A complementary density gradient of zwitterionic polymer brushes and NCAM peptides for selectively controlling directional migration of Schwann cells

Systematic Comparison of Commercial Hydrogels Revealed That a Synergy of Laminin and Strain-Stiffening Promotes Directed Migration of Neural Cells

Hydrogels have shown potential in replacing damaged nerve tissue, but the ideal hydrogel is yet to be found. In this study, various commercially available hydrogels were compared. Schwann cells, fibroblasts, and dorsal root ganglia neurons were seeded on the hydrogels, and their morphology, viability, proliferation, and migration were examined. Additionally, detailed analyses of the gels' rheological properties and topography were conducted. Our results demonstrate vast differences on cell elongation and directed migration on the hydrogels. Laminin was identified as the driver behind cell elongation and in combination with a porous, fibrous, and strain-stiffening matrix structure responsible for oriented cell motility. This study improves our understanding of cell-matrix interactions and thereby facilitates tailored fabrication of hydrogels in the future.

Multifaceted polymeric nerve guidance conduits with distinctive double-layered architecture and plasma-induced inner chemistry gradient for the repair of critical-sized defects

Despite tissue engineering advances, current nerve guidance conduits (NGCs) are still failing in repairing critical-sized defects. This study aims, therefore, at tackling large nerve gaps (2 cm) by designing NGCs possessing refined physicochemical properties enhancing the activity of Schwann cells (SCs) that support nerve regeneration over long distances. As such, a combinatorial strategy adopting novel plasma-induced surface chemistry and architectural heterogeneity was considered. A mechanically suitable copolymer (Polyactive®) was electrospun to produce nanofibrous NGCs mimicking the extracellular matrix. An innovative seamless double-layered architecture consisting of an inner wall comprised of bundles of aligned fibers with intercalated random fibers and an outer wall fully composed of random fibers was conceived to synergistically provide cell guidance cues and sufficient nutrient inflow. NGCs were subjected to argon plasma treatments using a dielectric barrier discharge (DBD) and a plasma jet (PJ). Surface chemical changes were examined by advanced X-ray photoelectron spectroscopy (XPS) micro-mappings. The DBD homogeneously increased the surface oxygen content from 17 % to 28 % on the inner wall. The PJ created a gradient chemistry throughout the inner wall with an oxygen content gradually increasing from 21 % to 30 %. In vitro studies revealed enhanced primary SC adhesion, elongation and proliferation on plasma-treated NGCs. A cell gradient was observed on the PJ-treated NGCs thus underlining the favorable oxygen gradient in promoting cell chemotaxis. A gradual change from circular to highly elongated SC morphologies mimicking the bands of Büngner was visualized along the gradient. Overall, plasma-treated NGCs are promising candidates paving the way towards critical nerve gap repair.

Fabrication of Polysulfobetaine Gradient Coating via Oxidation Polymerization of Pyrogallol To Modulate Biointerfaces

A surface with a gradient physical or chemical feature, such as roughness, hardness, wettability, and chemistry, serves as a powerful platform for high-throughput investigation of cell responses to a biointerface. In this work, we developed a continuous antifouling gradient surface using pyrogallol (PG) chemistry. A copolymer of a zwitterionic monomer, sulfobetaine methacrylate, and an amino monomer, aminoethyl methacrylate, were synthesized (pSBAE) and deposited on glass slides via the deposition of self-polymerized PG. A gradient of pSBAE was fabricated on glass slides in 7 min in the presence of an oxidant, ammonium persulfate, by withdrawing the reaction solution. The modified glass slide showed a wettability gradient, determined by measuring the water contact angle. Cell adhesion and protein adsorption were well correlated with surface wettability. We expect that this simple and faster method for the fabrication of a continuous chemical gradient is applicable for high-throughput screening of surface properties to modulate biointerfaces.

Micropatterns and peptide gradient on the inner surface of a guidance conduit synergistically promotes nerve regeneration in vivo

Both of the surface topographical features and distribution of biochemical cues can influence the cell-substrate interactions and thereby tissue regeneration in vivo. However, they have not been combined simultaneously onto a biodegradable scaffold to demonstrate the synergistic role so far. In this study, a proof-of-concept study is performed to prepare micropatterns and peptide gradient on the inner wall of a poly (D,L-lactide-co-caprolactone) (PLCL) guidance conduit and its advantages in regeneration of peripheral nerve in vivo. After linear ridges/grooves of 20/40 μm in width are created on the PLCL film, its surface is aminolyzed in a kinetically controlled manner to obtain the continuous gradient of amino groups, which are then transferred to CQAASIKVAV peptide density gradient via covalent coupling of glutaraldehyde. The Schwann cells are better aligned along with the stripes, and show a faster migration rate toward the region of higher peptide density. Implantation of the nerve guidance conduit made of the PLCL film having both the micropatterns and peptide gradient can significantly accelerate the regeneration of sciatic nerve in terms of rate, function recovery and microstructures, and reduction of fibrosis in muscle tissues. Moreover, this nerve conduit can also benefit the M2 polarization of macrophages and promote vascularization in vivo.

Cell Adhesion and Migration on Thickness Gradient Bilayer Polymer Brush Surfaces: Effects of Properties of Polymeric Materials of the Underlayer

In the field of tissue engineering and biomaterials, controlling the surface properties and mechanical properties of scaffold materials is crucial and has attracted much attention. Here, two types of bilayer polymer brushes composed of a hydrophilic underlying layer and a cationic surface layer [made of poly(2-aminoethyl methacrylate)] with a thickness gradient were prepared by surface-initiated atom-transfer radical polymerization. To investigate the influence of the stiffness as a mechanical property of the polymer brush on cell behavior, the underlayer was prepared from either 2-methacryloyloxyethyl phosphorylcholine or oligo(ethylene glycol) methyl ether methacrylate, with the bilayers designated as gradient poly(2-methacryloyloxyethyl phosphorylcholine)-block-poly(2-aminoethyl methacrylate) [grad-pMbA] and gradient poly(oligo[ethylene glycol] methyl ether methacrylate)-block-poly(2-aminoethyl methacrylate) [grad-pEGbA], respectively. Characterization of these surfaces was performed by spectroscopic ellipsometry, X-ray reflectivity, and determination of the zeta potential, static contact angle, and force curve. These diblock copolymer brushes with a thickness gradient helped to distinguish the effects of the mechanical and surface properties of the brushes on cell behavior. The attachment and motility of L929 fibroblasts and epithelial MCF 10A cells on the fabricated brushes were then assessed. L929 cells had a round shape on the thin surface layer of grad-pMbA and spread well on thicker areas. In contrast, MCF 10A cells spread well in areas of any thickness of either grad-pMbA or grad-pEGbA. Single MCF 10A cells migrated randomly on grad-pMbA, whereas grouped cells started to climb up along the thickness gradient of grad-pMbA. In contrast, both single and grouped MCF 10A cells migrated randomly on grad-pEGbA. These thickness gradient diblock copolymer brushes are simple, reproducible, and reasonable platforms that can facilitate practical applications of biomaterials, for example, in tissue engineering and biomaterials.

Development of nanotechnology-mediated precision radiotherapy for anti-metastasis and radioprotection

Radiotherapy (RT), including external beam RT and internal radiation therapy, uses high-energy ionizing radiation to kill tumor cells.

Micropatterned Poly(D,L-Lactide-Co-Caprolactone) Conduits With KHI-Peptide and NGF Promote Peripheral Nerve Repair After Severe Traction Injury

Severe traction injuries after stretch to peripheral nerves are common and challenging to repair. The nerve guidance conduits (NGCs) are promising in the regeneration and functional recovery after nerve injuries. To enhance the repair of severe nerve traction injuries, in this study KHIFSDDSSE (KHI) peptides were grafted on a porous and micropatterned poly(D,L-lactide-co-caprolactone) (PLCL) film (MPLCL), which was further loaded with a nerve growth factor (NGF). The adhesion number of Schwann cells (SCs), ratio of length/width (L/W), and percentage of elongated SCs were significantly higher in the MPLCL-peptide group and MPLCL-peptide-NGF group compared with those in the PLCL group in vitro. The electromyography (EMG) and morphological changes of the nerve after severe traction injury were improved significantly in the MPLCL-peptide group and MPLCL-peptide-NGF group compared with those in the PLCL group in vivo. Hence, the NGCs featured with both bioactive factors (KHI peptides and NGF) and physical topography (parallelly linear micropatterns) have synergistic effect on nerve reinnervation after severe traction injuries.

Zwitterionic nanogels with temperature sensitivity and redox-degradability for controlled drug release

Zwitterionic polymers play an attractive role in the application of stealthy nanocarriers for their excellent antifouling property. Herein, a zwitterionic nanogel with temperature sensitivity and redox-responsive degradability prepared by copolymerization of N-vinylcaprolactam (VCL) and 2-(methacryloyloxy) ethyldimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS) via aqueous precipitation polymerization. The prepared nanogels own ultra-high colloidal stability and non-specific protein adsorption resistance as a result of the incorporation of zwitterionic groups. Meanwhile, they exhibit sensitive temperature-induced swelling/collapse transition in aqueous solution and excellent redox-degradability ascribed to the presence of disulfide bonds. The nanogels loaded with anticancer drug doxorubicin (DOX) exhibit low leakage of DOX under physiological conditions (merely 23.8 % within 24 h), whereas striking release amount of DOX under reducing conditions combined with elevated temperature (93.4 % within 24 h). The measurement of cell viability showed that the cytotoxicity of blank nanogels to tumor cells (HeLa cells) was negligible, while the nanogels loaded with DOX had a prominent inhibitory impact on tumor cells.

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

Recent progress in creating complex and multiplexed surface-grafted macromolecular architectures

Surface-grafted macromolecules, including polymers, DNA, peptides, etc., are versatile modifications to tailor the interfacial functions in a wide range of fields. In this review, we aim to provide an overview of the most recent progress in engineering surface-grafted chains for the creation of complex and multiplexed surface architectures over micro- to macro-scopic areas. A brief introduction to surface grafting is given first. Then the fabrication of complex surface architectures is summarized with a focus on controlled chain conformations, grafting densities and three-dimensional structures. Furthermore, recent advances are highlighted for the generation of multiplexed arrays with designed chemical composition in both horizontal and vertical dimensions. The applications of such complicated macromolecular architectures are then briefly discussed. Finally, some perspective outlooks for future studies and challenges are suggested. We hope that this review will be helpful to those just entering this field and those in the field requiring quick access to useful reference information about the progress in the properties, processing, performance, and applications of functional surface-grafted architectures.

Tumor microenvironment-responsive multifunctional peptide coated ultrasmall gold nanoparticles and their application in cancer radiotherapy

Two important features are required for promising radiosensitizers: one is selective tumor cell targeting to enhance the therapeutic outcome via lethal DNA damage and the other is rapid clearance to enable excellent biocompatibility for potential clinical application. Herein, ultrasmall gold nanoparticles (Au NPs) with diameter smaller than 5 nm were prepared and covered with a multifunctional peptide to endow them with selective tumor cell uptake capability. Combined with X-ray irradiation, the responsive Au NPs demonstrated superior radio-sensitizing toxicity and rapid renal clearance in vivo. Methods: A responsive peptide (Tat-R-EK) consists of three build blocks were used: a cell and even nuclear penetrating block derived from human immunodeficiency virus-1 transactivator of transcription protein (Tat), an cathepsin B cleavable linker, and a zwitterionic antifouling block. Ultrasmall Au NPs were prepared and then covered by the peptide via the Au-S bonds between gold and thiol groups from cysteine. The morphology, colloidal stability and the responsiveness of obtained Au@Tat-R-EK NPs were studied using transmittance electron microscopy and dynamic laser scattering. The selective cancer cell uptake and accumulation of Au@Tat-R-EK NPs in cancer tissue were studied via ICP-MS in vitro and in vivo, respectively. The cytotoxicity of Au@Tat-R-EK NPs on HepG2 cancer cells was evaluated in terms of cell viability, DNA damage, intracellular reactive oxygen species generation, and apoptosis analysis. Finally, the biocompatibility and tumor destruction ability against orthotopic LM3 liver cancers were verified in vivo. Results: Multifunctional peptide modified ultrasmall Au NPs were successfully prepared. The Au NPs exhibited enough colloidal stability and cathepsin B-responsive surface change, leading to selectively uptake by cancer cells in vitro and accumulation to tumor sites in vivo. Combined with X-ray irradiation, the responsive Au NPs demonstrated superior radio-sensitizing cytotoxicity in vitro and therapeutic outcome on mouse liver cancer in vivo. The ultrasmall size enables rapid clearance of the Au NPs, guarantees the biocompatibility in vivo for potential clinical applications. Conclusion: Some obstacles faced by the Au NPs-based radiotherapy, such as short circulation half-life, non-specific distribution, slow clearance and low radio-sensitizing effect, were effective solved through rational design of the smart nanomedicine. This work provides new insight in designing tumor microenvironment-responsive nanomedicine in cancer radiotherapy.

Altered expression of glycoprotein non‑metastatic melanoma protein B in the distal sciatic nerve following injury

Glycoprotein non‑metastatic melanoma protein B (GPNMB) exerts neuroprotective effects on amyotrophic lateral sclerosis and cerebral ischemia reperfusion injury in the central nervous system. However, the expression and function of GPNMB in the peripheral nervous system, particularly following peripheral nerve injury, remains unknown. In the present study, the mRNAs and long non‑coding RNAs of the distal sciatic nerve were profiled via microarray analysis at days 0, 1, 3, 7, 14, 21 and 28 following transection. The results revealed that the expression of GPNMB mRNA was similar to the proliferation tendency of distal acute denervated Schwann cells (SCs), the results of which were further validated by reverse transcription quantitative polymerase chain reaction, western blot analysis and immunohistochemistry. To investigate the function of GPNMB on SCs, recombinant human GPNMB (rhGPNMB) was added to cultured denervated SCs from the distal stumps of transected sciatic nerve. The proliferation, expression and secretion of neurotrophic factors (NTFs) and neural adhesion molecules (NAMs) were subsequently detected. The results demonstrated that GPNMB expression was increased in distal sciatic nerve following transection in vivo, while rhGPNMB promoted the proliferation of SCs as well as expression and secretion of NTFs and NAMs in vitro. Therefore, GPNMB could be a novel strategy for peripheral nerve regeneration.

Surface-Anchored Graphene Oxide Nanosheets on Cell-Scale Micropatterned Poly(d,l-lactide-co-caprolactone) Conduits Promote Peripheral Nerve Regeneration

Regeneration and functional recovery of peripheral nerves remain formidable due to the inefficient physical and chemical cues in the available nerve guidance conduits (NGCs). Introducing micropatterns and bioactive substances into the inner wall of NGCs can effectively regulate the behavior of Schwann cells, the elongation of axons, and the phenotype of macrophages, thereby aiding the regeneration of injured nerve. In this study, linear micropatterns with ridges and grooves of 3/3, 5/5, 10/10, and 30/30 μm were created on poly(d,l-lactide-co-caprolactone) (PLCL) films following with surface aminolysis and electrostatic adsorption of graphene oxide (GO) nanosheets. The GO-modified micropatterns could significantly accelerate the collective migration of Schwann cells (SCs) and migration of SCs from their spheroids in vitro. Moreover, the SCs migrated directionally along the stripes with a fastest rate on the 3/3-GO film that had the largest cell adhesion force. The neurites of N2a cells were oriented along the micropatterns, and the macrophages tended to differentiate into the M2 type on the 3/3-GO film judged by the higher expression of Arg 1 and IL-10. The systematic histological and functional assessments of the regenerated nerves at 4 and 8 weeks post-surgery in vivo confirmed that the 3/3-GO NGCs had better performance to promote the nerve regeneration, and the CMAP, NCV, wet weight of gastrocnemius muscle, positive S100β and NF200 area percentages, and average myelinated axon diameter were more close to those of the autograft group at 8 weeks. This type of NGCs thus has a great potential for nerve regeneration.

Enhancing Schwann cell migration using concentration gradients of laminin-derived peptides

Neuroregeneration following peripheral nerve injury is largely mediated by Schwann cells (SC), the principal glial cell that supports neurons in the peripheral nervous system. Axonal regeneration in vivo is limited by the extent of SC migration into the gap between the proximal and distal nerve, however, little is known regarding the principal driving forces for SC migration. Engineered microenvironments, such as molecular and protein gradients, play a role in the migration of many cell types, including cancer cells and fibroblasts. However, haptotactic strategies have not been applied widely to SC. Herein, a series of tethered laminin-derived peptides were analyzed for their influence on SC adhesion, proliferation, and alignment. Concentration gradient substrates were fabricated using a controlled vapor deposition method, followed by covalent peptide attachment via a thiol-ene reaction, and characterized by X-ray photoelectron spectroscopy (XPS) and MALDI-MS imaging. While tethered RGD peptides supported SC adhesion and proliferation, concentration gradients of RGD had little influence on biased SC directional migration. In contrast, YIGSR promoted less SC attachment than RGD, yet YIGSR peptide gradients directed migration with a strong bias to the concentration profile. With YIGSR peptide, overall speed increased with the steepness of the peptide concentration profile. YIGSR gradients had no haptotactic effect on rat dermal fibroblast migration, in contrast to fibroblast migration on RGD gradients. The response of SC to these tethered peptide gradients will guide the development of translationally relevant constructs designed to facilitate endogenous SC infiltration into defects for nerve regeneration.

Enzyme-responsive multifunctional peptide coating of gold nanorods improves tumor targeting and photothermal therapy efficacy

It is well known that stealth coating effectively extends the circulation lifetime of nanomaterials in blood, which favors systemic delivery but also limits their cellular internalization and in turn prevents efficient tumor-targeting and accumulation. In this study, we address this dilemma by developing an enzyme-responsive zwitterionic stealth peptide coating capable of responding to matrix metalloproteinase-9 (MMP-9) which is overexpressed in tumor microenvironment. The peptide consists of a cell-penetrating Tat sequence, an MMP-9 cleavable sequence, and a zwitterionic antifouling sequence. Using this coating to protect photothermal gold nanorods (AuNRs), we found that responsive AuNRs showed both satisfactory systemic circulation lifetime and significantly enhanced cellular uptake in tumors, resulting in clearly improved photothermal therapeutic efficacy in mouse models. These results suggest that multifunctional peptide coated AuNRs sensitive to MMP-9 are promising nanomaterials, conferring both extended systemic circulation and enhanced tumor tissue accumulation, for more specific and efficient tumor therapy. STATEMENT OF SIGNIFICANCE: It is well known that stealth coating effectively extends the circulation lifetime of nanomaterials in blood, which favors systemic delivery but also limits their cellular internalization and in turn prevents efficient tumor-targeting and accumulation. In this study, we address this dilemma by developing an enzyme-responsive zwitterionic stealth peptide coating capable of responding to matrix metalloproteinase-9 (MMP-9) which is overexpressed in tumor microenvironment. The peptide consists of a cell-penetrating Tat sequence, an MMP-9 cleavable sequence, and a zwitterionic antifouling sequence. Using this coating to protect photothermal gold nanorods (AuNRs), we found that responsive AuNRs showed both satisfactory systemic circulation lifetime and significantly enhanced cellular uptake in tumors, resulting in clearly improved photothermal therapeutic efficacy in mouse models.

3-D geometry and irregular connectivity dictate neuronal firing in frequency domain and synchronization

The replication of the complex structure and three dimensional (3-D) interconnectivity of neurons in the brain is a great challenge. A few 3-D neuronal patterning approaches have been developed to mimic the cell distribution in the brain but none have demonstrated the relationship between 3-D neuron patterning and network connectivity. Here, we used photolithographic crosslinking to fabricate in vitro 3-D neuronal structures with distinct sizes, shapes or interconnectivities, i.e., milli-blocks, micro-stripes, separated micro-blocks and connected micro-blocks, which have spatial confinement from "Z" dimension to "XYZ" dimension. During a 4-week culture period, the 3-D neuronal system has shown high cell viability, axonal, dendritic, synaptic growth and neural network activity of cortical neurons. We further studied the calcium oscillation of neurons in different 3-D patterns and used signal processing both in Fast Fourier Transform (FFT) and time domain (TD) to model the fluorescent signal variation. We observed that the firing frequency decreased as the spatial confinement in 3-D system increased. Besides, the neuronal synchronization significantly decreased by irregularly connecting micro-blocks, indicating that network connectivity can be adjusted by changing the linking conditions of 3-D gels. Earlier works showed the importance of 3-D culture over 2-D in terms of cell growth. Here, we showed that not only 3-D geometry over 2-D culture matters, but also the spatial organization of cells in 3-D dictates the neuronal firing frequency and synchronicity.

Temperature-Gating Titania Nanotubes Regulate Migration of Endothelial Cells

External stimuli-responsive biomaterials represent a type of promising candidates for addressing the complexity of biological systems. In this study, a platform based on the combination of temperature-sensitive polymers and a nanotube array was developed for loading sphingosine 1-phosphate (S1P) and regulating the migration of endothelial cells (ECs) at desired conditions. The localized release dosage of effectors could be controlled by the change of environmental temperature. At a culture temperature above the lower critical solution temperature, the polymer "gatekeeper" with a collapsed conformation allowed the release of S1P, which in turn enhanced the migration of ECs. The migration rate of single cells was significantly enhanced up to 58.5%, and the collective migration distance was also promoted to 25.1% at 24 h and 33.2% at 48 h. The cell morphology, focal adhesion, organization of cytoskeleton, and expression of genes and proteins related to migration were studied to unveil the intrinsic mechanisms. The cell mobility was regulated by the released S1P, which would bind with the S1PR1 receptor on the cell membrane and trigger the Rho GTPase pathway.

Doxorubicin-conjugated pH-responsive gold nanorods for combined photothermal therapy and chemotherapy of cancer

Cancer chemotherapy can be hindered by drug resistance which leads to lower drug efficiency. Here, we have developed a drug delivery system that tethers doxorubicin to the surface of gold nanorods via a pH-sensitive linkage (AuNRs@DOX), for a combined photothermal and chemical therapy for cancer. First, AuNRs@DOX is ingested by HepG2 liver cancer cells. After endocytosis, the acidic pH triggers the release of doxorubicin, which leads to chemotherapeutic effects. The gold nanorods are not only carriers of DOX, but also photothermal conversion agents. In the presence of an 808 nm near-infrared laser, AuNRs@DOX significantly enhance the cytotoxicity of doxorubicin via the photothermal effect, which induces elevated apoptosis of hepG2 cancer cells, leading to better therapeutic effects in vitro and in vivo.

Folic acid modified cell membrane capsules encapsulating doxorubicin and indocyanine green for highly effective combinational therapy in vivo

A combination of chemotherapy and phototherapy has emerged as a promising strategy for cancer treatment. To achieve effective combinational therapy of cancer with reduced toxicity, it is highly desirable to improve the targeting of chemotherapeutic and near-infrared photosensitizers to enhance their accumulation in tumor. Here we report a novel tumor targeting cell membrane capsule (CMC), originate from living cells, to load doxorubicin hydrochloride (DOX) and indocyanine green (ICG), for combinational photo-chemotherapy against cancer. As a result, folic acid modified CMC (CMC-FA, with a diameter about 200 nm and a FA density of 0.4 molecule/nm²) showed 3-4 fold higher cell uptake by cancer cells in vitro and 2.3 times higher accumulation in mouse cancer xenografts in vivo than pristine CMC. DOX and ICG with therapeutically significant concentrations can be sequentially encapsulated into CMC-FA by temporary permeating the plasma membranes with high efficiency. The systematic administration of cancer targeting CMC-FA loaded with DOX and ICG could significantly inhibit tumor growth in mouse xenografts in the presence of a near-infrared light at 808 nm, without noticeable toxicity. These findings suggest that cancer targeting CMC may have considerable benefits in drug delivery and combinational cancer therapy.

STATEMENT OF SIGNIFICANCE

A combination of chemotherapy and photothermal/photodynamic therapy has emerged as a promising strategy for cancer therapy. In current study, a novel cancer targeting cell membrane capsule (CMC-FA), originate from living cells and surface modified with folic acid, was developed to load doxorubicin hydrochloride (DOX) and indocyanine green (ICG), for combinational photo-chemotherapy against cancer. The systematic administration of drug loaded CMC-FA can significantly inhibit tumor growth in mouse xenografts in the presence of a near-infrared light at 808 nm, without noticeable toxicity. This study provides a simple and robust strategy to develop biocompatible therapeutic cell membrane capsules, holds strong translational potential in precise cancer treatment.

A density gradient of VAPG peptides on a cell-resisting surface achieves selective adhesion and directional migration of smooth muscle cells over fibroblasts

Selective adhesion and migration of smooth muscle cells (SMCs) over fibroblasts (FIBs) is required to prevent adventitia fibrosis in vascular regeneration. In this study, a uniform cell-resisting layer of poly(ethylene glycol) (PEG) with a density gradient of azide groups was generated on a substrate by immobilizing two kinds of PEG molecules in a gradient manner. A density gradient of alkynyl-functionalized Val-Ala-Pro-Gly (VAPG) peptides was then prepared on the PEG layer via click chemistry. The VAPG density gradient was characterized by fluorescence imaging, revealing the gradual enhancement of the fluorescent intensity along the substrate direction. The adhesion and mobility of SMCs were selectively enhanced on the VAPG density gradient, leading to directional migration toward the higher peptide density (up to 84%). In contrast, the adhesion and mobility of FIBs were significantly weakened. The net displacement of SMCs also significantly increased compared with that on tissue culture polystyrene (TCPS) and that of FIBs on the gradient. The mitogen-activated protein kinase (MAPK) signaling pathways related to cell migration were studied, showing higher expressions of functional proteins from SMCs on the VAPG-modified surface in a density-dependent manner. For the first time the selective adhesion and directional migration of SMCs over FIBs was achieved by an elaborative design of a gradient surface, leading to a new insight in design of novel vascular regenerative materials.

STATEMENT OF SIGNIFICANCE

Selective cell adhesion and migration guided by regenerative biomaterials are extremely important for the regeneration of targeted tissues, which can avoid the drawbacks of incorrect and uncontrolled responses of tissue cells to implants. For example, selectivity of smooth muscle cells (SMCs) over fibroblasts (FIBs) is required to prevent adventitia fibrosis in vascular regeneration. Herein we prepare a uniform cell-repelling layer, on which SMCs-selective Val-Ala-Pro-Gly (VAPG) peptides are immobilized in a continuous manner. Selective adhesion and enhanced and directional migration of SMCs over FIBs are achieved by the interplay of cell-repelling layer and gradient SMCs-selective VAPG peptides, paving a new way for the design of novel vascular grafts with enhanced biological performance.

Design and Applications of Cell-Selective Surfaces and Interfaces

Tissue regeneration involves versatile types of cells. The accumulation and disorganized behaviors of undesired cells impair the natural healing process, leading to uncontrolled immune response, restenosis, and/or fibrosis. Cell-selective surfaces and interfaces can have specific and positive effects on desired types of cells, allowing tissue regeneration with restored structures and functions. This review outlines the importance of surfaces and interfaces of biomaterials with cell-selective properties. The chemical and biological cues including peptides, antibodies, and other molecules, physical cues such as topography and elasticity, and physiological cues referring mainly to interactions between cells-cells and cell-chemokines or cytokines are effective modulators for achieving cell selectivity upon being applied into the design of biomaterials. Cell-selective biomaterials have also shown practical significance in tissue regeneration, in particular for endothelialization, nerve regeneration, capture of stem cells, and regeneration of tissues of multiple structures and functions.

Gradient Material Strategies for Hydrogel Optimization in Tissue Engineering Applications

Although a number of combinatorial/high-throughput approaches have been developed for biomaterial hydrogel optimization, a gradient sample approach is particularly well suited to identify hydrogel property thresholds that alter cellular behavior in response to interacting with the hydrogel due to reduced variation in material preparation and the ability to screen biological response over a range instead of discrete samples each containing only one condition. This review highlights recent work on cell-hydrogel interactions using a gradient material sample approach. Fabrication strategies for composition, material and mechanical property, and bioactive signaling gradient hydrogels that can be used to examine cell-hydrogel interactions will be discussed. The effects of gradients in hydrogel samples on cellular adhesion, migration, proliferation, and differentiation will then be examined, providing an assessment of the current state of the field and the potential of wider use of the gradient sample approach to accelerate our understanding of matrices on cellular behavior.

Micropatterned poly(d,l-lactide-co-caprolactone) films entrapped with gelatin for promoting the alignment and directional migration of Schwann cells

Gelatin entrapped and micropatterned poly(d,l-lactide-co-caprolactone) (PLCL) film promotes the alignment and directional migration of Schwann cells.

Examining lysozyme structures on polyzwitterionic brush surfaces

Conformational structures of lysozyme at the interfaces of hydrophilic polymer poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide] (PMEDSAH), are examined to understand the role of protein-polymer interactions on the stability of lysozyme. This work underpins the effect of hydration layer on the structures of physically adsorbed lysozyme on PMEDSAH brushes. Hydrophilic nature and strength of hydration layers around brushes are controlled by varying the brush thickness and temperature. We measured that lysozyme is structurally less stable on 15nm thick hydrophilic PMEDSAH brushes at 75°C than at room temperature. To the contrary, 5-8nm thick brushes stretch in hydrated state by heating, hence yield higher structural stability of lysozyme. These results suggest that short polyzwitterionic brushes can facilitate improved biomaterial interactions that are essential for biosensors performing at elevated temperatures.

Favorable Biological Responses of Neural Cells and Tissue Interacting with Graphene Oxide Microfibers

Neural tissue engineering approaches show increasing promise for the treatment of neural diseases including spinal cord injury, for which an efficient therapy is still missing. Encouraged by both positive findings on the interaction of carbon nanomaterials such as graphene with neural components and the necessity of more efficient guidance structures for neural repair, we herein study the potential of reduced graphene oxide (rGO) microfibers as substrates for neural growth in the injured central neural tissue. Compact, bendable, and conductive fibers are obtained. When coated with neural adhesive molecules (poly-l-lysine and N-cadherin), these microfibers behave as supportive substrates of highly interconnected cultures composed of neurons and glial cells for up to 21 days. Synaptic contacts close to rGO are identified. Interestingly, the colonization by meningeal fibroblasts is dramatically hindered by N-cadherin coating. Finally, in vivo studies reveal the feasible implantation of these rGO microfibers as a guidance platform in the injured rat spinal cord, without evident signs of subacute local toxicity. These positive findings boost further investigation at longer implantation times to prove the utility of these substrates as components of advanced therapies for enhancing repair in the damaged central neural tissue including the injured spinal cord.

Controlling Molecular Weight of Hyaluronic Acid Conjugated on Amine-rich Surface: Toward Better Multifunctional Biomaterials for Cardiovascular Implants

The molecular weights (MWs) of hyaluronic acid (HA) in extracellular matrix secreted from both vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) play crucial roles in the cardiovascular physiology, as HA with appropriate MW influences important pathways of cardiovascular homeostasis, inhibits VSMC synthetic phenotype change and proliferation, inhibits platelet activation and aggregation, promotes endothelial monolayer repair and functionalization, and prevents inflammation and atherosclerosis. In this study, HA samples with gradients of MW (4 × 10³, 1 × 10⁵, and 5 × 10⁵ Da) were prepared by covalent conjugation to a copolymerized film of polydopamine and hexamethylendiamine (PDA/HD) as multifunctional coatings (PDA/HD-HA) with potential to improve the biocompatibility of cardiovascular biomaterials. The coatings immobilized with high-MW-HA (PDA/HD-HA-2: 1 × 10⁵ Da; PDA/HD-HA-3: 5 × 10⁵ Da) exhibited a remarkable suppression of platelet activation/aggregation and thrombosis under 15 dyn/cm² blood flow and simultaneously suppressed the adhesion and proliferation of VSMC and the adhesion, activation, and inflammatory cytokine release of macrophages. In particular, PDA/HD-HA-2 significantly enhanced VEC adhesion, proliferation, migration, and functional factors release, as well as the captured number of endothelial progenitor cells under dynamic condition. The in vivo results indicated that the multifunctional surface (PDA/HD-HA-2) created a favorable microenvironment of endothelial monolayer formation and functionalization for promoting reendothelialization and reducing restenosis of cardiovascular biomaterials.

Controlling the selective and directional migration of hepatocytes by a complementary density gradient of glycosylated hyperbranched polymers and poly(ethylene glycol) molecules

Repair and regeneration of defected tissues and organs depends strongly on the directional migration of targeted cells, for example, the enhancement of directional migration of hepatocytes could be helpful in liver regeneration and transplantation. Herein a complementary gradient of galactose-modified hyperbranched polymers (LA-HPMA) and poly(ethylene glycol) (PEG) molecules was designed and prepared on a same substrate. Characterizations of X-ray photoelectron spectrometry and quartz crystal microbalance with dissipation (QCM-d) demonstrated the unidirectional change in grafting density of LA-HPMA and PEG molecules, respectively. On the LA-HPMA/PEG complementary gradient surface, the human hepatoma (HepG2) cells showed preferential orientation and enhanced directional migration toward the region of lower PEG density and higher LA-HPMA density. By contrast, the mouse embryonic fibroblasts (NIH3T3) showed random migration irrelevant to the gradient. The success of the complementary gradient relies on the specific interaction between galactose and asialoglycoprotein receptor (ASGPR) expressed on HepG2 cells. STATEMENT OF SIGNIFICANCE.

Induced migration of endothelial cells into 3D scaffolds by chemoattractants secreted by pro-inflammatory macrophages in situ

Cell migration in scaffolds plays a crucial role in tissue regeneration, which can better mimic cell behaviors in vivo. In this study, a novel model has been proposed on controlling 3D cell migration in porous collagen-chitosan scaffolds with various pore structures under the stimulation of inflammatory cells to mimic the angiogenesis process. Endothelial cells (ECs) cultured atop the scaffolds in the Transwell molds which were placed into a well of a 24-well culture plate were promoted to migrate into the scaffolds by chemoattractants such as vascular endothelial growth factor (VEGF) and tumor necrosis factor-alpha (TNF-α) secreted by the pro-inflammatory macrophages incubated in the well culture plate. The phenotype of macrophages was mediated by 50 ng/ml interferon-gamma (IFN-γ) and different concentrations of lipopolysaccharide (LPS, 150-300 ng/ml). The cell migration depth had a positive correlation with LPS concentration, and thereby the TNF-α concentration. The ECs migrated easier to a deeper zone of the scaffolds prepared at - 10ºC (187 μm in pore diameter) than that at - 20ºC (108 μm in pore diameter) as well. The method provides a useful strategy to study the 3D cell migration, and is helpful to reveal the vascularization process during wound healing in the long run.

Poly(l-lactide) melt spun fiber-aligned scaffolds coated with collagen or chitosan for guiding the directional migration of osteoblasts in vitro

PLLA melt spun fiber-aligned scaffolds coated with collagen or chitosan enhance the viability, spreading, alignment and mobility of osteoblasts.

Biohybrid methacrylated gelatin/polyacrylamide hydrogels for cartilage repair

We prepared a biohybrid hydrogel based on acrylamide and GelMA, having good mechanical properties, thermal stability, and bioactivity for cartilage regeneration.

Preparation of an Arg-Glu-Asp-Val Peptide Density Gradient on Hyaluronic Acid-Coated Poly(ε-caprolactone) Film and Its Influence on the Selective Adhesion and Directional Migration of Endothelial Cells

Selective adhesion and migration of endothelial cells (ECs) over smooth muscle cells (SMCs) is very important in the rapid endothelialization of blood-contacting implants to prevent vascular restenosis. In this study, a uniform cell-resistant layer of methacrylate-functionalized hyaluronic acid (HA) was first immobilized on a poly(ε-caprolactone) (PCL) film via polydopamine coupling. Then, a density gradient of thiol-functionalized Arg-Glu-Asp-Val (REDV) peptide was prepared on the HA layer via thiol-ene click chemistry and the continuous injection method. The REDV gradient selectively enhanced EC adhesion and preferential directional migration toward the region of higher REDV density, reaching 86% directionality in the middle of the gradient. The migration rate of ECs was also significantly enhanced twofold compared with that on tissue culture polystyrene (TCPS). In contrast, the gradient significantly weakened the adhesion of SMCs to 25% of that on TCPS but had no obvious impact on the migration rate and directionality. Successful modulation of the selective adhesion and directional migration of ECs over SMCs on biodegradable polymers serves as an important step toward practical applications for guided tissue regeneration.

Peripheral Nerve Regeneration: Current Status and New Strategies Using Polymeric Materials

Experiments concerning peripheral nerve regeneration have been reported since the end of the 19^th century. The need to implement an effective surgical procedure in terms of functional recovery has resulted in the appearance of several approaches to solve this problem. Nerve autograft was the first approach studied and is still considered the gold standard. Since autografts require donor harvesting, other strategies involving the use of natural materials have also been studied. Nevertheless, the results were not very encouraging and attention has moved towards the use of nerve conduits made from polymers, whose properties can be easily tailored and which allow the nerve conduit to be easily processed into a variety of shapes and forms. Some of these materials are already approved by the US Food and Drug Administration (FDA), as is presented here. Furthermore, polymers with conductive properties have very recently been subject to intensive study in this field, since it is believed that such properties have a positive influence in the regeneration of the new axons. This manuscript intends to give a global view of the mechanisms involved in peripheral nerve regeneration and the main strategies used to recover motor and sensorial function of injured nerves.

Encapsulation of indocyanine green into cell membrane capsules for photothermal cancer therapy

Although indocyanine green (ICG) has promising applications in photothermal therapy (PPT) because of its low toxicity and high efficiency in inducing heat and singlet oxygen formation in response to near-infrared light with a wavelength of approximately 800nm, its clinical application has been restricted because of its rapid body clearance and poor water stability. Therefore, cell membrane capsules (CMCs) derived from mammalian cells were used to encapsulate negatively charged ICG by temporarily permeating the plasma membrane and resealing using positively charged doxorubicin hydrochloride (DOX). The resulting CMCs@DOX/ICG exhibited a spherical shape, with a diameter of approximately 800nm. The DOX and ICG encapsulation was confirmed by the UV-vis spectrum; a very small amount of DOX (0.8μg) and a very high amount of ICG (∼110μg) were encapsulated in 200μg CMCs. Encapsulation in the CMCs leads to sustained release of ICG, especially in the presence of positively charged DOX. The temperature enhancement and generation of ROS by ICG encapsulated in CMCs were confirmed upon laser irradiation in vitro, leading to cell death. CMCs@DOX/ICG also can significantly enhance the retention of ICG in a tumor after intratumoral injection in vivo. As a result, combination treatment with CMCs@DOX/ICG and laser irradiation demonstrated much better anticancer efficacy than that of free DOX/ICG and CMCs@ICG. The encapsulation of ICG into CMCs, especially with the assistance of DOX, significantly slows down the body clearance of ICG, with a retained PPT effect against tumors, an important step forward in the practical application of ICG in cancer therapy.

STATEMENT OF SIGNIFICANCE

In this study, cell membrane capsules (CMCs) derived from mammalian cells were used to encapsulate negatively charged indocyanine green (ICG) by temporarily permeating the plasma membrane and resealing, in the presence of positively charged doxorubicin hydrochloride (DOX). The resulting CMCs@DOX/ICG exhibited a spherical shape, with a diameter of approximately 800nm. Encapsulation in the CMCs leads to sustained release of ICG and thus slower clearance inside body, especially in the presence of positively charged DOX. The system provides a better photothermal effect against tumors, an important step forward in the practical application of ICG in cancer therapy.

Encapsulation of a photosensitizer into cell membrane capsules for photodynamic therapy

CMCs were used to encapsulate MB (CMCs@MB) using temporary permeation of the plasma membrane and resealing. Encapsulation in the CMCs leads to sustained release of MB with enhanced stability against enzymatic reduction and reduced toxicity.

Cellular uptake of poly(allylamine hydrochloride) microcapsules with different deformability and its influence on cell functions

It is important to understand the safety issue and cell interaction pattern of polyelectrolyte microcapsules with different deformability before their use in biomedical applications. In this study, SiO2, poly(sodium-p-styrenesulfonate) (PSS) doped CaCO3 and porous CaCO3 spheres, all about 4μm in diameter, were used as templates to prepare microcapsules with different inner structure and subsequent deformability. As a result, three kinds of covalently assembled poly(allylaminehydrochloride)/glutaraldehyde (PAH/GA) microcapsules with similar size but different deformability under external osmotic pressure were prepared. The impact of different microcapsules on cell viability and functions are studied using smooth muscle cells (SMCs), endothelial cells (ECs) and HepG2 cells. The results demonstrated that viabilities of SMCs, ECs and HepG2 cells were not significantly influenced by either of the three kinds of microcapsules. However, the adhesion ability of SMCs and ECs as well as the mobility of SMCs, ECs and HepG2 cells were significantly impaired after treatment with microcapsules in a deformability dependent manner, especially the microcapsules with lower deformability caused higher impairment on cell functions. The cellular uptake kinetics, uptake pathways, intracellular distribution of microcapsules are further investigated in SMCs to reveal the potential mechanism. The SMCs showed faster uptake rate and exocytosis rate of microcapsules with lower deformability (Cap@CaCO3/PSS and Cap@CaCO3), leading to higher intracellular accumulation of microcapsules with lower deformability and possibly larger retardation of cell functions. The results pointed out that the deformability of microcapsules is an important factor governing the biological performance of microcapsules, which requires careful adjustment for further biomedical applications.

Biomaterials for in situ tissue regeneration: development and perspectives

Biomaterials are of fundamental importance to in situ tissue regeneration, which has emerged as a powerful method to treat tissue defects. The development and perspectives of biomaterials for in situ tissue regeneration were summarized.

Monitoring the intracellular transformation process of surface-cleavable PLGA particles containing disulfide bonds by fluorescence resonance energy transfer

The FRET technique was used to quantify the surface cleavage kinetics of PLGA particles containing disulfide bonds in cells.

Development of zwitterionic copolymers with multi-shape memory effects and moisture-sensitive shape memory effects

This paper describes a new kind of zwitterionic copolymer having a multi-shape memory effect and a moisture-sensitive shape memory effect from DMAPS and acrylic acid (AA). In addition to dual-SME, the copolymer also shows triple-SME and quadruple-shape-memory effect.

Multifunctional REDV-conjugated zwitterionic polycarboxybetaine–polycaprolactone hybrid surfaces for enhanced antibacterial activity, anti-thrombogenicity and endothelial cell proliferation

Multifunctional PCL hybrid surfaces are developed by grafting of REDV–zwitterionic polycarboxybetaine conjugates via surface-initiated ATRP.