Biomimetic natural biomaterials for tissue engineering and regenerative medicine:new biosynthesis methods,recent advances,and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering(TE)and regenerative medicine.In contrast to conventional biomaterials or synthetic materials,biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix(ECM).Additionally,such materials have mechanical adaptability,micro-structure interconnectivity,and inherent bioactivity,making them ideal for the design of living implants for specific applications in TE and regenerative medicine.This paper provides an overview for recent progress of biomimetic natural biomaterials(BNBMs),including advances in their preparation,functionality,potential applications and future challenges.We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM.Moreover,we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications.Finally,we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Engineered hydrogels for brain tumor culture and therapy

Brain tumors’severity ranges from benign to highly aggressive and invasive.Bioengineering tools can assist in understanding the pathophysiology of these tumors from outside the body and facilitate development of suitable antitumoral treatments.Here,we first describe the physiology and cellular composition of brain tumors.Then,we discuss the development of threedimensional tissue models utilizing brain tumor cells.In particular,we highlight the role of hydrogels in providing a biomimetic support for the cells to grow into defined structures.Microscale technologies,such as electrospinning and bioprinting,and advanced cellular models aim to mimic the extracellular matrix and natural cellular localization in engineered tumor tissues.Lastly,we review current applications and prospects of hydrogels for therapeutic purposes,such as drug delivery and co-administration with other therapies.Through further development,hydrogels can serve as a reliable option for in vitro modeling and treatment of brain tumors for translational medicine.

Nanoengineered Shear-Thinning Hydrogel Barrier for Preventing Postoperative Abdominal Adhesions

More than 90%of surgical patients develop postoper-ative adhesions,and the incidence of hospital re-admissions can be as high as 20%.Current adhesion barriers present limited efficacy due to difficulties in application and incompatibility with minimally invasive interventions.To solve thisclinical limitation,we developed an injectable and sprayable shear-thinning hydrogel barrier(STHB)composed of silicate nanoplatelets and poly(ethylene oxide).We optimized this technology to recover mechanical integrity after stress,enabling its delivery though inject-able and sprayable methods.We also demonstrated limited cell adhesion and cytotoxicity to STHB compositions in vitro.The STHB was then tested in a rodent model of peritoneal injury to determine its e cacy preventing the formation of postoperative adhesions.After two weeks,the peritoneal adhesion index was used as a scoring method to determine the formation of postoperative adhesions,and STHB formulations presented superior e cacy compared to a commercially available adhesion barrier.Histological and immunohistochemical examination showed reduced adhesion formation and minimal immune infiltration in STHB formulations.Our technology demonstrated increased e cacy,ease of use in complex anatomies,and compatibility with di erent delivery methods,providing a robust universal platform to prevent postoperative adhesions in a wide range of surgical interventions.

Engineering in vitro human tissue models through bio‑design and manufacturing

In the era of burgeoning breakthroughs around medical and biomedical technologies,personalizing our medicine still sounds like a dream yet to be realized.Take cancer as an example,while the pool of anti-cancer therapeutic agents is tremendously large,pinpointing a drug or a combination of drugs that would always work out well for a given patient,remains quite impossible—in fact,we are not even close to this ideal scenario.Such an incapability,of course,originates primarily from the overly complex,volumetrically structured and dynamic microenvironments in a patient’s tumor,meaning that the same tumor as seen on Day 1 might be entirely different than when seen again a month later.

Gelatin methacryloyl granular scaffolds for localized mRNA delivery

Messenger RNA(mRNA)therapy is the intracellular delivery of mRNA to produce desired therapeutic proteins.Developing strategies for local mRNA delivery is still required where direct intra-articular injections are inappropriate for targeting a specific tissue.The mRNA delivery efficiency depends on protecting nucleic acids against nuclease-mediated degradation and safe site-specific intracellular delivery.Herein,novel mRNA-releasing matrices based on RGD-moiety-rich gelatin methacryloyl(GelMA)microporous annealed particle(MAP)scaffolds are reported.GelMA concentration in aerogel-based microgels(μgels)produced through a microfluidic process,MAP stiffnesses,and microporosity are crucial parameters for cell adhesion,spreading,and proliferation.After being loaded with mRNA complexes,MAP scaffolds composed of 10%GelMAμgels display excellent cell viability with increasing cell infiltration,adhesion,proliferation,and gene transfer.The intracellular delivery is achieved by the sustained release of mRNA complexes from MAP scaffolds and cell adhesion on mRNA-releasing scaffolds.These findings highlight that hybrid systems can achieve efficient protein expression by delivering mRNA complexes,making them promising mRNA-releasing biomaterials for tissue engineering.

Biomedical applications of engineered heparin-based materials

Heparin is a negatively charged polysaccharide with various chain lengths and a hydrophilic backbone.Due to its fascinating chemical and physical properties,nontoxicity,biocompatibility,and biodegradability,heparin has been extensively used in different fields of medicine,such as cardiovascular and hematology.This review highlights recent and future advancements in designing materials based on heparin for various biomedical applications.The physicochemical and mechanical properties,biocompatibility,toxicity,and biodegradability of heparin are discussed.In addition,the applications of heparin-based materials in various biomedical fields,such as drug/gene delivery,tissue engineering,cancer therapy,and biosensors,are reviewed.Finally,challenges,opportunities,and future perspectives in preparing heparin-based materials are summarized.

Cellulose-based composite scaffolds for bone tissue engineering and localized drug delivery

Natural bone constitutes a complex and organized structure of organic and inorganic components with limited ability to regenerate and restore injured tissues,especially in large bone defects.To improve the reconstruction of the damaged bones,tissue engineering has been introduced as a promising alternative approach to the conventional therapeutic methods including surgical interventions using allograft and autograft implants.Bioengineered composite scaffolds consisting of multifunctional biomaterials in combination with the cells and bioactive therapeutic agents have great promise for bone repair and regeneration.Cellulose and its derivatives are renewable and biodegradable natural polymers that have shown promising potential in bone tissue engineering applications.Cellulose-based scaffolds possess numerous advantages attributed to their excellent properties of non-toxicity,biocompatibility,biodegradability,availability through renewable resources,and the low cost of preparation and processing.Furthermore,cellulose and its derivatives have been extensively used for delivering growth factors and antibiotics directly to the site of the impaired bone tissue to promote tissue repair.This review focuses on the various classifications of cellulose-based composite scaffolds utilized in localized bone drug delivery systems and bone regeneration,including cellulose-organic composites,cellulose-inorganic composites,cellulose-organic/inorganic composites.We will also highlight the physicochemical,mechanical,and biological properties of the different cellulose-based scaffolds for bone tissue engineering applications.

Tissue adhesive hemostatic microneedle arrays for rapid hemorrhage treatment

Blood loss by hemorrhaging wounds accounts for over one-third of~5 million trauma fatalities worldwide every year.If not controlled in a timely manner,exsanguination can take lives within a few minutes.Developing new biomaterials that are easy to use by non-expert patients and promote rapid blood coagulation is an unmet medical need.Here,biocompatible,and biodegradable microneedle arrays(MNAs)based on gelatin methacryloyl(GelMA)biomaterial hybridized with silicate nanoplatelets(SNs)are developed for hemorrhage control.The SNs render the MNAs hemostatic,while the needle-shaped structure increases the contact area with blood,synergistically accelerating the clotting time from 11.5 min to 1.3 min in vitro.The engineered MNAs reduce bleeding by~92%compared with the untreated injury group in a rat liver bleeding model.SN-containing MNAs outperform the hemostatic effect of needle-free patches and a commercial hemostat in vivo via combining micro-and nanoengineered features.Furthermore,the tissue adhesive properties and mechanical interlocking support the suitability of MNAs for wound closure applications.These hemostatic MNAs may enable rapid hemorrhage control,particularly for patients in developing countries or remote areas with limited or no immediate access to hospitals.

Mesoporous silica rods with cone shaped pores modulate inflammation and deliver BMP-2 for bone regeneration

Biomaterials with suitable osteoimmunomodulation properties and ability to deliver osteoinductive biomolecules,such as bone morphogenetic proteins,are desired for bone regeneration.Herein,we report the development of mesoporous silica rods with large cone-shaped pores(MSR-CP)to load and deliver large protein drugs.It is noted that those cone-shaped pores on the surface modulated the immune response and reduced the pro-inflammatory reaction of stimulated macrophage.Furthermore,bone morphogenetic proteins 2(BMP-2)loaded MSR-CP facilitated osteogenic differentiation and promoted osteogenesis of bone marrow stromal cells.In vivo tests confirmed BMP-2 loaded MSR-CP improved the bone regeneration performance.This study provides a potential strategy for the design of drug delivery systems for bone regeneration.

Tunable hybrid hydrogels with multicellular spheroids for modeling desmoplastic pancreatic cancer

The tumor microenvironment consists of diverse,complex etiological factors.The matrix component of pancreatic ductal adenocarcinoma(PDAC)plays an important role not only in physical properties such as tissue rigidity but also in cancer progression and therapeutic responsiveness.Although significant efforts have been made to model desmoplastic PDAC,existing models could not fully recapitulate the etiology to mimic and understand the progression of PDAC.Here,two major components in desmoplastic pancreatic matrices,hyaluronic acid-and gelatin-based hydrogels,are engineered to provide matrices for tumor spheroids composed of PDAC and cancer-associated fibroblasts(CAF).Shape analysis profiles reveals that incorporating CAF contributes to a more compact tissue formation.Higher expression levels of markers associated with proliferation,epithelial to mesenchymal transition,mechanotransduction,and progression are observed for cancer-CAF spheroids cultured in hyper desmoplastic matrix-mimicking hydrogels,while the trend can be observed when those are cultured in desmoplastic matrix-mimicking hydrogels with the presence of transforming growth factor-β1(TGF-β1).The proposed multicellular pancreatic tumor model,in combination with proper mechanical properties and TGF-β1 supplement,makes strides in developing advanced pancreatic models for resembling and monitoring the progression of pancreatic tumors,which could be potentially applicable for realizing personalized medicine and drug testing applications.

Ultrathin-shell epitaxial Ag@Au core-shell nanowires for high-performance and chemically-stable electronic, optical, and mechanical devices

Silver nanowires (AgNWs) hold great promise for applications in wearable electronics, flexible solar cells, chemical and biological sensors, photonic/plasmonic circuits, and scanning probe microscopy (SPM) due to their unique plasmonic, mechanical, and electronic properties. However, the lifetime, reliability, and operating conditions of AgNW-based devices are significantly restricted by their poor chemical stability, limiting their commercial potentials. Therefore, it is crucial to create a reliable oxidation barrier on AgNWs that provides long-term chemical stability to various optical, electrical, and mechanical devices while maintaining their high performance. Here we report a room-temperature solution-phase approach to grow an ultra-thin, epitaxial gold coating on AgNWs to effectively shield the Ag surface from environmental oxidation. The Ag@Au core-shell nanowires (Ag@Au NWs) remain stable in air for over six months, under elevated temperature and humidity (80 °C and 100% humidity) for twelve weeks, in physiological buffer solutions for three weeks, and can survive overnight treatment of an oxidative solution (2% H2O2). The Ag@Au core-shell NWs demonstrated comparable performance as pristine AgNWs in various electronic, optical, and mechanical devices, such as transparent mesh electrodes, surface-enhanced Raman spectroscopy (SERS) substrates, plasmonic waveguides, plasmonic nanofocusing probes, and high-aspect-ratio, high-resolution atomic force microscopy (AFM) probes. These Au@Ag core-shell NWs offer a universal solution towards chemically-stable AgNW-based devices without compromising material property or device performance.

Rational design of hydrogels for immunomodulation

The immune system protects organisms against endogenous and exogenous harm and plays a key role in tissue development,repair and regeneration.Traditional immunomodulatory biologics exhibit limitations including degradation by enzymes,short half-life and lack of targeting ability.Encapsulating or binding these biologics within biomaterials is an effective way to address these problems.Hydrogels are promising immunomodulatory materials because of their prominent biocompatibility,tuneability and versatility.However,to take advantage of these opportunities and optimize material performance,it is important to more specifically elucidate,and leverage on,how hydrogels affect and control the immune response.Here,we summarize how key physical and chemical properties of hydrogels affect the immune response.We first provide an overview of underlying steps of the host immune response upon exposure to biomaterials.Then,we discuss recent advances in immunomodulatory strategies where hydrogels play a key role through(i)physical properties including dimensionality,stiffness,porosity and topography;(ii)chemical properties including wettability,electric property and molecular presentation;and(iii)the delivery of bioactive molecules via chemical or physical cues.Thus,this review aims to build a conceptual and practical toolkit for the design of immune-instructive hydrogels capable of modulating the host immune response.

Structure-activity relationship of pyrazol-4-ylpyridine derivatives and identification of a radiofluorinated probe for imaging the muscarinic acetylcholine receptor M4

There is an accumulating body of evidence implicating the muscarinic acetylcholine receptor4(M4)in schizophrenia and dementia with Lewy bodies,however,a clinically validated M4positron emission tomography(PET)radioligand is currently lacking.As such,the aim of this study was to develop a suitable M4PET ligand that allows the non-invasive visualization of M4in the brain.Structure-activity relationship studies of pyrazol-4-yl-pyridine derivates led to the discovery of target compound 12—a subtype-selective positive allosteric modulator(PAM).The radiofluorinated analogue,[18F]12,was synthesized in 28±10%radiochemical yield,>37 GBq/μmol and an excellent radiochemical purity>99%.Initial in vitro autoradiograms on rodent brain sections were performed in the absence of carbachol and showed moderate specificity as well as a low selectivity of[18F]12 for the M4-rich striatum.However,in the presence of carbachol,a significant increase in tracer binding was observed in the rat striatum,which was reduced by>60%under blocking conditions,thus indicating that orthosteric ligand interaction is required for efficient binding o f[18F]12 to the allosteric site.Remarkably,however,the presence of carbachol was not required for high specific binding in the non-human primate(NHP)and human striatum,and did not further improve the specificity and selectivity of[18F]12 in higher species.These results pointed towards significant species-differences and paved the way for a preliminary PET study in NHP,where peak brain uptake of[18F]12 was found in the putamen and temporal cortex.In conclusion,we report on the identification and preclinical development of the first radiofluorinated M4PET radioligand with promising attributes.The availability of a clinically validated M4PET radioligand harbors potential to facilitate drug development and provide a useful diagnostic tool for non-invasive imaging.

A machine learning-guided design and manufacturing of wearable nanofibrous acoustic energy harvesters

Nanofibrous acoustic energy harvesters(NAEHs)have emerged as promising wearable platforms for efficient noise-to-electricity conversion in distributed power energy systems and wearable sound amplifiers for assistive listening devices.However,their reallife efficacy is hampered by low power output,particularly in the low-frequency range(<1 kHz).This study introduces a novel approach to enhance the performance of NAEHs by applying machine learning(ML)techniques to guide the synthesis of electrospun polyvinylidene fluoride(PVDF)/polyurethane(PU)nanofibers,optimizing their application in wearable NAEHs.We use a feed-forward neural network along with solving an optimization problem to find the optimal input values of the electrospinning(applied voltage,nozzle-collector distance,electrospinning time,and drum rotation speed)to generate maximum output performance(acoustic-to-electricity conversion efficiency).We first prepared a dataset to train the network to predict the output power given the input variables with high accuracy.Upon introducing the neural network,we fix the network and then solve an optimization problem using a genetic algorithm to search for the input values that lead to the maximum energy harvesting efficiency.Our ML-guided wearable PVDF/PU NAEH platform can deliver a maximal acoustoelectric power density output of 829μW/cm^(3) within the surrounding noise levels.In addition,our system can function stably in a broad frequency(0.1-2 kHz)with a high energy conversion efficiency of 66%.Sound recognition analysis reveals a robust correlation exceeding 0.85 among lexically akin terms with varying sound intensities,contrasting with a diminished correlation below 0.27 for words with disparate semantic connotations.Overall,this work provides a previously unexplored route to utilize ML in advancing wearable NAEHs with excellent practicability.

Photonic control of ligand nanospacing in self-assembly regulates stem cell fate

Extracellular matrix(ECM)undergoes dynamic inflation that dynamically changes ligand nanospacing but has not been explored.Here we utilize ECM-mimicking photocontrolled supramolecular ligand-tunable Azo^(+)self-assembly composed of azobenzene derivatives(Azo^(+))stacked via cation-πinteractions and stabilized with RGD ligand-bearing poly(acrylic acid).Near-infrared-upconverted-ultraviolet light induces cis-Azo^(+)-mediated inflation that suppresses cation-πinteractions,thereby inflating liganded self-assembly.This inflation increases nanospacing of“closely nanospaced”ligands from 1.8 nm to 2.6 nm and the surface area of liganded selfassembly that facilitate stem cell adhesion,mechanosensing,and differentiation both in vitro and in vivo,including the release of loaded molecules by destabilizing water bridges and hydrogen bonds between the Azo^(+)molecules and loaded molecules.Conversely,visible light induces trans-Azo^(+)formation that facilitates cation-πinteractions,thereby deflating self-assembly with“closely nanospaced”ligands that inhibits stem cell adhesion,mechanosensing,and differentiation.In stark contrast,when ligand nanospacing increases from 8.7 nm to 12.2 nm via the inflation of self-assembly,the surface area of“distantly nanospaced”ligands increases,thereby suppressing stem cell adhesion,mechanosensing,and differentiation.Long-term in vivo stability of self-assembly via real-time tracking and upconversion are verified.This tuning of ligand nanospacing can unravel dynamic ligand-cell interactions for stem cell-regulated tissue regeneration.

Additively manufactured metallic biomaterials

Metal additive manufacturing(AM)has led to an evolution in the design and fabrication of hard tissue substitutes,enabling personalized implants to address each patient’s specific needs.In addition,internal pore architectures integrated within additively manufactured scaffolds,have provided an opportunity to further develop and engineer functional implants for better tissue integration,and long-term durability.In this review,the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted.After introducing metal AM processes,biocompatible metals adapted for integration with AM machines are presented.Then,we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including,topology optimization techniques,as well as unit cell patterns based on lattice networks,and triply periodic minimal surface.Here,the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed.Subsequently,the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters.We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation.Finally,we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.

Recent advances in biopolymer-based hemostatic materials

Hemorrhage is the leading cause of trauma-related deaths,in hospital and prehospital settings.Hemostasis is a complex mechanism that involves a cascade of clotting factors and proteins that result in the formation of a strong clot.In certain surgical and emergency situations,hemostatic agents are needed to achieve faster blood coagulation to prevent the patient from experiencing a severe hemorrhagic shock.Therefore,it is critical to consider appropriate materials and designs for hemostatic agents.Many materials have been fabricated as hemostatic agents,including synthetic and naturally derived polymers.Compared to synthetic polymers,natural polymers or biopolymers,which include polysaccharides and polypeptides,have greater biocompatibility,biodegradability and processibility.Thus,in this review,we focus on biopolymer-based hemostatic agents of different forms,such as powder,particles,sponges and hydrogels.Finally,we discuss biopolymer-based hemostatic materials currently in clinical trials and offer insight into next-generation hemostats for clinical translation.

The unique ORF8 protein from SARS-CoV-2 binds to human dendritic cells and induces a hyper-inflammatory cytokine storm

The novel coronavirus pandemic,first reported in December 2019,was caused by the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).SARS-CoV-2 infection leads to a strong immune response and activation of antigen-presenting cells,which can elicit acute respiratory distress syndrome(ARDS)characterized by the rapid onset of widespread inflammation,the so-called cytokine storm.In response to viral infections,monocytes are recruited into the lung and subsequently differentiate into dendritic cells(DCs).DCs are critical players in the development of acute lung inflammation that causes ARDS.Here,we focus on the interaction of a specific SARS-CoV-2 open reading frame protein,ORF8,with DCs.We show that ORF8 binds to DCs,causes pre-maturation of differentiating DCs,and induces the secretion of multiple proinflammatory cytokines by these cells.In addition,we identified DC-SIGN as a possible interaction partner of ORF8 on DCs.Blockade of ORF8 leads to reduced production of IL-1β,IL-6,IL-12p70,TNF-α,MCP-1(also named CCL2),and IL-10 by DCs.Therefore,a neutralizing antibody blocking the ORF8-mediated cytokine and chemokine response could be an improved therapeutic strategy against SARS-CoV-2.