In Situ Triggered Self-Contraction Bioactive Microgel Assembly Accelerates Diabetic Skin Wound Healing by Activating Mechanotransduction and Biochemical Pathway.

Chronic nonhealing skin wounds, characterized by reduced tissue contractility and inhibited wound cell survival under hyperglycemia and hypoxia, present a significant challenge in diabetic care. Here, an advanced self-contraction bioactive core-shell microgel assembly with robust tissue-adhesion (SMART-EXO) is introduced to expedite diabetic wound healing. The SMART-EXO dressing exhibits strong, reversible adhesion to damaged tissue due to abundant hydrogen and dynamic coordination bonds. Additionally, the core-shell microgel components and dynamic coordination bonds provide moderate rigidity, customizable self-contraction, and an interlinked porous architecture. The triggered in situ self-contraction of the SMART-EXO dressing enables active, tunable wound contraction, activating mechanotransduction in the skin and promoting the optimal fibroblast-to-myofibroblast conversion, collagen synthesis, and angiogenesis. Concurrently, the triggered contraction of SMART-EXO facilitates efficient loading and on-demand release of bioactive exosomes, contributing to re-epithelialization and wound microenvironment regulation in diabetic mice. RNA-seq results reveal the activation of critical signaling pathways associated with mechanosensing and exosome regulation, highlighting the combined biomechanical and biochemical mechanisms. These findings underscore SMART-EXO as a versatile, adaptable solution to the complex challenges of diabetic wound care.

Superporous sponge prepared by secondary network compaction with enhanced permeability and mechanical properties for non-compressible hemostasis in pigs.

Developing superporous hemostatic sponges with simultaneously enhanced permeability and mechanical properties remains challenging but highly desirable to achieve rapid hemostasis for non-compressible hemorrhage. Typical approaches to improve the permeability of hemostatic sponges by increasing porosity sacrifice mechanical properties and yield limited pore interconnectivity, thereby undermining the hemostatic efficacy and subsequent tissue regeneration. Herein, we propose a temperature-assisted secondary network compaction strategy following the phase separation-induced primary compaction to fabricate the superporous chitosan sponge with highly-interconnected porous structure, enhanced blood absorption rate and capacity, and fatigue resistance. The superporous chitosan sponge exhibits rapid shape recovery after absorbing blood and maintains sufficient pressure on wounds to build a robust physical barrier to greatly improve hemostatic efficiency. Furthermore, the superporous chitosan sponge outperforms commercial gauze, gelatin sponges, and chitosan powder by enhancing hemostatic efficiency, cell infiltration, vascular regeneration, and in-situ tissue regeneration in non-compressible organ injury models, respectively. We believe the proposed secondary network compaction strategy provides a simple yet effective method to fabricate superporous hemostatic sponges for diverse clinical applications.

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-π interactions and stabilized with RGD ligand-bearing poly(acrylic acid). Near-infrared-upconverted-ultraviolet light induces cis-Azo+-mediated inflation that suppresses cation-π interactions, 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 self-assembly 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-π interactions, 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.

Surface hydrophobization of hydrogels via interface dynamics-induced network reconfiguration.

Effective and easy regulation of hydrogel surface properties without changing the overall chemical composition is important for their diverse applications but remains challenging to achieve. We report a generalizable strategy to reconfigure hydrogel surface networks based on hydrogel-substrate interface dynamics for manipulation of hydrogel surface wettability and bioadhesion. We show that the grafting of hydrophobic yet flexible polymeric chains on mold substrates can significantly elevate the content of hydrophobic polymer backbones and reduce the presence of polar groups in hydrogel surface networks, thereby transforming the otherwise hydrophilic hydrogel surface into a hydrophobic surface. Experimental results show that the grafted highly dynamic hydrophobic chains achieved with optimal grafting density, chain length, and chain structure are critical for such substantial hydrogel surface network reconfiguration. Molecular dynamics simulations further reveal the atomistic details of the hydrogel network reconfiguration induced by the dynamic interface interactions. The hydrogels prepared using our strategy show substantially enhanced bioadhesion and transdermal delivery compared with the hydrogels of the same chemical composition but fabricated via the conventional method. Our findings provide important insights into the dynamic hydrogel-substrate interactions and are instrumental to the preparation of hydrogels with custom surface properties.

Supramolecular Hydrogel with Ultra-Rapid Cell-Mediated Network Adaptation for Enhancing Cellular Metabolic Energetics and Tissue Regeneration.

Cellular energetics plays an important role in tissue regeneration, and the enhanced metabolic activity of delivered stem cells can accelerate tissue repair and regeneration. However, conventional hydrogels with limited network cell adaptability restrict cell-cell interactions and cell metabolic activities. In this work, it is shown that a cell-adaptable hydrogel with high network dynamics enhances the glucose uptake and fatty acid ß-oxidation of encapsulated human mesenchymal stem cells (hMSCs) compared with a hydrogel with low network dynamics. It is further shown that the hMSCs encapsulated in the high dynamic hydrogels exhibit increased tricarboxylic acid (TCA) cycle activity, oxidative phosphorylation (OXPHOS), and adenosine triphosphate (ATP) biosynthesis via an E-cadherin- and AMP-activated protein kinase (AMPK)-dependent mechanism. The in vivo evaluation further showed that the delivery of MSCs by the dynamic hydrogel enhanced in situ bone regeneration in an animal model. It is believed that the findings provide critical insights into the impact of stem cell-biomaterial interactions on cellular metabolic energetics and the underlying mechanisms.

Biomimetic Hydrogels as the Inductive Endochondral Ossification Template for Promoting Bone Regeneration.

Repairing critical size bone defects (CSBD) is a major clinical challenge and requires effective intervention by biomaterial scaffolds. Inspired by the fact that the cartilaginous template-based endochondral ossification (ECO) process is crucial to bone healing and development, developing biomimetic biomaterials to promote ECO is recognized as a promising approach for repairing CSBD. With the unique highly hydrated 3D polymeric network, hydrogels can be designed to closely emulate the physiochemical properties of cartilage matrix to facilitate ECO. In this review, the various preparation methods of hydrogels possessing the specific physiochemical properties required for promoting ECO are introduced. The materiobiological impacts of the physicochemical properties of hydrogels, such as mechanical properties, topographical structures and chemical compositions on ECO, and the associated molecular mechanisms related to the BMP, Wnt, TGF-ß, HIF-1α, FGF, and RhoA signaling pathways are further summarized. This review provides a detailed coverage on the materiobiological insights required for the design and preparation of hydrogel-based biomaterials to facilitate bone regeneration.

Complex coacervate-derived hydrogel with asymmetric and reversible wet bioadhesion for preventing UV light-induced morbidities.

Protecting the skin from UV light irradiation in wet and underwater environments is challenging due to the weak adhesion of existing sunscreen materials but highly desired. Herein we report a polyethyleneimine/thioctic acid/titanium dioxide (PEI/TA/TiO2) coacervate-derived hydrogel with robust, asymmetric, and reversible wet bioadhesion and effective UV-light-shielding ability. The PEI/TA/TiO2 complex coacervate can be easily obtained by mixing a PEI solution and TA/TiO2 powder. The fluid PEI/TA/TiO2 coacervate deposited on wet skin can spread into surface irregularities and subsequently transform into a hydrogel with increased cohesion, thereby establishing interdigitated contact and adhesion between the bottom surface and skin. Meanwhile, the functional groups between the skin and hydrogel can form physical interactions to further enhance bioadhesion, whereas the limited movement of amine and carboxyl groups on the top hydrogel surface leads to low adhesion. Therefore, the coacervate-derived hydrogel exhibits asymmetric adhesiveness on the bottom and top surfaces. Moreover, the PEI/TA/TiO2 hydrogel formed on the skin could be easily removed using a NaHCO3 aqueous solution without inflicting damage. More importantly, the PEI/TA/TiO2 hydrogel can function as an effective sunscreen to block UV light and prevent UV-induced MMP-9 overexpression, inflammation, and DNA damage in animal skin. The advantages of PEI/TA/TiO2 coacervate-derived hydrogels include robust, asymmetric, and reversible wet bioadhesion, effective UV light-shielding ability, excellent biocompatibility, and easy preparation and usage, making them a promising bioadhesive to protect the skin from UV light-associated damage in wet and underwater environments.

Biomimetic Nanofibrillar Hydrogel with Cell-Adaptable Network for Enhancing Cellular Mechanotransduction, Metabolic Energetics, and Bone Regeneration.

The natural extracellular matrix, with its heterogeneous structure, provides a stable and dynamic biophysical framework and biochemical signals to guide cellular behaviors. It is challenging but highly desirable to develop a synthetic matrix that emulates the heterogeneous fibrous structure with macroscopic stability and microscopical dynamics and contains inductive biochemical signals. Herein, we introduce a peptide fiber-reinforced hydrogel in which the stiff ß-sheet fiber functions as a multivalent cross-linker to enhance the hydrogel's macroscopic stability. The dynamic imine cross-link between the peptide fiber and polymer network endows the hydrogel with a microscopically dynamic network. The obtained fibrillar nanocomposite hydrogel, with its cell-adaptable dynamic network, enhances cell-matrix and cell-cell interactions and therefore significantly promotes the mechanotransduction, metabolic energetics, and osteogenesis of encapsulated stem cells. Furthermore, the hydrogel can codeliver a fiber-attached inductive drug to further enhance osteogenesis and bone regeneration. We believe that our work provides valuable guidance for the design of cell-adaptive and bioactive biomaterials for therapeutic applications.

Mechanical manipulation of cancer cell tumorigenicity via heat shock protein signaling.

Biophysical cues of rigid tumor matrix play a critical role in cancer cell malignancy. We report that stiffly confined cancer cells exhibit robust growth of spheroids in the stiff hydrogel that exerts substantial confining stress on the cells. The stressed condition activated Hsp (heat shock protein)-signal transducer and activator of transcription 3 signaling via the transient receptor potential vanilloid 4-phosphatidylinositol 3-kinase/Akt axis, thereby up-regulating the expression of the stemness-related markers in cancer cells, whereas these signaling activities were suppressed in cancer cells cultured in softer hydrogels or stiff hydrogels with stress relief or Hsp70 knockdown/inhibition. This mechanopriming based on three-dimensional culture enhanced cancer cell tumorigenicity and metastasis in animal models upon transplantation, and pharmaceutically inhibiting Hsp70 improved the anticancer efficacy of chemotherapy. Mechanistically, our study reveals the crucial role of Hsp70 in regulating cancer cell malignancy under mechanically stressed conditions and its impacts on cancer prognosis-related molecular pathways for cancer treatments.

Erratum: Functionalization of SF/HAP Scaffold with GO-PEI-miRNA inhibitor Complexes to Enhance Bone Regeneration through Activating Transcription Factor 4: Erratum.

[This corrects the article DOI: 10.7150/thno.34676.].

Bioinspired Tumor-Targeting and Biomarker-Activatable Cell-Material Interfacing System Enhances Osteosarcoma Treatment via Biomineralization.

Osteosarcoma is an aggressive malignant tumor that primarily develops in children and adolescents. The conventional treatments for osteosarcoma often exert negative effects on normal cells, and chemotherapeutic drugs, such as platinum, can lead to multidrug resistance in tumor cells. Herein, this work reports a new bioinspired tumor-targeting and enzyme-activatable cell-material interface system based on DDDEEK-pY-phenylboronic acid (SAP-pY-PBA) conjugates. Using this tandem-activation system, this work selectively regulates the alkaline phosphatase (ALP) triggered anchoring and aggregation of SAP-pY-PBA conjugates on the cancer cell surface and the subsequent formation of the supramolecular hydrogel. This hydrogel layer can efficiently kill osteosarcoma cells by enriching calcium ions from tumor cells and forming a dense hydroxyapatite layer. Owing to the novel antitumor mechanism, this strategy neither hurts normal cells nor causes multidrug resistance in tumor cells, thereby showing an enhanced tumor treatment effect than the classical antitumor drug, doxorubicin (DOX). The outcome of this research demonstrates a new antitumor strategy based on a bioinspired enzyme-responsive biointerface combining supramolecular hydrogels with biomineralization.

Building Osteogenic Microenvironments with a Double-Network Composite Hydrogel for Bone Repair.

The critical factor determining the in vivo effect of bone repair materials is the microenvironment, which greatly depends on their abilities to promote vascularization and bone formation. However, implant materials are far from ideal candidates for guiding bone regeneration due to their deficient angiogenic and osteogenic microenvironments. Herein, a double-network composite hydrogel combining vascular endothelial growth factor (VEGF)-mimetic peptide with hydroxyapatite (HA) precursor was developed to build an osteogenic microenvironment for bone repair. The hydrogel was prepared by mixing acrylated ß-cyclodextrins and octacalcium phosphate (OCP), an HA precursor, with gelatin solution, followed by ultraviolet photo-crosslinking. To improve the angiogenic potential of the hydrogel, QK, a VEGF-mimicking peptide, was loaded in acrylated ß-cyclodextrins. The QK-loaded hydrogel promoted tube formation of human umbilical vein endothelial cells and upregulated the expression of angiogenesis-related genes, such as Flt1, Kdr, and VEGF, in bone marrow mesenchymal stem cells. Moreover, QK could recruit bone marrow mesenchymal stem cells. Furthermore, OCP in the composite hydrogel could be transformed into HA and release calcium ions facilitating bone regeneration. The double-network composite hydrogel integrated QK and OCP showed obvious osteoinductive activity. The results of animal experiments showed that the composite hydrogel enhanced bone regeneration in skull defects of rats, due to perfect synergistic effects of QK and OCP on vascularized bone regeneration. In summary, improving the angiogenic and osteogenic microenvironments by our double-network composite hydrogel shows promising prospects for bone repair.

Coacervation-Mediated Cytocompatible Formation of Supramolecular Hydrogels with Self-Evolving Macropores for 3D Multicellular Spheroid Culture.

Coacervation driven liquid-liquid phase separation of biopolymers has aroused considerable attention for diverse applications, especially for the construction of microstructured polymeric materials. Herein, a coacervate-to-hydrogel transition strategy is developed to create macroporous hydrogels (MPH), which are formed via the coacervation process of supramolecular assemblies (SA) built by the host-guest complexation between γ-cyclodextrin and anthracene dimer. The weak and reversible supramolecular crosslinks endow the SA with liquid-like rheological properties, which facilitate the formation of SA-derived macroporous coacervates and the subsequent transition to MPH (pore size ≈ 100 µm). The excellent structural dynamics (derived from SA) and the cytocompatible void-forming process of MPH can better accommodate the dramatic volumetric expansion associated with colony growth of encapsulated multicellular spheroids compared with the non-porous static hydrogel with similar initial mechanical properties. The findings of this work not only provide valuable guidance to the design of biomaterials with self-evolving structures but also present a promising strategy for 3D multicellular spheroid culture and other diverse biomedical applications.

"Slow walk" mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel.

Meniscus, the cushion in knee joint, is a load-bearing tissue that transfers mechanical forces to extracellular matrix (ECM) and tissue resident cells. The mechanoresponse of human tissue resident stem/progenitor cells in meniscus (hMeSPCs) is significant to tissue homeostasis and regeneration but is not well understood. This study reports that a mild cyclic tensile loading regimen of ∼1800 loads/day on hMeSPCs seeded in 3-dimensional (3D) photocrosslinked gelatin methacryloyl (GelMA) hydrogel is critical in maintaining cellular homeostasis. Experimentally, a "slow walk" biomimetic cyclic loading regimen (10% tensile strain, 0.5 Hz, 1 h/day, up to 15 days) is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator. The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability. Transcriptomic analysis reveals 332 mechanoresponsive genes, clustered into cell senescence, mechanical sensitivity, and ECM dynamics, associated with interleukins, integrins, and collagens/matrix metalloproteinase pathways. The cell-GelMA constructs show active ECM remodeling, traced using a green fluorescence tagged (GFT)-GelMA hydrogel. Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs, which gradually compensates for the hydrogel loss in the cultures. These findings demonstrate the strong tissue-forming ability of hMeSPCs, and the importance of mechanical factors in maintaining meniscus homeostasis.

Genetic diversity and structure of the 4th cycle breeding population of Chinese fir (Cunninghamia lanceolata (lamb.) hook).

Studying population genetic structure and diversity is crucial for the marker-assisted selection and breeding of coniferous tree species. In this study, using RAD-seq technology, we developed 343,644 high-quality single nucleotide polymorphism (SNP) markers to resolve the genetic diversity and population genetic structure of 233 Chinese fir selected individuals from the 4th cycle breeding program, representing different breeding generations and provenances. The genetic diversity of the 4th cycle breeding population was high with nucleotide diversity (Pi ) of 0.003, and Ho and He of 0.215 and 0.233, respectively, indicating that the breeding population has a broad genetic base. The genetic differentiation level between the different breeding generations and different provenances was low (Fst < 0.05), with population structure analysis results dividing the 233 individuals into four subgroups. Each subgroup has a mixed branch with interpenetration and weak population structure, which might be related to breeding rather than provenance, with aggregation from the same source only being in the local branches. Our results provide a reference for further research on the marker-assisted selective breeding of Chinese fir and other coniferous trees.

Water-Immiscible Coacervate as a Liquid Magnetic Robot for Intravascular Navigation.

Developing magnetic ultrasoft robots to navigate through extraordinarily narrow and confined spaces like capillaries in vivo requires synthesizing materials with excessive deformability, responsive actuation, and rapid adaptability, which are difficult to achieve with the current soft polymeric materials, such as elastomers and hydrogels. We report a magnetically actuatable and water-immiscible (MAWI) coacervate based on the assembled magnetic core-shell nanoparticles to function as a liquid robot. The degradable and biocompatible millimeter-sized MAWI coacervate liquid robot can remain stable under changing pH and salt concentrations, release loaded cargoes on demand, squeeze through an artificial capillary network within seconds, and realize intravascular targeting in vivo guided by an external magnetic field. We believe the proposed "coacervate-based liquid robot" can implement demanding tasks beyond the capability of conventional elastomer or hydrogel-based soft robots in the field of biomedicine and represents a distinct design strategy for high-performance ultrasoft robots.

A sandwiched patch toward leakage-free and anti-postoperative tissue adhesion sealing of intestinal injuries.

Ideal repair of intestinal injury requires a combination of leakage-free sealing and postoperative antiadhesion. However, neither conventional hand-sewn closures nor existing bioglues/patches can achieve such a combination. To this end, we develop a sandwiched patch composed of an inner adhesive and an outer antiadhesive layer that are topologically linked together through a reinforced interlayer. The inner adhesive layer tightly and instantly adheres to the wound sites via -NHS chemistry; the outer antiadhesive layer can inhibit cell and protein fouling based on the zwitterion structure; and the interlayer enhances the bulk resilience of the patch under excessive deformation. This complementary trilayer patch (TLP) possesses a unique combination of instant wet adhesion, high mechanical strength, and biological inertness. Both rat and pig models demonstrate that the sandwiched TLP can effectively seal intestinal injuries and inhibit undesired postoperative tissue adhesion. The study provides valuable insight into the design of multifunctional bioadhesives to enhance the treatment efficacy of intestinal injuries.

Enhancing cartilage repair with optimized supramolecular hydrogel-based scaffold and pulsed electromagnetic field.

Functional tissue engineering strategies provide innovative approach for the repair and regeneration of damaged cartilage. Hydrogel is widely used because it could provide rapid defect filling and proper structure support, and is biocompatible for cell aggregation and matrix deposition. Efforts have been made to seek suitable scaffolds for cartilage tissue engineering. Here Alg-DA/Ac-ß-CD/gelatin hydrogel was designed with the features of physical and chemical multiple crosslinking and self-healing properties. Gelation time, swelling ratio, biodegradability and biocompatibility of the hydrogels were systematically characterized, and the injectable self-healing adhesive hydrogel were demonstrated to exhibit ideal properties for cartilage repair. Furthermore, the new hydrogel design introduces a pre-gel state before photo-crosslinking, where increased viscosity and decreased fluidity allow the gel to remain in a semi-solid condition. This granted multiple administration routes to the hydrogels, which brings hydrogels the ability to adapt to complex clinical situations. Pulsed electromagnetic fields (PEMF) have been recognized as a promising solution to various health problems owing to their noninvasive properties and therapeutic potentials. PEMF treatment offers a better clinical outcome with fewer, if any, side effects, and wildly used in musculoskeletal tissue repair. Thereby we propose PEMF as an effective biophysical stimulation to be 4th key element in cartilage tissue engineering. In this study, the as-prepared Alg-DA/Ac-ß-CD/gelatin hydrogels were utilized in the rat osteochondral defect model, and the potential application of PEMF in cartilage tissue engineering were investigated. PEMF treatment were proven to enhance the quality of engineered chondrogenic constructs in vitro, and facilitate chondrogenesis and cartilage repair in vivo. All of the results suggested that with the injectable self-healing adhesive hydrogel and PEMF treatment, this newly proposed tissue engineering strategy revealed superior clinical potential for cartilage defect treatment.

Gaussian curvature-driven direction of cell fate toward osteogenesis with triply periodic minimal surface scaffolds.

Leaf photosynthesis, coral mineralization, and trabecular bone growth depend on triply periodic minimal surfaces (TPMSs) with hyperboloidal structure on every surface point with varying Gaussian curvatures. However, translation of this structure into tissue-engineered bone grafts is challenging. This article reports the design and fabrication of high-resolution three-dimensional TPMS scaffolds embodying biomimicking hyperboloidal topography with different Gaussian curvatures, composed of body inherent ß-tricalcium phosphate, by stereolithography-based three-dimensional printing and sintering. The TPMS bone scaffolds show high porosity and interconnectivity. Notably, compared with conventional scaffolds, they can reduce stress concentration, leading to increased mechanical strength. They are also found to support the attachment, proliferation, osteogenic differentiation, and angiogenic paracrine function of human mesenchymal stem cells (hMSCs). Through transcriptomic analysis, we theorize that the hyperboloid structure induces cytoskeleton reorganization of hMSCs, expressing elongated morphology on the convex direction and strengthening the cytoskeletal contraction. The clinical therapeutic efficacy of the TPMS scaffolds assessed by rabbit femur defect and mouse subcutaneous implantation models demonstrate that the TPMS scaffolds augment new bone formation and neovascularization. In comparison with conventional scaffolds, our TPMS scaffolds successfully guide the cell fate toward osteogenesis through cell-level directional curvatures and demonstrate drastic yet quantifiable improvements in bone regeneration.

Directed Conformational Switching of a Zinc Finger Analogue Regulates the Mechanosensing and Differentiation of Stem Cells.

The dynamic conformational changes in the secondary structures of proteins are essential to their functions and can regulate diverse cellular events. Herein we report the design of a synthetic polymer-based secondary structure analogue of a zinc finger (ZnF) by introducing a zinc coordination motif to overcome the free energy barrier predicted by theoretical calculations and fold-free polymer chains. The conformational switching between unfolded and folded state of the ZnF analogue can be triggered in situ to drastically manipulate the accessibility of conjugated cell adhesive ligands to the cell membrane receptors, thereby effectively controlling the adhesion, spreading, mechanosensing, and differentiation of stem cells. We believe that emulating the dynamic secondary structures of proteins via rational design of a folded synthetic polymer-cation complex is a promising strategy for developing bioactive materials to mediate desired cellular functions.