Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

Chemical Composition of Macroalgae Polysaccharides from Galician and Portugal Coasts: Seasonal Variations and Biological Properties

Crude polysaccharides extracted from the Codium sp. and Osmundea sp. macroalgae collected in different seasons (winter, spring and summer) from the Galician and North Portugal coasts were characterised, aiming to support their biomedical application to wound healing. An increase in polysaccharides' sulphate content was registered from winter to summer, and higher values were obtained for Osmundea sp. In turn, the monosaccharide composition constantly changed with a decrease in glucose in Osmundea sp. from spring to winter. For Codium sp., a higher increase was noticed regarding glucose content in the Galician and Portugal coasts. Galactose was the major monosaccharide in all the samples, remaining stable in all seasons and collection sites. These results corroborate the sulphate content and antioxidant activity, since the Osmundea sp.-derived polysaccharides collected in summer exhibited higher scavenging radical ability. The biocompatibility and wound scratch assays revealed that the Osmundea sp. polysaccharide extracted from the Portugal coast in summer possessed more potential for promoting fibroblast migration. This study on seasonal variations of polysaccharides, sulphate content, monosaccharide composition and, consequently, biological properties provides practical guidance for determining the optimal season for algae harvest to standardise preparations of polysaccharides for the biomedical field.

Interaction of Near-Infrared (NIR)-Light Responsive Probes with Lipid Membranes: A Combined Simulation and Experimental Study

Cancer is considered a major societal challenge for the next decade worldwide. Developing strategies for simultaneous diagnosis and treatment has been considered a promising tool for fighting cancer. For this, the development of nanomaterials incorporating prototypic near-infrared (NIR)-light responsive probes, such as heptamethine cyanines, has been showing very promising results. The heptamethine cyanine-incorporating nanomaterials can be used for a tumor's visualization and, upon interaction with NIR light, can also produce a photothermal/photodynamic effect with a high spatio-temporal resolution and minimal side effects, leading to an improved therapeutic outcome. In this work, we studied the interaction of 12 NIR-light responsive probes with lipid membrane models by molecular dynamics simulations. We performed a detailed characterization of the location, orientation, and local perturbation effects of these molecules on the lipid bilayer. Based on this information, the probes were divided into two groups, predicting a lower and higher perturbation of the lipid bilayer. From each group, one molecule was selected for testing in a membrane leakage assay. The experimental data validate the hypothesis that molecules with charged substituents, which function as two polar anchors for the aqueous phase while spanning the membrane thickness, are more likely to disturb the membrane by the formation of defects and pores, increasing the membrane leakage. The obtained results are expected to contribute to the selection of the most suitable molecules for the desired application or eventually guiding the design of probe modifications for achieving an optimal interaction with tumor cell membranes.

Three-Dimensionally Printed Hydrogel Cardiac Patch for Infarct Regeneration Based on Natural Polysaccharides

Myocardial infarction is one of the more common cardiovascular diseases, and remains the leading cause of death, globally. Hydrogels (namely, those using natural polymers) provide a reliable tool for regenerative medicine and have become a promising option for cardiac tissue regeneration due to their hydrophilic character and their structural similarity to the extracellular matrix. Herein, a functional ink based on the natural polysaccharides Gellan gum and Konjac glucomannan has, for the first time, been applied in the production of a 3D printed hydrogel with therapeutic potential, with the goal of being locally implanted in the infarcted area of the heart. Overall, results revealed the excellent printability of the bioink for the development of a stable, porous, biocompatible, and bioactive 3D hydrogel, combining the specific advantages of Gellan gum and Konjac glucomannan with proper mechanical properties, which supports the simplification of the implantation process. In addition, the structure have positive effects on endothelial cells' proliferation and migration that can promote the repair of injured cardiac tissue. The results presented will pave the way for simple, low-cost, and efficient cardiac tissue regeneration using a 3D printed hydrogel cardiac patch with potential for clinical application for myocardial infarction treatment in the near future.

Animal-derived products in science and current alternatives

More than fifty years after the 3Rs definition and despite the continuous implementation of regulatory measures, animals continue to be widely used in basic research. Their use comprises not only in vivo experiments with animal models, but also the production of a variety of supplements and products of animal origin for cell and tissue culture, cell-based assays, and therapeutics. The animal-derived products most used in basic research are fetal bovine serum (FBS), extracellular matrix proteins such as Matrigel™, and antibodies. However, their production raises several ethical issues regarding animal welfare. Additionally, their biological origin is associated with a high risk of contamination, resulting, frequently, in poor scientific data for clinical translation. These issues support the search for new animal-free products able to replace FBS, Matrigel™, and antibodies in basic research. In addition, in silico methodologies play an important role in the reduction of animal use in research by refining the data previously to in vitro and in vivo experiments. In this review, we depicted the current available animal-free alternatives in in vitro research.

DEVELOPMENT OF A NATURAL POLYMER-BASED HYDROGEL FOR BIOENGINEERED VASCULAR GRAFTS

Introduction

Cardiovascular diseases are a main cause of death globally, and their treatment implies various vascular repairs through different techniques like angioplasty, stent placement in the blocked artery, or bypass surgery. Artificial grafts would significantly reduce the number of non-treated patients, but middle and long-term failures compromise their clinical use.

Methods

Herein, we developed a hydrogel composed of gellan gum, gelatin, and sodium alginate for bioengineered vascular graft production. The vascular grafts were characterized by their swelling, porosity, biodegradability, and cytotoxic profile.

Results

The bioengineered materials were easily assembled due to the thermoresponsive nature of the hydrogel and had a vessel-like structure resembling the native vasculature. These vessels had a very controlled swelling degree, and notably, the hydrogel structure was stable and maintained its morphology. The vascular grafts had a porosity of 82.6 ± 4.3% and exhibited a controlled biodegradation rate with a maximum of 24.2 ± 3.0%. As expected, the natural materials used showed no cytotoxicity toward HUVECs cells since they are natural polymers described as biocompatible.

Conclusions

This developed natural hydrogel showed promising potential to be used to develop bioengineered vascular grafts.

Silk Sericin: A Promising Sustainable Biomaterial for Biomedical and Pharmaceutical Applications

Silk is a natural composite fiber composed mainly of hydrophobic fibroin and hydrophilic sericin, produced by the silkworm Bombyx mori. In the textile industry, the cocoons of B. mori are processed into silk fabric, where the sericin is substantially removed and usually discarded in wastewater. This wastewater pollutes the environment and water sources. However, sericin has been recognized as a potential biomaterial due to its biocompatibility, immunocompatibility, biodegradability, anti-inflammatory, antibacterial, antioxidant and photoprotective properties. Moreover, sericin can produce hydrogels, films, sponges, foams, dressings, particles, fibers, etc., for various biomedical and pharmaceutical applications (e.g., tissue engineering, wound healing, drug delivery, cosmetics). Given the severe environmental pollution caused by the disposal of sericin and its beneficial properties, there has been growing interest in upcycling this biomaterial, which could have a strong and positive economic, social and environmental impact.

Single-Step Self-Assembly of Zein–Honey–Chitosan Nanoparticles for Hydrophilic Drug Incorporation by Flash Nanoprecipitation

Zein- and chitosan-based nanoparticles have been described as promising carrier systems for food, biomedical and pharmaceutical applications. However, the manufacture of size-controlled zein and chitosan particles is challenging. In this study, an adapted anti-solvent nanoprecipitation method was developed. The effects of the concentration of zein and chitosan and the pH of the collection solution on the properties of the zein–honey–chitosan nanoparticles were investigated. Flash nanoprecipitation was demonstrated as a rapid, scalable, single-step method to achieve the self-assembly of zein–honey–chitosan nanoparticles. The nanoparticles size was tuned by varying certain formulation parameters, including the total concentration and ratio of the polymers. The zein–honey–chitosan nanoparticles’ hydrodynamic diameter was below 200 nm and the particles were stable for 30 days. Vitamin C was used as a hydrophilic model substance and efficiently encapsulated into these nanoparticles. This study opens a promising pathway for one-step producing zein–honey–chitosan nanoparticles by flash nanoprecipitation for hydrophilic compounds’ encapsulation.

Osmundea sp. macroalgal polysaccharide-based nanoparticles produced by flash nanocomplexation technique

The macroalgae-derived polysaccharides' biological potential has been explored due to their attractive intrinsic properties such as biocompatibility, biodegradability, and their ability to conjugate with other compounds. In particular, in the drug delivery systems field, the anionic macroalgae polysaccharides have been combined with cationic compounds through ionotropic gelation and/or bulk mixing. However, these techniques did not assure reproducibility, and the stability of nanoparticles is undesired. To overcome these limitations, herein, the polysaccharide extracted from Osmundea sp. was used to produce nanoparticles through the flash nanocomplexation technique. This approach rapidly mixed the negative charge of macroalgae polysaccharide with a positive chitosan charge on a millisecond timescale. Further, diclofenac (an anti-inflammatory drug) was also incorporated into complex nanoparticles. Overall, the gathered data showed that hydrodynamic diameter nanoparticles values lower than 100 nm, presenting a narrow size distribution and stability. Also, the diclofenac exhibited a targeted and sustained release profile in simulating inflammatory conditions. Likewise, the nanoparticles showed excellent biological properties, evidencing their suitability to be used to treat inflammatory skin diseases.

Xanthan Gum-Konjac Glucomannan Blend Hydrogel for Wound Healing

Hydrogels are considered to be the most ideal materials for the production of wound dressings since they display a three-dimensional structure that mimics the native extracellular matrix of skin as well as a high-water content, which confers a moist environment at the wound site. Until now, different polymers have been used, alone or blended, for the production of hydrogels aimed for this biomedical application. From the best of our knowledge, the application of a xanthan gum-konjac glucomannan blend has not been used for the production of wound dressings. Herein, a thermo-reversible hydrogel composed of xanthan gum-konjac glucomannan (at different concentrations (1% and 2% w/v) and ratios (50/50 and 60/40)) was produced and characterized. The obtained data emphasize the excellent physicochemical and biological properties of the produced hydrogels, which are suitable for their future application as wound dressings.

Incorporation of Cró thermal water in a dermocosmetic formulation: cytotoxicity effects, characterization and stability studies and efficacy evaluation

OBJECTIVE

Development of cosmetic formulations to provide a controlled release of hydrophilic active compounds from mineral medicinal waters constitutes an attractive challenge. The objective of this study was the development and the characterization of a dermocosmetic gel formulation with Cró thermal water, from Beira Interior of Portugal, as a major functional ingredient.

METHODS

Concentrations of mineral chemical elements of Cró thermal water were previously determined by inductively coupled plasma-optical emission spectrometry or mass spectrometry and cytotoxicity assays using thermal water were carried out on normal human dermal fibroblasts (NHDF) cells. Then, the Cró thermal water was included (more than 90%) in a developed gel formulation that was characterized through rheological and texture analysis and submitted to stability assays during 30 days. The effects on the skin volunteers, namely skin pH, the degree of hydration, transepidermal water loss and skin relief, were evaluated through non-invasive biometric techniques. A gel formulation including purified water was used as a control.

RESULTS

Cró thermal water is rich on several chemical elements in particular sodium, silica, potassium and calcium besides some trace elements, with important functions for the skin. NHDF cells adhered and proliferated in the presence of thermal water confirming the biocompatibility of the major component of the gel formulation. The developed gel formulation based on thermal water resulted in an improvement of textural parameters, comparing with the purified water-based one. Significant improvements in the cutaneous biometric parameters (degree of hydration, transepidermal water loss and skin relief) of volunteers were also registered for the gel formulation containing thermal water.

CONCLUSION

This study demonstrated for the first time the potential benefits of Cró thermal water in a gel formulation to be used in cosmetic and dermatological applications.

Electrospun polymeric nanofibres as wound dressings: A review

Skin wounds have significant morbidity and mortality rates associated. This is explained by the limited effectiveness of the currently available treatments, which in some cases do not allow the reestablishment of the structure and functions of the damaged skin, leading to wound infection and dehydration. These drawbacks may have an impact on the healing process and ultimately prompt patients' death. For this reason, researchers are currently developing new wound dressings that enhance skin regeneration. Among them, electrospun polymeric nanofibres have been regarded as promising tools for improving skin regeneration due to their structural similarity with the extracellular matrix of normal skin, capacity to promote cell growth and proliferation and bactericidal activity as well as suitability to deliver bioactive molecules to the wound site. In this review, an overview of the recent studies concerning the production and evaluation of electrospun polymeric nanofibrous membranes for skin regenerative purposes is provided. Moreover, the current challenges and future perspectives of electrospun nanofibrous membranes suitable for this biomedical application are highlighted.

A systematic analysis of orphan cyclins reveals CNTD2 as a new oncogenic driver in lung cancer

As lung cancer has increased to the most common cause of cancer death worldwide, prognostic biomarkers and effective targeted treatments remain lacking despite advances based on patients’ stratification. Multiple core cyclins, best known as drivers of cell proliferation, are commonly deregulated in lung cancer where they may serve as oncogenes. The recent expansion of the cyclin family raises the question whether new members might play oncogenic roles as well. Here, we investigated the protein levels of eight atypical cyclins in lung cancer cell lines and formalin-fixed and paraffin-embedded (FFPE) human tumors, as well as their functional role in lung cancer cells. Of the new cyclins evaluated, CNTD2 was significantly overexpressed in lung cancer compared to adjacent normal tissue, and exhibited a predominant nuclear location. CNTD2 overexpression increased lung cancer cell viability, Ki-67 intensity and clonogenicity and promoted lung cancer cell migration. Accordingly, CNTD2 enhanced tumor growth in vivo on A549 xenograft models. Finally, the analysis of gene expression data revealed a high correlation between elevated levels of CNTD2 and decreased overall survival in lung cancer patients. Our results reveal CNTD2 as a new oncogenic driver in lung cancer, suggesting value as a prognostic biomarker and therapeutic target in this disease.

Physicochemical fingerprinting of thermal waters of Beira Interior region of Portugal

Mineral natural waters and spas have been used for therapeutic purposes for centuries, with Portugal being a very rich country in thermal waters and spas that are mainly distributed by northern and central regions where Beira Interior region is located. The use of thermal waters for therapeutic purposes has always been aroused a continuous interest, being dependent on physicochemical fingerprinting of this type of waters the indication for a treatment in a specific pathological condition. In the present work, besides a literature review about the physicochemical composition of the thermal waters of the Beira Interior region and its therapeutic indications, it was carried out an exhaustive multivariate analysis-principal component analysis and cluster analysis-to assess the correlation between different physicochemical parameters and the therapeutic indications claims described for these spas and thermal waters. These statistical methods used for data analysis enables classification of thermal waters compositions into different groups, regarding to the different variable selected, making possible an interpretation of variables affecting water compositions. Actually, Monfortinho and Longroiva are clearly quite different of the others, and Cró and Fonte Santa de Almeida appear together in all analysis, suggesting a strong resemblance between these waters. Thereafter, the results obtained allow us to demonstrate the role of major components of the studied thermal waters on a particular therapeutic purpose/indication and hence based on compositional and physicochemical properties partially explain their therapeutic qualities and beneficial effects on human health. This classification agreed with the results obtained for the therapeutic indications approved by the Portuguese National Health Authority and proved to be a valuable tool for the regional typology of mineral medicinal waters, constituting an important guide of the therapeutic armamentarium for well and specific-oriented pathological disturbs.

Electrospun Polycaprolactone/Aloe Vera_Chitosan Nanofibrous Asymmetric Membranes Aimed for Wound Healing Applications

Today, none of the wound dressings available on the market is fully capable of reproducing all the features of native skin. Herein, an asymmetric electrospun membrane was produced to mimic both layers of skin. It comprises a top dense layer (manufactured with polycaprolactone) that was designed to provide mechanical support to the wound and a bottom porous layer (composed of chitosan and Aloe Vera) aimed to improve the bactericidal activity of the membrane and ultimately the healing process. The results obtained revealed that the produced asymmetric membranes displayed a porosity, wettability, as well as mechanical properties similar to those presented by the native skin. Fibroblast cells were able to adhere, spread, and proliferate on the surface of the membranes and the intrinsic structure of the two layers of the membrane is capable of avoiding the invasion of microorganisms while conferring bioactive properties. Such data reveals the potential of these asymmetric membranes, in the near future, to be applied as wound dressings.

Synthesis and characterization of a photocrosslinkable chitosan–gelatin hydrogel aimed for tissue regeneration

In the area of regenerative medicine different approaches have been studied to restore the native structure of damaged tissues. Herein, the suitability of a photocrosslinkable hydrogel for tissue engineering applications was studied.

In vivo high-content evaluation of three-dimensional scaffolds biocompatibility

While developing tissue engineering strategies, inflammatory response caused by biomaterials is an unavoidable aspect to be taken into consideration, as it may be an early limiting step of tissue regeneration approaches. We demonstrate the application of flat and flexible films exhibiting patterned high-contrast wettability regions as implantable platforms for the high-content in vivo study of inflammatory response caused by biomaterials. Screening biomaterials by using high-throughput platforms is a powerful method to detect hit spots with promising properties and to exclude uninteresting conditions for targeted applications. High-content analysis of biomaterials has been mostly restricted to in vitro tests where crucial information is lost, as in vivo environment is highly complex. Conventional biomaterials implantation requires the use of high numbers of animals, leading to ethical questions and costly experimentation. Inflammatory response of biomaterials has also been highly neglected in high-throughput studies. We designed an array of 36 combinations of biomaterials based on an initial library of four polysaccharides. Biomaterials were dispensed onto biomimetic superhydrophobic platforms with wettable regions and processed as freeze-dried three-dimensional scaffolds with a high control of the array configuration. These chips were afterward implanted subcutaneously in Wistar rats. Lymphocyte recruitment and activated macrophages were studied on-chip, by performing immunocytochemistry in the miniaturized biomaterials after 24 h and 7 days of implantation. Histological cuts of the surrounding tissue of the implants were also analyzed. Localized and independent inflammatory responses were detected. The integration of these data with control data proved that these chips are robust platforms for the rapid screening of early-stage in vivo biomaterials' response.

Isolation of human umbilical arterial smooth muscle cells (HUASMC)

The human umbilical cord (UC) is a biological sample that can be easily obtained just after birth. This biological sample is, most of the time, discarded and their collection does not imply any added risk to the newborn or mother s health. Moreover no ethical concerns are raised. The UC is composed by one vein and two arteries from which both endothelial cells (ECs) and smooth muscle cells (SMCs), two of the main cellular components of blood vessels, can be isolated. In this project the SMCs were obtained after enzymatic treatment of the UC arteries accordingly the experimental procedure previously described by Jaffe et al. After cell isolation they were kept in t-flash with DMEM-F12 supplemented with 5% of fetal bovine serum and were cultured for several passages. Cells maintained their morphological and other phenotypic characteristics in the different generations. The aim of this study was to isolate smooth muscle cells in order to use them as models for future assays with constrictor drugs, isolate and structurally characterize L-type calcium channels, to study cellular and molecular aspects of the vascular function and to use them in tissue engineering.

Development of a new chitosan hydrogel for wound dressing

Wound healing is a complex process involving an integrated response by many different cell types and growth factors in order to achieve rapid restoration of skin architecture and function. The present study evaluated the applicability of a chitosan hydrogel (CH) as a wound dressing. Scanning electron microscopy analysis was used to characterize CH morphology. Fibroblast cells isolated from rat skin were used to assess the cytotoxicity of the hydrogel. CH was able to promote cell adhesion and proliferation. Cell viability studies showed that the hydrogel and its degradation by-products are noncytotoxic. The evaluation of the applicability of CH in the treatment of dermal burns in Wistar rats was performed by induction of full-thickness transcutaneous dermal wounds. Wound healing was monitored through macroscopic and histological analysis. From macroscopic analysis, the wound beds of the animals treated with CH were considerably smaller than those of the controls. Histological analysis revealed lack of a reactive or a granulomatous inflammatory reaction in skin lesions with CH and the absence of pathological abnormalities in the organs obtained by necropsy, which supported the local and systemic histocompatibility of the biomaterial. The present results suggest that this biomaterial may aid the re-establishment of skin architecture.

Heart rate, heart rate variability, and blood pressure during perioperative stressor events in abdominal surgery

STUDY OBJECTIVE

To define the behavior of power spectral heart rate variability (PSHR) during potentially stressful events in the perioperative period, and relate it to changes in blood pressure (BP) and heart rate (HR).

DESIGN

Longitudinal clinical study.

SETTING

Operating room and recovery suites of a large tertiary care referral center.

PATIENTS

26 ASA physical status I, II, and III patients undergoing elective abdominal surgery.

INTERVENTIONS

Anesthesia was induced with thiopental sodium and fentanyl, and maintained with isoflurane/nitrous oxide (N2O)/relaxant or enflurane/N2O/relaxant. The trachea was intubated and intraabdominal surgery was performed.

MEASUREMENTS AND MAIN RESULTS

Observations consisted of HR, noninvasive blood pressure, and PSHR. They were made before and after induction of anesthesia, tracheal intubation, and surgical incision, and during maximal surgical stimulation and skin closure. HR and mean arterial pressure (MAP) maxima were also recorded for one hour before and after emergence from anesthesia. PSHR was obtained using a special algorithm and data acquisition system for real time spectral analysis of the instantaneous HRversus time function. The HR power spectrum parameters analyzed were low-frequency (LFA; powerband = 0.04 to 0.10 Hz), respiratory-induced frequency (RFA; powerband = respiratory frequency +/- 0.06 Hz), and the ratio of LFA to RFA. With induction of anesthesia, only RFA power decreased significantly. LFA power reduction became significant only after intubation and continued so until after incision. Immediately after induction, the decline in RFA power (vs. preinduction) was more pronounced when compared with the decline in LFA power (76% vs. 34%; p = 0.01). Hence, the ratio LFA/RFA increased significantly after induction of anesthesia. It was significantly higher than at postintubation, preincision, or skin closure. A significant elevation in LFA, LFA/RFA ratio, and BP occurred with maximal abdominal surgical stimulation. Only preinduction LFA, RFA, and LFA/ RFA ratio were predictive of MAP changes with induction of anesthesia (p = 0.006). In 8 of the 15 patients who had MAP changes of at least 10 mmHg with induction, PSHR indices correctly predicted a change of this magnitude. Late intraoperative HR maxima were positively correlated with the change in HR and incision (r2 = 0.58; p < 0.01). The change in BP with incision was positively correlated with early postoperative HR maxima (r2 = 0.60; p < 0.01).

CONCLUSIONS

On anesthetic induction, preoperative, but not intraoperative, spectral indices were predictive of BP changes. Power spectral analysis of HR may provide information about the autonomic state that is not evident from BP or HR. The HR power spectrum, in particular, indicated a striking autonomic imbalance immediately after the induction of anesthesia despite stable HR and BP. LFA and LFA/RFA ratio appeared to track sympathetic autonomic activation during abdominal surgical stimulation, but not during other perioperative stressor events.

Analysis of heart rate variability to assess hemodynamic alterations following induction of anesthesia

Extensive changes in hemodynamics and cardiac rhythm during induction of anesthesia may be mediated by altered responses of the autonomic nervous system to anesthetic agents. Analysis of the power spectrum of the heart rate (PSHR) variability can supply information about the autonomic nervous system, and may be used in order to assess this phenomenon. In this study, 78 patients undergoing coronary artery bypass graft surgery were evaluated. Anesthesia was induced with sufentanil, and neuromuscular blockade with vecuronium, a combination that may cause a decrease in heart rate. Before and after induction of anesthesia, the heart rate (HR), blood pressure (BP), cardiac output (CO), cardiac index (CI), and PSHR components were recorded. PSHR was obtained by using a special algorithm and data acquisition system for real-time spectral analysis. A low-frequency component (LFa, mainly sympathetic) was analyzed from a band of 0.04 Hz to 0.1 Hz. A high-frequency component (RFa, parasympathetic) was identified by the respiratory frequency spectrum. Alterations of the heart rate after induction of anesthesia were defined in order to separate the patient population into two groups: slow heart rate (slow-HR) and stable heart rate (stable-HR). Slow heart rate was defined as a decrease in HR of more than 20% of the baseline value. The variables were analyzed and compared between the slow-HR (n = 25) and stable-HR (n = 53) groups in order to verify the possibility of identifying patients prone to hemodynamic changes after anesthesia induction. There were no differences in preoperative HR, BP, CO, or CI between groups before anesthesia induction.(ABSTRACT TRUNCATED AT 250 WORDS)

[Circulatory assist device in counterpulsation]

PURPOSE

To test a circulatory assist device (CAD) developed in the University of São Paulo. Heart Institute, Bioengineering Division. It is a valveless chamber working through the counterpulsation principle, aiming at assistance to temporary the left ventricle.

PATIENTS AND METHODS

The CAD consists of a rigid polycarbonate shell, which houses in its interior a polyurethane bag with a maximum volume of 110 cm3, driven alternately by pressure and vacuum from an external electropneumatic device synchronized with the ECG. The device worked for 300 hours in a test bench simulating the cardiovascular system in order to verify its resistance to wear and fatigue. The CAD was implanted near the aortic root of five dogs, in whom cardiac failure was induced through the use of propranolol and plasma expanders. The CAD was driven for five periods of 2 minutes separated by pauses of equal duration. The hemodynamic parameters were measured during the mentioned periods.

RESULTS

"In vitro" testing resulted in no wear or fatigue. No leakage was observed. In the "in vivo" testing the averages obtained during the on and off periods of the device showed for the on periods; a) lowering of the systolic pressures of both the aorta (17.5%) and the left ventricle (LV) 15.1%), lowering of the final diastolic pressure of the LV (15.4%) and lowering of the diastolic pressure of the aorta (27.4%); b) increase in cardiac output (45.5%); c) increase of the endocardial viability ratio by 37.5%.

CONCLUSION

The tested device represents a therapeutic option in cases of acute left ventricle failure, since with it an improved cardiac performance was measured and an increased coronary perfusion can be presumed.

Thermographic study of laser on arteries

We analyzed the different effects of CO2, Nd-YAG, and argon lasers on aorta by using a Thermovision infrared system that registered the laser interaction with mongrel dog aorta. The images (thermograms) obtained were processed by a computer, which associated each area of the same temperature with a determined color. These thermograms were compared to histological analysis of the respective samples and the following results were obtained: (1) After the application of each laser there is very little propagation of heat in tissue. (2) The CO2 laser makes tissue reach 100 degrees C in less than 0.05 seconds. (3) The heat dissipation time was higher with the Nd-YAG laser due to higher scattering on tissue. Based on this research we conclude that the CO2 laser was best absorbed, the Nd-YAG laser penetrated human tissue with the best results, and the argon laser had the most significant backscattering.

Laser surgery in enclosed spaces: a review

We describe the results of experiments carried out in the arteries of dogs, rabbits, guinea pigs, and humans, normal or atheromatous, calcified, or not, with the application of the argon and CO2 laser, in vitro or in vivo, directly or indirectly. Similarly, we present the results of laser effects when radiation is delivered through a special catheter with the purpose of producing aortic insufficiency, opening pulmonary valvular stenosis, desobstructing carotid and coronary obstruction induced in dogs as well as atheromatous obstructions in human amputated legs. Arterial wall perforation was present in 50% of all cases. We suggest four options in order to diminish this adverse result: (1) the use of coherent optical bundles which will allow the proper guiding of the laser beam, (2) the construction of a special catheter for proper handling of the laser-carrying fiber, (3) a combination of optical and computer programs which will aid to identify calcified regions, and (4) the use of dyes which will be strongly and selectively absorbed by the atheromas and which will thus allow their destruction at low laser powers.