Particle-collision and porogen-leaching technique to fabricate polymeric porous scaffolds with microscale roughness of interior surfaces

A facile technique is herein reported to fabricate three-dimensional(3D) polymeric porous scaffolds with interior surfaces of a topographic microstructure favorable for cell adhesion.As demonstration,a well-known biodegradable polymer poly(lactide-co-glycolide)(PLGA) was employed as matrix.Under the porogen-leaching strategy,the large and soft porogens of paraffin were modified by colliding with small and hard salt particles,which generated micropits on the surfaces of paraffin spheres.The eventual PLGA scaffolds after leaching the modified porogens had thus interior surfaces of microscale roughness imprinted by those micropits.The microrough scaffolds were confirmed to benefit adhesion of bone marrow stromal cells(BMSCs) of rats and meanwhile not to hamper the proliferation and osteogenic differentiation of the cells.The insight and technique might be helpful for biomaterial designing in tissue engineering and regenerative medicine.     

Preparation of Porous Poly(ε‐caprolactone) Structures

Porous poly(ε‐caprolactone) structures have been prepared by leaching of compression moulded salt‐containing polymer precipitates. Coagulation takes place when a PCL solution containing dispersed water‐soluble salt particles is precipitated into an excess of non‐solvent. Porous scaffolds are obtained after leaching of the compression moulded polymer‐salt precipitate. This process yields scaffolds with a very homogeneous pore morphology and independent control of pore size and porosity.     

Strontium‐Substituted Hydroxyapatite‐Gelatin Biomimetic Scaffolds Modulate Bone Cell Response

Strontium has a beneficial role on bone remodeling and is proposed for the treatment of pathologies associated to excessive bone resorption, such as osteoporosis. Herein, the possibility to utilize a biomimetic scaffold as strontium delivery system is explored. Porous 3D gelatin scaffolds containing about 30% of strontium substituted hydroxyapatite (SrHA) or pure hydroxyapatite (HA) are prepared by freeze‐drying. The scaffolds display a very high open porosity, with an interconnectivity of 100%. Reinforcement with further amount of gelatin provokes a modest decrease of the average pore size, without reducing interconnectivity. Moreover, reinforced scaffolds display reduced water uptake ability and increased values of mechanical parameters when compared to as‐prepared scaffolds. Strontium displays a sustained release in phosphate buffered saline: the quantities released after 14 d from as‐prepared and reinforced scaffolds are just 14 and 18% of the initial content, respectively. Coculture of osteoblasts and osteoclasts shows that SrHA‐containing scaffolds promote osteoblast viability and activity when compared to HA‐containing scaffolds. On the other hand, osteoclastogenesis and osteoclast differentiation are significantly inhibited on SrHA‐containing scaffolds, suggesting that these systems could be usefully applied for local delivery of strontium in loci characterized by excessive bone resorption.     

Nano‐hydroxyapatite/polyamide66 composite tissue‐engineering scaffolds with anisotropy in morphology and mechanical behaviors

Based on a biomimetic conception, nano‐hydroxyapatite (n‐HA)/polyamide66 (PA66) composite scaffolds were prepared with anisotropic properties both in morphology and mechanical behavior. A novel improved thermally induced phase separation (TIPS) technique was developed to generate orientation‐structured scaffolds for tissue engineering. The physiochemical, morphological, and mechanical properties of the resultant scaffolds were evaluated. According to the results, the improved TIPS method exhibited good processability and reproducibility and enabled the composite scaffolds to have a high content of inorganic fillers. The morphological study proved that the n‐HA/PA66 scaffolds exhibited unidirectional microtubular architecture with high porosity (ca. 80–85%) and an optimal pore size ranging from 200 to 500 μm. Besides, the effect of n‐HA content on the morphology of the scaffolds was studied, and the results indicated that the obtained scaffolds presented an improvement in anisotropic morphology with increase of n‐HA content. The anisotropy was also evaluated in the mechanical properties of the scaffolds, that is, the longitudinal compressive strength and modulus were ～1.5 times of the transverse ones. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 658–669, 2009     

Poly[lactic‐co‐(glycolic acid)]‐Grafted Hyaluronic Acid Copolymer Micelle Nanoparticles for Target‐Specific Delivery of Doxorubicin

PLGA‐grafted HA copolymers were synthesized and utilized as target specific micelle carriers for DOX. For grafting hydrophobic PLGA chains onto the backbone of hydrophilic HA, HA was solubilized in an anhydrous DMSO by nano‐complexing with dimethoxy‐PEG. The carboxylic groups of HA were chemically grafted with PLGA, producing HA‐g‐PLGA copolymers. Resultant HA‐g‐PLGA self‐assembled in aqueous solution to form multi‐cored micellar aggregates and DOX was encapsulated during the self‐assembly. DOX‐loaded HA‐g‐PLGA micelle nanoparticles exhibited higher cellular uptake and greater cytotoxicity than free DOX for HCT‐116 cells that over‐expressed HA receptor, suggesting that they were taken up by the cells via HA receptor‐mediated endocytosis.

     

Friedel–crafts reactions of pendant vinyl groups in macroporous monosized poly(meta‐divinylbenzene) and poly(para‐divinylbenzene) particles

Residual vinyl groups in macroporous monosized polymer particles of poly(meta‐DVB) and poly(para‐DVB) prepared with toluene and 2‐EHA as porogens have been reacted with aluminum chloride as Friedel–Crafts catalyst with and without the presence of lauroyl chloride. In the reaction between aluminum chloride and pendant vinyl groups a post‐crosslinking by cationic polymerization takes place. A reaction occurring simultaneously is the addition of HCl to the double bonds. The progress of these reactions was studied by characterization of vinyl group conversion, pore size distribution, specific surface area, morphology, and swelling behavior. In the reaction with aluminum chloride the poly(para‐DVB) particles showed a substantially higher conversion of pendant vinyl groups than the particles made of poly(meta‐DVB) independent of porogen type. The reaction with aluminum chloride led to a reduced swelling in organic solvents and an increased rigidity of the particles prepared with toluene as porogen. This is confirmed by an increase in the total pore volume in the dry state and a change in the pore size distribution of these particles. Also in the reaction with lauroyl chloride poly(para‐DVB) particles have shown a higher conversion of pendant vinyl groups than poly(meta‐DVB) particles and the acylation was almost complete at the early stage of the reaction. The swelling in organic solvents is reduced as a result of the incorporation of acyl groups into the particles prepared with toluene as porogen. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1366–1378, 2000     

Fabrication of 3D electrospun structures from poly(lactide‐co‐glycolide acid)–nano‐hydroxyapatite composites

The fabrication of three‐dimensional (3D) electrospun composite scaffolds was presented in this study. Layers of electrospun meshes made from composites of poly(lactide‐co‐glycolide acid) (PLGA) and hydroxyapatite (HA) were stacked and sintered using pressurized gas. Three HA concentrations of 5, 10, and 20 wt % were tested, and the addition of the HA nanoparticles decreased the tensile mechanical properties of the meshes with 20 wt % HA. However, after the gas absorption process, the fibers within the mesh sintered, which improved the mechanical properties more than twofold. The fabrication of 3D, porous, electrospun scaffolds was also demonstrated. The resulting 3D scaffolds had open porosity of up to 70% and modulus of ～20 MPa. This technique improves on the current electrospinning technology by overcoming the challenges of depositing a thick, 3D structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Viscoelastic properties of poly(ε‐caprolactone) – hydroxyapatite micro‐ and nano‐composites

Various composites have been proposed in the literature for the fabrication of bioscaffolds for bone tissue engineering. These materials include poly(ε‐caprolactone) (PCL) with hydroxyapatite (HA). Since the biomaterial acts as the medium that transfers mechanical signals from the body to the cells, the fundamental properties of the biomaterials should be characterized. Furthermore, in order to control the processing of these materials into scaffolds, the characterization of the fundamental properties is also necessary. In this study, the physical, thermal, mechanical, and viscoelastic properties of the PCL‐HA micro‐ and nano‐composites were characterized. Although the addition of filler particles increased the compressive modulus by up to 450%, the thermal and viscoelastic properties were unaffected. Furthermore, although the presence of water plasticized the polymer, the viscoelastic behavior was only minimally affected. Testing the composites under various conditions showed that the addition of HA can strengthen PCL without changing its viscoelastic response. The results found in this study can be used to further understand and approximate the time‐dependent behavior of scaffolds for bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

The Surface Modification of Hydroxyapatite Nanoparticles by the Ring Opening Polymerization of γ‐Benzyl‐L‐glutamate N‐carboxyanhydride

The surface modification of hydroxyapatite (HA) nanoparticles by the ring opening polymerization (ROP) of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG‐NCA) was proposed to prepare the poly(γ‐benzyl‐L ‐glutamate) (PBLG)‐grafted HA nanoparticles (PBLG‐g‐HA) for the first time. HA nanoparticles were firstly treated by 3‐aminopropylthriethoxysilane (APS) and then the terminal amino groups of the modified HA particles initiated the ROP of BLG‐NCA to obtain PBLG‐g‐HA. The process was monitored by XPS and FT‐IR. The surface grafting amounts of PBLG on HA ranging from 12.1 to 43.1% were characterized by thermal gravimetric analysis (TGA). The powder X‐ray diffraction (XRD) analysis confirmed that the ROP only underwent on the surface of HA nanoparticles without changing its bulk properties. The SEM measurement showed that the PBLG‐g‐HA hybrid could form an interpenetrating net structure in the self‐assembly process. The PBLG‐g‐HA hybrid could maintain higher colloid stability than the pure HA nanoparticles. The in vitro cell cultures suggested the cell adhesion ability of PBLG‐g‐HA was much higher than that of pure HA.

     

Silica‐particle‐supported zwitterionic polymer monolith for microcolumn liquid chromatography

A silica‐particle‐supported zwitterionic polymeric monolithic column, shortened as supported column (S‐column), was prepared by the in situ polymerization of methacrylic acid, ethylene dimethacrylate, and 2‐(dimethylamino)ethyl methacrylate in the presence of a ternary porogenic solvent containing water, methanol, and cyclohexanol in a 250 μm id fused‐silica capillary prepacked with 5 μm bare silica particles. In the S‐column, a thin layer of the polymers was formed around the silica particles in the form of nanoglobules, leaving the interstitial spaces between the particles free for liquid flow. The effects of the preparation conditions on the morphology of the monolith were investigated by scanning electron microscopy and backpressure measurements. The selected volumetric ratio of porogens, monomer concentration, polymerization time, and temperature are 1:1:8 (water/methanol/cyclohexanol), 25% v/v, 5 h, and 60°C, respectively. The S‐column was evaluated by comparison with its conventional organic counterpart in terms of morphology, mechanical stability, permeability, swelling–shrinking behavior, capacity, and efficiency. The results demonstrate that the S‐column is superior to its counterpart in all the terms with the exception of permeability. The above merits and zwitterionic property of the S‐column were further confirmed by separate separations of four inorganic anions and three organic cations.     

One‐step synthesis of poly(lactic‐co‐glycolic acid)‐g‐poly‐1‐vinylpyrrolidin‐2‐one copolymers

The radical polymerization of 1‐vinylpyrrolidin‐2‐one (NVP) in poly(lactic‐co‐glycolic acid) (PLGA) 50:50 at 100 °C leads to amphiphilic PLGA‐g‐PVP copolymers. Their composition is determined by FT‐IR spectroscopy. Thermogravimetric analyses agree with FT‐IR determinations. Saponification of the PLGA‐g‐PVP polyester portion allows isolating the PVP side chains and measuring their molecular weight, from which the average chain transfer constant (C_T) of the PLGA units is estimated. The MALDI‐TOF spectra of PVP reveal the presence at one chain end of residues of either glycolic acid‐ or lactic acid‐ or lactic/glycolic acid dimers, trimers and one tetramer, the other terminal being hydrogen. This unequivocally demonstrates that grafting occurred. Accordingly, the orthogonal solvent pair ethyl acetate—methanol, while separating the components of PLGA/PVP intimate mixtures, fails to separate pure PVP or PLGA from the reaction products. All PLGA‐g‐PVP and PLGA/PLGA‐g‐PVP blends, but not PLGA/PVP blends, give long‐time stable dispersions in water. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1919–1928     

Photocrosslinked poly(ester‐anhydride) microspheres with macroporous structure

In this work, the new method of preparation biodegradable microspheres with macroporous structure is presented. Typical methods used for generation of porous structures in microspheres obtained from preformed polymers require the use of additional substances acting as porogens. In this study, the porosity was achieved as the effect of photocrosslinking, without porogens. Microspheres were prepared using emulsion solvent evaporation technique from functional poly(ester‐anhydride)s with different amount of allyl groups in the side chains. The crosslinking was carried out by UV irradiation during the solvent evaporation (photoinitiator was introduced to polymer solution). The size of microspheres obtained was in the range of 1.7 – 4 µm (small microspheres) or 31 – 50 µm (large ones) and depended on the conditions used in emulsion formulation process. Effectiveness of the crosslinking was characterized by the content of insoluble part of samples, and it was in the range of 42–89%. The content of insoluble part of sample of microspheres and their porosity were dependent on functionality of poly(ester‐anhydride)s, the amount of photoinitiator used, and also on size of microparticles. The small particles were always more crosslinked than the large ones, but the latter were more porous than the small ones. Crosslinked microparticles indicated higher loading efficiency of model compound and appeared to degrade faster than uncrosslinked ones, probably due to their high porosity. The high porosity of microspheres obtained would enable their eventual use in pulmonary drug delivery systems or in construction of porous scaffolds for tissue engineering. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel preparation method for microspheres by glycerol modified solid‐in‐oil‐in‐water multi‐emulsion

Biodegradable material poly(D, L ‐lactic‐co‐glycolic) acid (PLGA) plays an important role in drug‐sustained release systems. Here, we describe a glycerol modified solid‐in‐oil‐in‐water (m‐S/O/W) emulsion method for PLGA microspheres, in order to encapsulate proteins in PLGA by utilizing dextran glassy particles to protect the proteins from denaturing, unfolding, and aggregation during preparation and new external water phase to prevent the inner dextran glassy particles from leaking into the external water phase. External water phase containing 20, 40, 60, 80% glycerol showed that proteins released faster and more completely with increased glycerol content. According to their varied release profiles, microspheres of different formulations could be used to encapsulate vaccines or for delivering proteins over long‐term. Copyright © 2009 John Wiley & Sons, Ltd.     

Control of Osteogenic Differentiation and Mineralization of Human Mesenchymal Stem Cells on Composite Nanofibers Containing Poly[lactic‐co‐(glycolic acid)] and Hydroxyapatite

We fabricated composite fibrous scaffolds from blends of poly(lactide‐co‐glycolide) (PLGA) and nano‐sized hydroxyapatite (HA) via electrospinning. SEM‐EDX and AFM analysis demonstrated that HA was homogeneously dispersed in the nanofibers, and the roughness increased along with the amount of incorporated HA. When hMSCs were cultured on these PLGA/HA composite nanofibers, we found that incorporation of HA on the nanofibers did not affect cell viability whereas increased ALP activity and expression of osteogenic genes as well as the calcium mineralization of hMSCs. Our results indicate that the composite nanofibers can be offered as a potential bone regenerative biomaterial for stem cell based therapies.

     

Characterization and cytocompatibility of polydopamine on MAO‐HA coating supported on Mg‐Zn‐Ca alloy

Magnesium has been suggested as a potential biodegradable metal for the usage as orthopaedic implants. However, high degradation rate in physiological environment remains the biggest challenge, impeding wide clinical application of magnesium‐based biomaterials. In order to reduce its degradation rate and improve the biocompatibility, micro‐arc oxidation coating doped with HA particles (MAO‐HA) was applied as the inner coating, and polydopamine (PDA) film was synthesized by dopamine self‐polymerization as the outer coating. The microstructure evolution of the coating was characterized using scanning electron microscopy (SEM), atomic force microscope (AFM), X‐ray diffraction analyses (XRD), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray photoelectron spectroscopy (XPS). The results showed that PDA film had covered the entire surface of MAO‐HA coating and the pore size of MAO‐HA coating decreased. The root mean square (RMS) roughness of PDA/MAO‐HA coatings was approximately 106.46 nm, which was closer to the optimum surface roughness for cellular attachment as compared with MAO‐HA coatings. Contact angle measurement indicated that the surface wettability had been transformed from hydrophobic to hydrophilic due to the introduction of PDA. The PDA/MAO‐HA coatings exhibited better corrosion resistance in vitro, with the self‐corrosion potential increasing by 150 mV and the corrosion current density decreasing from 2.09 × 10^?5 A/cm ² to 1.46 × 10^?6 A/cm ² . In hydrogen evolution tests, the corrosion rates of the samples coated with PDA/MAO‐HA and MAO‐HA were 4.40 and 5.95 mm/y, respectively. MTS assay test and cell‐surface interactions experiment demonstrated that PDA/MAO‐HA coatings exhibited good cellular compatibility and could promote the adhesion and proliferation of MC3T3‐E1 cells.     

Aligned Bioactive Multi‐Component Nanofibrous Nanocomposite Scaffolds for Bone Tissue Engineering

The ability to mimic the chemical, physical and mechanical properties of the natural extra‐cellular matrix is a key requirement for tissue engineering scaffolds to be successful. In this study, we successfully fabricated aligned nanofibrous multi‐component scaffolds for bone tissue engineering using electrospinning. The chemical features were mimicked by using the natural components of bone: collagen and nano‐hydroxyapatite along with poly[(D ,L ‐lactide)‐co‐glycolide] as the major component. Anisotropic features were mimicked by aligning the nanofibers using a rotating mandrel collector. We evaluated the effect of incorporation of nano‐HA particles to the system. The morphology and mechanical properties revealed that,at low concentrations, nano‐HA acted as a reinforcement. However, at higher nano‐HA loadings, it was difficult to disrupt aggregations and, hence, a detrimental effect was observed on the overall scaffold properties. Thermal analysis showed that there were slight interactions between the individual components even though the polymers existed as a two‐phase system. Preliminary in vitro cell‐culture studies revealed that the scaffold supported cell adhesion and spreading. The cells assumed a highly aligned morphology along the direction of fiber orientation. Protein adsorption experiments revealed that the synergistic effect of increased surface area and the presence of nano‐HA in the polymer matrix enhanced total protein adsorption. Crosslinking with 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride resulted in improved mechanical properties of the scaffolds and improved degradation stability, under physiological conditions.

     

In Vivo Degradation Behavior of Porous Composite Scaffolds of Poly（lactide-co-glycolide） and Nano-hydroxyapatite Surface Grafted with Poly（L-lactide）

The biodegradable porous composite scaffold, composed of poly(lactide-co-glycolide)(PLGA) and hydroxyapatite nanoparticles(n-HAP) surface-grafted with poly(L-lactide)(PLLA)(g-HAP)(g-HAP/PLGA), was fabricated using the solvent casting/particulate leaching method, and its in vivo degradation behavior was investigated by the intramuscular implantation in rabbits. The composite of un-grafted n-HAP/PLGA and neat PLGA were used as controls. The scaffolds had interconnected pore structures with average pore sizes between 137 μm and 148 μm and porosities between 83% and 86%. There was no significant difference in the pore size and porosity among the three scaffolds. Compared with n-HAP/PLGA, the thermo-degradation temperature(Tc) of g-HAP/PLGA decreased while its glass transition temperature(Tg) increased. The weight change, grey value analysis of radiographs and SEM observation showed that the composite scaffolds of g-HAP/PLGA and n-HAP/PLGA showed slower degradation and higher mineralization than the pure PLGA scaffold after the intramuscular implantation. The rapid degradation of PLGA, g-HAP/PLGA and n-HAP/PLGA occurred at 8–12 weeks, 12–16 weeks and 16–20 weeks, respectively. Compared with n-HAP/PLGA, g-HAP/PLGA showed an improved absorption and biomineralization property mostly because of its improved distribution of HAP nanoparticles. The levels of both calcium and phosphorous in serum and urine could be affected to some extent at 3–4 weeks after the implantation of g-HAP/PLGA, but the biochemical detection of serum AST, ALT, ALP, and GGT as well as BUN and CRE showed no obvious influence on the functions of liver and kidney.     

Load‐bearing biodegradable polycaprolactone‐poly (lactic‐co‐glycolic acid)‐ beta tri‐calcium phosphate scaffolds for bone tissue regeneration

A biodegradable scaffold with tissue ingrowth and load‐bearing capabilities is required to accelerate the healing of bone defects. However, it is difficult to maintain the mechanical properties as well as biodegradability and porosity (necessary for bone ingrowth) at the same time. Therefore, in the present study, polycaprolactone (PCL) and poly (lactic‐co‐glycolic acid) (PLGA5050) were mixed in varying ratio and incorporated with 20 wt.% beta tri‐calcium phosphate (βTCP). The mixture was shaped under pressure into originally nonporous cylindrical constructs. It is envisioned that the fabricated constructs will develop porosity with the time‐dependent biodegradation of the polymer blend. The mechanical properties will be sustained since the decrease in mechanical properties associated with the dissolution of the PLGA, and the formation of the porous structure will be compensated with the new bone formation and ingrowth. To prove the hypothesis, we have systematically studied the effects of samples composition on the time‐dependent dissolution behavior, pore formation, and mechanical properties of the engineered samples, in vitro. The highest initial (of as‐prepared samples) values of the yield strength (0.021 ± 0.002 GPa) and the Young's modulus (0.829 ± 0.096 GPa) were exhibited by the samples containing 75 wt.% of PLGA. Increase of the PLGA concentration from 25 to 75 wt.% increased the rate of biodegradation by a factor of 3 upon 2 weeks in phosphate buffered saline (1 × PBS). The overall porosity and the pore sizes increased with the dissolution time indicating that the formation of in situ pores can indeed enable the migration of cells followed by vascularization and bone growth.     

Monodisperse Poly(lactide‐co‐glycolic acid)‐Based Nanocarriers for Gene Transfection

This contribution describes a simple, aerosol‐based method for fabricating monodisperse particles containing mixtures of poly(lactide‐co‐glycolic acid) [PLGA], protamine sulfate (Prot), and poly(l‐ lysine) [PLL] as nanocarriers for gene transfection. Aqueous solutions of PLGA, Prot, and PLL were collison‐atomized, and the resulting aerosolized droplets were dried “on the fly” to form solid particles, which then were electrostatically size‐classified into 50, 100, and 200 nm mobility diameter samples. Measurements of cell viability and transfection reveal that the fabricated nanocarriers have a lower cytotoxicity (>85% in cell viability) and a higher transfection efficiency [>8.7 × 10⁵ in relative light units (RLU) mg⁻¹] than does 25 kDa polyethyleneimine (≈50% and 6.8 × 10⁵ RLU mg⁻¹).     

Wound Healing Attributes of Polyelectrolyte Multilayers Prepared with Multi‐l‐arginyl‐poly‐l‐aspartate Pairing with Hyaluronic Acid and γ‐Polyglutamic Acid

Biodegradable multi‐l ‐arginyl‐poly‐l ‐aspartate (MAPA), more commonly cyanophycin, prepared with recombinant Escherichia coli contains a polyaspartate backbone with lysine and arginine as side chains. Two assemblies of polyelectrolyte multilayers (PEMs) are fabricated at three different concentration ratios of insoluble MAPA (iMAPA) with hyaluronic acid (iMAPA/HA) and with γ‐polyglutamic acid (iMAPA/γ‐PGA), respectively, utilizing a layer‐by‐layer approach. Both films with iMAPA and its counterpart, HA or γ‐PGA, as the terminal layer are prepared to assess the effect on film roughness, cell growth, and cell migration. iMAPA incorporation is higher for a higher concentration of the anionic polymer due to better charge interaction. The iMAPA/HA films when compared to iMAPA/γ‐PGA multilayers show least roughness. The growth rates of L929 fibroblast cells on the PEMs are similar to those on glass substrate, with no supplementary effect of the terminal layer. However, the migration rates of L929 cells increase for all PEMs. γ‐PGA incorporated films impart 50% enhancement to the cell migration after 12 h of culture as compared to the untreated glass, and the smooth films containing HA display a maximum 82% improvement. The results present the use of iMAPA to construct a new layer‐by‐layer system of polyelectrolyte biopolymers with a potential application in wound dressing.