Acoustic modification of collagen hydrogels facilitates cellular remodeling

Harnessing fine fibers in decellularized adipose-derived matrix for enhanced adipose regeneration

Decellularized Adipose-Derived Matrix (DAM) has the function of inducing adipogenesis, but the distribution of adipogenesis is uneven. We found for the first time that DAM contains two structural components: The tough fibers DAM (T-DAM) and the fine fibers DAM (F-DAM). T-DAM was a dense vortex structure composed of a large number of coarse fibers, characterized by myoblast-related proteins, which cannot achieve fat regeneration and forms a typical "adipose-free zone". While the F-DAM was a loose structure consisting of uniform fine fibers, has more matrix-related proteins and adipose-related proteins. It can not only better promote the adhesion and proliferation of adipose stem cells in vitro, but also achieve the regeneration of adipose tissue in vivo earlier and better, with a uniform range of adipogenesis. The F-DAM is the main and effective kind of DAM to initiate adipose tissue regeneration, which can be picked out by ultrasound fragmentation.

Polymeric biomaterials for wound healing applications: a comprehensive review

Chronic wounds have been a global health threat over the past few decades, requiring urgent medical and research attention. The factors delaying the wound-healing process include obesity, stress, microbial infection, aging, edema, inadequate nutrition, poor oxygenation, diabetes, and implant complications. Biomaterials are being developed and fabricated to accelerate the healing of chronic wounds, including hydrogels, nanofibrous, composite, foam, spongy, bilayered, and trilayered scaffolds. Some recent advances in biomaterials development for healing both chronic and acute wounds are extensively compiled here. In addition, various properties of biomaterials for wound-healing applications and how they affect their performance are reviewed. Based on the recent literature, trilayered constructs appear to be a convincing candidate for the healing of chronic wounds and complete skin regeneration because they mimic the full thickness of skin: epidermis, dermis, and the hypodermis. This type of scaffold provides a dense superficial layer, a bioactive middle layer, and a porous lower layer to aid the wound-healing process. The hydrophilicity of scaffolds aids cell attachment, cell proliferation, and protein adhesion. Other scaffold characteristics such as porosity, biodegradability, mechanical properties, and gas permeability help with cell accommodation, proliferation, migration, differentiation, and the release of bioactive factors.

The waves that make the pattern: a review on acoustic manipulation in biomedical research

Novel approaches, combining technology, biomaterial design, and cutting-edge cell culture, have been increasingly considered to advance the field of tissue engineering and regenerative medicine. Within this context, acoustic manipulation to remotely control spatial cellular organization within a carrier matrix has arisen as a particularly promising method during the last decade. Acoustic or sound-induced manipulation takes advantage of hydrodynamic forces exerted on systems of particles within a liquid medium by standing waves. Inorganic or organic particles, cells, or organoids assemble within the nodes of the standing wave, creating distinct patterns in response to the applied frequency and amplitude. Acoustic manipulation has advanced from micro- or nanoparticle arrangement in 2D to the assembly of multiple cell types or organoids into highly complex in vitro tissues. In this review, we discuss the past research achievements in the field of acoustic manipulation with particular emphasis on biomedical application. We survey microfluidic, open chamber, and high throughput devices for their applicability to arrange non-living and living units in buffer or hydrogels. We also investigate the challenges arising from different methods, and their prospects to gain a deeper understanding of in vitro tissue formation and application in the field of biomedical engineering.

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Work on sound waves to spatially control particulate systems is reviewed.

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Classification of surface acoustic waves, bulk acoustic waves, and Faraday waves.

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Sound can be used to arrange, separate, or filter polymer particles.

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Sound can pattern cells in 3D to induce morphogenesis.

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Long-term applied sound induces differentiation and tissue formation.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Bioprinting of Collagen: Considerations, Potentials, and Applications

Collagen is the most abundant extracellular matrix protein that is widely used in tissue engineering (TE). There is little research done on printing pure collagen. To understand the bottlenecks in printing pure collagen, it is imperative to understand collagen from a bottom-up approach. Here it is aimed to provide a comprehensive overview of collagen printing, where collagen assembly in vivo and the various sources of collagen available for TE application are first understood. Next, the current printing technologies and strategy for printing collagen-based materials are highlighted. Considerations and key challenges faced in collagen printing are identified. Finally, the key research areas that would enhance the functionality of printed collagen are presented.

Using Acoustic Fields to Fabricate ECM-Based Biomaterials for Regenerative Medicine Applications

Ultrasound is emerging as a promising tool for both characterizing and fabricating engineered biomaterials. Ultrasound-based technologies offer a diverse toolbox with outstanding capacity for optimization and customization within a variety of therapeutic contexts, including improved extracellular matrix-based materials for regenerative medicine applications. Non-invasive ultrasound fabrication tools include the use of thermal and mechanical effects of acoustic waves to modify the structure and function of extracellular matrix scaffolds both directly, and indirectly via biochemical and cellular mediators. Materials derived from components of native extracellular matrix are an essential component of engineered biomaterials designed to stimulate cell and tissue functions and repair or replace injured tissues. Thus, continued investigations into biological and acoustic mechanisms by which ultrasound can be used to manipulate extracellular matrix components within three-dimensional hydrogels hold much potential to enable the production of improved biomaterials for clinical and research applications.

A Green Approach towards Native Collagen Scaffolds: Environmental and Physicochemical Assessment

Native collagen scaffolds were prepared in this work, in which both materials and environmental approaches were considered with the aim of providing a global strategy towards more sustainable biomaterials. From the environmental perspective, it is worth mentioning that acid and enzymatic treatments have been avoided to extract collagen, allowing the reduction in the use of resources, in terms of chemicals, energy, and time, and leading to a low environmental load of this step in all the impact categories under analysis. With the incorporation of chitosan into the scaffold-forming formulations, physical interactions occurred between collagen and chitosan, but the native collagen structure was preserved, as observed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses. The incorporation of chitosan also led to more homogenous porous microstructures, with higher elastic moduli and compression resistance for both dry and hydrated scaffolds. Furthermore, hydrated scaffolds preserved their size and shape after some compression cycles.

Acoustic Fabrication of Collagen-Fibronectin Composite Gels Accelerates Microtissue Formation

Ultrasound can influence biological systems through several distinct acoustic mechanisms that can be manipulated by varying reaction conditions and acoustic exposure parameters. We recently reported a new ultrasound-based fabrication technology that exploits the ability of ultrasound to generate localized mechanical forces and thermal effects to control collagen fiber microstructure non-invasively. Exposing solutions of type I collagen to ultrasound during the period of microfibril assembly produced changes in collagen fiber structure and alignment, and increased the biological activity of the resultant collagen hydrogels. In the extracellular matrix, interactions between fibronectin and collagen fibrils influence the biological activity of both proteins. Thus, in the present study, we examined how addition of fibronectin to collagen solutions prior to ultrasound exposure affects protein organization and the biological activity of the composite hydrogels. Results indicate that ultrasound can alter the distribution of fibronectin within 3D hydrogels via thermal and non-thermal mechanisms to produce composite hydrogels that support accelerated microtissue formation. The use of acoustic energy to drive changes in protein conformation to functionalize biomaterials has much potential as a unique, non-invasive technology for tissue engineering and regenerative medicine.

Non-invasive acoustic fabrication methods to enhance collagen hydrogel bioactivity

Much attention has focused recently on utilizing components of the extracellular matrix (ECM) as natural building blocks for a variety of tissue engineering applications and regenerative medicine therapies. Consequently, new fabrication methods are being sought to enable molecular control over the structural characteristics of ECM molecules in order to improve their biological function. Exposing soluble collagen to acoustic forces associated with ultrasound propagation produces localized variations in collagen microfiber organization that in turn, promote cell behaviors essential for tissue regeneration, including cell migration and matrix remodeling. In the present study, mechanisms by which ultrasound interacts with polymerizing collagen to produce functional changes in collagen microstructure were investigated. The rate of collagen polymerization was manipulated by adjusting the pH of collagen solutions and the temperature at which gels were polymerized. Results demonstrate that the phase transition of type I collagen from fluid to gel triggered a simultaneous increase in acoustic absorption. This phase transition of collagen involves the lateral growth of early-stage collagen microfibrils and importantly, corresponded to a defined period of time during which exposure to ultrasound introduced both structural and functional changes to the resultant collagen hydrogels. Together, these experiments isolated a critical window in the collagen fiber assembly process during which mechanical forces associated with ultrasound propagation are effective in producing structural changes that underlie the ability of acoustically-modified collagen hydrogels to stimulate cell migration. These results demonstrate that changes in material properties associated with collagen polymerization are a fundamental component of the mechanism by which acoustic forces modify collagen biomaterials to enhance biological function.