Deepak M. Kalaskar

Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix (ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.

Current progress in use of adipose derived stem cells in peripheral nerve regeneration

Unlike central nervous system neurons; those in the peripheral nervous system have the potential for full regeneration after injury. Following injury, recovery is controlled by schwann cells which replicate and modulate the subsequent immune response. The level of nerve recovery is strongly linked to the severity of the initial injury despite the significant advancements in imaging and surgical techniques. Multiple experimental models have been used with varying successes to augment the natural regenerative processes which occur following nerve injury. Stem cell therapy in peripheral nerve injury may be an important future intervention to improve the best attainable clinical results. In particular adipose derived stem cells (ADSCs) are multipotent mesenchymal stem cells similar to bone marrow derived stem cells, which are thought to have neurotrophic properties and the ability to differentiate into multiple lineages. They are ubiquitous within adipose tissue; they can form many structures resembling the mature adult peripheral nervous system. Following early in vitro work; multiple small and large animal in vivo models have been used in conjunction with conduits, autografts and allografts to successfully bridge the peripheral nerve gap. Some of the ADSC related neuroprotective and regenerative properties have been elucidated however much work remains before a model can be used successfully in human peripheral nerve injury (PNI). This review aims to provide a detailed overview of progress made in the use of ADSC in PNI, with discussion on the role of a tissue engineered approach for PNI repair.

The Use of Adipose Stem Cells in Cranial Facial Surgery

Craniofacial malformations, have devastating psychosocial implications for many adults and children and causes huge socioeconomic burden. Currently craniofacial defects require soft tissue transfer, bone grafting techniques or difficult procedures such as microvascular free flaps. Such tissues are often limited in quantity, their harvest causes secondary large donor site defects and they lack the capability to fully restore previous form and function. Stem cell technology is being utilised for various tissue and organs of the body and consequently surgeons are eager to transfer these principles for craniofacial surgery. Adipose derived stem cells (ADSCs) are an exciting stem cell source for craniofacial surgeons due to their easy and painless isolation, relatively large abundance and familiarity with the harvesting procedure. ADSCs also have multiple desirable properties including adipogenic, osteogenic and chondrogenic potential, enhancement of angiogenesis and immunodulatory function. Due to these advantageous characteristics, ASDCs have been explored to repair craniofacial bone, soft tissue and cartilage. The desirable characteristics of ADSCs for craniofacial surgical applications will be explained. We report the experimental and clinical studies that have explored the use of ADSCs for bone, cartilage and soft tissue craniofacial defects. We conclude by establishing the key questions that are preventing the clinical application of ADSCs for craniofacial surgery.

Development of mechano-responsive polymeric scaffolds using functionalized silica nano-fillers for the control of cellular functions

We demonstrate an efficient method to produce mechano-responsive polymeric scaffolds which can alter cellular functions using two different functionalized (OH and NH2) silica nano-fillers. Fumed silica-hydroxyl and fumed silica-amine nano-fillers were mixed with a biocompatible polymer (POSS-PCU) at various wt% to produce scaffolds. XPS and mechanical testing demonstrate that bulk mechanical properties are modified without changing the scaffolds surface chemistry. Mechanical testing showed significant change in bulk properties of POSS-PCU scaffolds with an addition of silica nanofillers as low as 1% (P < 0.01). Scaffolds modified with NH2 silica showed significantly higher bulk mechanical properties compared to the one modified with the OH group. Enhanced cell adhesion, proliferation and collagen production over 14 days were observed on scaffolds with higher bulk mechanical properties (NH2) compared to those with lower ones (unmodified and OH modified) (P < 0.05) during in vitro analysis. This study provides an effective method of manufacturing mechano-responsive polymeric scaffolds, which can help to customize cellular responses for biomaterial applications.

Tissue-engineered lymphatic graft for the treatment of lymphedema.

BACKGROUND Lymphedema is a chronic debilitating condition and curative treatment is yet to be found. Tissue engineering approach, which combines cellular components, scaffold, and molecular signals hold great potential in the treatment of secondary lymphedema with the advent of lymphatic graft to reconstruct damaged collecting lymphatic vessel. This review highlights the ideal characteristics of lymphatic graft, the limitation and challenges faced, and the approaches in developing tissue-engineered lymphatic graft. METHODS Literature on tissue engineering of lymphatic system and lymphatic tissue biology was reviewed. RESULTS The prime challenge in the design and manufacturing of this graft is producing endothelialized conduit with intraluminal valves. Suitable scaffold material is needed to ensure stability and functionality of the construct. Endothelialization of the construct can be enhanced via biofunctionalization and nanotopography, which mimics extracellular matrix. Nanocomposite polymers with improved performance over existing biomaterials are likely to benefit the development of lymphatic graft. CONCLUSIONS With the in-depth understanding of tissue engineering, nanotechnology, and improved knowledge on the biology of lymphatic regeneration, the aspiration to develop successful lymphatic graft is well achievable.

Chemical group-dependent plasma polymerisation preferentially directs adipose stem cell differentiation towards osteogenic or chondrogenic lineages

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Micropatterning of nanocomposite polymer scaffolds using sacrificial phosphate glass fibers for tendon tissue engineering applications

This study presents a simple and reproducible method of micropatterning the novel nanocomposite polymer (POSS-PCU) using a sacrificial phosphate glass fiber template for tendon tissue engineering applications. The diameters of the patterned scaffolds produced were dependent on the diameter of the glass fibers (15 μm) used. Scaffolds were tested for their physical properties and reproducibility using various microscopy techniques. For the first time, we show that POSS-PCU supports growth of human tenocytes cells. Furthermore, we show that cellular alignment, their biological function and expression of various tendon related proteins such as scleraxis, collagen I and III, tenascin-C are significantly elevated on the micropatterned polymer surfaces compared to flat samples. This study demonstrated a simple, reproducible method of micropatterning POSS-PCU nanocomposite polymer for novel tendon repair applications, which when provided with physical cues could help mimic the microenvironment of tenocytes cells.

The influence of porosity on the hemocompatibility of polyhedral oligomeric silsesquioxane poly (caprolactone-urea) urethane.

BACKGROUND The physio-chemical properties of blood contacting biomaterials play an important role in determining their hemocompatibility. It is shown in literature that surface roughness and porosity have significant effect on hemocompatibility. In this study, we use a biocompatible, low thrombogenic nanocomposite polymer called POSS-PCU to test this hypothesis: would porosity compromise the hemocompatibility of POSS-PCU. We compared the hemocompatibility of POSS-PCU films of various pore sizes with PTFE, which is a commercially available material used in most blood contacting devices. METHODS Sterilized POSS-PCU films with different size pores were prepared as samples and porous PTFE film were selected as control. And all samples were subjected to SEM for topograpgy, mechanical test for characterization and hemocompatibility tests to evaluate contact activation, platelet adhesion and activation, as well as whole blood clotting response to the samples. RESULTS WCA significantly increased with the pore size of POSS-PCU film, whereas both tensile stress and strain decreased significantly as the sizes of pores increased. However, when compared to PTFE film with same size pores, POSS-PCU films showed both higher tensile stress and strain. Pore size had little impact over POSS-PCUs surface chemistry groups as tested by FTIR analysis. Contact activation and platelet adhesion essay also showed no significant difference between different POSS-PCU samples. However, in whole blood reactions, POSS-PCU with pores size around 2-5μm showed higher BCI than plain films and those with pores size around 35-45μm. POSS-PCU showed lower thrombogencity and higher hemocompatibility comparing with porous PTFE on the aspects of platelet activation, adhesion and whole blood reaction. SUMMARY AND CONCLUSIONS POSS-PCU polymer films as a biomaterial in chronic blood contacting implants show significant lower thrombogencity and higher hemocompatibility than porous PTFE film. It is desirable as a coating or covering material in small diameter stents for treating cardiovascular diseases, cerebral vascular diseases and peripheral arterial diseases.

Applications of 3D printing in the management of severe spinal conditions.

The latest and fastest-growing innovation in the medical field has been the advent of three-dimensional printing technologies, which have recently seen applications in the production of low-cost, patient-specific medical implants. While a wide range of three-dimensional printing systems has been explored in manufacturing anatomical models and devices for the medical setting, their applications are cutting-edge in the field of spinal surgery. This review aims to provide a comprehensive overview and classification of the current applications of three-dimensional printing technologies in spine care. Although three-dimensional printing technology has been widely used for the construction of patient-specific anatomical models of the spine and intraoperative guide templates to provide personalized surgical planning and increase pedicle screw placement accuracy, only few studies have been focused on the manufacturing of spinal implants. Therefore, three-dimensional printed custom-designed intervertebral fusion devices, artificial vertebral bodies and disc substitutes for total disc replacement, along with tissue engineering strategies focused on scaffold constructs for bone and cartilage regeneration, represent a set of promising applications towards the trend of individualized patient care.

Development of a Tissue‐Engineered Lymphatic Graft Using Nanocomposite Polymer for the Treatment of Secondary Lymphedema

Damage of the lymphatic vessels, commonly due to surgical resection for cancer treatment, leads to secondary lymphedema. Tissue engineering approach offers a possible solution to reconstruct this damage with the use of lymphatic graft to re-establish the lymphatic flow, hence preventing lymphedema. The aim of this study is to develop a tissue-engineered lymphatic graft using nanocomposite polymer and human dermal lymphatic endothelial cells (HDLECs). A nanocomposite polymer, the polyhedral oligomeric silsequioxane-poly(carbonate-urea)urethane (POSS-PCU), which has enhanced mechanical, chemical, and physical characteristics, was used to develop the lymphatic graft. POSS-PCU has been used clinically for the worlds first synthetic trachea, lacrimal duct, and is currently undergoing clinical trial for coronary artery bypass graft. Two designs and fabrication methods were used to manufacture the conduits. The fabrication method, the mechanical and physical properties, as well as the hydraulic conductivity were tested. This is followed by in vitro cell culture analysis to test the cytocompatibility of HDLEC with the polymer surface. Using the casted extrusion method, the nanocomposite lymphatic graft demonstrates desirable mechanical property and hydraulic conductivity to re-establish the lymphatic flow. The conduit has high tensile strength (casted: 74.86 ± 5.74 MPa vs. coagulated: 31.33 ± 3.71 MPa; P < 0.001), favorable kink resistance, and excellent suture retention property (casted vs. coagulated, P < 0.05). Cytocompatibility study showed that the POSS-PCU scaffold supports the attachment and growth of HDLECs. This study demonstrates the feasibility of developing a tissue-engineered lymphatic graft using the nanocomposite polymer. It displays excellent mechanical property and cytocompatibility to HDLECs, offering much promise for clinical applications and as a new treatment option for secondary lymphedema.