Integrating Fused Deposition Modeling and Melt Electrowriting for Engineering Branched Vasculature.

We demonstrate for the first time the combination of two additive manufacturing technologies used in tandem, fused deposition modelling (FDM) and melt electrowriting (MEW), to increase the range of possible MEW structures, with a focus on creating branched, hollow scaffolds for vascularization. First, computer-aided design (CAD) was used to design branched mold halves which were then used to FDM print conductive polylactic acid (cPLA) molds. Next, MEW was performed over the top of these FDM cPLA molds using polycaprolactone (PCL), an FDA-approved biomaterial. After the removal of the newly constructed MEW scaffolds from the FDM molds, complementary MEW scaffold halves were heat-melded together by placing the flat surfaces of each half onto a temperature-controlled platform, then pressing the heated halves together, and finally allowing them to cool to create branched, hollow constructs. This hybrid technique permitted the direct fabrication of hollow MEW structures that would otherwise not be possible to achieve using MEW alone. The scaffolds then underwent in vitro physical and biological testing. Specifically, dynamic mechanical analysis showed the scaffolds had an anisotropic stiffness of 1 MPa or 5 MPa, depending on the direction of the applied stress. After a month of incubation, normal human dermal fibroblasts (NHDFs) were seen growing on the scaffolds, which demonstrated that no deleterious effects were exerted by the MEW scaffolds constructed using FDM cPLA molds. The significant potential of our hybrid additive manufacturing approach to fabricate complex MEW scaffolds could be applied to a variety of tissue engineering applications, particularly in the field of vascularization.

Macrocystis pyrifera Lipids Reduce Cytokine-Induced Pro-Inflammatory Signalling and Barrier Dysfunction in Human Keratinocyte Models.

Atopic dermatitis is a chronic condition where epidermal barrier dysfunction and cytokine production by infiltrating immune cells exacerbate skin inflammation and damage. A total lipid extract from Macrocystis pyrifera, a brown seaweed, was previously reported to suppress inflammatory responses in monocytes. Here, treatment of human HaCaT keratinocytes with M. pyrifera lipids inhibited tumour necrosis factor (TNF)-α induced TNF receptor-associated factor 2 and monocyte chemoattractant protein (MCP)-1 protein production. HaCaT cells stimulated with TNF-α, interleukin (IL)-4, and IL-13 showed loss of claudin-1 tight junctions, but little improvement was observed following lipid pre-treatment. Three-dimensional cultures of HaCaT cells differentiated at the air-liquid interface showed increased MCP-1 production, loss of claudin-1 tight junctions, and trans-epidermal leakage with TNF-α, IL-4, and IL-13 stimulation, with all parameters reduced by lipid pre-treatment. These findings suggest that M. pyrifera lipids have anti-inflammatory and barrier-protective effects on keratinocytes, which may be beneficial for the treatment of atopic dermatitis or other skin conditions.

Three-Dimensional Printed Cellulose for Wound Dressing Applications.

Wounds are skin tissue damage due to trauma. Many factors inhibit the wound healing phase (hemostasis, inflammation, proliferation, and alteration), such as oxygenation, contamination/infection, age, effects of injury, sex hormones, stress, diabetes, obesity, drugs, alcoholism, smoking, nutrition, hemostasis, debridement, and closing time. Cellulose is the most abundant biopolymer in nature which is promising as the main matrix of wound dressings because of its good structure and mechanical stability, moisturizes the area around the wound, absorbs excess exudate, can form elastic gels with the characteristics of bio-responsiveness, biocompatibility, low toxicity, biodegradability, and structural similarity with the extracellular matrix (ECM). The addition of active ingredients as a model drug helps accelerate wound healing through antimicrobial and antioxidant mechanisms. Three-dimensional (3D) bioprinting technology can print cellulose as a bioink to produce wound dressings with complex structures mimicking ECM. The 3D printed cellulose-based wound dressings are a promising application in modern wound care. This article reviews the use of 3D printed cellulose as an ideal wound dressing and their properties, including mechanical properties, permeability aspect, absorption ability, ability to retain and provide moisture, biodegradation, antimicrobial property, and biocompatibility. The applications of 3D printed cellulose in the management of chronic wounds, burns, and painful wounds are also discussed.

Development and optimisation of hydroxyapatite-polyethylene glycol diacrylate hydrogel inks for 3D printing of bone tissue engineered scaffolds.

In the event of excessive damage to bone tissue, the self-healing process alone is not sufficient to restore bone integrity. Three-dimensional (3D) printing, as an advanced additive manufacturing technology, can create implantable bone scaffolds with accurate geometry and internal architecture, facilitating bone regeneration. This study aims to develop and optimise hydroxyapatite-polyethylene glycol diacrylate (HA-PEGDA) hydrogel inks for extrusion 3D printing of bone tissue scaffolds. Different concentrations of HA were mixed with PEGDA, and further incorporated with pluronic F127 (PF127) as a sacrificial carrier. PF127 provided good distribution of HA nanoparticle within the scaffolds and improved the rheological requirements of HA-PEGDA inks for extrusion 3D printing without significant reduction in the HA content after its removal. Higher printing pressures and printing rates were needed to generate the same strand diameter when using a higher HA content compared to a lower HA content. Scaffolds with excellent shape fidelity up to 75-layers and high resolution (∼200 µm) with uniform strands were fabricated. Increasing the HA content enhanced the compression strength and decreased the swelling degree and degradation rate of 3D printed HA-PEGDA scaffolds. In addition, the incorporation of HA improved the adhesion and proliferation of human bone mesenchymal stem cells (hBMSCs) onto the scaffolds. 3D printed scaffolds with 2 wt% HA promoted osteogenic differentiation of hBMSCs as confirmed by the expression of alkaline phosphatase activity and calcium deposition. Altogether, the developed HA-PEGDA hydrogel ink has promising potential as a scaffold material for bone tissue regeneration, with excellent shape fidelity and the ability to promote osteogenic differentiation of hBMSCs.

3D printing of chitooligosaccharide-polyethylene glycol diacrylate hydrogel inks for bone tissue regeneration.

To date, lack of functional hydrogel inks has limited 3D printing applications in tissue engineering. This study developed a series of photocurable hydrogel inks based on chitooligosaccharide (COS)-polyethylene glycol diacrylate (PEGDA) for extrusion-based 3D printing of bone tissue scaffolds. The scaffolds were prepared by aza-Michael addition of COS and PEGDA followed by photopolymerisation of unreacted PEGDA. The hydrogel inks showed sufficient shear thinning properties required for extrusion 3D printing. The printed scaffolds exhibited excellent shape fidelity and fine microstructure with a resolution of 250 µm. By increasing the COS content, the swelling ratio of the scaffolds decreased, while the compressive strength increased. 3D printed COS-PEGDA scaffolds showed high viability of human bone mesenchymal stem cells in vitro. In addition, scaffolds containing 2 wt% COS showed significantly higher alkaline phosphatase activity, calcium deposition, and bioactivity in simulated body fluid compared to the control (PEGDA). Altogether, 3D printed COS-PEGDA scaffolds represent promising candidates for bone tissue regeneration.

Green synthesis of chitooligosaccharide-PEGDA derivatives through aza-Michael reaction for biomedical applications.

Chitooligosaccharide (COS) as an emerging material carbohydrate polymer with huge potential in biomedical applications was prepared using a microwave-assisted process. The obtained COS exhibited reduced molecular weight (Mw) and higher water solubility in comparison to chitosan while preserving the main saccharide structure and same degree of deacetylation (DD). The optimized COS (13 kDa) was then used to synthesize a new family of COS-poly(ethylene glycol) diacrylate (PEGDA) derivatives based on aza-Michael addition of acrylate groups of PEGDA to the amine groups of COS in the absence of any exterior agents. The modulation of the reaction time, temperature, pH and NH2:acrylate molar ratio, had a strong influence on the Michael reaction progress. At higher degrees of conversion of acrylate groups, COS-PEGDA derivative formed gel with high biocompatibility towards human bone mesenchymal stem cells (hBMSCs). These COS-PEGDA hydrogels synthesized at mild conditions through a green chemistry are, therefore, an innovative system combining adequate biological performance, ease of preparation, and an environmentally friendly concept of production.

3D Living Dressing Improves Healing and Modulates Immune Response in a Thermal Injury Model.

Thermal injury trauma can induce a state of immunosuppression, causing wounds to become chronic in nature. Stem cell-based therapies represent a promising new approach to treat such wounds due to their capacity to self-renew and their multi-lineage potential. Mesenchymal stem cells (MSCs) are known to secrete endogenous factors that stimulate wound healing by promoting angiogenesis, extracellular matrix remodeling, skin regeneration, and by dampening down inflammation. MSC delivery in a biomaterial construct can augment their wound-healing capacity by concentrating cells at the burn site and upregulating trophic factor secretion. The work presented is the first to evaluate repair in an in vitro raft thermal injury model using a regenerative, dual cell delivery three-dimensional (3D) core/shell (c/s) "living dressing" construct. This previously characterized 3D c/s bioprinted construct, which delivers both MSCs and endothelial cells, was used to treat an in vitro 3D raft skin thermal injury wound model. The mesenchymal stromal cell line (T0523) was encapsulated within a gelatin-based shell bioink, and human umbilical vein endothelial cells within a chitosan-based core bioink to biofabricate a living dressing for enhanced thermal injury repair and regeneration. We hypothesized that the cell-laden c/s tissue engineered construct (TEC) would strengthen the wound's proangiogenic, anti-inflammatory, and skin regeneration potential. An in vitro thermal injury in a 3D raft skin model showed a slight delay in wound closure in the presence of the c/s TEC but was augmented by corresponding increases in the release of wound-healing factors, epidermal growth factor, matrix metalloproteinases-9, transforming growth factor-α, platelet-derived growth factor; a decrease in pro-inflammatory factor interleukin-6, and evidence of neovascularization.

A comparison between ß-tricalcium phosphate and chitosan poly-caprolactone-based 3D melt extruded composite scaffolds.

Melt extrusion 3D printing has become an attractive additive manufacturing technology to construct degradable scaffolds as tissue precursors in order to create clinically relevant medical devices. Towards this end, a commonly used synthetic polyester, poly-caprolactone (PCL), was used to make scaffolds composed of different biomaterial compositions to increase bioactivity using 3D melt pneumatic extrusion technology. Varying ratios of the natural biopolymer, chitosan, or the bioceramic, ß-tricalcium phosphate (TCP) were blended with PCL to fabricate support scaffolds with three-dimensional (3D) architecture for human bone-marrow derived mesenchymal stem cell (hBMSC) growth for potential bone regeneration application. In this study, basic printing requirements as well as biomaterial dynamic mechanical (DMA), elemental, and thermogravimetric (TGA) analysis results demonstrate material homogeneity as well as thermal stability. Scaffold morphology and microarchitecture were assessed using scanning electron microscopy (SEM) alongside in vitro scaffold degradation and biological characterisation. Human BMSC proliferation was assessed using fluorescence imaging, and quantitated via the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) colorimetric assay. These in vitro cell viability studies revealed that the highest chitosan concentration blend of 20% favoured the most hBMSC growth, exhibited the most swelling, and showed minimal degradation after 28 days. The 20% TCP blend had the second highest hBMSC growth, exhibited moderate swelling, and the fastest degradation rate. Overall, this study demonstrates the first direct comparison of a natural biopolymer-based, that is, chitosan, 3D melt extruded PCL composite with that of a bioceramic-based, that is, ß-TCP, PCL composite and their effects on hBMSC 3D proliferation. 3D melt extruded PCL-based composite scaffolds methodology offers a straightforward way to print scaffolds with good shape fidelity, interconnected porosities and enhanced bioactivity; and demonstrates their potential use for regenerative, bone repair applications.

Intervertebral Disc Tissue Engineering Using Additive Manufacturing.

Intervertebral disc (IVD) degeneration is one of the major causes of lower back pain, a common health condition that greatly affects the quality of life. With an increasing elderly population and changes in lifestyle, there exists a high demand for novel treatment strategies for damaged IVDs. Researchers have investigated IVD tissue engineering (TE) as a way to restore biological and mechanical functions by regenerating or replacing damaged discs using scaffolds with suitable cells. These scaffolds can be constructed using material extrusion additive manufacturing (AM), a technique used to build three-dimensional (3D), custom discs utilising computer-aided design (CAD). Structural geometry can be controlled via the manipulation of printing parameters, material selection, temperature, and various other processing parameters. To date, there are no clinically relevant TE-IVDs available. In this review, advances in AM-based approaches for IVD TE are briefly discussed in order to achieve a better understanding of the requirements needed to obtain more effective, and ultimately clinically relevant, IVD TE constructs.

Chitosan hydrogels in 3D printing for biomedical applications.

Tissue engineering and regenerative medicine have entered a new stage of development by the recent progress in biology, material sciences, and particularly an emerging additive manufacturing technique, three-dimensional (3D) printing. 3D printing is an advanced biofabrication technique which can generate patient-specific scaffolds with highly complex geometries while hosting cells and bioactive agents to accelerate tissue regeneration. Chitosan hydrogels themselves have been widely used for various biomedical applications due to its abundant availability, structural features and favorable biological properties; however, the 3D printing of chitosan-based hydrogels is still under early exploration. Therefore, 3D printing technologies represent a new avenue to explore the potential application of chitosan as an ink for 3D printing, or as a coating on other 3D printed scaffolds. The combination of chitosan-based hydrogels and 3D printing holds much promise in the development of next generation biomedical implants.

Three-Dimensional Melt-Electrowritten Polycaprolactone/Chitosan Scaffolds Enhance Mesenchymal Stem Cell Behavior.

Melt electrowriting (MEW) is an emerging technique that precisely fabricates microfibrous scaffolds, ideal for tissue engineering, where biomimetic microarchitectural detail is required. Polycaprolactone (PCL), a synthetic polymer, was selected as the scaffold material due to its biocompatibility, biodegradability, mechanical strength, and melt processability. To increase PCL bioactivity, a natural polymer, chitosan, was added to construct MEW fibrous composite scaffolds. To date, this is the first study of its kind detailing the effects of stem cell behavior on PCL containing chitosan MEW scaffolds. The aim of this study was to melt electrowrite a range of PCL/chitosan tissue-engineered constructs (TECs) and assess their suitability to promote the growth of human bone-marrow-derived mesenchymal stem cells (hBMSCs). In vitro physical and biological characterizations of melt-electrowritten TECs were performed. Physical characterization showed that reproducible, layered micron-range scaffolds could be successfully fabricated. As well, cell migration and proliferation were assessed via an assay to monitor cell infiltration throughout the three-dimensional (3D) melt-electrowritten scaffold structure. A statistically significant increase (∼140%) in hBMSC proliferation in 1 wt % chitosan PCL blends in comparison to PCL-only scaffolds was found when monitored over two weeks. Overall, our study demonstrates the fabrication of melt-electrowritten PCL/chitosan composite scaffolds with controlled microarchitecture and their potential use for regenerative, tissue engineering applications.

Advancements in the Delivery of Growth Factors and Cytokines for the Treatment of Cutaneous Wound Indications.

Significance: Wound healing involves the phasic production of growth factors (GFs) and cytokines to progress an acute wound to a resolved scar. Dysregulation of these proteins contributes to both wound chronicity and excessive scarring. Direct supplementation of GFs and cytokines for treatment of healing and scarring complications has, however, been disappointing. Failings likely relate to an inability to deliver recombinant proteins at physiologically relevant levels to an environment conducive to healing. Recent Advances: Inspired by the extracellular matrix, natural biomaterials have been developed that resemble human skin, and are capable of delivering bioactives. Hybrid biomaterials made using multiple polymers, fabrication methods, and proteins are proving efficacious in animal models of acute and impaired wound healing. Critical Issues: For clinical translation, these delivery systems must be tailored for specific wound indications and the correct phase of healing. GFs and cytokines must be delivered in a controlled manner that will target specific healing or scarring impairments. Preclinical assessment in clinically relevant animal models of impaired or excessive healing is critical. Future Directions: Clinical success will likely depend on the GF or cytokine selected, their compatibility with the chosen biomaterial(s), degradation rate of the fabricated system, and the degree of control over release kinetics. Further testing is essential to assess which wound indications are most suited to specific delivery systems and to prove whether they provide superior efficacy over direct protein therapies.

Melt Electrowritten Sandwich Scaffold Technique Using Sulforhodamine B to Monitor Stem Cell Behavior.

Background: Three-dimensional (3D) printing using melt electrowriting (MEW) technology is a recently developed technique to produce biocompatible micron-level mesh scaffolds layer-by-layer that can be seeded with cells for tissue engineering. Examining cell behavior, such as growth rate and migration, can be problematic in these opaque 3D scaffolds. A straightforward and quantitative method was developed to examine these cellular parameters on poly-ɛ-caprolactone (PCL) multilayered MEW scaffolds developed as components of the annulus fibrosus region of bioengineered intervertebral discs. Experiment: The anti-adhesion protein, bovine serum albumin (BSA), was used to coat plasticware to improve mesenchymal stem cell (T0523) adhesion to MEW scaffolds. Cells were seeded on circular MEW (cMEW) discs as defined growth starting points sandwiched between two test template scaffolds investigated at varying pore sizes. Cell expansion, growth, and migration were quantitated utilizing the protein-specific dye sulforhodamine B (SRB). Live cell imaging combined with image analysis were used to examine cell motility and expansion on 3D scaffolds. Results: After one coating of BSA, cells remained nonadherent for the duration of the study with cell spheroids formed and enlarging over 21 days and becoming entangled in MEW scaffold pores. Cells grown on the 250 µm pore size scaffolds exhibited a doubling time of 7 days, whereas the 400 µm pore size scaffolds time was 11.5 days. Conclusions: BSA coating of tissue culture dishes prevented surface adhesion of cells to vessel surfaces and promoted spheroid formation that encouraged attachment to the PCL scaffolds. Batch-printed cMEW scaffolds were useful as a defined starting point for quantitative assays that successfully measured cell migration, expansion and proliferation on test scaffolds. The SRB assay was shown to be a useful and straightforward way to quantitate cell numbers in multilayered MEW scaffolds. A pore size of 250 µm exhibited the fastest cell growth, spread, and expansion. Impact statement In this article, a new, useful, and straightforward method to quantitate cell numbers on three-dimensional (3D) melt electrowritten (MEW) scaffolds is presented. By using the sulforhodamine B assay on bovine serum albumin-coated dishes cell migration, expansion and proliferation in 3D printed MEW test scaffolds were quantitatively measured. Printed circular MEW (cMEW) scaffolds sandwiched between two MEW test scaffolds (Fig. 3) were used as defined cellular growth starting points with a particular pore size of 250 µm displaying the fastest cell growth and migration. This MEW sandwich technique could potentially be used to quantitate cell numbers and migration in other 3D multilayered MEW scaffold systems.

Peptide Chitosan/Dextran Core/Shell Vascularized 3D Constructs for Wound Healing.

Three-dimensional (3D) bioprinting has emerged to create novel cell-based therapies for regenerative medicine applications. Vascularized networks within engineered constructs are required, and toward this end, we report a promising strategy using core-shell (c/s) extrusion 3D-bioprinting technology that employs biomimetic biomaterials to construct regenerative, prevascularized scaffolds for wound care. A custom-designed cell-responsive bioink consisting of a 13% (w/v) cell-laden gelatin methacryloyl (GelMA) shell surrounding a peptide-functionalized, succinylated chitosan (C)/dextran aldehyde (D) cell-laden core was successfully bioprinted resulting in organized microdesigns exhibiting excellent cell viability and subsequent vessel formation. Our templating strategy takes advantage of GelMA's intrinsic thermoreversible properties of low degree of acryloyl functionalization used in combination with a lightly, chemically cross-linked peptide-CD core to serve as temporal structural supports that stabilize during extrusion onto a cooled platform. Mechanical integrity was further strengthened layer-by-layer via GelMA UV photo-cross-linking. We report the first example of GelMA used in combination with a peptide-CD bioink to c/s 3D-bioprint regenerative, prevascularized constructs for wound care. Particular cell adhesion and proteolytic peptide-CD functionalized pair combinations, P15/MMP-2 and P15/cRGD, were found to significantly increase growth of human bone-marrow-derived mesenchymal stems cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs). The constructs delivered two cell types: hBMSCs in the shell bioink and HUVECs within the core bioink. Cord-like, natural microvascularization was shown with endothelial cell marker expression as confirmed by immunofluorescence (IF) staining exhibiting tubelike structures. In addition, in vitro skin wound healing activity of the construct showed a ∼twofold rate of wound closure. Overall, c/s 3D-bioprinted, peptide-CD/GelMA constructs provided the appropriate microenvironment for in vitro stem and endothelial cell viability, delivery, and differentiation. We foresee these custom constructs as representing a fundamental step toward engineering larger scale regenerative, prevascularized tissues.

Keratinous materials: Structures and functions in biomedical applications.

Keratins are a family of fibrous proteins anticipated to possess wide-ranging biomedical applications due to their abundance, physicochemical properties and intrinsic biological activity. This review mainly focuses on the biomaterials derived from three major sources of keratins; namely human hair, wool and feather, that have effective applications in tissue engineering, wound healing and drug delivery. This article offers five viewpoints regarding keratin i) an introduction to keratin protein extraction and keratin-based scaffold fabrication methods ii) applications in nerve and bone tissue engineering iii) a review on the keratin dressings applied to different types of wounds to facilitate wound healing and thereby repair the skin iv) the utilization of keratinous materials as a carrier system for therapeutics with a controlled manner v) a discussion regarding the main challenges for using keratin in biomedical applications as well as its future prospects.

Melt-electrowriting with novel milk protein/PCL biomaterials for skin regeneration.

Demand for skin replacements is rapidly increasing as burn and full-thickness wounds are difficult to repair due to the low regeneration capability of innate tissues, as well as the physical drawbacks associated with currently available substitutes. To address this need, an emerging 3D printing technique, melt-electrowriting (MEW) was used to create novel bioactive scaffolds to promote skin regeneration. Polycaprolactone (PCL), a bioresorbable and biocompatible, synthetic polymer with Food and Drug Administration approval for use in the human body was selected as scaffold material due to its mechanical stability, flexibility, and superior melt processing properties. In order to increase PCL's biological functionality bioactive milk proteins (MPs) were blended with PCL. To date, this is the first study of its kind detailing the tissue regenerative capacity of PCL containing MPs as bioactive additives for skin regeneration using MEW. The aim of this study was to MEW MP/PCL tissue engineered constructs (TEC) and assess their suitability for generating tissue in vitro. The MPs, lactoferrin (LF) and whey protein (WP), were mixed with PCL individually at varying concentrations (0.05%, 0.1%, 0.25%), and in combination (COMB) at concentrations of 0.25% each. TECs were characterised chemically, physically, and their biological activity assessed in vitro. Physical characterisation of MEW MP/PCL scaffolds showed that reproducible, layered micron range scaffolds could be fabricated; displaying high porosity, low degradation, and rapid protein release. Biological activity, determined via an in vitro skin model using human keratinocytes (HaCaTs) and normal human dermal fibroblasts cells, showed significantly increased cell growth, spreading, and infiltration into LF (0.25%) containing scaffolds and COMB scaffolds when compared to PCL alone (p ≤ 0.05). These findings demonstrated that the combined addition of LF and WP increased the biological activity of MEW PCL scaffolds and could be potentially used as a TEC for deep tissue dermal regeneration.

3D-printed chitosan-based scaffolds: An in vitro study of human skin cell growth and an in-vivo wound healing evaluation in experimental diabetes in rats.

The fabrication of porous 3D printed chitosan (CH) scaffolds for skin tissue regeneration and their behavior in terms of biocompatibility, cytocompatibility and toxicity toward human fibroblasts (Nhdf) and keratinocytes (HaCaT), are presented and discussed. 3D cell cultures achieved after 20 and 35 days of incubation showed significant in vitro qualitative and quantitative cell growth as measured by neutral red staining and MTT assays and confirmed by scanning electron microphotographs. The best cell growth was obtained after 35 days on 3D scaffolds when the Nhdf and HaCaT cells, seeded together, filled the pores in the scaffolds. An early skin-like layer consisting of a mass of fibroblast and keratinocyte cells growing together was observed. The tests of 3D printed scaffolds in wound healing carried out on streptozotocin-induced diabetic rats demonstrate that 3D printed scaffolds improve the quality of the restored tissue with respect to both commercial patch and spontaneous healing.

A chitosan/dextran-based hydrogel as a delivery vehicle of human bone-marrow derived mesenchymal stem cells.

A chitosan/dextran-based (CD) injectable, surgical hydrogel has been developed and shown to be an effective post-operative aid in prevention of scar tissue formation in vivo. The CD hydrogel's effectiveness in a surgical setting prompted an investigation into its capacity as a potential delivery vehicle for bone marrow derived mesenchymal stem cells (BM-MSCs) for regenerative wound healing applications. By housing BM-MSCs within a biocompatible, injectable, hydrogel matrix, viability and protection in cultivation, as well as direct delivery to the damaged site in the host tissue may be achieved. In vitro BM-MSC cell viability in the presence of CD hydrogel was determined by LIVE/DEAD® fluoresence staining. Flow cytometry studies revealed expression of a conventional BM-MSC surface marker profile. A colony forming cell assay showed a slight statistically significant decrease in the number of colonies grown in CD hydrogel as compared to control cells. In addition, BM-MSCs in the CD hydrogel were able to successfully differentiate into adipocytes and osteocytes. In summary, the CD hydrogel supports MSC growth and differentiation; and therefore, may be used as a potential stem cell delivery vehicle for regenerative medicine and tissue engineering applications.

Cyclodextrin-polyhydrazine degradable gels for hydrophobic drug delivery.

An injectable and biocompatible hydrogel system was designed for hydrophobic drug delivery. This hydrogel consisted of degradable polymers with cyclodextrin (CD) moieties. CD groups were used to increase the solubility of a hydrophobic molecule (nicardipine) in an aqueous solution through the formation of the inclusion complex. Two sets of gels were prepared by mixing oxidized dextran (DA) and CD functionalized polyhydrazine (PH) at physiological conditions and different level of crosslinking via hydrazone bonds. Cytotoxicity studies on the gels and their components confirmed the biocompatibility of these materials. Gel-30 with higher crosslinking density showed a two week degradation period whereas this period was 10days for gel-10, with lower crosslinking density, to complete degradation. The results from swelling tests and rheological measurements were also found to be dependent on crosslinking density of the hydrogels. Release profile of the hydrogel displayed a sustained release of nicardipin up to 6days for gel-30 and a 4day release with initial burst release for gel-10.

Strong poly(ethylene oxide) based gel adhesives via oxime cross-linking.

There is a demand for materials to replace or augment the use of sutures and staples in surgical procedures. Currently available commercial surgical adhesives provide either high bond strength with biological toxicity or polymer and protein-based products that are biologically acceptable (though with potential sensitizing potential) but have much reduced bond strength. It is desirable to provide novel biocompatible and biodegradable surgical adhesives/sealants capable of high strength with minimal immune or inflammatory response. In this work, we report the end group derivatization of 8-arm star PEOs with aldehyde and amine end groups. Gels were prepared employing the Schiff-base chemistry between the aldehydes and the amines. Gel setting times, swelling behavior and rheological characterization were carried out for these gels. The mechanical-viscoelastic properties were found to be directly proportional to the crosslinking density of the gels, the 10K PEO gel was stiffer in comparison to the 20K PEO gel. The adhesive properties of these gels were tested using porcine skin and showed excellent adhesion properties. Cytotoxicity studies were carried out for the individual gel components using two different methods: (a) Crystal Violet Staining assay (CVS assay) and (b) impedance and cell index measurement by the xCELLigence system at concentrations >5%. Gels prepared by mixing 20% w/w solutions were also tested for cytotoxicity. The results revealed that the individual gel components as well as the prepared gels and their leachables were non-cytotoxic at these concentrations. STATEMENT OF SIGNIFICANCE: This work presents a new type of glue that is aimed at surgery applications using a water soluble star shaped polymer. It show excellent adhesion to skin and is tough and easy to use. We show that it is very biocompatible based on tests on live human cells, and could therefore in principle be used for internal surgery. Comparison with other reported and commercial glues shows that it is stronger than most, and does not swell in water to the same degree as many other water based bioadhesives.