Smart Biomaterials in Biomedical Applications: Current Advances and Possible Future Directions

Smart biomaterials with the capacity to alter their properties in response to an outside stimulus or from within the environment around them have picked up significant attention in the biomedical community. This is primarily due to the interest in their biomedical applications that may be anticipated from them in a considerable number of dynamic structures and devices. Shape-memory materials are some of these materials that have been exclusively used for these applications. They exhibit unique structural reconfiguration features they adapt as per the provided environmental conditions and can be designed for their enhanced biocompatibility. Numerous research initiatives have focused on these smart biocompatible materials over the last few decades to enhance their biomedical applications. Shape-memory materials play a significant role in this regard to meet new surgical and medical devices' requirements for special features and utility cases. Because of the favorable design variety, different biomedical shape-memory materials can be developed by modifying their chemical and physical behaviors to accommodate the desired requirements. In this review, recent advances and characteristics of smart biomaterials for biomedical applications are described. The authors also discuss about their clinical translations in tissue engineering, drug delivery, and medical devices.

Self-oxygenation of engineered living tissues orchestrates osteogenic commitment of mesenchymal stem cells

Oxygenating biomaterials can alleviate anoxic stress, stimulate vascularization, and improve engraftment of cellularized implants. However, the effects of oxygen-generating materials on tissue formation have remained largely unknown. Here, we investigate the impact of calcium peroxide (CPO)-based oxygen-generating microparticles (OMPs) on the osteogenic fate of human mesenchymal stem cells (hMSCs) under a severely oxygen deficient microenvironment. To this end, CPO is microencapsulated in polycaprolactone to generate OMPs with prolonged oxygen release. Gelatin methacryloyl (GelMA) hydrogels containing osteogenesis-inducing silicate nanoparticles (SNP hydrogels), OMPs (OMP hydrogels), or both SNP and OMP (SNP/OMP hydrogels) are engineered to comparatively study their effect on the osteogenic fate of hMSCs. OMP hydrogels associate with improved osteogenic differentiation under both normoxic and anoxic conditions. Bulk mRNAseq analyses suggest that OMP hydrogels under anoxia regulate osteogenic differentiation pathways more strongly than SNP/OMP or SNP hydrogels under either anoxia or normoxia. Subcutaneous implantations reveal a stronger host cell invasion in SNP hydrogels, resulting in increased vasculogenesis. Furthermore, time-dependent expression of different osteogenic factors reveals progressive differentiation of hMSCs in OMP, SNP, and SNP/OMP hydrogels. Our work demonstrates that endowing hydrogels with OMPs can induce, improve, and steer the formation of functional engineered living tissues, which holds potential for numerous biomedical applications, including tissue regeneration and organ replacement therapy.

Engineered Liposomes in Interventional Theranostics of Solid Tumors

Engineered liposomal nanoparticles have unique characteristics as cargo carriers in cancer care and therapeutics. Liposomal theranostics have shown significant progress in preclinical and clinical cancer models in the past few years. Liposomal hybrid systems have not only been approved by the FDA but have also reached the market level. Nanosized liposomes are clinically proven systems for delivering multiple therapeutic as well as imaging agents to the target sites in (i) cancer theranostics of solid tumors, (ii) image-guided therapeutics, and (iii) combination therapeutic applications. The choice of diagnostics and therapeutics can intervene in the theranostics property of the engineered system. However, integrating imaging and therapeutics probes within lipid self-assembly "liposome" may compromise their overall theranostics performance. On the other hand, liposomal systems suffer from their fragile nature, site-selective tumor targeting, specific biodistribution and premature leakage of loaded cargo molecules before reaching the target site. Various engineering approaches, viz., grafting, conjugation, encapsulations, etc., have been investigated to overcome the aforementioned issues. It has been studied that surface-engineered liposomes demonstrate better tumor selectivity and improved therapeutic activity and retention in cells/or solid tumors. It should be noted that several other parameters like reproducibility, stability, smooth circulation, toxicity of vital organs, patient compliance, etc. must be addressed before using liposomal theranostics agents in solid tumors or clinical models. Herein, we have reviewed the importance and challenges of liposomal medicines in targeted cancer theranostics with their preclinical and clinical progress and a translational overview.

3D Bioprinted Hydrogel Microfluidic Devices for Parallel Drug Screening

Conventional high-throughput screening (HTS) platforms suffer from the need for large cell volumes, high reagent consumption, significant assembly cost, and handling efforts. The assembly of three-dimensional (3D) bioprinted hydrogel-based microfluidic chips within platforms can address these problems. We present a continuous and seamless manufacturing approach to create a bioprinted microfluidic chips with a circular pattern scalable toward HTS platforms. Digital light processing 3D bioprinting is used to tune the local permeability of our chip, made of polyethylene glycol diacrylate and cell-laden gelatin methacryloyl, for creating predefined gradients of biochemical properties. We measured the flow-induced physical characteristics, the mass transport of drug agents, and the biological features of the proposed chip. We measured reactive oxygen species from the encapsulated cells through an integrated process and showed the capacity of the hydrogel-based chip for creating drug/agent gradients. This work introduces a chip design based on a hydrogel that can be changed and could be used for modern HTS platforms such as in vitro organoids.

Selection of natural biomaterials for micro-tissue and organ-on-chip models

The desired organ in micro-tissue models of organ-on-a-chip (OoC) devices dictates the optimum biomaterials, divided into natural and synthetic biomaterials. They can resemble biological tissues' biological functions and architectures by constructing bioactivity of macromolecules, cells, nanoparticles, and other biological agents. The inclusion of such components in OoCs allows them having biological processes, such as basic biorecognition, enzymatic cleavage, and regulated drug release. In this report, we review natural-based biomaterials that are used in OoCs and their main characteristics. We address the preparation, modification, and characterization methods of natural-based biomaterials and summarize recent reports on their applications in the design and fabrication of micro-tissue models. This article will help bioengineers select the proper biomaterials based on developing new technologies to meet clinical expectations and improve patient outcomes fusing disease modeling.

Multi-Organs-on-Chips for Testing Small-Molecule Drugs: Challenges and Perspectives

Organ-on-a-chip technology has been used in testing small-molecule drugs for screening potential therapeutics and regulatory protocols. The technology is expected to boost the development of novel therapies and accelerate the discovery of drug combinations in the coming years. This has led to the development of multi-organ-on-a-chip (MOC) for recapitulating various organs involved in the drug-body interactions. In this review, we discuss the current MOCs used in screening small-molecule drugs and then focus on the dynamic process of drug absorption, distribution, metabolism, and excretion. We also address appropriate materials used for MOCs at low cost and scale-up capacity suitable for high-performance analysis of drugs and commercial high-throughput screening platforms.

Layered double hydroxide-based nanocomposite scaffolds in tissue engineering applications

Layered double hydroxides (LDHs), when incorporated into biomaterials, provide a tunable composition, controllable particle size, anion exchange capacity, pH-sensitive solubility, high-drug loading efficiency, efficient gene and drug delivery, controlled release and effective intracellular uptake, natural biodegradability in an acidic medium, and negligible toxicity. In this review, we study potential applications of LDH-based nanocomposite scaffolds for tissue engineering. We address how LDHs provide new solutions for nanostructure stability and enhance in vivo studies' success.

Survival and Proliferation under Severely Hypoxic Microenvironments Using Cell-Laden Oxygenating Hydrogels

Different strategies have been employed to provide adequate nutrients for engineered living tissues. These have mainly revolved around providing oxygen to alleviate the effects of chronic hypoxia or anoxia that result in necrosis or weak neovascularization, leading to failure of artificial tissue implants and hence poor clinical outcome. While different biomaterials have been used as oxygen generators for in vitro as well as in vivo applications, certain problems have hampered their wide application. Among these are the generation and the rate at which oxygen is produced together with the production of the reaction intermediates in the form of reactive oxygen species (ROS). Both these factors can be detrimental for cell survival and can severely affect the outcome of such studies. Here we present calcium peroxide (CPO) encapsulated in polycaprolactone as oxygen releasing microparticles (OMPs). While CPO releases oxygen upon hydrolysis, PCL encapsulation ensures that hydrolysis takes place slowly, thereby sustaining prolonged release of oxygen without the stress the bulk release can endow on the encapsulated cells. We used gelatin methacryloyl (GelMA) hydrogels containing these OMPs to stimulate survival and proliferation of encapsulated skeletal myoblasts and optimized the OMP concentration for sustained oxygen delivery over more than a week. The oxygen releasing and delivery platform described in this study opens up opportunities for cell-based therapeutic approaches to treat diseases resulting from ischemic conditions and enhance survival of implants under severe hypoxic conditions for successful clinical translation.

Tissue Adhesives: From Research to Clinical Translation

Sutures, staples, clips and skin closure strips are used as the gold standard to close wounds after an injury. In spite of being the present standard of care, the utilization of these conventional methods is precarious amid complicated and sensitive surgeries such as vascular anastomosis, ocular surgeries, nerve repair, or due to the high-risk components included. Tissue adhesives function as an interface to connect the surfaces of wound edges and prevent them from separation. They are fluid or semi-fluid mixtures that can be easily used to seal any wound of any morphology - uniform or irregular. As such, they provide alternatives to new and novel platforms for wound closure methods. In this review, we offer a background on the improvement of distinctive tissue adhesives focusing on the chemistry of some of these products that have been a commercial success from the clinical application perspective. This review is aimed to provide a guide toward innovation of tissue bioadhesive materials and their associated biomedical applications.

3D Immunocompetent Organ-on-a-Chip Models

In recent years, engineering of various human tissues in microphysiologically relevant platforms, known as organs-on-chips (OOCs), has been explored to establish in vitro tissue models that recapitulate the microenvironments found in native organs and tissues. However, most of these models have overlooked the important roles of immune cells in maintaining tissue homeostasis under physiological conditions and in modulating the tissue microenvironments during pathophysiology. Significantly, gradual progress is being made in the development of more sophisticated microphysiologically relevant human-based OOC models that allow the studies of the key biophysiological aspects of specific tissues or organs, interactions between cells (parenchymal, vascular, and immune cells) and their extracellular matrix molecules, effects of native tissue architectures (geometry, dynamic flow or mechanical forces) on tissue functions, as well as unravelling the mechanism underlying tissue-specific diseases and drug testing. In this Progress Report, we discuss the different components of the immune system, as well as immune OOC platforms and immunocompetent OOC approaches that have simulated one or more components of the immune system. We also outline the challenges to recreate a fully functional tissue system in vitro with a focus on the incorporation of the immune system.

3D Printing metamaterials towards tissue engineering

The rapid growth and disruptive potentials of three-dimensional (3D) printing demand further research for addressing fundamental fabrication concepts and enabling engineers to realize the capabilities of 3D printing technologies. There is a trend to use these capabilities to develop materials that derive some of their properties via their structural organization rather than their intrinsic constituents, sometimes referred to as mechanical metamaterials. Such materials show qualitatively different mechanical behaviors despite using the same material composition, such as ultra-lightweight, super-elastic, and auxetic structures. In this work, we review current advancements in the design and fabrication of multi-scale advanced structures with properties heretofore unseen in well-established materials. We classify the fabrication methods as conventional methods, additive manufacturing techniques, and 4D printing. Following a comprehensive comparison of different fabrication methods, we suggest some guidelines on the selection of fabrication parameters to construct meta-biomaterials for tissue engineering. The parameters include multi-material capacity, fabrication resolution, prototyping speed, and biological compatibility.

Effects of simvastatin on matrix metalloproteinase regulation in IL-1β-induced SW1353 cells

The present study shows the basis for the anti-inflammatory effects of statins in interleukin 1β (IL-1β) induced SW1353 chondrosarcoma cell-line. The cells were pre-treated with simvastatin (5 μM, 10 μM, and 50 μM), followed by IL-1β (5 ng/mL) stimulation. Effects of simvastatin on cell viability and cytotoxicity of chondrocytes were measured with WST-1 and lactate dehydrogenase (LDH) assays, respectively. Under inflammatory conditions, in the absence/presence of simvastatin, the changes in matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase-1 (TIMP-1) expression levels were examined. Expression levels of MMP-1, -2, -3, -9, -13, and TIMP-1 and -2 were examined by qPCR. MMP-1, -9, -13, TIMP-1, and -2 levels were also determined by Western blotting. Gelatin zymography was performed to analyze the released and intracellular MMP-2 and MMP-9 activity levels. The results showed that simvastatin downregulated the degradation related genes MMP-3, MMP-13, MMP-2, MMP-9 and TIMP-2 in a dose-dependent manner.

Permeability mapping of gelatin methacryloyl hydrogels

We report the development of an efficient, customized spherical indentation-based testing method to systematically estimate the hydraulic permeability of gelatin methacryloyl (GelMA) hydrogels fabricated in a wide range of mass concentrations and photocrosslinking conditions. Numerical simulations and Biot's theory of poroelasticity were implemented to calibrate our experimental data. We correlated elastic moduli and permeability coefficients with different GelMA concentrations and crosslinking densities. Our model could also predict drug release rates from the GelMA hydrogels and diffusion of biomolecules into the three-dimensional GelMA hydrogels. The results potentially provide a design map for choosing desired GelMA-based hydrogels for use in drug delivery, tissue engineering, and regenerative medicine, which may be further expanded to predicting the permeability behaviors of various other hydrogel types.

STATEMENT OF SIGNIFICANCE

GelMA hydrogels have attracted increasing attention in recent years as matrices for cell cultures and biomolecule delivery. This inexpensive polymer is derived from gelatin functionalized with methacryloyl groups that can be crosslinked by photochemical reactions. Here we report the development of an efficient, customized testing method to systematically estimate the hydraulic permeability of GelMA hydrogels. Hydraulic permeability indicates the resistance of GelMA hydrogels to the movement of saturated fluid. We used the model to measure the elastic moduli and permeability coefficients, providing a permeability map for various GelMA hydrogel formulations.

Multiscale bioprinting of vascularized models

A basic prerequisite for the survival and function of three-dimensional (3D) engineered tissue constructs is the establishment of blood vessels. 3D bioprinting of vascular networks with hierarchical structures that resemble in vivo structures has allowed blood circulation within thick tissue constructs to accelerate vascularization and enhance tissue regeneration. Successful rapid vascularization of tissue constructs requires synergy between fabrication of perfusable channels and functional bioinks that induce angiogenesis and capillary formation within constructs. Combinations of 3D bioprinting techniques and four-dimensional (4D) printing concepts through patterning proangiogenic factors may offer novel solutions for implantation of thick constructs. In this review, we cover current bioprinting techniques for vascularized tissue constructs with vasculatures ranging from capillaries to large blood vessels and discuss how to implement these approaches for patterning proangiogenic factors to maintain long-term, stimuli-controlled formation of new capillaries.

Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures

For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues.

Anatomical and biomechanical evaluation of the tension band technique in patellar fractures

Tension band wiring for patellar fractures is common, but some recent reports refer to disadvantages of this approach. Our anatomical and biomechanical study focused on use of tension band techniques in patellar fractures. The anatomy of the patella and tendon insertion was examined with knee magnetic resonance imaging (MRI) and correlated with the technical requirements of the tension band. Tension band wiring over tendinous tissue was simulated and calculated with a cyclic biomechanical test on cow patellae. According to tension band templating on the MRI section, Kirschner wire insertion was needed for the tension band to turn over the tendinous tissue. The tension band became more stable while turning over less tendinous tissue and more adjacent bone surface. Nevertheless, cyclic loading tests indicate that all tension band applications in this study lose their initial stability. Excessive initial compression by the tension band resulted in bending of the Kirschner wire and thus reduction failure. For optimum stabilisation, tension force transfer should be done directly on bone or at least material that protects the tendon would be useful.

The effects of suramin in prevention of peritendinous adhesions following flexor tendon injury in a chicken model

Peritendinous adhesions are the most common complication of flexor tendon injuries. Overproduction of transforming growth factor Beta has been reported as a major cause of tissue fibrosis. This study investigated the effects of suramin, a known inhibitor of transforming growth factor Beta, on the formation of flexor tendon adhesions in a chicken model. Forty-two chicken flexor tendons that were divided partially were repaired using a modified Kessler technique. The chickens were divided into 3 groups. In group 1 (control), no suramin was administered to the tendon repair site; in group 2, 1 mg of suramin was injected around the tendon repair site; and in group 3, 2 mg of suramin was injected around the tendon repair site. At 6 weeks postoperatively, the animals were sacrificed, and functional, histologic, and biomechanical examinations were performed. There was no difference between the groups in terms of tendon excursion. Histologic evaluation showed adhesions were decreased in the groups treated with suramin. In the biomechanical evaluation, a statistically significant difference was present only between the group treated with 2 mg of suramin and the control group. Although suramin is effective in preventing peritendinous adhesions, it can reduce tendon strength as dose-dependent. Future studies should be performed with different doses to determine clinical application.