). Echocardiography before surgery and at 4 and 8 weeks after surgery measured the end-diastolic area (EDA) and fractional area change (%FAC). All animals were humanely killed 8 weeks after surgery and hearts were histologically assessed. RESULTS At 8 weeks, echocardiography revealed greater EDA values in the MI+sham group (23.6 ± 6.6 cm(2), mean ± standard deviaation) than in the MI+PEUU group (15.9 ± 2.5 cm(2)) (P < .05) and a lower %FAC in the MI+sham group (24.8 ± 7.6) than in the MI+PEUU group (35.9 ± 7.8) (P < .05). The infarcted ventricular wall was thicker in the MI+PEUU group (1.56 ± 0.5 cm) than in the MI+sham group (0.91 ± 0.24 cm) (P < .01). CONCLUSIONS Biodegradable elastomeric PEUU patch implantation onto the porcine heart 2 weeks post-MI attenuated left ventricular adverse remodeling and functional deterioration and was accompanied by increased neovascularization. These findings, although limited to a 2-month follow-up, may suggest an attractive clinical option to moderate post-MI cardiac failure.