Tissue engineering of artificial organs

Numerical modeling of oxygen diffusion in tissue spheroids undergoing fusion using function representation and finite volumes

A three-dimensional cell culture called a spheroid serves as a foundational entity in a wide variety of modern tissue engineering applications, including 3D-bioprinting and preclinical drug testing. Lack of oxygen within tissue spheroids hinders metabolism of cells and eventually leads to cell death. Prevention of necrosis is crucial to success of tissue engineering methods and such prevention requires estimation of cell viability in the spheroid. We propose a novel approach for numerical modeling of diffusion in tissue spheroids during their fusion. The approach is based on numerical solutions of partial differential equations and the application of Function Representation (FRep) framework for geometric modeling. We present modeling of oxygen diffusion based on meshes derived from the geometry of fusing spheroids, a method for selecting optimal spheroid size, and several statistics for estimating cellular viability. Our findings provide insights into oxygen diffusion in three-dimensional cell cultures thus improving the robustness of biotechnological methods that employ tissue spheroids.

GelMA-based hydrogel biomaterial scaffold: A versatile platform for regenerative endodontics

Endodontic therapy, while generally successful, is primarily limited to mature teeth, hence the pressing need to explore regenerative approaches. Gelatin methacryloyl (GelMA) hydrogels have emerged as pivotal biomaterials, promising a bright future for dental pulp regeneration. Despite advancements in tissue engineering and biomaterials, achieving true pulp tissue regeneration remains a formidable task. GelMA stands out for its injectability, rapid gelation, and excellent biocompatibility, serving as the cornerstone of scaffold materials. In the pursuit of dental pulp regeneration, GelMA holds significant potential, facilitating the delivery of stem cells, growth factors, and other vital substances crucial for tissue repair. Presently, in the field of dental pulp regeneration, researchers have been diligently utilizing GelMA hydrogels as engineering scaffolds to transport various effective substances to promote pulp regeneration. However, existing research is relatively scattered and lacks comprehensive reviews and summaries. Therefore, the primary objective of this article is to elucidate the application of GelMA hydrogels as regenerative scaffolds in this field, thereby providing clear direction for future researchers. Additionally, this article provides a comprehensive discussion on the synthesis, characterization, and application of GelMA hydrogels in root canal therapy regeneration. Furthermore, it offers new application strategies and profound insights into future challenges, such as optimizing GelMA formulations to mimic the complex microenvironment of pulp tissue and enhancing its integration with host tissues.

Silk fibroin-based biomaterials for disc tissue engineering

Low back pain is the major cause of disability worldwide, and intervertebral disc degeneration (IVDD) is one of the most important causes of low back pain. Currently, there is no method to treat IVDD that can reverse or regenerate intervertebral disc (IVD) tissue, but the recent development of disc tissue engineering (DTE) offers a new means of addressing these disadvantages. Among numerous biomaterials for tissue engineering, silk fibroin (SF) is widely used due to its easy availability and excellent physical/chemical properties. SF is usually used in combination with other materials to construct biological scaffolds or bioactive substance delivery systems, or it can be used alone. The present article first briefly outlines the anatomical and physiological features of IVD, the associated etiology and current treatment modalities of IVDD, and the current status of DTE. Then, it highlights the characteristics of SF biomaterials and their latest research advances in DTE and discusses the prospects and challenges in the application of SF in DTE, with a view to facilitating the clinical process of developing interventions related to IVD-derived low back pain caused by IVDD.

Regeneration of the digestive system in the crinoid Lamprometra palmata (Mariametridae, Comatulida)

The morphology and regeneration of the digestive system and tegmen after autotomy of the visceral mass in the crinoid Lamprometra palmata (Clark 1921) was studied. The gut has a five-lobed shape and is covered by a tegmen. The tegmen consists of epidermis and underlying connective tissue. The digestive tube can be divided into three parts: esophagus, intestine, and rectum. At 6 h post-autotomy, the calyx surface is covered by a layer of amoebocytes and juxtaligamental cells (JLCs). At 14-18 h, post-autotomy transdifferentiation of JLCs begins and give rise to the epidermis and cells of digestive system. On days 1-2 post-autotomy, JLCs undergo the mesenchymal-epithelial transition. Some JLCs turn into typical epidermal cells, while other JLCs form small closed epithelial structures that represent the gut anlage. On day 4 post-autotomy, the animals have a mouth opening and a small anal cone. On day 7 post-autotomy, the visceral mass and the digestive system become fully formed but are smaller than normal. A 24-h exposure of L. palmata individuals to a 10^-7 M colchicine solution did not slow down regeneration, and the timing of gut formation was similar to that in the control animals. We conclude that JLCs are the major cell source for gut and epidermis regeneration in L. palmata. The main mechanisms of morphogenesis are cell migration, mesenchymal-epithelial transition, and transdifferentiation.

Synthesis, characterization and applications of poly-aliphatic amine dendrimers and dendrons

In the current era, the dendrimers have vast potential applications in the area of electronics, healthcare, pharmaceuticals, biotechnology, engineering products, photonics, drug delivery, catalysis, electronic devices, nanotechnologies and environmental issues. This review recaps the synthesis, characterization and applications of poly-aliphatic amine dendrimers.

Three-dimensional bioprinting collagen/silk fibroin scaffold combined with neural stem cells promotes nerve regeneration after spinal cord injury

Many studies have shown that bio-scaffolds have important value for promoting axonal regeneration of injured spinal cord. Indeed, cell transplantation and bio-scaffold implantation are considered to be effective methods for neural regeneration. This study was designed to fabricate a type of three-dimensional collagen/silk fibroin scaffold (3D-CF) with cavities that simulate the anatomy of normal spinal cord. This scaffold allows cell growth in vitro and in vivo. To observe the effects of combined transplantation of neural stem cells (NSCs) and 3D-CF on the repair of spinal cord injury. Forty Sprague-Dawley rats were divided into four groups: sham (only laminectomy was performed), spinal cord injury (transection injury of T10 spinal cord without any transplantation), 3D-CF (3D scaffold was transplanted into the local injured cavity), and 3D-CF + NSCs (3D scaffold co-cultured with NSCs was transplanted into the local injured cavity. Neuroelectrophysiology, imaging, hematoxylin-eosin staining, argentaffin staining, immunofluorescence staining, and western blot assay were performed. Apart from the sham group, neurological scores were significantly higher in the 3D-CF + NSCs group compared with other groups. Moreover, latency of the 3D-CF + NSCs group was significantly reduced, while the amplitude was significantly increased in motor evoked potential tests. The results of magnetic resonance imaging and diffusion tensor imaging showed that both spinal cord continuity and the filling of injury cavity were the best in the 3D-CF + NSCs group. Moreover, regenerative axons were abundant and glial scarring was reduced in the 3D-CF + NSCs group compared with other groups. These results confirm that implantation of 3D-CF combined with NSCs can promote the repair of injured spinal cord. This study was approved by the Institutional Animal Care and Use Committee of People's Armed Police Force Medical Center in 2017 (approval No. 2017-0007.2).

“UroMaix” Scaffolds: Novel Collagen Matrices for Application in Tissue Engineering of the Urinary Tract

Reconstruction of bladder and ureter tissue is indicated in cases of injury, stenosis, infection or tumor. Substitution by ileum, colon or pure synthetic polymers generates a variety of complications. Biohybrid tissue mimicking structural and functional attributes of the multilayered wall architecture of the urinary conduit may be the solution to current problems.

This study reports on porcine urinary tract cells isolated and placed on UroMaix matrices with different degrees of cross-linking produced from highly purified type I collagen from medically approved porcine tissue. A patented procedure revealed membrane structures composed of a dense fibrous side and an open fibrous side. These scaffolds with the porcine urinary tract cells were incubated in a batch culture system for up to 14 days. Cell growth and topographical orientation were examined.

Urothelial cells showed maximum attachment and a significant increase of living cells on the dense fiber layer of UroMaix-1. No attachment of urothelial cells occurred on the other prototypes. Smooth muscle cells showed similar behavior within the open fiber layer of all UroMaix matrices. Both urothelial and smooth muscle cells retained their phenotypes as demonstrated by the immunostaining of epithelial cytokeratin 18 and the smooth muscle myosin heavy chain respectively. Thus we could show that UroMaix scaffolds support the attachment and proliferation of urinary tract cells. The elastomeric properties of the collagenous matrices promise attractive applications in the tissue engineering of the urinary tract with its high mechanical demands.

In Vitro Construction of Urinary Bladder Wall using Porcine Primary Cells Reseeded on Acellularized Bladder Matrix and Small Intestinal Submucosa

BACKGROUND

Partial or radical cystectomy requires replacement of the urinary reservoir normally achieved by using small or large bowel segments. Our aim was to establish tissue engineering of an bioartificial bladder wall using primary cultures of porcine urothelial (pUC) and bladder smooth muscle cells (pSMC) to be reseeded on different acellular biological matrices.

METHODS

Primary porcine cultures of pUC and pSMC were established from open bladder biopsy material 25 mm2 in size. Acellular matrix was generated either from a) porcine bladder wall segments or b) tubular small intestinal submucosa with the still attached decellularized muscularis layer. Reseeding of these matrices with primary cells was done in a two-dimensional static model and in a three-dimensional rotating bioreactor perfused with cell culture medium for a period of 6 weeks.

RESULTS

Prior to reseeding the cultured cells were characterized as pUC and pSMC by immunohistochemical staining with either anti-keratin 7 or anti-alpha actin. For both matrices a reseeded double layer cell system of pUC and pSMC could be identified after incubation in the described systems for 6 weeks.

CONCLUSIONS

Our results document successful generation of tissue engineered urinary bladder wall, which can be used in further large animal transplantation experiments.

Biomaterial-Supported Cell Transplantation Treatments for Spinal Cord Injury: Challenges and Perspectives

Spinal cord injury (SCI), resulting in para- and tetraplegia caused by the partial or complete disruption of descending motor and ascending sensory neurons, represents a complex neurological condition that remains incurable. Following SCI, numerous obstacles comprising of the loss of neural tissue (neurons, astrocytes, and oligodendrocytes), formation of a cavity, inflammation, loss of neuronal circuitry and function must be overcome. Given the multifaceted primary and secondary injury events that occur with SCI treatment options are likely to require combinatorial therapies. While several methods have been explored, only the intersection of two, cell transplantation and biomaterial implantation, will be addressed in detail here. Owing to the constant advance of cell culture technologies, cell-based transplantation has come to the forefront of SCI treatment in order to replace/protect damaged tissue and provide physical as well as trophic support for axonal regrowth. Biomaterial scaffolds provide cells with a protected environment from the surrounding lesion, in addition to bridging extensive damage and providing physical and directional support for axonal regrowth. Moreover, in this combinatorial approach cell transplantation improves scaffold integration and therefore regenerative growth potential. Here, we review the advances in combinatorial therapies of Schwann cells (SCs), astrocytes, olfactory ensheathing cells (OECs), mesenchymal stem cells, as well as neural stem and progenitor cells (NSPCs) with various biomaterial scaffolds.

What's in the Pipeline about Bladder Reconstructive Surgery? Some Remarks on the State of the Art

The fusion of engineering with cell biology and advances in biomaterials may lead to de novo construction of implantable organs. Engineering of neobladder from autologous urothelial and smooth muscle cells cultured on biocompatible, either synthetic or naturally-derived substrates, is now feasible in preclinical studies and may have clinical applicability in the near future. The development of a bioartificial bladder would warrant the prevention of both the metabolic and neoplastic shortcomings of the intestinal neobladder. Two tissue-engineering techniques for bladder reconstruction have been tested on animals: 1) the in vivo technique involves the use of naturally-derived biomaterials for functional native bladder regeneration 2) the in vitro technique involves the establishment of autologous urothelial and smooth muscle cell culture from the host's urinary tract, after which the cells are seeded on the biodegradable matrix-scaffold to create a composite graft that is implanted into the same host for complete histotectonic regeneration. Waiting for the creation of a complete tissue-engineered bladder with a trigone-shaped base, we suggest, in surgical oncology after radical cystectomy, the realization of conduit or continent pouch using tissue-engineered material.

Injectable natural polymer compound for tissue engineering of intervertebral disc: In vitro study

Intervertebral disc degeneration is recognized to be the leading cause for chronic low-back pain. Injectable hydrogel is one of the great interests for tissue engineering and cell encapsulation specially for intervertebral (IVD) affecting rate of regeneration success, in this study we assessed viscoelastic properties of a Chitosan-β glycerophosphate-hyaluronic acid, Chondroitin-6-sulfate, type 2 of Collagen, gelatin, fibroin silk (Ch-β-GP-HA-CS-Col-Ge-FS) hydrogel which was named as NP hydrogel that is natural extracellular matrix of IVD. Chitosan-based hydrogel was made in the ratio of 1.5%: 7%: 1%:1%:1%-1.5%-1% (Ch: β-GP: HA-CS-Col-Ge-FS). Gelation time and other rheological properties were studied using amplitude sweep and frequency sweep tests. Also, the cytotoxicity of the hydrogel invitro assessed by MTT and trypan blue tests. Morphology of the hydrogel and attachment of NP cells were evaluated by SEM. Our result showed that NP hydrogel in 4°C is an injectable transparent solution. It started gelation in 37°C after about 30min. Gelation temperature of NP hydrogel was 37°C. Storage modulus (G') of this hydrogel at 37°C was almost constant over a wide range of strain. MTT and trypan blue tests showed hydrogel was cytocompatible. The obtained results suggest that this hydrogel would be a natural and cytocompatible choice as an injectable scaffold for using in vivo study of IVD regeneration.

Sonographic abnormalities in augmented bladder using porcine intestinal submucosa (SIS)

ABSTRACT Among the different materials for bladder augmentation, porcine intestinal submucosa (SIS) is the most widely investigated and stands out for its ability as a cell scaffold. In this context, the ultrasound examination allows the detection of changes from the surgical procedure, enabling the early verification of potential complications and evaluation of patient outcomes. The aim of this paper is to describe the main sonographic findings in dogs submitted to cystoplasty using acellular SIS and seeded with homologous smooth muscle cells at 30 (M30) and 60 (M60) days postoperatively. Sonographic changes included irregularities and thickening of bladder wall especially at M30. Additionally, were visualized urinary sediment and uroliths in animals submitted to acellular SIS cistoplasty. Abdominal ultrasonography was useful in the postoperative evaluation of animals undergoing cystoplasty with acellular or seeded SIS.

Mitomycin-C-Loaded Alginate Carriers for Bladder Cancer Chemotherapy

In this study Mitomycin-C-loaded alginate carriers were prepared as an alternative system in the postoperative chemotherapy in bladder cancer. Alginate was preferred because of its constructive properties and it was prepared in a cylindrical shape to facilitate the insertion of the carrier for in vivo studies. The alginate carriers were prepared as calcium alginate gel as well as crosslinking agents. In the preparation of the alginate carriers, precipitation medium concentration, cross-linker concentration, and Mitomycin-C/alginate ratio were changed to obtain drug attachment to the inner wall of bladder and/or optimum release rate of the agent. Due to the hydrogel structure of the alginate, the swelling behavior of the polymer was evaluated by gravimetric determinations in aqueous media periodically. Swelling ratios of the alginate carriers were changed from 30 to 65% based on precipitation medium, cross-linker concentration, and swelling medium pH. For prediction of the bioadhesion of the alginate carriers to the inner surface of bladder, in vitro bioadhesion tests were performed by using fresh bladders which were taken from New Zealand rabbits. It was observed that the in vitro Mitomycin-C release and bioadhesion values were significantly changed with changing swelling ratios.

Mitomycin-C-loaded Alginate Carriers for Bladder Cancer Chemotherapy: In Vivo Studies

After a transurethral resection (TUR), chemotherapy and/or immunotherapy is usually applied for 6 to 36 weeks to prevent the recurrence of tumoral tissue. These therapies have many problems, so an alternative pharmacotherapeutic agent delivery system that would supply suitable drug levels for specific time periods was explored. A model pharmacotherapeutic agent, mitomycin-C, delivery system was prepared by using alginate, a mucoadhesive polymer, as the carrier. The alginate carriers were prepared by precipitation and cross-linked with ethylene glycol diglycydyl ether. The alginate carrier precipitation medium (CaCl2), cross-linker and mitomycin-C/alginate ratio were varied to obtain desired attachment to the inner wall of the bladder and provide optimum release rate of the agent. The carrier was cylindrically formed to facilitate insertion for in vivostudies. The mitomycin-C-loaded alginate carriers were implanted into the bladder of New Zealand rabbits. Swelling ratios of the alginate carriers varied from 20% to 45% based on precipitation medium and cross-linker concentration. Ultrasonographic and histopathological findings showed that alginate implants could be kept in position for 1 week.

Comparative Physico-chemical and in Vitro Properties of Fibrillated Collagen Scaffolds from Different Sources

Collagen from different sources was isolated and designed as scaffolds to act as a three-dimensional substrate for culturing human skin fibroblasts, which can be used as dermal substitutes. The thermodynamic behavior of the scaffolds developed was analyzed through Differential Scanning Calorimetric (DSC) and Thermogravimetric analysis (TGA). Analysis by Fourier Transform Infrared Spectroscopy (FTIR) revealed the functional groups in the scaffolds and the mechanical stability of various scaffolds was assessed through tensile strength analysis. Human skin fibroblasts were cultured on the developed scaffolds to assess their cellular interaction and behavior, and the morphological characteristics of the cultured fibroblasts were evaluated using Scanning Electron Microscopy (SEM). The collagen scaffold exhibited unique features when developed from various sources and it was observed that cells could grow and proliferate well and spread as a monolayer in the reconstituted collagen scaffold.

Fabrication and characterization of biodegradable polymeric films as a corneal stroma substitute

Background:

Biodegradable elastomeric materials such as poly glycerol sebacate (PGS) have gained much current attention in the field of soft tissue engineering. The present study reports the synthesis of PGS with molar ratios of 1:1, 2:3, and 3:2 of glycerol and sebacic acid via polycondensation reaction and tests the effect of PGS on human corneal epithelial (HCE) cells viability in vitro.

Materials and Methods:

PGS films were prepared by the casting method. We tried to fabricate PGS with different compositions and various properties as being a viable alternative to the corneal stroma in cornea tissue engineering. The chemical properties of the prepared polymer were investigated by means of attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR) analysis and the in vitro cytotoxicity was investigated by the Alamarblue method.

Results:

The functional groups observed in the PGS FTIR spectrums of PGS with various molar ratios were the same. However, the main difference was the time of completing the cross-linking reaction. The PGS prepared by 2:3 ratio as a molar ratio had the fastest and the 3:2 ratio had the lowest cross-linking rate because of the higher amount of sebacic acid. Results of the Alamarblue cytotoxicity test assay showed no deleterious effect on HCE cell viability and proliferation.

Conclusions:

PGS is a potentially good candidate material for corneal tissue engineering because of its lack of in vitro HCE cell toxicity.

Grafts of porcine small intestinal submucosa seeded with cultured homologous smooth muscle cells for bladder repair in dogs

Background

Due to numerous complications associated to gastrointestinal augmented cystoplasty, this study aimed to analyze the anatomic repair of the bladder of 10 female dogs using grafts of porcine small intestinal submucosa (SIS) seeded with cultured homologous smooth muscle cells, and compare them with the acellular SIS grafts.

Results

We assessed the possible side effects and complications of each type of graft by clinical examination, abdominal ultrasound and laboratory findings. Anatomic repair of neoformed bladder was assessed by histological staining for H/E and Masson's Trichrome, analyzed with a Nikon Photomicroscope connected to the system of image analysis Image J.

Conclusions

We propose that SIS associated to homologous smooth cells can improve the quality of tissue repair, and consequently decrease the potential complications inherent to acellular SIS.

Chitin-based materials in tissue engineering: applications in soft tissue and epithelial organ

Chitin-based materials and their derivatives are receiving increased attention in tissue engineering because of their unique and appealing biological properties. In this review, we summarize the biomedical potential of chitin-based materials, specifically focusing on chitosan, in tissue engineering approaches for epithelial and soft tissues. Both types of tissues play an important role in supporting anatomical structures and physiological functions. Because of the attractive features of chitin-based materials, many characteristics beneficial to tissue regeneration including the preservation of cellular phenotype, binding and enhancement of bioactive factors, control of gene expression, and synthesis and deposition of tissue-specific extracellular matrix are well-regulated by chitin-based scaffolds. These scaffolds can be used in repairing body surface linings, reconstructing tissue structures, regenerating connective tissue, and supporting nerve and vascular growth and connection. The novel use of these scaffolds in promoting the regeneration of various tissues originating from the epithelium and soft tissue demonstrates that these chitin-based materials have versatile properties and functionality and serve as promising substrates for a great number of future applications.

Intrinsics and dynamics of fat grafts: an in vitro study

BACKGROUND

Despite a revived interest in fat grafting procedures, clinicians still fail to demonstrate clearly the in vivo behavior of fat grafts as a dynamic tissue substitute. However, the basic principles in cellular biology teach us that cells can survive and develop, provided that a structural matrix exists that directs their behavior. The purpose of this in vitro study was to analyze that behavior of crude fat grafts, cultured on a three-dimensional laminin-rich matrix.

METHODS

Nonprocessed, human fat biopsy specimens (approximately 1 mm) were inoculated on Matrigel-coated wells to which culture medium was added. The control group consisted of fat biopsy specimens embedded in medium alone. The cellular proliferation pattern was followed over 6 weeks. Additional cultures of primary generated cellular spheroids were performed and eventually subjected to adipogenic differentiation media.

RESULTS

A progressive outgrowth of fibroblast-like cells from the core fat biopsy specimen was observed in both groups. Within the Matrigel group, an interconnecting three-dimensional network of spindle-shaped cells was established. This new cell colony reproduced spheroids that functioned again as solitary sources of cellular proliferation. Addition of differentiation media resulted in lipid droplet deposition in the majority of generated cells, indicating the initial steps of adipogenic differentiation.

CONCLUSIONS

The authors noticed that crude, nonprocessed fat biopsy specimens do have considerable potential for future tissue engineering-based applications, provided that the basic principles of developmental, cellular biology are respected. Spontaneous in vitro expansion of the stromal cells present in fat grafts within autologous and injectable matrices could create "off-the-shelf" therapies for reconstructive procedures.

The effect of hypoxia on in vitro prevascularization of a thick soft tissue

Prevascularizing an implantable tissue is one strategy to improve oxygen (O(2)) transport throughout larger tissues upon implantation. This study examined the role of hypoxia both during (i.e., as a stimulus) and after (i.e., mimicking implant conditions) vascularization of an implantable tissue. Tissues consisted of microcarrier beads coated with human umbilical vein endothelial cells embedded in fibrin. The fibrin was covered with a monolayer of normal human lung fibroblasts (NHLFs), or exposed to conditioned media from NHLFs. Capillary networks developed at 20% or 1% O(2) tension for 8 days. In some experiments, tissues were supplemented with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, whereas in others the tissues prevascularized at 20% O(2) were transferred to 1% O(2) for 8 additional days. Maximal capillary formation occurred in media conditioned by NHLFs at 20% O(2), supplemented with VEGF (concentration >10 pM). Hypoxia (1% O(2)) did not stimulate basic fibroblast growth factor production and decreased in vitro angiogenesis, despite an increase in endogenous VEGF production. Hypoxia also degraded a preformed capillary network within 4 days. Hence, strategies to prevascularize implantable tissues may not require the physical presence of stromal cells, but will likely require fibroblast-derived growth factors in addition to VEGF to maintain capillary growth.

Human clinical experience with adipose precursor cells seeded on hyaluronic acid-based spongy scaffolds

Histioconductive approaches to soft-tissue defects use scaffolds seeded with lineage- and tissue-specific progenitors to generate tissue which should reside in equilibrium with adjacent tissue. Scaffolds guide histiogenesis by ensuring cell-cell and cell-matrix interactions. Hyaluronic acid-based (HA) preadipocyte-seeded scaffolds were evaluated for their adipo-conductive potential and efficacy in humans. Preadipocytes were isolated from lipoaspirate material and seeded on HA scaffolds. The cellular bio-hybrid (ADIPOGRAFT) and an acellular control scaffold (HYAFF11) were implanted subcutaneously. At specific time points (2, 8 and 16 weeks) explants were analyzed histopathologically with immunohistochemistry. No adverse tissue effects occurred. Volume loss and consistent degradation of the HYAFF11 scaffolds compared to the ADIPOGRAFT group indicated progressive tissue integration. No consistent histological differences between both groups were observed. By 8 weeks all void spaces within the scaffolds were filled with cells with pronounced matrix deposition in the ADIPOGRAFT bio-hybrids. Here we show that HA scaffolds were stable cell carriers and had the potential to generate volume-retaining tissue. However, no adipogenic differentiation was observed within the preadipocyte-seeded scaffolds.

Tissue engineered venous matrices for potential applications in the urogenital tract

Tissue engineering is lacking inexpensive, easily applicable techniques for tissue replacement. We investigated the potential use of native veins for tissue-engineering applications in the urological field. Forty-eight porcine veins, half seeded with urothelial cells and half unseeded, were kept in vitro for 7 days. Four seeded and four unseeded scaffolds were analyzed after 3 and 7 days. The remaining 32 veins were implanted subcutaneously into 16 athymic mice. Four athymic mice were sacrificed after 2, 4, 8, and 12 weeks. Histochemistry, immunohistochemistry (anti-pancytokeratin AE1/AE3, anti-desmin), western blot analyses (CD31), and scanning electron microscopy were performed in the retrieved specimens. The histochemistry of the seeded matrices showed the presence of urothelial cells in vitro and in vivo. After 12 weeks, a multilayer of urothelial cells was present in the hemotoxylin and eosin staining, positive for anti-pancytokeratin AE1/AE3. The western blot analyses showed vascularization of the veins in vivo. The results of scanning electron microscopy revealed a cellular layer on the veins. Native venous matrices may be used as tissue-engineered constructs for reconstructing the urinary tract. The clinical relevance of this approach must be proven in a large-animal model.

CO-alkene polymers are biocompatible scaffolds for primary urothelial cells in vitro and in vivo

OBJECTIVE

To investigate CO-alkene polymers, novel synthetic nonbiodegradable polymers, as a potential biomaterial for urological applications.

MATERIALS AND METHODS

Porcine urothelial cells were seeded on cover glasses (96 wells; 10 000 cells/well) coated with CO-alkene polymers [propylene/N-Acetyl-O'-(hex-5-enyl)-l-tyrosine ethyl ester/CO (PTCO) and hexene-CO (HxCO)]. The following conditions were investigated: cells seeded; (i) on PTCO, (ii) on HxCO, (iii) in PTCO-conditioned medium, (iv) in HxCO-conditioned medium, (v) on glass without polymers, (vi) on polystyrene, and (vii) on polystyrene treated with 1.25% NaCl (toxic control). Cell counts, cell death detection assay, and a cell activity assay (XTT, a tetrazolium-based colorimetric assay) were performed after 3, 6 and 9 days. Urothelial-cell seeded-PTCO films (0.5 x 10(6) cells/cm(2)) were implanted into the subcutaneous space of athymic mice for up to 12 weeks and unseeded PTCO polymers were implanted as a negative control.

RESULTS

The urothelial cell adherence rates on the polymers were similar to those for glass and polystyrene. The cell activity (XTT assay) was higher in cells seeded on the polymers than in cells seeded on polystyrene and glass after 3 and 6 days. There were no significant differences between the apoptosis rates of all groups at the given sample times, except for the high levels in the toxic control. In vivo the urothelial cells survived on the polymers for 12 weeks with no adverse reactions in any of the mice.

CONCLUSIONS

CO-alkene polymers are biocompatible materials for urothelial cells in vitro and in vivo, and thus are potential biomaterials for the urogenital tract.

Evaluation of the viability of cultured corneal endothelial cells by quantitative electron probe X-ray microanalysis

Construction of artificial organs and tissues by tissue engineering is strongly dependent on the availability of viable cells. For that reason, the viability and the physiological status of cells kept in culture must be evaluated before the cells can be used for clinical purposes. In this work, we determined the viability of isolated rabbit corneal endothelial cells by trypan blue staining and quantitative electron probe X-ray microanalysis. Our results showed that the ionic content of potassium in cultured corneal endothelial cells tended to rise initially, but significantly decreased in cells in the fifth (and final) subculture, especially in comparison to cells in the fourth subculture (P < 0.001). However, the concentration of sulfur was higher in the fifth subculture than in the fourth subculture (P < 0.001), with a nonsignificant increase in sodium in the fifth subculture (P = 0.031). These data imply a remarkable decrease in the K/Na ratio from the fourth to the fifth subculture. Our microanalytical results, along with the morphological differences between cells in the last two subcultures, are compatible with an early phase of the preapoptotic process in the fifth subculture, and suggest that cells of the first four subcultures would be better candidates for tissue engineering.

[In vitro three-dimensional reconstruction of human bladder mucosa]

OBJECTIVE

The purpose of this study is to apply the in vitro keratinocyte culture techniques and the tissue engineering principles to human urothelium, to reconstruct an in vitro three-dimensional human bladder mucosa, suitable for grafting.

MATERIAL AND METHODS

Biopsy specimens of human bladder mucosa were obtained from patients undergoing suprapubic prostatectomy, in vitro cultured and finally, an immunohistochemical study was made.

RESULTS

A three-dimensional in vitro tissue was obtained, composed of a bio-artificial submucosa (fibrin gel and fibroblast) where the uroepithelial cells were seeding. We used a biodegradable polyglycolic acid mesh to facilitate the tissue manipulation and implantation. An immature epithelium was obtained with a weak immunostaining to cytokeratins. The immunohistochemical study could not demonstrate the development of basement membrane.

CONCLUSIONS

In vitro keratinocyte culture techniques could be applied to other epithelial tissues like the urothelium. We obtained a three-dimensional in vitro tissue suitable for grafting in a relatively short time, which needs the matrix interactions in order to mature.

Cranial Bone Regeneration Using a Composite Scaffold of Beta-Tricalcium Phosphate, Collagen, and Autologous Bone Fragments

OBJECTIVE

The aim of our study was to examine the tissue response and new bone formation induced by beta-tricalcium phosphate (beta-TCP), collagen, and autologous bone fragments with fibrin glue implanted into a cranial bone defect.

MATERIALS AND METHODS

Granulated beta-TCP and collagen from porcine skin were mixed and freeze-dried. The weight ratio of both materials was 98:2. The composite scaffold for bone regeneration was composed of this artificial material and autologous bone fragments. Five adult beagle dogs were used. A cranial bone defect (2 cmx2 cm) was created in each dog. The animals were divided into two groups. In group 1 (n=3), the cranial bone defect was closed by replacing the original free bone flap, and the residual fissure and burr holes were filled with the composite scaffold with fibrin glue. In group 2 (n=2), the bone defect was closed only by replacing the original free bone flap. Three months after the treatment, computed tomography and histologic examinations were done in all animals.

RESULTS

In all dogs in group 1, the defects were almost closed by new bone; whereas in group 2, the defects were filled with fibrous tissues instead of bone.

CONCLUSION

This study showed that the composite scaffold made of beta-TCP, collagen, and autologous bone fragments with fibrin glue enabled reconstruction of cranial bone defects without the usual fixation materials.

[Current status of tissue engineering in urology. Review of the literature]

In the eighties a new field of the medicine appears wich applies the principles of cellular cultivation to synthetic biodegradable polymers scaffolds with the purpose of creating autologous biological substitutes that could improve, maintain or restore the function of organs or damaged tissues. The Tissue Engineering constitutes a new discipline in full phase of development especially in USA, with multiple potential applications in several medical specialities. Our speciality can't remain indifferent to interest and encouraging future originated by this new science. In this work we have made a wide bibliographical revision in the Medline to know the antecedents, current state and the possible future applications of Tissue Engineering in Urology.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Ingénierie tissulaire et thérapie cellulaire en urologie

Tissue engineering refers to the techniques that are aimed at regeneration of human tissues and organs. Two elements are necessary for these techniques: matrix and cells. Matrix is the scaffold where tissues may organise. Cells are either autologous cells stimulated to regenerate in vivo, aided by implantation of matrix ("guided tissue regeneration"), or autologous cells cultured outside the body (in vitro) and later returned as auto-transplants. All types of conventional tissue reconstructive surgery need tissue engineering. These techniques have been introduced recently into the clinical practice. One of the main limitations of reconstructive surgery in genitourinary tract is the lack of autologous tissue. Two autotransplants could be distinguished: coherent tissue structure or cell suspensions. The great number of studies published in this area emphasizes the importance of the future clinical implication in urology.

Urethroplasty using a bovine pericardium graft: an experimental study using normal urethras from dogs

The use of bovine pericardium as a urethral patch to substitute a ventral segment of canine urethras was studied. Healing, epithelial growth, urethral permeability, fistulas, and calcification were analyzed. Thirty male mongrel dogs of medium and large size underwent resection of a ventral segment of the medial urethra measuring 2.0 x 0.5 cm, which was replaced with a bovine pericardium graft, treated with buffered glutaraldehyde and preserved in formaldehyde. Two running sutures of polygalactin 5-0 were applied, one on each side of the patch. The corpus spongiosum was closed with uninterrupted suture and the skin with interrupted suture of polygalactin 5-0. Six months later, the animals were examined and sacrificed under anesthesia. Retrograde urethrograms showed that the urethral healing was complete in six of the 30 animals, without stenosis, fistulas or dilations. Microscopic examination showed complete epithelization of these six urethras. The remaining 24 animals presented urethrocutaneous fistulas without stenosis, demonstrated by urethral catheterism using a 10-Fr plastic catheter. These data show that a successful urethral reconstruction of the penile urethra was possible in only 20% of the operated animals. Infection and leakage may be the cause of the urethrocutaneous fistulas present in 80% of cases. Further studies are necessary to determine whether such fistulas are avoidable. If they are, the bovine pericardium may well be an option in the treatment of urethral lesions in dogs.

Engineering of muscle tissue

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Tissue engineering and regenerative medicine is an emerging interdisciplinary field that applies the principles of biology and engineering to the development of viable substitutes that restore, maintain, or improve the function of human tissues and organs. Tissue engineering science has provided critical new knowledge that will deepen our understanding of the phenotype of an important category of cell types-the muscle cells-and this knowledge may enable meaningful advances in musculoskeletal tissue engineering. There are two principle strategies for the replacement of impaired muscle tissues. One approach uses the application of isolated and differentiated cells (in vivo tissue engineering), using a transport matrix for the cell delivery; the other uses in vitro-designed and pre-fabricated tissue equivalents (in vitro tissue engineering). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and differentiation, the three-dimensional environment, the architecture of the cells, and gene expression of the developmental process and the survival of the cells and integration in the host in in vivo experiments. As the techniques of tissue engineering become more sophisticated and as issues such as vascularization and innervation are addressed, the usefulness of these methods for reconstructive surgery may grow significantly.

Engineering of Multilayered Urinary Tissue in Vitro

Regeneration of the urinary conduit, using engineered autologous material, could have many clinical implications. The urinary system is composed of a three-layered wall consisting of different cell types. In this study we investigated the possibility to coculture these components in vitro into a continuous sheet for total autologous regeneration. To address this issue, human urothelial cells, fibroblasts, and smooth muscle cells were isolated separately and expanded in vitro. Cells were then cocultured by seeding them in layers in a "sandwich model." After coculturing the material was investigated histologically and with immunoassays. The different cells could be cocultured after being isolated and expanded separately in vitro. The cells formed a continuous sheet that could be enzymatically detached and that sustained mechanical handling. The morphology of different cell layers and the reaction to immunostaining indicated their preserved individual phenotype. In conclusion, we showed that human urothelial cells, fibroblasts, and smooth muscle cells can be expanded in vitro and cocultured to form a continuous cellular sheet consisting of three distinct layers of different types of cells. This could provide the surgeon with autologous tissue for urogenital reconstructive purposes.

[Tissue engineering in urology. Basic principles and application]

Tissue engineering is a rather new field of science. Despite this fact, some experimental investigations have already been applied in clinical studies. Compared to other medical fields, tissue engineering in urology is well established. Tissue-engineered bulking agents and tissue-engineered bladder augments are being investigated in clinical trials. Even though the knowledge gained in recent years is promising, the results of cellular therapies need to be critically judged before being finally applied in patients. Genetic engineering and stem cell research (adult undifferentiated cells) have had major impact on the field of tissue engineering over the past 2 years. By using the technology of genetic engineering, biochemical and functional qualities of tissues may be modified. Adult stem cells may help to substitute lost tissue in an autologous fashion by isolating undifferentiated cells from the body and by differentiating them into a desired cell type. These cells may be used to form native functional tissue to replace a diseased organ or organ part.

Bladder augmentation in dogs using the tissue capsule formed around a perivesical tissue expander

PURPOSE

Enterocystoplasty provides needed improvement in bladder storage parameters in many patients but it also generates significant morbidity. We evaluated the unusual potential alternative of using the capsule that forms around a standard silicone tissue expander placed perivesically to augment the bladder in dogs.

MATERIALS AND METHODS

Six mongrel dogs underwent baseline videourodynamics and assessment of serum electrolytes, followed by placement of a 250 to 500 cc perivesical silicone tissue expander. Four months after implantation the tissue expander was removed and the fibrous capsule around the expander was biopsied. The capsule was opened and anastomosed to the bladder to augment storage. Serum electrolytes were determined 2 and 4 weeks after augmentation. Videourodynamics were repeated after 3 to 5 months, that is at sacrifice. The harvested bladders underwent histological evaluation.

RESULTS

Five dogs underwent augmentation as described, while in an additional dog that underwent intraperitoneal placement of the tissue expander a fibrous capsule failed to form. Of the 5 augmented dogs 4 underwent repeat urodynamic and electrolyte evaluation with harvesting of the lower urinary tract, while 1 died of undetermined causes 3 weeks after augmentation. A distinct capsule formed in all dogs and augmentation was technically achievable. Anastomosis calcification in 3 dogs limited filling the augmenting capsule for cystography. Bladder capacity and compliance improved in all animals but it varied in degree. Histological examination of the capsule biopsies showed collagen rich connective tissue without epithelium or smooth muscle. After augmentation the capsular segment revealed urothelium in all cases with squamous metaplasia in 1. The subepithelial region had dense fibrosis and a thin band of osseous metaplasia occupied the lamina propria in all cases. Disorganized smooth muscle bundles were noted in all augmented bladders within the collagen of the capsule wall.

CONCLUSIONS

Bladder augmentation with the collagenous capsule formed over a perivesical tissue expander is technically feasible. There was evidence of epithelial and smooth muscle ingrowth from the native bladder with improved bladder capacity and compliance in all dogs. Osseous metaplasia of the luminal surface of the collagen based capsule that developed in all animals may have been responsible for anastomotic narrowing and limited filling on cystography.

Hybrid dendritic-linear polyester-ethers for in situ photopolymerization

Novel first through fourth generation hybrid dendritic-linear copolymers, composed entirely of building blocks known to be biocompatible or degradable to natural metabolites in vivo, are described. Specifically, these copolymers are composed of poly(ethylene glycol), glycerol, and succinic acid and are synthesized using a divergent approach in high yield. A photo-cross-linkable derivative of this copolymer successfully seals 4.1 mm corneal lacerations. The mechanism of tissue repair is likely one of physical entrapment where an interpenetrating network (IPN) is formed between the cross-linked copolymer and the tissue.

22 week assessment of bladder acellular matrix as a bladder augmentation material in a porcine model

Previous studies on the reconstruction of porcine bladder using bladder acellular matrix allograft (BAMA) have indicated positive preliminary results with respect to graft shrinkage and cellular repopulation. The current study was conducted to investigate the feasibility of using BAMA in a similar model of bladder reconstruction out to longer time frames (22 weeks). At predetermined time points, the macroscopic, histological and mechanical properties of explanted native and BAMA tissues were evaluated and compared. Macroscopically, contracture of the BAMA was observed. The peripheral regions of the grafts experienced extensive cellular repopulation. Towards the centre however, all grafts were consistently devoid of organized smooth muscle bundles and a well-developed urothelium. An alteration in both the amount and organization of collagen was also observed within this region. Significant differences (p < 0.05) in the rupture strain and the elastic modulus of the BAMA compared to native bladder tissue appear to correlate with macroscopic graft contracture as well as the fibroproliferative tissue response of the matrix.

Novel peptide-based biomaterial scaffolds for tissue engineering

Biomaterial scaffolds are components of cell-laden artificial tissues and transplantable biosensors. Some of the most promising new synthetic biomaterial scaffolds are composed of self-assembling peptides that can be modified to contain biologically active motifs. Peptide-based biomaterials can be fabricated to form two- and three-dimensional structures. Recent studies show that biomaterial promotion of multi-dimensional cell-cell interactions and cell density are crucial for proper cellular differentiation and for subsequent tissue formation. Other refinements in tissue engineering include the use of stem cells, cell pre-selection and growth factor pre-treatment of cells that are used for seeding scaffolds. These cell-culture technologies, combined with improved processes for defining the dimensions of peptide-based scaffolds, might lead to further improvements in tissue engineering. Novel peptide-based biomaterial scaffolds seeded with cells show promise for tissue repair and for other medical applications.

The growth of tissue engineering

This report draws upon data from a variety of sources to estimate the size, scope, and growth rate of the contemporary tissue engineering enterprise. At the beginning of 2001, tissue engineering research and development was being pursued by 3,300 scientists and support staff in more than 70 startup companies or business units with a combined annual expenditure of over $600 million. Spending by tissue engineering firms has been growing at a compound annual rate of 16%, and the aggregate investment since 1990 now exceeds $3.5 billion. At the beginning of 2001, the net capital value of the 16 publicly traded tissue engineering startups had reached $2.6 billion. Firms focusing on structural applications (skin, cartilage, bone, cardiac prosthesis, and the like) comprise the fastest growing segment. In contrast, efforts in biohybrid organs and other metabolic applications have contracted over the past few years. The number of companies involved in stem cells and regenerative medicine is rapidly increasing, and this area represents the most likely nidus of future growth for tissue engineering. A notable recent trend has been the emergence of a strong commercial activity in tissue engineering outside the United States, with at least 16 European or Australian companies (22% of total) now active.