Physicochemical effects of calcium on suppression of coastal sediment resuspension.

The coastal in-situ capping method can sequester contaminated sediment and suppress sediment resuspension. Few studies have investigated the suppression of sediment resuspension induced by calcium eluted from in-situ capping materials. We investigated the physicochemical suppression of calcium on sediment resuspension. A resuspension experiment was conducted in an annular flume using coastal sediment mixed with 0 g (CSM0), 1 g (CSM1), 5 g (CSM5), and 10 g (CSM10) of Ca(OH)2 under a stepwise increase in bottom shear stress. Calcium enhanced sediment erosion resistance, decreasing suspended sediment concentrations. Exponentially increased SSC in CSM0 and CSM1 was three times higher than that in linearly increased CSM10. Viscosity in CSM10 was approximately three times higher than that in CSM0 and CSM1. Calcium-induced cation exchange increased sediment viscosity via sediment structural rearrangement, calcium-silicate-hydrate production, and the development of larger aggregates. Consequently, calcium suppressed sediment resuspension by physiochemically changing the sediment properties.

Synthesis, Structural, and Mechanical Behavior of ß-Ca3(PO4)2-ZrO2 Composites Induced by Elevated Thermal Treatments.

Biocompatible ß-Ca3(PO4)2 and mechanically stable t-ZrO2 composites are currently being combined to overcome the demerits of the individual components. A series of five composites were synthesized using an aqueous precipitation technique. Their structural and mechanical stability was examined through X-ray diffraction, Rietveld refinement, FTIR, Raman spectroscopy, high-resolution scanning electron microscopy, and nanoindentation. The characterization results confirmed the formation of ß-Ca3(PO4)2-t-ZrO2 composites at 1100 °C. Heat treatment above 900 °C resulted in the degradation of the composites because of cationic interdiffusion between Ca2+ ions and O-2 vacancy in Zr4+ ions. Sequential thermal treatments correspond to four different fractional phases: calcium-deficient apatite, ß-Ca3(PO4)2, t-ZrO2, and m-ZrO2. The morphological features confirm in situ synthesis, which reveals abnormal grain growth with voids caused by the upsurge in ZrO2 content. The mechanical stability data indicate significant variation in Young's modulus and hardness throughout the composite.

Additive Fabrication and Characterization of Biomimetic Composite Bone Scaffolds with High Hydroxyapatite Content.

With the increased incidence of bone defects following trauma or diseases in recent years, three-dimensional porous scaffolds fabricated using bioprinting technologies have been widely explored as effective alternatives to conventional bone grafts, which provide cell-friendly microenvironments promoting bone repair and regeneration. However, the limited use of biomaterials poses a significant challenge to the robust and accurate fabrication of bioprinted bone scaffolds that enable effective regeneration of the target tissues. Although bioceramic/polymer composites can provide tunable biomimetic conditions, their effects on the bioprinting process are unclear. Thus, in this study, we fabricated hydroxyapatite (HA)/gelatin composite scaffolds containing large weight fractions of HA using extrusion-based bioprinting, with the aim to provide an adequate biomimetic environment for bone tissue regeneration with compositional and mechanical similarity to the natural bone matrix. The overall features of the bioprinted HA/gelatin composite scaffolds, including rheological, morphological, physicochemical, mechanical, and biological properties, were quantitatively assessed to determine the optimal conditions for both fabrication and therapeutic efficiency. The present results show that the bioprinted bioceramic/hydrogel scaffolds possess excellent shape fidelity; mechanical strength comparable to that of native bone; and enhanced bioactivity in terms of cell proliferation, attachment, and osteogenic differentiation. This study provides a suitable alternative direction for the fabrication of bioceramic/hydrogel-based scaffolds for bone repair based on bioprinting.

Influences of Molecular Weights on Physicochemical and Biological Properties of Collagen-Alginate Scaffolds.

For tissue engineering applications, biodegradable scaffolds containing high molecular weights (MW) of collagen and sodium alginate have been developed and characterized. However, the properties of low MW collagen-based scaffolds have not been studied in previous research. This work examined the distinctive properties of low MW collagen-based scaffolds with alginate unmodified and modified by subcritical water. Besides, we developed a facile method to cross-link water-soluble scaffolds using glutaraldehyde in an aqueous ethanol solution. The prepared cross-linked scaffolds showed good structural properties with high porosity (~93%) and high cross-linking degree (50-60%). Compared with collagen (6000 Da)-based scaffolds, collagen (25,000 Da)-based scaffolds exhibited higher stability against collagenase degradation and lower weight loss in phosphate buffer pH 7.4. Collagen (25,000 Da)-based scaffolds with modified alginate tended to improve antioxidant capacity compared with scaffolds containing unmodified alginate. Interestingly, in vitro coagulant activity assay demonstrated that collagen (25,000 Da)-based scaffolds with modified alginate (C25-A63 and C25-A21) significantly reduced the clotting time of human plasma compared with scaffolds consisting of unmodified alginate. Although some further investigations need to be done, collagen (25,000 Da)-based scaffolds with modified alginate should be considered as a potential candidate for tissue engineering applications.

Characterization of ionic cross-linked composite foams with different blend ratios of alginate/pectin on the synergistic effects for wound dressing application.

Alginate and pectin have been widely employed together in various industrial and biomedical applications due to their synergistic interaction. Although alginate and pectin have been used as composite materials in films, gels, and particles, research characterizing their properties in foams is scarce. Thus, in the present study, we fabricated alginate-pectin composite foams with different blending ratios (9:1, 7:3, and 5:5) using calcium ion cross-linking and characterized their properties. It was found that the G' values of rehydrated alginate-pectin 9:1 foam was higher than those of the other rehydrated foams in the rheological behavior. In addition, higher pectin levels in the composite foams led to more water being absorbed during swelling tests and the higher release of BSA in drug-release testing. In indirect and direct cytotoxicity testing, none of the foams exhibited cell cytotoxicity for fibroblast and keratinocyte cells. These results suggest that controlling the pectin content in alginate-pectin foams is key to adjusting their mechanical properties, water absorption, and drug-release ability. In addition, alginate-pectin composite foams are promising candidates for use in wound-dressing applications.

The Influence of Astaxanthin on the Proliferation of Adipose-derived Mesenchymal Stem Cells in Gelatin-Methacryloyl (GelMA) Hydrogels.

Recently, astaxanthin, a red lipophilic pigment belonging to the xanthophyllic family of carotenoids, has shown the feasibility of its uses in tissue engineering and regenerative medicine, due to its excellent antioxidant activities and its abilities to enhance the self-renewal potency of stem cells. In this study, we demonstrate the influence of astaxanthin on the proliferation of adipose-derived mesenchymal stem cells in tissue-engineered constructs. The tissue engineered scaffolds were fabricated using photopolymerizable gelatin methacryloyl (GelMA) with different concentrations of astaxanthin. The effects of astaxanthin on cellular proliferation in two-dimensional environments were assessed using alamar blue assay and reverse transcription polymerase chain reaction (RT-PCR). Then, rheological properties, chemical structures and the water absorption of the fabricated astaxanthin-incorporated GelMA hydrogels were characterized using NMR analysis, rheological analysis and a swelling ratio test. Finally, the influence in three-dimensional environments of astaxanthin-incorporated GelMA hydrogels on the proliferative potentials of adipose-derived stem cells was assessed using alamar blue assay and the confocal imaging with Live/dead staining. The experimental results of the study indicate that an addition of astaxanthin promises to induce stem cell potency via proliferation, and that it can be a useful tool for a three-dimensional culture system and various tissue engineering applications.

Enhanced rheological behaviors of alginate hydrogels with carrageenan for extrusion-based bioprinting.

Three-dimensional (3D) bioprinting using biocompatible materials is widely used in the field of tissue engineering and regenerative medicine. However, precise printing of 3D structures is challenging due to weak and uncontrollable mechanical properties of various hydrogels, thus limiting their potential in preclinical and clinical applications. In this study, our goal is to demonstrate the feasibility of precise fabrication of alginate/carrageenan composite scaffolds using extrusion-based 3D bioprinting. At first, the proper concentration of crosslinking agents was determined by the assessment of shear modulus of alginate-based hydrogels. Moreover, alginate/carrageenan composite hydrogels were prepared with different concentrations of carrageenan and used to measure their rheological properties. Based on the assessed viscosities and shear moduli of alginate and alginate/carrageenan hydrogels, printing resolutions in different printing parameters were simulated and presented in the printability maps. In addition, alginate and alginate/carrageenan scaffolds were bioprinted with various printing parameters and used to compare their printability with the simulated results. Also, 3D deposition of both alginate and alginate/carrageenan hydrogels were assessed and compared with each other by continuous monitoring of shape fidelity in 3D structures in ten layers and similar printing resolution. Finally, the cell viability of the 3D alginate/carrageenan composite scaffolds, printed using optimized printing parameters, was evaluated using live/dead staining and confocal fluorescence imaging. Thus, the results in the study show the potential uses of carrageenan for a prospective bioink with remarkable mechanical properties suitable for precise fabrication of 3D hydrogel scaffolds using bioprinting techniques.

Simvastatin Loaded Nano Hydroxyapatite in Bone Regeneration: A Study in the Rabbit Femoral Condyle.

BACKGROUND: Enhancement of the bone regenerative capacity of the bone substitutes could be achieved by incorporating bioactive agents such as proteins, and different drugs. Simvastatin, an inhibitor of cholesterol synthesis, stimulates bone formation by enhancing the expression of Bone Morphogenetic Protein-2 (BMP-2) in osteoblasts. OBJECTIVE: The objective of the study is to evaluate bone regeneration following simvastatin loaded nano-hydroxyapatite scaffold in the bone defect created on the femoral condyle of rabbits. METHODS: Twelve adult, New Zealand white rabbits were used in the study. Twenty-four defects of size 5x8 mm were created on the lateral aspect of the femoral condyle. The defects were filled with either Nano-Hydroxyapatite (nHA) particles alone or nHA with Simvastatin (SIM). The condyles were retrieved after 8 weeks and analyzed using micro CT and histology. RESULTS: The Bone Mineral Density (BMD) was significantly higher for the defects filled with SIM loaded nHA compared to the nHA site. Micro CT showed a significantly higher bone volume in the defects filled with Simvastatin loaded site compared to the control site. Quantitative analysis of the histologic sections also showed significantly higher bone volume in the defects filled with SIM loaded nHA (57.2±4.8) compared to nHA alone (50.1±5.5). CONCLUSION: Based on the results, it can be concluded that local delivery of simvastatin enhanced the bone regeneration in rabbit femoral condyle. Simvastatin could be used as an activator to enhance bone regeneration in bone defects along with hydroxyapatite ceramics.

ECM Based Bioink for Tissue Mimetic 3D Bioprinting.

To create tissue replacements with qualities similar to human tissues, and for ease of tissue loss repair, novel 3D printing fabrication methods have recently been introduced and popularized in the field of tissue engineering and regenerative medicine as an alternative to the scaffold fabrication methods. 3D printing may provide the fabricate process to better mimic the internal microstructure and external appearance. Printable bioink should be developed for stable 3D structure stratification. Advanced bioinks for 3D printing are rationally designed materials intended to improve the functionality of printed tissue scaffolds. The search for an appropriate bioink capable of providing a suitable microenvironment to support cellular activities is ongoing. The extracellular matrix (ECM) provides instructive cues for cell attachment, proliferation, differentiation, and ultimately tissue regeneration. The use of ECM-based biomaterials in regenerative medicine is therefore, rapidly expanding. In this respect, the decellularized ECM biomaterials have gained popularity as an excellent source of bioink, given its capability to inherit the intrinsic cues from a native ECM. In this chapter, we describe the current status of ECM-based biomaterials, the emerging trends in ECM bioink development, and bioink requirements that could enable proper selection of the bioink to fabricate an engineered tissue/organ. In particular, rheological properties of bioprinting materials are significant for printing resolution and shape fidelity. We propose a general method of measuring non-Newtonian rheological properties based on rotational rheometers in oscillatory mode. In addition, the mathematical modeling incorporating the power law model is discussed. These approaches can be easily used to optimize printing parameters and verify the bioink printability because a variety of dECM-based bioinks possess shear-thinning properties.

Coating Chitosan Thin Shells: A Facile Technique to Improve Dispersion Stability of Magnetoliposomes.

Magnetoliposomes (ML) have been emerging as a novel multifunctional nanoparticle with a wide range of biomedical and therapeutic applications over the past decade. Although the ML system has shown excellent performances, the stability and lipid peroxidation of liposomal components are still remaining as key issues and need to be solved for intensive applications. Changing zeta potential of nanoparticles' surface can be seen as a potential way to achieve the stable dispersion. In this work, we have employed the positive charged, abundant and cheap chitosan to coat ML in order to change the zeta potential of the ML system and examined the stability of chitosan@magnetoliposomes (CML) in long-term storage. The combining of pH-sensitive chitosan with temperature-sensitive phospholipid formed a novel pH- and temperature-sensitive nanoparticles which can be promisingly used as controllable drug release applications. These novel CML with chitosan thin shells showed excellent stability in long-term storage; meanwhile, the bare ML sample showed aggregations and forming micrometer-size particles. The CML system can achieve a drug encapsulation efficiency of nearly 50% and an enhanced drug release behavior under pH 5 at 45 °C.

In vivo photoacoustic monitoring using 700-nm region Raman source for targeting Prussian blue nanoparticles in mouse tumor model.

Photoacoustic imaging (PAI) is a noninvasive imaging tool to visualize optical absorbing contrast agents. Due to high ultrasonic resolution and superior optical sensitivity, PAI can be used to monitor nanoparticle-mediated cancer therapy. The current study synthesized Food and Drug Administration-approved Prussian blue (PB) in the form of nanoparticles (NPs) with the peak absorption at 712 nm for photoacoustically imaging tumor-bearing mouse models. To monitor PB NPs from the background tissue in vivo, we also developed a new 700-nm-region stimulated Raman scattering (SRS) source (pulse energy up to 200 nJ and repetition rate up to 50 kHz) and implemented optical-resolution photoacoustic microscopy (OR-PAM). The SRS-assisted OR-PAM system was able to monitor PB NPs in the tumor model with micrometer resolution. Due to strong light absorption at 712 nm, the developed SRS light yielded a two-fold higher contrast from PB NPs, in comparison with a 532-nm pumping source. The proposed laser source involved cost-effective and simple system implementation along with high compatibility with the fiber-based OR-PAM system. The study highlights the OR-PAM system in conjunction with the tunable-color SRS light source as a feasible tool to assist NP-mediated cancer therapy.

Fish bone peptide promotes osteogenic differentiation of MC3T3-E1 pre-osteoblasts through upregulation of MAPKs and Smad pathways activated BMP-2 receptor.

Fish bone, a by-product of fishery processing, is composed of protein, calcium, and other minerals. The objective of this study was to investigate the effects of a bioactive peptide isolated from the bone of the marine fish, Johnius belengerii, on the osteoblastic differentiation of MC3T3-E1 pre-osteoblasts. Post consecutive purification by liquid chromatography, a potent osteogenic peptide, composed of 3 amino acids, Lys-Ser-Ala (KSA, MW: 304.17 Da), was identified. The purified peptide promoted cell proliferation, alkaline phosphatase activity, mineral deposition, and expression levels of phenotypic markers of osteoblastic differentiation in MC3T3-E1 pre-osteoblast. The purified peptide induced phosphorylation of mitogen-activated protein kinases, including p38 mitogen-activated protein kinase, extracellular regulated kinase, and c-Jun N-terminal kinase as well as Smads. As attested by molecular modelling study, the purified peptide interacted with the core interface residues in bone morphogenetic protein receptors with high affinity. Thus, the purified peptide could serve as a potential pharmacological substance for controlling bone metabolism.

Hydroxyapatite Coated Iron Oxide Nanoparticles: A Promising Nanomaterial for Magnetic Hyperthermia Cancer Treatment.

Targeting cancer cells without injuring normal cells is the prime objective in treatment of cancer. In this present study, solvothermal and wet chemical precipitation techniques were employed to synthesize iron oxide (IO), hydroxyapatite (HAp), and hydroxyapatite coated iron oxide (IO-HAp) nanoparticles for magnetic hyperthermia mediated cancer therapy. The synthesized well dispersed spherical IO-HAp nanoparticles, magnetite, and apatite phases were confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Field emission transmission electron microscopy (FETEM) with Energy Dispersive X-ray spectroscopy (EDS). The non-toxic behavior of synthesized IO-HAp nanoparticles was confirmed by cytotoxicity assay (Trypan blue and MTT assay). The synthesized nanoparticles revealed a remarkable magnetic saturation of 83.2 emu/g for IO and 40.6 emu/g for IO-HAp nanoparticles in presence of 15,000 Oe (1.5 T) magnetic field at room temperature (300 K). The magnetic hyperthermia study that was performed with IO-HAp nanoparticles showed an excellent hyperthermia effect (SAR value 85 W/g) over MG-63 osteosarcoma cells. The in vitro hyperthermia temperature (~45 °C) was reached within 3 min, which shows a very high efficiency and kills nearly all of the experimental MG-63 osteosarcoma cells within 30 min exposure. These results could potentially open new perceptions for biomaterials that are aimed for anti-cancer therapies based on magnetic hyperthermia.

Therapeutic potential of dental stem cells.

Stem cell biology has become an important field in regenerative medicine and tissue engineering therapy since the discovery and characterization of mesenchymal stem cells. Stem cell populations have also been isolated from human dental tissues, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla, dental follicle progenitor cells, and periodontal ligament stem cells. Dental stem cells are relatively easily obtainable and exhibit high plasticity and multipotential capabilities. The dental stem cells represent a gold standard for neural-crest-derived bone reconstruction in humans and can be used for the repair of body defects in low-risk autologous therapeutic strategies. The bioengineering technologies developed for tooth regeneration will make substantial contributions to understand the developmental process and will encourage future organ replacement by regenerative therapies in a wide variety of organs such as the liver, kidney, and heart. The concept of developing tooth banking and preservation of dental stem cells is promising. Further research in the area has the potential to herald a new dawn in effective treatment of notoriously difficult diseases which could prove highly beneficial to mankind in the long run.

Effect of multiple-sweeping on ablation performance during ex vivo laser nephrectomy.

BACKGROUND AND OBJECTIVE: Fiber-assisted laser surgery has been employed as a minimally invasive method in various medical fields. In spite of multiple sweeping on tissue during laser treatments, the rate of tissue removal gradually decreases and eventually leads to longer irradiation times as well as deeper thermal injury. The objective of the current study was to quantitatively investigate the effect of multiple fiber sweeps on ablation performance during ex vivo 532-nm laser nephrectomy. MATERIALS AND METHODS: Porcine kidney tissue was used to evaluate variations in tissue ablation and coagulative necrosis after pre- and multiple-sweeping with a 532 nm wavelength at various fiber speeds (2, 4, and 6 mm/second). The distance between a fiber tip and tissue surface was initially set at 1.5 mm, and no further distance change was performed. Double-integrating spheres in conjunction with an adding-doubling method were employed to measure variations in optical properties of the tested tissue. The extent of ablation and coagulation was quantified to identify the role of multiple-sweeping at various fiber conditions. RESULTS: Optical property measurements showed a 30% decrease in light absorption but a more than threefold increase in light scattering after irreversible thermal denaturation. Pre-sweeping yielded insignificant effects on tissue coagulation due to almost consistent coagulation depths with numbers of pre-sweeps. Ablation depths increased with more numbers of fiber sweeps and slower fiber speeds whereas coagulation depths thickened primarily with the slower speeds. Multiple-sweeping induced saturation in ablation volume with the increasing numbers of multiple-sweeps irrespective of the fiber speed. CONCLUSION: A combination of coagulation barriers, spatial distribution of power, and temporal interplay of optical energy could attribute to continuously lessen the amount of the ablated tissue with the multiple sweeps. Optical power modulation with varying fiber conditions (speed and distance) will be examined to optimize surgical parameters and to sustain the equivalent ablation performance of the first sweep with the multiple sweeping for laser nephrectomy. Lasers Surg. Med. 48:616-623, 2016. © 2016 Wiley Periodicals, Inc.

Marine microorganisms as potential biofactories for synthesis of metallic nanoparticles.

The use of marine microorganisms as potential biofactories for green synthesis of metallic nanoparticles is a relatively new field of research with considerable prospects. This method is eco-friendly, time saving, and inexpensive and can be easily scaled up for large-scale synthesis. The increasing need to develop simple, nontoxic, clean, and environmentally safe production methods for nanoparticles and to decrease environmental impact, minimize waste, and increase energy productivity has become important in this field. Marine microorganisms are tiny organisms that live in marine ecosystems and account for >98% of biomass of the world's ocean. Marine microorganisms synthesize metallic nanoparticles either intracellularly or extracellularly. Marine microbially-produced metallic nanoparticles have received considerable attention in recent years because of their expected impact on various applications such as medicine, energy, electronic, and space industries. The present review discusses marine microorganisms as potential biofactories for the green synthesis of metallic nanoparticles and their potential applications.

Ultrasound-guided photoacoustic imaging-directed re-endothelialization of acellular vasculature leads to improved vascular performance.

As increasing effort is dedicated to investigating the regenerative capacity of decellularized tissues, research has progressed to recellularizing these tissues prior to implantation. The delivery and support of cells seeded throughout acellular scaffolds are typically conducted through the vascular axis of the tissues. However, it is unclear how cell concentration and injection frequency can affect the distribution of cells throughout the scaffold. Furthermore, what effects re-endothelialization have on vascular patency and function are not well understood. We investigated the use of ultrasound-guided photoacoustic (US/PA) imaging as a technique to visualize the distribution of microvascular endothelial cells within an optimized acellular construct upon re-endothelialization and perfusion conditioning. We also evaluated the vascular performance of the re-endothelialized scaffold using quantitative vascular corrosion casting (qVCC) and whole-blood perfusion. We found US/PA imaging was an effective technique to visualize the distribution of cells. Cellular retention following perfusion conditioning was also detected with US/PA imaging. Finally, we demonstrated that a partial recovery of vascular performance is possible following re-endothelialization-confirmed by fewer extravasations in qVCC and improved blood clearance following whole-blood perfusion. STATEMENT OF SIGNIFICANCE: Re-endothelialization is a method that enables decellularized tissue to become useful as a tissue engineering construct by creating a nutrient delivery and waste removal system for the entire construct. Our approach utilizes a decellularization method that retains the basement ECM of a highly vascularized tissue upon which endothelial cells can be injected to form an endothelium. The US/PA method allows for rapid visualization of cells within a construct several cm thick. This approach can be experimentally used to observe changes in cellular distribution over large intervals of time, to help optimize cell seeding parameters, and to verify cell retention within re-endothelialized constructs. This approach has temporal and depth advantages compared to section reconstruction and imaged fluorophores respectively.

Intravascular ultrasonic-photoacoustic (IVUP) endoscope with 2.2-mm diameter catheter for medical imaging.

Intravascular ultrasound (IVUS) imaging is extremely important for detection and characterization of high-risk atherosclerotic plaques as well as gastrointestinal diseases. Recently, intravascular photoacoustic (IVPA) imaging has been used to differentiate the composition of biological tissues with high optical contrast and ultrasonic resolution. The combination of these imaging techniques could provide morphological information and molecular screening to characterize abnormal tissues, which would help physicians to ensure vital therapeutic value and prognostic significance for patients before commencing therapy. In this study, integration of a high-frequency IVUS imaging catheter (45MHz, single-element, unfocused, 0.7mm in diameter) with a multi-mode optical fiber (0.6mm in core diameter, 0.22 NA), an integrated intravascular ultrasonic-photoacoustic (IVUP) imaging catheter, was developed to provide spatial and functional information on light distribution in a turbid sample. Simultaneously, IVUS imaging was co-registered to IVPA imaging to construct 3D volumetric sample images. In a phantom study, a polyvinyl alcohol (PVA) tissue-mimicking arterial vessel phantom with indocyanine green (ICG) and methylene blue (MB) inclusion was used to demonstrate the feasibility of mapping the biological dyes, which are used in cardiovascular and cancer diagnostics. For the ex vivo study, an excised sample of pig intestine with ICG was utilized to target the biomarkers present in the gastrointestinal tumors or the atherosclerotic plaques with the proposed hybrid technique. The results indicated that IVUP endoscope with the 2.2-mm diameter catheter could be a useful tool for medical imaging.

Combined ultrasound and photoacoustic imaging to noninvasively assess burn injury and selectively monitor a regenerative tissue-engineered construct.

Current biomedical imaging tools have limitations in accurate assessment of the severity of open and deep burn wounds involving excess bleeding and severe tissue damage. Furthermore, sophisticated imaging techniques are needed for advanced therapeutic approaches such as noninvasive monitoring of stem cells seeded and applied in a biomedical 3D scaffold to enhance wound repair. This work introduces a novel application of combined ultrasound (US) and photoacoustic (PA) imaging to assess both burn injury and skin tissue regeneration. Tissue structural damage and bleeding throughout the epidermis and dermis till the subcutaneous skin layer were imaged noninvasively by US/PA imaging. Gold nanoparticle-labeled adipose-derived stem cells (ASCs) within a PEGylated fibrin 3D gel were implanted in a rat model of cutaneous burn injury. ASCs were successfully tracked till 2 weeks and were distinguished from host tissue components (e.g., epidermis, fat, and blood vessels) through spectroscopic PA imaging. The structure and function of blood vessels (vessel density and perfusion) in the wound bed undergoing skin tissue regeneration were monitored both qualitatively and semi-quantitatively by the developed imaging approach. Imaging-based analysis demonstrated ASC localization in the top layer of skin and a higher density of regenerating blood vessels in the treated groups. This was corroborated with histological analysis showing localization of fluorescently labeled ASCs and smooth muscle alpha actin-positive blood vessels. Overall, the US/PA imaging-based strategy coupled with gold nanoparticles has a great potential for stem cell therapies and tissue engineering due to its noninvasiveness, safety, selectivity, and ability to provide long-term monitoring.

Imaging strategies for tissue engineering applications.

Tissue engineering has evolved with multifaceted research being conducted using advanced technologies, and it is progressing toward clinical applications. As tissue engineering technology significantly advances, it proceeds toward increasing sophistication, including nanoscale strategies for material construction and synergetic methods for combining with cells, growth factors, or other macromolecules. Therefore, to assess advanced tissue-engineered constructs, tissue engineers need versatile imaging methods capable of monitoring not only morphological but also functional and molecular information. However, there is no single imaging modality that is suitable for all tissue-engineered constructs. Each imaging method has its own range of applications and provides information based on the specific properties of the imaging technique. Therefore, according to the requirements of the tissue engineering studies, the most appropriate tool should be selected among a variety of imaging modalities. The goal of this review article is to describe available biomedical imaging methods to assess tissue engineering applications and to provide tissue engineers with criteria and insights for determining the best imaging strategies. Commonly used biomedical imaging modalities, including X-ray and computed tomography, positron emission tomography and single photon emission computed tomography, magnetic resonance imaging, ultrasound imaging, optical imaging, and emerging techniques and multimodal imaging, will be discussed, focusing on the latest trends of their applications in recent tissue engineering studies.