Fibrinogen and fibrin based micro and nano scaffolds incorporated with drugs, proteins, cells and genes for therapeutic biomedical applications

Biological scaffold as potential platforms for stem cells: Current development and applications in wound healing

Wound repair is a complex challenge for both clinical practitioners and researchers. Conventional approaches for wound repair have several limitations. Stem cell-based therapy has emerged as a novel strategy to address this issue, exhibiting significant potential for enhancing wound healing rates, improving wound quality, and promoting skin regeneration. However, the use of stem cells in skin regeneration presents several challenges. Recently, stem cells and biomaterials have been identified as crucial components of the wound-healing process. Combination therapy involving the development of biocompatible scaffolds, accompanying cells, multiple biological factors, and structures resembling the natural extracellular matrix (ECM) has gained considerable attention. Biological scaffolds encompass a range of biomaterials that serve as platforms for seeding stem cells, providing them with an environment conducive to growth, similar to that of the ECM. These scaffolds facilitate the delivery and application of stem cells for tissue regeneration and wound healing. This article provides a comprehensive review of the current developments and applications of biological scaffolds for stem cells in wound healing, emphasizing their capacity to facilitate stem cell adhesion, proliferation, differentiation, and paracrine functions. Additionally, we identify the pivotal characteristics of the scaffolds that contribute to enhanced cellular activity.

The Mechanical Properties of Blended Fibrinogen:Polycaprolactone (PCL) Nanofibers

Electrospinning is a process to produce versatile nanoscale fibers. In this process, synthetic and natural polymers can be combined to produce novel, blended materials with a range of physical, chemical, and biological properties. We electrospun biocompatible, blended fibrinogen:polycaprolactone (PCL) nanofibers with diameters ranging from 40 nm to 600 nm, at 25:75 and 75:25 blend ratios and determined their mechanical properties using a combined atomic force/optical microscopy technique. Fiber extensibility (breaking strain), elastic limit, and stress relaxation times depended on blend ratios but not fiber diameter. As the fibrinogen:PCL ratio increased from 25:75 to 75:25, extensibility decreased from 120% to 63% and elastic limit decreased from a range between 18% and 40% to a range between 12% and 27%. Stiffness-related properties, including the Young's modulus, rupture stress, and the total and relaxed, elastic moduli (Kelvin model), strongly depended on fiber diameter. For diameters less than 150 nm, these stiffness-related quantities varied approximately as D^-2; above 300 nm the diameter dependence leveled off. 50 nm fibers were five-ten times stiffer than 300 nm fibers. These findings indicate that fiber diameter, in addition to fiber material, critically affects nanofiber properties. Drawing on previously published data, a summary of the mechanical properties for fibrinogen:PCL nanofibers with ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 is provided.

Self-Assembled Fibrinogen Scaffolds Support Cocultivation of Human Dermal Fibroblasts and HaCaT Keratinocytes

Self-assembled fibrinogen scaffolds are highly attractive biomaterials to mimic native blood clots. To explore their potential for wound healing, we studied the interaction of cocultures of human dermal fibroblasts (HDFs) and HaCaT keratinocytes with nanofibrous, planar, and physisorbed fibrinogen. Cell viability analysis indicated that the growth of HDFs and HaCaTs was supported by all fibrinogen topographies until 14 days, either in mono- or coculture. Using scanning electron microscopy and cytoskeletal staining, we observed that the native morphology of both cell types was preserved on all topographies. Expression of the marker proteins vimentin and cytokeratin-14 showed that the native phenotype of fibroblasts and undifferentiated keratinocytes, respectively, was maintained. HDFs displayed their characteristic wound healing phenotype, characterized by expression of fibronectin. Finally, to mimic the multilayered microenvironment of skin, we established successive cocultures of both cells, for which we found consistently high metabolic activities. SEM analysis revealed that HaCaTs arranged into a confluent top layer after 14 days, while fluorescent labeling confirmed the presence of both cells in the layered structure after 6 days. In conclusion, all fibrinogen topographies successfully supported the cocultivation of fibroblasts and keratinocytes, with fibrinogen nanofibers being particularly attractive for skin regeneration due to their biomimetic porous architecture and the technical possibility to be detached from an underlying substrate.

Fibrinogen-based cell and spheroid sheets manipulating and delivery for mouse hindlimb ischemia

In this research, we introduced a novel strategy for fabricating cell sheets (CSs) prepared by simply adding a fibrinogen solution to growth medium without using any synthetic polymers or chemical agents. We confirmed that the fibrinogen-based CS could be modified for target tissue regardless of size, shape, and cell types. Also, fibrinogen-based CSs were versatile and could be used to form three-dimensional (3D) CSs such as multi-layered CSs and those mimicking native blood vessels. We also prepared fibrinogen-based spheroid sheets for the treatment of ischemic disease. The fibrinogen-based spheroid sheets had much higherin vitrotubule formation and released more angiogenic factors compared to other types of platform in this research. We transplanted fibrinogen-based spheroid sheets into a mouse hindlimb ischemia model and found that fibrinogen-based spheroid sheets showed significantly improved physiological function and blood perfusion rates compared to the other types of platform in this research.

Physical, Mechanical, and Biological Properties of Fibrin Scaffolds for Cartilage Repair

Articular cartilage is a highly organized tissue that provides remarkable load-bearing and low friction properties, allowing for smooth movement of diarthrodial joints; however, due to the avascular, aneural, and non-lymphatic characteristics of cartilage, joint cartilage has self-regeneration and repair limitations. Cartilage tissue engineering is a promising alternative for chondral defect repair. It proposes models that mimic natural tissue structure through the use of cells, scaffolds, and signaling factors to repair, replace, maintain, or improve the specific function of the tissue. In chondral tissue engineering, fibrin is a biocompatible biomaterial suitable for cell growth and differentiation with adequate properties to regenerate damaged cartilage. Additionally, its mechanical, biological, and physical properties can be enhanced by combining it with other materials or biological components. This review addresses the biological, physical, and mechanical properties of fibrin as a biomaterial for cartilage tissue engineering and as an element to enhance the regeneration or repair of chondral lesions.

Advances in Organ-on-a-Chip Materials and Devices

The organ-on-a-chip (OoC) paves a way for biomedical applications ranging from preclinical to clinical translational precision. The current trends in the in vitro modeling is to reduce the complexity of human organ anatomy to the fundamental cellular microanatomy as an alternative of recreating the entire cell milieu that allows systematic analysis of medicinal absorption of compounds, metabolism, and mechanistic investigation. The OoC devices accurately represent human physiology in vitro; however, it is vital to choose the correct chip materials. The potential chip materials include inorganic, elastomeric, thermoplastic, natural, and hybrid materials. Despite the fact that polydimethylsiloxane is the most commonly utilized polymer for OoC and microphysiological systems, substitute materials have been continuously developed for its advanced applications. The evaluation of human physiological status can help to demonstrate using noninvasive OoC materials in real-time procedures. Therefore, this Review examines the materials used for fabricating OoC devices, the application-oriented pros and cons, possessions for device fabrication and biocompatibility, as well as their potential for downstream biochemical surface alteration and commercialization. The convergence of emerging approaches, such as advanced materials, artificial intelligence, machine learning, three-dimensional (3D) bioprinting, and genomics, have the potential to perform OoC technology at next generation. Thus, OoC technologies provide easy and precise methodologies in cost-effective clinical monitoring and treatment using standardized protocols, at even personalized levels. Because of the inherent utilization of the integrated materials, employing the OoC with biomedical approaches will be a promising methodology in the healthcare industry.

Nanoengineered therapeutic scaffolds for burn wound management

BACKGROUND

Wound healing is a complex process, and selecting an appropriate treatment is crucial and varies from one wound to another. Among injuries, burn wounds are more challenging to treat. Different dressings and scaffolds come into play when skin is injured. These scaffolds provide the optimum environment for wound healing. With the advancements of nanoengineering, scaffolds have been engineered to improve wound healing with lower fatality rates.

OBJECTIVES

Nanoengineered systems have emerged as one of the promising candidates for burn wound management. This review paper aims to provide an in-depth understanding of burn wounds and the role of nanoengineering in burn wound management. The advantages of nanoengineered scaffolds, their properties, and their proven effectiveness have been discussed. Nanoparticles and nanofibers-based nanoengineered therapeutic scaffolds provide optimum protection, infection management, and accelerated wound healing due to their unique characteristics. These scaffolds increase cell attachment and proliferation for desired results.

RESULTS

The literature review suggested that the utilization of nanoengineered scaffolds has accelerated burn wound healing. Nanofibers provide better cell attachment and proliferation among different nanoengineered scaffolds due to their 3D structure mimics the body's extracellular matrix.

CONCLUSION

With the application of these advanced nanoengineered scaffolds, better burn wound management is possible due to sustained drug delivery, better cell attachment, and an infection-free environment.

Current Advances Toward the Encapsulation of Cas9

Genetic diseases present formidable hurdles in maintaining a good quality of life for those suffering from these ailments. Often, patients look to inadequate treatments to manage symptoms, which can result in harmful effects on the body. Through genetic engineering, scientists utilize the clustered regularly short palindromic repeat (CRISPR)-associated protein, known as Cas9, to treat the root of the problem. The Cas9 protein is often codelivered with guide RNAs or in ribonucleoprotein complexes (RNP) to ensure targeted delivery of the genetic tool as well as to limit off-target effects. This paper provides an overview of the current advances made toward the encapsulation and delivery of Cas9 to desired locations in the body through encapsulating nanoparticles. Several factors must be considered when employing the Cas9 system to allow gene editing to occur. Material selection is crucial to protect the payload of the delivery vector. Current literature indicates that lipid- and polymer-based nanoparticles show the most potential as delivery vessels for Cas9. Lipid nanoparticles greatly outpace polymer-based nanoparticles in the clinic, despite the benefits that polymers may introduce. When developing translatable systems, there are factors that have not yet been considered that are relevant to Cas9 delivery that are highlighted in this Viewpoint. The proper functioning of Cas9 is dependent on maintaining a proper internal environment; however, there are gaps in the literature regarding these optimal conditions. Interactions between charges of the Cas9 protein, codelivered molecules, and delivery vehicles could impact the effectiveness of the gene editing taking place. While the internal charges of nanoparticles and their effects on Cas9 are presently undetermined, nanoparticles currently offer the ideal delivery method for the Cas9 protein due to their adequate size, modifiable external charge, and ability to be modified. Overall, a cationic lipid-/polymer-based nanoparticle system was found to have the most prospects in Cas9 delivery thus far. By understanding the successes of other systems, translatable, polymer-based delivery vehicles may be developed.

Optimizing fibrin hydrogel toward effective neural progenitor cell delivery in spinal cord injury

Transplantation of neural progenitor cell (NPC) possessing the potential to differentiate into neurons may guard against spinal cord injury (SCI)- associated neuronal trauma. We propose that autologous-like NPC may reduce post-transplant immune response. The study used the rat SCI model to prove this concept. For isolation and expansion of rat NPC for cell-based SCI therapy, thein vitroprotocol standardized with human NPC seemed suitable. The primary aim of this study is to select a cell/neural tissue-compatible biomaterial for improving NPC survivalin vivo. The composition of the fibrin hydrogel is adjusted to obtain degradable, porous, and robust fibrin strands for supporting neural cell attachment, migration, and tissue regeneration. This study employed NPC culture to evaluate the cytocompatibility and suitability of the hydrogel, composed by adding graded concentrations of thrombin to a fixed fibrinogen concentration. The microstructure evaluation by scanning electron microscope guided the selection of a suitable composition for delivering the embedded cells. On adding more thrombin, fibrinogen clotted quickly but reduced porosity, pore size, and fiber strand thickness. The high activity of thrombin also affected NPC morphology and thein vitrocell survival. The selected hydrogel carried viable NPC and retained them at the injury site post-transplantation. The fibrin hydrogel played a protective role throughout the transfer process by providing cell attachment sites and survival signals. The fibrin and NPC together regulated the immune response at the SCI site reducing ED1^+ve/ED2^+vemacrophages in the early period of 8-16 d after injury. Migration ofβ-III tubulin^+veneural-like cells into the fibrin-injected control SCI is evident. The continuous use of a non-neurotoxic fibrin matrix could be a convenient strategy forin vitroNPC preparation, minimally invasive cell delivery, and better transplantation outcome.

Influence of Divalent Metal Ions on the Precipitation of the Plasma Protein Fibrinogen

Fibrinogen nanofibers are very attractive biomaterials to mimic the native blood clot architecture. Previously, we reported the self-assembly of fibrinogen nanofibers in the presence of monovalent salts and have now studied how divalent salts influence fibrinogen precipitation. Although the secondary fibrinogen structure was significantly altered with divalent metal ions, morphological analysis revealed exclusively smooth fibrinogen precipitates. In situ monitoring of the surface roughness facilitated predicting the tendency of various salts to form fibrinogen fibers or smooth films. Analysis of the chemical composition revealed that divalent salts were removed from smooth fibrinogen films upon rinsing while monovalent Na⁺ species were still present in fibrinogen fibers. Therefore, we assume that the decisive factor controlling the morphology of fibrinogen precipitates is direct ion-protein contact, which requires disruption of the ion-surrounding hydration shells. We conclude that in fibrinogen aggregates, this mechanism is effective only for monovalent ions, whereas divalent ions are limited to indirect fibrinogen adsorption.

The effect of fibrin formulation on cell migration in an in vitro tendon repair model

BACKGROUND

The purpose of this study was to determine the effect of fibrinogen concentration on cell viability and migration in a tissue culture tendon healing model.

METHODS

Forty-eight canine flexor digitorum profundus tendons were randomly divided into three groups. In each group the tendons were lacerated and repaired augmented with a canine bone marrow stromal cell seeded fibrin interposition patch using either 5 mg/ml fibrinogen and 25 U/ml thrombin (physiological as a control), 40 mg/ml fibrinogen and 250 U/ml thrombin (low adhesive), or 80 mg/ml fibrinogen and 250 U/ml thrombin (high adhesive). The sutured tendons were cultured for two or four weeks.

RESULTS

Failure load was not significantly different among the groups. Cell-labeling staining showed that the stromal cells migrated across the gap in the control and low adhesive groups, but there was no cell migration in the high adhesive group at two weeks.

CONCLUSION

A high fibrinogen concentration in a fibrin patch or glue may impede early cell migration.

LEVEL OF EVIDENCE

Not applicable because this study was a laboratory study.

Polymeric Biomaterials for the Treatment of Cardiac Post-Infarction Injuries

Cardiac regeneration aims to reconstruct the heart contractile mass, preventing the organ from a progressive functional deterioration, by delivering pro-regenerative cells, drugs, or growth factors to the site of injury. In recent years, scientific research focused the attention on tissue engineering for the regeneration of cardiac infarct tissue, and biomaterials able to anatomically and physiologically adapt to the heart muscle have been proposed as valuable tools for this purpose, providing the cells with the stimuli necessary to initiate a complete regenerative process. An ideal biomaterial for cardiac tissue regeneration should have a positive influence on the biomechanical, biochemical, and biological properties of tissues and cells; perfectly reflect the morphology and functionality of the native myocardium; and be mechanically stable, with a suitable thickness. Among others, engineered hydrogels, three-dimensional polymeric systems made from synthetic and natural biomaterials, have attracted much interest for cardiac post-infarction therapy. In addition, biocompatible nanosystems, and polymeric nanoparticles in particular, have been explored in preclinical studies as drug delivery and tissue engineering platforms for the treatment of cardiovascular diseases. This review focused on the most employed natural and synthetic biomaterials in cardiac regeneration, paying particular attention to the contribution of Italian research groups in this field, the fabrication techniques, and the current status of the clinical trials.

Cancer Cell Direct Bioprinting: A Focused Review

Three-dimensional printing technologies allow for the fabrication of complex parts with accurate geometry and less production time. When applied to biomedical applications, two different approaches, known as direct or indirect bioprinting, may be performed. The classical way is to print a support structure, the scaffold, and then culture the cells. Due to the low efficiency of this method, direct bioprinting has been proposed, with or without the use of scaffolds. Scaffolds are the most common technology to culture cells, but bioassembly of cells may be an interesting methodology to mimic the native microenvironment, the extracellular matrix, where the cells interact between themselves. The purpose of this review is to give an updated report about the materials, the bioprinting technologies, and the cells used in cancer research for breast, brain, lung, liver, reproductive, gastric, skin, and bladder associated cancers, to help the development of possible treatments to lower the mortality rates, increasing the effectiveness of guided therapies. This work introduces direct bioprinting to be considered as a key factor above the main tissue engineering technologies.

A Comparative Review of Natural and Synthetic Biopolymer Composite Scaffolds

Tissue engineering (TE) and regenerative medicine integrate information and technology from various fields to restore/replace tissues and damaged organs for medical treatments. To achieve this, scaffolds act as delivery vectors or as cellular systems for drugs and cells; thereby, cellular material is able to colonize host cells sufficiently to meet up the requirements of regeneration and repair. This process is multi-stage and requires the development of various components to create the desired neo-tissue or organ. In several current TE strategies, biomaterials are essential components. While several polymers are established for their use as biomaterials, careful consideration of the cellular environment and interactions needed is required in selecting a polymer for a given application. Depending on this, scaffold materials can be of natural or synthetic origin, degradable or nondegradable. In this review, an overview of various natural and synthetic polymers and their possible composite scaffolds with their physicochemical properties including biocompatibility, biodegradability, morphology, mechanical strength, pore size, and porosity are discussed. The scaffolds fabrication techniques and a few commercially available biopolymers are also tabulated.

Fibroblast Growth Factor in Diabetic Foot Ulcer: Progress and Therapeutic Prospects

Diabetic foot ulcer (DFU) is a combination of neuropathy and various degrees of peripheral vasculopathy in diabetic patients resulting in lower extremity infection, ulcer formation, and deep-tissue necrosis. The difficulty of wound healing in diabetic patients is caused by a high glucose environment and various biological factors in the patient. The patients' skin local microenvironment changes and immune chemotactic response dysfunction. Wounds are easy to be damaged and ulcerated repeatedly, but difficult to heal, and eventually develop into chronic ulcers. DFU is a complex biological process in which many cells interact with each other. A variety of growth factors released from wounds are necessary for coordination and promotion of healing. Fibroblast growth factor (FGF) is a family of cell signaling proteins, which can mediate various processes such as angiogenesis, wound healing, metabolic regulation and embryonic development through its specific receptors. FGF can stimulate angiogenesis and proliferation of fibroblasts, and it is a powerful angiogenesis factor. Twenty-three subtypes have been identified and divided into seven subfamilies. Traditional treatments for DFU can only remove necrotic tissue, delay disease progression, and have a limited ability to repair wounds. In recent years, with the increasing understanding of the function of FGF, more and more researchers have been applying FGF-1, FGF-2, FGF-4, FGF-7, FGF-21 and FGF-23 topically to DFU with good therapeutic effects. This review elaborates on the recently developed FGF family members, outlining their mechanisms of action, and describing their potential therapeutics in DFU.

Current Advances in 3D Bioprinting Technology and Its Applications for Tissue Engineering

Three-dimensional (3D) bioprinting technology has emerged as a powerful biofabrication platform for tissue engineering because of its ability to engineer living cells and biomaterial-based 3D objects. Over the last few decades, droplet-based, extrusion-based, and laser-assisted bioprinters have been developed to fulfill certain requirements in terms of resolution, cell viability, cell density, etc. Simultaneously, various bio-inks based on natural-synthetic biomaterials have been developed and applied for successful tissue regeneration. To engineer more realistic artificial tissues/organs, mixtures of bio-inks with various recipes have also been developed. Taken together, this review describes the fundamental characteristics of the existing bioprinters and bio-inks that have been currently developed, followed by their advantages and disadvantages. Finally, various tissue engineering applications using 3D bioprinting are briefly introduced.

Advances in the Research of Bioinks Based on Natural Collagen, Polysaccharide and Their Derivatives for Skin 3D Bioprinting

The skin plays an important role in protecting the human body, and wound healing must be set in motion immediately following injury or trauma to restore the normal structure and function of skin. The extracellular matrix component of the skin mainly consists of collagen, glycosaminoglycan (GAG), elastin and hyaluronic acid (HA). Recently, natural collagen, polysaccharide and their derivatives such as collagen, gelatin, alginate, chitosan and pectin have been selected as the matrix materials of bioink to construct a functional artificial skin due to their biocompatible and biodegradable properties by 3D bioprinting, which is a revolutionary technology with the potential to transform both research and medical therapeutics. In this review, we outline the current skin bioprinting technologies and the bioink components for skin bioprinting. We also summarize the bioink products practiced in research recently and current challenges to guide future research to develop in a promising direction. While there are challenges regarding currently available skin bioprinting, addressing these issues will facilitate the rapid advancement of 3D skin bioprinting and its ability to mimic the native anatomy and physiology of skin and surrounding tissues in the future.

Injectable Biomaterials for Dental Tissue Regeneration

Injectable biomaterials scaffolds play a pivotal role for dental tissue regeneration, as such materials are highly applicable in the dental field, particularly when compared to pre-formed scaffolds. The defects in the maxilla-oral area are normally small, confined and sometimes hard to access. This narrative review describes different types of biomaterials for dental tissue regeneration, and also discusses the potential use of nanofibers for dental tissues. Various studies suggest that tissue engineering approaches involving the use of injectable biomaterials have the potential of restoring not only dental tissue function but also their biological purposes.

The Effects of Fibrin-icariin Nanoparticle Loaded in Poly (lactic-co-glycolic) Acid Scaffold as a Localized Delivery System on Chondrogenesis of Human Adipose-derived Stem Cells

Background:

Nowadays, cartilage tissue engineering is the best candidate for regeneration of cartilage defects. This study evaluates the effect of fibrin/icariin (ICA) nanoparticles (F/I NPs) on chondrogenesis of stem cells.

Materials and Methods:

F/I NPs were characterized by Dynamic Light Scattering DLS. Poly (lactic-co-glycolic) acid (PLGA)-F/I NP scaffold was fabricated and assessed by scanning electron microscope. Human adipose-derived stem cells (hADSCs) were seeded on scaffold and induced for chondrogenesis. After 14 days, cell viability and gene expression were analyzed by the 3-(4, 5- dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. MTT assay and real-time polymerase chain reaction (RT-PCR).

Results:

The size and surface charge of F/I NP were about 28–30 nm and − 17, respectively. The average of pore size of PLGA and PLGA–fibrin/ICA was 230 and 340 μm, respectively. Cell viability of differentiated cells in P/F group was higher than others significantly (P ≤ 0.05). Furthermore, quantitative RT-PCR analysis demonstrated that ICA upregulated cartilaginous-specific gene expression. Furthermore, the results of the expression of type I collagen revealed that ICA downregulated this gene significantly (P < 0.01).

Conclusions:

The results indicated that F/I NP could be a potential factor for chondrogenesis of stem cells and downregulation of fibrocartilage marker.

The Evolving Neural Tissue Engineering Landscape of India

The healthcare sector in India is witnessing unprecedented advancement. Tissue engineering has become an integral part of healthcare and medicine, particularly where treatments involve functional restoration of any injured or deceased part of the body. Not falling behind much with the progressing medical and healthcare sector of India, tissue engineering is also gaining momentum in the country. Out of several arenas of tissue engineering, India has made its mark in orthopedic and bone regeneration, cosmetic and skin regeneration, and very importantly neural regeneration. There are several articles reviewing the progress and prospects of orthopedic and skin regeneration research in India. However, there is no systematic review on progress, prospects, and pitfalls associated with neural tissue engineering in Indian context. The existing ones mainly focus on the technical advancements in the field from a global perspective. Therefore, it is worthwhile to have an organized look at the evolving neural tissue engineering landscape of India. This review will walk the readers systematically through different aspects of the topic. The review starts with an introduction to the nervous system to help readers appreciate the complexity that must be dealt with while engineering neural tissue. This is followed with a global picture of the neural tissue engineering, prominent research groups working on neural tissue engineering in India, factors that have and are currently molding the prospects of this field, and concluding with an overall perspective on present and future of neural tissue engineering in India.

Hydrogel scaffolds based on blood plasma cryoprecipitate and collagen derived from various sources: Structural, mechanical and biological characteristics

At present there is a growing need for tissue engineering products, including the products of scaffold-technologies. Biopolymer hydrogel scaffolds have a number of advantages and are increasingly being used to provide means of cell transfer for therapeutic treatments and for inducing tissue regeneration. This work presents original hydrogel biopolymer scaffolds based on a blood plasma cryoprecipitate and collagen and formed under conditions of enzymatic hydrolysis. Two differently originated collagens were used for the scaffold formation. During this work the structural and mechanical characteristics of the scaffold were studied. It was found that, depending on the origin of collagen, scaffolds possess differences in their structural and mechanical characteristics. Both types of hydrogel scaffolds have good biocompatibility and provide conditions that maintain the three-dimensional growth of adipose tissue stem cells. Hence, scaffolds based on such a blood plasma cryoprecipitate and collagen have good prospects as cell carriers and can be widely used in regenerative medicine.

Barrera E. Development of Functionalized Carbon Nano-Onions Reinforced Zein Protein Hydrogel Interfaces for Controlled Drug Release

In the current study, poly 4-mercaptophenyl methacrylate-carbon nano-onions (PMPMA-CNOs = f-CNOs) reinforced natural protein (zein) composites (zein/f-CNOs) are fabricated using the acoustic cavitation technique. The influence of f-CNOs inclusion on the microstructural properties, morphology, mechanical, cytocompatibility, in-vitro degradation, and swelling behavior of the hydrogels are studied. The tensile results showed that zein/f-CNOs hydrogels fabricated by the acoustic cavitation system exhibited good tensile strength (90.18 MPa), compared with the hydrogels fabricated by the traditional method and only microwave radiation method. It reveals the magnitude of physisorption and degree of colloidal stability of f-CNOs within the zein matrix under acoustic cavitation conditions. The swelling behaviors of hydrogels were also tested and improved results were noticed. The cytotoxicity of hydrogels was tested with osteoblast cells. The results showed good cell viability and cell growth. To explore the efficacy of hydrogels as drug transporters, 5-fluorouracil (5-FU) release was measured under gastric and intestinal pH environment. The results showed pH-responsive sustained drug release over 15 days of study, and pH 7.4 showed a more rapid drug release than pH 2.0 and 4.5. Nonetheless, all the results suggest that zein/f-CNOs hydrogel could be a potential pH-responsive drug transporter for a colon-selective delivery system.

Controlling the Multiscale Structure of Nanofibrous Fibrinogen Scaffolds for Wound Healing

As a key player in blood coagulation and tissue repair, fibrinogen has gained increasing attention to develop nanofibrous biomaterial scaffolds for wound healing. Current techniques to prepare protein nanofibers, like electrospinning or extrusion, are known to induce lasting changes in the protein conformation. Often, such secondary changes are associated with amyloid transitions, which can evoke unwanted disease mechanisms. Starting from our recently introduced technique to self-assemble fibrinogen scaffolds in physiological salt buffers, we here investigated the morphology and secondary structure of our novel fibrinogen nanofibers. Aiming at optimum self-assembly conditions for wound healing scaffolds, we studied the influence of fibrinogen concentration and pH on the protein conformation. Using circular dichroism and Fourier-transform infrared spectroscopy, we observed partial transitions from α-helical structures to β-strands upon fiber formation. Interestingly, a staining with thioflavin T revealed that this conformational transition was not associated with any amyloid formation. Toward novel scaffolds for wound healing, which are stable in aqueous environment, we also introduced cross-linking of fibrinogen scaffolds in formaldehyde vapor. This treatment allowed us to maintain the nanofibrous morphology while the conformation of fibrinogen nanofibers was redeveloped toward a more native state after rehydration. Altogether, self-assembled fibrinogen scaffolds are excellent candidates for novel wound healing systems since their multiscale structures can be well controlled without inducing any pathogenic amyloid transitions.

Fibrin Gels Entrapment of a Poly-Cyclodextrin Nanocarrier as a Doxorubicin Delivery System in an Orthotopic Model of Neuroblastoma: Evaluation of In Vitro Activity and In Vivo Toxicity

PURPOSE

Fibrin gels (FBGs) are potential delivery vehicles for many drugs, and can be easily prepared from purified components. We previously demonstrated their applicability for the release of different doxorubicin (Dox) nanoparticles used clinically or in an experimental stage, such as its inclusion complex with the amino β-cyclodextrin polymer (oCD-NH₂/Dox). Here we extend these studies by in vitro and in vivo evaluations.

METHODS

An in vitro cytotoxicity model consisting of an overlay of a neuroblastoma (NB) cell-containing agar layer above a drug-loaded FBG layer was used. Local toxicity in vivo (histology and blood analysis) was studied in a mouse orthotopic NB model (SHSY5YLuc⁺ cells implanted into the left adrenal gland).

RESULTS

In vitro data show that FBGs loaded with oCD-NH₂/Dox have a slightly lower cytotoxicity against NB cell lines than those loaded with Dox. Fibrinogen (FG), and Ca²⁺ concentrations may modify this activity. In vivo data support a lower general and local toxicity for FBGs loaded with oCD-NH₂/Dox than those loaded with Dox.

CONCLUSION

Our results suggest a possible increase of the therapeutic index of Dox when locally administered through FBGs loaded with oCD-NH₂/Dox, opening the possibility of using these releasing systems for the treatment of neuroblastoma.

Cell-Free Demineralized Bone Matrix for Mesenchymal Stem Cells Survival and Colonization

Decellularized bone matrix is receiving much attention as biological scaffolds and implantable biomaterials for bone tissue regeneration. Here, we evaluated the efficacy of a cell-free demineralized bone matrix on mesenchymal stem cells (MSCs) survival and differentiation in vitro. The seeding of human umbilical cord-derived MSCs (hUC-SCs) on decellularized bone matrices up to 14 days was exploited, assessing their capability of scaffold colonization and evaluating gene expression of bone markers. Light and Scanning Electron Microscopies were used. The obtained cell-free decalcified structures showed elastic moduli attributable to both topology and biochemical composition. Morphological observation evidenced an almost complete colonization of the scaffolds after 14 days of culture. Moreover, in hUC-SCs cultured on decalcified scaffolds, without the addition of any osteoinductive media, there was an upregulation of Collagen Type I (COL1) and osteonectin (ON) gene expression, especially on day 14. Modifications in the expression of genes engaged in stemness were also detected. In conclusion, the proposed decellularized bone matrix can induce the in vitro hUC-SCs differentiation and has the potential to be tested for in in vivo tissue regeneration.

Bioprinted osteon-like scaffolds enhance in vivo neovascularization

Bone tissue engineers are facing a daunting challenge when attempting to fabricate bigger constructs intended for use in the treatment of large bone defects, which is the vascularization of the graft. Cell-based approaches and, in particular, the use of in vitro coculture of human umbilical vein endothelial cells (HUVECs) and human mesenchymal stem cells (hMSCs) has been one of the most explored options. We present in this paper an alternative method to mimic the spatial pattern of HUVECs and hMSCs found in native osteons based on the use of extrusion-based 3D bioprinting (3DP). We developed a 3DP biphasic osteon-like scaffold, containing two separate osteogenic and vasculogenic cell populations encapsulated in a fibrin bioink in order to improve neovascularization. To this end, we optimized the fibrin bioink to improve the resolution of printed strands and ensure a reproducible printing process; the influence of printing parameters on extruded strand diameter and cell survival was also investigated. The mechanical strength of the construct was improved by co-printing the fibrin bioink along a supporting PCL carrier scaffold. Compressive mechanical testing showed improved mechanical properties with an average compressive modulus of 131 ± 23 MPa, which falls in the range of cortical bone. HUVEC and hMSC laden fibrin hydrogels were printed in osteon-like patterns and cultured in vitro. A significant increase in gene expression of angiogenic markers was observed for the biomimetic scaffolds. Finally, biphasic scaffolds were implanted subcutaneously in rats. Histological analysis of explanted scaffolds showed a significant increase in the number of blood vessels per area in the 3D printed osteon-like scaffolds. The utilization of these scaffolds in constructing biomimetic osteons for bone regeneration demonstrated a promising capacity to improve neovascularization of the construct. These results indicates that proper cell orientation and scaffold design could play a critical role in neovascularization.

Fibrin-Modified Cellulose as a Promising Dressing for Accelerated Wound Healing

Dermal injuries and chronic wounds usually regenerate with scar formation. Successful treatment without scarring might be achieved by pre-seeding a wound dressing with cells. We aimed to prepare a wound dressing fabricated from sodium carboxymethylcellulose (Hcel^® NaT), combined with fibrin and seeded with dermal fibroblasts in vitro. We fabricated the Hcel^® NaT in a porous and homogeneous form (P form and H form, respectively) differing in structural morphology and in the degree of substitution of hydroxyl groups. Each form of Hcel^® NaT was functionalized with two morphologically different fibrin structures to improve cell adhesion and proliferation, estimated by an MTS assay. Fibrin functionalization of the Hcel^® NaT strongly enhanced colonization of the material with human dermal fibroblasts. Moreover, the type of fibrin structures influenced the ability of the cells to adhere to the material and proliferate on it. The fibrin mesh filling the void spaces between cellulose fibers better supported cell attachment and subsequent proliferation than the fibrin coating, which only enwrapped individual cellulose fibers. On the fibrin mesh, the cell proliferation activity on day 3 was higher on the H form than on the P form of Hcel^® NaT, while on the fibrin coating, the cell proliferation on day 7 was higher on the P form. The Hcel^® NaT wound dressing functionalized with fibrin, especially when in the form of a mesh, can accelerate wound healing by supporting fibroblast adhesion and proliferation.

Current development of biodegradable polymeric materials for biomedical applications

In the last half-century, the development of biodegradable polymeric materials for biomedical applications has advanced significantly. Biodegradable polymeric materials are favored in the development of therapeutic devices, including temporary implants and three-dimensional scaffolds for tissue engineering. Further advancements have occurred in the utilization of biodegradable polymeric materials for pharmacological applications such as delivery vehicles for controlled/sustained drug release. These applications require particular physicochemical, biological, and degradation properties of the materials to deliver effective therapy. As a result, a wide range of natural or synthetic polymers able to undergo hydrolytic or enzymatic degradation is being studied for biomedical applications. This review outlines the current development of biodegradable natural and synthetic polymeric materials for various biomedical applications, including tissue engineering, temporary implants, wound healing, and drug delivery.

The effects of cross-linked/uncross-linked electrospun fibrinogen/polycaprolactone nanofibers on the proliferation of normal human epidermal keratinocytes

The aim of this study was an investigation on the proliferation rate of normal human epidermal keratinocytes (NHEK) on the cross-linked and uncross-linked fibrinogen/polycaprolactone (Fbg/PCL) nanofibers to determine a suitable scaffold for skin tissue engineering. Nanofibrous scaffolds were prepared by electrospinning of different weight ratios of Fbg to PCL and were analyzed as morphology, surface chemical properties and cytocompatibility by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, respectively. The diameters of the blended uncross-linked scaffolds were in the range of 124±43 nm–209±155 nm. Cross-linking of scaffolds with glutaraldehyde did not make a significant change in the diameter of blended scaffolds in 16 h. Cross-linking also improved the tensile strength and weight loss rate of scaffolds. However, cross-linking demonstrated an unfavorable effect on the attachment and proliferation of NHEK cells. The proliferation study revealed that uncross-linked scaffolds containing 50% and 70% Fbg provide a better environment for the growth of NHEK cells, and can be considered promising scaffolds in tissue engineering applications.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Hierarchically aligned fibrin nanofiber hydrogel accelerated axonal regrowth and locomotor function recovery in rat spinal cord injury

BACKGROUND

Designing novel biomaterials that incorporate or mimic the functions of extracellular matrix to deliver precise regulatory signals for tissue regeneration is the focus of current intensive research efforts in tissue engineering and regenerative medicine.

METHODS AND RESULTS

To mimic the natural environment of the spinal cord tissue, a three-dimensional hierarchically aligned fibrin hydrogel (AFG) with oriented topography and soft stiffness has been fabricated by electrospinning and a concurrent molecular self-assembling process. In this study, the AFG was implanted into a rat dorsal hemisected spinal cord injury model to bridge the lesion site. Host cells invaded promptly along the aligned fibrin hydrogels to form aligned tissue cables in the first week, and then were followed by axonal regrowth. At 4 weeks after the surgery, neurofilament (NF)-positive staining fibers were detected near the rostral end as well as the middle site of defect, which aligned along the tissue cables. Abundant NF- and GAP-43-positive staining indicated new axon regrowth in the oriented tissue cables, which penetrated throughout the lesion site in 8 weeks. Additionally, the abundant blood vessels marked with RECA-1 had reconstructed within the lesion site at 4 weeks after surgery. Basso-Beattie-Bresnahan scoring showed that the locomotor performance of the AFG group recovered much faster than that of blank control group or the random fibrin hydrogel (RFG) group from 2 weeks after surgery. Furthermore, diffusion tensor imaging tractography of MRI confirmed the optimal axon fiber reconstruction compared with the RFG and control groups.

CONCLUSION

Taken together, our results suggested that the AFG scaffold provided an inductive matrix for accelerating directional host cell invasion, vascular system reconstruction, and axonal regrowth, which could promote and support extensive aligned axonal regrowth and locomotor function recovery.

Bioinks for 3D bioprinting: an overview

Bioprinting is an emerging technology with various applications in making functional tissue constructs to replace injured or diseased tissues. It is a relatively new approach that provides high reproducibility and precise control over the fabricated constructs in an automated manner, potentially enabling high-throughput production. During the bioprinting process, a solution of a biomaterial or a mixture of several biomaterials in the hydrogel form, usually encapsulating the desired cell types, termed the bioink, is used for creating tissue constructs. This bioink can be cross-linked or stabilized during or immediately after bioprinting to generate the final shape, structure, and architecture of the designed construct. Bioinks may be made from natural or synthetic biomaterials alone, or a combination of the two as hybrid materials. In certain cases, cell aggregates without any additional biomaterials can also be adopted for use as a bioink for bioprinting processes. An ideal bioink should possess proper mechanical, rheological, and biological properties of the target tissues, which are essential to ensure correct functionality of the bioprinted tissues and organs. In this review, we provide an in-depth discussion of the different bioinks currently employed for bioprinting, and outline some future perspectives in their further development.

Evaluation of Fibrin-Based Interpenetrating Polymer Networks as Potential Biomaterials for Tissue Engineering

Interpenetrating polymer networks (IPNs) have gained great attention for a number of biomedical applications due to their improved properties compared to individual components alone. In this study, we investigated the capacity of newly-developed naturally-derived IPNs as potential biomaterials for tissue engineering. These IPNs combine the biologic properties of a fibrous fibrin network polymerized at the nanoscale and the mechanical stability of polyethylene oxide (PEO). First, we assessed their cytotoxicity in vitro on L929 fibroblasts. We further evaluated their biocompatibility ex vivo with a chick embryo organotypic culture model. Subcutaneous implantations of the matrices were subsequently conducted on nude mice to investigate their biocompatibility in vivo. Our preliminary data highlighted that our biomaterials were non-cytotoxic (viability above 90%). The organotypic culture showed that the IPN matrices induced higher cell adhesion (across all the explanted organ tissues) and migration (skin, intestine) than the control groups, suggesting the advantages of using a biomimetic, yet mechanically-reinforced IPN-based matrix. We observed no major inflammatory response up to 12 weeks post implantation. All together, these data suggest that these fibrin-based IPNs are promising biomaterials for tissue engineering.

A unique heterologous fibrin sealant (HFS) as a candidate biological scaffold for mesenchymal stem cells in osteoporotic rats

Background

The injection of mesenchymal stem cells (MSCs) directly into the bone of osteoporotic (OP) patients for rapid recovery has been studied worldwide. Scaffolds associated with MSCs are used to maintain and avoid cell loss after application. A unique heterologous fibrin sealant (HFS) derived from snake venom was evaluated for the cytotoxicity of its main components and as a three-dimensional biological scaffold for MSCs to repair a critical femur defect in osteoporotic rats.

Methods

The cytotoxicity of HFS was assessed using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazoliumbromide (MTT) assay and transmission electron microscopy. The cells were cultured, characterized by flow cytometry and differentiated into the osteogenic lineage. Two-month-old rats underwent ovariectomy to induce OP. After 3 months, a 5 mm critical bone defect was made in the distal end of the rat femurs and filled with HFS; HFS + MSCs; and HFS + MSCs D (differentiated into the osteogenic lineage) to evaluate the effects. An injury control group (injury and no treatment) and blank control group (no injury and no treatment) were also included. The animals were observed at days 14 and 28 by microtomographic (micro-CT) analyses, histologic and biochemical analysis, as well as scanning electron microscopy.

Results

The results revealed that one of the compounds of HFS, the thrombin-like enzyme extracted from snake venom, had no cytotoxic effects on the MSCs. OP was successfully induced, as demonstrated by the significant differences in the levels of 17β-estradiol, Micro-CT analyses and alkaline phosphatase between the ovariectomized (OVX) and non-ovariectomized (NOVX) groups. The histological data revealed that at 14 days after surgery in both the OVX and NOVX animals, the HFS + CTMs and HFS + CTMsD showed a higher formation of bone cells at the site in relation to the control group (without treatment). Collagen formation was evidenced through bone neoformation in all treated and control groups. No morphological differences in the femurs of the NOVX and OVX animals were observed after the surgical procedure. Scanning electron microscopy (SEM) confirmed the histological analysis.

Conclusions

The new HFS composed of two non-toxic components for MSCs showed capacity to promote the recovery of the bone lesions in OVX and NOVX animals at 14 days after surgery. In addition, the HFS enabled the differentiation of MSCs into MSCs D in the group treated with HFS + MSCs. Using the MSCs and/or MSCs D together with this biopharmaceutical could potentially enable significant advances in the treatment of osteoporotic fractures. Future clinical trials will be necessary to confirm these results.

Spatially and Temporally Controlled Hydrogels for Tissue Engineering

Recent years have seen tremendous advances in the field of hydrogel-based biomaterials. One of the most prominent revolutions in this field has been the integration of elements or techniques that enable spatial and temporal control over hydrogels' properties and functions. Here, we critically review the emerging progress of spatiotemporal control over biomaterial properties towards the development of functional engineered tissue constructs. Specifically, we will highlight the main advances in the spatial control of biomaterials, such as surface modification, microfabrication, photo-patterning, and three-dimensional (3D) bioprinting, as well as advances in the temporal control of biomaterials, such as controlled release of molecules, photocleaving of proteins, and controlled hydrogel degradation. We believe that the development and integration of these techniques will drive the engineering of next-generation engineered tissues.

Mechanically stable fibrin scaffolds promote viability and induce neurite outgrowth in neural aggregates derived from human induced pluripotent stem cells

Recent work demonstrated that 3D fibrin scaffolds function as an effective substrate for engineering tissues from pluripotent stem cells. However, the rapid degradation rate of fibrin remains a major limitation when differentiating human pluripotent stem cells for tissue engineering applications. The addition of crosslinking agents, such as genipin, during the polymerization process increases scaffold stability while decreasing the degradation rate of fibrin. Genipin crosslinking alters the physical characteristics of the fibrin scaffolds, which influences the behaviour of the differentiating cells seeded inside. It also possesses neuritogenic and neuroprotective properties, making it particularly attractive for engineering neural tissue from pluripotent stem cells. Here we show that genipin enhances neuronal differentiation of neural progenitors derived from human induced pluripotent stem cells (hiPSCs) in 2D culture and genipin concentration influences the morphological and mechanical properties of 3D fibrin scaffolds. These mechanically stable genipin-crosslinked fibrin scaffolds support hiPSC-derived neural aggregates and induce neurite outgrowth while remaining intact for 2 weeks as opposed to 5 days for unmodified fibrin scaffolds.

Hydrothermal Fabrication of Highly Porous Titanium Bio-Scaffold with a Load-Bearable Property

Porous titanium (P_Ti) is considered as an effective material for bone scaffold to achieve a stiffness reduction. Herein, biomimetic (bio-)scaffolds were made of sintered P_Ti, which used NaCl as the space holder and had it removed via the hydrothermal method. X-ray diffraction results showed that the subsequent sintering temperature of 1000 °C was the optimized temperature for preparing P_Ti. The compressive strength of P_Ti was measured using a compression test, which revealed an excellent load-bearing ability of above 70 MPa for that with an addition of 50 wt % NaCl (P_Ti_50). The nano-hardness of P_Ti, tested upon their solid surface, was presumably consistent with the density of pores vis-à-vis the addition of NaCl. Overall, a load-bearable P_Ti with a highly porous structure (e.g., P_Ti_50 with a porosity of 43.91% and a pore size around 340 μm) and considerable compressive strength could be obtained through the current process. Cell proliferation (MTS) and lactate dehydrogenase (LDH) assays showed that all P_Ti samples exhibited high cell affinity and low cell mortality, indicating good biocompatibility. Among them, P_Ti_50 showed relatively good in-cell morphology and viability, and is thus promising as a load-bearable bio-scaffold.

Protein nanocoatings on synthetic polymeric nanofibrous membranes designed as carriers for skin cells

Protein-coated resorbable synthetic polymeric nanofibrous membranes are promising for the fabrication of advanced skin substitutes. We fabricated electrospun polylactic acid and poly(lactide-co-glycolic acid) nanofibrous membranes and coated them with fibrin or collagen I. Fibronectin was attached to a fibrin or collagen nanocoating, in order further to enhance the cell adhesion and spreading. Fibrin regularly formed a coating around individual nanofibers in the membranes, and also formed a thin noncontinuous nanofibrous mesh on top of the membranes. Collagen also coated most of the fibers of the membrane and randomly created a soft gel on the membrane surface. Fibronectin predominantly adsorbed onto a thin fibrin mesh or a collagen gel, and formed a thin nanofibrous structure. Fibrin nanocoating greatly improved the attachment, spreading, and proliferation of human dermal fibroblasts, whereas collagen nanocoating had a positive influence on the behavior of human HaCaT keratinocytes. In addition, fibrin stimulated the fibroblasts to synthesize fibronectin and to deposit it as an extracellular matrix. Fibrin coating also showed a tendency to improve the ultimate tensile strength of the nanofibrous membranes. Fibronectin attached to fibrin or to a collagen coating further enhanced the adhesion, spreading, and proliferation of both cell types.

Biomaterial Strategies for Delivering Stem Cells as a Treatment for Spinal Cord Injury

Ongoing clinical trials are evaluating the use of stem cells as a way to treat traumatic spinal cord injury (SCI). However, the inhibitory environment present in the injured spinal cord makes it challenging to achieve the survival of these cells along with desired differentiation into the appropriate phenotypes necessary to regain function. Transplanting stem cells along with an instructive biomaterial scaffold can increase cell survival and improve differentiation efficiency. This study reviews the literature discussing different types of instructive biomaterial scaffolds developed for transplanting stem cells into the injured spinal cord. We have chosen to focus specifically on biomaterial scaffolds that direct the differentiation of neural stem cells and pluripotent stem cells since they offer the most promise for producing the cell phenotypes that could restore function after SCI. In terms of biomaterial scaffolds, this article reviews the literature associated with using hydrogels made from natural biomaterials and electrospun scaffolds for differentiating stem cells into neural phenotypes. It then presents new data showing how these different types of scaffolds can be combined for neural tissue engineering applications and provides directions for future studies.

The potential applications of fibrin-coated electrospun polylactide nanofibers in skin tissue engineering

Fibrin plays an important role during wound healing and skin regeneration. It is often applied in clinical practice for treatment of skin injuries or as a component of skin substitutes. We prepared electrospun nanofibrous membranes made from poly(l-lactide) modified with a thin fibrin nanocoating. Fibrin surrounded the individual fibers in the membrane and also formed a thin fibrous mesh on several places on the membrane surface. The cell-free fibrin nanocoating remained stable in the cell culture medium for 14 days and did not change its morphology. On membranes populated with human dermal fibroblasts, the rate of fibrin degradation correlated with the degree of cell proliferation. The cell spreading, mitochondrial activity, and cell population density were significantly higher on membranes coated with fibrin than on nonmodified membranes, and this cell performance was further improved by the addition of ascorbic acid in the cell culture medium. Similarly, fibrin stimulated the expression and synthesis of collagen I in human dermal fibroblasts, and this effect was further enhanced by ascorbic acid. The expression of beta₁-integrins was also improved by fibrin, and on pure polylactide membranes, it was slightly enhanced by ascorbic acid. In addition, ascorbic acid promoted deposition of collagen I in the form of a fibrous extracellular matrix. Thus, the combination of nanofibrous membranes with a fibrin nanocoating and ascorbic acid seems to be particularly advantageous for skin tissue engineering.

Fibrin gels loaded with cisplatin and cisplatin-hyaluronate complexes tested in a subcutaneous human melanoma model

Fibrin gels are attractive biomaterials for local delivery of a variety of agents, from drugs to proteins. Similarly, polymer-anticancer-drug conjugates and nanoparticles are emerging as potential candidates for cancer treatment. Combining these different approaches, we have studied the efficacy of fibrin gels loaded with cisplatin (DDP) and a complex of DDP with hyaluronate (DDP-HA) for tumor growth inhibition in a melanoma model. Loaded gels prepared at relatively high fibrinogen concentration (22 mg/ml) showed good in vitro antiproliferative activities, prolonged release of the anticancer drug, and a long persistence (10-15 days) in vivo when implanted subcutaneously (sc) in immunodeficient mice. Gels loaded with DDP or DDP-HA containing 1/3 or even 1/6 of their systemic dose (6 mg/kg) and positioned under the tumor mass in mice bearing a sc human SK-Mel-28 tumor showed an antitumor activity better than that of the original parent compound given intraperitoneally (ip). Moreover, in an additional experiment in vivo, fibrin gels loaded with N-trimethyl chitosan-based nanoparticles containing a DDP-HA complex were assayed, resulting in a further 8 % improvement of anticancer activity, with lesser adverse systemic toxic effects. Taken together, these results suggest that the combination of fibrin gels and drugs complexed with suitable macromolecules holds great promise for loco-regional anticancer therapy of melanoma and other surgically removable cancer types.

Nanometer-sized extracellular matrix coating on polymer-based scaffold for tissue engineering applications

Surface modification can play a crucial role in enhancing cell adhesion to synthetic polymer-based scaffolds in tissue engineering applications. Here, we report a novel approach for layer-by-layer (LbL) fabrication of nanometer-size fibronectin and gelatin (FN-G) layers on electrospun fibrous poly(carbonate urethane)urea (PCUU) scaffolds. Alternate immersions into the solutions of fibronectin and gelatin provided thickness-controlled FN-G nano-layers (PCUU(FN-G) ) which maintained the scaffold's 3D structure and width of fibrous bundle of PCUU as evidenced by scanning electron miscroscopy. The PCUU(FN-G) scaffold improved cell adhesion and proliferation of bladder smooth muscles (BSMCs) when compared to uncoated PCUU. The high affinity of PCUU(FN-G) for cells was further demonstrated by migration of adherent BSMCs from culture plates to the scaffold. Moreover, the culture of UROtsa cells, human urothelium-derived cell line, on PCUU(FN-G) resulted in an 11-15 μm thick multilayered cell structure with cell-to-cell contacts although many UROtsa cells died without forming cell connections on PCUU. Together these results indicate that this approach will aid in advancing the technology for engineering bladder tissues in vitro. Because FN-G nano-layers formation is based on nonspecific physical adsorption of fibronectin onto polymer and its subsequent interactions with gelatin, this technique may be applicable to other polymer-based scaffold systems for various tissue engineering/regenerative medicine applications.

Evaluation of the ability of natural and synthetic scaffolds in providing an appropriate environment for growth and chondrogenic differentiation of adipose-derived mesenchymal stem cells

BACKGROUND

Although progenitor cells have been observed in articular cartilage, this part has a limited ability to repair due to a lack of blood supply. Formerly, tissue engineering was mainly based on collecting chondrocytes from the joint surface, culturing them on resorbable scaffolds such as poly D, L-lactic glycolic acid (PLGA) and then autologous transplantation. In recent times, due to difficulties in collecting chondrocytes, most of the researchers are focused on stem cells for producing these cells. Among the important factors in this approach, is using appropriate scaffolds with good mechanical and biological properties to provide optimal environment for growth and development of stem cells. In this study, we evaluated the potential of fibrin glue, PLGA and alginate scaffolds in providing a suitable environment for growth and chondrogenic differentiation of mesenchymal stem cells (MSCs) in the presence of transforming growth factor-β3.

MATERIALS AND METHODS

Fibrin glue, PLGA and alginate scaffolds were prepared and MSCs were isolated from human adipose tissue. Cells were cultured separately on the scaffolds and 2 weeks after differentiation, chondrogenic genes, cell proliferation ability and morphology in each scaffold were evaluated using real time-polymerase chain reaction, MTT chondrogenic assay and histological examination, respectively.

RESULTS

Proliferation of differentiated adipose tissue derived mesenchymal stem cells (AD-MSCs) to chondrogenic cells in Fibrin glue were significantly higher than in other scaffolds. Also, Fibrin glue caused the highest expression of chondrogenic genes compared to the other scaffolds. Histological examination revealed that the pores of the Fibrin glue scaffolds were filled with cells uniformly distributed.

CONCLUSION

According to the results of the study, it can be concluded that natural scaffolds such as fibrin can be used as an appropriate environment for cartilage differentiation.

Autologous serum improves bone formation in a primary stable silica-embedded nanohydroxyapatite bone substitute in combination with mesenchymal stem cells and rhBMP-2 in the sheep model

New therapeutic strategies are required for critical size bone defects, because the gold standard of transplanting autologous bone from an unharmed area of the body often leads to several severe side effects and disadvantages for the patient. For years, tissue engineering approaches have been seeking a stable, axially vascularized transplantable bone replacement suitable for transplantation into the recipient bed with pre-existing insufficient conditions. For this reason, the arteriovenous loop model was developed and various bone substitutes have been vascularized. However, it has not been possible thus far to engineer a primary stable and axially vascularized transplantable bone substitute. For that purpose, a primary stable silica-embedded nanohydroxyapatite (HA) bone substitute in combination with blood, bone marrow, expanded, or directly retransplanted mesenchymal stem cells, recombinant human bone morphogenetic protein 2 (rhBMP-2), and different carrier materials (fibrin, cell culture medium, autologous serum) was tested subcutaneously for 4 or 12 weeks in the sheep model. Autologous serum lead to an early matrix change during degradation of the bone substitute and formation of new bone tissue. The best results were achieved in the group combining mesenchymal stem cells expanded with 60 μg/mL rhBMP-2 in autologous serum. Better ingrowth of fibrovascular tissue could be detected in the autologous serum group compared with the control (fibrin). Osteoclastic activity indicating an active bone remodeling process was observed after 4 weeks, particularly in the group with autologous serum and after 12 weeks in every experimental group. This study clearly demonstrates the positive effects of autologous serum in combination with mesenchymal stem cells and rhBMP-2 on bone formation in a primary stable silica-embedded nano-HA bone grafting material in the sheep model. In further experiments, the results will be transferred to the sheep arteriovenous loop model in order to engineer an axially vascularized primary stable bone replacement in clinically relevant size for free transplantation.