Confined compression of collagen hydrogels

Reconstituted collagen hydrogels are often used for in vitro studies of cell-matrix interaction and as scaffolds for tissue engineering. Understanding the mechanical and transport behaviours of collagen hydrogels is therefore extremely important, albeit difficult due to their very high water content (typically > 99.5%). In the present study the mechanical behaviour of collagen hydrogels in confined compression was investigated using biphasic theory (J. Biomech. Eng. 102 (1980) 73), to ascertain whether the technique is sufficiently sensitive to determine differences in the characteristics of hydrogels of between 0.2% and 0.4% collagen. Peak stress, equilibrium stress, aggregate modulus and hydraulic permeability of the hydrogels exhibited sensitivity to collagen content, demonstrating that the technique is clearly able to discriminate between hydrogels with small differences in collagen content and may also be sensitive to factors that affect matrix remodelling. The results also offer additional insight into the deformation-dependent permeability of collagen hydrogels. This study suggests that confined compression, together with biphasic theory, is a suitable technique for assessing the mechanical properties of collagen hydrogels

Computational analysis of collagen delivery to the striatum

Introduction In recent years, cell therapy has emerged as a promising therapeutic strategy for Parkinson’s disease. To increase cell viability, biomaterials are used to facilitate cell deposition, through injection, to the site of interest. However, the existing cell delivery approaches have shown limited success in clinical translation 1 .This study aims to develop a device for the delivery of a cell-embedded in situ forming hydrogel. Here, computational approaches on the delivery of collagen to the striatum are presented, to gain insight into different parameters affecting the delivery. Methods The delivery of collagen to the striatum was modelled computationally in the two-dimensional space. The striatum was modelled as a circular space, with an area of 3.98 cm2 corresponding to the mean volume of putamen in Parkinson’s disease patients2 . Within the finite volume method framework, the flow of collagen was considered incompressible, with non-Newtonian fluid behavior characterized experimentally, and constant inlet velocity corresponding to a maximum delivery volume. Results The effects of collagen injection on the velocity and pressure fields within the striatum were examined. Velocity streamlines and wall shear stress (WSS) values were also analysed near the edges of the needle, at the entrance of the collagen to the striatum. High WSS values may influence cell viability on the site of delivery. Conclusion Intrastriatal injection of a cell embedded hydrogel is a complex process which is not yet well characterized. Computational analysis of the delivery can assist to identify the obstacles facing clinical translation. Further analysis is required including 3D reconstruction from MRI images and computational modelling in the three-dimensional space

Flow simulation of a natural polymer in a syringe-needle delivery device

Neurodegenerative diseases, such as Parkinson's disease, affect a large num- ber of the erderly population and still remain untreated. In recent years, cell therapy has emerged as a promising therapeutic strategy. To increase cell viability, biomaterials are of- ten used as scaffolds and facilitate cell deposition, through injection, to the site of interest. However, fluid forces acting on the cells during injection may lead to their disruption or death. This study aims to develop a novel device for the delivery of a cell-embedded, in situ forming, collagen hydrogel. A preliminary simulation study on constricted channels rep- resenting the syringe was performed to gain insight into the effect of needle diameter and syringe geometry. Straight needles emanating co-axially from syringes of various geome- tries were computationally modelled in the two-dimensional space, using OpenFOAMⓇ. The natural collagen solution was modelled as a continuum medium, without cells, and the flow was assumed incompressible, with non-Newtonian fluid constitutive behaviour. The effects of needle diameter and syringe geometry on velocity and shear stresses were examined. The results highlight the importance of geometric characteristics on the design of new cell delivery devices. If cells pass from the syringe barrel to the needle, the pressure drop and the increased velocity could damage them. This is more likely to occur using higher Gauge needles. Further analysis is required including simulations of cells during injection and analysis of their deformation

Towards an effective, needle-based delivery device for Parkinson's disease : a simulation study on the impact of needle diameter

Recently, several therapies have emerged for Parkinson’s disease, a challenging neurodegenerative disorder. However, clinical translation is restricted, partially due to limitations in delivering therapeutics to the Central Nervous System (CNS)which cannot be reached by systemic administration. An alternative method, that bypasses the blood brain barrier and offers high-concentrated deposition in the diseased region, is intrastriatal delivery of a cell-loaded in situ forming collagen hydrogel. However, this strategy has disadvantages, including neuroimmune response and haemorrhage. To minimize these responses, an optimised medical device should be designed. Of main consideration is the volume dispensed and the needle dimensions. Current approaches use 18-20-Gaugediameter needles and multiple cranial penetrations [1]. Additionally, fluid forces acting on cells may lead to cell disruption and death [2]. This study aims to develop a novel device for the effective delivery of a cell-loaded in situ forming collagen hydrogel to the CNS. A simulation study on constricted channels representing the needle was performed to gain insight into the optimal needle diameter

Bioinspired silica as drug delivery systems and their biocompatibility

Silica nanoparticles have been shown to have great potential as drug delivery systems (DDS), however, their fabrication often involves harsh chemicals and energy intensive laborious methods. This work details the employment of a bioinspired "green" method for the controlled synthesis of silica, use of the products to entrap and release drug molecules and their cytotoxicity in order to develop novel DDS. Bioinspired silica synthesis occurs at pH 7, room temperature and in less than 5 minutes, resulting in a rapid, cheaper and greener route. Drugs were loaded into silica during the silica formation, thus allowing a one step and one pot method for simultaneous silica synthesis and drug loading. We established that the drug release profile can be modulated by synthetic parameters, which can allow design of tailored DDS. A systematic investigation using a two level factorial design was adopted in order to identify the key synthetic parameters and quantify their effects on silica formation, drug loading and drug release. The observation that these new DDS are considerably less cytotoxic than their current counterparts, and exhibit additional benefits such as green synthesis and ease of functionalization, strengthens the argument for their future use in DDS and other biomedical applications. © 2014 the Partner Organisations

Follow-up study evaluating the long term outcome of chondromimetic in the treatment of osteochondral defects in the knee

© 2020 by the authors. Scaffolds are thought to be a key element needed for successful cartilage repair treatments, and this prospective extension study aimed to evaluate long-term structural and clinical outcomes following osteochondral defect treatment with a cell-free biphasic scaffold. Structural outcomes were assessed using quantitative 3-D magnetic resonance imaging (MRI) and morphological segmentation to determine the percentage of defect filling and repair cartilage T2 relaxation times, and clinical outcomes were determined with the modified Cincinnati Rating System, and the Knee Injury and Osteoarthritis Outcome Score (KOOS). Seventeen subjects with osteochondral defects in the knee were treated with ChondroMimetic scaffolds, from which 15 returned for long-term evaluation at a mean follow-up of 7.9 - 0.3 years. The defects treated were trochlear donor sites for mosaicplasty in 13 subjects, and medial femoral condyle defects in 2 subjects. MRI analysis of scaffold-treated defects found a mean total defect filling of 95.2 - 3.6%, and a tissue mean T2 relaxation time of 52.5 - 4.8 ms, which was identical to the T2 of ipsilateral control cartilage (52.3 - 9.2 ms). The overall modified Cincinnati Rating System score was statistically significant from baseline (p = 0.0065), and KOOS subscales were equivalent to other cartilage repair techniques. ChondroMimetic treatment resulted in a consistently high degree of osteochondral defect filling with durable, cartilage-like repair tissue at 7.9 years, potentially associated with clinical improvement

Manipulating the mechanical strength and biological stability of collagen-based scaffolds for tissue engineering

This thesis was previously held under moratorium from 20th February 2013 until 1st April 2020.Collagen, the most abundant structural protein in the body, has become the most widely used matrix for tissue engineering. Implanted collagen undergoes a constant process of remodelling, and it is the balance of collagen synthesis and its gradual breakdown by the cells of the body that will determine its strength and effectiveness as a scaffold. It has been shown that collagen for implantation is degraded more quickly than cells are able to synthesise new collagen, resulting in a rapid reduction in matrix strength. The collagen is broken down by tissue/cell derived collagenases, which are members of the matrix metalloproteinase (MMP) family of enzymes. Angiotensin converting enzyme (ACE) inhibitors have long been used successfully to treat hypertension. More recently, some ACE inhibitors have also been shown to inhibit certain MMPs. The purpose of this thesis was to investigate the potential of the ACE inhibitors captopril and enalapril to inhibit enzymatic collagen degradation, and ultimately slow down the rate at which collagen is degraded by cells of the body. Both captopril and enalapril were shown to inhibit enzymatic collagen degradation in a dose-dependent manner, at concentrations that are non-toxic to cells in culture. To determine whether the ACE inhibitors were able to affect the mechanical properties of fibroblast-populated collagen lattices (FPCLs), a technique was developed for the characterisation of their time-dependent properties. The technique, which facilitates estimation of the stiffness and hydraulic permeability of hydrogel samples via confined compression and biphasic theory, may also be suitable for characterising other inherently weak hydrated tissues, and therefore may be of great value to anyone interested in doing so. Having demonstrated that the technique was sensitive to small variations in collagen content, it was used to compare the mechanical properties of FPCLs, where it was shown that FPCLs treated with captopril or enalapril were stiffer than control FPCLs after 6 days in culture. It seems likely that the retention of matrix stiffness is attributable to a reduction in the rate of substrate degradation by collagenolytic enzymes, which in turn can be attributed to their inhibition by the ACE inhibitors, though the mechanism of inhibition is still not fully understood. The potential to manipulate the strength and stability of collagen implants by treating them with ACE inhibitors has major implications throughout the fields of tissue engineering, regenerative medicine and cosmetic surgery.Collagen, the most abundant structural protein in the body, has become the most widely used matrix for tissue engineering. Implanted collagen undergoes a constant process of remodelling, and it is the balance of collagen synthesis and its gradual breakdown by the cells of the body that will determine its strength and effectiveness as a scaffold. It has been shown that collagen for implantation is degraded more quickly than cells are able to synthesise new collagen, resulting in a rapid reduction in matrix strength. The collagen is broken down by tissue/cell derived collagenases, which are members of the matrix metalloproteinase (MMP) family of enzymes. Angiotensin converting enzyme (ACE) inhibitors have long been used successfully to treat hypertension. More recently, some ACE inhibitors have also been shown to inhibit certain MMPs. The purpose of this thesis was to investigate the potential of the ACE inhibitors captopril and enalapril to inhibit enzymatic collagen degradation, and ultimately slow down the rate at which collagen is degraded by cells of the body. Both captopril and enalapril were shown to inhibit enzymatic collagen degradation in a dose-dependent manner, at concentrations that are non-toxic to cells in culture. To determine whether the ACE inhibitors were able to affect the mechanical properties of fibroblast-populated collagen lattices (FPCLs), a technique was developed for the characterisation of their time-dependent properties. The technique, which facilitates estimation of the stiffness and hydraulic permeability of hydrogel samples via confined compression and biphasic theory, may also be suitable for characterising other inherently weak hydrated tissues, and therefore may be of great value to anyone interested in doing so. Having demonstrated that the technique was sensitive to small variations in collagen content, it was used to compare the mechanical properties of FPCLs, where it was shown that FPCLs treated with captopril or enalapril were stiffer than control FPCLs after 6 days in culture. It seems likely that the retention of matrix stiffness is attributable to a reduction in the rate of substrate degradation by collagenolytic enzymes, which in turn can be attributed to their inhibition by the ACE inhibitors, though the mechanism of inhibition is still not fully understood. The potential to manipulate the strength and stability of collagen implants by treating them with ACE inhibitors has major implications throughout the fields of tissue engineering, regenerative medicine and cosmetic surgery

Compression testing of collagen hydrogels

Paper detailing the process of compression testing of collagen hydrogels

Culture of 3T3 fibroblasts in collagen gels in the presence of ACE inhibitors

Conference submission on the development of a culture of 3T3 fibroblasts in collagen gels in the presence of ACE inhibitors presented at the annual congress of the british toxicology societ

The effect of cell ingrowth on the mechanical behaviour of anchored collagen gels

Collagen gels are often used in studies of cell-matrix interactions and as scaffolds for tissue engineering. However, the effect of cell proliferation on their bulk mechanical properties is still poorly understood. We recently published a method for extracting meaningful mechanical properties from collagen gels of > 99.5% water, using confined compression and biphasic theory (J Biomech 46 (2013) 837). In the present study we used this technique to investigate the effects of cell ingrowth on the transient mechanical behaviour of highly hydrated collagen gels