Optimization of suture-free laser-assisted vessel repair by solder-doped electrospun poly(ε-caprolactone) scaffold

Marker-Independent Monitoring of in vitro and in vivo Degradation of Supramolecular Polymers Applied in Cardiovascular in situ Tissue Engineering

The equilibrium between scaffold degradation and neotissue formation, is highly essential for in situ tissue engineering. Herein, biodegradable grafts function as temporal roadmap to guide regeneration. The ability to monitor and understand the dynamics of degradation and tissue deposition in in situ cardiovascular graft materials is therefore of great value to accelerate the implementation of safe and sustainable tissue-engineered vascular grafts (TEVGs) as a substitute for conventional prosthetic grafts. In this study, we investigated the potential of Raman microspectroscopy and Raman imaging to monitor degradation kinetics of supramolecular polymers, which are employed as degradable scaffolds in in situ tissue engineering. Raman imaging was applied on in vitro degraded polymers, investigating two different polymer materials, subjected to oxidative and enzymatically-induced degradation. Furthermore, the method was transferred to analyze in vivo degradation of tissue-engineered carotid grafts after 6 and 12 months in a sheep model. Multivariate data analysis allowed to trace degradation and to compare the data from in vitro and in vivo degradation, indicating similar molecular observations in spectral signatures between implants and oxidative in vitro degradation. In vivo degradation appeared to be dominated by oxidative pathways. Furthermore, information on collagen deposition and composition could simultaneously be obtained from the same image scans. Our results demonstrate the sensitivity of Raman microspectroscopy to determine degradation stages and the assigned molecular changes non-destructively, encouraging future exploration of this techniques for time-resolved quality assessment of in situ tissue engineering processes.

Review of Laser Therapy in Cardiovascular Diseases

Introduction: In recent years, there has been a rise in laser therapy for the treatment of cardiovascular diseases. Methods: This paper attempted to represent recent advances in laser therapy in cardiovascular tissue repairs. Three standard techniques have been explicitly described here in cardiovascular tissue repairs by laser. Results: One of the advantages of using laser therapy in cardiovascular diseases is its non-invasiveness. It also reduces the treatment process pain and prevents massive surgical incisions and bleeding throughout the operation. Laser therapy can ensure an alternative method to treat the ischemic region of the heart and creating anastomosis of vessels. Conclusion: With professional technologies and endoscopic surgery method development, the role of using lasers has become much more precise and more transparent in cardiovascular diseases.

Improving the strength of sutureless laser-assisted vessel repair using preloaded longitudinal compression on tissue edge

BACKGROUND AND OBJECTIVE

Little is known about the approximation of coapted edges in sutureless laser-assisted vessel welding. Tissue shrinkage by laser irradiation may cause coapted edges to separate, reducing strength of welding. This may be avoided by preloaded longitudinal compression on the tissue edges to be welded. This study compared welding strength with and without preloaded compression in ex vivo animal experiments.

MATERIALS AND METHODS

This study evaluated 24 samples of harvested porcine carotid arteries, each having a length of 3 cm and an inner diameter of 1.0-2.0 mm. A half circumferential incision was made at the center of each sample. A steel shaft 2.0 mm in diameter was inserted into each sample to approximate the incised edges. The samples were longitudinally compressed to 6 mm. Incision sites were repaired by irradiation with a 970-nm diode laser. No glue or die was used. The repair strength was evaluated by measuring the bursting point (BP) of all samples. In a pilot study, the welding conditions, including power, duration, and interval of the laser spots, were tested by trial and error in 18 samples, including six treated under optimum conditions. As a control group, six samples were welded under optimum conditions, but without compression.

RESULTS

Optimum conditions, consisting of 2.4 W power, 30-second duration, and 1-mm intervals of laser spots, yielded the highest BP (623 ± 236 mmHg), which was significantly higher than in the control group without compression (204 ± 208 mmHg, P = 0.009). Defining BP > 400 mmHg as successful repair, the success rates in the compression and control groups were 83% and 17%, respectively.

CONCLUSION

Preloaded longitudinal compression on the coapted edges may be important for sutureless laser-assisted vessel repair and anastomosis and may affect the strength of welding. Lasers Surg. Med. 49:533-538, 2017. © 2017 Wiley Periodicals, Inc.

Hydrolytic and oxidative degradation of electrospun supramolecular biomaterials: In vitro degradation pathways

The emerging field of in situ tissue engineering (TE) of load bearing tissues places high demands on the implanted scaffolds, as these scaffolds should provide mechanical stability immediately upon implantation. The new class of synthetic supramolecular biomaterial polymers, which contain non-covalent interactions between the polymer chains, thereby forming complex 3D structures by self assembly. Here, we have aimed to map the degradation characteristics of promising (supramolecular) materials, by using a combination of in vitro tests. The selected biomaterials were all polycaprolactones (PCLs), either conventional and unmodified PCL, or PCL with supramolecular hydrogen bonding moieties (either 2-ureido-[1H]-pyrimidin-4-one or bis-urea units) incorporated into the backbone. As these materials are elastomeric, they are suitable candidates for cardiovascular TE applications. Electrospun scaffold strips of these materials were incubated with solutions containing enzymes that catalyze hydrolysis, or solutions containing oxidative species. At several time points, chemical, morphological, and mechanical properties were investigated. It was demonstrated that conventional and supramolecular PCL-based polymers respond differently to enzyme-accelerated hydrolytic or oxidative degradation, depending on the morphological and chemical composition of the material. Conventional PCL is more prone to hydrolytic enzymatic degradation as compared to the investigated supramolecular materials, while, in contrast, the latter materials are more susceptible to oxidative degradation. Given the observed degradation pathways of the examined materials, we are able to tailor degradation characteristics by combining selected PCL backbones with additional supramolecular moieties. The presented combination of in vitro test methods can be employed to screen, limit, and select biomaterials for pre-clinical in vivo studies targeted to different clinical applications.

Laser-assisted vessel welding: state of the art and future outlook

Laser-assisted vascular welding (LAVW) is an experimental technique being developed as an alternative to suture anastomosis. In comparison to mechanical anastomosis, LAVW is less traumatic, non-immunogenic, provides immediate water tight sealant, and possibly a faster and easier procedure for minimally invasive surgery. This review focuses on technical advances to improve welding strength and to reduce thermal damage in LAVW. In terms of welding strength, LAVW has evolved from the photothermally-induced microvascular anastomosis, requiring stay sutures to support welding strength, to sutureless anastomoses of medium-sized vessels, withstanding physiological and supraphysiological pressure. Further improvements in anastomotic strength could be achieved by the use of chromophore-containing albumin solder and the employment of (biocompatible) polymeric scaffolds. The anastomotic strength and the stability of welds achieved with such a modality, referred to as scaffold- and solder-enhanced LAVW (ssLAVW), are dependent on the intermolecular bonding of solder molecules (cohesive bonding) and the bonding between solder and tissue collagen (adhesive bonding). Presently, the challenges of ssLAVW include (1) obtaining an optimal balance between cohesive and adhesive bonding and (2) minimizing thermal damage. The modulation of thermodynamics during welding, the application of semi-solid solder, and the use of a scaffold that supports both cohesive and adhesive strength are essential to improve welding strength and to limit thermal damage.

Laser-assisted vascular welding: optimization of acute and post-hydration welding strength

BACKGROUND

Liquid solder laser-assisted vascular welding using biocompatible polymeric scaffolds (ssLAVW) is a novel technique for vascular anastomoses. Although ssLAVW has pronounced advantages over conventional suturing, drawbacks include low welding strength and extensive thermal damage.

AIM

To determine optimal ssLAVW parameters for maximum welding strength and minimal thermal damage.

METHODS

Substudy 1 compared breaking strength (BS) of aortic strips welded with electrospun poly(ε-caprolactone) (PCL) or poly(lactic-co-glycolic acid) (PLGA) scaffold, 670-nm laser, 50-s single-spot continuous lasing (SSCL), and semi-solid solder (48% bovine serum albumin (BSA)/0.5% methylene blue (MB)/3% hydroxypropylmethylcellulose (HPMC)). Substudy 2 compared the semi-solid solder to 48% BSA/0.5% MB/0.38% genipin and 48% BSA/0.5% MB/3% HPMC/0.38% genipin solder. Substudy 3 compared SSCL to single-spot pulsed lasing (SSPL).

RESULTS

PCL-ssLAVW yielded an acute BS of 248.0 ± 54.0 N/cm² and remained stable up to 7d of hydration. PLGA-ssLAVW obtained higher acute BS (408.6 ± 78.8 N/cm²) but revealed structural defects and a BS of 109.4 ± 42.6 N/cm² after 14 d of hydration. The addition of HPMC and genipin improved the 14-d BS of PLGA-sLAVW (223.9 ± 19.1 N/cm²). Thermal damage was reduced with SSPL compared with SSCL.

CONCLUSIONS

PCL-ssLAVW yielded lower but more stable welds than PLGA-ssLAVW. The addition of HPMC and genipin to the solder increased the post-hydration BS of PLGA-ssLAVW. SSPL regimen reduced thermal damage. PLGA-ssLAVW using 48% BSA/0.5% MB/3% HPMC/0.38% genipin solder and SSPL constitutes the most optimal welding modality.

RELEVANCE FOR PATIENTS

Surgical patients requiring vascular anastomoses may benefit from the advantages that ssLAVW potentially offers over conventional sutures (gold standard). These include no needle trauma and remnant suture materials in the patient, reduction of foreign body reaction, immediate liquid-tight sealing, and the possibility of a faster and easier procedure for minimally invasive and endoscopic anastomotic techniques.

Recent advances in electrospinning technology and biomedical applications of electrospun fibers

Electrospinning technology underwent rapid development in recent years, which can be used for fabricating electrospun fibers with different morphologies and multidimensional structures. These fibers are widely applied in medical diagnosis, tissue engineering, replica molding and other applications. Here we review the recent advances in the electrospinning technology, especially technical progress in fabricating electrospun fibers and assemblies with multidimensional structures, and the biomedical applications of these fibers.

Ex vivo proof-of-concept of end-to-end scaffold-enhanced laser-assisted vascular anastomosis of porcine arteries

OBJECTIVE

The low welding strength of laser-assisted vascular anastomosis (LAVA) has hampered the clinical application of LAVA as an alternative to suture anastomosis. To improve welding strength, LAVA in combination with solder and polymeric scaffolds (ssLAVA) has been optimized in vitro. Currently, ssLAVA requires proof-of-concept in a physiologically representative ex vivo model before advancing to in vivo studies. This study therefore investigated the feasibility of ex vivo ssLAVA in medium-sized porcine arteries.

METHODS

Scaffolds composed of poly(ε-caprolactone) (PCL) or poly(lactic-co-glycolic acid) (PLGA) were impregnated with semisolid solder and placed over coapted aortic segments. ssLAVA was performed with a 670-nm diode laser. In the first substudy, the optimum number of laser spots was determined by bursting pressure analysis. The second substudy investigated the resilience of the welds in a Langendorf-type pulsatile pressure setup, monitoring the number of failed vessels. The type of failure (cohesive vs adhesive) was confirmed by electron microscopy, and thermal damage was assessed histologically. The third substudy compared breaking strength of aortic repairs made with PLGA and semisolid genipin solder (ssLAVR) to repairs made with BioGlue.

RESULTS

ssLAVA with 11 lasing spots and PLGA scaffold yielded the highest bursting pressure (923 ± 56 mm Hg vs 703 ± 96 mm Hg with PCL ssLAVA; P = .0002) and exhibited the fewest failures (20% vs 70% for PCL ssLAVA; P = .0218). The two failed PLGA ssLAVA arteries leaked at 19 and 22 hours, whereas the seven failed PCL ssLAVA arteries burst between 12 and 23 hours. PLGA anastomoses broke adhesively, whereas PCL welds failed cohesively. Both modalities exhibited full-thickness thermal damage. Repairs with PLGA scaffold yielded higher breaking strength than BioGlue repairs (323 ± 28 N/cm(2) vs 25 ± 4 N/cm(2), respectively; P = .0003).

CONCLUSIONS

PLGA ssLAVA yields greater anastomotic strength and fewer anastomotic failures than PCL ssLAVA. Aortic repairs with BioGlue were inferior to those produced with PLGA ssLAVR. The results demonstrate the feasibility of ssLAVA/R as an alternative method to suture anastomosis or tissue sealant. Further studies should focus on reducing thermal damage.

ε-Caprolactone in micro-chambered ceramic beads--a new carrier for gentamicin

PURPOSE

The purpose of this preliminary and descriptive study was to evaluate a biodegradable drug delivery system in combination with an innovative ceramic implant.

METHODS

The delivery of gentamicin of standardized samples was measured in the laboratory using ultra-high-performance liquid chromatography. Biocompatibility and biodegradation of the materials was investigated in an animal experiment in sheep up to 14 months. As carrier ε-caprolactone, 1:1 mixed with gentamicin, intruded into micro-chambered β-tricalcium-phosphate beads (MCB®) was studied.

RESULTS AND DISCUSSION

Gentamicin was released in calculable concentrations during the first 30 days. The release from ε-caprolactone was higher than that from polymethylmethacrylate and more predictable. The caprolactone carrier was reabsorbed by osteoclasts.

Biodegradable polymer scaffold, semi-solid solder, and single-spot lasing for increasing solder-tissue bonding in suture-free laser-assisted vascular repair

We recently showed the fortifying effect of poly-caprolactone (PCL) scaffold in liquid solder-mediated laser-assisted vascular repair (ssLAVR) of porcine carotid arteries, yielding a mean ± SD leaking point pressure of 488 ± 111 mmHg. Despite supraphysiological pressures, the frequency of adhesive failures was indicative of weak bonding at the solder-tissue interface. As a result, this study aimed to improve adhesive bonding by using a semi-solid solder and single-spot vs. scanning irradiation. In the first experiment, in vitro ssLAVR (n=30) was performed on porcine abdominal aorta strips using a PCL scaffold with a liquid or semi-solid solder and a 670-nm diode laser for dual-pass scanning. In the second experiment, the scanning method was compared to single-spot lasing. The third experiment investigated the stability of the welds following hydration under quasi-physiological conditions. The welding strength was defined by acute breaking strength (BS). Solder-tissue bonding was examined by scanning electron microscopy and histological analysis was performed for thermal damage analysis. Altering solder viscosity from liquid to semi-solid solder increased the BS from 78 ± 22 N/cm(2) to 131 ± 38 N/cm(2) . Compared to scanning ssLAVR, single-spot lasing improved adhesive bonding to a BS of 257 ± 62 N/cm(2) and showed fewer structural defects at the solder-tissue interface but more pronounced thermal damage. The improvement in adhesive bonding was associated with constantly stronger welds during two weeks of hydration. Semi-solid solder and single-spot lasing increased welding strength by reducing solder leakage and improving adhesive bonding, respectively. The improvement in adhesive bonding was associated with enhanced weld stability during hydration.

Clinical application of laser treatment for cardiovascular surgery

BACKGROUND

Recently, several kinds of lasers have been widely employed in the field of medicine and surgery. However, laser applications are very rare in the field of cardiovascular surgery throughout the world. So, we have experimentally tried to use lasers in the field of cardiovascular surgery. There were three categories: 1) Transmyocardial laser revascularization (TMLR), 2) Laser vascular anastomosis, and 3) Laser angioplasty in the peripheral arterial diseases. By the way, surgery for ischemic heart disease has been widely performed in Japan. Especially coronary artery bypass grafting (CABG) for these patients has been done as a popular surgical method. Among these patients there are a few cases for whom CABG and percutaneous coronary intervention (PCI) could not be carried out, because of diffuse stenosis and small caliber of coronary arteries. Materials and methods of TMLR: A new method of tranasmyocardial revascularization by CO2 laser (output 100 W, irradiation time 0.2 sec) was experimentally performed to save severely ill patients. In this study, a feasibility of transmyocardial laser revascularization from left ventricular cavity through artificially created channels by laser was precisely evaluated.

RESULTS

In trials on dogs laser holes 0.2mm in diameter have been shown microscopically to be patent even 3 years after their creation, thus this procedure could be used as a new method of transmyocardial laser revascularization. Clinical application of TMLR: Subsequently, transmyocardial laser revascularization was employed in a 55-year-old male patient with severe angina pectoris who had undergone pericardiectomy 7 years before. He was completely recovered from severe chest pain. Conclusions of TMLR: This patient was the first successful case in the world with TMLR alone. This method might be done for the patients who percutaneous coronary intervention and coronary artery bypass grafting could be carried out. Laser vascular anastomosis: At present time, in vascular surgery there are some problems to keep long-term patency after anastomosis of the conventional suture method, especially for small-caliber vessels. Materials and methods of Laser vascular anastomosis: From these standpoints, a low energy CO2 laser was employed experimentally in vascular anastomosis for small-caliber vessels. Resullts of Laser vascular anastomosis: From preliminary experiments it could be concluded that the optimal laser output was 20-40 mW and irradiation time was 6-12 sec/mm for vascular anastomosis of small-caliber vessels in the extremities. And then, histologic findings and intensity of the laser anastomotic sites were investigated thereafter. Subseqently, good enough intensity and good healing of laser anastomotic sites as well as the conventional suture method could be observed. There were no statistic differences between laser and suture methods. A feasibility of laser anastomosis could be considered and clinical application could be recognized. Clinical applications of Laser vascular anastomosis: On February 21, 1985, arterio-venous laser anastomosis for the patient with renal failure was smoothly done and she could accept hemodialysis. Conclusions of Laser vascular anastomosis: This patient was the first clinical successful case in the world. Thereafter, Laser vascular anastomosis were in 111 patients with intermittent claudication, refractory crural ulcer, and coronary disorders. Thereafter, they are going well. Laser angioplasty: Laser angioplasty for peripheral arterial diseases. There are many methods to treat peripheral arterial diseases such as balloon method, atherectomy, laser technique and stenting graft in the field of endovascular treatment. Recent years, minimal invasive treatment should be employed even in the surgical treatment. However, there are different images between these methods. Materials and methods of Laser angioplasty: We have chosen to use laser for endovascular treatment for peripheral arterial diseases. We have tried to check between laser energy and vessel wall. Results of Laser angioplasty: Subsequently, it could be concluded that optimal conditions for laser angioplasty were 6 W in output and irradiation time was 5 sec. And with another method of feedback control system, temperature of metal tip probe was 200°C and irradiation time was 5 sec for each shot. And histological study and feasibility of angioscopic guidance could be done and clinical application was started. Until now, 115 patients were successfully treated with their life longevity. Conclusions of Laser angioplasty: Thus, laser applications were useful methods to treat a lot of patients with some ischemic problems.