Engineering tissues and organs

Pancreatic cancer organotypics: High throughput, preclinical models for pharmacological agent evaluation

Pancreatic cancer carries a terrible prognosis, as the fourth most common cause of cancer death in the Western world. There is clearly a need for new therapies to treat this disease. One of the reasons no effective treatment has been developed in the past decade may in part, be explained by the diverse influences exerted by the tumour microenvironment. The tumour stroma cross-talk in pancreatic cancer can influence chemotherapy delivery and response rate. Thus, appropriate preclinical in vitro models which can bridge simple 2D in vitro cell based assays and complex in vivo models are required to understand the biology of pancreatic cancer. Here we discuss the evolution of 3D organotypic models, which recapitulare the morphological and functional features of pancreatic ductal adenocarcinoma (PDAC). Organotypic cultures are a valid high throughput preclinical in vitro model that maybe a useful tool to help establish new therapies for PDAC. A huge advantage of the organotypic model system is that any component of the model can be easily modulated in a short time-frame. This allows new therapies that can target the cancer, the stromal compartment or both to be tested in a model that mirrors the in vivo situation. A major challenge for the future is to expand the cellular composition of the organotypic model to further develop a system that mimics the PDAC environment more precisely. We discuss how this challenge is being met to increase our understanding of this terrible disease and develop novel therapies that can improve the prognosis for patients.

Therapeutic foam scaffolds incorporating biopolymer-shelled mesoporous nanospheres with growth factors

A novel therapeutic scaffolding system of engineered nanocarriers within a foam matrix for the long-term and sequential delivery of growth factors is reported. Mesoporous silica nanospheres were first functionalized to have an enlarged mesopore size (12.2nm) and aminated surface, which was then shelled by a biopolymer, poly(lactic acid) (PLA) or poly(ethylene glycol) (PEG), via electrospraying. The hybrid nanocarrier was subsequently combined with collagen to produce foam scaffolds. Bovine serum albumin (BSA), used as a model protein, was effectively loaded within the enlarged nanospheres. The biopolymer shell substantially prolonged the release period of BSA (2-3weeks from shelled nanospheres vs. within 1week from bare nanospheres), and the release rate was highly dependent on the shell composition (PEG>PLA). Collagen foam scaffolding of the shelled nanocarrier further slowed down the protein release, while enabling the incorporation of a rapidly releasing protein, which is effective for sequential protein delivery. Acidic fibroblast growth factor (aFGF), loaded onto the shelled-nanocarrier scaffolds, was released over a month at a highly sustainable rate, profiling a release pattern similar to that of BSA. The biological activity of the aFGF was evidenced by the significant proliferation of osteoblastic precursor cells in the aFGF-releasing scaffolds. Furthermore, the aFGF-delivering scaffolds implanted in rat subcutaneous tissue for 2weeks showed a substantially enhanced invasion of fibroblasts with a homogeneous population. Taken together, it is concluded that the biopolymer encapsulation of mesoporous nanospheres effectively prolongs the release of growth factors over weeks to a month, providing a nanocarrier platform for a long-term growth factor delivery. Moreover, the foam scaffolding of the nanocarrier system is a potential therapeutic three-dimensional matrix for cell culture and tissue engineering.

Tissue engineering for the oncologic urinary bladder

Urinary diversion after radical cystectomy in patients with bladder cancer normally takes the form of an ileal conduit or neobladder. However, such diversions are associated with a number of complications including increased risk of infection. A plausible alternative is the construction of a neobladder (or bladder tissue) in vitro using autologous cells harvested from the patient. Biomaterials can be used as a scaffold for naturally occurring regenerative stem cells to latch onto to regrow the bladder smooth muscle and epithelium. Such engineered tissues show great promise in urologic tissue regeneration, but are faced with a number of challenges. For example, the differentiation mesenchymal stem cells from various sources can be difficult and the smooth muscle cells formed do not precisely mimic the natural cells.

In vitro reconstitution of human kidney structures for renal cell therapy

BACKGROUND

Recent advances in cell therapies have provided potential opportunities for the treatment of chronic kidney diseases (CKDs). We investigated whether human kidney structures could be preformed in vitro for subsequent implantation in vivo to maximize tissue-forming efficiency.

METHODS

Human renal cells were isolated from unused donor kidneys. Human renal cells were cultured and expanded. Migration was analyzed using growth factors. To form structures, cells were placed in a three-dimensional culture system. Cells were characterized by immunofluorescence, western blots and fluorescence-activated cell sorting using renal cell-specific markers for podocin, proximal and distal tubules and collecting ducts. An albumin uptake assay was used to analyze function. Three-dimensional cultures were implanted into athymic rat kidneys to evaluate survival.

RESULTS

Human renal cells were effectively expanded in culture and retained their phenotype, migration ability and albumin uptake functions. Human renal cell in three-dimensional culture-formed tubules, which stained positively for proximal, distal tubule and collecting duct markers, and this was confirmed by western blot. Polarity of the tubular cells was determined by the presence of E-cadherin, N-cadherin and Na-K ATPase. Colocalization of labeled albumin and proximal tubule markers proved functionality and specificity of the newly formed tubules. An in vivo study showed that cells survived in the kidney for up to 6 weeks.

CONCLUSIONS

These findings demonstrate that human renal cell grown in three-dimensional culture are able to generate kidney structures in vitro. This system may ultimately be developed into an efficient cell-based therapy for patients with CKD.

Kidney spheroids recapitulate tubular organoids leading to enhanced tubulogenic potency of human kidney-derived cells

Cell-based approaches utilizing autologous human renal cells require their isolation, expansion in vitro, and reintroduction back into the host for renal tissue regeneration. Nevertheless, human kidney epithelial cells (hKEpCs) lose their phenotype, dedifferentiate, and assume the appearance of fibroblasts after relatively few passages in culture. We hypothesized that growth conditions may influence hKEpC phenotype and function. hKEpCs retrieved from human nephrectomy tissue samples showed the ability to reproducibly form kidney spheres when grown in suspension culture developed in nonadherent conditions. Genetic labeling and time-lapse microscopy indicated, at least in part, the aggregation of hKEpCs into 3D spheroids rather than formation of pure clonally expanded spheres. Characterization of hKEpC spheroids by real-time polymerase chain reaction and FACS analysis showed upregulation of some renal developmental and "stemness" markers compared with monolayer and mostly an EpCAM(+)CD24(+)CD133(+)CD44(+) spheroid cell phenotype. Oligonucleotide microarrays, which were used to identify global transcriptional changes accompanying spheroid formation, showed predominantly upregulation of cell matrix/cell contact molecules and cellular biogenesis processes and downregulation of cell cycle, growth, and locomotion. Accordingly, hKEpC spheroids slowly proliferated as indicated by low Ki-67 staining, but when grafted in low cell numbers onto the chorioallantoic membrane (CAM) of the chick embryo, they exclusively reconstituted various renal tubular epithelia. Moreover, efficient generation of kidney spheroids was observed after long-term monolayer culture resulting in reestablishment of tubulogenic capacity upon CAM grafting. Thus, generation of a tubular organoid in hKEpC spheroids may provide a functional benefit for kidney-derived cells in vivo.

In vitro generation of three-dimensional renal structures

End-stage renal disease is currently being treated effectively by transplantation. However, increasing demand and donor shortage make this treatment challenging. Recent advances in cell-based therapies have provided potential opportunities to alleviate the current challenges of donor shortage. In this study we developed a system to generate renal structures in vitro using primary kidney cells. This system involves the cultivation of expanded primary renal cells in a three-dimensional collagen-based culture system. After one week of growth, individual renal cells began to form renal structures resembling tubules and glomeruli. Histologically, these structures show phenotypic resemblance to native kidney structures. The reconstituted tubules stained positively for Tamm-Horsfall protein, which is expressed in the thick ascending limb of Henle's Loop and distal convoluted tubules. These results show that renal structures can be reconstituted in a three-dimensional culture system, which may eventually be used for renal cell therapy applications.

Challenges in tissue engineering

Almost 30 years have passed since a term 'tissue engineering' was created to represent a new concept that focuses on regeneration of neotissues from cells with the support of biomaterials and growth factors. This interdisciplinary engineering has attracted much attention as a new therapeutic means that may overcome the drawbacks involved in the current artificial organs and organ transplantation that have been also aiming at replacing lost or severely damaged tissues or organs. However, the tissues regenerated by this tissue engineering and widely applied to patients are still very limited, including skin, bone, cartilage, capillary and periodontal tissues. What are the reasons for such slow advances in clinical applications of tissue engineering? This article gives the brief overview on the current tissue engineering, covering the fundamentals and applications. The fundamentals of tissue engineering involve the cell sources, scaffolds for cell expansion and differentiation and carriers for growth factors. Animal and human trials are the major part of the applications. Based on these results, some critical problems to be resolved for the advances of tissue engineering are addressed from the engineering point of view, emphasizing the close collaboration between medical doctors and biomaterials scientists.

Two-photon microscopes and in vivo multiphoton tomographs--powerful diagnostic tools for tissue engineering and drug delivery

Near-infrared multiphoton microscopes and in vivo femtosecond laser tomographs are novel powerful diagnostic tools for intra-tissue drug screening and high-resolution structural imaging applicable to many areas of biomedical research. Deep tissue cells and extracellular matrix (ECM) compartments can be visualized in situ with submicron resolution without the need for tissue processing. In particular, the reduced fluorescent coenzyme NAD(P)H, flavoproteins, keratin, melanin, and elastin are detected by two-photon excited autofluorescence, whereas myosin, tubulin and the ECM protein collagen can be imaged additionally by second harmonic generation (SHG). Therefore, these innovative multiphoton technologies have been used to probe architecture and state of a variety of native tissues, as well as of tissue-engineered constructs, giving insights on the interaction between scaffolds and seeded cells in vitro prior implantation. Moreover, non-invasive 4-D multiphoton tomographs are employed in clinical studies to examine the diffusion behavior, the intra-tissue accumulation of topically applied cosmetic and pharmaceutical components, and their interaction with skin cells.

[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.

Esophageal reconstruction with ECM and muscle tissue in a dog model

An in vivo study was conducted to determine if an extracellular matrix (ECM) scaffold co-localized with autologous muscle tissue could achieve constructive remodeling of esophageal tissue without stricture. ECM derived from the porcine urinary bladder was processed, decellularized, configured into a tube shape, and terminally sterilized for use as a bioscaffold for esophageal reconstruction in a dog model. Twenty-two dogs were divided into four groups, three groups of five and one group of seven. Groups 1 and 2 were repaired with either ECM alone or muscle tissue alone, respectively. Groups 3 and 4 were repaired with ECM plus either a partial (30%) covering with muscle tissue or a complete (100%) covering with muscle tissue, respectively. Animals in groups 1 and 2 were sacrificed within approximately 3 weeks because of the formation of intractable esophageal stricture. Four of five dogs in group 3 and six of seven dogs in group 4 were survived for 26 days to 230 days and showed constructive remodeling of esophageal tissue with the formation of well organized esophageal tissue layers, minimal stricture, esophageal motility, and a normal clinical outcome. Mechanical testing of a subset of the remodeled esophageal tissue from animals in groups 3 and 4 showed progressive remodeling from a relatively stiff, non-compliant ECM tube structure toward a tissue with near normal biomechanical properties. We conclude that ECM bioscaffolds plus autologous muscle tissue, but not ECM scaffolds or muscle tissue alone, can facilitate the in situ reconstitution of structurally and functionally acceptable esophageal tissue.

Evaluation of Smooth Muscle Cell Response Using Two Types of Porous Polylactide Scaffolds with Differing Pore Topography

The goal of tissue engineering is to create bioartificial tissues for the replacement of failed or nonfunctional tissue. Porous tissue-engineered scaffolds may be created through a solvent-casting/porogen-leaching technique. Almost exclusively, sodium chloride (NaCl) is the porogen of choice. Previous studies have demonstrated the importance of porosity and pore size in cell adhesion and tissue development, yet the impact of porogen morphology and the chemical effect of porogen residual has not been fully explored. Poly-L-lactide (PLLA) scaffolds were manufactured by a solvent-casting, particulate-leaching method with either glucose or NaCl porogen in an effort to vary pore characteristics and, subsequently, cell adhesion and tissue development. Porogen influence on scaffold morphology and topography was compared via histological techniques and qualitative surface characteristics. Using an in vitro model, scaffolds were seeded with rat aortic smooth muscle cells (SMCs) and evaluated over a 28-day period. Cell attachment and proliferation were subsequently evaluated. Results indicate that initial SMC attachment is higher for scaffolds manufactured with NaCl rather than glucose. The proliferation of SMCs was higher for scaffolds manufactured with glucose and, by day 28, scaffolds manufactured with glucose supported a higher cell population than those processed using NaCl porogen.

Engineering of vaginal tissue in vivo

Congenital vaginal anomalies and cloacal malformations may require extensive surgical reconstruction. Surgical challenges are often encountered because of the limited amounts of native tissue available. We investigated the feasibility of using vaginal epithelial and smooth muscle cells for the engineering of vaginal tissues in vivo. Vaginal epithelial and smooth muscle cells of female rabbits were grown, expanded in culture, and characterized immunocytochemically. Vaginal epithelial and smooth muscle cells were seeded on polyglycolic acid (PGA) scaffolds at 10 x 10(6) and 20 x 10(6) cells/cm(3), respectively. The cell-seeded scaffolds were subcutaneously implanted into nude mice. The animals were killed 1, 4, and 6 weeks after implantation. Immunocytochemical and histochemical analyses were performed with pancytokeratins AE1/AE3 and with smooth muscle-specific alpha-actin antibodies to confirm the reconstituted tissue phenotype. Western blot analyses and electrical field stimulation studies were also performed to further characterize the tissue-engineered constructs. Vaginal epithelial cells were serially identified with anti-pancytokeratins AE1/AE3 at all culture stages. Smooth muscle cells in culture stained positively with alpha-smooth muscle actin antibodies. One week after implantation in vivo, the retrieved polymer scaffolds demonstrated multilayered tissue strips of both cell types, and penetrating native vasculature was also noted. Increased organization of the smooth muscle and epithelial tissue was evident by 4 weeks. There was no evidence of tissue formation in the controls. Immunocytochemical analyses using anti-pancytokeratins confirmed the presence of vaginal epithelial cells in each of the constructs. Anti-alpha-actin smooth muscle antibodies also confirmed the presence of multilayered smooth muscle fibers and tissue at each time point. Western blot analyses of the scaffolds confirmed the expression of cytokeratin and smooth muscle actin proteins when compared with controls. The contractile properties of the tissue-engineered vaginal constructs in response to electrical field stimulation were similar to those of normal vaginal tissue. Vaginal epithelial and smooth muscle cells can be easily cultured and expanded in vitro. Cell-seeded polymer scaffolds are able to form vascularized vaginal tissue in vivo that have phenotypic and functional properties similar to those of normal vaginal tissues. This is the first demonstration in tissue engineering wherein vaginal epithelial and smooth muscle cells are reconstituted in vivo into vaginal tissue. This technology may be pursued further experimentally in order to achieve the engineering of vaginal tissues for clinical applications.

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.

Evaluation and treatment of the overactive bladder

The overactive bladder is characterized by symptoms of frequency, urgency, and urge incontinence, substantially affecting the quality of life of millions of people throughout the world. The symptoms are associated with significant social, psychological, occupational, domestic, physical, and sexual problems. Despite the considerable impact of this condition on quality of life, sufferers are often unwilling to discuss their problem with family members or health care professionals. This situation is unfortunate, for much can be done to alleviate the symptoms of this distressing condition. It is therefore of utmost importance that medical education about symptoms of the overactive bladder and other related problems be improved to help health care professionals identify and treat patients who will benefit from therapy. This article reviews current thinking regarding definition, epidemiology, quality of life effects, evaluation, and management of the overactive bladder.

Tissue engineering: current state and prospects

Organ shortage and suboptimal prosthetic or biological materials for repair or replacement of diseased or destroyed human organs and tissues are the main motivation for increasing research in the emerging field of tissue engineering. No organ or tissue is excluded from this multidisciplinary research field, which aims to provide vital tissues with the abilities to function, grow, repair, and remodel. There are several approaches to tissue engineering, including the use of cells, scaffolds, and the combination of the two. The most common approach is biodegradable or resorbable scaffolds configured to the shape of the new tissue (e.g. a heart valve). This scaffold is seeded with cells, potentially derived from either biopsies or stem cells. The seeded cells proliferate, organize, and produce cellular and extracellular matrix. During this matrix formation, the starter matrix is degraded, resorbed, or metabolized. First clinical trials using skin or cartilage substitutes are currently under way. Both the current state of the field and future prospects are discussed.