Long-lasting infiltration anaesthesia by lidocaine-loaded biodegradable nanoparticles in hydrogel in rats

Nanomedicine and voltage-gated sodium channel blockers in pain management: a game changer or a lost cause?

Pain, a complex and debilitating condition affecting millions globally, is a significant concern, especially in the context of post-operative recovery. This comprehensive review explores the complexity of pain and its global impact, emphasizing the modulation of voltage-gated sodium channels (VGSC or NaV channels) as a promising avenue for pain management with the aim of reducing reliance on opioids. The article delves into the role of specific NaV isoforms, particularly NaV 1.7, NaV 1.8, and NaV 1.9, in pain process and discusses the development of sodium channel blockers to target these isoforms precisely. Traditional local anesthetics and selective NaV isoform inhibitors, despite showing varying efficacy in pain management, face challenges in systemic distribution and potential side effects. The review highlights the potential of nanomedicine in improving the delivery of local anesthetics, toxins and selective NaV isoform inhibitors for a targeted and sustained release at the site of pain. This innovative strategy seeks to improve drug bioavailability, minimize systemic exposure, and optimize therapeutic outcomes, holding significant promise for secure pain management and enhancing the quality of life for individuals recovering from surgical procedures or suffering from chronic pain.

Sustained release local anesthetics for pain management: relevance and formulation approaches

This review attempted to ascertain the rationale for the formulation of sustained-release local anesthetics and summarize the various formulation approaches designed to date to achieve sustained and localized local analgesic effects. The incidence of pain, which is the concern of patients as well as health care professionals, is increasing due to accidents, surgical procedures, and other diseases. Local anesthetics can be used for the management of moderate to severe acute and chronic pain. They also allow regional analgesia, in situations where the cause and source of the pain are limited to a particular site or region, without the need for loss of consciousness or systemic administration of other analgesics thereby decreasing the risk of potential toxicities. Though they have an interesting antipain efficacy, the short duration of action of local anesthetics makes the need for their multiple injections or opioid adjuvants mandatory. To overcome this problem, different formulations are being designed that help achieve prolonged analgesia with a single dose of administration. Combination with adjuvants, liposomal formulations, lipid-based nanoparticles, thermo-responsive nanogels, microspheres, microcapsules, complexation with multivalent counterions and HP-β-CD, lipid-based nanoparticles, and bio-adhesive films, and polymeric matrices are among the approaches. Further safety studies are required to ensure the safe and effective utilization of sustained-release local anesthetics. Moreover, the release kinetics of the various formulations should be adequately established.

Translating Therapeutic Microgels into Clinical Applications

Microgels are crosslinked, water-swollen networks with a 10 nm to 100 µm diameter and can be modified chemically or biologically to render them biocompatible for advanced clinical applications. Depending on their intended use, microgels require different mechanical and structural properties, which can be engineered on demand by altering the biochemical composition, crosslink density of the polymer network, and the fabrication method. Here, the fundamental aspects of microgel research and development, as well as their specific applications for theranostics and therapy in the clinic, are discussed. A detailed overview of microgel fabrication techniques with regards to their intended clinical application is presented, while focusing on how microgels can be employed as local drug delivery materials, scavengers, and contrast agents. Moreover, microgels can act as scaffolds for tissue engineering and regeneration application. Finally, an overview of microgels is given, which already made it into pre-clinical and clinical trials, while future challenges and chances are discussed. This review presents an instructive guideline for chemists, material scientists, and researchers in the biomedical field to introduce them to the fundamental physicochemical properties of microgels and guide them from fabrication methods via characterization techniques and functionalization of microgels toward specific applications in the clinic.

Synthesis of nanocapsules blended polymeric hydrogel loaded with bupivacaine drug delivery system for local anesthetics and pain management

Local anesthetics are used clinically for the control of postoperative pain management. This study aimed to develop chitosan (CS) with genipin (GP) hydrogels as the hydrophilic lipid shell loaded poly(ε-caprolactone) (PC) nanocapsules as the hydrophobic polymeric core composites (CS-GP/PC) to deliver bupivacaine (BPV) for the prolongation of anesthesia and pain relief. The swelling ratio, in vitro degradation, and rheological properties enhancement of CS-GP/PC polymeric hydrogel. The incorporation of PC nanocapsules into CS-GP hydrogels was confirmed by SEM, FTIR, and XRD analysis. Scanning electron microscopy results demonstrated that the CS-GP hydrogels and CS-GP/PC polymeric hydrogels have a porous structure, the pore dimensions being non-uniform with diameters between 25 and 300 μm. The in vitro drug release profile of CS-GP/PC polymeric hydrogel has been achieved 99.2 ± 1.12% of BPV drug release in 36 h. Cellular viability was evaluated using the CCK-8 test on 3T3 fibroblast cells revealed that the obtained CS-GP/PC polymeric hydrogel with BPV exhibited no obvious cytotoxicity. The CS-GP/PC polymeric hydrogel loaded with BPV showed significant improvement in pain response compared to the control group animals for at least 7 days. When compared with BPV solution, CS-GP hydrogel and CS-GP/PC polymeric hydrogel improved the skin permeation of BPV 3-fold and 5-fold in 24 h, respectively. In vitro and in vivo results pointed out PC nanocapsules loaded CS-GP hydrogel can act as effective drug carriers, thus prolonging and enhancing the anesthetic effect of BPV. Histopathological results demonstrated the excellent biodegradability and biocompatibility of the BPV-loaded CS-GP/PC polymeric hydrogel system on 7, 14, and 21 days without neurotoxicity.

HIGHLIGHTS

Preparation and characterization of CS-GP/PC polymeric hydrogel system.

BPV-loaded CS-GP/PC exhibited prolonged in vitro release in PBS solution.

Cytotoxicity of BPV-loaded CS-GP/PC polymeric hydrogel against fibroblast (3T3) cells.

Development of CS-GP/PC a promising skin drug-delivery system for local anesthetic BPV.

Near-infrared triggered ropivacaine liposomal gel for adjustable and prolonged local anaesthesia

Local analgesics effectively allow patients to relieve postoperative pain and reduce the need for inhaled general anesthetics or opioids. Compared with other similar long-acting local anesthetics, ropivacaine (Rop) is widely used due to its potential to minimize cardiotoxicity. However, the relatively short duration of Rop efficacy, which lasts for several hours after injection, is considered insufficient for long-term acute and chronic pain treatment. At present, repeated injections or indwelling catheters are used to achieve long-term drug delivery, which can easily cause infection and inflammation. To achieve externally controllable analgesia for a prolonged time, we prepared near-infrared (NIR)-responsive Rop liposomes (Rop@Lip) containing photosensitizers PdPC(OBu)₈ and unsaturated phospholipid DLPC. The particle size of the Rop@Lip was 234.73 ± 5.21 nm, the PDI was 0.42 ± 0.02, and the drug encapsulation rate was 94.62 ± 1.1%. The release of Rop was highly NIR-dependent in vitro and in vivo. To ensure that the liposomes reside around the nerve for an extended period, we next designed an in situ gel with chitosan (CS) and β-sodium glycerophosphate (β-GP) to form a liposomal gel (Lip/Gel). This Lip/Gel composite drug delivery system could be retained in vivo for 10 d, reduce the side effects caused by drug overdose, and prolong the duration of efficacy. In summary, the NIR-responsive Rop composite drug delivery system generated in this paper can effectively solve the shortcomings of traditional local injections, reduce the toxicity and side effects of free Rop, and provide a basis for a light-responsive delivery system of analgesic drugs.

KM-416, a novel phenoxyalkylaminoalkanol derivative with anticonvulsant properties exerts analgesic, local anesthetic, and antidepressant-like activities. Pharmacodynamic, pharmacokinetic, and forced degradation studies

Anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic, neuropathic pain. We obtained a phenoxyalkylaminoalkanol derivative, KM-416 which had previously demonstrated a significant anticonvulsant activity and had also been shown to bind to 5-HT_1A, α₂-receptors and SERT and not to exhibit mutagenic properties. As KM-416 is a promising compound in our search for drug candidates, in the present study we further assessed its pharmacological profile (analgesic, local anesthetic, and antidepressant-like activities) accompanied with patch-clamp studies. Considering the importance of drug safety, its influence on the cardiovascular system was also evaluated. Moreover, KM-416 was subjected to forced degradation and pharmacokinetic studies to examine its stability and pharmacokinetic parameters. KM-416 revealed a significant antinociceptive activity in the tonic - the formalin test, neurogenic - the capsaicin test, and neuropathic pain model - streptozotocin-induced peripheral neuropathy. Moreover, it exerted a local anesthetic effect. In addition, KM-416 exhibited anti-depressant like activity. The results from the patch-clamp studies indicated that KM-416 can inhibit currents elicited by activation of NMDA receptors, while it also exhibited a voltage-dependent inhibition of Na⁺ currents. KM-416 did not influence ventricular depolarization and repolarization. Following oral administration, pharmacokinetics of KM-416 was characterized by a rapid absorption in the rat. The brain-to-plasma AUC ratio was 6.7, indicating that KM-416 was well distributed to brain. The forced degradation studies showed that KM-416 was very stable under stress conditions. All these features made KM-416 a promising drug candidate for further development against neuropathic pain and epilepsy.

Evaluation of a regional nerve block with an experimental formulation of encapsulated lidocaine in sheep

OBJECTIVE

To compare the duration of nociceptive and proprioceptive blockade from an experimental encapsulated lidocaine preparation with that of conventional lidocaine.

STUDY DESIGN

Prospective, blinded, randomly assigned, crossover study.

ANIMALS

A total of six adult Dorset ewes, American Society of Anesthesiologists physical status I or II, weighing 60.4 ± 18.0 kg (mean ± standard deviation).

METHODS

Under general anesthesia and guided by electrolocation, the common peroneal nerve was blocked unilaterally with encapsulated lidocaine (0.1 mL kg^-1, 200 mg mL^-1) or conventional lidocaine hydrochloride (0.1 mL kg^-1, 20 mg mL^-1). Each sheep was administered both treatments with an interval of 2 weeks between treatments. Nociception and proprioception were scored (scales of 0-3) before anesthesia, at 0.5, 1, 2, 4, 8, 12, 16, 20 and 24 hours after completion of local anesthetic injection, and every 12 hours thereafter for 9 days. Nociceptive and proprioceptive blockade ended the first time each score reached '0'; maximum blockade duration was considered and recorded to be the time point immediately prior to this end point. Significance of differences between treatments for duration of blockade was tested with the Wilcoxon rank-sum test. Effects of time and treatment on nociceptive and proprioceptive blockade were evaluated with mixed-effect models. Significance was set at p < 0.05.

RESULTS

Compared with conventional lidocaine, nociceptive blockade lasted 88 hours longer with encapsulated lidocaine (p = 0.008), and proprioceptive blockade lasted 6 hours longer (p = 0.03). Significant effects of time (p < 0.0001), treatment (p = 0.0435) and treatment∗time (p < 0.0001) were observed for nociception. Significant effects of time (p < 0.0001) and treatment∗time (p = 0.0058) were observed for proprioception.

CONCLUSION

Encapsulated lidocaine produced nociceptive blockade with a duration substantially longer than conventional lidocaine.

CLINICAL RELEVANCE

Sustained-release encapsulated lidocaine alleviates pain and may minimize systemic analgesic use.

Thermoresponsive Nanogels Based on Different Polymeric Moieties for Biomedical Applications

Nanogels, or nanostructured hydrogels, are one of the most interesting materials in biomedical engineering. Nanogels are widely used in medical applications, such as in cancer therapy, targeted delivery of proteins, genes and DNAs, and scaffolds in tissue regeneration. One salient feature of nanogels is their tunable responsiveness to external stimuli. In this review, thermosensitive nanogels are discussed, with a focus on moieties in their chemical structure which are responsible for thermosensitivity. These thermosensitive moieties can be classified into four groups, namely, polymers bearing amide groups, ether groups, vinyl ether groups and hydrophilic polymers bearing hydrophobic groups. These novel thermoresponsive nanogels provide effective drug delivery systems and tissue regeneration constructs for treating patients in many clinical applications, such as targeted, sustained and controlled release.

In vitro and in vivo studies of micro-depots using tailored microemulsion for sustained local anaesthesia

In clinical practice, lidocaine is used as local anesthetic for the management of post-operative pain. The commercial formulation including gels, injections and ointments showed short duration of action (1 to 2 h). In this paper, the efforts have being made to develop tailored lidocaine-microemulsion (o/w), which on penetration in the skin layer cause micro-depots formation due to destabilization of the microemulsion system. To identify the microemulsion region, pseudo ternary diagrams were constructed using Capmul MCM as oil, Pluronic F68 as tri-block surfactant, polyethylene glycol 200 as co-surfactant at 1:4 and 1:6 ratios (S:Co-S). The selected 5%w/v lidocaine loaded microemulsion [Ld-ME-2(1:4)] was stable in thermodynamic test and during shelf life period (3 months). In ex vivo permeability study, the lidocaine release from Ld-ME-2(1:4) microemulsion was sustained in comparison to the marketed lidocaine ointment. The skin irritation study confirmed the safety of lidocaine loaded microemulsion. Tail flick test showed improved and sustain local anaesthetic effect in comparison to the market ointment. The improved efficacy of microemulsion system, was due to high penetration in the skin layer due to local precipitation of lidocaine from microemulsion. The findings suggest that the tailored microemulsion could be a potential strategy to prolong the local anaesthesia.

3,3'-Diindolylmethane nanoencapsulation improves its antinociceptive action: Physicochemical and behavioral studies

This study aimed to characterize the physicochemical properties of 3,3'-diindolylmethane (DIM)-loaded nanocapsules (NCs) as well as the antinociceptive effect using distinct animal models (hot plate test, formalin-induced nociception and complete Freud's adjuvant induced paw inflammation). The DIM-loaded NCs (composed by primula oil and ethylcellulose) were characterized using differential scanning calorimetry, thermogravimetric analysis, Fourier-transformed infrared spectroscopy, X-ray diffractometry and scanning electron microscopy. The physicochemical characterization demonstrated that DIM could be molecularly dispersed into the NCs, whose size was nanometric with a spherical shape. An improvement in DIM thermal stability was achieved by its encapsulation and there were no interactions among the formula components. For the nociceptive evaluation, male adult Swiss mice were pretreated with the NCs or free DIM by the intragastric route at the dose of 10 mg/Kg (time-response curve), 5 or 2.5 mg/Kg (dose-response curve). The behavioral tests were performed over an experimental period of 0.5-8 h. Both free and nanoencapsulated DIM reduced the mechanical hypernociception induced by CFA, mitigated nociceptive behavior of formalin-induced neurogenic and inflammatory pain and increased paw withdrawal latency assessed by the hot-plate test. Importantly, the DIM nanoencapsulation promoted a rapid initiation and prolonged the bioactive antinociceptive action (up to 8 h) as well as reduced the effective dose in comparison to its free form. In summary, this study reported that the NCs had adequate nanometric size, increased DIM stability and its antinociceptive action in different animal models, suggesting that the formulation may be a possible therapeutic alternative to the management of pain and inflammatory-related pathologies.

Hybrid Hydrogel Composed of Polymeric Nanocapsules Co-Loading Lidocaine and Prilocaine for Topical Intraoral Anesthesia

This study reports the development of nanostructured hydrogels for the sustained release of the eutectic mixture of lidocaine and prilocaine (both at 2.5%) for intraoral topical use. The local anesthetics, free or encapsulated in poly(ε-caprolactone) nanocapsules, were incorporated into CARBOPOL hydrogel. The nanoparticle suspensions were characterized in vitro in terms of particle size, polydispersity, and surface charge, using dynamic light scattering measurements. The nanoparticle concentrations were determined by nanoparticle tracking analysis. Evaluation was made of physicochemical stability, structural features, encapsulation efficiency, and in vitro release kinetics. The CARBOPOL hydrogels were submitted to rheological, accelerated stability, and in vitro release tests, as well as determination of mechanical and mucoadhesive properties, in vitro cytotoxicity towards FGH and HaCaT cells, and in vitro permeation across buccal and palatal mucosa. Anesthetic efficacy was evaluated using Wistar rats. Nanocapsules were successfully developed that presented desirable physicochemical properties and a sustained release profile. The hydrogel formulations were stable for up to 6 months under critical conditions and exhibited non-Newtonian pseudoplastic flows, satisfactory mucoadhesive strength, non-cytotoxicity, and slow permeation across oral mucosa. In vivo assays revealed higher anesthetic efficacy in tail-flick tests, compared to a commercially available product. In conclusion, the proposed hydrogel has potential for provision of effective and longer-lasting superficial anesthesia at oral mucosa during medical and dental procedures. These results open perspectives for future clinical trials.

Current progress and challenges of nanoparticle-based therapeutics in pain management

Pain is a widespread and growing health problem worldwide that exerts a considerable social and economic impact on both patients and healthcare systems and, therefore, on society in general. Although current treatment modalities include a wide variety of pharmacological and non-pharmacological approaches, due to the complexity of pain and individual differences in clinical response these options are not always effective in mitigating and relieving pain. In addition, some pain drugs such as non-steroidal anti-inflammatory drugs (NSAIDs), local anesthetics and opioids show several unfavorable side effects. Therefore, current research advances in this medical field are based on the development of potential treatments to address many of the unmet needs and to overcome the existing limitations in pain management. Nanoparticle drug delivery systems present an exciting opportunity as alternative platforms to improve efficacy and safety of medications currently in use. Herein, we review a broad range of nanoparticle formulations (organic nanostructures and inorganic nanoparticles), which have been developed to encapsulate an array of painkillers, paying special attention to the key advantages that these systems offer, (compared to the use of the free drug), as well as to the more relevant results of preclinical studies in animal models. Additionally, we will briefly discuss the impact of some of these nanoformulations in clinical trials.

Pharmacologic Properties of Novel Local Anesthetic Agents in Anesthesia Practice

Therapeutic duration of traditional local anesthetics when used in peripheral nerve blocks is normally limited. This article describes novel approaches to extend the duration of peripheral nerve blocks currently available or in development. Three newer approaches on extending the duration of peripheral nerve blocks include site-1 sodium channel blockers, novel local anesthetics delivery systems, and novel adjuvants of local anesthetics. Compared with plain amide-based and ester-based local anesthetics, alternative approaches show significant promise in decreasing postoperative pain, rescue opioid requirement, hospital length-of-stay, and overall health care cost, without compromising the established safety profile of traditional local anesthetics.

Nanotechnology application to local anaesthesia (LA)

Several advancements have been made on the exact release of local anaesthetics formulation and its efficiency at inducing motor and sensory block for an extended time has been harnessed in clinical practice. The use of sustained release formulations delivers analgesia for a lengthier period of time with one administration, thereby reducing complications that usually arise with administration of conventional analgesia. In addition, controlled release of an anaesthetic drug is said to prevent overdosing, reduced side effects, especially cardiotoxicity, neurotoxicity and tissue lesions. The use of nanotechnology knowledge via liposomal formulation has recorded high successful results in pain control and quick patient recovery.

Preparation of Thermosensitive Gel for Controlled Release of Levofloxacin and Their Application in the Treatment of Multidrug-Resistant Bacteria

Levofloxacin is a synthetic broad-spectrum antibacterial agent for oral or intravenous administration. Chemically, levofloxacin is the levorotatory isomer (L-isomer) of racemate ofloxacin, a fluoroquinolone antibacterial agent. Quinolone derivatives rapidly and specifically inhibit the synthesis of bacterial DNA. Levofloxacin has in vitro activity against a broad range of aerobic and anaerobic Gram-positive and Gram-negative bacteria. However, formulation of combined poloxamers thermoregulated (as Pluronic® F127) and levofloxacin for use in multiresistant bacterial treatment were poorly described in the current literature. Thus, the aim of the present work is to characterize poloxamers for levofloxacin controlled release and their use in the treatment of multidrug bacterial resistance. Micelles were produced in colloidal dispersions, with a diameter between 5 and 100 nm, which form spontaneously from amphiphilic molecules under certain conditions as concentration and temperature. Encapsulation of levofloxacin into nanospheres showed efficiency and enhancement of antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae when compared with only levofloxacin. Furthermore, all formulations were not cytotoxic for NIH/3T3 cell lineage. In conclusion, poloxamers combined with levofloxacin have shown promising results, better than alone, decreasing the minimal inhibitory concentration of the studied bacterial multiresistance strains. In the future, this new formulation will be used after being tested in animal models in patients with resistant bacterial strains.

Nano-formulations of drugs: Recent developments, impact and challenges

Nano-formulations of medicinal drugs have attracted the interest of many researchers for drug delivery applications. These nano-formulations enhance the properties of conventional drugs and are specific to the targeted delivery site. Dendrimers, polymeric nanoparticles, liposomes, nano-emulsions and micelles are some of the nano-formulations that are gaining prominence in pharmaceutical industry for enhanced drug formulation. Wide varieties of synthesis methods are available for the preparation of nano-formulations to deliver drugs in biological system. The choice of synthesis methods depend on the size and shape of particulate formulation, biochemical properties of drug, and the targeted site. This article discusses recent developments in nano-formulation and the progressive impact on pharmaceutical research and industries. Additionally, process challenges relating to consistent generation of nano-formulations for drug delivery are discussed.

Long-term effect of ropivacaine nanoparticles for sciatic nerve block on postoperative pain in rats

Purpose

The analgesic effect of ropivacaine (Rop) for nerve block lasts only ~3–6 hours for single use. The aim of this study was to develop long-acting regional anesthetic Rop nanoparticles and investigate the effects of sciatic nerve block on postoperative pain in rats.

Materials and methods

Rop nanoparticles were developed using polyethylene glycol-co-polylactic acid (PELA). One hundred and twenty adult male Wistar rats were randomly divided into four groups (n=30, each): Con (control group; 0.9% saline, 200 µL), PELA (PELA group; 10 mg), Rop (Rop group; 0.5%, 200 µL), and Rop-PELA (Rop-PELA group; 10%, 10 mg). Another 12 rats were used for the detection of Rop concentration in plasma. The mechanical withdrawal threshold and thermal withdrawal latency were measured at 2 hours, 4 hours, 8 hours, 1 day, 2 days, 3 days, 5 days, and 7 days after incision. The expression of c-FOS was determined by immunohistochemistry at 2 hours, 8 hours, 48 hours, and 7 days. Nerve and organ toxicities were also evaluated at 7 days.

Results

The duration of Rop absorption in the plasma of the Rop-PELA group was longer (>8 hours) than that of the Rop group (4 hours). Mechanical withdrawal threshold and thermal withdrawal latency in the Rop-PELA group were higher than that in other groups (4 hours–3 days). c-FOS expression in the Rop-PELA group was lower than that in the control group at 2 hours, 8 hours, and 48 hours and lower than that in the Rop group at 8 hours and 48 hours after paw incision. Slight foreign body reactions were observed surrounding the sciatic nerve at 7 days. No obvious pathophysiological change was found in the major organs after Rop-PELA administration at 7 days.

Conclusion

Rop-PELA provides an effective analgesia for nerve block over 3 days after single administration, and the analgesic mechanism might be mediated by the regulation of spinal c-FOS expression. However, its potential long-term tissue toxicity needs to be further investigated.

Sustained relief of pain from osteosynthesis surgery of rib fracture by using biodegradable lidocaine-eluting nanofibrous membranes

Various effective methods are available for perioperative pain control in osteosynthesis surgery, but they are seldom applied intraoperatively. The aim of this study was to evaluate a biodegradable poly([d,l]-lactide-co-glycolide) (PLGA)/lidocaine nanofibrous membrane for perioperative pain control in rib fracture surgery. Scanning electron microscopy showed high porosity of the membrane, and an ex vivo high-performance liquid chromatography study revealed an excellent release profile for both burst and controlled release of lidocaine within 30days. Additionally, the PLGA/lidocaine nanofibrous membrane was applied in an experimental rabbit rib osteotomy model. Implantation of the membrane around the osteotomized rib during osteosynthesis surgery resulted in a significant increase in weight gain, food and water consumption, and daily activity compared to the study group without the membrane. In addition, all osteotomized ribs were united. Thus, application of the PLGA/lidocaine nanofibrous membrane may be effective for sustained relief of pain in oeteosynthesis surgery.

Pain management via local anesthetics and responsive hydrogels

Acute and chronic pain control is a significant clinical challenge that has been largely unmet. Local anesthetics are widely used for the control of post-operative pain and in the therapy of acute and chronic pain. While a variety of approaches are currently used to prolong the duration of action of local anesthetics, an optimal strategy to achieve neural blockage for several hours to days with minimal toxicity has yet to be identified. Several drug delivery systems such as liposomes, microparticles and nanoparticles have been investigated as local anesthetic delivery vehicles to achieve prolonged anesthesia. Recently, injectable responsive hydrogels raise significant interest for the localized delivery of anesthetic molecules. This paper discusses the potential of injectable hydrogels to prolong the action of local anesthetics.

Poloxamer-based binary hydrogels for delivering tramadol hydrochloride: sol-gel transition studies, dissolution-release kinetics, in vitro toxicity, and pharmacological evaluation

In this work, poloxamer (PL)-based binary hydrogels, composed of PL 407 and PL 188, were studied with regard to the physicochemical aspects of sol-gel transition and pharmaceutical formulation issues such as dissolution-release profiles. In particular, we evaluated the cytotoxicity, genotoxicity, and in vivo pharmacological performance of PL 407 and PL 407-PL 188 hydrogels containing tramadol (TR) to analyze its potential treatment of acute pain. Drug-micelle interaction studies showed the formation of PL 407-PL 188 binary systems and the drug partitioning into the micelles. Characterization of the sol-gel transition phase showed an increase on enthalpy variation values that were induced by the presence of TR hydrochloride within the PL 407 or PL 407-PL 188 systems. Hydrogel dissolution occurred rapidly, with approximately 30%-45% of the gel dissolved, reaching ~80%-90% up to 24 hours. For in vitro release assays, formulations followed the diffusion Higuchi model and lower K(rel) values were observed for PL 407 (20%, K(rel) = 112.9 ± 10.6 μg · h(-1/2)) and its binary systems PL 407-PL 188 (25%-5% and 25%-10%, K(rel) =80.8 ± 6.1 and 103.4 ± 8.3 μg · h(-1/2), respectively) in relation to TR solution (K(rel) =417.9 ± 47.5 μg · h(-1/2), P<0.001). In addition, the reduced cytotoxicity (V79 fibroblasts and hepatocytes) and genotoxicity (V79 fibroblasts), as well as the prolonged analgesic effects (>72 hours) pointed to PL-based hydrogels as a potential treatment, by subcutaneous injection, for acute pain.

Extended release local anesthetic agents in a postoperative arthritic pain model

Local anesthetics play an important role in postoperative pain management in orthopedic joint procedures. The aim of this study was to determine the effect of an intraoperative extra-articular injection of poly(DL-lactic acid co castor oil 3:7), p(DLLA:CO) 3:7 loaded with 15% bupivacaine, for postoperative analgesia following knee arthroplasty. Prolonged release local anesthetic formulation was synthesized by mixing p(DLLA:CO) 3:7 with bupivacaine base. Under anesthesia, the knee joint of Sprague-Dawley rats was exposed, a hole drilled in the femoral trochlea. 0.2 mL of either 15% polymer-bupivacaine formulation or plain bupivacaine (control) was injected locally and compared with a nonsurgery control group. Mechanical hyperalgesia was determined by counting the vocalizations and leg withdrawal after joint squeezing. Behavioral assessments over a day postoperative period revealed a reduction in rearing and ambulation in an open-field apparatus in animals of both experimental groups compared with the nonsurgery control. The vocalizations during the hyperalgesia test increased compared with the control at 24 h. At 48 h, 3.667 ± 0.5138, p = 0.0076 vocalizations were recorded for the plain bupivacaine group versus 1.417 ± 0.5138, p < 0.0001 in the 15% polymer-bupivacaine formulation. Bupivacaine encapsulated in p(DLLA:CO) 3:7 extended the duration of the analgesia compared with plain drug in rats and could represent effective postoperative analgesic in orthopedic joint procedures.

Polymer-based stimuli-responsive nanosystems for biomedical applications

The application of organic polymers and inorganic/organic hybrid systems in numerous fields of biotechnology has seen a considerable growth in recent years. Typically, organic polymers with diverse structures, compositional variations and differing molecular weights have been utilized to assemble polymeric nanosystems such as polymeric micelles, polymersomes, and nanohydrogels with unique features and structural properties. The architecture of these polymeric nanosystems involves the use of both hydrophobic and hydrophilic polymeric blocks, making them suitable as vehicles for diagnostic and therapeutic applications. Recently, "smart" or "intelligent" polymers have attracted significant attention in the biomedical field wherein careful introduction of specific polymeric modalities changes a banal polymeric nanosystem to an advanced stimuli-responsive nanosystem capable of performing extraordinary functions in response to an internal or external trigger such as pH, temperature, redox, enzymes, light, magnetic, or ultrasound. Further, incorporation of inorganic nanoparticles such as gold, silica, or iron oxide with surface-bound stimuli-responsive polymers offers additional advantages and multifunctionality in the field of nanomedicine. This review covers the physical properties and applications of both organic and organic/inorganic hybrid nanosystems with specific recent breakthroughs in drug delivery, imaging, tissue engineering, and separations and provides a brief discussion on the future direction.

Polymer nanogels: a versatile nanoscopic drug delivery platform

In this review we put the spotlight on crosslinked polymer nanogels, a promising platform that has the characteristics of an "ideal" drug delivery vehicle. Some of the key aspects of drug delivery vehicle design like stability, response to biologically relevant stimuli, passive targeting, active targeting, toxicity and ease of synthesis are discussed. We discuss several delivery systems in this light and highlight some examples of systems, which satisfy some or all of these design requirements. In particular, we point to the advantages that crosslinked polymeric systems bring to drug delivery. We review some of the synthetic methods of nanogel synthesis and conclude with the diverse applications in drug delivery where nanogels have been fruitfully employed.

Chapter 9 - Nanoparticles influence pathophysiology of spinal cord injury and repair

Spinal cord injury (SCI) is a serious clinical problem for which no suitable therapeutic strategies have been worked out so far. Recent studies suggest that the SCI and its pathophysiological responses could be altered by systemic exposure to nanoparticles. Thus, SCI when made in animals intoxicated with engineered nanoparticles from metals or silica dust worsened the outcome. On the other hand, drugs tagged with titanium (TiO(2)) nanoparticles or encapsulated in liposomes could enhance their neuroprotective efficacy following SCI. Thus, to expand our knowledge on nanoparticle-induced alterations in the spinal cord pathophysiology further research is needed. These investigations will help to develop new strategies to achieve neuroprotection in SCI, for example, using nanodrug delivery. New results from our laboratory showed that nanoparticle-induced exacerbation of cord pathology following trauma can be reduced when the suitable drugs tagged with TiO(2) nanowires were administered into the spinal cord as compared to those drugs given alone. This indicates that nanoparticles depending on the exposure and its usage could induce both neurotoxicity and neuroprotection. This review discusses the potential adverse or therapeutic utilities of nanoparticles in SCI largely based on our own investigations. In addition, possible mechanisms of nanoparticle-induced exacerbation of cord pathology or enhanced neuroprotection following nanodrug delivery is described in light of recently available data in this rapidly emerging field of nanoneurosciences.