Controlling the pore sizes and related properties of inverse opal scaffolds for tissue engineering applications

Smart colloidal photonic crystal sensors

Smart colloidal photonic crystals (PCs) with stimuli-responsive periodic micro/nano-structures, photonic bandgaps, and structural colors have shown unique advantages (high sensitivity, visual readout, wireless characteristics, etc.) in sensing by outputting diverse structural colors and reflection signals. In this review, smart PC sensors are summarized according to their fabrications, structures, sensing mechanisms, and applications. The fabrications of colloidal PCs are mainly by self-assembling the well-defined nanoparticles into the periodical structure (supersaturation-, polymerization-, evaporation-, shear-, interaction-, and field-induced self-assembly process). Their structures can be divided into two groups: closely packed and non-closely packed nano-structures. The sensing mechanisms can be explained by Bragg's law, including the change in the effective refractive index, lattice constant, and the order degree. The sensing applications are detailly introduced according to the analytes of the target, including solvents, vapors, humidity, mechanical force, temperature, electrical field, magnetic field, pH, ions/molecules, and so on. Finally, the corresponding challenges and the future potential prospects of artificial smart colloidal PCs in the sensing field are discussed.

Advances in In Vitro Blood-Air Barrier Models and the Use of Nanoparticles in COVID-19 Research

Respiratory infections caused by coronaviruses (CoVs) have become a major public health concern in the past two decades as revealed by the emergence of SARS-CoV in 2002, MERS-CoV in 2012, and SARS-CoV-2 in 2019. The most severe clinical phenotypes commonly arise from exacerbation of immune response following the infection of alveolar epithelial cells localized at the pulmonary blood-air barrier. Preclinical rodent models do not adequately represent the essential genetic properties of the barrier, thus necessitating the use of humanized transgenic models. However, existing monolayer cell culture models have so far been unable to mimic the complex lung microenvironment. In this respect, air-liquid interface models, tissue engineered models, and organ-on-a-chip systems, which aim to better imitate the infection site microenvironment and microphysiology, are being developed to replace the commonly used monolayer cell culture models, and their use is becoming more widespread every day. On the contrary, studies on the development of nanoparticles (NPs) that mimic respiratory viruses, and those NPs used in therapy are progressing rapidly. The first part of this review describes in vitro models that mimic the blood-air barrier, the tissue interface that plays a central role in COVID-19 progression. In the second part of the review, NPs mimicking the virus and/or designed to carry therapeutic agents are explained and exemplified.

Regenerated silk fibroin based on small aperture scaffolds and marginal sealing hydrogel for osteochondral defect repair

BACKGROUND

Osteochondral defects pose an enormous challenge without satisfactory repair strategy to date. In particular, the lateral integration of neo-cartilage into the surrounding native cartilage is a difficult and inadequately addressed problem determining tissue repair's success.

METHODS

Regenerated silk fibroin (RSF) based on small aperture scaffolds was prepared with n-butanol innovatively. Then, the rabbit knee chondrocytes and bone mesenchymal stem cells (BMSCs) were cultured on RSF scaffolds, and after induction of chondrogenic differentiation, cell-scaffold complexes strengthened by a 14 wt% RSF solution were prepared for in vivo experiments.

RESULTS

A porous scaffold and an RSF sealant exhibiting biocompatibility and excellent adhesive properties are developed and confirmed to promote chondrocyte migration and differentiation. Thus, osteochondral repair and superior horizontal integration are achieved in vivo with this composite.

CONCLUSIONS

Overall, the new approach of marginal sealing around the RSF scaffolds exhibits preeminent repair results, confirming the ability of this novel graft to facilitate simultaneous regeneration of cartilage-subchondral bone.

Achieving Functionality and Multifunctionality through Bulk and Interfacial Structuring of Colloidal-Crystal-Templated Materials

Over the past 25 years, the field of colloidal crystal templating of inverse opal or three-dimensionally ordered macroporous (3DOM) structures has made tremendous progress. The degree of structural control over multiple length scales, understanding of mechanical properties, and complexity of systems in which 3DOM materials are a component have increased substantially. In addition, we are now seeing applications of 3DOM materials that make use of multiple features of their architecture at the same time. This Feature Article focuses on the different properties of 3DOM materials that provide functionality, including a relatively large surface area, the interconnectedness of the pores and the resulting good accessibility of the internal surface, the nanostructured features of the walls, the structural hierarchy and periodicity, well-defined surface roughness, and relative mechanical robustness at low density. It provides representative examples that illustrate the properties of interest related to applications including energy storage and conversion systems, sensors, catalysts, sorbents, photonics, actuators, and biomedical materials or devices.

Reversed-engineered human alveolar lung-on-a-chip model

Here, we present a physiologically relevant model of the human pulmonary alveoli. This alveolar lung-on-a-chip platform is composed of a three-dimensional porous hydrogel made of gelatin methacryloyl with an inverse opal structure, bonded to a compartmentalized polydimethylsiloxane chip. The inverse opal hydrogel structure features well-defined, interconnected pores with high similarity to human alveolar sacs. By populating the sacs with primary human alveolar epithelial cells, functional epithelial monolayers are readily formed. Cyclic strain is integrated into the device to allow biomimetic breathing events of the alveolar lung, which, in addition, makes it possible to investigate pathological effects such as those incurred by cigarette smoking and severe acute respiratory syndrome coronavirus 2 pseudoviral infection. Our study demonstrates a unique method for reconstitution of the functional human pulmonary alveoli in vitro, which is anticipated to pave the way for investigating relevant physiological and pathological events in the human distal lung.

An open-source handheld extruder loaded with pore-forming bioink for in situ wound dressing

The increasing demand in rapid wound dressing and healing has promoted the development of intraoperative strategies, such as intraoperative bioprinting, which allows deposition of bioinks directly at the injury sites to conform to their specific shapes and structures. Although successes have been achieved to varying degrees, either the instrumentation remains complex and high-cost or the bioink is insufficient for desired cellular activities. Here, we report the development of a cost-effective, open-source handheld bioprinter featuring an ergonomic design, which was entirely portable powered by a battery pack. We further integrated an aqueous two-phase emulsion bioink based on gelatin methacryloyl with the handheld system, enabling convenient shape-controlled in situ bioprinting. The unique pore-forming property of the emulsion bioink facilitated liquid and oxygen transport as well as cellular proliferation and spreading, with an additional ability of good elasticity to withstand repeated mechanical compressions. These advantages of our pore-forming bioink-loaded handheld bioprinter are believed to pave a new avenue for effective wound dressing potentially in a personalized manner down the future.

Colloidal systems toward 3D cell culture scaffolds

Three-dimensional porous scaffolds are essential for the development of tissue engineering and regeneration, as biomimetic supports to recreate the microenvironment present in natural tissues. To successfully achieve the growth and development of a specific kind of tissue, porous matrices should be able to influence cell behavior by promoting close cell-cell and cell-matrix interactions. To achieve this goal, the scaffold must fulfil a set of conditions, including ordered interconnected porosity to promote cell diffusion and vascularization, mechanical strength to support the tissue during continuous ingrowth, and biocompatibility to avoid toxicity. Among various building approaches to the construction of porous matrices, selected strategies afford hierarchical scaffolds with such defined properties. The control over porosity, microstructure or morphology, is crucial to the fabrication of high-end, reproducible scaffolds for the target application. In this review, we provide an insight into recent advances toward the colloidal fabrication of hierarchical scaffolds. After identifying the main requirements for scaffolds in biomedical applications, conceptual building processes are introduced. Examples of tissue regeneration applications are provided for different scaffold types, highlighting their versatility and biocompatibility. We finally provide a prospect about the current state of the art and limitations of porous scaffolds, along with challenges that are to be addressed, so these materials consolidate in the fields of tissue engineering and drug delivery.

Oriented Neural Spheroid Formation and Differentiation of Neural Stem Cells Guided by Anisotropic Inverse Opals

Isotropic inverse opal structures have been extensively studied for the ability to manipulate cell behaviors such as attachment, migration, and spheroid formation. However, their use in regulate the behaviors of neural stem cells has not been fully explored, besides, the isotropic inverse opal structures usually lack the ability to induce the oriented cell growth which is fundamental in neural regeneration based on neural stem cell therapy. In this paper, the anisotropic inverse opal substrates were obtained by mechanically stretching the poly (vinylidene fluoride) (PVDF) inverse opal films. The anisotropic inverse opal substrates possessed good biocompatibility, optical properties and anisotropy, provided well guidance for the formation of neural spheroids, the alignment of neural stem cells, the differentiation of neural stem cells, the oriented growth of derived neurons and the dendritic complexity of the newborn neurons. Thus, we conclude that the anisotropic inverse opal substrates possess great potential in neural regeneration applications.

Fabrication of Bioactive Inverted Colloidal Crystal Scaffolds Using Expanded Polystyrene Beads

Inverted colloidal crystal (ICC) hydrogel scaffolds have emerged as a new class of three-dimensional cell culture matrix that represents a unique opportunity to reproduce lymphoid tissue microenvironments. ICC geometry promotes the formation of stromal cell networks and their interaction with hematopoietic cells, a core cellular process in lymphoid tissues. When subdermally implanted, ICC hydrogel scaffolds direct unique foreign body responses to form a vascularized stromal tissue with prolonged attraction of hematopoietic cells, which together resemble lymphoid tissue microenvironments. While conceptually simple, fabrication of ICC hydrogel scaffold requires multiple steps and laborious handling of delicate materials. Here, we introduce a facile route for ICC hydrogel scaffold fabrication using expanded polystyrene (EPS) beads. EPS beads shrink and fuse in a tunable manner under pressurized thermal conditions, which serves as colloidal crystal templates for ICC scaffold fabrication. Inclusion of collagen in the precursor solution greatly simplified preparation of bioactive hydrogel scaffolds. The resultant EPS-templated bioactive ICC hydrogel scaffolds demonstrate characteristic features required for lymphoid tissue modeling in both in vitro and in vivo settings. We envision that the presented method will facilitate widespread implementation of ICC hydrogel scaffolds for lymphoid tissue engineering and other emerging applications. Impact statement Inverted colloidal crystal (ICC) hydrogel scaffolds have emerged as a new class of three-dimensional cell culture matrix that represents a unique opportunity for lymphoid tissue modeling and other emerging novel bioengineering applications. While conceptually simple, fabrication of the ICC hydrogel scaffold requires multiple steps and laborious handling of delicate materials with highly toxic chemicals. The presented method for ICC hydrogel scaffold fabrication using expanded polystyrene (EPS) beads is simple, cost-effective, and involves less toxic chemicals than conventional methods, while retaining comparable biological significance. We envision that EPS bead-based hydrogel scaffold fabrication will greatly facilitate the widespread implementation of ICC hydrogel scaffolds and their practical applications.

A General Strategy for Extrusion Bioprinting of Bio-Macromolecular Bioinks through Alginate-Templated Dual-Stage Crosslinking

The recently developed 3D bioprinting technology has greatly improved the ability to generate biomimetic tissues that are structurally and functionally relevant to their human counterparts. The selection of proper biomaterials as the bioinks is a key step toward successful bioprinting. For example, viscosity of a bioink is an important rheological parameter to determine the flexibility in deposition of free-standing structures and the maintenance of architectural integrity following bioprinting. This requirement, however, has greatly limited the selection of bioinks, especially for those naturally derived due to their commonly low mechanical properties. Here the generalization of a mechanism for extrusion bioprinting of bio-macromolecular components, mainly focusing on collagen and its derivatives including gelatin and gelatin methacryloyl, is reported. Specifically, a templating strategy is adopted using a composite bioink containing both the desired bio-macromolecular component and a polysaccharide alginate. The physically crosslinkable alginate component serves as the temporal structural support to stabilize the shape of the construct during bioprinting; upon subsequent chemical or physical crosslinking of the bio-macromolecular component, alginate can be selectively removed to leave only the desired bio-macromolecule. It is anticipated that this strategy is general, and can be readily expanded for use of a wide variety of other bio-macromolecular bioinks.

Engineered circulatory scaffolds for building cardiac tissue

Heart failure (HF) is the terminal state of cardiovascular disease (CVD), leading numerous patients to death every year. Cardiac tissue engineering is a multidisciplinary field of creating functional cardiac patches in vitro to promote cardiac function after transplantation onto damaged zone, giving the hope for patients with end-stage HF. However, the limited thickness of cardiac patches results in the graft failure of survival and function due to insufficient blood supply. To date, prevascularized cardiac tissue, with the use of circulatory scaffolds, holds the promise to be inosculated and perfused with host vasculature to eventually promote cardiac pumping function. Circulatory scaffolds play its role to provide oxygen and nutrients and take metabolic wastes away, and achieve anastomosis with host vasculature in vivo. Of worth note, heart-on-a-chip based on circulatory scaffolds now has been considered as a valuable unit to broaden the research for building cardiac tissue. In this review, we will present recent different strategies to engineer circulatory scaffolds for building cardiac tissue with microvasculature, followed by its current state and future direction.

Inverse Opal Scaffolds with Gradations in Mineral Content for Spatial Control of Osteogenesis

The design and fabrication of inverse opal scaffolds with gradations in mineral content to achieve spatial control of osteogenesis are described. The gradient in mineral content is established via the diffusion-limited transport of hydroxyapatite nanoparticles in a closely packed lattice of gelatin microbeads. The mineral-graded scaffold has an array of uniform pores and interconnected windows to facilitate efficient transport of nutrients and metabolic wastes, ensuring high cell viability. The graded distribution of mineral content can provide biochemical and mechanical cues for spatially regulating the osteogenic differentiation of adipose-derived stromal cells. This new class of scaffolds holds promise for engineering the interfaces between mineralized and unmineralized tissues.

Microscale Liquid Transport in Polycrystalline Inverse Opals across Grain Boundaries

Delivering liquid through the void spaces in porous metals is a daunting challenge for a variety of emerging interface technologies ranging from battery electrodes to evaporation surfaces. Hydraulic transport characteristics of well-ordered porous media are governed by the pore distribution, porosity, and morphology. Much like energy transport in polycrystalline solids, hydraulic transport in semi-ordered porous media is predominantly limited by defects and grain boundaries. Here, we report the wicking performances for porous copper inverse opals having pore diameters from 300 to 1000 nm by measuring the capillary-driven liquid rise. The capillary performance parameter within single crystal domain (K_ij/R_eff = 10⁻³ to 10⁻² µm) is an order of magnitude greater than the collective polycrystal (K_eff/R_eff = ~10⁻⁵ to 10⁻³ µm) due to the hydraulic resistances (i.e. grain boundaries between individual grains). Inspired by the heterogeneity found in biological systems, we report that the capillary performance parameter of gradient porous copper (K_eff/R_eff = ~10⁻³ µm), comparable to that of single crystals, overcomes hydraulic resistances through providing additional hydraulic routes in three dimensions. The understanding of microscopic liquid transport physics through porous crystals and across grain boundaries will help to pave the way for the spatial design of next-generation heterogeneous porous media.

Inverse Opal Scaffolds and Their Biomedical Applications

Three-dimensional porous scaffolds play a pivotal role in tissue engineering and regenerative medicine by functioning as biomimetic substrates to manipulate cellular behaviors. While many techniques have been developed to fabricate porous scaffolds, most of them rely on stochastic processes that typically result in scaffolds with pores uncontrolled in terms of size, structure, and interconnectivity, greatly limiting their use in tissue regeneration. Inverse opal scaffolds, in contrast, possess uniform pores inheriting from the template comprised of a closely packed lattice of monodispersed microspheres. The key parameters of such scaffolds, including architecture, pore structure, porosity, and interconnectivity, can all be made uniform across the same sample and among different samples. In conjunction with a tight control over pore sizes, inverse opal scaffolds have found widespread use in biomedical applications. In this review, we provide a detailed discussion on this new class of advanced materials. After a brief introduction to their history and fabrication, we highlight the unique advantages of inverse opal scaffolds over their non-uniform counterparts. We then showcase their broad applications in tissue engineering and regenerative medicine, followed by a summary and perspective on future directions.

Fabrication of Inverted Colloidal Crystal Poly(ethylene glycol) Scaffold: A Three-dimensional Cell Culture Platform for Liver Tissue Engineering

The ability to maintain hepatocyte function in vitro, for the purpose of testing xenobiotics' cytotoxicity, studying virus infection and developing drugs targeted at the liver, requires a platform in which cells receive proper biochemical and mechanical cues. Recent liver tissue engineering systems have employed three-dimensional (3D) scaffolds composed of synthetic or natural hydrogels, given their high water retention and their ability to provide the mechanical stimuli needed by the cells. There has been growing interest in the inverted colloidal crystal (ICC) scaffold, a recent development, which allows high spatial organization, homotypic and heterotypic cell interaction, as well as cell-extracellular matrix (ECM) interaction. Herein, we describe a protocol to fabricate the ICC scaffold using poly (ethylene glycol) diacrylate (PEGDA) and the particle leaching method. Briefly, a lattice is made from microsphere particles, after which a pre-polymer solution is added, properly polymerized, and the particles are then removed, or leached, using an organic solvent (e.g., tetrahydrofuran). The dissolution of the lattice results in a highly porous scaffold with controlled pore sizes and interconnectivities that allow media to reach cells more easily. This unique structure allows high surface area for the cells to adhere to as well as easy communication between pores, and the ability to coat the PEGDA ICC scaffold with proteins also shows a marked effect on cell performance. We analyze the morphology of the scaffold as well as the hepatocarcinoma cell (Huh-7.5) behavior in terms of viability and function to explore the effect of ICC structure and ECM coatings. Overall, this paper provides a detailed protocol of an emerging scaffold that has wide applications in tissue engineering, especially liver tissue engineering.

Scaling up self-assembly: bottom-up approaches to macroscopic particle organization

This review presents an overview of recent work in the field of non-Brownian particle self-assembly. Compared to nanoparticles that naturally self-assemble due to Brownian motion, larger, non-Brownian particles (d > 6 μm) are less prone to autonomously organize into crystalline arrays. The tendency for particle systems to experience immobilization and kinetic arrest grows with particle radius. In order to overcome this kinetic limitation, some type of external driver must be applied to act as an artificial "thermalizing force" upon non-Brownian particles, inducing particle motion and subsequent crystallization. Many groups have explored the use of various agitation methods to overcome the natural barriers preventing self-assembly to which non-Brownian particles are susceptible. The ability to create materials from a bottom-up approach with these characteristics would allow for precise control over their pore structure (size and distribution) and surface properties (topography, functionalization and area), resulting in improved regulation of key characteristics such as mechanical strength, diffusive properties, and possibly even photonic properties. This review will highlight these approaches, as well as discuss the potential impact of bottom-up macroscale particle assembly. The applications of such technology range from customizable and autonomously self-assembled niche microenvironments for drug delivery and tissue engineering to new acoustic dampening, battery, and filtration materials, among others. Additionally, crystals made from non-Brownian particles resemble naturally derived materials such as opals, zeolites, and biological tissue (i.e. bone, cartilage and lung), due to their high surface area, pore distribution, and tunable (multilevel) hierarchy.

Engineered regenerated bacterial cellulose scaffolds for application in in vitro tissue regeneration

Regenerated bacterial cellulose scaffolds were synthesized through solvent casting and particulate leaching method for application in in vitro tissue regeneration.

Cell-friendly inverse opal-like hydrogels for a spatially separated co-culture system

Three-dimensional macroporous scaffolds have extensively been studied for cell-based tissue engineering but their use is mostly limited to mechanical support for cell adhesion and growth on the surface of macropores. Here, a templated fabrication method is described to prepare cell-friendly inverse opal-like hydrogels (IOHs) allowing both cell encapsulation within the hydrogel matrix and cell seeding on the surface of macropores. Ionically crosslinked alginate microbeads and photocrosslinkable biocompatible polymers are used as a sacrificial template and as a matrix, respectively. The alginate microbeads are easily removed by a chelating agent, with minimal toxicity for the encapsulated cells during template removal. The outer surface of macropores in IOHs can also provide a space for cell adherence. The cells encapsulated or attached in IOHs are able to remain viable and to proliferate over time. The elastic modulus and cell-adhesion properties of IOHs can be easily controlled and tuned. Finally, it is demonstrated that IOH can be used to co-culture two distinct cell populations in different spatial positions. This cell-friendly IOH system provides a 3D scaffold for organizing different cell types in a controllable microenvironment to investigate biological processes such as stem cell niches or tumor microenvironments.

Optical-resolution photoacoustic microscopy for volumetric and spectral analysis of histological and immunochemical samples

Optical-resolution photoacoustic microscopy (OR-PAM) is an imaging modality with superb penetration depth and excellent absorption contrast. Here we demonstrate, for the first time, that this technique can advance quantitative analysis of conventional chromogenic histochemistry. Because OR-PAM can quantify the absorption contrast at different wavelengths, it is feasible to spectrally resolve the specific biomolecules involved in a staining color. Furthermore, the tomographic capability of OR-PAM allows for noninvasive volumetric imaging of a thick sample without microtoming it. By immunostaining the sample with different chromogenic agents, we further demonstrated the ability of OR-PAM to resolve different types of cells in a coculture sample with imaging depths up to 1 mm. Taken together, the integration of OR-PAM with (immuno)histochemistry offers a simple and versatile technique with broad applications in cell biology, pathology, tissue engineering, and related biomedical studies.

An overview of inverted colloidal crystal systems for tissue engineering

Scaffolding is at the heart of tissue engineering but the number of techniques available for turning biomaterials into scaffolds displaying the features required for a tissue engineering application is somewhat limited. Inverted colloidal crystals (ICCs) are inverse replicas of an ordered array of monodisperse colloidal particles, which organize themselves in packed long-range crystals. The literature on ICC systems has grown enormously in the past 20 years, driven by the need to find organized macroporous structures. Although replicating the structure of packed colloidal crystals (CCs) into solid structures has produced a wide range of advanced materials (e.g., photonic crystals, catalysts, and membranes) only in recent years have ICCs been evaluated as devices for medical/pharmaceutical and tissue engineering applications. The geometry, size, pore density, and interconnectivity are features of the scaffold that strongly affect the cell environment with consequences on cell adhesion, proliferation, and differentiation. ICC scaffolds are highly geometrically ordered structures with increased porosity and connectivity, which enhances oxygen and nutrient diffusion, providing optimum cellular development. In comparison to other types of scaffolds, ICCs have three major unique features: the isotropic three-dimensional environment, comprising highly uniform and size-controllable pores, and the presence of windows connecting adjacent pores. Thus far, this is the only technique that guarantees these features with a long-range order, between a few nanometers and thousands of micrometers. In this review, we present the current development status of ICC scaffolds for tissue engineering applications.

Monolithic photonic crystals created by partial coalescence of core-shell particles

Colloidal crystals and their derivatives have been intensively studied and developed during the past two decades due to their unique photonic band gap properties. However, complex fabrication procedures and low mechanical stability severely limit their practical uses. Here, we report stable photonic structures created by using colloidal building blocks composed of an inorganic core and an organic shell. The core-shell particles are convectively assembled into an opal structure, which is then subjected to thermal annealing. During the heat treatment, the inorganic cores, which are insensitive to heat, retain their regular arrangement in a face-centered cubic lattice, while the organic shells are partially fused with their neighbors; this forms a monolithic structure with high mechanical stability. The interparticle distance and therefore stop band position are precisely controlled by the annealing time; the distance decreases and the stop band blue shifts during the annealing. The composite films can be further treated to give a high contrast in the refractive index. The inorganic cores are selectively removed from the composite by wet etching, thereby providing an organic film containing regular arrays of air cavities. The high refractive index contrast of the porous structure gives rise to pronounced structural colors and high reflectivity at the stop band position.

Photochemistry-based method for the fabrication of SnO(2) monolayer ordered porous films with size-tunable surface pores for direct application in resistive-type gas sensor

A new photochemistry-based method was introduced for fabricating SnO2 monolayer ordered porous films with size-tunable surface pores on ceramic tubes used for gas sensors. The growth of the spherical pore walls was controlled by two times irradiation of the ultraviolet light using polystyrene microsphere two-dimensional colloidal crystal as a template. The surface pore size of the final obtained porous films was well tuned by changing the second irradiation time rather than replacing the template microspheres. The monolayer ordered porous films on the tubes were directly used, for the first time, as gas sensors. The sensitivity of the sensor depended on the surface pore size and was carefully analyzed by ethanol gas detection. The sensor also exhibited short response-recovery time and long-term stability at lower than 300 °C in practical applications. Therefore, this study opens up a kind of construction method for gas sensors, provides a new strategy for controlling the surface pore size of the monolayer ordered porous film, and introduces a new type of sensitivity-controllable gas sensor.

Non-invasive and in situ characterization of the degradation of biomaterial scaffolds by volumetric photoacoustic microscopy

Degradation is among the most important properties of biomaterial scaffolds, which are indispensable for regenerative medicine. The currently used method relies on the measurement of mass loss across different samples and cannot track the degradation of an individual scaffold in situ. Here we report, for the first time, the use of multiscale photoacoustic microscopy to non-invasively monitor the degradation of an individual scaffold. We could observe alterations to the morphology and structure of a scaffold at high spatial resolution and deep penetration, and more significantly, quantify the degradation of an individual scaffold as a function of time, both in vitro and in vivo. In addition, the remodeling of vasculature inside a scaffold can be visualized simultaneously using a dual-wavelength scanning mode in a label-free manner. This optoacoustic method can be used to monitor the degradation of individual scaffolds, offering a new approach to non-invasively analyze and quantify biomaterial-tissue interactions in conjunction with the assessment of in vivo vascular parameters.

Fabrication of Cell Patches Using Biodegradable Scaffolds with a Hexagonal Array of Interconnected Pores (SHAIPs)

Cell patches are widely used for healing injuries on the surfaces or interfaces of tissues such as those of epidermis and myocardium. Here we report a novel type of porous scaffolds made of poly(D,L-lactic-co-glycolic acid) for fabricating cell patches. The scaffolds have a single layer of spherical pores arranged in a unique hexagonal pattern and are therefore referred to as "scaffolds with a hexagonal array of interconnected pores (SHAIPs)". SHAIPs contain both uniform pores and interconnecting windows that can facilitate the exchange of biomacromolecules, ensure homogeneous cell seeding, and promote cell migration. As a proof-of-concept demonstration, we have created skeletal muscle patches with a thickness of approximately 150 μm using SHAIPs. The myoblasts seeded in the scaffolds maintained high viability and were able to differentiate into multi-nucleated myotubes. Moreover, neovasculature could efficiently develop into the patches upon subcutaneous implantation in vivo.