Altered structural and mechanical properties in decellularized rabbit carotid arteries

Successful management of a 24-year-old pregnant woman with necrotising fasciitis of the forearm

A 24-year-old woman who was 24 weeks pregnant presented to the emergency department with septic shock and an elbow wound that had become infected. She sustained an injury to the tip of the right elbow on a light switch 4 days prior. In the space of 1 day, she developed a necrotising soft tissue infection, which was rapidly spread to the forearm with florid sepsis. Her initial serum C reactive protein was 392 mg/L, and white cell count was 32×10⁹/L. The patient was treated promptly with aggressive surgical debridement and broad-spectrum antibiotics. An early multidisciplinary approach including orthopaedic surgeons, anaesthetics, intensive care, obstetrics, microbiologists and paediatrics was taken. Ultimately, both mother and child had an excellent outcome, the former of whom only had minimal soft tissue resection and primary wound closure. Emphasis is made on first treating the mother as the patient and priority.

Repeated Loading Behavior of Pediatric Porcine Common Carotid Arteries

Rapid flexion and extension of the neck may occur during scenarios associated with traumatic brain injury (TBI), and understanding the mechanical response of the common carotid artery (CCA) to longitudinal stretch may enhance understanding of contributing factors that may influence CCA vasospasm and exacerbate ischemic injury associated with TBI. Immature (4-week-old) porcine CCAs were tested under subcatastrophic (1.5 peak stretch ratio) cyclic loading at 3 Hz for 30 s. Under subcatastrophic cyclic longitudinal extension, the immature porcine CCA displays softening behavior. This softening can be represented by decreasing peak stress and increasing corner stretch values with an increasing number of loading cycles. This investigation is an important first step in the exploration of fatiguelike behavior in arterial tissue that may be subjected to repeated longitudinal loads.

Mechanical behavior of the abdominal aortic aneurysm assessed by biaxial tests in the rat xenograft model

This paper addresses the mechanical biaxial behavior of degraded arteries obtained by the rat xenograft model. For that, a pressure myograph was used to perform extension-inflation tests on abdominal aortic aneurysms (AAAs). Furthermore, residual stresses in the aneurismal wall were assessed by opening angle tests. Thus, the changes in mechanical behavior between native murine aortas, decellularized guinea pig aortas (the grafts) and degraded aortas (AAAs) were investigated. It was shown that decellularized and degraded aortas exhibited a different mechanical behavior than native murine aortas. Indeed, decellularized aortas presented a marked decrease in circumferential stretch and distensibility compared with native aortas. Moreover, we evidenced an exacerbation of these changes in mechanical behavior for AAAs, which showed the lowest distension and distensibility at 100mmHg. The opening angle test also revealed a complete loss of residual stresses in the degraded arterial wall given the non opening of rings extracted from AAAs.

Development and Characterization of a Porcine Mitral Valve Scaffold for Tissue Engineering

Decellularized scaffolds represent a promising alternative for mitral valve (MV) replacement. This work developed and characterized a protocol for the decellularization of whole MVs. Porcine MVs were decellularized with 0.5% (w/v) SDS and 0.5% (w/v) SD and sterilized with 0.1% (v/v) PAA. Decellularized samples were seeded with human foreskin fibroblasts and human adipose-derived stem cells to investigate cellular repopulation and infiltration, and with human colony-forming endothelial cells to investigate collagen IV formation. Histology revealed an acellular scaffold with a generally conserved histoarchitecture, but collagen IV loss. Following decellularization, no significant changes were observed in the hydroxyproline content, but there was a significant reduction in the glycosaminoglycan content. SEM/TEM analysis confirmed cellular removal and loss of some extracellular matrix components. Collagen and elastin were generally preserved. The endothelial cells produced newly formed collagen IV on the non-cytotoxic scaffold. The protocol produced acellular scaffolds with generally preserved histoarchitecture, biochemistry, and biomechanics.

Poly(ethylmethacrylate-co-diethylaminoethyl acrylate) coating improves endothelial re-population, bio-mechanical and anti-thrombogenic properties of decellularized carotid arteries for blood vessel replacement

Decellularized vascular scaffolds are promising materials for vessel replacements. However, despite the natural origin of decellularized vessels, issues such as biomechanical incompatibility, immunogenicity risks and the hazards of thrombus formation, still need to be addressed. In this study, we coated decellularized vessels obtained from porcine carotid arteries with poly (ethylmethacrylate-co-diethylaminoethylacrylate) (8g7) with the purpose of improving endothelial coverage and minimizing platelet attachment while enhancing the mechanical properties of the decellularized vascular scaffolds. The polymer facilitated binding of endothelial cells (ECs) with high affinity and also induced endothelial cell capillary tube formation. In addition, platelets showed reduced adhesion on the polymer under flow conditions. Moreover, the coating of the decellularized arteries improved biomechanical properties by increasing its tensile strength and load. In addition, after 5 days in culture, ECs seeded on the luminal surface of 8g7-coated decellularized arteries showed good regeneration of the endothelium. Overall, this study shows that polymer coating of decellularized vessels provides a new strategy to improve re-endothelialization of vascular grafts, maintaining or enhancing mechanical properties while reducing the risk of thrombogenesis. These results could have potential applications in improving tissue-engineered vascular grafts for cardiovascular therapies with small caliber vessels.

A mathematical model for the determination of forming tissue moduli in needled-nonwoven scaffolds

Formation of engineering tissues (ET) remains an important scientific area of investigation for both clinical translational and mechanobiological studies. Needled-nonwoven (NNW) scaffolds represent one of the most ubiquitous biomaterials based on their well-documented capacity to sustain tissue formation and the unique property of substantial construct stiffness amplification, the latter allowing for very sensitive determination of forming tissue modulus. Yet, their use in more fundamental studies is hampered by the lack of: (1) substantial understanding of the mechanics of the NNW scaffold itself under finite deformations and means to model the complex mechanical interactions between scaffold fibers, cells, and de novo tissue; and (2) rational models with reliable predictive capabilities describing their evolving mechanical properties and their response to mechanical stimulation. Our objective is to quantify the mechanical properties of the forming ET phase in constructs that utilize NNW scaffolds. We present herein a novel mathematical model to quantify their stiffness based on explicit considerations of the modulation of NNW scaffold fiber-fiber interactions and effective fiber stiffness by surrounding de novo ECM. Specifically, fibers in NNW scaffolds are effectively stiffer than if acting alone due to extensive fiber-fiber cross-over points that impart changes in fiber geometry, particularly crimp wavelength and amplitude. Fiber-fiber interactions in NNW scaffolds also play significant role in the bulk anisotropy of the material, mainly due to fiber buckling and large translational out-of-plane displacements occurring to fibers undergoing contraction. To calibrate the model parameters, we mechanically tested impregnated NNW scaffolds with polyacrylamide (PAM) gels with a wide range of moduli with values chosen to mimic the effects of surrounding tissues on the scaffold fiber network. Results indicated a high degree of model fidelity over a wide range of planar strains. Lastly, we illustrated the impact of our modeling approach quantifying the stiffness of engineered ECM after in vitro incubation and early stages of in vivo implantation obtained in a concurrent study of engineered tissue pulmonary valves in an ovine model.

STATEMENT OF SIGNIFICANCE

Regenerative medicine has the potential to fully restore diseased tissues or entire organs with engineered tissues. Needled-nonwoven scaffolds can be employed to serve as the support for their growth. However, there is a lack of understanding of the mechanics of these materials and their interactions with the forming tissues. We developed a mathematical model for these scaffold-tissue composites to quantify the mechanical properties of the forming tissues. Firstly, these measurements are pivotal to achieve functional requirements for tissue engineering implants; however, the theoretical development yielded critical insight into particular mechanisms and behaviors of these scaffolds that were not possible to conjecture without the insight given by modeling, let alone describe or foresee a priori.

Determining the optimal protocol for preparing an acellular scaffold of tissue engineered small-diameter blood vessels

Although detergent-based decellularization protocols have been widely used to obtain a natural extracellular matrix (ECM) scaffold in tissue engineering, some key challenges still exist. To achieve an optimum natural decellularized scaffold for the construction of tissue-engineered small-diameter blood vessels (TEBV), porcine carotid arteries (PCAs) were decellularized by combining sodium dodecyl sulfate (SDS), sodium deoxycholate (SDC) and Triton X-100 (Triton) in different concentrations. Tissue samples were processed and their histological, biochemical and biomechanical characteristics were investigated. Results showed that only two methods 0.5% (SDS + SDC) and 1% (SDS + SDC) could completely remove of the cellular contents and preserve the native ECM architecture. Furthermore, 1% (SDS + SDC) based methods acquire preferable porosity and suitable mechanical strength. Residual Triton in the ECM scaffold holds intensive cytotoxity. In conclusion, 1%(SDS + SDC) based method can obtain a superior PCAs scaffold for the construction of TEBV. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 619-631, 2018.

Decellularized extracellular matrices for tissue engineering applications

Decellularization removes cellular antigens while preserving the ultrastructure and composition of extracellular matrix (ECM). Decellularized ECM (DECM) scaffolds have been widely used in various tissue engineering applications with varying levels of success. The mechanical, architectural and bioactive properties of a DECM scaffold depend largely on the method of decellularization and dictate its clinical efficacy. This article highlights the advantages and challenges associated with the clinical use of DECM scaffolds. Poor mechanical strength is a significant disadvantage of some DECM scaffolds in the repair of load-bearing tissues as well as critical-size defects, where long-term mechanical support is required for the regenerating tissue. Combining DECM scaffolds with synthetic biocompatible polymers could provide a useful strategy to circumvent the issues of poor mechanical stability. This article reviews studies that have combined DECM scaffolds from various tissues with synthetic polymers to create hybrid scaffolds using electrospinning. These hybrid scaffolds provide a mechanical backbone while retaining the bioactive properties of DECM, thus offering a significant advantage for tissue engineering and regenerative medicine applications.

A fiber-progressive-engagement model to evaluate the composition, microstructure, and nonlinear pseudoelastic behavior of porcine arteries and decellularized derivatives

The theoretical fiber-progressive-engagement model was proposed to describe the pseudoelastic behavior of an artery pre- and post-decellularization treatments. Native porcine arteries were harvested and decellularized with 0.05% trypsin for 12 h. The uniaxial tensile test data were fitted to the fiber-progressive-engagement model proposed herein. The effects of decellularization on the morphology, structural characteristics, and composition of vessel walls were studied. The experimental stress-strain curve was fitted to the model in the longitudinal and circumferential direction, which demonstrated the adequacy of the proposed model (R²>0.99). The initial and turning strains were similar in the longitudinal and circumferential directions in the aorta, suggesting the occurrence of collagen conjugation in both directions. Discrepancies in the initial and turning strain and initial and stiff modulus in both directions in the coronary artery revealed the anisotropic features of this vessel. Decellularization induced a decrease in the initial and turning strains, a slight change in the initial modulus, and a substantial decrease in the stiffness modulus. The decrease in the initial and turning strain can be attributed to the loss of waviness of collagen bundles because of the considerable decrease in elastin and glycosaminoglycan contents. This simple non-linear model can be used to determine the fiber modulus and waviness degree of vascular tissue. Based on these results, this mechanical test can be used as a screening tool for the selection of an optimized decellularization protocol for arterial tissues.

STATEMENT OF SIGNIFICANCE

Decellularized vascular graft has potential in clinical application, such as coronary artery bypass surgery, peripheral artery bypass surgery or microsurgery. An ideal decellularization protocol requires balance in cell removal efficiency and extracellular matrix preserving. Both biochemical and biomechanical properties are crucial to the success of scaffold in cell seeding and animal study. A comprehensive understanding of the composition, microstructure, and mechanical behavior of the arterial wall is the key to the development of decellularized vascular grafts. For this purpose, we proposed this "Fiber-Progressive-Engagement" model to evaluate the microstructure, composition and mechanical properties of porcine coronary artery. The model provides a new perspective regarding the non-linear behavior of arterial tissue and its decellularized derivatives. It can be widely applied to different types of tissues, as demonstrated in the aorta and coronary artery. This model has several advantages; it provides an improved fit of non-linear curves (R²>0.99), can be used to elucidate the pseudoelastic properties of porcine vascular tissues using the concept of fiber engagement, and can estimate an elastic modulus with greater accuracy (compared to the graphical estimation or calculation by simple linear fittings), as well as to plot typical stress-strain curves.

Diameter and thickness-related variations in mechanical properties of degraded arterial wall in the rat xenograft model

The purpose of this study was to evaluate the diameter and thickness-related variations in mechanical properties of degraded arterial wall. To this end, ring tests were performed on 31 samples from the rat xenograft model of abdominal aortic aneurysm (AAA) and failure properties were determined. An inverse finite element method was then employed to identify the material parameters of a hyperelastic and incompressible strain energy function. Correlations with outer diameter and wall thickness of the rings were examined. Furthermore, we investigated the changes in mechanical properties between the grafts, which consist in guinea pig decellularized aortas, native murine aortas and degraded aortas (AAAs). Decellularized aortas presented a significantly lower ultimate strain associated with a higher stiffening rate compared to native aortas. AAAs exhibited a significantly lower ultimate stress than other groups and an extensible-but-stiff behavior. The proposed approach revealed correlations of ultimate stress and material parameters of aneurysmal aortas with outer diameter and thickness. In particular, the negative correlations of the material parameter accounting for the response of the non-collagenous matrix with diameter and thickness (r=-0.67 and r=-0.73, p<0.001) captured the gradual loss of elastin with dilatation observed in histology (r=-0.97, p<0.001). Moreover, it exposed the progressive weakening of the wall with enlargement and thickening (r=-0.64 and r=-0.69, p<0.001), suggesting that wall thickness and diameter may be indicators of rupture risk in the rat xenograft model.

Poly(ɛ-caprolactone)/gelatin composite electrospun scaffolds with porous crater-like structures for tissue engineering

Electrospinning has been widely used to fabricate scaffolds imitating the structure of natural extracellular matrix (ECM). However, conventional electrospinning produces tightly compacted nanofiber layers with only small superficial pores and a lack of bioactivity, which limit the usefulness of electrospinning in biomedical applications. Thus, a porous poly(ε-caprolactone) (PCL)/gelatin composite electrospun scaffold with crater-like structures was developed. Porous crater-like structures were created on the scaffold by a gas foaming/salt leaching process; this unique fiber structure had more large pore areas and higher porosity than the conventional electrospun fiber network. Various ratios of PCL/gelatin (concentration ratios: 100/0, 75/25, and 50/50) composite electrospun scaffolds with and without crater-like structures were characterized by their microstructures, surface chemistry, degradation, mechanical properties, and ability to facilitate cell growth and infiltration. The combination of PCL and gelatin endowed the scaffold with both structural stability of PCL and bioactivity of gelatin. All ratios of scaffolds with crater-like structures showed fairly similar surface chemistry, degradation rates, and mechanical properties to equivalent scaffolds without crater-like structures; however, craterized scaffolds displayed higher human mesenchymal stem cell (hMSC) proliferation and infiltration throughout the scaffolds after 7-day culture. Therefore, these results demonstrated that PCL/gelatin composite electrospun scaffolds with crater-like structures can provide a structurally and biochemically improved three-dimensional ECM-mimicking microenvironment.

Decellularisation and histological characterisation of porcine peripheral nerves

Peripheral nerve injuries affect a large proportion of the global population, often causing significant morbidity and loss of function. Current treatment strategies include the use of implantable nerve guide conduits (NGC's) to direct regenerating axons between the proximal and distal ends of the nerve gap. However, NGC's are limited in their effectiveness at promoting regeneration Current NGCs are not suitable as substrates for supporting either neuronal or Schwann cell growth, as they lack an architecture similar to that of the native extracellular matrix (ECM) of the nerve. The aim of this study was to create an acellular porcine peripheral nerve using a novel decellularisation protocol, in order to eliminate the immunogenic cellular components of the tissue, while preserving the three‐dimensional histoarchitecture and ECM components. Porcine peripheral nerve (sciatic branches were decellularised using a low concentration (0.1%; w/v) sodium dodecyl sulphate in conjunction with hypotonic buffers and protease inhibitors, and then sterilised using 0.1% (v/v) peracetic acid. Quantitative and qualitative analysis revealed a ≥95% (w/w) reduction in DNA content as well as preservation of the nerve fascicles and connective tissue. Acellular nerves were shown to have retained key ECM components such as collagen, laminin and fibronectin. Slow strain rate to failure testing demonstrated the biomechanical properties of acellular nerves to be comparable to fresh controls. In conclusion, we report the production of a biocompatible, biomechanically functional acellular scaffold, which may have use in peripheral nerve repair. Biotechnol. Bioeng. 2016;113: 2041–2053. © 2016 The Authors. Biotechnology and Bioengineering published by Wiley Periodicals, Inc.

Perfusion-decellularized skeletal muscle as a three-dimensional scaffold with a vascular network template

There exists a great need for repair grafts with similar volume to human skeletal muscle that can promote the innate ability of muscle to regenerate following volumetric muscle loss. Perfusion decellularization is an attractive technique for extracellular matrix (ECM) scaffold from intact mammalian organ or tissue which has been successfully used in tissue reconstruction. The perfusion-decellularization of skeletal muscle has been poorly assessed and characterized, but the bioactivity and functional capacity of the obtained perfusion skeletal muscle ECM (pM-ECM) to remodel in vivo is unknown. In the present study, pM-ECM was prepared from porcine rectus abdominis (RA). Perfusion-decellularization of porcine RA effectively removed cellular and nuclear material while retaining the intricate three-dimensional microarchitecture and vasculature networks of the native RA, and many of the bioactive ECM components and mechanical properties. In vivo, partial-thickness abdominal wall defects in rats repaired with pM-ECM showed improved neovascularization, myogenesis and functional recellularization compared to porcine-derived small intestinal submucosa (SIS). These findings show the biologic potential of RA pM-ECM as a scaffold for supporting site appropriate, tissue reconstruction, and provide a better understanding of the importance maintaining the tissue-specific complex three-dimensional architecture of ECM during decellularization and regeneration.

Fabrication and characterisation of biomimetic, electrospun gelatin fibre scaffolds for tunica media-equivalent, tissue engineered vascular grafts

It is increasingly recognised that biomimetic, natural polymers mimicking the extracellular matrix (ECM) have low thrombogenicity and functional motifs that regulate cell-matrix interactions, with these factors being critical for tissue engineered vascular grafts especially grafts of small diameter. Gelatin constitutes a low cost substitute of soluble collagen but gelatin scaffolds so far have shown generally low strength and suture retention strength. In this study, we have devised the fabrication of novel, electrospun, multilayer, gelatin fibre scaffolds, with controlled fibre layer orientation, and optimised gelatin crosslinking to achieve not only compliance equivalent to that of coronary artery but also for the first time strength of the wet tubular acellular scaffold (swollen with absorbed water) same as that of the tunica media of coronary artery in both circumferential and axial directions. Most importantly, for the first time for natural scaffolds and in particular gelatin, high suture retention strength was achieved in the range of 1.8-1.94 N for wet acellular scaffolds, same or better than that for fresh saphenous vein. The study presents the investigations to relate the electrospinning process parameters to the microstructural parameters of the scaffold, which are further related to the mechanical performance data of wet, crosslinked, electrospun scaffolds in both circumferential and axial tubular directions. The scaffolds exhibited excellent performance in human smooth muscle cell (SMC) proliferation, with SMCs seeded on the top surface adhering, elongating and aligning along the local fibres, migrating through the scaffold thickness and populating a transverse distance of 186 μm and 240 μm 9 days post-seeding for scaffolds of initial dry porosity of 74 and 83%, respectively.

An in vivo study of a gold nanocomposite biomaterial for vascular repair

Currently vascular repairs are treated using synthetic or biologic patches, however these patches have an array of complications, including calcification, rupture, re-stenosis, and intimal hyperplasia. An active patch material composed of decellularized tissue conjugated to gold nanoparticles (AuNPs) was developed and the long term biocompatibility and cellular integration was investigated. Porcine abdominal aortic tissue was decellularized and conjugated with 100 nm gold nanoparticles (AuNP). These patches were placed over a longitudinal arteriotomy of the thoracic aorta in six pigs. The animals were monitored for six months. Gross, histological, and immunohistochemical analyses of the patches were performed after euthanasia. Grossly there was minimal scar tissue with the patches still visible on the outer surface of the vessel. The inner lumen was smooth with a seamless transition from patch to native tissue. Histology demonstrated infiltration of host cells into the patch material. The immunohistochemical results demonstrated an endothelial cell layer forming over the patch within the vessel. Smooth muscle cells were repopulating the biomaterial in all animals. These results demonstrated that the AuNP biomaterial patch integrated well with the host tissue and did not failed over the six month implantation time.

Effect of Intensified Decellularization of Equine Carotid Arteries on Scaffold Biomechanics and Cytotoxicity

Decellularized equine carotid arteries (dEAC) are suggested to represent an alternative for alloplastic vascular grafts in haemodialysis patients to achieve vascular access. Recently it was shown that intensified detergent treatment completely removed cellular components from dEAC and thereby significantly reduced matrix immunogenicity. However, detergents may also affect matrix composition and stability and render scaffolds cytotoxic. Therefore, intensively decellularized carotids (int-dEAC) were now evaluated for their biomechanical characteristics (suture retention strength, burst pressure and circumferential compliance at arterial and venous systolic and diastolic pressure), matrix components (collagen and glycosaminoglycan content) and indirect and direct cytotoxicity (WST-8 assay and endothelial cell seeding) and compared with native (n-EAC) and conventionally decellularized carotids (con-dEAC). Both decellularization protocols comparably reduced matrix compliance (venous pressure compliance: 32.2 and 27.4% of n-EAC; p < 0.01 and arterial pressure compliance: 26.8 and 23.7% of n-EAC, p < 0.01) but had no effect on suture retention strength and burst pressure. Matrix characterization revealed unchanged collagen contents but a 39.0% (con-dEAC) and 26.4% (int-dEAC, p < 0.01) reduction of glycosaminoglycans, respectively. Cytotoxicity was not observed in either dEAC matrix which was also displayed by an intact endothelial lining after seeding. Thus, even intensified decellularization generates matrix scaffolds highly suitable for vascular tissue engineering purposes, e.g., the generation of haemodialysis shunts.

Age-related vascular stiffening: causes and consequences

Arterial stiffening occurs with age and is closely associated with the progression of cardiovascular disease. Stiffening is most often studied at the level of the whole vessel because increased stiffness of the large arteries can impose increased strain on the heart leading to heart failure. Interestingly, however, recent evidence suggests that the impact of increased vessel stiffening extends beyond the tissue scale and can also have deleterious microscale effects on cellular function. Altered extracellular matrix (ECM) architecture has been recognized as a key component of the pre-atherogenic state. Here, the underlying causes of age-related vessel stiffening are discussed, focusing on age-related crosslinking of the ECM proteins as well as through increased matrix deposition. Methods to measure vessel stiffening at both the macro- and microscale are described, spanning from the pulse wave velocity measurements performed clinically to microscale measurements performed largely in research laboratories. Additionally, recent work investigating how arterial stiffness and the changes in the ECM associated with stiffening contributed to endothelial dysfunction will be reviewed. We will highlight how changes in ECM protein composition contribute to atherosclerosis in the vessel wall. Lastly, we will discuss very recent work that demonstrates endothelial cells (ECs) are mechano-sensitive to arterial stiffening, where changes in stiffness can directly impact EC health. Overall, recent studies suggest that stiffening is an important clinical target not only because of potential deleterious effects on the heart but also because it promotes cellular level dysfunction in the vessel wall, contributing to a pathological atherosclerotic state.

Decellularization of porcine carotid by the recipient's serum and evaluation of its biocompatibility using a rat autograft model

Recently, decellularized tissues for organ transplantation and regeneration have been actively studied in the field of tissue engineering. In the decellularization process, surfactants such as sodium dodecyl sulfate (SDS) have been most commonly used to remove cellular components from the tissue. However, the residual surfactant may be cytotoxic in vivo and has been reported to hinder remodeling after implantation. In addition, treatment with surfactants may destroy the important extracellular matrix (ECM) structure that allows the decellularized tissue to function as a scaffold for cells. In this study, decellularized tissues with high biocompatibility were created using the recipient's serum. By immersing a heterogeneous tissue in serum conditioned to activate the complement system and DNase I, its cellular components could be removed. Compared to an SDS-treated graft, the serum-treated graft preserved the native structure of its ECM. When subcutaneously implanted into an isogenic inbred rat, the graft treated with the recipient's serum resulted in less immunorejection than did the SDS-treated graft.

Transplantation of devitalized muscle scaffolds is insufficient for appreciable de novo muscle fiber regeneration after volumetric muscle loss injury

Volumetric muscle loss (VML) is a traumatic and functionally debilitating muscle injury with limited treatment options. Developmental regenerative therapies for the repair of VML typically comprise an ECM scaffold. In this study, we tested if the complete reliance on host cell migration to a devitalized muscle scaffold without myogenic cells is sufficient for de novo muscle fiber regeneration. Devitalized (muscle ECM with no living cells) and, as a positive control, vital minced muscle grafts were transplanted to a VML defect in the tibialis anterior muscle of Lewis rats. Eight weeks post-injury, devitalized grafts did not appreciably promote de novo muscle fiber regeneration within the defect area, and instead remodeled into a fibrotic tissue mass. In contrast, transplantation of vital minced muscle grafts promoted de novo muscle fiber regeneration. Notably, pax7+ cells were absent in remote regions of the defect site repaired with devitalized scaffolds. At 2 weeks post-injury, the devitalized grafts were unable to promote an anti-inflammatory phenotype, while vital grafts appeared to progress to a pro-regenerative inflammatory response. The putative macrophage phenotypes observed in vivo were supported in vitro, in which soluble factors released from vital grafts promoted an M2-like macrophage polarization, whereas devitalized grafts failed to do so. These observations indicate that although the remaining muscle mass serves as a source of myogenic cells in close proximity to the defect site, a devitalized scaffold without myogenic cells is inadequate to appreciably promote de novo muscle fiber regeneration throughout the VML defect.

Development of an acellular tumor extracellular matrix as a three-dimensional scaffold for tumor engineering

Tumor engineering is defined as the construction of three-dimensional (3D) tumors in vitro with tissue engineering approaches. The present 3D scaffolds for tumor engineering have several limitations in terms of structure and function. To get an ideal 3D scaffold for tumor culture, A549 human pulmonary adenocarcinoma cells were implanted into immunodeficient mice to establish xenotransplatation models. Tumors were retrieved at 30-day implantation and sliced into sheets. They were subsequently decellularized by four procedures. Two decellularization methods, Tris-Trypsin-Triton multi-step treatment and sodium dodecyl sulfate (SDS) treatment, achieved complete cellular removal and thus were chosen for evaluation of histological and biochemical properties. Native tumor tissues were used as controls. Human breast cancer MCF-7 cells were cultured onto the two 3D scaffolds for further cell growth and growth factor secretion investigations, with the two-dimensional (2D) culture and cells cultured onto the Matrigel scaffolds used as controls. Results showed that Tris-Trypsin-Triton multi-step treated tumor sheets had well-preserved extracellular matrix structures and components. Their porosity was increased but elastic modulus was decreased compared with the native tumor samples. They supported MCF-7 cell repopulation and proliferation, as well as expression of growth factors. When cultured within the Tris-Trypsin-Triton treated scaffold, A549 cells and human colorectal adenocarcinoma cells (SW-480) had similar behaviors to MCF-7 cells, but human esophageal squamous cell carcinoma cells (KYSE-510) had a relatively slow cell repopulation rate. This study provides evidence that Tris-Trypsin-Triton treated acellular tumor extracellular matrices are promising 3D scaffolds with ideal spatial arrangement, biomechanical properties and biocompatibility for improved modeling of 3D tumor microenvironments.

A new method using xenogeneicacellular dermal matrix in the reconstruction of lacrimal drainage

Aims

To prospectively evaluate the reliability and efficacy of a new treatment for the reconstruction of the lacrimal duct using a new histo-engineered material, xenogeneic (bovine) acellular dermal matrix.

Method

Five patients (five eyes) with partial or total absence of the lacrimal duct were included in the study. Four patients (four eyes) suffered from traumatic injuries to the lacrimal duct and one patient (one eye) had congenital absence of the lacrimal drainage system. A pedal graft of conjunctiva was taken from the fornix area and rolled into a tube structure after being attached to the acellular dermal matrix.

Results

The average duration of follow-up for the patients was 7.2 months (ranging from 6 to 12 months). After surgery, the new duct in the nasal cavity could be observed above the middle turbinate by nasal endoscopy. Patency was confirmed by pressing in the area of the lacrimal sac and visualising air bubbles in the nasal cavity. Additionally, the meatus above the middle turbinate of the nasal cavity was stained and visualised after patients underwent Jones dye test 1 (JDT1). Five tear ducts proved to be effective through irrigation testing and epiphora symptoms were alleviated in all cases.

Conclusions

The newly reconstructed lacrimal duct, formed by the shift of autogenous conjunctival petal and the attachment of acellular dermal matrix, was successful in all five cases and suggests a new solution for the complex lacrimal duct lesion and congenital anomalies of the lacrimal duct.

On the decellularization of fresh or frozen human umbilical arteries: implications for small-diameter tissue engineered vascular grafts

Most tissues, including those to be decellularized for tissue engineering applications, are frozen for long term preservation. Such conventional cryopreservation has been shown to alter the structure and mechanical properties of tissues. Little is known, however, how freezing affects decellularization of tissues. The purpose of this study was two-fold: to examine the effects of freezing on decellularization of human umbilical arteries (HUAs), which represent a potential scaffolding material for small-diameter tissue-engineered vascular grafts, and to examine how decellularization affects the mechanical properties of frozen HUAs. Among many decellularization methods, hypotonic sodium dodecyl sulfate solution was selected as the decellularizing agent and tested on fresh HUAs to optimize decellularization conditions. The efficiency of decellularization was evaluated by DNA assay and histology every 12 up to 48 h. The optimized decellularization protocol was then performed on frozen HUAs. The stiffness, burst pressure, and suture retention strength of fresh HUAs and frozen HUAs before and after decellularization were also examined. It appeared that freezing decreased the efficiency of decellularization, which may be attributed to the condensed extracellular matrix caused by freezing. While the stiffness of fresh HUAs did not change significantly after decellularization, decellularization reduced the compliance of frozen HUAs. Interestingly, the stiffness of decellularized frozen HUAs was similar to that of decellularized fresh HUAs. Although little difference in stiffness was observed, we suggest avoiding freezing if more efficient and complete decellularization is desired.

Optimum parameters for freeze-drying decellularized arterial scaffolds

Decellularized arterial scaffolds have achieved success in advancing toward clinical use as vascular grafts. However, concerns remain regarding long-term preservation and sterilization of these scaffolds. Freeze drying offers a means of overcoming these concerns. In this study, we investigated the effects of various freeze-drying protocols on decellularized porcine carotid arteries and consequently, determined the optimum parameters to fabricate a stable, preserved scaffold with unaltered mechanical properties. Freeze drying by constant slow cooling to two final temperatures ((Tf), -10 °C and -40 °C) versus instant freezing was investigated by histological examination and mechanical testing. Slow cooling to Tf= -10 °C produced a stiffer and less distensible response than the non freeze-dried scaffolds and resulted in disruption to the collagen fibers. The mechanical response of Tf= -40 °C scaffolds demonstrated disruption to the elastin network, which was confirmed with histology. Snap freezing scaffolds in liquid nitrogen and freeze drying to Tf= -40 °C with a precooled shelf at -60 °C produced scaffolds with unaltered mechanical properties and a histology resembling non-freeze-dried scaffolds. The results of this study demonstrate the importance of optimizing the nucleation and ice crystal growth/size to ensure homogenous drying, preventing extracellular matrix disruption and subsequent inferior mechanical properties. This new manufacturing protocol creates the means for the preservation and sterilization of decellularized arterial scaffolds while simultaneously maintaining the mechanical properties of the tissue.

Perfusion-decellularized pancreas as a natural 3D scaffold for pancreatic tissue and whole organ engineering

Approximately 285 million people worldwide suffer from diabetes, with insulin supplementation as the most common treatment measure. Regenerative medicine approaches such as a bioengineered pancreas has been proposed as potential therapeutic alternatives. A bioengineered pancreas will benefit from the development of a bioscaffold that supports and enhances cellular function and tissue development. Perfusion-decellularized organs are a likely candidate for use in such scaffolds since they mimic compositional, architectural and biomechanical nature of a native organ. In this study, we investigate perfusion-decellularization of whole pancreas and the feasibility to recellularize the whole pancreas scaffold with pancreatic cell types. Our result demonstrates that perfusion-decellularization of whole pancreas effectively removes cellular and nuclear material while retaining intricate three-dimensional microarchitecture with perfusable vasculature and ductal network and crucial extracellular matrix (ECM) components. To mimic pancreatic cell composition, we recellularized the whole pancreas scaffold with acinar and beta cell lines and cultured up to 5 days. Our result shows successful cellular engraftment within the decellularized pancreas, and the resulting graft gave rise to strong up-regulation of insulin gene expression. These findings support biological utility of whole pancreas ECM as a biomaterials scaffold for supporting and enhancing pancreatic cell functionality and represent a step toward bioengineered pancreas using regenerative medicine approaches.

Pressure shift freezing as potential alternative for generation of decellularized scaffolds

Background. Protocols using chemical reagents for scaffold decellularization can cause changes in the properties of the matrix, depending on the type of tissue and the chemical reagent. Technologies using physical techniques may be possible alternatives for the production grafts with potential superior matrix characteristics. Material and Methods. We tested four different technologies for scaffold decellularization. Group 1: high hydrostatic pressure (HHP), 1 GPa; Group 2: pressure shift freezing (PSF); Group 3: pulsed electric fields (PEF); Group 4: control group: detergent (SDS). The degree of decellularization was assessed by histological analysis and the measurement of residual DNA. Results. Tissue treated with PSF showed a decellularization with a penetration depth (PD) of 1.5 mm and residual DNA content of 24% ± 3%. HHD treatment caused a PD of 0.2 mm with a residual DNA content of 28% ± .4%. PD in PEF was 0.5 mm, and the residual DNA content was 49% ± 7%. In the SDS group, PD was found to be 5 mm, and the DNA content was determined at 5% ± 2%. Conclusion. PSF showed promising results as a possible technique for scaffold decellularization. The penetration depth of PSF has to be optimized, and the mechanical as well as the biological characteristics of decellularized grafts have to be evaluated.

Detergent-Enzymatic Decellularization of Swine Blood Vessels: Insight on Mechanical Properties for Vascular Tissue Engineering

Small caliber vessels substitutes still remain an unmet clinical need; few autologous substitutes are available, while synthetic grafts show insufficient patency in the long term. Decellularization is the complete removal of all cellular and nuclear matters from a tissue while leaving a preserved extracellular matrix representing a promising tool for the generation of acellular scaffolds for tissue engineering, already used for various tissues with positive outcomes. The aim of this work is to investigate the effect of a detergent-enzymatic decellularization protocol on swine arteries in terms of cell removal, extracellular matrix preservation, and mechanical properties. Furthermore, the effect of storage at −80°C on the mechanical properties of the tissue is evaluated. Swine arteries were harvested, frozen, and decellularized; histological analysis revealed complete cell removal and preserved extracellular matrix. Furthermore, the residual DNA content in decellularized tissues was far low compared to native one. Mechanical testings were performed on native, defrozen, and decellularized tissues; no statistically significant differences were reported for Young’s modulus, ultimate stress, compliance, burst pressure, and suture retention strength, while ultimate strain and stress relaxation of decellularized vessels were significantly different from the native ones. Considering the overall results, the process was confirmed to be suitable for the generation of acellular scaffolds for vascular tissue engineering.

In vivo and in vitro measurements of pulmonary arterial stiffness: A brief review

During the progression of pulmonary hypertension (PH), proximal pulmonary arteries (PAs) undergo remodeling such that they become thicker and the elastic modulus increases. Both of these changes increase the vascular stiffness. The increase in pulmonary vascular stiffness contributes to increased right ventricular (RV) afterload, which causes RV hypertrophy and eventually failure. Studies have found that proximal PA stiffness or its inverse, compliance, is strongly related to morbidity and mortality in patients with PH. Therefore, accurate in vivo measurement of PA stiffness is useful for prognoses in patients with PH. It is also important to understand the structural changes in PAs that occur with PH that are responsible for stiffening. Here, we briefly review the most common parameters used to quantify stiffness and in vivo and in vitro methods for measuring PA stiffness in human and animal models. For in vivo approaches, we review invasive and noninvasive approaches that are based on measurements of pressure and inner or outer diameter or cross-sectional area. For in vitro techniques, we review several different testing methods that mimic one, two or several aspects of physiological loading (e.g., uniaxial and biaxial testing, dynamic inflation-force testing). Many in vivo and in vitro measurement methods exist in the literature, and it is important to carefully choose an appropriate method to measure PA stiffness accurately. Therefore, advantages and disadvantages of each approach are discussed.

Mechanical evaluation of decellularized porcine thoracic aorta

BACKGROUND

Decellularized tissues are expected to have major cellular immunogenic components removed and in the meantime maintain similar mechanical strength and extracellular matrix (ECM) structure. However, the decellularization processes likely cause alterations of the ECM structure and thus influence the mechanical properties. In the present study, the effects of different decellularization protocols on the (passive) mechanical properties of the resulted porcine aortic ECM were evaluated.

METHODS

Decellularization methods using anionic detergent (sodium dodecyl sulfate), enzymatic detergent (Trypsin), and non-ionic detergent [tert-octylphenylpolyoxyethylen (Triton X-100)] were adopted to obtain decellularized porcine aortic ECM. Histologic studies and scanning electron microscopy were performed to confirm the removal of cells and to examine the structure of ECM. Biaxial tensile testing was used to characterize both the elastic and viscoelastic mechanical behaviors of decellularized ECM.

RESULTS

All three decellularization protocols remove the cells effectively. The major ECM structure is preserved under sodium dodecyle sulfate (SDS) and Triton X-100 treatments. However, the structure of Trypsin treated ECM is severely disrupted. SDS and Triton X-100 decellularized ECM exhibits similar elastic properties as intact aorta tissues. Decellularized ECM shows less stress relaxation than intact aorta due to the removal of cells. Creep behavior is negligible for both decellularized ECM and intact aortas.

CONCLUSION

SDS and Triton X-100 decellularized ECM tissue appeared to maintain the critical mechanical and structural properties and might work as a potential material for further vascular tissue engineering.

Form Follows Function: Advances in Trilayered Structure Replication for Aortic Heart Valve Tissue Engineering

Tissue engineering the aortic heart valve is a challenging endeavor because of the particular hemodynamic and biologic conditions present in the native aortic heart valve. The backbone of an ideal valve substitute should be a scaffold that is strong enough to withstand billions of repetitive bending, flexing and stretching cycles, while also being slowly degradable to allow for remodeling. In this review we highlight three overlooked aspects that might influence the long term durability of tissue engineered valves: replication of the native valve trilayered histoarchitecture, duplication of the three-dimensional shape of the valve and cell integration efforts focused on getting the right number and type of cells to the right place within the valve structure and driving them towards homeostatic maintenance of the valve matrix. We propose that the trilayered structure in the native aortic valve that includes a middle spongiosa layer cushioning the motions of the two external fibrous layers should be our template for creation of novel scaffolds with improved mechanical durability. Furthermore, since cells adapt to micro-loads within the valve structure, we believe that interstitial cell remodeling of the valvular matrix will depend on the accurate replication of the structures and loads, resulting in successful regeneration of the valve tissue and extended durability.

Mass transfer trends occurring in engineered ex vivo tissue scaffolds

In vivo the vasculature provides an effective delivery system for cellular nutrients; however, artificial scaffolds have no such mechanism, and the ensuing limitations in mass transfer result in limited regeneration. In these investigations, the regional mass transfer properties that occur through a model scaffold derived from the human umbilical vein (HUV) were assessed. Our aim was to define the heterogeneous behavior associated with these regional variations, and to establish if different decellularization technologies can modulate transport conditions to improve microenvironmental conditions that enhance cell integration. The effect of three decellularization methods [Triton X-100 (TX100), sodium dodecyl sulfate (SDS), and acetone/ethanol (ACE/EtOH)] on mass transfer, cellular migration, proliferation, and metabolic activity were assessed. Results show that regional variation in tissue structure and composition significantly affects both mass transfer and cell function. ACE/EtOH decellularization was shown to increase albumin mass flux through the intima and proximate-medial region (0-250 μm) when compared with sections decellularized with TX100 or SDS; although, mass flux remained constant over all regions of the full tissue thickness when using TX100. Scaffolds decellularized with TX100 were shown to promote cell migration up to 146% further relative to SDS decellularized samples. These results show that depending on scaffold derivation and expectations for cellular integration, specificities of the decellularization chemistry affect the scaffold molecular architecture resulting in variable effects on mass transfer and cellular response.

Progressive structural and biomechanical changes in elastin degraded aorta

Aortic aneurysm is an important clinical condition characterized by common structural changes such as the degradation of elastin, loss of smooth muscle cells, and increased deposition of fibrillary collagen. With the goal of investigating the relationship between the mechanical behavior and the structural/biochemical composition of an artery, this study used a simple chemical degradation model of aneurysm and investigated the progressive changes in mechanical properties. Porcine thoracic aortas were digested in a mild solution of purified elastase (5 U/mL) for 6, 12, 24, 48, and 96 h. Initial size measurements show that disruption of the elastin structure leads to increased artery dilation in the absence of periodic loading. The mechanical properties of the digested arteries, measured with a biaxial tensile testing device, progress through four distinct stages termed (1) initial-softening, (2) elastomer-like, (3) extensible-but-stiff, and (4) collagen-scaffold-like. While stages 1, 3, and 4 are expected as a result of elastin degradation, the S-shaped stress versus strain behavior of the aorta resulting from enzyme digestion has not been reported previously. Our results suggest that gradual changes in the structure of elastin in the artery can lead to a progression through different mechanical properties and thus reveal the potential existence of an important transition stage that could contribute to artery dilation during aneurysm formation.

Mechanical characterization of a customized decellularized scaffold for vascular tissue engineering

Several challenges persist when attempting to utilize decellularized tissue as a scaffold for vascular tissue engineering. Namely: poor cell infiltration/migration, excessive culture times associated with repopulating the scaffolds, and the achievement of a quiescent medial layer. In an attempt to create an optimum vascular scaffold, we customized the properties of decellularized porcine carotid arteries by: (i) creating cavities within the medial layer to allow direct injection of cells, and (ii) controlling the amount of collagen digestion to increase the porosity. Histological examination of our customized scaffold revealed a highly porous tissue structure containing consistent medial cavities running longitudinally through the porous scaffold wall. Mechanical testing of the customized scaffold showed that our minimal localized disruption to the ECM does not have a detrimental effect on the bulk mechanical response of the tissue. The results demonstrate that an increased stiffness and reduced distensibility occurs after decellularization when compared to the native tissue, however post scaffold customization we can revert the scaffold tensile properties back to that of the native tissue. This most noteworthy result occurs in the elastin dominant phase of the tensile response of the scaffold, indicating that no disruption has occurred to the elastin network by our decellularization and customization techniques. Additionally, the bulk seeding potential of the customized scaffold was demonstrated by direct injection of human smooth muscle cells through the medial cavities. The optimum cell dispersion was observed in the highest porosity scaffold, with large cell numbers retained within the medial layer after 24 h static culture. In summary, this study presents a novel customized decellularized vascular scaffold that has the capability of bulk seeding the media, and in tandem to this method, the porosity of the scaffold has been increased without compromising the mechanical integrity.

Tissue engineering of small-diameter vascular grafts by endothelial progenitor cells seeding heparin-coated decellularized scaffolds

Successful construction of a small-diameter bioartificial vascular graft remains a great challenge. This study reports on novel tissue engineering vascular grafts (TEVGs) constructed by endothelial progenitor cells and heparin-coated decellularized vessels (DV). The DVs were fabricated from canine carotid arteries with observable depletion of cellular components. After heparin coating, the scaffolds possessed excellent antithrombogeneity. Canine endothelial progenitor cells harvested from peripheral blood were expanded and seeded onto heparin-coated DVs and cocultured in a custom-made bioreactor to construct TEVGs. Thereafter, the TEVGs were implanted into the carotid arteries of cell-donor dogs. After 3 months of implantation, the luminal surfaces of TEVGs exhibited complete endothelium regeneration, however, only a few disorderly cells and thrombosis overlaid the luminal surfaces of control DVs grafts, and immunofluorescent staining showed that the seeded cells existed in the luminal sides and the medial parts of the explanted TEVGs and partially contributed to the endothelium formation. Specifically, TEVGs exhibited significantly smaller hyperplastic neointima area compared with the DVs, not only at midportion (0.64 ± 0.08 vs. 2.13 ± 0.12 mm(2) , p < 0.001), but also at anastomotic sites (proximal sites, 1.03 ± 0.09 vs. 3.02 ± 0.16 mm(2), p < 0.001; distal sites, 1.84 ± 0.15 vs. 3.35 ± 0.21 mm(2), p < 0.001). Moreover, TEVGs had a significantly higher patency rate than the DVs after 3 months of implantation (19/20 vs. 12/20, p < 0.01). Overall, this study provided a new strategy to develop small-diameter TEVGs with excellent biocompatibility and high patency rate.

Combined use of decellularized allogeneic artery conduits with autologous transdifferentiated adipose-derived stem cells for facial nerve regeneration in rats

Natural biological conduits containing seed cells have been widely used as an alternative strategy for nerve gap reconstruction to replace traditional nerve autograft techniques. The purpose of this study was to investigate the effects of a decellularized allogeneic artery conduit containing autologous transdifferentiated adipose-derived stem cells (dADSCs) on an 8-mm facial nerve branch lesion in a rat model. After 8 weeks, functional evaluation of vibrissae movements and electrophysiological assessment, retrograde labeling of facial motoneurons and morphological analysis of regenerated nerves were performed to assess nerve regeneration. The transected nerves reconstructed with dADSC-seeded artery conduits achieved satisfying regenerative outcomes associated with morphological and functional improvements which approached those achieved with Schwann cell (SC)-seeded artery conduits, and superior to those achieved with artery conduits alone or ADSC-seeded artery conduits, but inferior to those achieved with nerve autografts. Besides, numerous transplanted PKH26-labeled dADSCs maintained their acquired SC-phenotype and myelin sheath-forming capacity inside decellularized artery conduits and were involved in the process of axonal regeneration and remyelination. Collectively, our combined use of decellularized allogeneic artery conduits with autologous dADSCs certainly showed beneficial effects on nerve regeneration and functional restoration, and thus represents an alternative approach for the reconstruction of peripheral facial nerve defects.

Comparison of three methods for the derivation of a biologic scaffold composed of adipose tissue extracellular matrix

Extracellular matrix (ECM)-based scaffold materials have been used successfully in both preclinical and clinical tissue engineering and regenerative medicine approaches to tissue reconstruction. Results of numerous studies have shown that ECM scaffolds are capable of supporting the growth and differentiation of multiple cell types in vitro and of acting as inductive templates for constructive tissue remodeling after implantation in vivo. Adipose tissue represents a potentially abundant source of ECM and may represent an ideal substrate for the growth and adipogenic differentiation of stem cells harvested from this tissue. Numerous studies have shown that the methods by which ECM scaffold materials are prepared have a dramatic effect upon both the biochemical and structural properties of the resultant ECM scaffold material as well as the ability of the material to support a positive tissue remodeling outcome after implantation. The objective of the present study was to characterize the adipose ECM material resulting from three methods of decellularization to determine the most effective method for the derivation of an adipose tissue ECM scaffold that was largely free of potentially immunogenic cellular content while retaining tissue-specific structural and functional components as well as the ability to support the growth and adipogenic differentiation of adipose-derived stem cells. The results show that each of the decellularization methods produced an adipose ECM scaffold that was distinct from both a structural and biochemical perspective, emphasizing the importance of the decellularization protocol used to produce adipose ECM scaffolds. Further, the results suggest that the adipose ECM scaffolds produced using the methods described herein are capable of supporting the maintenance and adipogenic differentiation of adipose-derived stem cells and may represent effective substrates for use in tissue engineering and regenerative medicine approaches to soft tissue reconstruction.

Indentation measurements of the subendothelial matrix in bovine carotid arteries

Artery biomechanics are an important factor in cardiovascular function and atherosclerosis development; as such, the macro-mechanics of whole arteries are well-characterized. However, much less is known about the mechanical properties of individual layers in the blood vessel wall. Since there is significant evidence to show that cells can sense the mechanical properties of their matrix, it is critical to characterize the mechanical properties of these individual layers at the scale sensed by cells. Here, we measured subendothelium mechanics in bovine carotid arteries using atomic force microscopy (AFM) indentation. To specifically indent the subendothelium, we evaluated three potential de-endothelialization methods: scraping, paper imprinting, and saponin incubation. Using scanning electron microscopy, histology stains, immunohistochemistry, and multiphoton microscopy, we found that scraping was the only effective de-endothelialization method capable of removing endothelial cells and leaving the subendothelial matrix largely intact. To determine the indentation modulus of the subendothelial matrix, both untreated and scraped (de-endothelialized) bovine carotid arteries were indented with a spherical AFM probe and the data were fit using the Hertz model. Both the endothelium on the untreated artery and the en face subendothelium had similar indentation moduli: E=2.5 ± 1.9 and 2.7 ± 1.1 kPa, respectively. These measurements are the first to quantify the micro-scale mechanics of the subendothelial layer, and constitute a critical step in understanding the relationship between altered subendothelial micromechanics and disease progression.

Effect of decellularization protocol on the mechanical behavior of porcine descending aorta

Enzymatic-detergent decellularization treatments may use a combination of chemical reagents to reduce vascular tissue to sterilized scaffolds, which may be seeded with endothelial cells and implanted with a low risk of rejection. However, these chemicals may alter the mechanical properties of the native tissue and contribute to graft compliance mismatch. Uniaxial tensile data obtained from native and decellularized longitudinal aortic tissue samples was analyzed in terms of engineering stress and fit to a modified form of the Yeoh rubber model. One decellularization protocol used SDS, while the other two used TritonX-100, RNase-A, and DNase-I in combination with EDTA or sodium-deoxycholate. Statistical significance of Yeoh model parameters was determined by paired t-test analysis. The TritonX-100/EDTA and 0.075% SDS treatments resulted in relatively variable mechanical changes and did not effectively lyse VSMCs in aortic tissue. The TritonX-100/sodium-deoxycholate treatment effectively lysed VSMCs and was characterized by less variability in mechanical behavior. The data suggests a TritonX-100/sodium-deoxycholate treatment is a more effective option than TritonX-100/EDTA and SDS treatments for the preparation of aortic xenografts and allografts because it effectively lyses VSMCs and is the least likely treatment, among those considered, to promote a decrease in mechanical compliance.

Characterization of the complete fiber network topology of planar fibrous tissues and scaffolds

Understanding how engineered tissue scaffold architecture affects cell morphology, metabolism, phenotypic expression, as well as predicting material mechanical behavior has recently received increased attention. In the present study, an image-based analysis approach that provides an automated tool to characterize engineered tissue fiber network topology is presented. Micro-architectural features that fully defined fiber network topology were detected and quantified, which include fiber orientation, connectivity, intersection spatial density, and diameter. Algorithm performance was tested using scanning electron microscopy (SEM) images of electrospun poly(ester urethane)urea (ES-PEUU) scaffolds. SEM images of rabbit mesenchymal stem cell (MSC) seeded collagen gel scaffolds and decellularized rat carotid arteries were also analyzed to further evaluate the ability of the algorithm to capture fiber network morphology regardless of scaffold type and the evaluated size scale. The image analysis procedure was validated qualitatively and quantitatively, comparing fiber network topology manually detected by human operators (n = 5) with that automatically detected by the algorithm. Correlation values between manual detected and algorithm detected results for the fiber angle distribution and for the fiber connectivity distribution were 0.86 and 0.93 respectively. Algorithm detected fiber intersections and fiber diameter values were comparable (within the mean +/- standard deviation) with those detected by human operators. This automated approach identifies and quantifies fiber network morphology as demonstrated for three relevant scaffold types and provides a means to: (1) guarantee objectivity, (2) significantly reduce analysis time, and (3) potentiate broader analysis of scaffold architecture effects on cell behavior and tissue development both in vitro and in vivo.