Nanofibrous scaffold prepared by electrospinning of poly(vinyl alcohol)/gelatin aqueous solutions

A series of nanofibrous scaffolds were prepared by electrospinning of poly(vinyl alcohol) (PVA)/gelatin aqueous solution. PVA and gelatin was dissolved in pure water and blended in full range, then being electrospun to prepared nanofibers, followed by being crosslinked with glutaraldehyde vapor and heat treatment to form nanofibrous scaffold. Field emission scanning electron microscope (FESEM) images of the nanofibers manifested that the fiber average diameters decreased from 290 to 90 nm with the increasing of gelatin. In vitro degradation rates of the nanofibers were also correlated with the composition and physical properties of electrospinning solutions. Cytocompatibility of the scaffolds was evaluated by cells morphology and MTT assay. The FESEM images revealed that NIH 3T3 fibroblasts spread and elongated actively on the scaffolds with spindle‐like and star‐type shape. The results of cell attachment and proliferation on the nanofibrous scaffolds suggested that the cytotoxicity of all samples are grade 1 or grade 0, indicating that the material had sound biosafety as biomaterials. Compared with pure PVA and gelatin scaffolds, the hybrid ones possess improved biocompatibility and controllability. These results indicate that the PVA/gelatin nanofibrous have potential as skin scaffolds or wound dressing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymer blending or fiber blending: A comparative study using chitosan and poly(ε-caprolactone) electrospun fibers

Nonwoven membranes of poly(ε-caprolactone) (PCL) and chitosan (CS) were produced according to the two methods: by blending the polymers in solution followed by electrospinning – polymer blending method – and by simultaneous deposition of fibers electrospun from separate solutions – fiber blending (FB) method. The two production methods were compared by assessing fiber morphology, mass loss, swelling degree, water contact angle, and mechanical properties of the resulting electrospun membranes. Furthermore, the adhesion, proliferation, and morphology of human dermal fibroblasts on the eight types of scaffold produced were evaluated to assess if the blending method used would influence cell–scaffold interaction. Cell adhesion to the different scaffolds lied in the interval 40–60%, with the CS scaffold presenting the lowest value. Interestingly, cell proliferation was the same when comparing polymer blending and FB scaffolds having 3:1 or 1:3 PCL/CS ratios but very different when the ratio was 1:1 – the FB scaffold sustained a proliferation rate double that of the polymer blending scaffold. This work shows that, when blending polymers to improve the properties of a scaffold for tissue engineering or 3D cell culture, their spatial distribution may considerably affect scaffold's properties and should be considered as another parameter requiring optimization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47191.     

4-Vinylbenzene Boronic Acid–Hydroxy Apatite/Polyvinyl Alcohol Based Nanofiber Scaffold Synthesized by UV-Activated Reactive Electrospinning

In this study, we prepared photo-crosslinked modified HAP (hydroxy apatite)/polyvinyl alcohol (PVA) composite nanofiber scaffold for cell growth applications. HAP was synthesized and then modified with 4-vinylbenzene boronic acid (VBBA) to obtain 4-VBBA-HAP. By means of the simultaneous UV electrospinning technique 4-VBBA-HAP/PVA composite was obtained. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy) and Fourier transform infrared spectroscopy technique. Nanofibers were treated with collagen solution via the spraying method. For the cell culture applications ECV304 and SAOS cells were seeded on the chosen electrospun fibrous scaffolds.     

Dual drug spatiotemporal release from functional gradient scaffolds prepared using 3D bioprinting and electrospinning

Functional gradient scaffolds play an important role in osteochondral tissue engineering because they can meet the essential requirement for a gradual transition of both physical and chemical properties in osteochondral tissue regeneration. There is a requirement for 3D composite osteochondral regeneration scaffolds with multiscale structures that are capable of controlling release of multiple biomolecules. To this end, this article describes a 3D bioprinting platform integrated forming system designed to produce various drug‐loaded scaffolds. A novel scaffold was fabricated by the self‐developed 3D bioprinting platform combining extrusion deposition with multi‐nozzle electrospinning. For temporally controlled release of gentamycin sulfate (GS) and desferoxamine (DFO), blend electrospun GS/polyvinyl alcohol (PVA) and coaxial electrospun core (PVA‐DFO)/shell (polycaprolactone; PCL) fibers were deposited in the scaffold. After a 25‐day time‐lapse release study in vitro, results showed GS released faster than DFO during the early stages and sustained release of DFO for long periods. For spatially controlled release of DFO, the vertically gradient gelatin/sodium alginate (SA) scaffolds presented to enable the release amount of DFO in a gradient mode. The experiment and test results demonstrate the validity of the 3D bioprinting platform integrated forming system and the excellent properties of such scaffolds for performing multidrug spatiotemporal release. POLYM. ENG. SCI., 56:170–177, 2016. © 2015 Society of Plastics Engineers     

Fabrication and characterization of electrospun fibrous nanocomposite scaffolds based on poly(lactide‐co‐glycolide)/poly(vinyl alcohol) blends

Tissue engineering involves the fabrication of three‐dimensional scaffolds to support cellular in‐growth and proliferation. Ideally, the scaffolds should be similar to the native extracellular matrix (ECM). Electrospun polymer nanofibrous scaffolds are appropriate candidates for ECM mimetic materials since they mimic the nanoscale properties of ECM. Electrospun polymer nanocomposites based on poly(lactide‐co‐glycolide) (PLGA)/poly(vinyl alcohol) (PVA) and organically modified montmorillonite (OMMT) were prepared by a solution intercalation technique followed by electrospinning. The morphology of fibrous scaffolds based on these nanocomposites was investigated using scanning electron microscopy. The scaffolds showed highly porous structure within the nanofibres of diameters ranging from 400 to 700 nm. X‐ray diffractometry gave evidence of good dispersion of the OMMT in the blends with exfoliated morphology. Measurements of the water uptake and water contact angle of the fibrous scaffolds indicated significant improvement in the hydrophilicity of the scaffolds. Evaluations of the mechanical properties and unrestricted somatic stem cell culture of the electrospun fibrous nanocomposite scaffolds revealed that the PLGA90/PVA10/1.5% OMMT and PLGA90/PVA10/3% OMMT samples are the most useful from the tissue engineering application viewpoint. Copyright © 2010 Society of Chemical Industry     

Plasma polymerization‐modified bacterial polyhydroxybutyrate nanofibrillar scaffolds

The design and the development of novel scaffold materials for tissue engineering have attracted much interest in recent years. Especially, the prepared nanofibrillar scaffold materials from biocompatible and biodegradable polymers by electrospinning are promising materials to be used in biomedical applications. In this study, we propose to produce low‐cost and cell‐friendly bacterial electrospun PHB polymeric scaffolds by using Alcaligenes eutrophus DSM 545 strain to PHB production. The produced PHB was characterized by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Nanofibrous scaffolds were fabricated via electrospinning method that has a fiber diameter approximately 700–800 nm. To investigate cell attachment, cell growth, and antioxidant enzyme activity on positively and negatively charged PHB scaffold, PHB surface was modified by plasma polymerization technique using polyethylene glycol (PEG) and ethylenediamine (EDA). According to the results of superoxide dismutase (SOD) activity study, PEG‐modified nanofibrillar scaffolds indicated more cellular resistance against oxidative stress compared to the EDA modification. As can be seen in cell proliferation results, EDA modification enhanced the cell proliferation more than PEG modification, while PEG modification is better as compared with nonmodified scaffolds. In general, through plasma polymerization technique, surface modified nanofibrillar structures are effective substrates for cell attachment and outgrowth. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced chondrogenic differentiation of human bone marrow mesenchymal stem cells on PCL/PLGA electrospun with different alignments and compositions

The simultaneous effect of electrospun scaffold alignment and polymer composition on chondrogenic differentiation of human bone marrow mesenchymal stem cells (hBMMSC) is investigated. Aligned and randomly oriented polycaprolactone/poly(lactic-co-glycolic acid) (PLGA) hybrid electrospun scaffolds with two different ratios are fabricated by electrospinning. It is found that aligned nanofibrous scaffolds support higher chondrogenic differentiation of hBMMSCs compared to random ones. The aligned scaffolds show a higher expression level of chondrogenic markers such as type II collagen and aggrecan. It is concluded that the aligned nanofibrous scaffold with higher PLGA ratio could significantly enhance hBMMSC proliferation and differentiation to chondrocytes.     

Electrospun three‐dimensional silk fibroin nanofibrous scaffold

Practical application to three‐dimensional (3‐D) tissue culture has been limited by the structural restriction of two‐dimensional (2‐D) nature of electrospun nanofiber mat. In this study, for constructing 3‐D nanofibrous structure as real 3‐D tissue engineering scaffold, we developed new fabrication process with silk fibroin (SF) by electrospinning and evaluated the features of this SF nanofiber scaffold (SFNS) through morphological and cell‐culture analyses. Foam type of the SFNS exhibited high porosity as well as large pores and its cell proliferation well occurred inside (inner spaces of pores), which makes this suitable for 3‐D cell‐culture scaffold. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Silver Loaded Nanofibrous Curdlan Mat for Diabetic Wound Healing: An In Vitro and In Vivo Study

A fibrous scaffold of curdlan/poly(vinyl alcohol) (PVA) blend is prepared by electrospinning technique and antimicrobial property is imparted to it by the addition of silver nitrate (1, 3, and 5 wt%). All the scaffolds except the PVA/curdlan with 5 wt% AgNO₃ show good viability of Swiss 3T3 fibroblast cells. Significant reductions in the growth of Staphylococcus aureus and Escherichia coli are also observed in all the scaffolds. In vitro scratch assay and cell adhesion studies indicate that the scaffold containing 1% AgNO₃ shows significant wound healing and better cell spreading. The in vivo results also show faster healing of excision wounds in diabetic rats treated with the same material when compared to the control and the commercial sample. Furthermore, downregulation of proinflammatory cytokines and upregulation of anti‐inflammatory cytokines on the skin of the treated animals confirm that PVA/curdlan/1% AgNO₃ electrospun mat could be a promising material for diabetic wound healing.     

UV‐reactive electrospinning of keratin/4‐vinyl benzene boronic acid–hydroxyapatite/poly(vinyl alcohol) composite nanofibers

Keratins are the major structural fibrous proteins of hair, feathers, wool, and nail. Because keratin is protein based, cheap, and biocompatible, it has found applications from tissue engineering to textile industry. Simultaneous UV‐reactive electrospinning technique is used to fabricate nanofiber scaffolds with 4‐vinyl benzene boronic acid–hydroxyapatite/poly(vinyl alcohol) composite containing different amounts of keratin. Human hair as keratin supports the scaffolds for cell culture applications in our study. Our aim was to obtain nanofiber scaffolds which were designed to be nontoxic. The structure and the morphology of electrospun membranes were investigated by scanning electron microscopy and Fourier transform infrared spectroscopy technique. For the cell culture applications, endothelium (ECV 304) and sarcoma osteogenic (SAOS) cells were seeded on the electrospun fibrous scaffolds. Nanofiber scaffolds were found to have an average diameter of 350 ± 20 nm. These scaffolds provided a medium for cells to grow. POLYM. COMPOS., 38:1371–1377, 2017. © 2015 Society of Plastics Engineers     

A facile method for fabricating nano/microfibrous three-dimensional scaffold with hierarchically porous to enhance cell infiltration

The integration of electrospinning and traditional needle punching technologies were demonstrated for fabricating a new three-dimensional (3D) scaffold to enhance the cellular infiltration. This 3D scaffold combined the advantages of electrospun polycaprolactone (PCL) nanofibrous mats and carded chitosan microfibrous webs to construct hierarchically porous, which have three regions: the large pores (about 500 μm) on the nanofibrous mats generated by needle punching, could induce the massive cells infiltration into the inner scaffold; the small pores (30–200 μm) of the microfibrous webs allowed space for continuous cellular infiltration; and the inherent smaller pores of the nanofibrous mats (1–17 μm) which play a key role in providing a platforms for cell adhesion and proliferation. In addition, the 3D scaffold exhibited appropriate mechanical properties and significantly high initial cell attachment, proliferation, and infiltration, suggesting that its great potential in tissue engineering. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47046     

Fabrication of PLA/PEG/MWCNT electrospun nanofibrous scaffolds for anticancer drug delivery

In the present study, polylactic acid (PLA)/polyethylene glycol (PEG)/multiwalled carbon nanotube (MWCNT) electrospun nanofibrous scaffolds were prepared via electrospinning process and their applications for the anticancer drug delivery system were investigated. A response surface methodology based on Box–Behnken design (BBD) was used to evaluate the effect of key parameters of electrospinning process including solution concentration, feeding rate, tip–collector distance (TCD) and applied voltage on the morphology of PLA/PEG/MWCNT nanofibrous scaffolds. In optimum conditions (concentration of 8.15%, feeding rate of 0.2 mL/h, voltage of 18.50 kV and TCD of 13.0 cm), the minimum experimental fiber diameter was found to be 225 nm which was in good agreement with the predicted value by the BBD analysis (228 nm). In vitro drug release study of doxorubicin (DOX)‐loaded nanofibrous scaffolds, higher drug content induced an extended release of drug. Also, drug release rate was not dependent on drug/polymer ratio in different electrospun nanofibrous formulations. The equation of M_t = c₀ + kt^0.5was used to describe the kinetic data of DOX release from electrospun nanofibers. The cell viability of DOX‐loaded nanofibrous scaffolds was evaluated using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide, a tetrazole assay on lung cancer A549 cell lines. We propose that DOX‐incorporated PLA/PEG/MWCNT nanofibrous scaffold could be used as a superior candidate for antitumor drug delivery. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41286.     

Biocompatible polymeric electrospun matrices: Micro–nanotopography effect on cell behavior

This work reports a preliminary biological study performed on nanofibrous biocompatible polylactidecopolycaprolactone (PLA-PCL) scaffolds intended for tissue regeneration. The aim was to evaluate how matrix surface topography affects cell adhesion and proliferation. Scaffolds prepared by electrospinning either equipped with plane or rotating mandrel collectors, were characterized for their surface topography and nanofiber size. Cell culture studies were carried out using mouse embryonic fibroblast cells lines (NIH-3T3), as model for skin, murine neuroblastoma neuro-2α cell line, as model for neuronal tissue, and mouse mesenchymal stem cells (MSCs), because of their differentiation ability. Imaging analysis by scanning electron microscope and laser scanning confocal microscopy together with cell viability (MTT, L 3-(4,5-dymethiltiazol-2-y)-2,5 diphenyltetrazolium bromide) test, were performed on cell cultures at fixed time laps. The results showed that electrospun nanofibers supported growth and proliferation of the tested cell lines, but electrospun matrices obtained with rotating mandrel showed significantly higher cell viability that follows the orientation of electrospun nanofibers.     

Facile preparation and cytocompatibility of poly(lactic acid)/poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) hybrid fibrous scaffolds

A fibrous scaffold is required to provide three‐dimensional (3D) cell growth microenvironments and appropriate synergistic cell guidance cues. In this study, porous scaffolds with different mass ratio of poly(lactic acid) to poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3HB‐co‐4HB)) for tissue engineering were prepared by a modified particle leaching method. The effect of the addition of P(3HB‐co‐4HB) on microstructural morphology, compression property, swelling behavior, and enzymatic degradation of hybrid scaffolds was systematically investigated. The results indicated that this method was simple but efficient to prepare highly interconnected biomimetic 3D hybrid scaffolds (PP50/50 and PP33/67) with fibrous pore walls. The cytocompatibility of hybrid scaffolds was evaluated by in vitro culture of mesenchymal stem cells. The cell‐cultured hybrid scaffolds presented a complete 3D porous structure, thus allowing cell proliferation on the surface and infiltration into the inner part of scaffolds. The obtained hybrid scaffolds with pore size ranging from 200 to 450 µm, over 90% porosity, adjustable biodegradability, and water‐uptake capability will be promising for cartilage tissue engineering applications. POLYM. ENG. SCI., 54:2902–2910, 2014. © 2014 Society of Plastics Engineers     

Fabrication and characterization of chitosan/PVA with hydroxyapatite biocomposite nanoscaffolds

Nanofibrous biocomposite scaffolds of chitosan (CS), PVA, and hydroxyapatite (HA) were prepared by electrospinning. The scaffolds were characterized by FTIR, SEM, TEM, and XRD techniques. Tensile testing was used for the characterization of mechanical properties. Mouse fibroblasts (L929) attachment and proliferation on the nanofibrous scaffold were investigated by MTT assay and SEM observation. FTIR, TEM, and XRD results showed the presence of nanoHA in the scaffolds. The scaffolds have porous nanofibrous morphology with random fibers in the range of 100–700 nm diameters. The CS/PVA (90/10) fibrous matrix (without HA) showed a tensile strength of 3.1 ± 0.2 MPa and a tensile modulus 10 ± 1 MPa with a strain at failure of 21.1 ± 0.6%. Increase the content of HA up to 2% increased the ultimate tensile strength and tensile modulus, but further increase HA up to 5–10% caused the decrease of tensile strength and tensile modulus. The attachment and growth of mouse fibroblast was on the surface of nanofibrous structure, and cells' morphology characteristics and viability were unaffected. A combination of nanofibrous CS/PVA and HA that mimics the nanoscale features of the extra cellular matrix could be promising for application as scaffolds for tissue regeneration, especially in low or nonload bearing areas. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of Calendula officinalis-loaded PCL/gum arabic nanocomposite scaffolds for wound healing applications

Medicinal plants such as Calendula officinalis (C. officinalis) are commonly used for skin wounds’ treatment. On the other hand, gum arabic (GA) has a lot of potential for use in wound healing because of its unique physio-chemical properties. Wound healing activity of gum arabic (GA) and Calendula officinalis (C. officinalis) along with good mechanical properties of poly (ε-caprolactone) (PCL) can produce a suitable nanofibrous scaffold for skin tissue engineering as well as wound dressing application. In this study, PCL/C. officinalis/GA nanofibrous scaffolds with diameter distribution in the range of 85–290 nm were prepared via electrospinning. Characteristics of the nanofibrous scaffolds, i.e., morphology, scaffold compounds, porosity, mechanical and antibacterial properties, hydrophilicity and degradability in phosphate buffer saline (PBS) were investigated. Cell viability and proliferation of scaffolds were evaluated by MTT [3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay. Results indicated that hydrophilicity of the PCL/C. officinalis/GA scaffolds was higher than the PCL scaffold. The tensile strength and elongation of the PCL/C. officinalis/GA scaffolds were in the range of 2.13–4.41 MPa and 26.37–74.37%, respectively, which are very suitable for skin tissue engineering. The porosity of the scaffolds was higher than 60% and was appropriate for the proliferation of fibroblast cells. The nanocomposite scaffold also showed suitable degradability and antimicrobial activity. Moreover, cell culture indicated that GA and C. officinalis promoted cell attachment and proliferation. It can be concluded that the nanofibrous calendula-loaded PCL/GA scaffolds are well suited for regenerating skin.

     

Electrospinning of polyvinylalcohol–polycaprolactone composite scaffolds for tissue engineering applications

Random nanofibrous composite scaffolds of PVA/PCL bilayer were fabricated by electrospinning method. The bilayer nanofibrous scaffolds were subjected to detailed structural, morphological, chemical, and thermal analysis using XRD, SEM, FTIR, and DSC. Morphological investigations revealed that the prepared nanofibers have uniform morphology and the average fiber diameters for bilayer samples A, B, and C are 203, 252, and 244 nm, respectively. The obtained scaffolds have a porous structure with porosity of 77, 89.2, and 78.3 % for bilayer samples A, B, and C, respectively. FTIR analysis ensured complete evaporation of solvent and formation of non-interactive bilayers. Biocompatibility of the membranes was investigated by studying the adhesion of mouse NIH 3T3 fibroblasts for 72 h, and its enhanced adhesion and proliferation proved its mettle as a potential scaffold for tissue engineering applications.     

5-Fluorouracil-loaded poly(vinyl alcohol)/chitosan blend nanofibers: morphology,drug release and cell culture studies

Electrospun polymeric nanofibers as carriers for anticancer drugs have received a great deal of attention to treat tumor cells. This work was aimed to prepare an optimized nanofibrous sample based on poly(vinyl alcohol) (PVA)/chitosan (CS) blend, and then evaluate it containing 5-fluorouracil (5-FU) in terms of morphology, drug release, and cell culture. The electrospinning conditions to produce PVA/CS (50/50) blend nanofibers with an average diameter of approximately 150.8 nm were adjusted as follows: applied voltage 17 kV, needle tip to collector distance 60 cm, and flow rate 0.1 mL/h. The obtained results from Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed that there were no chemical interactions between the polymers and drug during the electrospinning process and the uniform morphology without beads. Moreover, to prolong 5-FU release from the blend nanofibers, three layered samples consisting of PVA/CS blend and poly (ε-caprolactone) (PCL) [PVA/CS-PCL 3-layers] were electrospun. On the other hand, by adding PCL in the PVA/CS blend nanofibers, the samples showed more hydrophobic property. Eventually, thiazolyl blue (MTT) assay along with NIH 3T3 cells culture proved that the sample could kill more than 80% of the cells. This formulation could be a promising candidate for cancer therapy potentially.

     

Evaluation of the chondrogenic differentiation of mesenchymal stem cells on hybrid biomimetic scaffolds

Hybrid materials are widely and promisingly used as scaffolds in cartilage tissue remodeling. In this study, hybrid scaffolds consist of polycaprolactone (PCL), poly(vinyl alcohol) (PVA) with/without gelatin (GEL) to mimic natural cartilage extracellular matrix (ECM) were investigated. Scaffolds were prepared by freeze drying and characterized by scanning electron microscopy and compressive mechanical testing. Biological assays of mesenchymal stem cell (MSC) cultures, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide, and dimethyl methylene blue were performed, and real‐time polymerization chain reaction analysis of the cartilage‐specific ECM gene marker expression was done. The results show an open interconnected porous structure with a compression modulus of 1.27 ± 0.04 MPa. The surface of the scaffolds showed an excellent efficiency in the adhesion and proliferation of MSCs. A significant increase in the proteoglycan content from 3.70 ± 0.96 to 5.4 ± 1.13 μg/mL was observed after 14 days in the PCL–PVA–GEL scaffolds. The expression amount of the sex‐determining region Y–Box 9 (SOX9) and collagen II (COL2) mRNA levels of the MSCs showed significant increases in SOX9 and COL2, respectively in comparison with PCL–PVA scaffold. The study revealed that the aforementioned scaffold as a blend of natural and synthetic polymers may be a promising substrate in tissue engineering for cartilage repair with MSC transplantation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40635.     

Enhancement of scaffolding properties for poly(3-hydroxybutyrate): blending with poly-β-alanine and wet electrospinning

Poly-β-alanine (PBA), and its derivatives poly(α-methyl-β-alanine) and poly[N-(3-methoxypropyl-β-alanine) were synthesized by hydrogen transfer polymerization (HTP). Porous 3?D matrices of poly(3-hydroxybutyrate) (P3HB) reinforced with PBA/its derivatives were obtained via lyophilization and wet electrospinning. However, mechanical properties of the porous matrices prepared by wet electrospinning were found to present superior performance for tissue engineering applications. Cell culture study was performed by using wet electrospun P3HB matrices doped with 10% (w/w) PBA which show better manipulation ability, chemical and mechanical properties. Scaffolds of P3HB-PBA (10% w/w) blend was determined to demonstrate better cell attachment and proliferation compared to the scaffolds of pure P3HB.