Urethral strictures can cause significant discomfort and progressive urinary tract damage if left untreated. Current reconstructive options, including urethral resection and buccal mucosa grafting, are associated with several limitations such as donor-site morbidity, limited tissue availability, and variable long-term outcomes. To address these challenges, we developed a novel multilayered 3D-bioprinted urethral construct designed to closely mimic the native urethral architecture. Using an Integrated Tissue and Organ Printing System (ITOP) equipped with a rotating mandrel, tubular urethral constructs were fabricated with distinct layers consisting of urothelial cells (UC), basement membrane (BM), smooth muscle cells (SMC), and supportive polycaprolactone (PCL). Autologous UC and SMC isolated from urinary bladder tissue were incorporated into a fibrinogen-based hydrogel bioink. Following in vitro maturation, the constructs were evaluated using viability assays, immunohistochemistry, and biomechanical testing. Live/Dead staining demonstrated an average cell viability of 75% for both UC and SMC populations. Immunostaining confirmed appropriate localization of the different cell types within their respective layers. Tensile testing showed that constructs matured for 14 days developed stable and elastic tissue-like mechanical properties. To further improve construct handling and structural integrity, horizontal reinforcement bands were incorporated into the PCL layer. Using this approach, 4 cm-long and 0.5 cm-diameter urethral constructs with native-like multilayered organization were successfully fabricated. This novel 3D-bioprinting strategy demonstrates strong potential for generating customizable and biologically relevant urethral grafts for future reconstructive applications. Ongoing in vitro optimization and planned in vivo evaluation in a porcine model aim to further validate the structural and functional performance of the construct and support future clinical translation for urethral and other tubular tissue reconstruction.

Vascular tissue engineering has the potential to make a significant impact on the treatment of a wide variety of medical conditions, including providing in vitro generated vascularized tissue and organ constructs for transplantation. Since the first report on the construction of a biological blood vessel, significant research and technological advances have led to the generation of clinically relevant large and small diameter tissue engineered vascular grafts (TEVGs). However, developing a biocompatible blood-contacting surface is still a major challenge. Researchers are using biomimicry to generate functional vascular grafts and vascular networks. A multi-disciplinary approach is being used that includes biomaterials, cells, pro-angiogenic factors and microfabrication technologies. Techniques to achieve spatiotemporal control of vascularization include use of topographical engineering and controlled-release of growth/pro-angiogenic factors. Use of decellularized natural scaffolds has gained popularity for engineering complex vascularized organs for potential clinical use. Pre-vascularization of constructs prior to implantation has also been shown to enhance its anastomosis after implantation. Host-implant anastomosis is a phenomenon that is still not fully understood. However, it will be a critical factor in determining the in vivo success of a TEVGs or bioengineered organ. Many clinical studies have been conducted using TEVGs, but vascularized tissue/organ constructs are still in the research & development stage. In addition to technical challenges, there are commercialization and regulatory challenges that need to be addressed. In this review we examine recent advances in the field of vascular tissue engineering, with a focus on technology trends, challenges and potential clinical applications.

Biomaterials have substantial value in tissue engineering and regenerative medicine, but translating advances in biomaterials science into products with clinical applications involves multiple challenges, which are usually overlooked when proof of concept is the primary goal. Key issues encountered during research and development include unforeseen technical challenges for manufacturing, limited commercialization expertise, and insufficient preclinical safety/risk assessment. Increasing the role academic institutions play in the translation process, connecting research scientists with experts in process development and commercialization, and establishing academic–industry partnerships, will encourage successful translation of biomaterials to clinical applications. Incorporation of quality by design and process analytical technology approaches into the biomaterials manufacturing process can improve quality, efficiency, and cost-effectiveness. Additionally, establishment of consistent regulatory guidelines and standards for manufacturing, quality control, and postmarketing assessment will be critical to the successful translation of novel biomaterials in regenerative medicine.

In the United States, approximately 1 million patients live with end-stage renal disease (ESRD), with more than 100,000 new diagnoses every year. Although hemodialysis has increased the survival of patients with ESRD, transplantation remains the only curative treatment currently. However, kidney transplantation is severely limited by shortage of kidney donors, complications due to chronic immunosuppressive therapy posttransplantation and long-term graft failure. These limitations have led researchers to search for alternative therapeutic modalities that could improve, restore, or replace either partial or total renal function. In this context, tissue engineering and regenerative medicine presents with viable approaches to develop new and innovative therapies for renal failure. This chapter describes an overview of new developments related to kidney tissue regeneration.

Oxygen generating biomaterials represent a new trend in regenerative medicine that aims to generate and supply oxygen at the site of requirement, to support tissue healing and regeneration. To enhance the healing of dermal wounds, we have developed a highly portable, in situ oxygen generating wound dressings that uses sodium percarbonate (SPO) and calcium peroxide (CPO) as chemical oxygen sources. The dressing continuously generated oxygen for more than 3 days, after which it was replaced. In the in vivo testing on porcine full-thickness porcine wound model, the SPO/CPO dressing showed enhanced wound healing during the 8 week study period. Quantitative measurements of wound healing related parameters, such as wound closure, reepithelialization, epidermal thickness and collagen content of dermis showed that supplying oxygen topically using the SPO/CPO dressing significantly accelerated the wound healing. An increase in neovascularization, as determined using Von Willebrand factor (vWF) and CD31 staining, was also observed in the presence of SPO/CPO dressing. This novel design for a wound dressing that contains oxygen generating biomaterials (SPO/CPO) for supplying topical oxygen, may find utility in treating various types of acute to chronic wounds.

The innate ability of stem cells to self-renew and differentiate into multiple cell types makes them a promising source for tissue engineering and regenerative medicine applications. Their capacity for self-renewal and differentiation is largely influenced by the combination of physical, chemical, and biological signals found in the stem cell niche, both temporally and spatially. Embryonic and adult stem cells are potentially useful for cell-based approaches; however, regulating stem cell behavior remains a major challenge in their clinical use. Most of the current approaches for controlling stem cell fate do not fully address all of the complex signaling pathways that drive stem cell behaviors in their natural microenvironments. To overcome this limitation, a new generation of biomaterials is being developed for use as three-dimensional synthetic microenvironments that can mimic the regulatory characteristics of natural extracellular matrix (ECM) proteins and ECM-bound growth factors. These synthetic microenvironments are currently being investigated as a substrate with surface immobilization and controlled release of bioactive molecules to direct the stem cell fate in vitro, as a tissue template to guide and improve the neo-tissue formation both in vitro and in vivo, and as a delivery vehicle for cell therapy in vivo. The continued advancement of such an intelligent biomaterial system as the synthetic extracellular microenvironment holds the promise of improved therapies for numerous debilitating medical conditions for which no satisfactory cure exists today.

The objective of this research was to examine the capabilities of QSPR (Quantitative Structure Property Relationship) modeling to predict specific biological responses (fibrinogen adsorption, cell attachment and cell proliferation index) on thin films of different polymethacrylates. Using 33 commercially available monomers it is theoretically possible to construct a library of over 40,000 distinct polymer compositions. A subset of these polymers were synthesized and solvent cast surfaces were prepared in 96 well plates for the measurement of fibrinogen adsorption. NIH 3T3 cell attachment and proliferation indices were measured on spin coated thin films of these polymers. Based on the experimental results of these polymers, separate models were built for homo-, co-, and terpolymers in the library with good correlation between experiment and predicted values. The ability to predict biological responses by simple QSPR models for large numbers of polymers has important implications in designing biomaterials for specific biological or medical applications.

This article systematically reviews the status of in vitro and in vivo percutaneous permeation of selected compounds reported in the literature and attempts to relate these permeation data to formulations and biochemical changes occurring in human skin, animal skins and skin equivalents. A substantial portion of the article is dedicated in reviewing the status of commercially available drugs and their delivery methods. Information on permeation modifier compounds and in vivo/in vitro (IVIVC) correlations is also provided in order to obtain a complete picture of the research status in the dermatopharmaceutical field.

Textured surfaces obtained by UV laser ablation of poly(ethylene terephthalate) films were used to study the effect of shape and spacing of surface features on cellular response. Two distinct patterns, cones and ripples with spacing from 2 to 25 μm, were produced. Surface features with different shapes and spacings were produced by varying pulse repetition rate, laser fluence, and exposure time. The effects of the surface texture parameters, i.e., shape and spacing, on cell attachment, proliferation, and morphology of neonatal human dermal fibroblasts and mouse fibroblasts were studied. Cell attachment was the highest in the regions with cones at ≈4 μm spacing. As feature spacing increased, cell spreading decreased, and the fibroblasts became more circular, indicating a stress-mediated cell shrinkage. This study shows that UV laser ablation is a useful alternative to lithographic techniques to produce surface patterns for controlling cell attachment and growth on biomaterial surfaces.

The role of reactive oxygen species (ROS)-mediated cell signal transduction pathways emanating from engineered cell substrates remains unclear. To elucidate the role, polymers derived from the amino acid L-tyrosine were used as synthetic matrix substrates. Variations in their chemical properties were created by co-polymerizing hydrophobic L-tyrosine derivatives with uncharged hydrophilic poly(ethylene glycol) (PEG, Mw 1,000 Da), and negatively charged desaminotyrosyl-tyrosine (DT). These substrates were characterized for their intrinsic ability to generate ROS, as well as their ability to elicit Saos-2 cell responses in terms of intracellular ROS production, actin remodeling, and apoptosis. PEG-containing substrates induced both exogenous and intracellular ROS production, whereas the charged substrates reduced production of both types, indicating a coupling of exogenous ROS generation and intracellular ROS production. Furthermore, PEG -mediated ROS induction caused nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase and an increase in caspase-3 activity, confirming a link with apoptosis. PEG-rich pro-oxidant substrates caused cytoskeletal actin remodeling through [1, actin cleavage by caspase 3 into fractins. The fractins co-localized to the mitochondria and reduced the mitochondrial membrane potential. The remnant cytosolic beta-actin was polymerized and condensed, events consistent with apoptotic cell shrinkage. The cytoskeletal remodeling was integral to the further augmentation of intracellular ROS production. Conversely, the anti-oxidant DT-containing charged substrates suppressed the entire cascade of apoptotic progression. We demonstrate that ROS activity serves an important role in "outside in" signaling for cells grown on substrates: the ROS activity couples exogenous stress, driven by substrate composition, to changes in intracellular signaling. This signaling causes cell apoptosis, which is mediated by actin remodeling.

: Skin Equivalents (SE) or Human Skin Equivalents (HSEs) are skin substitutes that can serve as models for testing the skin permeability of agents from formulations, or for evaluation of formulations themselves on the skin. We have developed a collagen based HSE and HSE containing electrospun poly(DTE carbonate) polymer scaffolds in our laboratory. The culture of these full thickness skin equivalents has been optimized by modification of the culture media and conditions required for growth in order to mimic the barrier properties of human skin in vivo. The HSE has been characterized for morphology, lipid composition and barrier properties and compared to a commercially available skin equivalent, and shows similar permeability to a wide range of agents. Skin derived cells were found to populate and proliferate in the electrospun scaffold, which imparts structural stability to the collagen based HSE model. Use of cocultures of human dermal fibroblasts and human keratinocytes, and conditions such as addition of ascorbic acid are being used to look at effects on morphogenesis and barrier properties of the epidermal layer in these HSE models. Once developed, these skin equivalents can serve as effective models for determination of the permeation of chemical warfare agents (CWAs) or their mimics or the barrier properties of creams such as SERPACWA (Skin Exposure Reduction Paste Against Chemical Warfare Agents).