In vitro nerve repair--in vivo. The reconstruction of peripheral nerves by entubulation with biodegradeable glass tubes--a preliminary report

Effects of Bioactive Glasses (BGs) on Exosome Production and Secretion: A Critical Review

There is an increasing trend toward the application of bioactive glasses in different areas of biomedicine, including tissue engineering and oncology. The reason for this increase is mostly attributed to the inherent properties of BGs, such as excellent biocompatibility, and the ease of tailoring their properties by changing, for example, the chemical composition. Previous experiments have demonstrated that the interactions between BGs and their ionic dissolution products, and mammalian cells, can affect and change cellular behaviors, and thereby govern the performance of living tissues. However, limited research exists on their critical role in the production and secretion of extracellular vesicles (EVs) such as exosomes. Exosomes are nanosized membrane vesicles that carry various therapeutic cargoes such as DNA, RNA, proteins, and lipids, and thereby can govern cell-cell communication and subsequent tissue responses. The use of exosomes is currently considered a cell-free approach in tissue engineering strategies, due to their positive roles in accelerating wound healing. On the other hand, exosomes are known as key players in cancer biology (e.g., progression and metastasis), due to their capability to carry bioactive molecules between tumor cells and normal cells. Recent studies have demonstrated that the biological performance of BGs, including their proangiogenic activity, is accomplished with the help of exosomes. Indeed, therapeutic cargos (e.g., proteins) produced in BG-treated cells are transferred by a specific subset of exosomes toward target cells and tissues, and lead to a biological phenomenon. On the other hand, BGs are suitable delivery vehicles that can be utilized for the targeted delivery of exosomes to cells and tissues of interest. Therefore, it seems necessary to have a deeper understanding of the potential effects of BGs in the production of exosomes in cells that are involved in tissue repair and regeneration (mostly mesenchymal stem cells), as well as in those that play roles in cancer progression (e.g., cancer stem cells). This review aims to present an updated report on this critical issue, to provide a roadmap for future research in the fields of tissue engineering and regenerative medicine.

Repair of Long Peripheral Nerve Defects in Sheep: A Translational Model for Nerve Regeneration

Despite advances in microsurgery, full functional recovery of severe peripheral nerve injuries is not commonly attained. The sheep appears as a good preclinical model since it presents nerves with similar characteristics to humans. In this study, we induced 5 or 7 cm resection in the peroneal nerve and repaired with an autograft. Functional evaluation was performed monthly. Electromyographic and ultrasound tests were performed at 6.5 and 9 months postoperation (mpo). No significant differences were found between groups with respect to functional tests, although slow improvements were seen from 5 mpo. Electrophysiological tests showed compound muscle action potentials (CMAP) of small amplitude at 6.5 mpo that increased at 9 mpo, although they were significantly lower than the contralateral side. Ultrasound tests showed significantly reduced size of tibialis anterior (TA) muscle at 6.5 mpo and partially recovered size at 9 mpo. Histological evaluation of the grafts showed good axonal regeneration in all except one sheep from autograft 7 cm (AG7) group, while distal to the graft there was a higher number of axons than in control nerves. The results indicate that sheep nerve repair is a useful model for investigating long-gap peripheral nerve injuries.

Cerium Containing Bioactive Glasses: A Review

Bioactive glasses (BGs) for biomedical applications are doped with therapeutic inorganic ions (TIIs) in order to improve their performance and reduce the side effects related to the surgical implant. Recent literature in the field shows a rekindled interest toward rare earth elements, in particular cerium, and their catalytic properties. Cerium-doped bioactive glasses (Ce-BGs) differ in compositions, synthetic methods, features, and in vitro assessment. This review provides an overview on the recent development of Ce-BGs for biomedical applications and on the evaluation of their bioactivity, cytocompatibility, antibacterial, antioxidant, and osteogenic and angiogenic properties as a function of their composition and physicochemical parameters.

Bioactive Materials for Soft Tissue Repair

Over the past decades, age-related pathologies have increased abreast the aging population worldwide. The increased age of the population indicates that new tools, such as biomaterials/scaffolds for damaged tissues, which display high efficiency, effectively and in a limited period of time, for the regeneration of the body's tissue are needed. Indeed, scaffolds can be used as templates for three-dimensional tissue growth in order to promote the tissue healing stimulating the body's own regenerative mechanisms. In tissue engineering, several types of biomaterials are employed, such as bioceramics including calcium phosphates, bioactive glasses, and glass-ceramics. These scaffolds seem to have a high potential as biomaterials in regenerative medicine. In addition, in conjunction with other materials, such as polymers, ceramic scaffolds may be used to manufacture composite scaffolds characterized by high biocompatibility, mechanical efficiency and load-bearing capabilities that render these biomaterials suitable for regenerative medicine applications. Usually, bioceramics have been used to repair hard tissues, such as bone and dental defects. More recently, in the field of soft tissue engineering, this form of scaffold has also shown promising applications. Indeed, soft tissues are continuously exposed to damages, such as burns or mechanical traumas, tumors and degenerative pathology, and, thereby, thousands of people need remedial interventions such as biomaterials-based therapies. It is known that scaffolds can affect the ability to bind, proliferate and differentiate cells similar to those of autologous tissues. Therefore, it is important to investigate the interaction between bioceramics and somatic/stem cells derived from soft tissues in order to promote tissue healing. Biomimetic scaffolds are frequently employed as drug-delivery system using several therapeutic molecules to increase their biological performance, leading to ultimate products with innovative functionalities. This review provides an overview of essential requirements for soft tissue engineering biomaterials. Data on recent progresses of porous bioceramics and composites for tissue repair are also presented.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Bioactive Glass-Based Endodontic Sealer as a Promising Root Canal Filling Material without Semisolid Core Materials

Endodontic treatment for a tooth with damaged dental pulp aims to both prevent and cure apical periodontitis. If the tooth is re-infected as a result of a poorly obturated root canal, periapical periodontitis may set-in due to invading bacteria. To both avoid any re-infection and improve the success rate of endodontic retreatment, a treated root canal should be three-dimensionally obturated with a biocompatible filling material. Recently, bioactive glass, one of the bioceramics, is focused on the research area of biocompatible biomaterials for endodontics. Root canal sealers derived from bioactive glass-based have been developed and applied in clinical endodontic treatments. However, at present, there is little evidence about the patient outcomes, sealing mechanism, sealing ability, and removability of the sealers. Herein, we have developed a bioactive glass-based root canal sealer and provided evidence concerning its physicochemical properties, biocompatibility, sealing ability, and removability. We also review the classification of bioceramics and characteristics of bioactive glass. Additionally, we describe the application of bioactive glass to facilitate the development of a new root canal sealer. Furthermore, this review shows the potential application of bioactive glass-based cement as a root canal filling material in the absence of semisolid core material.

Bioactive Glasses: Where Are We and Where Are We Going?

Bioactive glasses caused a revolution in healthcare and paved the way for modern biomaterial-driven regenerative medicine. The first 45S5 glass composition, invented by Larry Hench fifty years ago, was able to bond to living bone and to stimulate osteogenesis through the release of biologically-active ions. 45S5-based glass products have been successfully implanted in millions of patients worldwide, mainly to repair bone and dental defects and, over the years, many other bioactive glass compositions have been proposed for innovative biomedical applications, such as soft tissue repair and drug delivery. The full potential of bioactive glasses seems still yet to be fulfilled, and many of today's achievements were unthinkable when research began. As a result, the research involving bioactive glasses is highly stimulating and requires a cross-disciplinary collaboration among glass chemists, bioengineers, and clinicians. The present article provides a picture of the current clinical applications of bioactive glasses, and depicts six relevant challenges deserving to be tackled in the near future. We hope that this work can be useful to both early-stage researchers, who are moving with their first steps in the world of bioactive glasses, and experienced scientists, to stimulate discussion about future research and discover new applications for glass in medicine.

Structures and properties of phosphate-based bioactive glasses from computer simulation: a review

Computer simulations have enabled breakthroughs in understanding the connections between the atomic structure and properties of bioactive phosphate glasses.

Biocompatibility of Different Nerve Tubes

Bridging nerve gaps with suitable grafts is a major clinical problem. The autologous nerve graft is considered to be the gold standard, providing the best functional results; however, donor site morbidity is still a major disadvantage. Various attempts have been made to overcome the problems of autologous nerve grafts with artificial nerve tubes, which are “ready-to-use” in almost every situation. A wide range of materials have been used in animal models but only few have been applied to date clinically, where biocompatibility is an inevitable prerequisite. This review gives an idea about artificial nerve tubes with special focus on their biocompatibility in animals and humans.

An evaluation using techniques to assess muscle and nerve regeneration of a flexible glass wrap in the repair of peripheral nerves

In this study a flexible biodegradable wrap is compared with microsurgical epineurial suturing in the repair of cleanly divided peripheral nerves. Five groups of twelve sheep were used; one control group and four neurotmesis and repair groups. The four repair groups were; (1) Epineurial suture repair using a microscope and 9/0 polyamide; (2) Wrap secured by Tisseel glue; (3) Wrap secured by polycaprolactone glue; (4) Wrap secured by suturing. Regeneration of the median nerve was assessed by electromyography, nerve conduction studies, wet muscle mass measurements, and morphometry. The results suggested that nerve regeneration in the wrap+Tisseel glue group was as good as that in the epineurial repair group. The use of polycaprolactone glue is not recommended in nerve repair. Placement of the wrap was easy to learn and quick to carry out under direct vision. The wrap used in this study could prove to be a useful alternative to epineurial suturing to repair peripheral nerves and may have a particularly unique role in the developing world and battlefield.

Use of a static magnetic field to promote recovery after peripheral nerve injury

Object

While pulsed electromagnetic stimulation has been shown to enhance peripheral nerve regeneration, the effect of a static magnetic field on nerve repair is less clear. The aim of this study was to establish what effect an imposed exogenous static magnetic field has on peripheral nerve regeneration after transection and repair.

Methods

Three groups of six adult sheep were used. The first group acted as normal controls. In the second group, the median nerve was divided and immediately repaired by entubulation within a “controlled-release” biodegradable glass tube. In the third group, small magnets were applied to the sides of the biodegradable glass tubes before the median nerve was repaired using these magnetic tubes. The sheep were allowed to recover and were reexamined 10 months later. The animals underwent comprehensive morphometric (cross-sectional morphometry and measurement of internodal lengths), electrophysiological (determinations of stimulated jitter, maximum conduction velocity, refractory period, and F waves), and isometric tension (isometric twitch and tetanic tension) assessments.

Conclusions

Exogenously applied static electromagnetic fields do not enhance peripheral nerve regeneration.

Development of fibrous biodegradable polymer conduits for guided nerve regeneration

The technique of microbraiding with modification was employed as a novel method for the fabrication of fibrous tubular scaffolds for nerve tissue engineering purposes. The biodegradable polymers used in this study were poly(L-lactide-co-glycolide) (10:90) and chitosan. The polymeric fibers were microbraided around a Teflon mandrel to make it as a tubular construct. The conduits were then studied for their surface morphology, swelling behaviour and biocompatibility. The surface morphology was analysed by scanning electron microscope, swelling behaviour by weight increase due to water uptake and biocompatibility by in vitro cytotoxicity assessment in terms of cell morphology and cell viability by the MTT assay of polymer extract treated cells. These conduits may also be used for regeneration of tissues, which require tubular scaffolds such as blood vessel, spinal cord, intestine etc.

Bioresorbable glass fibres facilitate peripheral nerve regeneration

This is a proof of principle report showing that fibres of Bioglass 45S5 can form a biocompatible scaffold to guide regrowing peripheral axons in vivo. We demonstrate that cultured rat Schwann cells and fibroblasts grow on Bioglass fibres in vitro using SEM and immunohistochemistry, and provide qualitative and quantitative evidence of axonal regeneration through a Silastic conduit filled with Bioglass fibres in vivo (across a 0.5 cm interstump gap in the sciatic nerves of adult rats). Axonal regrowth at 4 weeks is indistinguishable from that which occurs across an autograft. Bioglass fibres are not only biocompatible and bioresorbable, which are absolute requirements of successful devices, but are also amenable to bioengineering, and therefore have the potential for use in the most challenging clinical cases, where there are long inter-stump gaps to be bridged.

A composite poly-hydroxybutyrate-glial growth factor conduit for long nerve gap repairs

There is considerable evidence that peripheral nerves have the potential to regenerate in an appropriate microenvironment. We have developed a novel artificial nerve guide composed of poly 3-hydroxybutyrate (PHB) filled with glial growth factor (GGF) suspended in alginate hydrogel. Gaps of 2-4 cm in rabbit common peroneal nerve were bridged using a PHB conduit containing either GGF in alginate hydrogel (GGF) or alginate alone (Alginate), or with an empty PHB conduit (Empty). Tissues were harvested 21, 42 and 63 days post-operatively. Schwann cell and axonal regeneration were assessed using quantitative immunohistochemistry. At 21 days, addition of GGF increased significantly the distance of axonal and Schwann cells regeneration in comparison with that observed in Alginate and Empty conduits for both gap lengths. The axons bridged the 2-cm GGF conduits gap by 63 days, with a comparable rate of regeneration seen in 4-cm conduits. Schwann cells and axonal regeneration quantity was similar for both gap lengths in each group. However, at all time points the quantity of axonal and Schwann cells regeneration in GGF grafts was significantly greater than in both Alginate and Empty conduits, the latter showing better regeneration than Alginate conduits. The results indicate an inhibitory effect of alginate on regeneration, which is partially reversed by the addition of GGF to the conduits. In conclusion, GGF stimulates a progressive and sustainable regeneration increase in long nerve gap conduits.

Neural tissue engineering: strategies for repair and regeneration

Nerve regeneration is a complex biological phenomenon. In the peripheral nervous system, nerves can regenerate on their own if injuries are small. Larger injuries must be surgically treated, typically with nerve grafts harvested from elsewhere in the body. Spinal cord injury is more complicated, as there are factors in the body that inhibit repair. Unfortunately, a solution to completely repair spinal cord injury has not been found. Thus, bioengineering strategies for the peripheral nervous system are focused on alternatives to the nerve graft, whereas efforts for spinal cord injury are focused on creating a permissive environment for regeneration. Fortunately, recent advances in neuroscience, cell culture, genetic techniques, and biomaterials provide optimism for new treatments for nerve injuries. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the current approaches that are being explored to aid peripheral nerve regeneration and spinal cord repair.

Facial nerve regeneration through progesterone-loaded chitosan prosthesis. A preliminary report

Biodegradable nerve guides have represented new treatment alternatives for nerve repairing. They are gradually biodegradable, exert biological effects directly to the injured nerve, and act as drug- or cell-delivery devices. Furthermore, progesterone (PROG) has been demonstrated to promote injured peripheral nerve regeneration. In this study, it was hypothesized that PROG delivered from chitosan prostheses provides better facial nerve regenerative response than chitosan prostheses with no PROG. As there are no reports on the use of the former as nerve-guide material in the regeneration of injured nerves, this is the main objective of the present work. Chitosan prostheses containing PROG were used to bridge 10-mm gaps in rabbit facial nerves. The regenerated nerves were evaluated 45 days after implantation in animals with the use of light microscopy and morphometric analysis. Gas chromatography was used in order to quantify PROG content in prosthesis prior to and after implantation in subcutaneous tissue at different periods of up to 60 days. In addition, the prosthesis walls were evaluated with histological techniques in order to assess their integrity and the surrounding tissue reaction. Chitosan prostheses allowed PROG release during the time needed for nerve regeneration. At 45 days myelinated nerve fibers were observed in both the proximal and distal stumps. This parameter and the N ratio were higher in the progesterone-treated group when compared to that of the vehicle control. Findings indicate that chitosan prostheses were useful in nerve regeneration, acting as a long-lasting PROG delivery device a faster nerve regeneration.

Somatotopic organization of the facial nucleus is disrupted after lesioning and regeneration of the facial nerve: the histological representation of synkinesis

OBJECTIVE

After facial nerve repair, involuntary movement of part of the face during voluntary movement of another part of the face is common. We describe an animal model of facial nerve lesion, repair, and regeneration that demonstrates abnormal organization of the facial nucleus; this model may be used to study synkinesis.

METHODS

In 18 rats, the facial nerve was cut completely, proximal to the parotid gland, and immediately sutured end-to-end. After a period of regeneration of 1 to 10 months, retrograde fluorescence labeling of the distal branches of the facial nerve was performed. The distribution of the tracers in the facial nucleus was assessed in both the lesioned animals and in a nonlesioned group (n = 20).

RESULTS

In the control animals, muscle groups were somatotopically represented in the facial nucleus. After lesioning, repair, and regeneration, the somatotopy of the facial nucleus was disrupted. Axons projected from the facial nucleus to incorrect peripheral muscle groups, and aberrant branches were observed to simultaneously innervate different subdivisions of the facial nerve. The numbers of aberrant axons and branches did not change significantly during periods of regeneration ranging from 1 to 10 months.

CONCLUSION

Our model provides a clear demonstration of the failure of adult facial nerve axons to make correct connections with their distal targets during regeneration. This model may be used to assess strategies aimed at minimizing synkinesis and, by assessing histology together with behavior, provides a more robust model than those previously described.

Assessment of the method and timing of repair of a brachial plexus traction injury in an animal model for obstetric brachial plexus palsy

A Sunderland type IV traction injury to the C6 root of adult sheep or newborn lamb brachial plexus was used as a model for obstetric traction injury to the C5 root in humans. In one experimental cohort the injury was created and repaired using interfascicular nerve autografts or coaxially aligned freeze-thawed skeletal muscle autografts in a group of adult sheep and in a group of newborn lambs. In a second cohort a similar injury was created and repaired either immediately or after a delay of 30 days, using either interfascicular nerve autografts or coaxially aligned freeze-thawed skeletal muscle autografts in four groups of six newborn lambs. In all cases both functional and morphometric indices of nerve regeneration were poorer in the injured and repaired nerves than in normal nerves. In lambs the method of repair made no difference and no significant differences were found for any of the indices of nerve function or morphology. In sheep the use of muscle grafts was associated with a poorer outcome than the use of nerve autografts. Where a delay of 30 days had elapsed between injury and repair, the results using nerve autografts were not significantly different. Where freeze-thawed muscle autografts had been used, the maturation of the regenerated nerve fibres after delay was significantly poorer than after immediate repair. The electrophysiological variables CV(max) and jitter, which may be applied clinically, were found to be good discriminators of recovery in all of the animals and in respect of all procedures.

Obstetric brachial plexus palsy: a comparison of the degree of recovery after repair of a C6 ventral root avulsion in newborn and adult sheep

The C6 motor rootlets were avulsed from the spinal cord in six newborn lambs to simulate a birth lesion of the upper root of the brachial plexus. Six 1-year-old sheep were used for comparison, and treated in a similar manner. The injury was repaired immediately in each group using an autologous coaxial freeze-thawed skeletal muscle graft. The animals were allowed to recover for 1 year after the surgery. The C6 root was then examined electrophysiologically and morphologically. The results were compared with those obtained from a group of untreated intact 1-year-old sheep. The fibre and axon diameters and myelin sheath thickness were significantly different in the group repaired as lambs when compared with the group repaired at the age of 1 year. There was also a significantly increased maximum conduction velocity and a greater range of conduction velocities within the nerve in the lambs. Central motor latency was significantly slower in the sheep than in the lambs. These findings would suggest a greater potential for recovery in the lambs after brachial plexus root avulsion injuries.

The use of conventional and invaginated autologous vein grafts for nerve repair by means of entubulation

Nerve repair by entubulation has re-emerged recently as a possible means of enhancing the microenvironment at the site of repair by inclusion within the tube of various trophic factors. To this end, a modification of the vein-graft technique has been used by turning it inside out before repair, to expose the adventitial surface to the regenerating axons. A comparative study of standard vein grafting versus the inside-out technique was carried out in two equal-sized groups of inbred Lewis rats. Jugular vein isografts were derived from litter mates. The sciatic nerve was transected and repaired by entubulation using the standard vein graft in one group and the inside-out graft in the other group. Morpho-metric and electrophysiological assessment were carried out 3 months after repair. When the animals were assessed it was found that both the standard-vein-graft group and the inside-out group exhibited a reduction in all of the morphometric and electrophysiological variables when compared to normal nerves. The mean axon diameter, fibre diameter and myelin sheath thickness were, however, found to be greater in the group that underwent the inside-out repair. The superior morphometric results seen in the inside-out group were not matched by improved electrophysiological performance. It is concluded that the use of the inside-out technique confers no functional benefit over standard vein grafting.

Obstetric brachial plexus palsy: a large animal model for traction injury and its repair. Part 1: age of the recipient

A Sunderland type IV traction injury to the C6 root of the sheep or lamb brachial plexus was used as a model for obstetric traction injury to the C5 root in humans. The injury was created and immediately repaired using interfascicular nerve autografts in a group of adult sheep and a group of newborn lambs. The animals were examined using electrophysiological and morphometric techniques 1 year after operation. It was found that the recovery of neuromuscular function was superior in the lambs. The implication is that nerves in newborn animals have a better potential for regeneration than that seen in older individuals. This is discussed with reference to the management of obstetric brachial plexus palsy.