Poly(ɛ-caprolactone) acrylates synthesized using a facile method for fabricating networks to achieve controllable physicochemical properties and tunable cell responses

Synergistic large segmental bone repair by 3D printed bionic scaffolds and engineered ADSC nanovesicles: Towards an optimized regenerative microenvironment

Achieving sufficient bone regeneration in large segmental defects is challenging, with the structure of bone repair scaffolds and their loaded bioactive substances crucial for modulating the local osteogenic microenvironment. This study utilized digital laser processing (DLP)-based 3D printing technology to successfully fabricate high-precision methacryloylated polycaprolactone (PCLMA) bionic bone scaffold structures. Adipose-derived stem cell-engineered nanovesicles (ADSC-ENs) were uniformly and stably modified onto the bionic scaffold surface using a perfusion device, constructing a conducive microenvironment for tissue regeneration and long bone defect repair through the scaffold's structural design and the vesicles' biological functions. Scanning electron microscopy (SEM) examination of the scaffold surface confirmed the efficient loading of ADSC-ENs. The material group loaded with vesicles (PCLMA-BAS-ENs) demonstrated good cell compatibility and osteogenic potential when analyzed for the adhesion and osteogenesis of primary rabbit bone marrow mesenchymal stem cells (BMSCs) on the material surface. Tested in a 15 mm critical rabbit radial defect model, the PCLMA-BAS-ENs scaffold facilitated near-complete bone defect repair after 12 weeks. Immunofluorescence and proteomic results indicated that the PCLMA-BAS-ENs scaffold significantly improved the osteogenic microenvironment at the defect site in vivo, promoted angiogenesis, and enhanced the polarization of macrophages towards M2 phenotype, and facilitated the recruitment of BMSCs. Thus, the PCLMA-BAS-ENs scaffold was proven to significantly promote the repair of large segmental bone defects. Overall, this strategy of combining engineered vesicles with highly biomimetic scaffolds to promote large-segment bone tissue regeneration holds great potential in orthopedic and other regenerative medicine applications.

Opposite Mechanical Preference of Bone/Nerve Regeneration in 3D-Printed Bioelastomeric Scaffolds/Conduits Consistently Correlated with YAP-Mediated Stem Cell Osteo/Neuro-Genesis

To systematically unveil how substrate stiffness, a critical factor in directing cell fate through mechanotransduction, correlates with tissue regeneration, novel biodegradable and photo-curable poly(trimethylene carbonate) fumarates (PTMCFs) for fabricating elastomeric 2D substrates and 3D bone scaffolds/nerve conduits, are presented. These substrates and structures with adjustable stiffness serve as a unique platform to evaluate how this mechanical cue affects the fate of human umbilical cord mesenchymal stem cells (hMSCs) and hard/soft tissue regeneration in rat femur bone defect and sciatic nerve transection models; whilst, decoupling from topographical and chemical cues. In addition to a positive relationship between substrate stiffness (tensile modulus: 90-990 kPa) and hMSC adhesion, spreading, and proliferation mediated through Yes-associated protein (YAP), opposite mechanical preference is revealed in the osteogenesis and neurogenesis of hMSCs as they are significantly enhanced on the stiff and compliant substrates, respectively. In vivo tissue regeneration demonstrates the same trend: bone regeneration prefers the stiffer scaffolds; while, nerve regeneration prefers the more compliant conduits. Whole-transcriptome analysis further shows that upregulation of Rho GTPase activity and the downstream genes in the compliant group promote nerve repair, providing critical insight into the design strategies of biomaterials for stem cell regulation and hard/soft tissue regeneration through mechanotransduction.

Volumetric Printing of Thiol-Ene Photo-Cross-Linkable Poly(ε-caprolactone): A Tunable Material Platform Serving Biomedical Applications

Current thoroughly described biodegradable and cross-linkable polymers mainly rely on acrylate cross-linking. However, despite the swift cross-linking kinetics of acrylates, the concomitant brittleness of the resulting materials limits their applicability. Here, photo-cross-linkable poly(ε-caprolactone) networks through orthogonal thiol-ene chemistry are introduced. The step-growth polymerized networks are tunable, predictable by means of the rubber elasticity theory and it is shown that their mechanical properties are significantly improved over their acrylate cross-linked counterparts. Tunability is introduced to the materials, by altering M_c (or the molar mass between cross-links), and its effect on the thermal properties, mechanical strength and degradability of the materials is evaluated. Moreover, excellent volumetric printability is illustrated and the smallest features obtained via volumetric 3D-printing to date are reported, for thiol-ene systems. Finally, by means of in vitro and in vivo characterization of 3D-printed constructs, it is illustrated that the volumetrically 3D-printed materials are biocompatible. This combination of mechanical stability, tunability, biocompatibility, and rapid fabrication by volumetric 3D-printing charts a new path toward bedside manufacturing of biodegradable patient-specific implants.

Fabrication and examination of polyorganophosphazene/polycaprolactone-based scaffold with degradation, in vitro and in vivo behaviors suitable for tissue engineering applications

The present study aimed to synthesis a proper scaffold consisting of hydroxylated polyphosphazene and polycaprolactone (PCL), focusing on its potential use in tissue engineering applications. The first grafting of PCL to poly(propylene glycol)phosphazene (PPGP) was performed via ROP of ε-caprolactone, whereas PPGP act as a multisite macroinitiator. The prepared poly(propylene glycol phosphazene)-graft-polycaprolactone (PPGP-g-PCL) were evaluated by essential tests, including NMR, FTIR, FESEM-EDS, TGA, DSC and contact angle measurement. The quantum calculations were performed to investigate molecular geometry and its energy, and HOMO and LUMO of PPGP-g-PCL in Materials Studio2017. MD simulations were applied to describe the interaction of the polymer on phospholipid membrane (POPC128b) in Material Studio2017. The C2C12 and L929 cells were used to probe the cell-surface interactions on synthetic polymers surfaces. Cells adhesion and proliferation onto scaffolds were evaluated using FESEM and MTT assay. In vitro analysis indicated enhanced cell adhesion, high proliferation rate, and excellent viability on scaffolds for both cell types. The polymer was further tested via intraperitoneal implantation in mice that showed no evidence of adverse inflammation and necrosis at the site of the scaffold implantation; in return, osteogenesis, new-formed bone and in vivo degradation of the scaffold were observed. Herein, in vitro and in vivo assessments confirm PPGP-g-PCL, as an appropriate scaffold for tissue engineering applications.

Tough Photo-Cross-Linked PCL-Hydroxyapatite Composites for Bone Tissue Engineering

Acrylate-based photo-cross-linked poly(ε-caprolactone) (PCL) tends to show low elongation and strength. Incorporation of osteo-inductive hydroxyapatite (HAp) further enhances this effect, which limits its applicability in bone tissue engineering. To overcome this, the thiol-ene click reaction is introduced for the first time in order to photo-cross-link PCL composites with 0, 10, 20, and 30 wt % HAp nanoparticles. It is demonstrated that the elongation at break and ultimate strength increase 10- and 2-fold, respectively, when the photopolymerization mechanism is shifted from a radical chain-growth (i.e., acrylate cross-linking) toward a radical step-growth polymerization (i.e., thiol-ene cross-linking). Additionally, it is illustrated that osteoblasts can attach to and proliferate on the surface of the photo-cross-linked PCL-HAp composites. Finally, the incorporation of HAp nanoparticles is shown to reduce the ALP activity of osteoblasts. Overall, thiol-ene cross-linked PCL-HAp composites can be considered as promising potential materials for bone tissue engineering.

Polycaprolactone usage in additive manufacturing strategies for tissue engineering applications: A review

Polycaprolactone (PCL) has been extensively applied on tissue engineering because of its low-melting temperature, good processability, biodegradability, biocompatibility, mechanical resistance, and relatively low cost. The advance of additive manufacturing (AM) technologies in the past decade have boosted the fabrication of customized PCL products, with shorter processing time and absence of material waste. In this context, this review focuses on the use of AM techniques to produce PCL scaffolds for various tissue engineering applications, including bone, muscle, cartilage, skin, and cardiovascular tissue regeneration. The search for optimized geometry, porosity, interconnectivity, controlled degradation rate, and tailored mechanical properties are explored as a tool for enhancing PCL biocompatibility and bioactivity. In addition, rheological and thermal behavior is discussed in terms of filament and scaffold production. Finally, a roadmap for future research is outlined, including the combination of PCL struts with cell-laden hydrogels and 4D printing.

Synthesis of Poly(ε-caprolactone) Diacrylate for Micelle-Cross-Linked Sodium AMPS Hydrogel for Use as Controlled Drug Delivery Wound Dressing

This study focuses on the synthesis of poly(ε-caprolactone) diacrylate (PCLDA) for the fabrication of micelle-cross-linked sodium AMPS wound dressing hydrogels. The novel synthetic approach of PCLDA is functionalizing a PCL diol with acrylic acid. The influences of varying the PCL diol/AA molar ratio and temperature on the suitable conditions for the synthesis of PCLDA are discussed. The hydrogel was synthesized through micellar copolymerization of sodium 2-acrylamido-2-methylpropane sulfonate (Na-AMPS) as a basic monomer and PCLDA as a hydrophobic association monomer. In this study, an attempt was made to develop new hydrogel wound dressings meant for the release of antibacterial drugs (ciprofloxacin and silver sulfadiazine). The chemical structures, morphology, porosity, and water interaction of the hydrogels were characterized. The hydrogels' swelling ratio and water vapor transmission rate (WVTR) showed a high swelling capacity (4688-10753%) and good WVTR (approximately 2000 g·m^-2·day^-1), which can be controlled through variation of the PCLDA concentration. The mechanical property results confirmed that PCLDA improved the mechanical properties of the hydrogel; the stress increased from 37 to 68 kPa, and the strain increased from 198 to 360% with increasing PCLDA (0-30% wt of Na-AMPS). These hydrogels presented no cytotoxicity based on over 70% cell viability responses (L929 fibroblasts) using an in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, the drug release mechanism, kinetic models, and antibacterial activity were determined. The results demonstrated that antibiotics were released from the hydrogel with a Fickian diffusion mechanism and antibacterial activity against Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus). Based on the results obtained, and bearing in mind that further progress still needs to be made, the fabricated hydrogels show considerable potential for meeting the stringent property requirements of hydrogel wound dressings.

The Effect of Heat Treatment toward Glycerol-Based, Photocurable Polymeric Scaffold: Mechanical, Degradation and Biocompatibility

Photocurable polymers have become increasingly important for their quick prototyping and high accuracy when used in three dimensional (3D) printing. However, some of the common photocurable polymers are known to be brittle, cytotoxic and present low impact resistance, all of which limit their applications in medicine. In this study, thermal treatment was studied for its effect and potential applications on the mechanical properties, degradability and biocompatibility of glycerol-based photocurable polymers, poly(glycerol sebacate) acrylate (PGSA). In addition to the slight increase in elongation at break, a two-fold increase in both Young's modulus and ultimate tensile strength were also observed after thermal treatment for the production of thermally treated PGSA (tPGSA). Moreover, the degradation rate of tPGSA significantly decreased due to the increase in crosslinking density in thermal treatment. The significant increase in cell viability and metabolic activity on both flat films and 3D-printed scaffolds via digital light processing-additive manufacturing (DLP-AM) demonstrated high in vitro biocompatibility of tPGSA. The histological studies and immune staining indicated that tPGSA elicited minimum immune responses. In addition, while many scaffolds suffer from instability through sterilization processes, it was proven that once glycerol-based polymers have been treated thermally, the influence of autoclaving the scaffolds were minimized. Therefore, thermal treatment is considered an effective method for the overall enhancement and stabilization of photocurable glycerol-based polymeric scaffolds in medicine-related applications.

Characterization of a novel semi-interpenetrating hydrogel network fabricated by polyethylene glycol diacrylate/polyvinyl alcohol/tragacanth gum as a wound dressing

In this research, a novel semi-interpenetrating hydrogel network comprised of polyethylene glycol diacrylate (PEGDA)/polyvinyl alcohol (PVA)/tragacanth gum (TG) with adaptable mechanical, biological, and physical characteristics was fabricated for wound healing purposes. The chemical structure of the films and the surface morphology were examined by FTIR and SEM, respectively. In addition, swelling ratio, mechanical characteristics, water vapor transmission rate (WVTR), gel fraction, and degradability of the hydrogels were assessed. To evaluate their cytocompatibility, MTT assay and cell attachment studies were performed. The FTIR results showed that the vinyl peaks were eliminated during crosslinking between PEGDA chains. The results also showed that incorporating PVA into the networks increases the swelling ration and decreases the porosity. Furthermore, as the ratio of PEGDA to PVA increased, WVTR ratio, cell adhesion, and elongation of the networks increased. It was also found that, when the amount of PEGDA reduced, degradation rate of the networks decreased. The results verified the non-toxic nature of PEGDA/PVA/TG hydrogel networks. Finally, the antibacterial results demonstrated that the highest antibacterial activities against bacterial pathogens is related to the TG-containing film. Therefore, PEGDA/PVA/TG hydrogel networks can be favorable wound dressings.

Hierarchical ordering and multilayer structure of poly(ε-caprolactone) end-functionalized by a liquid crystalline unit: role of polymer crystallization

This study elucidates the role of polymer crystallization in the structural organization of LC end-functionalized polymers and offers a potential method to tune the hierarchical structures of end-functionalized polymers.

Smooth Muscle Cell Responses to Poly(ε-Caprolactone) Triacrylate Networks with Different Crosslinking Time

Poly(ε-caprolactone) triacrylate (PCLTA) is attractive in tissue engineering because of its good biocompatibility and processability. The crosslinking time strongly influences PCLTAs cellular behaviors. To investigate these influences, PCLTAs with different molecular weights were crosslinked under UV light for times ranging from 1 to 20 min. The crosslinking efficiency of PCLTA increased with decreasing the molecular weight and increasing crosslinking time which could increase the gel fraction and network stiffness and decrease the swelling ratio. Then, the PCLTA networks crosslinked for different time were used as substrates for culturing rat aortic smooth muscle cells (SMCs). SMC attachment and proliferation all increased when the PCLTA molecular weight increased from 8k to 10k and then to 20k at the same crosslinking time. For the same PCLTA, SMC attachment, proliferation, and focal adhesions increased with increasing the crosslinking time, in particular, between the substrates crosslinked for less than 3 min and longer than 5 min. This work will provide a good experimental basis for the application of PCLTA.

Nanoengineered Light-Activatable Polybubbles for On-Demand Therapeutic Delivery

Vaccine coverage is severely limited in developing countries due to inefficient protection of vaccine functionality as well as lack of patient compliance to receive the additional booster doses. Thus, there is an urgent need to design a thermostable vaccine delivery platform that also enables release of the bolus after predetermined time. Here, the formation of injectable and light-activatable polybubbles for vaccine delivery is reported. In vitro studies show that polybubbles enable delayed burst release, irrespective of cargo types, namely small molecule and antigen. The extracorporeal activation of polybubbles is achieved by incorporating near-infrared (NIR)-sensitive gold nanorods (AuNRs). Interestingly, light-activatable polybubbles can be used for on-demand burst release of cargo. In vitro, ex vivo, and in vivo studies demonstrate successful activation of AuNR-loaded polybubbles. Overall, the light-activatable polybubble technology can be used for on-demand delivery of various therapeutics including small molecule drugs, immunologically relevant protein, peptide antigens, and nucleic acids.

Biomimetic Designer Scaffolds Made of D,L-Lactide-ɛ-Caprolactone Polymers by 2-Photon Polymerization

IMPACT STATEMENT

In tissue engineering (TE), the establishment of cell targeting materials, which mimic the conditions of the physiological extracellular matrix (ECM), seems to be a mission impossible without advanced materials and fabrication techniques. With this in mind we established a toolbox based on (D,L)-lactide-ɛ-caprolactone methacrylate (LCM) copolymers in combination with a nano-micromaskless lithography technique, the two-photon polymerization (2-PP) to mimic the hierarchical structured and complex milieu of the natural ECM. To demonstrate the versatility of this toolbox, we choose two completely different application scenarios in bone and tumor TE to show the high potential of this concept in therapeutic and diagnostic application.

Synthetic bioresorbable poly-α-hydroxyesters as peripheral nerve guidance conduits; a review of material properties, design strategies and their efficacy to date

Implantable tubular devices known as nerve guidance conduits (NGCs) have drawn considerable interest as an alternative to autografting in the repair of peripheral nerve injuries.

Effect of Molecular Weight and Functionality on Acrylated Poly(caprolactone) for Stereolithography and Biomedical Applications

Degradable polymers are integral components in many biomedical polymer applications. The ability of these materials to decompose in situ has become a critical component for tissue engineering, allowing scaffolds to guide cell and tissue growth while facilitating gradual regeneration of native tissue. The objective of this work is to understand the role of prepolymer molecular weight and functionality of photocurable poly(caprolactone) (PCL) in determining reaction kinetics, mechanical properties, polymer degradation, biocompatibility, and suitability for stereolithography. PCL, a degradable polymer used in a number of biomedical applications, was functionalized with acrylate groups to enable photopolymerization and three-dimensional printing via stereolithography. PCL prepolymers with different molecular weights and functionalities were studied to understand the role of molecular structure in reaction kinetics, mechanical properties, and degradation rates. The mechanical properties of photocured PCL were dependent on cross-link density and directly related to the molecular weight and functionality of the prepolymers. High-molecular weight, low-functionality PCLDA prepolymers exhibited a lower modulus and a higher strain at break, while low-molecular weight, high-functionality PCLTA prepolymers exhibited a lower strain at break and a higher modulus. Additionally, degradation profiles of cross-linked PCL followed a similar trend, with low cross-link density leading to degradation times up to 2.5 times shorter than those of more highly cross-linked polymers. Furthermore, photopolymerized PCL showed biocompatibility both in vitro and in vivo, causing no observed detrimental effects on seeded murine-induced pluripotent stem cells or when implanted into pig retinas. Finally, the ability to create three-dimensional PCL structures is shown by fabrication of simple structures using digital light projection stereolithography. Low-molecular weight, high-functionality PCLTA prepolymers printed objects with feature sizes near the hardware resolution limit of 50 μm. This work lays the foundation for future work in fabricating microscale PCL structures for a wide range of tissue regeneration applications.

Stereocomplexation, Thermal and Mechanical Properties of Conetworks Composed of Star-Shaped l-Lactide, d-Lactide and ε-Caprolactone Oligomers Utilizing Sugar Alcohols as Core Molecules

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-mscLAO/3CLO, m = 4, 5 or 6) by the crosslinking reactions of erythritol, xylitol or sorbitol-based m-armed star-shaped l-lactide and d-lactide oligomers (HmSLLAO and HmSDLAO), a glycerol-based 3-armed star-shaped ε-caprolactone oligomer (H3SCLO) and hexamethylene diisocyanate (HDI) at the weight ratios of HmSLLAO/HmSDLAO = 1/1 and (HmSLLAO + HmSDLAO)/H3CLO = 100/0, 75/25, 50/50, 25/75 or 0/100). The influence of the arm number on the crystallization behavior, thermal and mechanical properties of SPN-mscLAO/3CLOs were systematically investigated by comparing with those of sugar-alcohol-based homochiral polymer network (SPN-mLLAO, m = 4, 5 or 6) prepared by the reaction of HmSLLAO and HDI. Stereocomplex (sc) crystallites are dominantly formed for SPN-mscLAO/3CLOs 100/0⁻25/75, whereas SPN-mLLAOs were amorphous. The higher order of melting temperature of sc-crystals for SPN-mscLAO/3CLOs 100/0⁻25/75 was m = 5 > m = 6 > m = 4. The sc-crystallinities of SPN-4scLAO/3CLOs 100/0⁻50/50 were significantly lower than those of SPN-mscLAO/3CLOs 100/0⁻50/50 (m = 5 and 6). The larger order of the sc-spherulite size at crystallization temperature of 110 °C was m = 5 > m = 6 > m = 4 for SPN-mscLAO/3CLO 100/0. The size and number of sc-spherulites decreased with increasing crystallization temperature over the range of 110⁻140 °C and with increasing CLO fraction. Among all the networks, SPN-5scLAO/3CLOs 75/25 and 50/50 exhibited the highest and second highest tensile toughnesses (21.4 and 20.3 MJ·m-3), respectively.

An injectable poly(caprolactone trifumarate-gelatin microparticles) (PCLTF-GMPs) scaffold for irregular bone defects: Physical and mechanical characteristics

Recently, a modified form of a three-dimension (3D) porous poly(caprolactone-trifumarate) (PCLTF) scaffold has been produced using a fabrication technique that involves gelatin microparticles porogen leaching. This poly(caprolactone trifumarate-gelatin microparticles) (PCLTF-GMPs) scaffold has been shown to be biocompatible, more flowable clinically, and has a shorter degradation time as compared to its existing predecessors. In this report, a detailed characterization of this new scaffold was performed by testing its cytocompatibility, analyzing the surface topography, and understanding its thermal, physical and mechanical properties. The result showed that the PCLTF-GMPs has no critical cytotoxic effect. To confirm improvement, the surface properties were compared against the older version of PCLTF fabricated using salt porogen leaching. This PCLTF-GMPs scaffold showed no significant difference (unpaired t-test; p>0.05) in mechanical properties before and after gelatin leaching. However, it is mechanically weaker when compared to its predecessors. It has a high biodegradability rate of 16weeks. The pore size produced ranges from 40 to 300μm, and the RMS roughness is 613.7±236.9nm. These characteristics are condusive for osteoblast in-growth, as observed by the extension of filopodia across the macropores. Overall, this newly produced material has good thermal, physical and mechanical properties that complements its biocompatibility and ease of use.

Porous crosslinked polycaprolactone hydroxyapatite networks for bone tissue engineering

In this study, porous scaffolds were produced by a thermal crosslinking of polycaprolactone diacrylate in the presence of hydroxyapatite (HA) and particulate leaching technique with sodium chloride as the water soluble porogen for bone tissue engineering applications. The prepared scaffolds were characterized using techniques such as Field Emission Scanning Electron Microscopy, Differential Scanning Calorimetry, and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. Moreover, dynamic mechanical properties were investigated using Dynamic Mechanical Thermal Analysis. The obtained scaffolds present a porous structure with interconnected pores and porosity around 73%. It was found that the incorporation of HA particles to polycaprolactone (PCL) matrix resulted in an increased crystallinity. Moreover, both the storage modulus (E') and glass transition temperature (T_g) increased, while the loss factor (tan δ) decreased due to the hindrance of the HA particles to the mobility of polymer segments. Cytocompatability of the scaffolds was assessed by MTT assay and cell attachment studies. Osteoconductivity of the scaffolds was investigated with cells alkaline phosphatase extraction. The levels of alkaline phosphatase activity were found to be higher for PCL/HA network scaffold than for PCL network scaffold. In addition, cytocompatibility of the PCL/HA network scaffold indicated no toxicity, and cells were attached and spread to the scaffold walls.

Biomedical Applications of Biodegradable Polyesters

The focus in the field of biomedical engineering has shifted in recent years to biodegradable polymers and, in particular, polyesters. Dozens of polyester-based medical devices are commercially available, and every year more are introduced to the market. The mechanical performance and wide range of biodegradation properties of this class of polymers allow for high degrees of selectivity for targeted clinical applications. Recent research endeavors to expand the application of polymers have been driven by a need to target the general hydrophobic nature of polyesters and their limited cell motif sites. This review provides a comprehensive investigation into advanced strategies to modify polyesters and their clinical potential for future biomedical applications.

Roles of hydroxyapatite allocation and microgroove dimension in promoting preosteoblastic cell functions on photocured polymer nanocomposites through nuclear distribution and alignment

This study clarifies how hydroxyapatite (HA) allocation and microgroove dimension affect mouse preosteoblastic MC3T3-E1 cell functions on microgrooved substrates of polymer nanocomposites. Using replica molding from micromachined silicon wafer templates, we fabricated photocured poly(ε-caprolactone) triacrylate (PCLTA)/HA nanocomposite substrates with parallel microgrooves (two groove widths of 5 and 15 μm and one groove depth of 5 μm). Four types of microgrooved substrates were made: "homogeneous" ones of PCLTA and PCLTA/HA with uniform distribution and two "heterogeneous" laminated microgrooved substrates with HA only in the PCLTA matrix in the ridges or bottom. These substrates were used to regulate MC3T3-E1 cell attachment, proliferation, alignment, nuclear circularity and distribution, and mineralization. MC3T3-E1 cell attachment and proliferation were much higher on the microgrooved substrates of PCLTA/HA than on those of PCLTA, in particular, on the 5 μm wide microgrooved substrate with PCLTA/HA ridges and PCLTA bottom. The shape and distribution of MC3T3-E1 cytoskeleton and nuclei were altered by the substrate topography and HA allocation. For 5 μm wide heterogeneous microgrooved substrates with HA only in the ridges, MC3T3-E1 cells exhibited better spreading perpendicular to the microgrooves but tended to extend along the microgrooves containing HA in the bottom. The widest cells and the roundest/largest cell nuclei were observed on the heterogeneous substrate with PCLTA/HA ridges, while the narrowest cells with the best elongation were found on the homogeneous PCLTA/HA substrate. The trend in MC3T3-E1 cell mineralization on the substrates was consistent with that in cell/nuclear elongation. Osteocalcin mRNA expression was significantly higher on the PCLTA/HA substrates than on the PCLTA ones and also on the microgrooved substrates of PCLTA/HA than on the flat ones, regardless of the groove width of 5 or 15 μm.

Development of silica grafted poly(1,8-octanediol-co-citrates) hybrid elastomers with highly tunable mechanical properties and biocompatibility

By a facile polymerization, we synthesized a series of silica grafted poly (1,8-octanediol-co-citrate) (SPOC) hybrid elastomers with highly tunable physicochemical properties and bioactivities.

Poly(γ-glutamic acid) induced homogeneous mineralization of the poly(ethylene glycol)-co-2-hydroxyethyl methacrylate cryogel for potential application in bone tissue engineering

Homogeneous mineralization of a polymeric cryogel could be induced by poly(γ-glutamic acid) and benefit the cell response of the cryogel.

Novel biodegradable poly(propylene fumarate)-co-poly(l-lactic acid) porous scaffolds fabricated by phase separation for tissue engineering applications

Scaffolds with intrinsically interconnected porous structures are highly desirable in tissue engineering and regenerative medicine. In this study, three-dimensional polymer scaffolds with highly interconnected porous structures were fabricated by thermally induced phase separation of novel synthesized biodegradable poly(propylene fumarate)-co-poly(l-lactic acid) in a dioxane/water binary system. Defined porous scaffolds were achieved by optimizing conditions to attain interconnected porous structures. The effect of phase separation parameters on scaffold morphology were investigated, including polymer concentration (1, 3, 5, 7, and 9%), quench time (1, 4, and 8 min), dioxane/water ratio (83/17, 85/15, and 87/13 wt/wt), and freeze temperature (-20, -80, and -196 °C). Interesting pore morphologies were created by adjusting these processing parameters, e.g., flower-shaped (5%; 85/15; 1 min; -80 °C), spherulite-like (5%; 85/15; 8 min; -80 °C), and bead-like (5%; 87/13; 1 min; -80 °C) morphology. Modulation of phase separation conditions also resulted in remarkable differences in scaffold porosities (81% to 91%) and thermal properties. Furthermore, scaffolds with varied mechanic strengths, degradation rates, and protein adsorption capabilities could be fabricated using the phase separation method. In summary, this work provides an effective route to generate multi-dimensional porous scaffolds that can be applied to a variety of hydrophobic polymers and copolymers. The generated scaffolds could potentially be useful for various tissue engineering applications including bone tissue engineering.

3D-Printable Biodegradable Polyester Tissue Scaffolds for Cell Adhesion

Additive manufacturing, or three-dimensional (3D) printing, has emerged as a viable technique for the production of vascularized tissue engineering scaffolds. In this report, a biocompatible and biodegradable poly(tri(ethylene glycol) adipate) dimethacrylate was synthesized and characterized for suitability in soft-tissue scaffolding applications. The polyester dimethacrylate exhibited highly efficient photocuring, hydrolyzability, and 3D printability in a custom microstereolithography system. The photocured polyester film demonstrated significantly improved cell attachment and viability as compared with controls. These results indicate promise of novel, printable polyesters for 3D patterned, vascularized soft-tissue engineering scaffolds.

Enhanced femoral nerve regeneration after tubulization with a tyrosine-derived polycarbonate terpolymer: effects of protein adsorption and independence of conduit porosity

Following complete nerve transection, entubulation of the nerve stumps helps guide axons to reconnect distally. In this study, a biodegradable and noncytotoxic tyrosine-derived polycarbonate terpolymer composed of 89.5 mol% desaminotyrosyl tyrosine ethyl ester (DTE), 10 mol% desaminotyrosyl tyrosine (DT), and 0.5 mol% poly(ethylene glycol) (PEG, molecular weight [Mw]=1 kDa) [designated as E10-0.5(1K)] was used to fabricate conduits for peripheral nerve regeneration. These conduits were evaluated against commercially available nonporous polyethylene (PE) tubes. The two materials are characterized in vitro for differences in surface properties, and the conduits are then evaluated in vivo in a critical-sized nerve defect in the mouse femoral nerve model. Conduits were fabricated from E10-0.5(1K) in both porous [P-E10-0.5(1K)] and nonporous [NP-E10-0.5(1K)] configurations. The results illustrate that adsorption of laminin, fibronectin, and collagen type I was enhanced on E10-0.5(1K) compared to PE. In addition, in vivo the E10-0.5(1K) conduits improved functional recovery over PE conduits, producing regenerated nerves with a fivefold increase in the number of axons, and an eightfold increase in the percentage of myelinated axons. These increases were observed for both P-E10-0.5(1K) and NP-E10-0.5(1K) after 15 weeks. When conduits were removed at 7 or 14 days following implantation, an increase in Schwann cell proteins and fibrin matrix formation was observed in E10-0.5(1K) conduits over PE conduits. These results indicate that E10-0.5(1K) is a pro-regenerative material for peripheral nerves and that the porosity of P-E10-0.5(1K) conduits was inconsequential in this model of nerve injury.

Multiwalled CNT-pHEMA composite conduit for peripheral nerve repair

A nerve conduit is designed to improve peripheral nerve regeneration by providing guidance to the nerve cells. Conductivity of such guides is reported to enhance this process. In the current study, a nerve guide was constructed from poly(2-hydroxyethyl methacrylate) (pHEMA), which was loaded with multiwalled carbon nanotubes (mwCNT) to introduce conductivity. PHEMA hydrogels were designed to have a porous structure to facilitate the transportation of the compounds needed for cell nutrition and growth and also for waste removal. We showed that when loaded with relatively high concentrations of mwCNTs (6%, w/w in hydrogels), the pHEMA guide was more conductive and more hydrophobic than pristine pHEMA hydrogel. The mechanical properties of the composites were better when they carried mwCNT. Elastic modulus of 6% mwCNT loaded pHEMA was twofold higher (0.32 ± 0.06 MPa) and similar to that of the soft tissues. Electrical conductivity was significantly improved (11.4-fold) from 7 × 10(-3) Ω(-1).cm(-1) (pHEMA) to 8.0 × 10(-2) Ω(-1).cm(-1) (6% mwCNT loaded pHEMA). On application of electrical potential, the SHSY5Y neuroblastoma cells seeded on mwCNTs carrying pHEMA maintained their viability, whereas those on pure pHEMA could not, indicating that mwCNT helped conduct electricity and make them more suitable as nerve conduits.

Biomimetic calcium carbonate concentric microgrooves with tunable widths for promoting MC3T3-E1 cell functions

Biomimetic, self-assembled calcium carbonate (CaCO(3) ) concentric microgrooves with groove widths of 5.0 and 10 μm were fabricated through simply controlling incubation temperature. Mouse pre-osteoblastic MC3T3-E1 cells were cultured on flat and microgrooved substrates of CaCO(3) and their adhesion, spreading, proliferation, alkaline phosphatase activity, and calcium content were remarkably enhanced by the microgrooves, in particular, the narrower ones. Furthermore, focal adhesions and actin filaments of MC3T3-E1 cells could be aligned on both 5.0-μm and 10-μm-wide CaCO(3) grooves. Compared with the original round nuclei on the flat substrates and expanded round nuclei on the narrower microgrooves, the MC3T3-E1 cell nuclei on 10-μm-wide CaCO(3) grooves demonstrated preferred entrapment in the grooves and significant alignment with a smaller area after two-day culture.

Regulating MC3T3-E1 cells on deformable poly(ε-caprolactone) honeycomb films prepared using a surfactant-free breath figure method in a water-miscible solvent

Honeycomb poly(ε-caprolactone) (PCL) films with tunable pore diameters of 3.5, 6.0, and 10 μm were fabricated directly from solutions in water-miscible, relatively nontoxic tetrahydrofuran using the breath-figure method without assistance of a surfactant. These honeycomb PCL films were characterized in terms of structures and enhanced hydrophobicity. Aiming at fostering bone tissue engineering outcomes, we cultured mouse preosteoblastic MC3T3-E1 cells on these honeycomb films as well as on the flat control, and evaluated their adhesion, spreading, proliferation, alkaline phosphatase (ALP) activity, and calcium content. These cell behaviors were further correlated with the expression levels of integrin subunits of α(1), α(2), β(1), and bone-specific gene markers of ALP, collagen type I (COL I), osteocalcin (OCN), and osteopontin (OPN). Honeycomb PCL films remarkably promoted MC3T3-E1 cell adhesion, spreading, proliferation, differentiation, and gene expression. This effect was more prominent when the pore diameter was smaller in the studied range. In addition, honeycomb PCL films were stretched into groove-like structures, on which MC3T3-E1 cells were aligned with a smaller cell area, a higher percentage of aligned cells, and a higher cell elongation ratio when the pores were smaller.

Photocured biodegradable polymer substrates of varying stiffness and microgroove dimensions for promoting nerve cell guidance and differentiation

Photocross-linkable and biodegradable polymers have great promise in fabricating nerve conduits for guiding axonal growth in peripheral nerve regeneration. Here, we photocross-linked two poly(ε-caprolactone) triacrylates (PCLTAs) with number-average molecular weights of ~7000 and ~10,000 g mol(-1) into substrates with parallel microgrooves. Cross-linked PCLTA7k was amorphous and soft, while cross-linked PCLTA10k was semicrystalline with a stiffer surface. We employed different dimensions of interests for the parallel microgrooves, that is, groove widths of 5, 15, 45, and 90 μm and groove depths of 0.4, 1, 5, and 12 μm. The behaviors of rat Schwann cell precursor line (SpL201) cells with the glial nature and pheochromocytoma (PC12) cells with the neuronal nature were studied on these microgrooved substrates, showing distinct preference to the substrates with different mechanical properties. We found different threshold sensitivities of the two nerve cell types to topographical features when their cytoskeleton and nuclei were altered by varying the groove depth and width. Almost all of the cells were aligned in the narrowest and deepest microgrooves or around the edge of microgrooves. Oriented SpL201 cell movement had a higher motility as compared to unaligned ones. After forskolin treatment, SpL201 cells demonstrated significantly upregulated S-100 and O4 on stiffer substrates or narrower microgrooves, suggesting more differentiation toward early Schwann cells (SCs). PC12 neurites were oriented with enhanced extension in narrower microgrooves. The present results not only improve our fundamental understanding on nerve cell-substrate interactions, but also offer useful conduit materials and appropriate feature dimensions to foster guidance for axonal growth in peripheral nerve regeneration.

Decoupling polymer properties to elucidate mechanisms governing cell behavior

Determining how a biomaterial interacts with cells ("structure-function relationship") reflects its eventual clinical applicability. Therefore, a fundamental understanding of how individual material properties modulate cell-biomaterial interactions is pivotal to improving the efficacy and safety of clinically translatable biomaterial systems. However, due to the coupled nature of material properties, their individual effects on cellular responses are difficult to understand. Structure-function relationships can be more clearly understood by the effective decoupling of each individual parameter. In this article, we discuss three basic decoupling strategies: (1) surface modification, (2) cross-linking, and (3) combinatorial approaches (i.e., copolymerization and polymer blending). Relevant examples of coupled material properties are briefly reviewed in each section to highlight the need for improved decoupling methods. This follows with examples of more effective decoupling techniques, mainly from the perspective of three primary classes of synthetic materials: polyesters, polyethylene glycol, and polyacrylamide. Recent strides in decoupling methodologies, especially surface-patterning and combinatorial techniques, offer much promise in further understanding the structure-function relationships that largely govern the success of future advancements in biomaterials, tissue engineering, and drug delivery.

Optimal poly(L-lysine) grafting density in hydrogels for promoting neural progenitor cell functions

Recently, we have developed a photopolymerizable poly(L-lysine) (PLL) that can be covalently incorporated into poly(ethylene glycol) diacrylate (PEGDA) hydrogels to improve their bioactivity by providing positive charges. To explore the potential of these PLL-grafted PEGDA hydrogels as a cell delivery vehicle and luminal filler in nerve guidance conduits for peripheral and central nerve regeneration, we varied the number of pendent PLL chains in the hydrogels by photo-cross-linking PEGDA with weight compositions of PLL (φ(PLL)) of 0, 1, 2, 3, and 5%. We further investigated the effect of PLL grafting density on E14 mouse neural progenitor cell (NPC) behavior including cell viability, attachment, proliferation, differentiation, and gene expression. The amount of actually grafted PLL and charge densities were characterized, showing a proportional increase with the feed composition φ(PLL). NPC viability in 3D hydrogels was significantly improved in a PLL grafting density-dependent manner at days 7 and 14 postencapsulation. Similarly, NPC attachment and proliferation were promoted on the PLL-grafted hydrogels with increasing φ(PLL) up to 2%. More intriguingly, NPC lineage commitment was dramatically altered by the amount of grafted PLL chains in the hydrogels. NPC differentiation demonstrated a parabolic or nonmonotonic dependence on φ(PLL), resulting in cells mostly differentiated toward mature neurons with extensive neurite formation and astrocytes rather than oligodendrocytes on the PLL-grafted hydrogels with φ(PLL) of 2%, whereas the neutral hydrogels and PLL-grafted hydrogels with higher φ(PLL) of 5% support NPC differentiation less. Gene expression of lineage markers further illustrated this trend, indicating that PLL-grafted hydrogels with an optimal φ(PLL) of 2% could be a promising cell carrier that promoted NPC functions for treatment of nerve injuries.

Biodegradable photo-crosslinked polymer substrates with concentric microgrooves for regulating MC3T3-E1 cell behavior

Both intrinsic material properties and topographical features are critical in influencing cell-biomaterial interactions. We present a systematic investigation of regulating mouse pre-osteoblastic MC3T3-E1 cell behavior on biodegradable polymer substrates with distinct mechanical properties and concentric microgrooves. The precursors for fabricating substrates used here were two poly(ϵ-caprolactone) triacrylates (PCLTAs) synthesized from poly(ϵ-caprolactone) triols with molecular weights of ∼7000 and ∼10000 g mol(-1) . These two PCLTAs were photo-crosslinked into PCL networks with distinct thermal, rheological, and mechanical properties at physiological temperature because of their different crystallinities and melting temperatures. Microgrooved substrates with four groove widths of 7.5, 16.1, 44.2, and 91.2 μm and three groove depths of 0.2, 1, and 10 μm were prepared through replica molding, i.e., photo-crosslinking PCLTA on micro-fabricated silicon wafers with pre-designed concentric groove patterns. MC3T3-E1 cell attachment and proliferation could be better supported by the stiffer substrates while not significantly influenced by the microgrooves. Microgroove dimensions could regulate MC3T3-E1 cell alignment, nuclear shape and distribution, mineralization, and gene expression. Among the microgrooves with a fixed depth of 10 μm, the smallest width of 7.5 μm could align and elongate the cytoskeleton and nuclei most efficiently. Strikingly, higher mineral deposition and upregulation of osteocalcin gene expression were found in the narrower microgrooves when the groove depth was 10 μm.

Poly(ε-caprolactone)-banded spherulites and interaction with MC3T3-E1 cells

We report that protein adsorption, cell attachment, and cell proliferation were enhanced on spherulites-roughened polymer surfaces. Banded spherulites with concentric alternating succession of ridges and valleys were observed on spin-coated thin films of poly(ε-caprolactone) (PCL) and two series of PCL binary homoblends composed of high- and low-molecular-weight components when they were isothermally crystallized at 25-52 °C. Their thermal properties, crystallization kinetics, and surface morphology were examined. The melting temperature (T(m)), crystallinity (χ(c)), crystallization rate, and spherulitic patterns showed strong dependence on the crystallization temperature (T(c)) and the blend composition. The surface roughness of the spherulites was higher when T(c) was higher; thus, the larger surface area formed in banded spherulites could adsorb more serum proteins from cell culture media. In vitro mouse preosteoblastic MC3T3-E1 cell attachment, proliferation, and nuclear localization were assessed on the hot-compressed flat disks and spherulites-roughened films of the high-molecular-weight PCL and one of its homoblends. The number of attached MC3T3-E1 cells and the proliferation rate were greater on the rougher surfaces than those on the flat ones. It is interesting to note that cell nuclei were preferentially, though not absolutely, located in or close to the valleys of the banded spherulites. The percentage of cell nuclei in the valleys was higher than 78% when the ridge height and adjacent ridge distance were ~350 and ~35 nm, respectively. This preference was weaker when the ridge height was lower or at a higher cell density. These results suggest that isothermal crystallization of semicrystalline polymers can be an effective thermal treatment method to achieve controllable surface roughness and pattern for regulating cell behaviors in tissue-engineering applications.

Promoting nerve cell functions on hydrogels grafted with poly(L-lysine)

We present a novel photopolymerizable poly(L-lysine) (PLL) and use it to modify polyethylene glycol diacrylate (PEGDA) hydrogels for creating a better, permissive nerve cell niche. Compared with their neutral counterparts, these PLL-grafted hydrogels greatly enhance pheochromocytoma (PC12) cell survival in encapsulation, proliferation, and neurite growth and also promote neural progenitor cell proliferation and differentiation capacity, represented by percentages of both differentiated neurons and astrocytes. The role of efficiently controlled substrate stiffness in regulating nerve cell behavior is also investigated and a polymerizable cationic small molecule, [2-(methacryloyloxy)ethyl]-trimethylammonium chloride (MTAC), is used to compare with this newly developed PLL. The results indicate that these PLL-grafted hydrogels are promising biomaterials for nerve repair and regeneration.

Lubricated biodegradable polymer networks for regulating nerve cell behavior and fabricating nerve conduits with a compositional gradient

We present a method of tuning surface chemistry and nerve cell behavior by photo-cross-linking methoxy poly(ethylene glycol) monoacrylate (mPEGA) with hydrophobic, semicrystalline poly(ε-caprolactone) diacrylate (PCLDA) at various weight compositions of mPEGA (ø(m)) from 2 to 30%. Improved surface wettability is achieved with corresponding decreases in friction, water contact angle, and capability of adsorbing proteins from cell culture media because of repulsive PEG chains tethered in the network. The responses of rat Schwann cell precursor line (SpL201), rat pheochromocytoma (PC12), and E14 mouse neural progenitor cells (NPCs) to the modified surfaces are evaluated. Nonmonotonic or parabolic dependence of cell attachment, spreading, proliferation, and differentiation on ø(m) is identified for these cell types with maximal values at ø(m) of 5-7%. In addition, NPCs demonstrate enhanced neuronal differentiated lineages on the mPEGA/PCLDA network at ø(m) of 5% with intermediate wettability and surface energy. This approach lays the foundation for fabricating heterogeneous nerve conduits with a compositional gradient along the wall thickness, which are able to promote nerve cell functions within the conduit while inhibiting cell attachment on the outer wall to prevent potential fibrous tissue formation following implantation.

Photocrosslinkable polyesters and poly(ester anhydride)s for biomedical applications

Crosslinking is a feasible way to prepare biodegradable polymers with potential in biomedical applications such as controlled release of active agents and tissue engineering. A synthesis route in which functional telechelic aliphatic polyester oligomers are used as precursors for the preparation of crosslinked polyesters and poly(ester anhydride)s is described. Mechanical properties, degradation characteristics and rate, and bioactivity can be modified widely by controlling the chemical composition and architecture of the crosslinkable oligomers. In tissue engineering, photocrosslinking allows to use crosslinkable oligomers in advanced manufacturing techniques like micromolding in capillaries, stereolithography and two-photon polymerization.

Exposed hydroxyapatite particles on the surface of photo-crosslinked nanocomposites for promoting MC3T3 cell proliferation and differentiation

We present a systematic study for investigating the role of exposed hydroxyapatite (HA) nanoparticles in influencing surface characteristics and mouse pre-osteoblastic MC3T3-E1 cell behavior using nanocomposites prepared by photo-crosslinking poly(ε-caprolactone) diacrylate (PCLDA) with HA. PCLDA530 and PCLDA2000 synthesized from poly(ε-caprolactone) diol precursors with nominal molecular weights of 530 and 2000 g mol(-1) were used as the polymer matrices. Crosslinked PCLDA530 was amorphous while crosslinked PCLDA2000 was semi-crystalline. Crosslinked PCLDA/HA composites with different compositions of HA (10%, 20% and 30%) as well as crosslinked PCLDAs were characterized in terms of their composition-dependent physicochemical properties. The tensile, compressive and shear moduli were greatly enhanced by incorporating HA nanoparticles with the polymer matrices. The disk surfaces of original crosslinked PCLDA/HA nanocomposites were removed by cutting using a blade to expose HA nanoparticles that were embedded in the polymer substrates. The composition of HA was much higher on the cut surface, particularly in semi-crystalline crosslinked PCLDA2000/HA nanocomposites. The surface characteristics of original and cut crosslinked PCLDA/HA nanocomposites were compared and correlated with cell behavior on these nanocomposites. MC3T3-E1 cell attachment, proliferation and differentiation were significantly enhanced when the HA composition was increased in original crosslinked PCLDA/HA nanocomposites due to more bioactive HA, higher surface stiffness and rougher topography. More exposed HA on the surface of cut semi-crystalline PCLDA2000/HA nanocomposites resulted in improved hydrophilicity and significantly better MC3T3 cell attachment, proliferation and differentiation compared with the original surfaces. This study suggests that HA nanoparticles may not be fully exploited in polymer/HA nanocomposites where the top polymer surface covers the particles. The removal of this polymer layer can generate more desirable surfaces and osteoconductivity for bone repair and regeneration.