Conductive Polymers: Opportunities and Challenges in Biomedical Applications.

Research pertaining to conductive polymers has gained significant traction in recent years, and their applications range from optoelectronics to material science. For all intents and purposes, conductive polymers can be described as Nobel Prize-winning materials, given that their discoverers were awarded the Nobel Prize in Chemistry in 2000. In this review, we seek to describe the chemical forms and functionalities of the main types of conductive polymers, as well as their synthesis methods. We also present an in-depth analysis of composite conductive polymers that contain various nanomaterials such as graphene, fullerene, carbon nanotubes, and paramagnetic metal ions. Natural polymers such as collagen, chitosan, fibroin, and hydrogel that are structurally modified for them to be conductive are also briefly touched upon. Finally, we expound on the plethora of biomedical applications that harbor the potential to be revolutionized by conductive polymers, with a particular focus on tissue engineering, regenerative medicine, and biosensors.

Emerging roles of exosomal miRNAs in breast cancer drug resistance.

Breast cancer (BC), as a heterogeneous disease, is considered as one of the most common malignancies in women worldwide. The resistance of BC cells to therapeutic agents has remained a big challenge in the treatment of BC patients. Some factors such as cytokines, exosomes, and soluble receptors were recognized as crucial agents involved in the development of drug resistance. However, the exact mechanisms underlying the drug resistance is still unknown. There is growing evidence to support the emerging roles of exosomes, especially exosomal miRNAs, in tumor initiation, angiogenesis, proliferation, migration, invasion, metastasis, and drug resistance. Therefore, identification of BC-specific exosomal miRNAs and their underlying mechanisms would be helpful to define sensitivity to therapeutic drugs and establish an appropriate therapeutic strategy. This review focuses mainly on the roles of exosomal miRNAs and their associated mechanisms in the resistance of BC cells to therapeutic agents, as well as critically examines the potential of these macromolecules as a treatment biomarker in BC patients.

Comparison of the antibacterial effects of a short cationic peptide and 1% silver bioactive glass against extensively drug-resistant bacteria, Pseudomonas aeruginosa and Acinetobacter baumannii, isolated from burn patients.

We have already established that a short cationic peptide (CM11) has high antimicrobial activity against a number of bacterial pathogens. Considering the untreatable problem of burn infections caused by Pseudomonas aeruginosa and Acinetobacter baumannii, this study evaluated and compared antibacterial effects of the CM11 peptide and 1% silver-doped bioactive glass (AgBG) against extensively drug-resistant strains of these bacteria which were isolated from burn patients. Accordingly, the bacteria were isolated from burn patients and their antibiotic resistance patterns and mechanisms were fully determined. The isolated bacterial from patients were resistant to almost all commonly used antibiotics and silver treatment. The isolates acquired their resistance through inactivation of their porin, the overexpression of efflux pump, and beta-lactamase. CM11 peptide and 1% AgBG had minimum inhibitory concentration (MIC) of ≥ 16 µg ml-1 and ≥ 4 mg ml-1 for clinical isolates, respectively. The minimum bactericidal concentration (MBC) of peptide and 1% AgBG for resistant bacteria was ≥ 32 µg ml-1 and ≥ 4 mg ml-1, respectively. Among the clinical isolates, two P. aeruginosa isolates and one A. baumannii isolate were resistant to 1% AgBG disk. The CM11 peptide also showed high biocompatibility in vivo and no cytotoxicity against fibroblasts and adipose-derived mesenchymal stem cells in concentrations ≤ 64 µg ml-1 and ≤ 32 µg ml-1, respectively, while the safe concentration of 1% AgBG for these cells was ≤ 16 µg ml-1. In conclusion, these findings indicated that the 1% silver is not safe and effective for treatment of such infections. The data suggest that CM11 peptide therapy is a reliable and safe strategy that can be used for the treatment of burn infections caused by antimicrobial-resistant isolates. The next stage of the study will be a multicenter clinical trial.

3D Protein-Based Bilayer Artificial Skin for the Guided Scarless Healing of Third-Degree Burn Wounds in Vivo.

Severe burn injuries can lead to delays in healing and devastating scar formation. Attempts have been made to develop a suitable skin substitute for the scarless healing of such skin wounds. Currently, there is no effective strategy for completely scarless healing after the thermal injuries. In our recent work, we fabricated and evaluated a 3D protein-based artificial skin made from decellularized human amniotic membrane (AM) and electrospun nanofibrous silk fibroin (ESF) in vitro. We also characterized both biophysical and cell culture investigation to establish in vitro performance of the developed bilayer scaffolds. In this report, we evaluate the appropriate utility of this fabricated bilayered artificial skin in vivo with particular emphasis on healing and scar formation due to the biochemical and biomechanical complexity of the skin. For this work, AM and AM/ESF membranes alone or seeded with adipose-tissue-derived mesenchymal stem cells (AT-MSCs) are implanted on full-thickness burn wounds in mice. The healing efficacy and scar formation are evaluated at 7, 14, and 28 days post-implantation in vivo. Our data reveal that ESF accelerates the wound-healing process through the early recruitment of inflammatory cells such as macrophages into the defective site as well as the up-regulation of angiogenic factors from the AT-MSCs and the facilitation of the remodeling phase. In vivo application of the prepared AM/ESF membrane seeded with the AT-MSCs reduces significantly the post-burn scars. The in vivo data suggest that the potential applications of the AM/ESF bilayered artificial skin may be considered a clinical translational product with stem cells to guide the scarless healing of severe burn injuries.

Translational Regenerative Therapies for Chronic Spinal Cord Injury.

Spinal cord injury is a chronic and debilitating neurological condition that is currently being managed symptomatically with no real therapeutic strategies available. Even though there is no consensus on the best time to start interventions, the chronic phase is definitely the most stable target in order to determine whether a therapy can effectively restore neurological function. The advancements of nanoscience and stem cell technology, combined with the powerful, novel neuroimaging modalities that have arisen can now accelerate the path of promising novel therapeutic strategies from bench to bedside. Several types of stem cells have reached up to clinical trials phase II, including adult neural stem cells, human spinal cord stem cells, olfactory ensheathing cells, autologous Schwann cells, umbilical cord blood-derived mononuclear cells, adult mesenchymal cells, and autologous bone-marrow-derived stem cells. There also have been combinations of different molecular therapies; these have been either alone or combined with supportive scaffolds with nanostructures to facilitate favorable cell⁻material interactions. The results already show promise but it will take some coordinated actions in order to develop a proper step-by-step approach to solve impactful problems with neural repair.

The regenerative role of adipose-derived stem cells (ADSC) in plastic and reconstructive surgery.

The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs offers a paradigm shift in plastic and reconstructive surgery. The use of either embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC) in clinical situations is limited because of regulations and ethical considerations even though these cells are theoretically highly beneficial. Adult mesenchymal stem cells appear to be an ideal stem cell population for practical regenerative medicine. Among these cells, adipose-derived stem cells (ADSC) have the potential to differentiate the mesenchymal, ectodermal and endodermal lineages and are easy to harvest. Additionally, adipose tissue yields a high number of ADSC per volume of tissue. Based on this background knowledge, the purpose of this review is to summarise and describe the proliferation and differentiation capacities of ADSC together with current preclinical data regarding the use of ADSC as regenerative tools in plastic and reconstructive surgery.

Hearts beating through decellularized scaffolds: whole-organ engineering for cardiac regeneration and transplantation.

Whole-organ decellularization and tissue engineering approaches have made significant inroads during recent years. If proven to be successful and clinically viable, it is highly likely that this field would be poised to revolutionize organ transplantation surgery. In particular, whole-heart decellularization has captured the attention and imagination of the scientific community. This technique allows for the generation of a complex three-dimensional (3D) extracellular matrix scaffold, with the preservation of the intrinsic 3D basket-weave macroarchitecture of the heart itself. The decellularized scaffold can then be recellularized by seeding it with cells and incubating it in perfusion bioreactors in order to create functional organ constructs for transplantation. Indeed, research into this strategy of whole-heart tissue engineering has consequently emerged from the pages of science fiction into a proof-of-concept laboratory undertaking. This review presents current trends and advances, and critically appraises the concepts involved in various approaches to whole-heart decellularization and tissue engineering.

Development of a Tissue-Engineered Lymphatic Graft Using Nanocomposite Polymer for the Treatment of Secondary Lymphedema.

Damage of the lymphatic vessels, commonly due to surgical resection for cancer treatment, leads to secondary lymphedema. Tissue engineering approach offers a possible solution to reconstruct this damage with the use of lymphatic graft to re-establish the lymphatic flow, hence preventing lymphedema. The aim of this study is to develop a tissue-engineered lymphatic graft using nanocomposite polymer and human dermal lymphatic endothelial cells (HDLECs). A nanocomposite polymer, the polyhedral oligomeric silsequioxane-poly(carbonate-urea)urethane (POSS-PCU), which has enhanced mechanical, chemical, and physical characteristics, was used to develop the lymphatic graft. POSS-PCU has been used clinically for the world's first synthetic trachea, lacrimal duct, and is currently undergoing clinical trial for coronary artery bypass graft. Two designs and fabrication methods were used to manufacture the conduits. The fabrication method, the mechanical and physical properties, as well as the hydraulic conductivity were tested. This is followed by in vitro cell culture analysis to test the cytocompatibility of HDLEC with the polymer surface. Using the casted extrusion method, the nanocomposite lymphatic graft demonstrates desirable mechanical property and hydraulic conductivity to re-establish the lymphatic flow. The conduit has high tensile strength (casted: 74.86 ± 5.74 MPa vs. coagulated: 31.33 ± 3.71 MPa; P < 0.001), favorable kink resistance, and excellent suture retention property (casted vs. coagulated, P < 0.05). Cytocompatibility study showed that the POSS-PCU scaffold supports the attachment and growth of HDLECs. This study demonstrates the feasibility of developing a tissue-engineered lymphatic graft using the nanocomposite polymer. It displays excellent mechanical property and cytocompatibility to HDLECs, offering much promise for clinical applications and as a new treatment option for secondary lymphedema.

Quantum dot nanoparticle for optimization of breast cancer diagnostics and therapy in a clinical setting.

Breast cancer is the most common cancer in the world. Sentinel lymph node (SLN) biopsy is used for staging of axillary lymph nodes. Organic dyes and radiocolloid are currently used for SLN mapping, but expose patients to ionizing radiation, are unstable during surgery and cause local tissue damage. Quantum dots (QD) could be used for SLN mapping without the need for biopsy. Surgical resection of the primary tumor is the optimal treatment for early-diagnosed breast cancer, but due to difficulties in defining tumor margins, cancer cells often remain leading to reoccurrences. Functionalized QD could be used for image-guided tumor resection to allow visualization of cancer cells. Near Infrared QD are photostable and have improved deep tissue penetration. Slow elimination of QD raises concerns of potential accumulation. Nevertheless, promising findings with cadmium-free QD in recent in vivo studies and first in-human trial suggest huge potential for cancer diagnostic and therapy.

Development of mechano-responsive polymeric scaffolds using functionalized silica nano-fillers for the control of cellular functions.

We demonstrate an efficient method to produce mechano-responsive polymeric scaffolds which can alter cellular functions using two different functionalized (OH and NH2) silica nano-fillers. Fumed silica-hydroxyl and fumed silica-amine nano-fillers were mixed with a biocompatible polymer (POSS-PCU) at various wt% to produce scaffolds. XPS and mechanical testing demonstrate that bulk mechanical properties are modified without changing the scaffold's surface chemistry. Mechanical testing showed significant change in bulk properties of POSS-PCU scaffolds with an addition of silica nanofillers as low as 1% (P<0.01). Scaffolds modified with NH2 silica showed significantly higher bulk mechanical properties compared to the one modified with the OH group. Enhanced cell adhesion, proliferation and collagen production over 14days were observed on scaffolds with higher bulk mechanical properties (NH2) compared to those with lower ones (unmodified and OH modified) (P<0.05) during in vitro analysis. This study provides an effective method of manufacturing mechano-responsive polymeric scaffolds, which can help to customize cellular responses for biomaterial applications.

Next generation covered stents made from nanocomposite materials: A complete assessment of uniformity, integrity and biomechanical properties.

Covered stents are stents wrapped with a thin polymeric membrane, and are typically used to treat vessel aneurysms and seal perforated arteries. Current covered stents suffer from restenosis due to limitations in material and fabrication methods which leaves metallic struts directly exposed to blood. We have developed a biocompatible and haemocompatible nanocomposite polymer, polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU). We devised a novel combination of ultrasonic spray atomisation system and dip-coating process to produce small calibre covered stents with metal struts fully embedded within the membrane, which also yields greater coating uniformity. Stent-polymer bonding was enhanced via silanisation and coating of reactive pre-polymer. Platelet studies supported the non-thrombogenicity of POSS-PCU. Biomechanical performances including diametrical compliance, bending strength, radial strength and recoil were evaluated and optimised. This proof-of-principle manufacturing technique could lead to the development of next-generation small calibre adult and paediatric covered stents. These stents are currently undergoing preclinical trial. From the Clinical Editor: The use of stents to treat vascular diseases is now the standard of care in the clinical setting. Nonetheless, a major problem of the current stents is the risk of restenosis and thrombosis. The authors developed a nanocomposite material using polyhedral oligomeric silsesquioxane and poly(carbonate-urea) urethane (POSS-PCU) and incorporated into metallic stents. Preliminary data have already shown promising results. It is envisaged that this would further lead to better stent technology in the future.

Immunomodulatory effect of a decellularized skeletal muscle scaffold in a discordant xenotransplantation model.

Decellularized (acellular) scaffolds, composed of natural extracellular matrix, form the basis of an emerging generation of tissue-engineered organ and tissue replacements capable of transforming healthcare. Prime requirements for allogeneic, or xenogeneic, decellularized scaffolds are biocompatibility and absence of rejection. The humoral immune response to decellularized scaffolds has been well documented, but there is a lack of data on the cell-mediated immune response toward them in vitro and in vivo. Skeletal muscle scaffolds were decellularized, characterized in vitro, and xenotransplanted. The cellular immune response toward scaffolds was evaluated by immunohistochemistry and quantified stereologically. T-cell proliferation and cytokines, as assessed by flow cytometry using carboxy-fluorescein diacetate succinimidyl ester dye and cytometric bead array, formed an in vitro surrogate marker and correlate of the in vivo host immune response toward the scaffold. Decellularized scaffolds were free of major histocompatibility complex class I and II antigens and were found to exert anti-inflammatory and immunosuppressive effects, as evidenced by delayed biodegradation time in vivo; reduced sensitized T-cell proliferative activity in vitro; reduced IL-2, IFN-γ, and raised IL-10 levels in cell-culture supernatants; polarization of the macrophage response in vivo toward an M2 phenotype; and improved survival of donor-derived xenogeneic cells at 2 and 4 wk in vivo. Decellularized scaffolds polarize host responses away from a classical TH1-proinflammatory profile and appear to down-regulate T-cell xeno responses and TH1 effector function by inducing a state of peripheral T-cell hyporesponsiveness. These results have substantial implications for the future clinical application of tissue-engineered therapies.

Conjugation with RGD Peptides and Incorporation of Vascular Endothelial Growth Factor Are Equally Efficient for Biofunctionalization of Tissue-Engineered Vascular Grafts.

The blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) has recently been considered promising for vascular tissue engineering. However, it was shown that PHBV/PCL grafts require biofunctionalization to achieve high primary patency rate. Here we compared immobilization of arginine-glycine-aspartic acid (RGD)-containing peptides and the incorporation of vascular endothelial growth factor (VEGF) as two widely established biofunctionalization approaches. Electrospun PHBV/PCL small-diameter grafts with either RGD peptides or VEGF, as well as unmodified grafts were implanted into rat abdominal aortas for 1, 3, 6, and 12 months following histological and immunofluorescence assessment. We detected CD31⁺/CD34⁺/vWF⁺ cells 1 and 3 months postimplantation at the luminal surface of PHBV/PCL/RGD and PHBV/PCL/VEGF, but not in unmodified grafts, with the further observation of CD31⁺CD34-vWF⁺ phenotype. These cells were considered as endothelial and produced a collagen-positive layer resembling a basement membrane. Detection of CD31⁺/CD34⁺ cells at the early stages with subsequent loss of CD34 indicated cell adhesion from the bloodstream. Therefore, either conjugation with RGD peptides or the incorporation of VEGF promoted the formation of a functional endothelial cell layer. Furthermore, both modifications increased primary patency rate three-fold. In conclusion, both of these biofunctionalization approaches can be considered as equally efficient for the modification of tissue-engineered vascular grafts.

In situ Endothelialization: Bioengineering Considerations to Translation.

Improving patency rates of current cardiovascular implants remains a major challenge. It is widely accepted that regeneration of a healthy endothelium layer on biomaterials could yield the perfect blood-contacting surface. Earlier efforts in pre-seeding endothelial cells in vitro demonstrated success in enhancing patency, but translation to the clinic is largely hampered due to its impracticality. In situ endothelialization, which aims to create biomaterial surfaces capable of self-endothelializing upon implantation, appears to be an extremely promising solution, particularly with the utilization of endothelial progenitor cells (EPCs). Nevertheless, controlling cell behavior in situ using immobilized biomolecules or physical patterning can be complex, thus warranting careful consideration. This review aims to provide valuable insight into the rationale and recent developments in biomaterial strategies to enhance in situ endothelialization. In particular, a discussion on the important bio-/nanoengineering considerations and lessons learnt from clinical trials are presented to aid the future translation of this exciting paradigm.

Novel POSS-PCU Nanocomposite Material as a Biocompatible Coating for Quantum Dots.

Quantum dots (QDs) are fluorescent nanoparticles with unique photophysical properties that enable them to potentially replace traditional organic dyes and fluorescent proteins in various bioimaging applications. However, the inherent toxicity of their cores based on cadmium salts limits their widespread biomedical use. We have developed a novel nanocomposite polymer emulsion based on polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) that can be used to coat quantum dots to nullify their toxicity and enhance photostability. Here we report the synthesis and characterization of a novel POSS-PCU nanocomposite polymer emulsion and describe its application for coating QDs for biological application. The polymer was synthesized by a process of emulsion polymerization and formed stable micelles of ∼33 nm in diameter. CdTe/CdS/ZnS QDs were efficiently stabilized by the polymer emulsion through encapsulation within the polymer micelles. Characterization studies showed no significant change in the unique photophysical properties of QDs after coating. The polymer was biocompatible to HepG2, HUVECs, and mouse skeletal muscle cells at 2.5% after 24 h exposure on in vitro testing. Polymer encapsulated QDs showed enhanced photostability on exposure to high degrees of UV irradiation and air as well as significantly reduced cytotoxicity on exposure to HepG2 cells at 30 µg/mL for 24 h. We have therefore concluded that the POSS-PCU polymer emulsion has the potential to make a biocompatible and photostable coating for QDs enabling a host of biomedical applications to take this technology to the next level.

A potential platform for developing 3D tubular scaffolds for paediatric organ development.

Children suffer from damaged or loss of hollow organs i.e. trachea, oesophagus or arteries from birth defects or diseases. Generally these organs possess an outer matrix consisting of collagen, elastin, and cells such as smooth muscle cells (SMC) and a luminal layer consisting of endothelial or epithelial cells, whilst presenting a barrier to luminal content. Tissue engineering research enables the construction of such organs and this study explores this possibility with a bioabsorbable nanocomposite biomaterial, polyhedral oligomeric silsesquioxane poly(ε-caprolactone) urea urethane (POSS-PCL).Our established methods of tubular graft extrusion were modified using a porogen-incorporated POSS-PCL and a new lamination method was explored. Porogen (40, 60 or 105 µm) were introduced to POSS-PCL, which were fabricated into a bilayered, dual topography matching the exterior and luminal interior of tubular organs. POSS-PCL with different amounts of porogen were tested for their suitability as a SMC layer by measuring optimal interactions with human adipose derived stem cells. Angiogenesis potential was tested with the chorioallantoic membrane assay. Tensile strength and burst pressures of bilayared tubular grafts were determined. Scaffolds made with 40 µm porogen demonstrated optimal adipose derived stem cell integration and the scaffolds were able to accommodate angiogenesis. Mechanical properties of the grafts confirmed their potential to match the relevant physiological and biophysical parameters. This study presents a platform for the development of hollow organs for transplantation based on POSS-PCL. These bilayered-tubular structures can be tailor-made for cellular integration and match physico-mechanical properties of physiological systems of interest. More specific luminal cell integration and sources of SMC for the external layer could be further explored.

Fluorescence lifetime imaging and FRET-induced intracellular redistribution of Tat-conjugated quantum dot nanoparticles through interaction with a phthalocyanine photosensitiser.

The interaction of Tat-conjugated PEGylated CdSe/ZnS quantum dots (QD) with the amphiphilic disulfonated aluminium phthalocyanine photosensitiser is investigated in aqueous solution and in a human breast cancer cell line. In aqueous solution, the QDs and phthalocyanine form stable nanocomposites. Using steady-state and time-resolved fluorescence measurements combined with singlet oxygen detection, efficient Förster resonance energy transfer (FRET) is observed with the QDs acting as donors, and the phthalocyanine photosensitiser, which mediates production of singlet oxygen, as acceptors. In cells, the Tat-conjugated QDs localise in lysosomes and the QD fluorescence lifetimes are close to values observed in aqueous solution. Strong FRET-induced quenching of the QD lifetime is observed in cells incubated with the nanocomposites using fluorescence lifetime imaging microscopy (FLIM). Using excitation of the QDs at wavelengths where phthalocyanine absorption is negligible, FRET-induced release of QDs from endo/lysosomes is confirmed using confocal imaging and FLIM, which is attributed to photooxidative damage to the endo/lysosomal membranes mediated by the phthalocyanine acceptor.

Quantification of reactive oxygen species generation by photoexcitation of PEGylated quantum dots.

Photocatalytic generation of reactive oxygen species (ROS) from quantum dots (QDs) has been widely reported yet quantitative studies of ROS formation and their quantum yields are lacking. This study investigates the generation of ROS by water soluble PEGylated CdSe/ZnS QDs with red emission. PEGylation of QDs is commonly used to confer water solubility and minimise uptake by organs of the reticuloendothelial system; therefore studies of ROS formation are of biomedical relevance. Using non-photolytic visible wavelength excitation, the superoxide anion radical is shown to be the primary ROS species generated with a quantum efficiency of 0.35%. The yield can be significantly enhanced in the presence of the electron donor, nicotinamide adenine dinucleotide (NADH), as demonstrated by oxygen consumption measurements and electron paramagnetic resonance spectroscopy with in situ illumination. Direct production of singlet oxygen is not detectable from the QDs alone. A comparison is made with ROS generation by the same QDs complexed with a sulfonated phthalocyanine which can generate singlet oxygen via Förster resonance energy transfer between the QDs and the phthalocyanine.

Tissue-engineered lymphatic graft for the treatment of lymphedema.

BACKGROUND: Lymphedema is a chronic debilitating condition and curative treatment is yet to be found. Tissue engineering approach, which combines cellular components, scaffold, and molecular signals hold great potential in the treatment of secondary lymphedema with the advent of lymphatic graft to reconstruct damaged collecting lymphatic vessel. This review highlights the ideal characteristics of lymphatic graft, the limitation and challenges faced, and the approaches in developing tissue-engineered lymphatic graft. METHODS: Literature on tissue engineering of lymphatic system and lymphatic tissue biology was reviewed. RESULTS: The prime challenge in the design and manufacturing of this graft is producing endothelialized conduit with intraluminal valves. Suitable scaffold material is needed to ensure stability and functionality of the construct. Endothelialization of the construct can be enhanced via biofunctionalization and nanotopography, which mimics extracellular matrix. Nanocomposite polymers with improved performance over existing biomaterials are likely to benefit the development of lymphatic graft. CONCLUSIONS: With the in-depth understanding of tissue engineering, nanotechnology, and improved knowledge on the biology of lymphatic regeneration, the aspiration to develop successful lymphatic graft is well achievable.