Noninvasive ultrasound imaging for assessment of intact microstructure of extracellular matrix in tissue engineering

Porous Polylactide Microparticles as Effective Fillers for Hydrogels

High-strength composite hydrogels based on collagen or chitosan-genipin were obtained via mixing using highly porous polylactide (PLA) microparticles with diameters of 50-75 µm and porosity values of over 98%. The elastic modulus of hydrogels depended on the filler concentration. The modulus increased from 80 kPa to 400-600 kPa at a concentration of porous particles of 12-15 wt.% and up to 1.8 MPa at a filling of 20-25 wt.% for collagen hydrogels. The elastic modulus of the chitosan-genipin hydrogel increases from 75 kPa to 900 kPa at a fraction of particles of 20 wt.%. These elastic modulus values cover a range of strength properties from connective tissue to cartilage tissue. It is important to note that the increase in strength in this case is accompanied by a decrease in the density of the material, that is, an increase in porosity. PLA particles were loaded with C-phycocyanin and showed an advanced release profile up to 48 h. Thus, composite hydrogels mimic the structure, biomechanics and release of biomolecules in the tissues of a living organism.

Fluorescence, ultrasonic and photoacoustic imaging for analysis and diagnosis of diseases

Biomedical imaging technology, which allows us to peer deeply within living subjects and visually explore the delivery and distribution of agents in living things, is producing tremendous opportunities for the early diagnosis and precise therapy of diseases. In this feature article, based on reviewing the latest representative examples of progress together with our recent efforts in the bioimaging field, we intend to introduce three typical kinds of non-invasive imaging technologies, i.e., fluorescence, ultrasonic and photoacoustic imaging, in which optical and/or acoustic signals are employed for analyzing various diseases. In particular, fluorescence imaging possesses a series of outstanding advantages, such as high temporal resolution, as well as rapid and sensitive feedback. Hence, in the first section, we will introduce the latest studies on developing novel fluorescence imaging methods for imaging bacterial infections, cancer and lymph node metastasis in a long-term and real-time manner. However, the issues of imaging penetration depth induced by photon scattering and light attenuation of biological tissue limit their widespread in vivo imaging applications. Taking advantage of the excellect penetration depth of acoustic signals, ultrasonic imaging has been widely applied for determining the location, size and shape of organs, identifying normal and abnormal tissues, as well as confirming the edges of lesions in hospitals. Thus, in the second section, we will briefly summarize recent advances in ultrasonic imaging techniques for diagnosing diseases in deep tissues. Nevertheless, the absence of lesion targeting and dependency on a professional technician may lead to the possibility of false-positive diagnosis. By combining the merits of both optical and acoustic signals, newly-developed photoacoustic imaging, simultaneously featuring higher temporal and spatial resolution with good sensitivity, as well as deeper penetration depth, is discussed in the third secretion. In the final part, we further discuss the major challenges and prospects for developing imaging technology for accurate disease diagnosis. We believe that these non-invasive imaging technologies will introduce a new perspective for the precise diagnosis of various diseases in the future.

Advances in non-invasive biosensing measures to monitor wound healing progression

Impaired wound healing is a significant financial and medical burden. The synthesis and deposition of extracellular matrix (ECM) in a new wound is a dynamic process that is constantly changing and adapting to the biochemical and biomechanical signaling from the extracellular microenvironments of the wound. This drives either a regenerative or fibrotic and scar-forming healing outcome. Disruptions in ECM deposition, structure, and composition lead to impaired healing in diseased states, such as in diabetes. Valid measures of the principal determinants of successful ECM deposition and wound healing include lack of bacterial contamination, good tissue perfusion, and reduced mechanical injury and strain. These measures are used by wound-care providers to intervene upon the healing wound to steer healing toward a more functional phenotype with improved structural integrity and healing outcomes and to prevent adverse wound developments. In this review, we discuss bioengineering advances in 1) non-invasive detection of biologic and physiologic factors of the healing wound, 2) visualizing and modeling the ECM, and 3) computational tools that efficiently evaluate the complex data acquired from the wounds based on basic science, preclinical, translational and clinical studies, that would allow us to prognosticate healing outcomes and intervene effectively. We focus on bioelectronics and biologic interfaces of the sensors and actuators for real time biosensing and actuation of the tissues. We also discuss high-resolution, advanced imaging techniques, which go beyond traditional confocal and fluorescence microscopy to visualize microscopic details of the composition of the wound matrix, linearity of collagen, and live tracking of components within the wound microenvironment. Computational modeling of the wound matrix, including partial differential equation datasets as well as machine learning models that can serve as powerful tools for physicians to guide their decision-making process are discussed.

How the Nonwoven Polymer Volume Microstructure Is Transformed under Tension in an Aqueous Environment

The fibrous porous structure of polymers can mimic the extracellular matrix of the native tissue, therefore such polymers have a good potential for use in regenerative medicine. Organs and tissues within the body exhibit different mechanical properties depending on their functionality, thus artificial scaffolds should have mechanical behaviors similar to the extracellular matrix in conditions like living organisms, primarily in aqueous media. Several methods have been investigated in aquatic environments, including noninvasive techniques based on ultrasonic focused beams for biological objectives. In this study we explored the tensile behavior of poly(L-lactide) nonwoven polymer scaffolds using high-frequency ultrasound microscopy combined with a horizontal testing machine, which provided a visualization of the reorganization and transformation of the dynamic volume microstructure. The mechanisms of unwinding, elongation, orientation, and deformation of polymer fibers under uniaxial tension were revealed. We observed an association between the lined plastic deformation from 100 to 400% and the formation of multiple necks in the fibers, which caused stress relaxation and significant rarefaction of the fibrous microstructure. It was shown that both peaks on the stress–strain curve corresponded to the microstructure of aligned fibers in terms of initial diameter and thinning fibers. We discuss the possible influence of these microstructure transformations on cell behavior.

Preclinical Development of Bioengineered Allografts Derived from Decellularized Human Diaphragm

Volumetric muscle loss (VML) is the traumatic/surgical loss of skeletal muscle, causing aesthetic damage and functional impairment. Suboptimal current surgical treatments are driving research towards the development of optimised regenerative therapies. The grafting of bioengineered scaffolds derived from decellularized skeletal muscle may be a valid option to promote structural and functional healing. In this work, a cellular human diaphragm was considered as a scaffold material for VML treatment. Decellularization occurred through four detergent-enzymatic protocols involving (1) sodium dodecyl sulfate (SDS), (2) SDS + Tergitol^TM, (3) sodium deoxycholate, and (4) Tergitol^TM. After decellularization, cells, DNA (≤50 ng/mg of tissue), and muscle fibres were efficiently removed, with the preservation of collagen/elastin and 60%–70% of the glycosaminoglycan component. The detergent-enzymatic treatments did not affect the expression of specific extracellular matrix markers (Collagen I and IV, Laminin), while causing the loss of HLA-DR expression to produce non-immunogenic grafts. Adipose-derived stem cells grown by indirect co-culture with decellularized samples maintained 80%–90% viability, demonstrating the biosafety of the scaffolds. Overall, the tested protocols were quite equivalent, with the patches treated by SDS + Tergitol^TM showing better collagen preservation. After subcutaneous implant in Balb/c mice, these acellular diaphragmatic grafts did not elicit a severe immune reaction, integrating with the host tissue.

Noninvasive high-frequency acoustic microscopy for 3D visualization of microstructure and estimation of elastic properties during hydrolytic degradation of lactide and ε-caprolactone polymers

The monitoring of degradation processes' kinetics in polymers is one of the attractive possibilities of ultrasound technique applications that provide non-destructive imaging of polymers' internal microstructure and measurements of elastic properties. In this work, biodegradable polymers and copolymers based on L,L-lactide, D,L-lactide and ε-caprolactone have been studied at different stages of hydrolysis at 37 °C by high-frequency (100 and 200 MHz) ultrasound. The acoustic microscopy technique has been developed to reveal changes in the internal microstructure and bulk sound speed in polymer samples over a hydrolysis period of 25 weeks. Ultrasound imaging provides visualization of amorphous and crystalline phases, internal imperfections, variation in packing density, and other microstructural features. Acoustic images demonstrate nucleation, growth, and the changes in internal inhomogeneities in polymers during degradation accompanied by a decrease in the polymers' molecular weight. We associate the changes in the elastic properties (the speed of a longitudinal wave) with crystallinity variations in polymers during hydrothermal aging. The results of the ultrasound investigations are supplemented by gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray spectroscopy. STATEMENT OF SIGNIFICANCE: Monitoring the kinetics of degradation processes in polymers is one of the attractive possibilities of applying ultrasound techniques that provide non-destructive imaging of the polymers' internal microstructure and measurements of elastic properties. In this work, visualization of nucleation, growth, and evolution of internal inhomogeneities in the volume of polymers and variation of values of speed of longitudinal and transverse sound waves during hydrolysis are compared with measurements of molecular weight, density, data of DSC curves, and X-ray scattering analysis. We discuss several common phenomena that occur in the volume of poly(L-lactide) and poly(D,L-lactide) over the degradation process as well as improvement of elastic properties of the poly(ε -caprolactone) and poly(L-lactide-co-caprolactone) during hydrothermal aging.